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Li H, Wang C, Yu X, Luo Y, Wang H. Measurement of Cerebral Oxygen Extraction Fraction Using Quantitative BOLD Approach: A Review. PHENOMICS (CHAM, SWITZERLAND) 2023; 3:101-118. [PMID: 36939794 PMCID: PMC9883382 DOI: 10.1007/s43657-022-00081-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 09/29/2022] [Accepted: 10/11/2022] [Indexed: 12/12/2022]
Abstract
Quantification of brain oxygenation and metabolism, both of which are indicators of the level of brain activity, plays a vital role in understanding the cerebral perfusion and the pathophysiology of brain disorders. Magnetic resonance imaging (MRI), a widely used clinical imaging technique, which is very sensitive to magnetic susceptibility, has the possibility of substituting positron emission tomography (PET) in measuring oxygen metabolism. This review mainly focuses on the quantitative blood oxygenation level-dependent (qBOLD) method for the evaluation of oxygen extraction fraction (OEF) in the brain. Here, we review the theoretic basis of qBOLD, as well as existing acquisition and quantification methods. Some published clinical studies are also presented, and the pros and cons of qBOLD method are discussed as well.
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Affiliation(s)
- Hongwei Li
- Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, 220 Handan Road, Yangpu District, Shanghai, 200433 China
| | - Chengyan Wang
- Human Phenome Institute, Fudan University, Shanghai, 201203 China
| | - Xuchen Yu
- Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, 220 Handan Road, Yangpu District, Shanghai, 200433 China
| | - Yu Luo
- Department of Radiology, Shanghai Fourth People’s Hospital Affiliated to Tongji University School of Medicine, Shanghai, 200434 China
| | - He Wang
- Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, 220 Handan Road, Yangpu District, Shanghai, 200433 China
- Human Phenome Institute, Fudan University, Shanghai, 201203 China
- Key Laboratory of Computational Neuroscience and Brain-Inspired Intelligence, (Fudan University), Ministry of Education, Shanghai, 200433 China
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2
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Zhang T, Guo R, Li Y, Zhao Y, Li Y, Liang ZP. T 2 ' mapping of the brain from water-unsuppressed 1 H-MRSI and turbo spin-echo data. Magn Reson Med 2022; 88:2198-2207. [PMID: 35844075 DOI: 10.1002/mrm.29386] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 06/14/2022] [Accepted: 06/22/2022] [Indexed: 11/08/2022]
Abstract
PURPOSE To obtain high-quality T 2 ' $$ {\mathrm{T}}_2^{\prime } $$ maps of brain tissues from water-unsuppressed magnetic resonance spectroscopic imaging (MRSI) and turbo spin-echo (TSE) data. METHODS T 2 ' $$ {\mathrm{T}}_2^{\prime } $$ mapping can be achieved using T 2 * $$ {\mathrm{T}}_2^{\ast } $$ mapping from water-unsuppressed MRSI data and T 2 $$ {\mathrm{T}}_2 $$ mapping from TSE data. However, T 2 * $$ {\mathrm{T}}_2^{\ast } $$ mapping often suffers from signal dephasing and distortions caused by B 0 $$ {\mathrm{B}}_0 $$ field inhomogeneity; T 2 $$ {\mathrm{T}}_2 $$ measurements may be biased due to system imperfections, especially for T 2 $$ {\mathrm{T}}_2 $$ -weighted image with small number of TEs. In this work, we corrected the B 0 $$ {\mathrm{B}}_0 $$ field inhomogeneity effect on T 2 * $$ {\mathrm{T}}_2^{\ast } $$ mapping using a subspace model-based method, incorporating pre-learned spectral basis functions of the water signals. T 2 $$ {\mathrm{T}}_2 $$ estimation bias was corrected using a TE-adjustment method, which modeled the deviation between measured and reference T 2 $$ {\mathrm{T}}_2 $$ decays as TE shifts. RESULTS In vivo experiments were performed to evaluate the performance of the proposed method. High-quality T 2 * $$ {\mathrm{T}}_2^{\ast } $$ maps were obtained in the presence of large field inhomogeneity in the prefrontal cortex. Bias in T 2 $$ {\mathrm{T}}_2 $$ measurements obtained from TSE data was effectively reduced. Based on the T 2 * $$ {\mathrm{T}}_2^{\ast } $$ and T 2 $$ {\mathrm{T}}_2 $$ measurements produced by the proposed method, high-quality T 2 ' $$ {\mathrm{T}}_2^{\prime } $$ maps were obtained, along with neurometabolite maps, from MRSI and TSE data that were acquired in about 9 min. The results obtained from acute stroke and glioma patients demonstrated the feasibility of the proposed method in the clinical setting. CONCLUSIONS High-quality T 2 ' $$ {\mathrm{T}}_2^{\prime } $$ maps can be obtained from water-unsuppressed 1 H-MRSI and TSE data using the proposed method. With further development, this method may lay a foundation for simultaneously imaging oxygenation and neurometabolic alterations of brain disorders.
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Affiliation(s)
- Tianxiao Zhang
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Rong Guo
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.,Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Yudu Li
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.,Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Yibo Zhao
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.,Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Yao Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Zhi-Pei Liang
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.,Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
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3
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Miao X, Paez AG, Rajan S, Cao D, Liu D, Pantelyat AY, Rosenthal LI, van Zijl PCM, Bassett SS, Yousem DM, Kamath V, Hua J. Functional Activities Detected in the Olfactory Bulb and Associated Olfactory Regions in the Human Brain Using T2-Prepared BOLD Functional MRI at 7T. Front Neurosci 2021; 15:723441. [PMID: 34588949 PMCID: PMC8476065 DOI: 10.3389/fnins.2021.723441] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Accepted: 08/16/2021] [Indexed: 11/17/2022] Open
Abstract
Olfaction is a fundamental sense that plays a vital role in daily life in humans, and can be altered in neuropsychiatric and neurodegenerative diseases. Blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) using conventional echo-planar-imaging (EPI) based sequences can be challenging in brain regions important for olfactory processing, such as the olfactory bulb (OB) and orbitofrontal cortex, mainly due to the signal dropout and distortion artifacts caused by large susceptibility effects from the sinonasal cavity and temporal bone. To date, few studies have demonstrated successful fMRI in the OB in humans. T2-prepared (T2prep) BOLD fMRI is an alternative approach developed especially for performing fMRI in regions affected by large susceptibility artifacts. The purpose of this technical study is to evaluate T2prep BOLD fMRI for olfactory functional experiments in humans. Olfactory fMRI scans were performed on 7T in 14 healthy participants. T2prep BOLD showed greater sensitivity than GRE EPI BOLD in the OB, orbitofrontal cortex and the temporal pole. Functional activation was detected using T2prep BOLD in the OB and associated olfactory regions. Habituation effects and a bi-phasic pattern of fMRI signal changes during olfactory stimulation were observed in all regions. Both positively and negatively activated regions were observed during olfactory stimulation. These signal characteristics are generally consistent with literature and showed a good intra-subject reproducibility comparable to previous human BOLD fMRI studies. In conclusion, the methodology demonstrated in this study holds promise for future olfactory fMRI studies in the OB and other brain regions that suffer from large susceptibility artifacts.
