1
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Zhang M, Rodgers CT. Bayesian optimization of gradient trajectory for parallel-transmit pulse design. Magn Reson Med 2024; 91:2358-2373. [PMID: 38193277 DOI: 10.1002/mrm.30007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 12/02/2023] [Accepted: 12/21/2023] [Indexed: 01/10/2024]
Abstract
PURPOSE Spoke pulses improve excitation homogeneity in parallel-transmit MRI. We propose an efficient global optimization algorithm, Bayesian optimization of gradient trajectory (BOGAT), for single-slice and simultaneous multislice imaging. THEORY AND METHODS BOGAT adds an outer loop to optimize kT-space positions. For each position, the RF coefficients are optimized (e.g., with magnitude least squares) and the cost function evaluated. Bayesian optimization progressively estimates the cost function. It automatically chooses the kT-space positions to sample, to achieve fast convergence, often coming close to the globally optimal spoke positions. We investigated the typical features of spokes cost functions by a grid search with field maps comprising 85 slabs from 14 volunteers. We tested BOGAT in this database, and prospectively in a phantom and in vivo. We compared the vendor-provided Fourier transform approach with the same magnitude least squares RF optimizer. RESULTS The cost function is nonconvex and seen empirically to be piecewise smooth with discontinuities where the underlying RF optimum changes sharply. BOGAT converged to within 10% of the global minimum cost within 30 iterations in 93% of slices in our database. BOGAT achieved up to 56% lower flip angle RMS error (RMSE) or 55% lower pulse energy in phantoms versus the Fourier transform approach, and up to 30% lower RMSE and 29% lower energy in vivo with 7.8 s extra computation. CONCLUSION BOGAT efficiently estimated near-global optimum spoke positions for the two-spoke tests, reducing flip-angle RMSE and/or pulse energy in a computation time (˜10 s), which is suitable for online optimization.
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Affiliation(s)
- Minghao Zhang
- Wolfson Brain Imaging Center, University of Cambridge, Cambridge, UK
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2
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Freire MJ, Marqués R, Tornero J. Magnetoinductive metasurface of capacitively-loaded split rings for local field homogenization in a 7 T MRI birdcage: A simulation study. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 357:107586. [PMID: 37944423 DOI: 10.1016/j.jmr.2023.107586] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 10/30/2023] [Accepted: 11/01/2023] [Indexed: 11/12/2023]
Abstract
The transmit field B1+ in a 7 T birdcage is inherently inhomogeneous due to the effects of wavelengths on tissue. This work investigates the homogenization of this field through metasurfaces that consist of a two-dimensional planar array of capacitively loaded conducting rings. The metasurfaces are placed in the intermediate space between the head and the birdcage on either side of the head. The periodical structure of this type of metasurface supports magnetoinductive waves because of the mutual inductive coupling existing between the elements of the array. The analysis takes advantage of this coupling and exploits the excitation of a standing magnetoinductive wave across the arrays, which creates a strong local field that contributes to locally homogenize the field of the birdcage. The presence of the arrays does not detune the birdcage, so that they can be used with commercial birdcages that operate both to transmit and to receive.
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Affiliation(s)
- Manuel J Freire
- Department of Electronics and Electromagnetism, University of Seville, Spain.
| | - Ricardo Marqués
- Department of Electronics and Electromagnetism, University of Seville, Spain
| | - Jesús Tornero
- Center for Clinical Neuroscience-Hospital Los Madroños, Brunete, Spain
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3
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Schallmo MP, Weldon KB, Kamath RS, Moser HR, Montoya SA, Killebrew KW, Demro C, Grant AN, Marjańska M, Sponheim SR, Olman CA. The Psychosis Human Connectome Project: Design and rationale for studies of visual neurophysiology. Neuroimage 2023; 272:120060. [PMID: 36997137 PMCID: PMC10153004 DOI: 10.1016/j.neuroimage.2023.120060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Revised: 03/22/2023] [Accepted: 03/27/2023] [Indexed: 04/01/2023] Open
Abstract
Visual perception is abnormal in psychotic disorders such as schizophrenia. In addition to hallucinations, laboratory tests show differences in fundamental visual processes including contrast sensitivity, center-surround interactions, and perceptual organization. A number of hypotheses have been proposed to explain visual dysfunction in psychotic disorders, including an imbalance between excitation and inhibition. However, the precise neural basis of abnormal visual perception in people with psychotic psychopathology (PwPP) remains unknown. Here, we describe the behavioral and 7 tesla MRI methods we used to interrogate visual neurophysiology in PwPP as part of the Psychosis Human Connectome Project (HCP). In addition to PwPP (n = 66) and healthy controls (n = 43), we also recruited first-degree biological relatives (n = 44) in order to examine the role of genetic liability for psychosis in visual perception. Our visual tasks were designed to assess fundamental visual processes in PwPP, whereas MR spectroscopy enabled us to examine neurochemistry, including excitatory and inhibitory markers. We show that it is feasible to collect high-quality data across multiple psychophysical, functional MRI, and MR spectroscopy experiments with a sizable number of participants at a single research site. These data, in addition to those from our previously described 3 tesla experiments, will be made publicly available in order to facilitate further investigations by other research groups. By combining visual neuroscience techniques and HCP brain imaging methods, our experiments offer new opportunities to investigate the neural basis of abnormal visual perception in PwPP.
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Affiliation(s)
- Michael-Paul Schallmo
- Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN.
| | - Kimberly B Weldon
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN; Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN
| | - Rohit S Kamath
- Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN
| | - Hannah R Moser
- Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN
| | - Samantha A Montoya
- Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN
| | - Kyle W Killebrew
- Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN
| | - Caroline Demro
- Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN; Department of Psychology, University of Minnesota, Minneapolis, MN
| | - Andrea N Grant
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Małgorzata Marjańska
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Scott R Sponheim
- Veterans Affairs Medical Center, Minneapolis, MN; Department of Psychiatry and Behavioral Sciences, University of Minnesota, Minneapolis, MN
| | - Cheryl A Olman
- Department of Psychology, University of Minnesota, Minneapolis, MN; Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
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4
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Yang T, Li Y, Ye Z, Yao S, Li Q, Yuan Y, Song B. Diffusion Weighted Imaging of the Abdomen and Pelvis: Recent Technical Advances and Clinical Applications. Acad Radiol 2023; 30:470-482. [PMID: 36038417 DOI: 10.1016/j.acra.2022.07.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 07/20/2022] [Accepted: 07/23/2022] [Indexed: 01/25/2023]
Abstract
Diffusion weighted imaging (DWI) serves as one of the most important functional magnetic resonance imaging techniques in abdominal and pelvic imaging. It is designed to reflect the diffusion of water molecules and is particularly sensitive to the malignancies. Yet, the limitations of image distortion and artifacts in single-shot DWI may hamper its widespread use in clinical practice. With recent technical advances in DWI, such as simultaneous multi-slice excitation, computed or reduced field-of-view techniques, as well as advanced shimming methods, it is possible to achieve shorter acquisition time, better image quality, and higher robustness in abdominopelvic DWI. This review discussed the recent advances of each DWI approach, and highlighted its future perspectives in abdominal and pelvic imaging, hoping to familiarize physicians and radiologists with the technical improvements in this field and provide future research directions.
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Affiliation(s)
- Ting Yang
- Department of Radiology, West China Hospital, Sichuan University, Chengdu, China
| | - Ying Li
- Department of Radiology, West China Hospital, Sichuan University, Chengdu, China
| | - Zheng Ye
- Department of Radiology, West China Hospital, Sichuan University, Chengdu, China
| | - Shan Yao
- Department of Radiology, West China Hospital, Sichuan University, Chengdu, China
| | - Qing Li
- MR Collaborations, Siemens Healthcare, Shanghai, China
| | - Yuan Yuan
- Department of Radiology, West China Hospital, Sichuan University, Chengdu, China
| | - Bin Song
- Department of Radiology, West China Hospital, Sichuan University, Chengdu, China; Department of Radiology, Sanya People's Hospital, Sanya, Hainan, China.
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5
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Abstract
Especially after the launch of 7 T, the ultrahigh magnetic field (UHF) imaging community achieved critically important strides in our understanding of the physics of radiofrequency interactions in the human body, which in turn has led to solutions for the challenges posed by such UHFs. As a result, the originally obtained poor image quality has progressed to the high-quality and high-resolution images obtained at 7 T and now at 10.5 T in the human torso. Despite these tremendous advances, work still remains to further improve the image quality and fully capitalize on the potential advantages UHF has to offer.
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6
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Fritz FJ, Poser BA, Roebroeck A. MESMERISED: Super-accelerating T 1 relaxometry and diffusion MRI with STEAM at 7 T for quantitative multi-contrast and diffusion imaging. Neuroimage 2021; 239:118285. [PMID: 34147632 DOI: 10.1016/j.neuroimage.2021.118285] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 06/14/2021] [Accepted: 06/16/2021] [Indexed: 12/17/2022] Open
Abstract
There is an increasing interest in quantitative imaging of T1, T2 and diffusion contrast in the brain due to greater robustness against bias fields and artifacts, as well as better biophysical interpretability in terms of microstructure. However, acquisition time constraints are a challenge, particularly when multiple quantitative contrasts are desired and when extensive sampling of diffusion directions, high b-values or long diffusion times are needed for multi-compartment microstructure modeling. Although ultra-high fields of 7 T and above have desirable properties for many MR modalities, the shortening T2 and the high specific absorption rate (SAR) of inversion and refocusing pulses bring great challenges to quantitative T1, T2 and diffusion imaging. Here, we present the MESMERISED sequence (Multiplexed Echo Shifted Multiband Excited and Recalled Imaging of STEAM Encoded Diffusion). MESMERISED removes the dead time in Stimulated Echo Acquisition Mode (STEAM) imaging by an echo-shifting mechanism. The echo-shift (ES) factor is independent of multiband (MB) acceleration and allows for very high multiplicative (ESxMB) acceleration factors, particularly under moderate and long mixing times. This results in super-acceleration and high time efficiency at 7 T for quantitative T1 and diffusion imaging, while also retaining the capacity to perform quantitative T2 and B1 mapping. We demonstrate the super-acceleration of MESMERISED for whole-brain T1 relaxometry with total acceleration factors up to 36 at 1.8 mm isotropic resolution, and up to 54 at 1.25 mm resolution qT1 imaging, corresponding to a 6x and 9x speedup, respectively, compared to MB-only accelerated acquisitions. We then demonstrate highly efficient diffusion MRI with high b-values and long diffusion times in two separate cases. First, we show that super-accelerated multi-shell diffusion acquisitions with 370 whole-brain diffusion volumes over 8 b-value shells up to b = 7000 s/mm2 can be generated at 2 mm isotropic in under 8 minutes, a data rate of almost a volume per second, or at 1.8 mm isotropic in under 11 minutes, achieving up to 3.4x speedup compared to MB-only. A comparison of b = 7000 s/mm2 MESMERISED against standard MB pulsed gradient spin echo (PGSE) diffusion imaging shows 70% higher SNR efficiency and greater effectiveness in supporting complex diffusion signal modeling. Second, we demonstrate time-efficient sampling of different diffusion times with 1.8 mm isotropic diffusion data acquired at four diffusion times up to 290 ms, which supports both Diffusion Tensor Imaging (DTI) and Diffusion Kurtosis Imaging (DKI) at each diffusion time. Finally, we demonstrate how adding quantitative T2 and B1+ mapping to super-accelerated qT1 and diffusion imaging enables efficient quantitative multi-contrast mapping with the same MESMERISED sequence and the same readout train. MESMERISED extends possibilities to efficiently probe T1, T2 and diffusion contrast for multi-component modeling of tissue microstructure.
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Affiliation(s)
- F J Fritz
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands; Institut für Systemische Neurowissenschaften, Zentrum für Experimentelle Medizin, Universitätklinikum Hamburg-Eppendorf (UKE), Hamburg, Deutschland
| | - B A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands
| | - A Roebroeck
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, the Netherlands.
