1
|
Zhao C, Shao X, Shou Q, Ma SJ, Gokyar S, Graf C, Stollberger R, Wang DJ. Whole-Cerebrum distortion-free three-dimensional pseudo-continuous arterial spin labeling at 7T. Neuroimage 2023; 277:120251. [PMID: 37364741 PMCID: PMC10528743 DOI: 10.1016/j.neuroimage.2023.120251] [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: 04/24/2023] [Revised: 06/21/2023] [Accepted: 06/23/2023] [Indexed: 06/28/2023] Open
Abstract
Fulfilling potentials of ultrahigh field for pseudo-Continuous Arterial Spin Labeling (pCASL) has been hampered by B1/B0 inhomogeneities that affect pCASL labeling, background suppression (BS), and the readout sequence. This study aimed to present a whole-cerebrum distortion-free three-dimensional (3D) pCASL sequence at 7T by optimizing pCASL labeling parameters, BS pulses, and an accelerated Turbo-FLASH (TFL) readout. A new set of pCASL labeling parameters (Gave = 0.4 mT/m, Gratio = 14.67) was proposed to avoid interferences in bottom slices while achieving robust labeling efficiency (LE). An OPTIM BS pulse was designed based on the range of B1/B0 inhomogeneities at 7T. A 3D TFL readout with 2D-CAIPIRINHA undersampling (R = 2 × 2) and centric ordering was developed, and the number of segments (Nseg) and flip angle (FA) were varied in simulation to achieve the optimal trade-off between SNR and spatial blurring. In-vivo experiments were performed on 19 subjects. The results showed that the new set of labeling parameters effectively achieved whole-cerebrum coverage by eliminating interferences in bottom slices while maintaining a high LE. The OPTIM BS pulse achieved 33.3% higher perfusion signal in gray matter (GM) than the original BS pulse with a cost of 4.8-fold SAR. Incorporating a moderate FA (8°) and Nseg (2), whole-cerebrum 3D TFL-pCASL imaging was achieved with a 2 × 2 × 4 mm3 resolution without distortion and susceptibility artifacts compared to 3D GRASE-pCASL. In addition, 3D TFL-pCASL showed a good to excellent test-retest repeatability and potential of higher resolution (2 mm isotropic). The proposed technique also significantly improved SNR when compared to the same sequence at 3T and simultaneous multislice TFL-pCASL at 7T. By combining a new set of labeling parameters, OPTIM BS pulse, and accelerated 3D TFL readout, we achieved high resolution pCASL at 7T with whole-cerebrum coverage, detailed perfusion and anatomical information without distortion, and sufficient SNR.
Collapse
Affiliation(s)
- Chenyang Zhao
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, United States
| | - Xingfeng Shao
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, United States
| | - Qinyang Shou
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, United States
| | - Samantha J Ma
- Siemens Medical Solutions USA, Los Angeles, CA, United States
| | - Sayim Gokyar
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, United States
| | - Christina Graf
- Institute of Biomedical Imaging, Graz University of Technology, Austria
| | | | - Danny Jj Wang
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, United States; Department of Neurology, Keck School of Medicine, University of Southern California, United States.
| |
Collapse
|
2
|
Zhao C, Shao X, Shou Q, Ma SJ, Gokyar S, Graf C, Stollberger R, Wang DJJ. Whole-Cerebrum distortion-free three-dimensional pseudo-Continuous Arterial Spin Labeling at 7T. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.04.24.23289051. [PMID: 37163115 PMCID: PMC10168494 DOI: 10.1101/2023.04.24.23289051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Fulfilling potentials of ultrahigh field for pseudo-Continuous Arterial Spin Labeling (pCASL) has been hampered by B1/B0 inhomogeneities that affect pCASL labeling, background suppression (BS), and the readout sequence. This study aimed to present a whole-cerebrum distortion-free three-dimensional (3D) pCASL sequence at 7T by optimizing pCASL labeling parameters, BS pulses, and an accelerated Turbo-FLASH (TFL) readout. A new set of pCASL labeling parameters (Gave=0.4mT/m, Gratio=14.67) was proposed to avoid interferences in bottom slices while achieving robust labeling efficiency (LE). An OPTIM BS pulse was designed based on the range of B1/B0 inhomogeneities at 7T. A 3D TFL readout with 2D-CAIPIRINHA undersampling (R=2×2) and centric ordering was developed, and the number of segments (Nseg) and flip angle (FA) were varied in simulation to achieve the optimal trade-off between SNR and spatial blurring. In-vivo experiments were performed on 19 subjects. The results showed that the new set of labeling parameters effectively achieved whole-cerebrum coverage by eliminating interferences in bottom slices while maintaining a high LE. The OPTIM BS pulse achieved 33.3% higher perfusion signal in gray matter (GM) than the original BS pulse with a cost of 4.8-fold SAR. Incorporating a moderate FA (8 ° ) and Nseg (2), whole-cerebrum 3D TFL-pCASL imaging was achieved with a 2×2×4 mm 3 resolution without distortion and susceptibility artifacts compared to 3D GRASE-pCASL. In addition, 3D TFL-pCASL showed a good to excellent test-retest repeatability and potential of higher resolution (2 mm isotropic). The proposed technique also significantly improved SNR when compared to the same sequence at 3T and simultaneous multislice TFL-pCASL at 7T. By combining a new set of labeling parameters, OPTIM BS pulse, and accelerated 3D TFL readout, we achieved high resolution pCASL at 7T with whole-cerebrum coverage, detailed perfusion and anatomical information without distortion, and sufficient SNR.