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Affiliation(s)
- Xinyuan Miao
- Neurosection, Division of MRI Research, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, MD, United States.,F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
| | - Adrian G Paez
- Neurosection, Division of MRI Research, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, MD, United States.,F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
| | - Suraj Rajan
- Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
| | - Di Cao
- Neurosection, Division of MRI Research, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, MD, United States.,F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States.,Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States
| | - Dapeng Liu
- Neurosection, Division of MRI Research, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, MD, United States.,F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
| | - Alex Y Pantelyat
- Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
| | - Liana I Rosenthal
- Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
| | - Peter C M van Zijl
- Neurosection, Division of MRI Research, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, MD, United States.,F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
| | - Susan S Bassett
- Department of Psychiatry and Behavioral Sciences, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
| | - David M Yousem
- Department of Radiology, Johns Hopkins Hospital, Baltimore, MD, United States
| | - Vidyulata Kamath
- Department of Psychiatry and Behavioral Sciences, School of Medicine, Johns Hopkins University, Baltimore, MD, United States
| | - Jun Hua
- Neurosection, Division of MRI Research, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, MD, United States.,F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
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Khajehim M, Christen T, Tam F, Graham SJ. Streamlined magnetic resonance fingerprinting: Fast whole-brain coverage with deep-learning based parameter estimation. Neuroimage 2021; 238:118237. [PMID: 34091035 DOI: 10.1016/j.neuroimage.2021.118237] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 05/26/2021] [Accepted: 06/02/2021] [Indexed: 01/02/2023] Open
Abstract
Magnetic resonance fingerprinting (MRF) is a quantitative MRI (qMRI) framework that provides simultaneous estimates of multiple relaxation parameters as well as metrics of field inhomogeneity in a single acquisition. However, current challenges exist in the forms of (1) scan time; (2) need for custom image reconstruction; (3) large dictionary sizes; (4) long dictionary-matching time. This study aims to introduce a novel streamlined magnetic-resonance fingerprinting (sMRF) framework based on a single-shot echo-planar imaging (EPI) sequence to simultaneously estimate tissue T1, T2, and T2* with integrated B1+ correction. Encouraged by recent work on EPI-based MRF, we developed a method that combines spin-echo EPI with gradient-echo EPI to achieve T2 in addition to T1 and T2* quantification. To this design, we add simultaneous multi-slice (SMS) acceleration to enable full-brain coverage in a few minutes. Moreover, in the parameter-estimation step, we use deep learning to train a deep neural network (DNN) to accelerate the estimation process by orders of magnitude. Notably, due to the high image quality of the EPI scans, the training process can rely simply on Bloch-simulated data. The DNN also removes the need for storing large dictionaries. Phantom scans along with in-vivo multi-slice scans from seven healthy volunteers were acquired with resolutions of 1.1×1.1×3 mm3 and 1.7×1.7×3 mm3, and the results were validated against ground truth measurements. Excellent correspondence was found between our T1, T2, and T2* estimates and results obtained from standard approaches. In the phantom scan, a strong linear relationship (R = 1-1.04, R2>0.96) was found for all parameter estimates, with a particularly high agreement for T2 estimation (R2>0.99). Similar findings are reported for the in-vivo human data for all of our parameter estimates. Incorporation of DNN results in a reduction of parameter estimation time on the order of 1000 x and a reduction in storage requirements on the order of 2500 x while achieving highly similar results as conventional dictionary matching (%differences of 7.4 ± 0.4%, 3.6 ± 0.3% and 6.0 ± 0.4% error in T1, T2, and T2* estimation). Thus, sMRF has the potential to be the method of choice for future MRF studies by providing ease of implementation, fast whole-brain coverage, and ultra-fast T1/T2/T2* estimation.
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Affiliation(s)
- Mahdi Khajehim
- Department of Medical Biophysics, University of Toronto, 101 College St Suite 15-701, Toronto, ON M5G 1L7, Canada.
| | - Thomas Christen
- Grenoble Institute of Neuroscience, Inserm, Grenoble, France
| | - Fred Tam
- Hurvitz Brain Sciences Research Program, Sunnybrook Research Institute, Toronto, ON, Canada
| | - Simon J Graham
- Department of Medical Biophysics, University of Toronto, 101 College St Suite 15-701, Toronto, ON M5G 1L7, Canada; Hurvitz Brain Sciences Research Program, Sunnybrook Research Institute, Toronto, ON, Canada
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5
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Liu Y, Ye Q, Zeng F, Jiang X, Cai B, Lv W, Wen J. Library-driven approach for fast implementation of the voxel spread function to correct magnetic field inhomogeneity artifacts for gradient-echo sequences. Med Phys 2021; 48:3714-3720. [PMID: 33914914 DOI: 10.1002/mp.14904] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Revised: 03/15/2021] [Accepted: 04/12/2021] [Indexed: 11/10/2022] Open
Abstract
PURPOSE Previously developed Voxel Spread Function (VSF) method (Yablonskiy, et al, MRM, 2013;70:1283) provides solution to correct artifacts induced by macroscopic magnetic field inhomogeneity in the images obtained by multi-Gradient-Recalled-Echo (mGRE) techniques. The goal of this study was to develop a library-driven approach for fast VSF implementation. METHODS The VSF approach describes the contribution of the magnetic field inhomogeneity effects on the mGRE signal decay in terms of the F-function calculated from mGRE phase and magnitude images. A pre-calculated library accounting for a variety of background field gradients caused by magnetic field inhomogeneity was used herein to speed up the calculation of F-function. Quantitative R2* maps from the mGRE data collected from two healthy volunteers were generated using the library as validation. RESULTS As compared with direct calculation of the F-function based on a voxel-wise approach, the new library-driven method substantially reduces computational time from several hours to few minutes, while, at the same time, providing similar accuracy of R2* mapping. CONCLUSION The new procedure proposed in this study provides a fast post-processing algorithm that can be incorporated in the quantitative analysis of mGRE data to account for background field inhomogeneity artifacts, thus can facilitate the applications of mGRE-based quantitative techniques in clinical practices.