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7
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Paez A, Gu C, Cao Z. Robust RF shimming and small-tip-angle multispoke pulse design with finite-difference regularization. Magn Reson Med 2021; 86:1472-1481. [PMID: 33934406 DOI: 10.1002/mrm.28820] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 03/29/2021] [Accepted: 04/07/2021] [Indexed: 01/07/2023]
Abstract
PURPOSE A new regularizer is proposed for the magnitude least-squares optimization algorithm, to ensure robust parallel transmit RF shimming and small-tip-angle multispoke pulse designs for ultrahigh-field MRI. METHODS A finite-difference regularization term is activated as an additional regularizer in the iterative magnitude-least-squares based pulse design algorithm when an unwanted flip angle null distribution is detected. Both simulated and experimental B 1 + maps from different transmit arrays and different human subjects at 7 T were used to evaluate the proposed algorithm. The algorithm was further demonstrated in experiment with dynamic multislice RF shimming for a single-shot gradient-echo EPI for human functional MRI at 7 T. RESULTS The proposed finite-difference regularizer effectively prevented excitation null to be formed for RF shimming and small-tip-angle multispoke pulses, and improved the latter with a monotonic trade-off relationship between flip angle error and RF power. The proposed algorithm was demonstrated to be effective with several head-array geometries by simulation and with a commercial head array with 12 healthy human subjects by experiment. During a functional MRI scan at 7 T with dynamic RF shimming, the proposed algorithm ensured high image SNR throughout the human brain, compared with near-complete local signal loss by the conventional magnitude-least-squares algorithm. CONCLUSION Using finite-difference regularization to avoid unwanted solutions, the robustness of RF shimming and small-tip-angle multispoke pulse design algorithms are improved, with better flip angle homogeneity and a monotonic trade-off relationship between flip angle error and RF power.
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Affiliation(s)
- Adrian Paez
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.,Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Chunming Gu
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.,Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - Zhipeng Cao
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.,Department of Radiology, Vanderbilt University Medical Center, Nashville, Tennessee, USA
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8
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Sanchez Panchuelo RM, Mougin O, Turner R, Francis ST. Quantitative T1 mapping using multi-slice multi-shot inversion recovery EPI. Neuroimage 2021; 234:117976. [PMID: 33781969 PMCID: PMC8204273 DOI: 10.1016/j.neuroimage.2021.117976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 02/27/2021] [Accepted: 03/13/2021] [Indexed: 11/12/2022] Open
Abstract
An efficient multi-slice inversion–recovery EPI (MS-IR-EPI) sequence for fast, high spatial resolution, quantitative T1 mapping is presented, using a segmented simultaneous multi-slice acquisition, combined with slice order shifting across multiple acquisitions. The segmented acquisition minimises the effective TE and readout duration compared to a single-shot EPI scheme, reducing geometric distortions to provide high quality T1 maps with a narrow point-spread function. The precision and repeatability of MS-IR-EPI T1 measurements are assessed using both T1-calibrated and T2-calibrated ISMRM/NIST phantom spheres at 3 and 7 T and compared with single slice IR and MP2RAGE methods. Magnetization transfer (MT) effects of the spectrally-selective fat-suppression (FS) pulses required for in vivo imaging are shown to shorten the measured in-vivo T1 values. We model the effect of these fat suppression pulses on T1 measurements and show that the model can remove their MT contribution from the measured T1, thus providing accurate T1 quantification. High spatial resolution T1 maps of the human brain generated with MS-IR-EPI at 7 T are compared with those generated with the widely implemented MP2RAGE sequence. Our MS-IR-EPI sequence provides high SNR per unit time and sharper T1 maps than MP2RAGE, demonstrating the potential for ultra-high resolution T1 mapping and the improved discrimination of functionally relevant cortical areas in the human brain.
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Affiliation(s)
- Rosa M Sanchez Panchuelo
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom; NIHR Nottingham Biomedical Research Centre, University of Nottingham, Nottingham, United Kingdom.
| | - Olivier Mougin
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom
| | - Robert Turner
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom; Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Susan T Francis
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom; NIHR Nottingham Biomedical Research Centre, University of Nottingham, Nottingham, United Kingdom
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9
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Improved 7 Tesla transmit field homogeneity with reduced electromagnetic power deposition using coupled Tic Tac Toe antennas. Sci Rep 2021; 11:3370. [PMID: 33564013 PMCID: PMC7873125 DOI: 10.1038/s41598-020-79807-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 11/26/2020] [Indexed: 12/28/2022] Open
Abstract
Recently cleared by the FDA, 7 Tesla (7 T) MRI is a rapidly growing technology that can provide higher resolution and enhanced contrast in human MRI images. However, the increased operational frequency (~ 297 MHz) hinders its full potential since it causes inhomogeneities in the images and increases the power deposition in the tissues. This work describes the optimization of an innovative radiofrequency (RF) head coil coupled design, named Tic Tac Toe, currently used in large scale human MRI scanning at 7 T; to date, this device was used in more than 1,300 neuro 7 T MRI scans. Electromagnetic simulations of the coil were performed using the finite-difference time-domain method. Numerical optimizations were used to combine the calculated electromagnetic fields produced by these antennas, based on the superposition principle, resulting in homogeneous magnetic field distributions at low levels of power deposition in the tissues. The simulations were validated in-vivo using the Tic Tac Toe RF head coil system on a 7 T MRI scanner.
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10
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Shin D, Ji S, Lee D, Lee J, Oh SH, Lee J. Deep Reinforcement Learning Designed Shinnar-Le Roux RF Pulse Using Root-Flipping: DeepRF SLR. IEEE TRANSACTIONS ON MEDICAL IMAGING 2020; 39:4391-4400. [PMID: 32833629 DOI: 10.1109/tmi.2020.3018508] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A novel approach of applying deep reinforcement learning to an RF pulse design is introduced. This method, which is referred to as DeepRFSLR, is designed to minimize the peak amplitude or, equivalently, minimize the pulse duration of a multiband refocusing pulse generated by the Shinar Le-Roux (SLR) algorithm. In the method, the root pattern of SLR polynomial, which determines the RF pulse shape, is optimized by iterative applications of deep reinforcement learning and greedy tree search. When tested for the designs of the multiband pulses with three and seven slices, DeepRFSLR demonstrated improved performance compared to conventional methods, generating shorter duration RF pulses in shorter computational time. In the experiments, the RF pulse from DeepRFSLR produced a slice profile similar to the minimum-phase SLR RF pulse and the profiles matched to that of the computer simulation. Our approach suggests a new way of designing an RF by applying a machine learning algorithm, demonstrating a "machine-designed" MRI sequence.
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11
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Moeller S, Pisharady Kumar P, Andersson J, Akcakaya M, Harel N, Ma RE, Wu X, Yacoub E, Lenglet C, Ugurbil K. Diffusion Imaging in the Post HCP Era. J Magn Reson Imaging 2020; 54:36-57. [PMID: 32562456 DOI: 10.1002/jmri.27247] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 05/11/2020] [Accepted: 05/13/2020] [Indexed: 02/06/2023] Open
Abstract
Diffusion imaging is a critical component in the pursuit of developing a better understanding of the human brain. Recent technical advances promise enabling the advancement in the quality of data that can be obtained. In this review the context for different approaches relative to the Human Connectome Project are compared. Significant new gains are anticipated from the use of high-performance head gradients. These gains can be particularly large when the high-performance gradients are employed together with ultrahigh magnetic fields. Transmit array designs are critical in realizing high accelerations in diffusion-weighted (d)MRI acquisitions, while maintaining large field of view (FOV) coverage, and several techniques for optimal signal-encoding are now available. Reconstruction and processing pipelines that precisely disentangle the acquired neuroanatomical information are established and provide the foundation for the application of deep learning in the advancement of dMRI for complex tissues. Level of Evidence: 3 Technical Efficacy Stage: Stage 3.
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Affiliation(s)
- Steen Moeller
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Pramod Pisharady Kumar
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Jesper Andersson
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Mehmet Akcakaya
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, USA
| | - Noam Harel
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Ruoyun Emily Ma
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Xiaoping Wu
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Essa Yacoub
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Christophe Lenglet
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Kamil Ugurbil
- Center for Magnetic Resonance Research; Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
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12
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Schmitter S, Adriany G, Waks M, Moeller S, Aristova M, Vali A, Auerbach EJ, Van de Moortele PF, Ugurbil K, Schnell S. Bilateral Multiband 4D Flow MRI of the Carotid Arteries at 7T. Magn Reson Med 2020; 84:1947-1960. [PMID: 32187742 DOI: 10.1002/mrm.28256] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 01/31/2020] [Accepted: 02/24/2020] [Indexed: 12/26/2022]
Abstract
PURPOSE Simultaneous multislab (SMSb) 4D flow MRI was developed and implemented at 7T for accelerated acquisition of the 3D blood velocity vector field in both carotid bifurcations. METHODS SMSb was applied to 4D flow to acquire blood velocities in both carotid bifurcations in sagittal orientation using a local transmit/receive coil at 7T. B 1 + transmit efficiency was optimized by B 1 + shimming. SMSb 4D flow was obtained in 8 healthy subjects in single-band (SB) and multiband (MB) fashion. Additionally, MB data were retrospectively undersampled to simulate GRAPPA R = 2 (MB2_GRAPPA2), and both SB datasets were added to form an artificial MB dataset (SumSB). The band separation performance was quantified by signal leakage. Peak velocity and total flow values were calculated and compared to SB via intraclass correlation analysis (ICC). RESULTS Clean slab separation was achieved yielding a mean signal leakage of 13% above the mean SB noise level. Mean total flow for MB2, SumSB, and MB_GRAPPA2 deviated less than 9% from the SB values. Peak velocities averaged over all vessels and subjects were 0.48 ± 0.11 m/s for SB, 0.47 ± 0.12 m/s for SumSB, 0.50 ± 0.13 m/s for MB2, and 0.53 ± 0.13 m/s for MB2_GRAPPA2. ICC revealed excellent absolute agreement and consistency of total flow for all methods compared to SB2. Peak velocity showed good to excellent agreement and consistency for SumSB and MB2 and MB2_GRAPPA2 method showed poor to excellent agreement and good to excellent consistency. CONCLUSION Simultaneous multislab 4D Flow MRI allows accurate quantification of total flow and peak velocity while reducing scan times.
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Affiliation(s)
- Sebastian Schmitter
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA.,Physikalisch-Technische Bundesanstalt, Braunschweig and Berlin, Germany
| | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA
| | - Matt Waks
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA
| | - Steen Moeller
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA
| | - Maria Aristova
- McCormick School of Engineering, Northwestern University, Evanston, USA.,Feinberg School of Medicine, Northwestern University, Chicago, USA
| | - Alireza Vali
- Feinberg School of Medicine, Northwestern University, Chicago, USA
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA
| | | | - Kamil Ugurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA
| | - Susanne Schnell
- Feinberg School of Medicine, Northwestern University, Chicago, USA
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13
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Bhandari R, Kirilina E, Caan M, Suttrup J, De Sanctis T, De Angelis L, Keysers C, Gazzola V. Does higher sampling rate (multiband + SENSE) improve group statistics - An example from social neuroscience block design at 3T. Neuroimage 2020; 213:116731. [PMID: 32173409 PMCID: PMC7181191 DOI: 10.1016/j.neuroimage.2020.116731] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Revised: 02/27/2020] [Accepted: 03/09/2020] [Indexed: 02/06/2023] Open
Abstract
Multiband (MB) or Simultaneous multi-slice (SMS) acquisition schemes allow the acquisition of MRI signals from more than one spatial coordinate at a time. Commercial availability has brought this technique within the reach of many neuroscientists and psychologists. Most early evaluation of the performance of MB acquisition employed resting state fMRI or the most basic tasks. In this study, we tested whether the advantages of using MB acquisition schemes generalize to group analyses using a cognitive task more representative of typical cognitive neuroscience applications. Twenty-three subjects were scanned on a Philips 3 T scanner using five sequences, up to eight-fold acceleration with MB-factors 1 to 4, SENSE factors up to 2 and corresponding TRs of 2.45s down to 0.63s, while they viewed (i) movie blocks showing complex actions with hand object interactions and (ii) control movie blocks without hand object interaction. Data were processed using a widely used analysis pipeline implemented in SPM12 including the unified segmentation and canonical HRF modelling. Using random effects group-level, voxel-wise analysis we found that all sequences were able to detect the basic action observation network known to be recruited by our task. The highest t-values were found for sequences with MB4 acceleration. For the MB1 sequence, a 50% bigger voxel volume was needed to reach comparable t-statistics. The group-level t-values for resting state networks (RSNs) were also highest for MB4 sequences. Here the MB1 sequence with larger voxel size did not perform comparable to the MB4 sequence. Altogether, we can thus recommend the use of MB4 (and SENSE 1.5 or 2) on a Philips scanner when aiming to perform group-level analyses using cognitive block design fMRI tasks and voxel sizes in the range of cortical thickness (e.g. 2.7 mm isotropic). While results will not be dramatically changed by the use of multiband, our results suggest that MB will bring a moderate but significant benefit.