Collapse
Affiliation(s)
- Chenyang Zhao
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California
| | - Xingfeng Shao
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California
| | - Qinyang Shou
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California
| | - Samantha J. Ma
- Siemens Medical Solutions USA, Los Angeles, California, USA
| | - Sayim Gokyar
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California
| | - Christina Graf
- Institute of Biomedical Imaging, Graz University of Technology
| | | | - Danny JJ Wang
- Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California
- Department of Neurology, Keck School of Medicine, University of Southern California
| |
Collapse
|
3
|
Yetisir F, Poser BA, Grant PE, Adalsteinsson E, Wald LL, Guerin B. Parallel transmission 2D RARE imaging at 7T with transmit field inhomogeneity mitigation and local SAR control. Magn Reson Imaging 2022; 93:87-96. [PMID: 35940379 PMCID: PMC9789791 DOI: 10.1016/j.mri.2022.08.006] [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: 05/04/2022] [Revised: 07/15/2022] [Accepted: 08/02/2022] [Indexed: 12/26/2022]
Abstract
PURPOSE We develop and test a parallel transmit (pTx) pulse design framework to mitigate transmit field inhomogeneity with control of local specific absorption rate (SAR) in 2D rapid acquisition with relaxation enhancement (RARE) imaging at 7T. METHODS We design large flip angle RF pulses with explicit local SAR constraints by numerical simulation of the Bloch equations. Parallel computation and analytical expressions for the Jacobian and the Hessian matrices are employed to reduce pulse design time. The refocusing-excitation "spokes" pulse pairs are designed to satisfy the Carr-Purcell-Meiboom-Gill (CPMG) condition using a combined magnitude least squares-least squares approach. RESULTS In a simulated dataset, the proposed approach reduced peak local SAR by up to 56% for the same level of refocusing uniformity error and reduced refocusing uniformity error by up to 59% (from 32% to 7%) for the same level of peak local SAR compared to the circularly polarized birdcage mode of the pTx array. Using explicit local SAR constraints also reduced peak local SAR by up to 46% compared to an RF peak power constrained design. The excitation and refocusing uniformity error were reduced from 20%-33% to 4%-6% in single slice phantom experiments. Phantom experiments demonstrated good agreement between the simulated excitation and refocusing uniformity profiles and experimental image shading. CONCLUSION PTx-designed excitation and refocusing CPMG pulse pairs can mitigate transmit field inhomogeneity in the 2D RARE sequence. Moreover, local SAR can be decreased significantly using pTx, potentially leading to better slice coverage, enabling larger flip angles or faster imaging.
Collapse
Affiliation(s)
- Filiz Yetisir
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA.
| | - Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Universiteitssingel 40, 6229 ER Maastricht, the Netherlands
| | - P Ellen Grant
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA; Department of Radiology, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA
| | - Elfar Adalsteinsson
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA; Institute for Medical Engineering and Science, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA
| | - Lawrence L Wald
- Department of Radiology, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA; Athinoula A. Martinos Center for Biomedical Imaging, MA General Hospital, 149 13th Street, Charlestown, MA 02129, USA
| | - Bastien Guerin
- Department of Radiology, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA; Athinoula A. Martinos Center for Biomedical Imaging, MA General Hospital, 149 13th Street, Charlestown, MA 02129, USA
| |
Collapse
|
4
|
He X, Auerbach EJ, Garwood M, Kobayashi N, Wu X, Metzger GJ. Parallel transmit optimized 3D composite adiabatic spectral-spatial pulse for spectroscopy. Magn Reson Med 2021; 86:17-32. [PMID: 33497006 PMCID: PMC8545499 DOI: 10.1002/mrm.28682] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 12/22/2020] [Accepted: 12/23/2020] [Indexed: 01/05/2023]
Abstract
PURPOSE To develop a 3D composite adiabatic spectral-spatial pulse for refocusing in spin-echo spectroscopy acquisitions and to compare its performance against standard acquisition methods. METHODS A 3D composite adiabatic pulse was designed by modulating a train of parallel transmit-optimized 2D subpulses with an adiabatic envelope. The spatial and spectral profiles were simulated and validated by experiments to demonstrate the feasibility of the design in both single and double spin-echo spectroscopy acquisitions. Phantom and in vivo studies were performed to evaluate the pulse performance and compared with semi-LASER with respect to localization performance, sequence timing, signal suppression, and specific absorption rate. RESULTS Simultaneous 2D spatial localization with water and lipid suppression was achieved with the designed refocusing pulse, allowing high-quality spectra to be acquired with shorter minimum TE/TR, reduced SAR, as well as adaptation to spatially varying B0 and B 1 + field inhomogeneities in both prostate and brain studies. CONCLUSION The proposed composite pulse can serve as a more SAR efficient alternative to conventional localization methods such as semi-LASER at ultrahigh field for spin echo-based spectroscopy studies. Subpulse parallel-transmit optimization provides the flexibility to manage the tradeoff among multiple design criteria to accommodate different field strengths and applications.
Collapse
Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Edward J. Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Michael Garwood
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Naoharu Kobayashi
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Gregory J. Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| |
Collapse
|
5
|
Landheer K, Noeske R, Garwood M, Juchem C. UTE-SPECIAL for3D localization at an echo time of 4 ms on a clinical 3 T scanner. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 311:106670. [PMID: 31927513 PMCID: PMC7045707 DOI: 10.1016/j.jmr.2019.106670] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 12/04/2019] [Accepted: 12/13/2019] [Indexed: 05/08/2023]
Abstract
Reducing the echo time of magnetic resonance spectroscopy experiments is appealing because it increases the available signal and reduces J-evolution of coupled metabolites. In this manuscript a novel sequence, referred to as Ultrashort echo TimE, SPin ECho, full Intensity Acquired Localized (UTE-SPECIAL), is described which is able to achieve ultrashort echo times (4 ms) on a standard clinical 3 T MR system while recovering the entirety of the available magnetization. UTE-SPECIAL obtains full 3D spatial localization through a 2D adiabatic inversion pulse which is cycled "on" and "off" every other repetition, in combination with a slice-selective excitation pulse. In addition to an ultrashort echo time, UTE-SPECIAL has negligible chemical shift displacement artefact and, because it uses no slice-selective refocusing pulse, has no signal cancellation at the borders for J-coupled metabolites. Spectra with an ultrashort echo time of 4 ms are demonstrated in vivo at 3 T, as well as J-resolved spectra obtained in a phantom and a healthy volunteer.
Collapse
Affiliation(s)
- Karl Landheer
- Biomedical Engineering, Columbia University Fu Foundation School of Engineering and Applied Science, New York, NY, United States.
| | | | - Michael Garwood
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, United States
| | - Christoph Juchem
- Biomedical Engineering, Columbia University Fu Foundation School of Engineering and Applied Science, New York, NY, United States; Radiology, Columbia University College of Physicians and Surgeons, New York, NY, United States
| |
Collapse
|
6
|
Bao Q, Ma L, Liberman G, Solomon E, Martinho RP, Frydman L. Dynamic T
2
mapping by multi‐spin‐echo spatiotemporal encoding. Magn Reson Med 2020; 84:895-907. [DOI: 10.1002/mrm.28158] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 11/28/2019] [Accepted: 12/11/2019] [Indexed: 12/12/2022]
Affiliation(s)
- Qingjia Bao
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Lingceng Ma
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Gilad Liberman
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Eddy Solomon
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Ricardo P. Martinho
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| | - Lucio Frydman
- Department of Chemical and Biological Physics Weizmann Institute Rehovot Israel
| |
Collapse
|
7
|
He X, Ertürk MA, Grant A, Wu X, Lagore RL, DelaBarre L, Eryaman Y, Adriany G, Auerbach EJ, Van de Moortele PF, Uğurbil K, Metzger GJ. First in-vivo human imaging at 10.5T: Imaging the body at 447 MHz. Magn Reson Med 2019; 84:289-303. [PMID: 31846121 DOI: 10.1002/mrm.28131] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 11/25/2019] [Accepted: 11/26/2019] [Indexed: 01/31/2023]
Abstract
PURPOSE To investigate the feasibility of imaging the human torso and to evaluate the performance of several radiofrequency (RF) management strategies at 10.5T. METHODS Healthy volunteers were imaged on a 10.5T whole-body scanner in multiple target anatomies, including the prostate, hip, kidney, liver, and heart. Phase-only shimming and spoke pulses were used to demonstrate their performance in managing the B 1 + inhomogeneity present at 447 MHz. Imaging protocols included both qualitative and quantitative acquisitions to show the feasibility of imaging with different contrasts. RESULTS High-quality images were acquired and demonstrated excellent overall contrast and signal-to-noise ratio. The experimental results matched well with predictions and suggested good translational capabilities of the RF management strategies previously developed at 7T. Phase-only shimming provided increased efficiency, but showed pronounced limitations in homogeneity, demonstrating the need for the increased degrees of freedom made possible through single- and multispoke RF pulse design. CONCLUSION The first in-vivo human imaging was successfully performed at 10.5T using previously developed RF management strategies. Further improvement in RF coils, transmit chain, and full integration of parallel transmit functionality are needed to fully realize the benefits of 10.5T.