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Affiliation(s)
- Ying Liu
- Department of Radiology, The First Affiliated Hospital of USTC (Anhui Provincial Hospital), Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Qiong Ye
- High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, China
| | - Feiyan Zeng
- Department of Radiology, The First Affiliated Hospital of USTC (Anhui Provincial Hospital), Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Xiaohua Jiang
- The First Affiliated Hospital of USTC (Anhui Provincial Hospital), Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Bin Cai
- Department of Radiation Oncology, Washington University in St. Louis, St. Louis, MO, USA
| | - Weifu Lv
- Department of Radiology, The First Affiliated Hospital of USTC (Anhui Provincial Hospital), Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Jie Wen
- Department of Radiology, The First Affiliated Hospital of USTC (Anhui Provincial Hospital), Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
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6
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Mullen M, Garwood M. Contemporary approaches to high-field magnetic resonance imaging with large field inhomogeneity. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2020; 120-121:95-108. [PMID: 33198970 PMCID: PMC7672259 DOI: 10.1016/j.pnmrs.2020.07.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 07/16/2020] [Accepted: 07/18/2020] [Indexed: 06/11/2023]
Abstract
Despite its importance as a clinical imaging modality, magnetic resonance imaging remains inaccessible to most of the world's population due to its high cost and infrastructure requirements. Substantial effort is underway to develop portable, low-cost systems able to address MRI access inequality and to enable new uses of MRI such as bedside imaging. A key barrier to development of portable MRI systems is increased magnetic field inhomogeneity when using small polarizing magnets, which degrades image quality through distortions and signal dropout. Many approaches address field inhomogeneity by using a low polarizing field, approximately ten to hundreds of milli-Tesla. At low-field, even a large relative field inhomogeneity of several thousand parts-per-million (ppm) results in resonance frequency dispersion of only 1-2 kHz. Under these conditions, with necessarily wide pulse bandwidths, fast spin-echo sequences may be used at low field with negligible subject heating, and a broad range of other available imaging sequences can be implemented. However, high-field MRI, 1.5 T or greater, can provide substantially improved signal-to-noise ratio and image contrast, so that higher spatial resolution, clinical quality images may be acquired in significantly less time than is necessary at low-field. The challenge posed by small, high-field systems is that the relative field inhomogeneity, still thousands of ppm, becomes tens of kilohertz over the imaging volume. This article describes the physical consequences of field inhomogeneity on established gradient- and spin-echo MRI sequences, and suggests ways to reduce signal dropout and image distortion from field inhomogeneity. Finally, the practicality of currently available image contrasts is reviewed when imaging with a high magnetic field with large inhomogeneity.
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Affiliation(s)
- Michael Mullen
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
| | - Michael Garwood
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
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7
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He Y, Wang M, Yu X. High spatiotemporal vessel-specific hemodynamic mapping with multi-echo single-vessel fMRI. J Cereb Blood Flow Metab 2020; 40:2098-2114. [PMID: 31696765 PMCID: PMC7786852 DOI: 10.1177/0271678x19886240] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
High-resolution fMRI enables noninvasive mapping of the hemodynamic responses from individual penetrating vessels in animal brains. Here, a 2D multi-echo single-vessel fMRI (MESV-fMRI) method has been developed to map the fMRI signal from arterioles and venules with a 100 ms sampling rate at multiple echo times (TE, 3-30 ms) and short acquisition windows (<1 ms). The T2*-weighted signal shows the increased extravascular effect on venule voxels as a function of TE. In contrast, the arteriole voxels show an increased fMRI signal with earlier onset than venules voxels at the short TE (3 ms) with increased blood inflow and volume effects. MESV-fMRI enables vessel-specific T2* mapping and presents T2*-based fMRI time courses with higher contrast-to-noise ratios (CNRs) than the T2*-weighted fMRI signal at a given TE. The vessel-specific T2* mapping also allows semi-quantitative estimation of the oxygen saturation levels (Y) and their changes (ΔY) at a given blood volume fraction upon neuronal activation. The MESV-fMRI method enables vessel-specific T2* measurements with high spatiotemporal resolution for better modeling of the fMRI signal based on the hemodynamic parameters.
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Affiliation(s)
- Yi He
- Translational Neuroimaging and Neural Control Group, High Field Magnetic Resonance Department, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,Graduate Training Centre of Neuroscience, International Max Planck Research School, University of Tuebingen, Tuebingen, Germany.,Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
| | - Maosen Wang
- Translational Neuroimaging and Neural Control Group, High Field Magnetic Resonance Department, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,Graduate Training Centre of Neuroscience, International Max Planck Research School, University of Tuebingen, Tuebingen, Germany
| | - Xin Yu
- Translational Neuroimaging and Neural Control Group, High Field Magnetic Resonance Department, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA
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8
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Soellradl M, Strasser J, Lesch A, Stollberger R, Ropele S, Langkammer C. Adaptive slice-specific z-shimming for 2D spoiled gradient-echo sequences. Magn Reson Med 2020; 85:818-830. [PMID: 32909334 PMCID: PMC7693070 DOI: 10.1002/mrm.28468] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Revised: 07/01/2020] [Accepted: 07/16/2020] [Indexed: 12/22/2022]
Abstract
Purpose To reduce the misbalance between compensation gradients and macroscopic field gradients, we introduce an adaptive slice‐specific z‐shimming approach for 2D spoiled multi‐echo gradient‐echoe sequences in combination with modeling of the signal decay. Methods Macroscopic field gradients were estimated for each slice from a fast prescan (15 seconds) and then used to calculate slice‐specific compensation moments along the echo train. The coverage of the compensated field gradients was increased by applying three positive and three negative moments. With a forward model, which considered the effect of the slice profile, the z‐shim moment, and the field gradient, R2∗ maps were estimated. The method was evaluated in phantom and in vivo measurements at 3 T and compared with a spoiled multi‐echo gradient‐echo and a global z‐shimming approach without slice‐specific compensation. Results The proposed method yielded higher SNR in R2∗ maps due to a broader range of compensated macroscopic field gradients compared with global z‐shimming. In global white matter, the mean interquartile range, proxy for SNR, could be decreased to 3.06 s−1 with the proposed approach, compared with 3.37 s−1 for global z‐shimming and 3.52 s−1 for uncompensated multi‐echo gradient‐echo. Conclusion Adaptive slice‐specific compensation gradients between echoes substantially improved the SNR of R2∗ maps, and the signal could also be rephased in anatomical areas, where it has already been completely dephased.
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Affiliation(s)
- Martin Soellradl
- Department of Neurology, Medical University of Graz, Graz, Austria
| | | | - Andreas Lesch
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria
| | - Rudolf Stollberger
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria
| | - Stefan Ropele
- Department of Neurology, Medical University of Graz, Graz, Austria
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9
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Soellradl M, Lesch A, Strasser J, Pirpamer L, Stollberger R, Ropele S, Langkammer C. Assessment and correction of macroscopic field variations in 2D spoiled gradient-echo sequences. Magn Reson Med 2019; 84:620-633. [PMID: 31868260 PMCID: PMC7216950 DOI: 10.1002/mrm.28139] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 11/04/2019] [Accepted: 11/29/2019] [Indexed: 01/13/2023]
Abstract
Purpose To model and correct the dephasing effects in the gradient‐echo signal for arbitrary RF excitation pulses with large flip angles in the presence of macroscopic field variations. Methods The dephasing of the spoiled 2D gradient‐echo signal was modeled using a numerical solution of the Bloch equations to calculate the magnitude and phase of the transverse magnetization across the slice profile. Additionally, regional variations of the transmit RF field and slice profile scaling due to macroscopic field gradients were included. Simulations, phantom, and in vivo measurements at 3 T were conducted for R2∗ and myelin water fraction (MWF) mapping. Results The influence of macroscopic field gradients on R2∗ and myelin water fraction estimation can be substantially reduced by applying the proposed model. Moreover, it was shown that the dephasing over time for flip angles of 60° or greater also depends on the polarity of the slice‐selection gradient because of phase variation along the slice profile. Conclusion Substantial improvements in R2∗ accuracy and myelin water fraction mapping coverage can be achieved using the proposed model if higher flip angles are required. In this context, we demonstrated that the phase along the slice profile and the polarity of the slice‐selection gradient are essential for proper modeling of the gradient‐echo signal in the presence of macroscopic field variations.