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Affiliation(s)
- Ritu Bhandari
- Netherlands Institute for Neuroscience, KNAW, Amsterdam, the Netherlands.
| | - Evgeniya Kirilina
- Center for Cognitive Neuroscience, Free University, Berlin, Germany; Max Plank Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
| | - Matthan Caan
- Spinoza Centre for Neuroimaging, Amsterdam, the Netherlands; Amsterdam UMC, University of Amsterdam, Biomedical Engineering & Physics, Amsterdam, the Netherlands
| | - Judith Suttrup
- Netherlands Institute for Neuroscience, KNAW, Amsterdam, the Netherlands
| | - Teresa De Sanctis
- Netherlands Institute for Neuroscience, KNAW, Amsterdam, the Netherlands
| | - Lorenzo De Angelis
- Netherlands Institute for Neuroscience, KNAW, Amsterdam, the Netherlands
| | - Christian Keysers
- Netherlands Institute for Neuroscience, KNAW, Amsterdam, the Netherlands; Department of Psychology, University of Amsterdam, the Netherlands
| | - Valeria Gazzola
- Netherlands Institute for Neuroscience, KNAW, Amsterdam, the Netherlands; Department of Psychology, University of Amsterdam, the Netherlands.
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14
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Moeller S, Ramanna S, Lenglet C, Pisharady PK, Auerbach EJ, Delabarre L, Wu X, Akcakaya M, Ugurbil K. Self-navigation for 3D multishot EPI with data-reference. Magn Reson Med 2020; 84:1747-1762. [PMID: 32115756 DOI: 10.1002/mrm.28231] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 02/01/2020] [Accepted: 02/04/2020] [Indexed: 02/03/2023]
Abstract
PURPOSE In this study, we sought to develop a self-navigation strategy for improving the reconstruction of diffusion weighted 3D multishot echo planar imaging (EPI). We propose a method for extracting the phase correction information from the acquisition itself, eliminating the need for a 2D navigator, further accelerating the acquisition. METHODS In-vivo acquisitions at 3T with 0.9 mm and 1.5 mm isotropic resolutions were used to evaluate the performance of the self-navigation strategy. Sensitivity to motion was tested using a large difference in pitch position of the head. Using a multishell diffusion weighted acquisition, tractography results were obtained at (0.9 mm)3 to validate the quality with conventional acquisition. RESULTS The use of 3D multislab EPI with self-navigation enables 3D diffusion-weighted spin echo EPI acquisitions that have the same efficiency as 2D single-shot acquisition. For matched acquisition time the image signal-to-noise ratio (SNR) between 3D and 2D acquisition is shown to be comparable for whole-brain coverage with (1.5 mm)3 resolution and for (0.9 mm)3 resolution the 3D acquisition has higher SNR than what can be obtained with 2D acquisitions using current state-of-art multiband techniques. The self-navigation technique was shown to be stable under inter-volume motion. In tractography analysis, the higher resolution afforded by our technique enabled clear delineation of the tapetum and posterior corona radiata. CONCLUSION The proposed self-navigation approach utilized a self-consistent phase in 3D diffusion weighted acquisitions. Its efficiency and stability were demonstrated for a plurality of common acquisitions. The proposed self-navigation approach allows for faster acquisition of 3D multishot EPI desirable for large field of view and/or higher resolution.
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Affiliation(s)
- Steen Moeller
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Sudhir Ramanna
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Christophe Lenglet
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Pramod K Pisharady
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Lance Delabarre
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Mehmet Akcakaya
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Kamil Ugurbil
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.,Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
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15
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Cao Z, Yan X, Gore JC, Grissom WA. Designing parallel transmit head coil arrays based on radiofrequency pulse performance. Magn Reson Med 2019; 83:2331-2342. [PMID: 31722120 DOI: 10.1002/mrm.28068] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 09/23/2019] [Accepted: 10/16/2019] [Indexed: 12/27/2022]
Abstract
PURPOSE A new approach to design parallel transmit (pTx) head arrays is proposed that integrates transmit radiofrequency pulse designs with electromagnetic modeling of array coil elements. THEORY AND METHODS An approach to design pTx head arrays is proposed that finds optimal groupings of a large number of coils into a small number of channels. An algorithm is proposed to extend array-compressed parallel transmit pulse design by adding the ability to optimally select and prune coil elements, in addition to optimizing compression weights. The performance of the method is demonstrated in simulations of dynamic multislice shimming of the human brain in axial, coronal, and sagittal directions, and of reduced field-of-view excitation targeting the human occipital lobe, with simulated electromagnetic field maps from a group of 5 human head models at 7T. RESULTS For both dynamic multislice shimming and reduced field-of-view excitation, the method successfully designed pTx arrays that simultaneously achieved in general 15% lower mean excitation errors with 20% lower SDs, along with 20% lower mean global averaged specific absorption rate and 50% lower SD than previously reported pTx head array designs. CONCLUSION With the proposed optimal coil element selection algorithm, the array-compressed parallel transmit pulse design can be extended to design pTx transmit head arrays with joint consideration of the fields within the sample and the radiofrequency pulse. The pTx arrays from such an approach achieved higher transmit excitation accuracy, lower radiofrequency heating in subjects, and more robust performance across subjects compared with previously reported pTx head arrays with the same number of channels.
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Affiliation(s)
- Zhipeng Cao
- Department of Radiology, Vanderbilt University Medical Center, Nashville, Tennessee.,Vanderbilt University Institute of Imaging Science, Nashville, Tennessee
| | - Xinqiang Yan
- Department of Radiology, Vanderbilt University Medical Center, Nashville, Tennessee.,Vanderbilt University Institute of Imaging Science, Nashville, Tennessee
| | - John C Gore
- Department of Radiology, Vanderbilt University Medical Center, Nashville, Tennessee.,Vanderbilt University Institute of Imaging Science, Nashville, Tennessee.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee
| | - William A Grissom
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee
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16
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Gras V, Poser BA, Wu X, Tomi-Tricot R, Boulant N. Optimizing BOLD sensitivity in the 7T Human Connectome Project resting-state fMRI protocol using plug-and-play parallel transmission. Neuroimage 2019; 195:1-10. [DOI: 10.1016/j.neuroimage.2019.03.040] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 02/21/2019] [Accepted: 03/19/2019] [Indexed: 12/18/2022] Open
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17
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Abstract
Magnetic resonance imaging (MRI) has been driven toward ultrahigh magnetic fields (UHF) in order to benefit from correspondingly higher signal-to-noise ratio and spectral resolution. Technological challenges associated with UHF, such as increased radiofrequency (RF) energy deposition and RF excitation inhomogeneity, limit realization of the full potential of these benefits. Parallel RF transmission (pTx) enables decreases in the inhomogeneity of RF excitations and in RF energy deposition by using multiple-transmit RF coils driven independently and operating simultaneously. pTx plays a fundamental role in UHF MRI by bringing the potential applications of UHF into reality. In this review article, we review the recent developments in pTx pulse design and RF safety in pTx. Simultaneous multislice imaging and inner volume imaging using pTx are reviewed with a focus on UHF applications. Emerging pTx design approaches using improved pTx design frameworks and calibrations are reviewed together with calibration-free approaches that remove the necessity of time-consuming calibrations necessary for successful pTx. Lastly, we focus on the safety of pTx that is improved by using intersubject variability analysis, proactively managing pTx and temperature-based pTx approaches.
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Affiliation(s)
- Cem M. Deniz
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY
- RF Test Labs, LLC, New York, NY
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18
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Li N, Li L, Zhang Y, Ferraris Araneta M, Johnson C, Shen J. Quantification of in vivo transverse relaxation of glutamate in the frontal cortex of human brain by radio frequency pulse-driven longitudinal steady state. PLoS One 2019; 14:e0215210. [PMID: 30995237 PMCID: PMC6469797 DOI: 10.1371/journal.pone.0215210] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 03/28/2019] [Indexed: 12/13/2022] Open
Abstract
PURPOSE The principal excitatory neurotransmitter glutamate plays an important role in many central nervous system disorders. Because glutamate resides predominantly in glutamatergic neurons, its relaxation properties reflect the intracellular environment of glutamatergic neurons. This study developed an improved echo time-independent technique for measuring transverse relaxation time and demonstrated that this radio frequency (RF)-driven longitudinal steady state technique can reliably measure glutamate transverse relaxation in the frontal cortex, where structural and functional abnormalities have been associated with psychiatric symptoms. METHOD Bloch and Monte Carlo simulations were performed to improve and optimize the RF-driven, longitudinal, steady-state (MARzss) technique to significantly shorten scan time and increase measurement precision. Optimized four-flip angle measurements at 0°,12°, 24°, and 36° with matched repetition time were used in nine human subjects (6F, 3M; 27-49 years old) at 7 Tesla. Longitudinal and transverse relaxation rates for glutamate were measured from a 2 x 2 x 2 cm3 voxel placed in three different brain regions: gray matter-dominated medial prefrontal lobe, white matter-dominated left frontal lobe, and gray matter-dominated occipital lobe. RESULTS Compared to the original MARzss technique, the scan time per voxel for measuring glutamate transverse relaxation was shortened by more than 50%. In the medial frontal, left frontal, and occipital voxels, the glutamate T2 was found to be 117.5±12.9 ms (mean ± standard deviation, n = 9), 107.3±12.1 (n = 9), and 124.4±16.6 ms (n = 8), respectively. CONCLUSIONS The improvements described in this study make the MARZSS technique a viable tool for reliably measuring glutamate relaxation from human subjects in a typical clinical setting. It is expected that this improved technique can be applied to characterize the intracellular environment of glutamatergic neurons in a variety of brain disorders.
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Affiliation(s)
- Ningzhi Li
- Section on Magnetic Spectroscopy, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Linqing Li
- Functional Magnetic Resonance Imaging Core Facility, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Yan Zhang
- Magnetic Resonance Spectroscopy Core, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Maria Ferraris Araneta
- Magnetic Resonance Spectroscopy Core, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Christopher Johnson
- Section on Magnetic Spectroscopy, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Jun Shen
- Section on Magnetic Spectroscopy, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States of America
- Magnetic Resonance Spectroscopy Core, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland, United States of America
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19
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Uğurbil K, Auerbach E, Moeller S, Grant A, Wu X, Van de Moortele PF, Olman C, DelaBarre L, Schillak S, Radder J, Lagore R, Adriany G. Brain imaging with improved acceleration and SNR at 7 Tesla obtained with 64-channel receive array. Magn Reson Med 2019; 82:495-509. [PMID: 30803023 DOI: 10.1002/mrm.27695] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 12/28/2018] [Accepted: 01/25/2019] [Indexed: 12/27/2022]
Abstract
PURPOSE Despite the clear synergy between high channel counts in a receive array and magnetic fields ≥ 7 Tesla, to date such systems have been restricted to a maximum of 32 channels. Here, we examine SNR gains at 7 Tesla in unaccelerated and accelerated images with a 64-receive channel (64Rx) RF coil. METHODS A 64Rx coil was built using circular loops tiled in 2 separable sections of a close-fitting form; custom designed preamplifier boards were integrated into each coil element. A 16-channel transmitter arranged in 2 rows along the z-axis was employed. The performance of the 64Rx array was experimentally compared to that of an industry-standard 32-channel receive (32Rx) array for SNR in unaccelerated images and for noise amplification under parallel imaging. RESULTS SNR gains were observed in the periphery but not in the center of the brain in unaccelerated imaging compared to the 32Rx coil. With either 1D or 2D undersampling of k-space, or with slice acceleration together with 1D undersampling of k-space, significant reductions in g-factor noise were observed throughout the brain, yielding effective gains in SNR in the entire brain compared to the 32Rx coil. Task-based FMRI data with 12-fold 2D (slice and phase-encode) acceleration yielded excellent quality functional maps with the 64Rx coil but was significantly beyond the capabilities of the 32Rx coil. CONCLUSION The results confirm the expectations from modeling studies and demonstrate that whole-brain studies with up to 16-fold, 2D acceleration would be feasible with the 64Rx coil.