Collapse
Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Andrea Grant
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Russell L Lagore
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Lance DelaBarre
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Yiğitcan Eryaman
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Eddie J Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | | | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| |
Collapse
|
8
|
Green EM, Blunck Y, Tahayori B, Farrell PM, Korte JC, Johnston LA. Spin Lock Adiabatic Correction (SLAC) for B 1-insensitive pulse design at 7T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 308:106595. [PMID: 31542447 DOI: 10.1016/j.jmr.2019.106595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 08/09/2019] [Accepted: 09/08/2019] [Indexed: 06/10/2023]
Abstract
A new framework for B1 insensitive adiabatic pulse design is proposed, denoted Spin Lock Adiabatic Correction (SLAC), which counteracts deviations from ideal behaviour through inclusion of an additional correction component during pulse design. SLAC pulses are theoretically derived, then applied to the design of enhanced BIR-4 and hyperbolic secant pulses to demonstrate practical utility of the new pulses. At 7T, SLAC pulses are shown to improve the flip angle homogeneity compared to a standard adiabatic pulse with validation in both simulations and phantom experiments, under SAR equivalent experimental conditions. The SLAC framework can be applied to any arbitrary adiabatic pulse to deliver excitation with increased B1 insensitivity.
Collapse
Affiliation(s)
- Edward M Green
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia.
| | - Yasmin Blunck
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia.
| | - Bahman Tahayori
- Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia; Department of Medical Physics and Biomedical Engineering, Shiraz University of Medical Sciences, Shiraz, Iran; Center for Neuromodulation and Pain, Shiraz, Iran.
| | - Peter M Farrell
- Department of Electrical and Electronic Engineering, The University of Melbourne, Melbourne, VIC, Australia.
| | - James C Korte
- Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia; Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
| | - Leigh A Johnston
- Melbourne Brain Centre Imaging Unit, The University of Melbourne, Melbourne, VIC, Australia; Department of Biomedical Engineering, The University of Melbourne, Melbourne, VIC, Australia.
| |
Collapse
|
9
|
Mullen M, Gutierrez A, Kobayashi N, Haupt J, Garwood M. Accelerated imaging with segmented 2D pulses using parallel imaging and virtual coils. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 305:185-194. [PMID: 31302513 PMCID: PMC6711164 DOI: 10.1016/j.jmr.2019.07.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 07/02/2019] [Accepted: 07/03/2019] [Indexed: 06/10/2023]
Abstract
Large magnetic field inhomogeneity can be a significant cause of spatial flip-angle variation when using ordinary, limited-bandwidth RF pulses. Multidimensional RF pulses are particularly sensitive to inhomogeneity due to their extended pulse length, which decreases their bandwidth. Previously, it was shown that, by breaking a 2D pulse into multiple undersampled k-space segments, the excitation bandwidth can be increased at the expense of increased imaging time. The present study shows how this increased imaging time can be offset by undersampling acquisition k-space in a phase-encoded dimension that is in the direction of excitation segmentation. Data from each segment are viewed as originating from "virtual receive coils" rather than multiple physical coils. The undersampled data are reconstructed using parallel imaging techniques (e.g. as in GRAPPA). The method was tested in vivo with brain imaging at both 3 T and 4 T, and used in conjunction with a 32-channel head coil and conventional GRAPPA on the 3 T data. Relationships with existing techniques and future applications are discussed.
Collapse
Affiliation(s)
- Michael Mullen
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA; School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA
| | | | - Naoharu Kobayashi
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA
| | - Jarvis Haupt
- Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA
| | - Michael Garwood
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
| |
Collapse
|
10
|
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.
Collapse
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
| |
Collapse
|
11
|
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.
Collapse
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
| |
Collapse
|