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Affiliation(s)
- Martin Soellradl
- Department of Neurology, Medical University of Graz, Graz, Austria
| | - Andreas Lesch
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria
| | | | - Lukas Pirpamer
- Department of Neurology, Medical University of Graz, Graz, Austria
| | - Rudolf Stollberger
- Institute of Medical Engineering, Graz University of Technology, Graz, Austria
| | - Stefan Ropele
- Department of Neurology, Medical University of Graz, Graz, Austria
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Cherukara MT, Stone AJ, Chappell MA, Blockley NP. Model-based Bayesian inference of brain oxygenation using quantitative BOLD. Neuroimage 2019; 202:116106. [PMID: 31430532 PMCID: PMC7334042 DOI: 10.1016/j.neuroimage.2019.116106] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Revised: 07/30/2019] [Accepted: 08/16/2019] [Indexed: 11/17/2022] Open
Abstract
Streamlined Quantitative BOLD (sqBOLD) is an MR technique that can non-invasively measure physiological parameters including Oxygen Extraction Fraction (OEF) and deoxygenated blood volume (DBV) in the brain. Current sqBOLD methodology rely on fitting a linear model to log-transformed data acquired using an Asymmetric Spin Echo (ASE) pulse sequence. In this paper, a non-linear model implemented in a Bayesian framework was used to fit physiological parameters to ASE data. This model makes use of the full range of available ASE data, and incorporates the signal contribution from venous blood, which was ignored in previous analyses. Simulated data are used to demonstrate the intrinsic difficulty in estimating OEF and DBV simultaneously, and the benefits of the proposed non-linear model are shown. In vivo data are used to show that this model improves parameter estimation when compared with literature values. The model and analysis framework can be extended in a number of ways, and can incorporate prior information from external sources, so it has the potential to further improve OEF estimation using sqBOLD.
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Affiliation(s)
- Matthew T Cherukara
- Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK.
| | - Alan J Stone
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Michael A Chappell
- Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK
| | - Nicholas P Blockley
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
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11
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Stone AJ, Harston GWJ, Carone D, Okell TW, Kennedy J, Blockley NP. Prospects for investigating brain oxygenation in acute stroke: Experience with a non-contrast quantitative BOLD based approach. Hum Brain Mapp 2019; 40:2853-2866. [PMID: 30860660 PMCID: PMC6563088 DOI: 10.1002/hbm.24564] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 02/25/2019] [Accepted: 02/26/2019] [Indexed: 12/13/2022] Open
Abstract
Metabolic markers of baseline brain oxygenation and tissue perfusion have an important role to play in the early identification of ischaemic tissue in acute stroke. Although well established MRI techniques exist for mapping brain perfusion, quantitative imaging of brain oxygenation is poorly served. Streamlined-qBOLD (sqBOLD) is a recently developed technique for mapping oxygenation that is well suited to the challenge of investigating acute stroke. In this study a noninvasive serial imaging protocol was implemented, incorporating sqBOLD and arterial spin labelling to map blood oxygenation and perfusion, respectively. The utility of these parameters was investigated using imaging based definitions of tissue outcome (ischaemic core, infarct growth and contralateral tissue). Voxel wise analysis revealed significant differences between all tissue outcomes using pairwise comparisons for the transverse reversible relaxation rate (R 2 '), deoxygenated blood volume (DBV) and deoxyghaemoglobin concentration ([dHb]; p < 0.01 in all cases). At the patient level (n = 9), a significant difference was observed for [dHb] between ischaemic core and contralateral tissue. Furthermore, serial analysis at the patient level (n = 6) revealed significant changes in R 2 ' between the presentation and 1 week scans for both ischaemic core (p < 0.01) and infarct growth (p < 0.05). In conclusion, this study presents evidence supporting the potential of sqBOLD for imaging oxygenation in stroke.
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Affiliation(s)
- Alan J Stone
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - George W J Harston
- Acute Vascular Imaging Centre, Radcliffe Department of Medicine, University of Oxford, Oxford, UK
| | - Davide Carone
- Acute Vascular Imaging Centre, Radcliffe Department of Medicine, University of Oxford, Oxford, UK
| | - Thomas W Okell
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - James Kennedy
- Acute Vascular Imaging Centre, Radcliffe Department of Medicine, University of Oxford, Oxford, UK
| | - Nicholas P Blockley
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
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12
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Hong T, Han D, Kim D. Simultaneous estimation of PD, T1, T2, T2*, and ∆B0using magnetic resonance fingerprinting with background gradient compensation. Magn Reson Med 2018; 81:2614-2623. [DOI: 10.1002/mrm.27556] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Revised: 09/10/2018] [Accepted: 09/11/2018] [Indexed: 12/25/2022]
Affiliation(s)
- Taehwa Hong
- Department of Electrical and Electronic Engineering Yonsei University Seoul Korea
| | - Dongyeob Han
- Department of Electrical and Electronic Engineering Yonsei University Seoul Korea
| | - Dong‐Hyun Kim
- Department of Electrical and Electronic Engineering Yonsei University Seoul Korea
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13
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Lee D, Lee J, Lee J, Nam Y. Single-scan z-shim method for reducing susceptibility artifacts in gradient echo myelin water imaging. Magn Reson Med 2018; 80:1101-1109. [DOI: 10.1002/mrm.27127] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 01/14/2018] [Accepted: 01/21/2018] [Indexed: 11/11/2022]
Affiliation(s)
- Doohee Lee
- Department of Electrical and Computer Engineering; Seoul National University; Seoul Korea
| | - Jingu Lee
- Department of Electrical and Computer Engineering; Seoul National University; Seoul Korea
| | - Jongho Lee
- Department of Electrical and Computer Engineering; Seoul National University; Seoul Korea
| | - Yoonho Nam
- Department of Radiology; Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea; Seoul Korea
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14
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Wagner D, Eslinger PJ, Barrett AM. Decreased leftward 'aiming' motor-intentional spatial cuing in traumatic brain injury. Neuropsychology 2017; 30:731-741. [PMID: 27571220 DOI: 10.1037/neu0000252] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
OBJECTIVE To characterize the mediation of attention and action in space following traumatic brain injury (TBI). METHOD Two exploratory analyses were performed to determine the influence of spatial 'Aiming' motor versus spatial 'Where' bias on line bisection in TBI participants. The first experiment compared performance according to severity and location of injury in TBI. The second experiment examined bisection performance in a larger TBI sample against a matched control group. In both experiments, participants bisected lines in near and far space using an apparatus that allowed for the fractionation of spatial Aiming versus Where error components. RESULTS In the first experiment, participants with severe injuries tended to incur rightward error when starting from the right in far space, compared with participants with mild injuries. In the second experiment, when performance was examined at the individual level, more participants with TBI tended to incur rightward motor error compared to controls. CONCLUSIONS TBI may cause frontal-subcortical cognitive dysfunction and asymmetric motor perseveration, affecting spatial Aiming bias on line bisection. Potential effects on real-world function need further investigation. (PsycINFO Database Record
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Affiliation(s)
- Daymond Wagner