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Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Edward Auerbach
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Steen Moeller
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Andrea Grant
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Xiaoping Wu
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | | | - Cheryl Olman
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Lance DelaBarre
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | | | - Jerahmie Radder
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Russell Lagore
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Gregor Adriany
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
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20
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van Gemert J, Brink W, Webb A, Remis R. High-permittivity pad design tool for 7T neuroimaging and 3T body imaging. Magn Reson Med 2018; 81:3370-3378. [PMID: 30561797 PMCID: PMC6519234 DOI: 10.1002/mrm.27629] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2018] [Revised: 10/18/2018] [Accepted: 11/16/2018] [Indexed: 11/20/2022]
Abstract
Purpose High‐permittivity materials in the form of flexible “dielectric pads” have proved very useful for addressing RF inhomogeneities in high field MRI systems. Finding the optimal design of such pads is, however, a tedious task, reducing the impact of this technique. We present an easy‐to‐use software tool which allows researchers and clinicians to design dielectric pads efficiently on standard computer systems, for 7T neuroimaging and 3T body imaging applications. Methods The tool incorporates advanced computational methods based on field decomposition and model order reduction as a framework to efficiently evaluate the B1+ fields resulting from dielectric pads. The tool further incorporates optimization routines which can either optimize the position of a given dielectric pad, or perform a full parametric design. The optimization procedure can target either a single target field, or perform a sweep to explore the trade‐off between homogeneity and efficiency of the B1+ field in a specific region of interest. The 3T version further allows for shifting of the imaging landmark to enable different imaging targets to be centered in the body coil. Results Example design results are shown for imaging the inner ear at 7T and for cardiac imaging at 3T. Computation times for all cases are approximately a minute per target field. Conclusion The developed tool can be easily used to design dielectric pads for any 7T neuroimaging and 3T body imaging application within minutes. This bridges the gap between the advanced design methods and the practical application by the MR community.
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Affiliation(s)
- Jeroen van Gemert
- Circuits & Systems Group, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, Delft, The Netherlands
| | - Wyger Brink
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Andrew Webb
- Circuits & Systems Group, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, Delft, The Netherlands
| | - Rob Remis
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
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21
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Ladd ME, Bachert P, Meyerspeer M, Moser E, Nagel AM, Norris DG, Schmitter S, Speck O, Straub S, Zaiss M. Pros and cons of ultra-high-field MRI/MRS for human application. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2018; 109:1-50. [PMID: 30527132 DOI: 10.1016/j.pnmrs.2018.06.001] [Citation(s) in RCA: 250] [Impact Index Per Article: 41.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 06/06/2018] [Accepted: 06/07/2018] [Indexed: 05/08/2023]
Abstract
Magnetic resonance imaging and spectroscopic techniques are widely used in humans both for clinical diagnostic applications and in basic research areas such as cognitive neuroimaging. In recent years, new human MR systems have become available operating at static magnetic fields of 7 T or higher (≥300 MHz proton frequency). Imaging human-sized objects at such high frequencies presents several challenges including non-uniform radiofrequency fields, enhanced susceptibility artifacts, and higher radiofrequency energy deposition in the tissue. On the other side of the scale are gains in signal-to-noise or contrast-to-noise ratio that allow finer structures to be visualized and smaller physiological effects to be detected. This review presents an overview of some of the latest methodological developments in human ultra-high field MRI/MRS as well as associated clinical and scientific applications. Emphasis is given to techniques that particularly benefit from the changing physical characteristics at high magnetic fields, including susceptibility-weighted imaging and phase-contrast techniques, imaging with X-nuclei, MR spectroscopy, CEST imaging, as well as functional MRI. In addition, more general methodological developments such as parallel transmission and motion correction will be discussed that are required to leverage the full potential of higher magnetic fields, and an overview of relevant physiological considerations of human high magnetic field exposure is provided.
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Affiliation(s)
- Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Medicine, University of Heidelberg, Heidelberg, Germany; Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany; Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
| | - Peter Bachert
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany.
| | - Martin Meyerspeer
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; MR Center of Excellence, Medical University of Vienna, Vienna, Austria.
| | - Ewald Moser
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; MR Center of Excellence, Medical University of Vienna, Vienna, Austria.
| | - Armin M Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
| | - David G Norris
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands; Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
| | - Sebastian Schmitter
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.
| | - Oliver Speck
- Department of Biomedical Magnetic Resonance, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany; German Center for Neurodegenerative Diseases, Magdeburg, Germany; Center for Behavioural Brain Sciences, Magdeburg, Germany; Leibniz Institute for Neurobiology, Magdeburg, Germany.
| | - Sina Straub
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
| | - Moritz Zaiss
- High-Field Magnetic Resonance Center, Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany.
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22
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Wu X, Auerbach EJ, Vu AT, Moeller S, Van de Moortele PF, Yacoub E, Uğurbil K. Human Connectome Project-style resting-state functional MRI at 7 Tesla using radiofrequency parallel transmission. Neuroimage 2018; 184:396-408. [PMID: 30237033 DOI: 10.1016/j.neuroimage.2018.09.038] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2018] [Revised: 09/13/2018] [Accepted: 09/15/2018] [Indexed: 01/16/2023] Open
Abstract
We investigate the utility of radiofrequency (RF) parallel transmission (pTx) for whole-brain resting-state functional MRI (rfMRI) acquisition at 7 Tesla (7T). To this end, Human Connectome Project (HCP)-style data acquisitions were chosen as a showcase example. Five healthy subjects were scanned in pTx and single-channel transmit (1Tx) modes. The pTx data were acquired using a prototype 16-channel transmit system and a commercially available Nova 8-channel transmit 32-channel receive RF head coil. Additionally, pTx single-spoke multiband (MB) pulses were designed to image sagittal slices. HCP-style 7T rfMRI data (1.6-mm isotropic resolution, 5-fold slice and 2-fold in-plane acceleration, 3600 image volumes and ∼ 1-h scan) were acquired with pTx and the results were compared to those acquired with the original 7T HCP rfMRI protocol. The use of pTx significantly improved flip-angle uniformity across the brain, with coefficient of variation (i.e., std/mean) of whole-brain flip-angle distribution reduced on average by ∼39%. This in turn yielded ∼17% increase in group temporal SNR (tSNR) as averaged across the entire brain and ∼10% increase in group functional contrast-to-noise ratio (fCNR) as averaged across the grayordinate space (including cortical surfaces and subcortical voxels). Furthermore, when placing a seed in either the posterior parietal lobe or putamen to estimate seed-based dense connectome, the increase in fCNR was observed to translate into stronger correlation of the seed with the rest of the grayordinate space. We have demonstrated the utility of pTx for slice-accelerated high-resolution whole-brain rfMRI at 7T; as compared to current state-of-the-art, the use of pTx improves flip-angle uniformity, increases tSNR, enhances fCNR and strengthens functional connectivity estimation.
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Affiliation(s)
- Xiaoping Wu
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, MN, United States.
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, MN, United States
| | - An T Vu
- Center for Imaging of Neurodegenerative Diseases, VA Healthcare System, San Francisco, CA, United States
| | - Steen Moeller
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, MN, United States
| | | | - Essa Yacoub
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, MN, United States
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, MN, United States
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23
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Garwood M, Uğurbil K. RF pulse methods for use with surface coils: Frequency-modulated pulses and parallel transmission. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 291:84-93. [PMID: 29705035 PMCID: PMC5943143 DOI: 10.1016/j.jmr.2018.01.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 01/24/2018] [Indexed: 06/08/2023]
Abstract
The first use of a surface coil to obtain a 31P NMR spectrum from an intact rat by Ackerman and colleagues initiated a revolution in magnetic resonance imaging (MRI) and spectroscopy (MRS). Today, we take it for granted that one can detect signals in regions external to an RF coil; at the time, however, this concept was most unusual. In the approximately four decade long period since its introduction, this simple idea gave birth to an increasing number of innovations that has led to transformative changes in the way we collect data in an in vivo magnetic resonance experiment, particularly with MRI of humans. These innovations include spatial localization and/or encoding based on the non-uniform B1 field generated by the surface coil, leading to new spectroscopic localization methods, image acceleration, and unique RF pulses that deal with B1 inhomogeneities and even reduce power deposition. Without the surface coil, many of the major technological advances that define the extraordinary success of MRI in clinical diagnosis and in biomedical research, as exemplified by projects like the Human Connectome Project, would not have been possible.
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Affiliation(s)
- Michael Garwood
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN 55455 USA.
| | - Kamil Uğurbil
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN 55455 USA
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24
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Brunheim S, Gratz M, Johst S, Bitz AK, Fiedler TM, Ladd ME, Quick HH, Orzada S. Fast and accurate multi-channel B1+ mapping based on the TIAMO technique for 7T UHF body MRI. Magn Reson Med 2018; 79:2652-2664. [PMID: 28994132 DOI: 10.1002/mrm.26925] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 08/21/2017] [Accepted: 08/26/2017] [Indexed: 01/11/2023]
Abstract
PURPOSE Current methods for mitigation of transmit field B1+ inhomogeneities at ultrahigh field (UHF) MRI by multi-channel radiofrequency (RF) shimming rely on accurate B1+ mapping. This can be time consuming when many RF channels have to be mapped for in vivo body MRI, where the B1 maps should ideally be acquired within a single breath-hold. Therefore, a new B1+ mapping technique (B1TIAMO) is proposed. METHODS The performance of this technique is validated against an established method (DREAM) in phantom measurements for a cylindrical head phantom with an 8-channel transmit/receive (Tx/Rx) array. Furthermore, measurements for a 32-channel Tx/Rx remote array are conducted in a large body phantom and the |B1+| map reliability is validated against simulations of the transmit RF field distribution. Finally, in vivo results of this new mapping technique for human abdomen are presented. RESULTS For the head phantom (8-channel Tx/Rx coil), the single |B1+| comparison between B1 TIAMO, the direct DREAM measurements, and simulation data showed good agreement with 10-19% difference. For the large body phantom (32-channel Tx/Rx coil), B1TIAMO matched the RF field simulations well. CONCLUSION The results demonstrate the potential to acquire 32 accurate single-channel B1+ maps for large field-of-view body imaging within only a single breath-hold of 16 s at 7T UHF MRI. Magn Reson Med 79:2652-2664, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Sascha Brunheim
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Marcel Gratz
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Sören Johst
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
| | - Andreas K Bitz
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, FH Aachen-University of Applied Sciences, Aachen, Germany
| | - Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Mark E Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stephan Orzada
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
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25
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Wu X, Auerbach EJ, Vu AT, Moeller S, Lenglet C, Schmitter S, Van de Moortele PF, Yacoub E, Uğurbil K. High-resolution whole-brain diffusion MRI at 7T using radiofrequency parallel transmission. Magn Reson Med 2018; 80:1857-1870. [PMID: 29603381 DOI: 10.1002/mrm.27189] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2017] [Revised: 02/20/2018] [Accepted: 03/02/2018] [Indexed: 12/21/2022]
Abstract
PURPOSE Investigating the utility of RF parallel transmission (pTx) for Human Connectome Project (HCP)-style whole-brain diffusion MRI (dMRI) data at 7 Tesla (7T). METHODS Healthy subjects were scanned in pTx and single-transmit (1Tx) modes. Multiband (MB), single-spoke pTx pulses were designed to image sagittal slices. HCP-style dMRI data (i.e., 1.05-mm resolutions, MB2, b-values = 1000/2000 s/mm2 , 286 images and 40-min scan) and data with higher accelerations (MB3 and MB4) were acquired with pTx. RESULTS pTx significantly improved flip-angle detected signal uniformity across the brain, yielding ∼19% increase in temporal SNR (tSNR) averaged over the brain relative to 1Tx. This allowed significantly enhanced estimation of multiple fiber orientations (with ∼21% decrease in dispersion) in HCP-style 7T dMRI datasets. Additionally, pTx pulses achieved substantially lower power deposition, permitting higher accelerations, enabling collection of the same data in 2/3 and 1/2 the scan time or of more data in the same scan time. CONCLUSION pTx provides a solution to two major limitations for slice-accelerated high-resolution whole-brain dMRI at 7T; it improves flip-angle uniformity, and enables higher slice acceleration relative to current state-of-the-art. As such, pTx provides significant advantages for rapid acquisition of high-quality, high-resolution truly whole-brain dMRI data.