- Department of Neurology, Milton S. Hershey Medical Center
| | - Paul J Eslinger
- Departments of Neurology, Neural & Behavioral Sciences, Pediatrics, and Radiology, Penn State College of Medicine
| | - A M Barrett
- Stroke Rehabilitation Research, Kessler Foundation, Departments of Physical Medicine and Rehabilitation/Neurology and Neurosciences, Rutgers/New Jersey Medical School
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15
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Stone AJ, Blockley NP. A streamlined acquisition for mapping baseline brain oxygenation using quantitative BOLD. Neuroimage 2016; 147:79-88. [PMID: 27915118 DOI: 10.1016/j.neuroimage.2016.11.057] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 10/08/2016] [Accepted: 11/22/2016] [Indexed: 10/20/2022] Open
Abstract
Quantitative BOLD (qBOLD) is a non-invasive MR technique capable of producing quantitative measurements of the haemodynamic and metabolic properties of the brain. Here we propose a refinement of the qBOLD methodology, dubbed streamlined-qBOLD, in order to provide a clinically feasible method for mapping baseline brain oxygenation. In streamlined-qBOLD confounding signal contributions are minimised during data acquisition through the application of (i) a Fluid Attenuated Inversion Recovery (FLAIR) preparation to remove cerebral spinal fluid (CSF) signal contamination, (ii) a Gradient Echo Slice Excitation Profile Imaging (GESEPI) acquisition to reduce the effect of macroscopic magnetic field gradients and (iii) an Asymmetric Spin Echo (ASE) pulse sequence to directly measure the reversible transverse relaxation rate, R2'. Together these features simplify the application of the qBOLD model, improving the robustness of the resultant parametric maps. A theoretical optimisation framework was used to optimise acquisition parameters in relation to signal to noise ratio. In a healthy subject group (n = 7) apparent elevations in R2' caused by partial volumes of CSF were shown to be reduced with the application of CSF nulling. Significant decreases in R2' (p < 0.001) and deoxygenated blood volume (p < 0.01) were seen in cortical grey matter, across the group, with the application of CSF suppression. Quantitative baseline brain oxygenation parameter maps were calculated using qBOLD modelling and compared with literature values.
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Affiliation(s)
- Alan J Stone
- FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
| | - Nicholas P Blockley
- FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
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16
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Guérin B, Stockmann JP, Baboli M, Torrado-Carvajal A, Stenger AV, Wald LL. Robust time-shifted spoke pulse design in the presence of large B0 variations with simultaneous reduction of through-plane dephasing, B1+ effects, and the specific absorption rate using parallel transmission. Magn Reson Med 2016; 76:540-54. [PMID: 26444717 PMCID: PMC4824674 DOI: 10.1002/mrm.25902] [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: 04/17/2015] [Revised: 07/29/2015] [Accepted: 07/30/2015] [Indexed: 11/09/2022]
Abstract
PURPOSE To design parallel transmission spokes pulses with time-shifted profiles for joint mitigation of intensity variations due to B1+ effects, signal loss due to through-plane dephasing, and the specific absorption rate (SAR) at 7T. METHODS We derived a slice-averaged small tip angle (SA-STA) approximation of the magnetization signal at echo time that depends on the B1+ transmit profiles, the through-slice B0 gradient and the amplitude and time-shifts of the spoke waveforms. We minimize a magnitude least-squares objective based on this signal equation using a fast interior-point approach with analytical expressions of the Jacobian and Hessian. RESULTS Our algorithm runs in less than three minutes for the design of two-spoke pulses subject to hundreds of local SAR constraints. On a B0/B1+ head phantom, joint optimization of the channel-dependent time-shifts and spoke amplitudes allowed signal recovery in high-B0 regions at no increase of SAR. Although the method creates uniform magnetization profiles (ie, uniform intensity), the flip angle varies across the image, which makes it ill-suited to T1-weighted applications. CONCLUSIONS The SA-STA approach presented in this study is best suited to T2*-weighted applications with long echo times that require signal recovery around high B0 regions. Magn Reson Med 76:540-554, 2016. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Bastien Guérin
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
| | - Jason P Stockmann
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Physics Department, Harvard University, Cambridge, Massachusetts, USA
| | - Mehran Baboli
- John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA
| | - Angel Torrado-Carvajal
- Medical Image Analysis and Biometry Laboratory, University Rey Juan Carlos, Mostoles Spain
- Madrid-MIT M+ Vision Consortium, Madrid, Spain
| | - Andrew V Stenger
- John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA
| | - Lawrence L Wald
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Harvard-MIT Division of Health Sciences Technology, Cambridge, Massachusetts, USA
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17
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Improving the specificity of R2′ to the deoxyhaemoglobin content of brain tissue: Prospective correction of macroscopic magnetic field gradients. Neuroimage 2016; 135:253-60. [DOI: 10.1016/j.neuroimage.2016.04.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Revised: 03/30/2016] [Accepted: 04/06/2016] [Indexed: 11/23/2022] Open
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18
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Straub S, Ladd ME, Wetscherek A, Laun FB. On contrast mechanisms in p-space imaging. Magn Reson Med 2015; 75:2526-33. [DOI: 10.1002/mrm.25812] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 04/15/2015] [Accepted: 05/23/2015] [Indexed: 01/28/2023]
Affiliation(s)
- Sina Straub
- Department of Medical Physics in Radiology; German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Mark E. Ladd
- Department of Medical Physics in Radiology; German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Andreas Wetscherek
- Department of Medical Physics in Radiology; German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Frederik B. Laun
- Department of Medical Physics in Radiology; German Cancer Research Center (DKFZ); Heidelberg Germany
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19
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Wastling SJ, Barker GJ. Designing hyperbolic secant excitation pulses to reduce signal dropout in gradient-echo echo-planar imaging. Magn Reson Med 2014; 74:661-72. [PMID: 25203420 DOI: 10.1002/mrm.25444] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Revised: 08/14/2014] [Accepted: 08/14/2014] [Indexed: 12/24/2022]
Abstract
PURPOSE To design hyperbolic secant (HS) excitation pulses to reduce signal dropout in the orbitofrontal and inferior temporal regions in gradient-echo echo-planar imaging (GE-EPI) for functional MRI (fMRI) applications. METHODS An algorithm based on Bloch simulations optimizes the HS pulse parameters needed to give the desired signal response across the range of susceptibility gradients observed in the human head (approximately ±250 μT·m(-1) ). The impact of the HS pulse on the signal, temporal signal-to-noise ratio, blood oxygen level-dependent (BOLD) sensitivity, and ability to detect resting state BOLD signal changes was assessed in six healthy male volunteers at 3T. RESULTS The optimized HS pulse (μ = 4.25, β = 3040 Hz, A0 = 12.3 μT, Δf = 4598 Hz) had a near uniform signal response for through-plane susceptibility gradients in the range ±250 μT·m(-1) . Signal, temporal signal-to-noise ratio, BOLD sensitivity, and the detectability of resting state networks were all partially recovered in the orbitofrontal and inferior temporal regions; however, there were signal losses of up to 50% in regions of homogeneous field (and signal loss from in-plane susceptibility gradients remained). CONCLUSION The HS pulse reduced signal dropout and could be used to acquire task and resting state fMRI data without loss of spatial coverage or temporal resolution.
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20
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Mei CS, Chu R, Hoge WS, Panych LP, Madore B. Accurate field mapping in the presence of B0 inhomogeneities, applied to MR thermometry. Magn Reson Med 2014; 73:2142-51. [PMID: 24975329 DOI: 10.1002/mrm.25338] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2014] [Revised: 06/03/2014] [Accepted: 06/05/2014] [Indexed: 11/06/2022]
Abstract
PURPOSE To describe how B0 inhomogeneities can cause errors in proton resonance frequency (PRF) shift thermometry, and to correct for these errors. METHODS With PRF thermometry, measured phase shifts are converted into temperature measurements through the use of a scaling factor proportional to the echo time, TE. However, B0 inhomogeneities can deform, spread, and translate MR echoes, potentially making the "true" echo time vary spatially within the imaged object and take on values that differ from the prescribed TE value. Acquisition and reconstruction methods able to avoid or correct for such errors are presented. RESULTS Tests were performed in a gel phantom during sonication, and temperature measurements were made with proper shimming as well as with intentionally introduced B0 inhomogeneities. Errors caused by B0 inhomogeneities were observed, described, and corrected by the proposed methods. No statistical difference was found between the corrected results and the reference results obtained with proper shimming, while errors by more than 10% in temperature elevation were corrected for. The approach was also applied to an abdominal in vivo dataset. CONCLUSION Field variations induce errors in measured field values, which can be detected and corrected. The approach was validated for a PRF thermometry application.
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Affiliation(s)
- Chang-Sheng Mei
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.,Department of Physics, Soochow University, Taipei, Taiwan, Republic of China
| | - Renxin Chu
- Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - W Scott Hoge
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Lawrence P Panych
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Bruno Madore
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
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21
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Han D, Nam Y, Gho SM, Kim DH. Volumetric R2* mapping using z-shim multi-echo gradient echo imaging. Magn Reson Med 2014; 73:1164-70. [DOI: 10.1002/mrm.25206] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 02/14/2014] [Accepted: 02/14/2014] [Indexed: 12/18/2022]
Affiliation(s)
- Dongyeob Han
- Department of Electrical and Electronic Engineering; Yonsei University; Seoul Korea
| | - Yoonho Nam
- Department of Electrical and Electronic Engineering; Yonsei University; Seoul Korea
| | - Sung-Min Gho
- Department of Electrical and Electronic Engineering; Yonsei University; Seoul Korea
| | - Dong-Hyun Kim
- Department of Electrical and Electronic Engineering; Yonsei University; Seoul Korea
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22
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Yablonskiy DA, Sukstanskii AL, Luo J, Wang X. Voxel spread function method for correction of magnetic field inhomogeneity effects in quantitative gradient-echo-based MRI. Magn Reson Med 2013; 70:1283-92. [PMID: 23233445 PMCID: PMC3604169 DOI: 10.1002/mrm.24585] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Revised: 10/29/2012] [Accepted: 11/14/2012] [Indexed: 11/10/2022]
Abstract
PURPOSE Macroscopic magnetic field inhomogeneities adversely affect different aspects of MRI images. In quantitative MRI when the goal is to quantify biological tissue parameters, they bias and often corrupt such measurements. The goal of this article is to develop a method for correction of macroscopic field inhomogeneities that can be applied to a variety of quantitative gradient-echo-based MRI techniques. METHODS We have reanalyzed a basic theory of gradient echo MRI signal formation in the presence of background field inhomogeneities and derived equations that allow for correction of magnetic field inhomogeneity effects based on the phase and magnitude of gradient echo data. We verified our theory by mapping effective transverse relaxation rate in computer simulated, phantom, and in vivo human data collected with multi-gradient echo sequences. RESULTS The proposed technique takes into account voxel spread function effects and allowed obtaining virtually free from artifacts effective transverse relaxation rate maps for all simulated, phantom and in vivo data except of the edge areas with very steep field gradients. CONCLUSION The voxel spread function method, allowing quantification of tissue specific effective transverse relaxation rate-related tissue properties, has a potential to breed new MRI biomarkers serving as surrogates for tissue biological properties similar to longitudinal and transverse relaxation rate constants widely used in clinical and research MRI.
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Affiliation(s)
- Dmitriy A Yablonskiy
- Department of Radiology, Washington University in St. Louis, St. Louis, Missouri, USA
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23
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Ebrahimi B, Crane JA, Knudsen BE, Macura SI, Grande JP, Lerman LO. Evolution of cardiac and renal impairment detected by high-field cardiovascular magnetic resonance in mice with renal artery stenosis. J Cardiovasc Magn Reson 2013; 15:98. [PMID: 24160179 PMCID: PMC3874758 DOI: 10.1186/1532-429x-15-98] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 10/16/2013] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Renal artery stenosis (RAS) promotes hypertension and cardiac dysfunction. The 2-kidney, 1-clip mouse model in many ways resembles RAS in humans and is amenable for genetic manipulation, but difficult to evaluate noninvasively. We hypothesized that cardiovascular magnetic resonance (CMR) is capable of detecting progressive cardiac and renal dysfunction in mice with RAS and monitoring the progression of the disease longitudinally. METHODS RAS was induced at baseline in eighteen mice by constricting the renal artery. Nine additional animals served as normal controls. CMR scans (16.4 T) were performed in all mice one week before and 2 and 4 weeks after baseline. Renal volumes and hemodynamics were assessed using 3D fast imaging with steady-state precession and arterial spin labelling, and cardiac function using CMR cine. Renal hypoxia was investigated using blood oxygen-level dependent (BOLD) MR. RESULTS Two weeks after surgery, mean arterial pressure was elevated in RAS mice. The stenotic kidney (STK) showed atrophy, while the contra-lateral kidney (CLK) showed hypertrophy. Renal blood flow (RBF) and cortical oxygenation level declined in the STK but remained unchanged in CLK. Moreover, cardiac end-diastolic and stroke volumes decreased and myocardial mass increased. At 4 weeks, STK RBF remained declined and the STK cortex and medulla showed development of hypoxia. Additionally, BOLD detected a mild hypoxia in CLK cortex. Cardiac end-diastolic and stroke volumes remained reduced and left ventricular hypertrophy worsened. Left ventricular filling velocities (E/A) indicated progression of cardiac dysfunction towards restrictive filling. CONCLUSIONS CMR detected longitudinal progression of cardiac and renal dysfunction in 2K, 1C mice. These observations support the use of high-field CMR to obtain useful information regarding chronic cardiac and renal dysfunction in small animals.