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Affiliation(s)
- Xiaoping Wu
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - An T Vu
- Center for Imaging of Neurodegenerative Diseases, VA Healthcare System, San Francisco, California
| | - Steen Moeller
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Christophe Lenglet
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Sebastian Schmitter
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota.,Physikalisch-Technische Bundesanstalt, Berlin, Germany
| | | | - Essa Yacoub
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, Radiology, Medical School, University of Minnesota, Minneapolis, Minnesota
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26
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Ianni JD, Cao Z, Grissom WA. Machine learning RF shimming: Prediction by iteratively projected ridge regression. Magn Reson Med 2018; 80:1871-1881. [PMID: 29572990 DOI: 10.1002/mrm.27192] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Revised: 02/22/2018] [Accepted: 03/05/2018] [Indexed: 11/11/2022]
Abstract
PURPOSE To obviate online slice-by-slice RF shim optimization and reduce B1+ mapping requirements for patient-specific RF shimming in high-field magnetic resonance imaging. THEORY AND METHODS RF Shim Prediction by Iteratively Projected Ridge Regression (PIPRR) predicts patient-specific, SAR-efficient RF shims with a machine learning approach that merges learning with training shim design. To evaluate it, a set of B1+ maps was simulated for 100 human heads for a 24-element coil at 7T. Features were derived from tissue masks and the DC Fourier coefficients of the coils' B1+ maps in each slice, which were used for kernelized ridge regression prediction of SAR-efficient RF shim weights. Predicted shims were compared to directly designed shims, circularly polarized mode, and nearest-neighbor shims predicted using the same features. RESULTS PIPRR predictions had 87% and 13% lower B1+ coefficients of variation compared to circularly polarized mode and nearest-neighbor shims, respectively, and achieved homogeneity and SAR similar to that of directly designed shims. Predictions were calculated in 4.92 ms on average. CONCLUSION PIPRR predicted uniform, SAR-efficient RF shims, and could save a large amount of B1+ mapping and computation time in RF-shimmed ultra-high field magnetic resonance imaging.
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Affiliation(s)
- Julianna D Ianni
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee
| | - Zhipeng Cao
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee
| | - William A Grissom
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee.,Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee.,Department of Radiology, Vanderbilt University, Nashville, Tennessee.,Department of Electrical Engineering, Vanderbilt University, Nashville, Tennessee
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27
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Poser BA, Setsompop K. Pulse sequences and parallel imaging for high spatiotemporal resolution MRI at ultra-high field. Neuroimage 2018; 168:101-118. [PMID: 28392492 PMCID: PMC5630499 DOI: 10.1016/j.neuroimage.2017.04.006] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 04/01/2017] [Accepted: 04/03/2017] [Indexed: 12/18/2022] Open
Abstract
The SNR and CNR benefits of ultra-high field (UHF) have helped push the envelope of achievable spatial resolution in MRI. For applications based on susceptibility contrast where there is a large CNR gain, high quality sub-millimeter resolution imaging is now being routinely performed, particularly in fMRI and phase imaging/QSM. This has enabled the study of structure and function of very fine-scale structures in the brain. UHF has also helped push the spatial resolution of many other MRI applications as will be outlined in this review. However, this push in resolution comes at a cost of a large encoding burden leading to very lengthy scans. Developments in parallel imaging with controlled aliasing and the move away from 2D slice-by-slice imaging to much more SNR-efficient simultaneous multi-slice (SMS) and 3D acquisitions have helped address this issue. In particular, these developments have revolutionized the efficiency of UHF MRI to enable high spatiotemporal resolution imaging at an order of magnitude faster acquisition. In addition to describing the main approaches to these techniques, this review will also outline important key practical considerations in using these methods in practice. Furthermore, new RF pulse design to tackle the B1+ and SAR issues of UHF and the increased SAR and power requirement of SMS RF pulses will also be touched upon. Finally, an outlook into new developments of smart encoding in more dimensions, particularly through using better temporal/across-contrast encoding and reconstruction will be described. Just as controlled aliasing fully exploits spatial encoding in parallel imaging to provide large multiplicative gains in accelerations, the complimentary use of these new approaches in temporal and across-contrast encoding are expected to provide exciting opportunities for further large gains in efficiency to further push the spatiotemporal resolution of MRI.
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Affiliation(s)
- Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands.
| | - Kawin Setsompop
- Department of Radiology, Harvard Medical School, Boston, MA, USA; Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
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28
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Uğurbil K. Imaging at ultrahigh magnetic fields: History, challenges, and solutions. Neuroimage 2018; 168:7-32. [PMID: 28698108 PMCID: PMC5758441 DOI: 10.1016/j.neuroimage.2017.07.007] [Citation(s) in RCA: 83] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 07/05/2017] [Accepted: 07/07/2017] [Indexed: 01/06/2023] Open
Abstract
Following early efforts in applying nuclear magnetic resonance (NMR) spectroscopy to study biological processes in intact systems, and particularly since the introduction of 4 T human scanners circa 1990, rapid progress was made in imaging and spectroscopy studies of humans at 4 T and animal models at 9.4 T, leading to the introduction of 7 T and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has provided numerous technological solutions to challenges posed at these ultrahigh fields, and demonstrated the existence of significant advantages in signal-to-noise ratio and biological information content. Primary difference from lower fields is the deviation from the near field regime at the radiofrequencies (RF) corresponding to hydrogen resonance conditions. At such ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image non-uniformities for a given sample-coil configuration because of destructive and constructive interferences. These non-uniformities were initially considered detrimental to progress of imaging at high field strengths. However, they are advantageous for parallel imaging in signal reception and transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies and improvements in instrumentation and imaging methods, today ultrahigh fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques.
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Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota Medical School, Minneapolis, MN 55455, USA.
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29
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Ertan K, Taraghinia S, Sadeghi A, Atalar E. A z-gradient array for simultaneous multi-slice excitation with a single-band RF pulse. Magn Reson Med 2017; 80:400-412. [PMID: 29205480 DOI: 10.1002/mrm.27031] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 11/13/2017] [Accepted: 11/13/2017] [Indexed: 12/25/2022]
Abstract
PURPOSE Multi-slice radiofrequency (RF) pulses have higher specific absorption rates, more peak RF power, and longer pulse durations than single-slice RF pulses. Gradient field design techniques using a z-gradient array are investigated for exciting multiple slices with a single-band RF pulse. THEORY AND METHODS Two different field design methods are formulated to solve for the required current values of the gradient array elements for the given slice locations. The method requirements are specified, optimization problems are formulated for the minimum current norm and an analytical solution is provided. A 9-channel z-gradient coil array driven by independent, custom-designed gradient amplifiers is used to validate the theory. RESULTS Performance measures such as normalized slice thickness error, gradient strength per unit norm current, power dissipation, and maximum amplitude of the magnetic field are provided for various slice locations and numbers of slices. Two and 3 slices are excited by a single-band RF pulse in simulations and phantom experiments. CONCLUSION The possibility of multi-slice excitation with a single-band RF pulse using a z-gradient array is validated in simulations and phantom experiments. Magn Reson Med 80:400-412, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Koray Ertan
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
| | - Soheil Taraghinia
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
| | - Alireza Sadeghi
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara, Turkey
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30
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Gras V, Mauconduit F, Vignaud A, Amadon A, Le Bihan D, Stöcker T, Boulant N. Design of universal parallel-transmit refocusing k T -point pulses and application to 3D T 2 -weighted imaging at 7T. Magn Reson Med 2017; 80:53-65. [PMID: 29193250 DOI: 10.1002/mrm.27001] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 10/02/2017] [Accepted: 10/16/2017] [Indexed: 12/18/2022]
Abstract
PURPOSE T2 -weighted sequences are particularly sensitive to the radiofrequency (RF) field inhomogeneity problem at ultra-high-field because of the errors accumulated by the imperfections of the train of refocusing pulses. As parallel transmission (pTx) has proved particularly useful to counteract RF heterogeneities, universal pulses were recently demonstrated to save precious time and computational efforts by skipping B1 calibration and online RF pulse tailoring. Here, we report a universal RF pulse design for non-selective refocusing pulses to mitigate the RF inhomogeneity problem at 7T in turbo spin-echo sequences with variable flip angles. METHOD Average Hamiltonian theory was used to synthetize a single non-selective refocusing pulse with pTx while optimizing its scaling properties in the presence of static field offsets. The design was performed under explicit power and specific absorption rate constraints on a database of 10 subjects using a 8Tx-32Rx commercial coil at 7T. To validate the proposed design, the RF pulses were tested in simulation and applied in vivo on 5 additional test subjects. RESULTS The root-mean-square rotation angle error (RA-NRMSE) evaluation and experimental data demonstrated great improvement with the proposed universal pulses (RA-NRMSE ∼8%) compared to the standard circularly polarized mode of excitation (RA-NRMSE ∼26%). CONCLUSION This work further completes the spectrum of 3D universal pulses to mitigate RF field inhomogeneity throughout all 3D MRI sequences without any pTx calibration. The approach returns a single pulse that can be scaled to match the desired flip angle train, thereby increasing the modularity of the proposed plug and play approach. Magn Reson Med 80:53-65, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Vincent Gras
- CEA, DRF, Joliot, NeuroSpin, Unirs, CEA Saclay, Gif sur Yvette, France
| | | | - Alexandre Vignaud
- CEA, DRF, Joliot, NeuroSpin, Unirs, CEA Saclay, Gif sur Yvette, France
| | - Alexis Amadon
- CEA, DRF, Joliot, NeuroSpin, Unirs, CEA Saclay, Gif sur Yvette, France
| | - Denis Le Bihan
- CEA, DRF, Joliot, NeuroSpin, Unirs, CEA Saclay, Gif sur Yvette, France
| | - Tony Stöcker
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Nicolas Boulant
- CEA, DRF, Joliot, NeuroSpin, Unirs, CEA Saclay, Gif sur Yvette, France
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31
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Wu W, Miller KL. Image formation in diffusion MRI: A review of recent technical developments. J Magn Reson Imaging 2017; 46:646-662. [PMID: 28194821 PMCID: PMC5574024 DOI: 10.1002/jmri.25664] [Citation(s) in RCA: 79] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Accepted: 01/25/2017] [Indexed: 12/13/2022] Open
Abstract
Diffusion magnetic resonance imaging (MRI) is a standard imaging tool in clinical neurology, and is becoming increasingly important for neuroscience studies due to its ability to depict complex neuroanatomy (eg, white matter connectivity). Single-shot echo-planar imaging is currently the predominant formation method for diffusion MRI, but suffers from blurring, distortion, and low spatial resolution. A number of methods have been proposed to address these limitations and improve diffusion MRI acquisition. Here, the recent technical developments for image formation in diffusion MRI are reviewed. We discuss three areas of advance in diffusion MRI: improving image fidelity, accelerating acquisition, and increasing the signal-to-noise ratio. LEVEL OF EVIDENCE 5 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:646-662.
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Affiliation(s)
- Wenchuan Wu
- FMRIB Centre, Nuffield Department of Clinical NeurosciencesUniversity of OxfordOxfordUK
| | - Karla L. Miller
- FMRIB Centre, Nuffield Department of Clinical NeurosciencesUniversity of OxfordOxfordUK
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32
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Gras V, Boland M, Vignaud A, Ferrand G, Amadon A, Mauconduit F, Le Bihan D, Stöcker T, Boulant N. Homogeneous non-selective and slice-selective parallel-transmit excitations at 7 Tesla with universal pulses: A validation study on two commercial RF coils. PLoS One 2017; 12:e0183562. [PMID: 28827835 PMCID: PMC5565195 DOI: 10.1371/journal.pone.0183562] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Accepted: 08/07/2017] [Indexed: 11/21/2022] Open
Abstract
Parallel transmission (pTx) technology, despite its great potential to mitigate the transmit field inhomogeneity problem in magnetic resonance imaging at ultra-high field (UHF), suffers from a cumbersome calibration procedure, thereby making the approach problematic for routine use. The purpose of this work is to demonstrate on two different 7T systems respectively equipped with 8-transmit-channel RF coils from two different suppliers (Rapid-Biomed and Nova Medical), the benefit of so-called universal pulses (UP), optimized to produce uniform excitations in the brain in a population of adults and making unnecessary the calibration procedures mentioned above. Non-selective and slice-selective UPs were designed to return homogeneous excitation profiles throughout the brain simultaneously on a group of ten subjects, which then were subsequently tested on ten additional volunteers in magnetization prepared rapid gradient echo (MPRAGE) and multi-slice gradient echo (2D GRE) protocols. The results were additionally compared experimentally with the standard non-pTx circularly-polarized (CP) mode, and in simulation with subject-specific tailored excitations. For both pulse types and both coils, the UP mode returned a better signal and contrast homogeneity than the CP mode. Retrospective analysis of the flip angle (FA) suggests that the FA deviation from the nominal FA on average over a healthy adult population does not exceed 11% with the calibration-free parallel-transmit pulses whereas it goes beyond 25% with the CP mode. As a result the universal pulses designed in this work confirm their relevance in 3D and 2D protocols with commercially available equipment. Plug-and-play pTx implementations henceforth become accessible to exploit with more flexibility the potential of UHF for brain imaging.