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MESH Headings
- Animals
- Arterial Pressure
- Atrophy
- Cardio-Renal Syndrome/diagnosis
- Cardio-Renal Syndrome/etiology
- Cardio-Renal Syndrome/physiopathology
- Disease Models, Animal
- Disease Progression
- Heart Rate
- Hypertension, Renovascular/diagnosis
- Hypertension, Renovascular/etiology
- Hypertension, Renovascular/physiopathology
- Hypertrophy
- Hypertrophy, Left Ventricular/diagnosis
- Hypertrophy, Left Ventricular/etiology
- Hypertrophy, Left Ventricular/physiopathology
- Kidney/blood supply
- Kidney/pathology
- Magnetic Resonance Imaging, Cine
- Male
- Mice
- Mice, 129 Strain
- Predictive Value of Tests
- Renal Artery Obstruction/complications
- Renal Artery Obstruction/diagnosis
- Renal Artery Obstruction/physiopathology
- Renal Circulation
- Time Factors
- Ventricular Dysfunction, Left/diagnosis
- Ventricular Dysfunction, Left/etiology
- Ventricular Dysfunction, Left/physiopathology
- Ventricular Function, Left
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Affiliation(s)
- Behzad Ebrahimi
- Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota, USA
| | - John A Crane
- Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota, USA
| | - Bruce E Knudsen
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA
| | - Slobodan I Macura
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota, USA
| | - Joseph P Grande
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA
| | - Lilach O Lerman
- Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota, USA
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24
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Pannetier NA, Sohlin M, Christen T, Schad L, Schuff N. Numerical modeling of susceptibility-related MR signal dephasing with vessel size measurement: phantom validation at 3T. Magn Reson Med 2013; 72:646-58. [PMID: 24167116 DOI: 10.1002/mrm.24968] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Revised: 08/05/2013] [Accepted: 09/04/2013] [Indexed: 11/09/2022]
Abstract
PURPOSE MRI is used to obtain quantitative oxygenation and blood volume information from the susceptibility-related MR signal dephasing induced by blood vessels. However, analytical models that fit the MR signal are usually not accurate over the range of small blood vessels. Moreover, recent studies have demonstrated limitations in the simultaneous assessment of oxygenation and blood volume. In this study, a multiparametric MRI framework that aims to measure vessel radii in addition to magnetic susceptibility and volume fraction was introduced. METHODS The protocol consisted of gradient-echo sampling of the spin-echo, diffusion, T2, and B0 acquisitions. After correction steps, the data were postprocessed with a versatile numerical model of the MR signal. An important analytical model was implemented for comparison. The approach was validated in phantoms with coiling strings as proxy for blood vessels. RESULTS The feasibility of the vessel radius measurement is demonstrated. The numerical model shows an improved accuracy compared with the analytical approach. However, both methods overestimate the radius. The simultaneous measurement of the magnetic susceptibility and the volume fraction remains challenging. CONCLUSION The results suggest that this approach could be interesting in vivo to better characterize the microvasculature without contrast agent.
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Affiliation(s)
- Nicolas A Pannetier
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA; Center for Imaging of Neurodegenerative Diseases, Department of Veterans Affairs Medical Center, San Francisco, California, USA
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25
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Oh SS, Oh SH, Nam Y, Han D, Stafford RB, Hwang J, Kim DH, Park H, Lee J. Improved susceptibility weighted imaging method using multi-echo acquisition. Magn Reson Med 2013; 72:452-8. [PMID: 24105838 DOI: 10.1002/mrm.24940] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Revised: 07/19/2013] [Accepted: 08/09/2013] [Indexed: 01/05/2023]
Abstract
PURPOSE To introduce novel acquisition and postprocessing approaches for susceptibility weighted imaging (SWI) to remove background field inhomogeneity artifacts in both magnitude and phase data. METHODS The proposed method acquires three echoes in a three-dimensional gradient echo (GRE) sequence, with a field compensation gradient (z-shim gradient) applied to the third echo. The artifacts in the magnitude data are compensated by signal estimation from all three echoes. The artifacts in phase signals are removed by modeling the background phase distortions using Gaussians. The method was applied in vivo and compared with conventional SWI. RESULTS The method successfully compensates for background field inhomogeneity artifacts in magnitude and phase images, and demonstrated improved SWI images. In particular, vessels in frontal lobe, which were not observed in conventional SWI, were identified in the proposed method. CONCLUSION The new method improves image quality in SWI by restoring signal in the frontal and temporal regions.
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Affiliation(s)
- Sung Suk Oh
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA; Department of Electrical Engineering, KAIST, Daejeon, Korea
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26
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Cao Z, Oh S, Sica CT, McGarrity JM, Horan T, Luo W, Collins CM. Bloch-based MRI system simulator considering realistic electromagnetic fields for calculation of signal, noise, and specific absorption rate. Magn Reson Med 2013; 72:237-47. [PMID: 24006153 DOI: 10.1002/mrm.24907] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2013] [Revised: 07/10/2013] [Accepted: 07/10/2013] [Indexed: 01/09/2023]
Abstract
PURPOSE To describe and introduce new software capable of accurately simulating MR signal, noise, and specific absorption rate (SAR) given arbitrary sample, sequence, static magnetic field distribution, and radiofrequency magnetic and electric field distributions for each transmit and receive coil. THEORY AND METHODS Using fundamental equations for nuclear precession and relaxation, signal reception, noise reception, and calculation of SAR, a versatile MR simulator was developed. The resulting simulator was tested with simulation of a variety of sequences demonstrating several common imaging contrast types and artifacts. The simulation of intravoxel dephasing and rephasing with both tracking of the first order derivatives of each magnetization vector and multiple magnetization vectors was examined to ensure adequate representation of the MR signal. A quantitative comparison of simulated and experimentally measured SNR was also performed. RESULTS The simulator showed good agreement with our expectations, theory, and experiment. CONCLUSION With careful design, an MR simulator producing realistic signal, noise, and SAR for arbitrary sample, sequence, and fields has been created. It is hoped that this tool will be valuable in a wide variety of applications.