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Affiliation(s)
- Vincent Gras
- CEA/DRF/Joliot/NeuroSpin/Unirs, Gif sur Yvette, France
| | - Markus Boland
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | | | | | - Alexis Amadon
- CEA/DRF/Joliot/NeuroSpin/Unirs, Gif sur Yvette, France
| | | | | | - Tony Stöcker
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Nicolas Boulant
- CEA/DRF/Joliot/NeuroSpin/Unirs, Gif sur Yvette, France
- * E-mail:
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Hsu YC, Lattanzi R, Chu YH, Cloos MA, Sodickson DK, Lin FH. Mitigation of B1+ inhomogeneity using spatially selective excitation with jointly designed quadratic spatial encoding magnetic fields and RF shimming. Magn Reson Med 2017; 78:577-587. [PMID: 27696518 PMCID: PMC5538365 DOI: 10.1002/mrm.26397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 08/05/2016] [Accepted: 08/06/2016] [Indexed: 11/05/2022]
Abstract
PURPOSE The inhomogeneity of flip angle distribution is a major challenge impeding the application of high-field MRI. We report a method combining spatially selective excitation using generalized spatial encoding magnetic fields (SAGS) with radiofrequency (RF) shimming to achieve homogeneous excitation. This method can be an alternative approach to address the challenge of B1+ inhomogeneity using nonlinear gradients. METHODS We proposed a two-step algorithm that jointly optimizes the combination of nonlinear spatial encoding magnetic fields and the combination of multiple RF transmitter coils and then optimizes the locations, RF amplitudes, and phases of the spokes. RESULTS Our results show that jointly designed SAGS and RF shimming can provide a more homogeneous flip angle distribution than using SAGS or RF shimming alone. Compared with RF shimming alone, our approach can reduce the relative standard deviation of flip angle by 56% and 52% using phantom and human head data, respectively. CONCLUSION The jointly designed SAGS and RF shimming method can be used to achieve homogeneous flip angle distributions when fully parallel RF transmission is not available. Magn Reson Med 78:577-587, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Yi-Cheng Hsu
- Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan
| | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 1 Ave. New York, NY 10016 USA
| | - Ying-Hua Chu
- Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan
| | - Martijn A. Cloos
- Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 1 Ave. New York, NY 10016 USA
| | - Daniel K. Sodickson
- Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 1 Ave. New York, NY 10016 USA
| | - Fa-Hsuan Lin
- Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan
- Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland
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High resolution data analysis strategies for mesoscale human functional MRI at 7 and 9.4T. Neuroimage 2017; 164:48-58. [PMID: 28416453 PMCID: PMC5745233 DOI: 10.1016/j.neuroimage.2017.03.058] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 02/22/2017] [Accepted: 03/28/2017] [Indexed: 01/22/2023] Open
Abstract
The advent of ultra-high field functional magnetic resonance imaging (fMRI) has greatly facilitated submillimeter resolution acquisitions (voxel volume below (1 mm³)), allowing the investigation of cortical columns and cortical depth dependent (i.e. laminar) structures in the human brain. Advanced data analysis techniques are essential to exploit the information in high resolution functional measures. In this article, we use recent, exemplary 9.4 T human functional and anatomical data to review the advantages and disadvantages of (1) pooling high resolution data across regions of interest for cortical depth profile analysis, (2) pooling across cortical depths for mapping patches of cortex while discarding depth-dependent (i.e. columnar) effects, and (3) isotropic sampling without pooling to assess individual voxel’s responses. A set of cortical depth meshes may be a solution to sampling information tangentially while keeping correspondence across depths. For quantitative analysis of the spatial organization in fine-grained structures, a cortical grid approach is advantageous. We further extend this general framework by combining it with a previously introduced cortical layer volume-preserving (equi-volume) approach. This framework can readily accommodate the research questions which allow for spatial smoothing within or across layers. We demonstrate and discuss that equi-volume sampling yields a slight advantage over equidistant sampling given the current limitations of fMRI voxel size, participant motion, coregistration and segmentation. Our 9.4 T human anatomical and functional data indicate the advantage over lower fields including 7 T and demonstrate the practical applicability of T2* and T2-weighted fMRI acquisitions. High resolution regular cortical grids are advantageous for local applications. Equi-volume sampling is slightly advantageous over equidistant sampling in-vivo. Isotropic submillimeter cortical sampling without spatial pooling requires high SNR. 9.4 T human T2 and T2* BOLD fMRI are practically feasible and provide high SNR. 9.4 T T2*-weighted 0.35 mm iso. res. anatomical images for laminar contrast in vivo.
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35
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Schmitter S, Moeller S, Wu X, Auerbach EJ, Metzger GJ, Van de Moortele PF, Uğurbil K. Simultaneous multislice imaging in dynamic cardiac MRI at 7T using parallel transmission. Magn Reson Med 2017; 77:1010-1020. [PMID: 26949107 DOI: 10.1002/mrm.26180] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Revised: 01/08/2016] [Accepted: 02/03/2016] [Indexed: 12/25/2022]
Abstract
PURPOSE Cardiac MRI at 7T suffers from contrast heterogeneity that can be mitigated with parallel transmission (pTX) and, when performed during breath-hold, from a limited number of slices that can be multiplied with multiband (MB) radiofrequency pulses by simultaneous excitation of multiple slices (SMS). The goal of this study was to apply both approaches simultaneously. METHODS Using a 16-channel transmit/receive body coil, pTX SMS was applied with/without CAIPIRINHA with a modified gradient echo cine sequence. Different calibration schemes were investigated for the slice-GRAPPA reconstruction kernels as a function of the cardiac cycle. RESULTS Excellent slice separation for MB = 2 was achieved with CAIPIRINHA, with slice leakage values below 3% for 99% of all voxels. A critical finding of this study was the variation of the MB leakage factor in the heart by as much as 30% throughout the cardiac cycle, which was reduced greatly when reconstruction kernels were calibrated on multiple cardiac phases. Acceptable results were still obtained when applying further acceleration with MB = 3 in combination with in-plane GRAPPA. In one case, two-spoke pulses were compared with one-spoke pulses, resulting as expected in improved homogeneity. CONCLUSION pTX SMS imaging at 7T can address contrast heterogeneity while allowing larger slice coverage in cardiac MRI performed under breath-hold. Magn Reson Med 77:1010-1020, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Sebastian Schmitter
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Steen Moeller
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Xiaoping Wu
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Edward J Auerbach
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Gregory J Metzger
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | | | - Kâmil Uğurbil
- University of Minnesota, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
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Harada T, Kudo K, Uwano I, Yamashita F, Kameda H, Matsuda T, Sasaki M, Shirato H. Breath-holding during the Calibration Scan Improves the Reproducibility of Parallel Transmission at 7T for Human Brain. Magn Reson Med Sci 2017; 16:23-31. [PMID: 27001392 PMCID: PMC5600040 DOI: 10.2463/mrms.mp.2015-0137] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Purpose: The B0 and B1+ maps required for calculation of the radiofrequency (RF) pulse of parallel transmission (pTx) are obtained in calibration scans; however, they may be affected by respiratory motion. We aimed to compare the reproducibility of B0 and B1+ maps and gradient echo (GRE) images of the brain scanned with pTx at 7T between free-breathing (FB) and breath-holding (BH) conditions during the calibration scan. Methods: Nine healthy volunteers were scanned by 7T MRI using a two-channel quadrature head coil. In the pTx calibration scans performed with FB and BH, the B0 map was obtained from two different TE images and the B1+ map was calculated by the Bloch-Siegert method. A GRE image (gradient-recalled-acquisition in steady state) was also obtained with RF shimming and RF design of pTx with spoke method, as well as quadrature transmission (qTx). All the scans were repeated over five sessions. The reproducibility of the B0 and B1+ maps and GRE image was evaluated with region-of-interest measurements using inter-session standard deviation (SD) and coefficient of variation (CV) values. Intensity homogeneity of GRE images was also assessed with in-plane CV. Results: Inter-session SDs of B0 and B1+ maps were significantly smaller in BH (P < 0.01). Inter-session CVs of GRE images were significantly smaller in qTx than BH and FB (P < 0.01, both); however, the CVs of BH were significantly smaller (P < 0.01). In-plane CVs of FB and BH with RF shimming were not significantly different with qTx; however, CVs of FB and BH with RF design were significantly smaller than those of qTx (P < 0.05 and P < 0.01, respectively). Conclusion: BH could improve the reproducibility of B0 and B1+ maps in pTx calibration scans and GRE images. These results might facilitate the development of pTx in human brain at 7T.
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Affiliation(s)
- Taisuke Harada
- Department of Radiation Medicine, Hokkaido University Graduate School of Medicine
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Tse DHY, Wiggins CJ, Poser BA. High-resolution gradient-recalled echo imaging at 9.4T using 16-channel parallel transmit simultaneous multislice spokes excitations with slice-by-slice flip angle homogenization. Magn Reson Med 2016; 78:1050-1058. [PMID: 27774641 PMCID: PMC5574011 DOI: 10.1002/mrm.26501] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 08/30/2016] [Accepted: 09/17/2016] [Indexed: 11/26/2022]
Abstract
Purpose In order to fully benefit from the improved signal‐to‐noise and contrast‐to‐noise ratios at 9.4T, the challenges of
B1+ inhomogeneity and the long acquisition time of high‐resolution 2D gradient‐recalled echo (GRE) imaging were addressed. Theory and Methods Flip angle homogenized excitations were achieved by parallel transmission (pTx) of 3‐spoke pulses, designed by magnitude least‐squares optimization in a slice‐by‐slice fashion; the acquisition time reduction was achieved by simultaneous multislice (SMS) pulses. The slice‐specific spokes complex radiofrequency scaling factors were applied to sinc waveforms on a per‐channel basis and combined with the other pulses in an SMS slice group to form the final SMS‐pTX pulse. Optimal spokes locations were derived from simulations. Results Flip angle maps from presaturation TurboFLASH showed improvement of flip angle homogenization with 3‐spoke pulses over CP‐mode excitation (normalized root‐mean‐square error [NRMSE] 0.357) as well as comparable excitation homogeneity across the single‐band (NRMSE 0.119), SMS‐2 (NRMSE 0.137), and SMS‐3 (NRMSE 0.132) 3‐spoke pulses. The application of the 3‐spoke SMS‐3 pulses in a 48‐slice GRE protocol, which has an in‐plane resolution of 0.28 × 0.28 mm, resulted in a 50% reduction of scan duration (total acquisition time 6:52 min including reference scans). Conclusion Time‐efficient flip angle homogenized high‐resolution GRE imaging at 9.4T was accomplished by using slice‐specific SMS‐pTx spokes excitations. Magn Reson Med 78:1050–1058, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Desmond H Y Tse
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands
| | | | - Benedikt A Poser
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands
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Padormo F, Beqiri A, Hajnal JV, Malik SJ. Parallel transmission for ultrahigh-field imaging. NMR IN BIOMEDICINE 2016; 29:1145-61. [PMID: 25989904 PMCID: PMC4995736 DOI: 10.1002/nbm.3313] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Revised: 03/27/2015] [Accepted: 03/29/2015] [Indexed: 05/24/2023]
Abstract
The development of MRI systems operating at or above 7 T has provided researchers with a new window into the human body, yielding improved imaging speed, resolution and signal-to-noise ratio. In order to fully realise the potential of ultrahigh-field MRI, a range of technical hurdles must be overcome. The non-uniformity of the transmit field is one of such issues, as it leads to non-uniform images with spatially varying contrast. Parallel transmission (i.e. the use of multiple independent transmission channels) provides previously unavailable degrees of freedom that allow full spatial and temporal control of the radiofrequency (RF) fields. This review discusses the many ways in which these degrees of freedom can be used, ranging from making more uniform transmit fields to the design of subject-tailored RF pulses for both uniform excitation and spatial selection, and also the control of the specific absorption rate. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.
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Affiliation(s)
- Francesco Padormo
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Arian Beqiri
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Joseph V Hajnal
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
- Centre for the Developing Brain, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Shaihan J Malik
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
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Setsompop K, Feinberg DA, Polimeni JR. Rapid brain MRI acquisition techniques at ultra-high fields. NMR IN BIOMEDICINE 2016; 29:1198-221. [PMID: 26835884 PMCID: PMC5245168 DOI: 10.1002/nbm.3478] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 11/28/2015] [Accepted: 12/02/2015] [Indexed: 05/04/2023]
Abstract
Ultra-high-field MRI provides large increases in signal-to-noise ratio (SNR) as well as enhancement of several contrast mechanisms in both structural and functional imaging. Combined, these gains result in a substantial boost in contrast-to-noise ratio that can be exploited for higher-spatial-resolution imaging to extract finer-scale information about the brain. With increased spatial resolution, however, there is a concurrent increased image-encoding burden that can cause unacceptably long scan times for structural imaging and slow temporal sampling of the hemodynamic response in functional MRI - particularly when whole-brain imaging is desired. To address this issue, new directions of imaging technology development - such as the move from conventional 2D slice-by-slice imaging to more efficient simultaneous multislice (SMS) or multiband imaging (which can be viewed as "pseudo-3D" encoding) as well as full 3D imaging - have provided dramatic improvements in acquisition speed. Such imaging paradigms provide higher SNR efficiency as well as improved encoding efficiency. Moreover, SMS and 3D imaging can make better use of coil sensitivity information in multichannel receiver arrays used for parallel imaging acquisitions through controlled aliasing in multiple spatial directions. This has enabled unprecedented acceleration factors of an order of magnitude or higher in these imaging acquisition schemes, with low image artifact levels and high SNR. Here we review the latest developments of SMS and 3D imaging methods and related technologies at ultra-high field for rapid high-resolution functional and structural imaging of the brain. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - David A. Feinberg
- Helen Wills Institute for Neuroscience, University of California, Berkeley, CA, USA
- Advanced MRI Technologies, Sebastopol, CA, USA
| | - Jonathan R. Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
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Wu X, Tian J, Schmitter S, Vaughan JT, Uğurbil K, Van de Moortele PF. Distributing coil elements in three dimensions enhances parallel transmission multiband RF performance: A simulation study in the human brain at 7 Tesla. Magn Reson Med 2016; 75:2464-72. [PMID: 26997332 PMCID: PMC6014621 DOI: 10.1002/mrm.26194] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Revised: 01/18/2016] [Accepted: 02/10/2016] [Indexed: 12/26/2022]
Abstract
PURPOSE We explore the advantages of using a double-ring radiofrequency (RF) array and slice orientation to design parallel transmission (pTx) multiband (MB) pulses for simultaneous multislice (SMS) imaging with whole-brain coverage at 7 Tesla (T). METHODS A double-ring head array with 16 elements split evenly in two rings stacked in the z-direction was modeled and compared with two single-ring arrays consisting of 8 or 16 elements. The array performance was evaluated by designing band-specific pTx MB pulses with local specific absorption rate (SAR) control. The impact of slice orientations was also investigated. RESULTS The double-ring array consistently and significantly outperformed the other two single-ring arrays, with peak local SAR reduced by up to 40% at a fixed excitation error of 0.024. For all three arrays, exciting sagittal or coronal slices yielded better RF performance than exciting axial or oblique slices. CONCLUSIONS A double-ring RF array can be used to drastically improve SAR versus excitation fidelity tradeoff for pTx MB pulse design for brain imaging at 7 T; therefore, it is preferable against single-ring RF array designs when pursuing various biomedical applications of pTx SMS imaging. In comparing the stripline arrays, coronal and sagittal slices are more advantageous than axial and oblique slices for pTx MB pulses. Magn Reson Med 75:2464-2472, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Xiaoping Wu
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - Jinfeng Tian
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - Sebastian Schmitter
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - J Tommy Vaughan
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
| | - Kâmil Uğurbil
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, MN
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Manoliu A, Ho M, Nanz D, Dappa E, Boss A, Grodzki DM, Liu W, Chhabra A, Andreisek G, Kuhn FP. MR neurographic orthopantomogram: Ultrashort echo-time imaging of mandibular bone and teeth complemented with high-resolution morphological and functional MR neurography. J Magn Reson Imaging 2016; 44:393-400. [PMID: 26854879 DOI: 10.1002/jmri.25178] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 01/20/2016] [Indexed: 12/22/2022] Open
Abstract
PURPOSE Panoramical radiographs or cone-beam computed tomography (CT) are the standard-of-care in dental imaging to assess teeth, mandible, and mandibular canal pathologies, but do not allow assessment of the inferior alveolar nerve itself nor of its branches. We propose a new technique for "MR neurographic orthopantomograms" exploiting ultrashort echo-time (UTE) imaging of bone and teeth complemented with high-resolution morphological and functional MR neurography. MATERIALS AND METHODS The Institutional Review Board approved the study in 10 healthy volunteers. Imaging of the subjects mandibles at 3.0T (Magnetom Skyra, Siemens-Healthcare) using a 64-channel head coil with isotropic spatial resolution for subsequent multiplanar reformatting, was performed. Bone images were acquired using a 3D PETRA sequence (TE, 0.07 msec). Morphological nerve imaging was performed using a dedicated 3D PSIF and 3D SPACE STIR sequence. Functional MR neurography was accomplished using a new accelerated diffusion-tensor-imaging (DTI) prototype sequence (2D SMS-accelerated RESOLVE). Qualitative and quantitative image analysis was performed and descriptive statistics are provided. RESULTS Image acquisition and subsequent postprocessing into the MR neurographic orthopantomogram by overlay of morphological and functional images were feasible in all 10 volunteers without artifacts. All mandibular bones and mandibular nerves were assessable and considered normal. Fiber tractography with quantitative evaluation of physiological diffusion properties of mandibular nerves yielded the following mean ± SD values: fractional anisotropy, 0.43 ± 0.07; mean diffusivity (mm(2) /s), 0.0014 ± 0.0002; axial diffusivity, 0.0020 ± 0.0002, and radial diffusivity, 0.0011 ± 0.0001. CONCLUSION The proposed technique of MR neurographic orthopantomogram exploiting UTE imaging complemented with high-resolution morphological and functional MR neurography was feasible and allowed comprehensive assessment of osseous texture and neural microarchitecture in a single examination. J. Magn. Reson. Imaging 2016;44:393-400.
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Affiliation(s)
- Andrei Manoliu
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Michael Ho
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Daniel Nanz
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Evelyn Dappa
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Andreas Boss
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | | | - Wei Liu
- Siemens Shenzhen Magnetic Resonance Ltd, Shenzhen, China
| | - Avneesh Chhabra
- Department of Radiology, Southwestern Medical Center, Dallas, Texas, USA
| | - Gustav Andreisek
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Felix P Kuhn
- Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
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Aigner CS, Clason C, Rund A, Stollberger R. Efficient high-resolution RF pulse design applied to simultaneous multi-slice excitation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 263:33-44. [PMID: 26773524 DOI: 10.1016/j.jmr.2015.11.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 11/23/2015] [Accepted: 11/25/2015] [Indexed: 06/05/2023]
Abstract
RF pulse design via optimal control is typically based on gradient and quasi-Newton approaches and therefore suffers from slow convergence. We present a flexible and highly efficient method that uses exact second-order information within a globally convergent trust-region CG-Newton method to yield an improved convergence rate. The approach is applied to the design of RF pulses for single- and simultaneous multi-slice (SMS) excitation and validated using phantom and in vivo experiments on a 3T scanner using a modified gradient echo sequence.
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Affiliation(s)
- Christoph Stefan Aigner
- Institute of Medical Engineering, Graz University of Technology, Stremayrgasse 16, 8010 Graz, Austria; BioTechMed Graz, 8010 Graz, Austria.
| | - Christian Clason
- Faculty of Mathematics, University of Duisburg-Essen, 45117 Essen, Germany
| | - Armin Rund
- Institute for Mathematics and Scientific Computing, University of Graz, Heinrichstrasse 36, 8010 Graz, Austria
| | - Rudolf Stollberger
- Institute of Medical Engineering, Graz University of Technology, Stremayrgasse 16, 8010 Graz, Austria; BioTechMed Graz, 8010 Graz, Austria
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Sbrizzi A, Poser BA, Tse DHY, Hoogduin H, Luijten PR, van den Berg CAT. RF peak power reduction in CAIPIRINHA excitation by interslice phase optimization. NMR IN BIOMEDICINE 2015; 28:1393-1401. [PMID: 26387856 DOI: 10.1002/nbm.3360] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Revised: 06/18/2015] [Accepted: 06/18/2015] [Indexed: 06/05/2023]
Abstract
The purpose of this work was to show that the overall peak power of RF pulses for CAIPIRINHA excitation can be substantially reduced by applying interslice phase relaxation. The optimal phases are scan dependent and can be quickly calculated by the proposed method. The multi-band RF pulse design is implemented as the minimization of a linear objective function with quadratic constraints. The interslice phase is considered to be a variable for optimization. In the case of a phase cycling scheme (CAIPIRINHA), the peak power is considered over all pulses. The computation time (about 1 s) is compatible with online RF pulse design. It is shown that the optimal interslice phases depend on the CAIPIRINHA scheme used and that RF peak power is reduced when the CAIPIRINHA phase cycling is taken into account in the optimization. The proposed method is extremely fast and results in RF pulses with low peak power for CAIPIRINHA excitation. The MATLAB implementation is given in the appendix; it allows for online determination of scan-dependent phase parameters. Furthermore, the method can be easily extended to pTx shimming systems in the context of multi-slice excitations, and this possibility is included in the software.
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Affiliation(s)
- Alessandro Sbrizzi
- Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Benedikt A Poser
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Desmond H Y Tse
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
- Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands
| | - Hans Hoogduin
- Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Peter R Luijten
- Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands
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Wu X, Zhang X, Tian J, Schmitter S, Hanna B, Strupp J, Pfeuffer J, Hamm M, Wang D, Nistler J, He B, Vaughan JT, Ugurbil K, Van de Moortele PF. Comparison of RF body coils for MRI at 3 T: a simulation study using parallel transmission on various anatomical targets. NMR IN BIOMEDICINE 2015; 28:1332-44. [PMID: 26332290 PMCID: PMC4573930 DOI: 10.1002/nbm.3378] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Revised: 07/17/2015] [Accepted: 07/20/2015] [Indexed: 05/09/2023]
Abstract
The performance of multichannel transmit coil layouts and parallel transmission (pTx) RF pulse design was evaluated with respect to transmit B1 (B1 (+)) homogeneity and specific absorption rate (SAR) at 3 T for a whole body coil. Five specific coils were modeled and compared: a 32-rung birdcage body coil (driven either in a fixed quadrature mode or a two-channel transmit mode), two single-ring stripline arrays (with either 8 or 16 elements), and two multi-ring stripline arrays (with two or three identical rings, stacked in the z axis and each comprising eight azimuthally distributed elements). Three anatomical targets were considered, each defined by a 3D volume representative of a meaningful region of interest (ROI) in routine clinical applications. For a given anatomical target, global or local SAR controlled pTx pulses were designed to homogenize RF excitation within the ROI. At the B1 (+) homogeneity achieved by the quadrature driven birdcage design, pTx pulses with multichannel transmit coils achieved up to about eightfold reduction in local and global SAR. When used for imaging head and cervical spine or imaging thoracic spine, the double-ring array outperformed all coils, including the single-ring arrays. While the advantage of the double-ring array became much less pronounced for pelvic imaging, with a substantially larger ROI, the pTx approach still provided significant gains over the quadrature birdcage coil. For all design scenarios, using the three-ring array did not necessarily improve the RF performance. Our results suggest that pTx pulses with multichannel transmit coils can reduce local and global SAR substantially for body coils while attaining improved B1 (+) homogeneity, particularly for a "z-stacked" double-ring design with coil elements arranged on two transaxial rings.
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Affiliation(s)
- Xiaoping Wu
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
| | - Xiaotong Zhang
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States
| | - Jinfeng Tian
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
| | - Sebastian Schmitter
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
| | - Brian Hanna
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
| | - John Strupp
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
| | | | | | | | | | - Bin He
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States
- Institute for Engineering in Medicine, University of Minnesota, Minneapolis, MN, United States
| | - J. Thomas Vaughan
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
| | - Kamil Ugurbil
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
| | - Pierre-Francois Van de Moortele
- University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, United States
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Wen Q, Kelley DAC, Banerjee S, Lupo JM, Chang SM, Xu D, Hess CP, Nelson SJ. Clinically feasible NODDI characterization of glioma using multiband EPI at 7 T. NEUROIMAGE-CLINICAL 2015; 9:291-9. [PMID: 26509116 PMCID: PMC4579286 DOI: 10.1016/j.nicl.2015.08.017] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 08/08/2015] [Accepted: 08/27/2015] [Indexed: 12/22/2022]
Abstract
Recent technological progress in the multiband echo planer imaging (MB EPI) technique enables accelerated MR diffusion weighted imaging (DWI) and allows whole brain, multi-b-value diffusion imaging to be acquired within a clinically feasible time. However, its applications at 7 T have been limited due to B1 field inhomogeneity and increased susceptibility artifact. It is an ongoing debate whether DWI at 7 T can be performed properly in patients, and a systematic SNR comparison for multiband spin-echo EPI between 3 T and 7 T has not been methodically studied. The goal of this study was to use MB EPI at 7 T in order to obtain 90-directional multi-shell DWI within a clinically feasible acquisition time for patients with glioma. This study included an SNR comparison between 3 T and 7 T, and the application of B1 mapping and distortion correction procedures for reducing the impact of variations in B0 and B1. The optimized multiband sequence was applied in 20 patients with glioma to generate both DTI and NODDI maps for comparison of values in tumor and normal appearing white matter (NAWM). Our SNR analysis showed that MB EPI at 7 T was comparable to that at 3 T, and the data quality acquired in patients was clinically acceptable. NODDI maps provided unique contrast within the T2 lesion that was not seen in anatomical images or DTI maps. Such contrast may reflect the complexity of tissue compositions associated with disease progression and treatment effects. The ability to consistently obtain high quality diffusion data at 7 T will contribute towards the implementation of a comprehensive brain MRI examination at ultra-high field. NODDI characterization of glioma at 7 T within 6 min with multiband EPI An SNR comparison was performed between 7 T and 3 T SE-EPI. SNR was comparable between 7 T and 3 T multiband SE-EPI. NODDI maps provided unique contrast within the glioma T2 lesion.
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Affiliation(s)
- Qiuting Wen
- UCSF/UCB Joint Graduate Group in Bioengineering, University of California, San Francisco (UCSF), San Francisco, CA, USA ; Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | | | | | - Janine M Lupo
- Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Susan M Chang
- Department of Neurological Surgery, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Duan Xu
- Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Christopher P Hess
- Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA
| | - Sarah J Nelson
- UCSF/UCB Joint Graduate Group in Bioengineering, University of California, San Francisco (UCSF), San Francisco, CA, USA ; Department of Radiology and Biomedical Imaging, University of California, San Francisco (UCSF), San Francisco, CA, USA ; Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA, USA
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Barth M, Breuer F, Koopmans PJ, Norris DG, Poser BA. Simultaneous multislice (SMS) imaging techniques. Magn Reson Med 2015; 75:63-81. [PMID: 26308571 PMCID: PMC4915494 DOI: 10.1002/mrm.25897] [Citation(s) in RCA: 347] [Impact Index Per Article: 38.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 07/25/2015] [Accepted: 07/27/2015] [Indexed: 12/25/2022]
Abstract
Simultaneous multislice imaging (SMS) using parallel image reconstruction has rapidly advanced to become a major imaging technique. The primary benefit is an acceleration in data acquisition that is equal to the number of simultaneously excited slices. Unlike in‐plane parallel imaging this can have only a marginal intrinsic signal‐to‐noise ratio penalty, and the full acceleration is attainable at fixed echo time, as is required for many echo planar imaging applications. Furthermore, for some implementations SMS techniques can reduce radiofrequency (RF) power deposition. In this review the current state of the art of SMS imaging is presented. In the Introduction, a historical overview is given of the history of SMS excitation in MRI. The following section on RF pulses gives both the theoretical background and practical application. The section on encoding and reconstruction shows how the collapsed multislice images can be disentangled by means of the transmitter pulse phase, gradient pulses, and most importantly using multichannel receiver coils. The relationship between classic parallel imaging techniques and SMS reconstruction methods is explored. The subsequent section describes the practical implementation, including the acquisition of reference data, and slice cross‐talk. Published applications of SMS imaging are then reviewed, and the article concludes with an outlook and perspective of SMS imaging. Magn Reson Med 75:63–81, 2016. © 2015 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance.
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Affiliation(s)
- Markus Barth
- Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia.,Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands
| | - Felix Breuer
- Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany
| | - Peter J Koopmans
- Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.,FMRIB Centre, University of Oxford, Oxford, United Kingdom
| | - David G Norris
- Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands.,Erwin L. Hahn Institute for Magnetic Resonance Imaging, UNESCO-Weltkulturerbe Zollverein, Leitstand Kokerei Zollverein, Essen, Germany.,MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands
| | - Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.,Maastricht Brain Imaging Center (M-BIC), Maastricht University, Maastricht, The Netherlands
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Vu AT, Auerbach E, Lenglet C, Moeller S, Sotiropoulos SN, Jbabdi S, Andersson J, Yacoub E, Ugurbil K. High resolution whole brain diffusion imaging at 7T for the Human Connectome Project. Neuroimage 2015; 122:318-31. [PMID: 26260428 DOI: 10.1016/j.neuroimage.2015.08.004] [Citation(s) in RCA: 130] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Revised: 07/31/2015] [Accepted: 08/01/2015] [Indexed: 11/16/2022] Open
Abstract
Mapping structural connectivity in healthy adults for the Human Connectome Project (HCP) benefits from high quality, high resolution, multiband (MB)-accelerated whole brain diffusion MRI (dMRI). Acquiring such data at ultrahigh fields (7T and above) can improve intrinsic signal-to-noise ratio (SNR), but suffers from shorter T2 and T2(⁎) relaxation times, increased B1(+) inhomogeneity (resulting in signal loss in cerebellar and temporal lobe regions), and increased power deposition (i.e. specific absorption rate (SAR)), thereby limiting our ability to reduce the repetition time (TR). Here, we present recent developments and optimizations in 7T image acquisitions for the HCP that allow us to efficiently obtain high quality, high resolution whole brain in-vivo dMRI data at 7T. These data show spatial details typically seen only in ex-vivo studies and complement already very high quality 3T HCP data in the same subjects. The advances are the result of intensive pilot studies aimed at mitigating the limitations of dMRI at 7T. The data quality and methods described here are representative of the datasets that will be made freely available to the community in 2015.
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Affiliation(s)
- A T Vu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA.
| | - E Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - C Lenglet
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - S Moeller
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - S N Sotiropoulos
- Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, UK
| | - S Jbabdi
- Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, UK
| | - J Andersson
- Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), University of Oxford, UK
| | - E Yacoub
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
| | - K Ugurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN 55455, USA
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Wu X, Schmitter S, Auerbach EJ, Uğurbil K, Van de Moortele PF. A generalized slab-wise framework for parallel transmit multiband RF pulse design. Magn Reson Med 2015; 75:1444-56. [PMID: 25994797 DOI: 10.1002/mrm.25689] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 02/10/2015] [Accepted: 02/17/2015] [Indexed: 11/05/2022]
Abstract
PURPOSE We propose a new slab-wise framework to design parallel transmit multiband pulses for volumetric simultaneous multislice imaging with a large field of view along the slice direction (FOVs). THEORY AND METHODS The slab-wise framework divides FOVs into a few contiguous slabs and optimizes pulses for each slab. Effects of relevant design parameters including slab number and transmit B1 (B1+) mapping slice placement were investigated for human brain imaging by designing pulses with global or local SAR control based on electromagnetic simulations of a 7T head RF array. Pulse design using in vivo B1+ maps was demonstrated and evaluated with Bloch simulations. RESULTS RF performance with respect to SAR reduction or B1+ homogenization across the entire human brain improved with increasing slabs; however, this improvement was nonlinear and leveled off at ∼12 slabs when the slab thickness reduced to ∼12 mm. The impact of using different slice placements for B1+ mapping was small. CONCLUSION Compared with slice-wise approaches where each of the many imaging slices requires both B1+ mapping and pulse optimization, the proposed slab-wise design framework attained comparable RF performance while drastically reducing the number of required pulses; therefore, it can be used to increase time efficiency for B1+ mapping, pulse calculation, and sequence preparation.
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Affiliation(s)
- Xiaoping Wu
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Sebastian Schmitter
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Edward J Auerbach
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Kâmil Uğurbil
- University of Minnesota Medical School, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
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Guérin B, Setsompop K, Ye H, Poser BA, Stenger AV, Wald LL. Design of parallel transmission pulses for simultaneous multislice with explicit control for peak power and local specific absorption rate. Magn Reson Med 2015; 73:1946-53. [PMID: 24938991 PMCID: PMC4269582 DOI: 10.1002/mrm.25325] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Revised: 05/26/2014] [Accepted: 05/27/2014] [Indexed: 11/11/2022]
Abstract
PURPOSE To design parallel transmit (pTx) simultaneous multislice (SMS) spokes pulses with explicit control for peak power and local and global specific absorption rate (SAR). METHODS We design SMS pTx least-squares and magnitude least squares spokes pulses while constraining local SAR using the virtual observation points (VOPs) compression of SAR matrices. We evaluate our approach in simulations of a head (7T) and a body (3T) coil with eight channels arranged in two z-rows. RESULTS For many of our simulations, control of average power by Tikhonov regularization of the SMS pTx spokes pulse design yielded pulses that violated hardware and SAR safety limits. On the other hand, control of peak power alone yielded pulses that violated local SAR limits. Pulses optimized with control of both local SAR and peak power satisfied all constraints and therefore had the best excitation performance under limited power and SAR constraints. These results extend our previous results for single slice pTx excitations but are more pronounced because of the large power demands and SAR of SMS pulses. CONCLUSIONS Explicit control of local SAR and peak power is required to generate optimal SMS pTx excitations satisfying both the system's hardware limits and regulatory safety limits.
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Affiliation(s)
- Bastien Guérin
- Department of Radiology, Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA
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Schmitter S, Wu X, Uğurbil K, Van de Moortele PF. Design of parallel transmission radiofrequency pulses robust against respiration in cardiac MRI at 7 Tesla. Magn Reson Med 2014; 74:1291-305. [PMID: 25411131 DOI: 10.1002/mrm.25512] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 09/15/2014] [Accepted: 10/13/2014] [Indexed: 12/18/2022]
Abstract
PURPOSE Two-spoke parallel transmission (pTX) radiofrequency (RF) pulses have been demonstrated in cardiac MRI at 7T. However, current pulse designs rely on a single set of B1(+)/B0 maps that may not be valid for subsequent scans acquired at another phase of the respiration cycle because of organ displacement. Such mismatches may yield severe excitation profile degradation. METHODS B1(+)/B0 maps were obtained, using 16 transmit channels at 7T, at three breath-hold positions: exhale, half-inhale, and inhale. Standard and robust RF pulses were designed using maps obtained at exhale only, and at multiple respiratory positions, respectively. Excitation patterns were analyzed for all positions using Bloch simulations. Flip-angle homogeneity was compared in vivo in cardiac CINE acquisitions. RESULTS Standard one- and two-spoke pTX RF pulses are sensitive to breath-hold position, primarily due to B1(+) alterations, with high dependency on excitation trajectory for two spokes. In vivo excitation inhomogeneity varied from nRMSE = 8.2% (exhale) up to 32.5% (inhale) with the standard design; much more stable results were obtained with the robust design with nRMSE = 9.1% (exhale) and 10.6% (inhale). CONCLUSION A new pTX RF pulse design robust against respiration induced variations of B1(+)/B0 maps is demonstrated and is expected to have a positive impact on cardiac MRI in breath-hold, free-breathing, and real-time acquisitions.
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Affiliation(s)
- Sebastian Schmitter
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Xiaoping Wu
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
| | - Kâmil Uğurbil
- University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA
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