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Affiliation(s)
- Zhipeng Cao
- Department of Bioengineering, The Pennsylvania State University, Hershey, Pennsylvania, USA; Department of Radiology, The Pennsylvania State University, Hershey, Pennsylvania, USA
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27
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Kwon OI, Woo EJ, Du YP, Hwang D. A tissue-relaxation-dependent neighboring method for robust mapping of the myelin water fraction. Neuroimage 2013; 74:12-21. [PMID: 23384527 DOI: 10.1016/j.neuroimage.2013.01.064] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Revised: 01/17/2013] [Accepted: 01/23/2013] [Indexed: 10/27/2022] Open
Abstract
Quantitative assessment of the myelin content in white matter (WM) using MRI has become a useful tool for investigating myelin-related diseases, such as multiple sclerosis (MS). Myelin water fraction (MWF) maps can be estimated pixel-by-pixel by a determination of the T₂ or T₂* spectrum from signal decay measurements at each individual image pixel. However, detection of parameters from the measured decay curve, assuming a combination of smooth multi-exponential curves, results in a nonlinear and seriously ill-posed problem. In this paper, we propose a new method to obtain a stable MWF map robust to the presence of noise while sustaining sufficient resolution, which uses weighted combinations of measured decay signals in a spatially independent neighborhood to combine tissues with similar relaxation parameters. To determine optimal weighting factors, we define a spatially independent neighborhood for each pixel and a distance with respect to decay rates that effectively includes pixels with similar decay characteristics, and which therefore have similar relaxation parameters. We recover the MWF values by using optimally weighted decay curves. We use numerical simulations and in vitro and in vivo experimental brain data scanned with a multi-gradient-echo sequence to demonstrate the feasibility of our proposed algorithm and to highlight its advantages compared to the conventional method.
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Affiliation(s)
- Oh In Kwon
- Department of Mathematics, Konkuk University, Republic of Korea
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Nam Y, Han D, Kim DH. Single-scan R2⁎ measurement with macroscopic field inhomogeneity correction. Neuroimage 2012; 63:1790-9. [DOI: 10.1016/j.neuroimage.2012.08.062] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 08/20/2012] [Accepted: 08/21/2012] [Indexed: 10/27/2022] Open
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Yang C, Poser B, Deng W, Stenger VA. Spectral decomposition of susceptibility artifacts for spectral-spatial radiofrequency pulse design. Magn Reson Med 2012; 68:1905-10. [PMID: 22334396 PMCID: PMC3355209 DOI: 10.1002/mrm.24208] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Revised: 12/14/2011] [Accepted: 01/19/2012] [Indexed: 11/08/2022]
Abstract
Susceptibility induced signal loss is a limitation in gradient echo functional MRI. The through-plane artifact in axial slices is particularly problematic due to the inferior position of air cavities in the brain. Spectral-spatial radiofrequency pulses have recently been shown to reduce signal loss in a single excitation. The pulses were successfully demonstrated assuming a linear relationship between susceptibility gradient and frequency, however, the exact frequency and spatial distribution of the susceptibility gradient in the brain is unknown. We present a spiral spectroscopic imaging sequence with a time-shifted radiofrequency pulse that can spectrally decompose the through-plane susceptibility gradient for spectral-spatial radiofrequency pulse design. Maps of the through-plane susceptibility gradient as a function of frequency were generated for the human brain at 3T. We found that the linear relationship holds well for the whole brain with an optimal slope of -1.0 μT/m/Hz.
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Affiliation(s)
- Cungeng Yang
- Department of Medicine, University of Hawaii John A. Burns School of Medicine, Honolulu, Hawaii
| | - Benedikt Poser
- Department of Medicine, University of Hawaii John A. Burns School of Medicine, Honolulu, Hawaii
| | - Weiran Deng
- Department of Medicine, University of Hawaii John A. Burns School of Medicine, Honolulu, Hawaii
| | - V. Andrew Stenger
- Department of Medicine, University of Hawaii John A. Burns School of Medicine, Honolulu, Hawaii
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Wagner M, Jurcoane A, Volz S, Magerkurth J, Zanella FE, Neumann-Haefelin T, Deichmann R, Singer OC, Hattingen E. Age-related changes of cerebral autoregulation: new insights with quantitative T2'-mapping and pulsed arterial spin-labeling MR imaging. AJNR Am J Neuroradiol 2012; 33:2081-7. [PMID: 22700750 DOI: 10.3174/ajnr.a3138] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND PURPOSE Cerebral perfusion and O(2) metabolism are affected by physiologic age-related changes. High-resolution motion-corrected quantitative T2'-imaging and PASL were used to evaluate differences in deoxygenated hemoglobin and CBF of the gray matter between young and elderly healthy subjects. Further combined T2'-imaging and PASL were investigated breathing room air and 100% O(2) to evaluate age-related changes in cerebral autoregulation. MATERIALS AND METHODS Twenty-two healthy volunteers 60-88 years of age were studied. Two scans of high-resolution motion-corrected T2'-imaging and PASL-MR imaging were obtained while subjects were either breathing room air or breathing 100% O(2). Manual and automated regions of interest were placed in the cerebral GM to extract values from the corresponding maps. Results were compared with those of a group of young healthy subjects previously scanned with the identical protocol as that used in the present study. RESULTS There was a significant decrease of cortical CBF (P < .001) and cortical T2' values (P < .001) between young and elderly healthy subjects. In both groups, T2' remained unchanged under hyperoxia compared with normoxia. Only in the younger but not in the elderly group could a significant (P = .02) hyperoxic-induced decrease of the CBF be shown. CONCLUSIONS T2'-mapping and PASL in the cerebral cortex of healthy subjects revealed a significant decrease of deoxygenated hemoglobin and of CBF with age. The constant deoxyHb level breathing 100% O(2) compared with normoxia in young and elderly GM suggests an age-appropriate cerebral autoregulation. At the younger age, hyperoxic-induced CBF decrease may protect the brain from hyperoxemia.
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Affiliation(s)
- M Wagner
- Institute of Neuroradiology, Goethe University Frankfurt am Main, Frankfurt am Main, Germany.
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31
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Lemasson B, Christen T, Serduc R, Maisin C, Bouchet A, Le Duc G, Rémy C, Barbier EL. Evaluation of the relationship between MR estimates of blood oxygen saturation and hypoxia: effect of an antiangiogenic treatment on a gliosarcoma model. Radiology 2012; 265:743-52. [PMID: 22996750 DOI: 10.1148/radiol.12112621] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
PURPOSE To assess the reproducibility of the magnetic resonance (MR) estimate of blood oxygen saturation (sO(2)) in the rat brain, to evaluate the relationship between low MR estimate of sO(2) values and tissue hypoxia in a hypoxic and necrotic glioscarcoma model (9L gliosarcoma cells), and to evaluate the capability of the MR estimate of sO(2) parameter to help identify modifications induced by an antiangiogenic treatment (sorafenib) in 9L gliosarcoma tumors. MATERIALS AND METHODS Experiments were performed with permits from the French Ministry of Agriculture. Forty-eight male rats bearing a 9L gliosarcoma were randomized in untreated and treated (sorafenib) groups. MR blood volume fraction and MR estimate of sO(2) parameters were estimated 1 day before and 1, 3, 5, and 8 days after the start of the treatment. The in vivo MR estimate of sO(2) measurement was correlated with the ex vivo hypoxia assessment by using pimonidazole staining. Paired and unpaired t tests, as well as parametric Pearson tests, were used for the statistical analyses. RESULTS In healthy tissues, MR estimate of sO(2) measurements were comparable to literature values and were reproducible (mean across all animals, 68.0% ± 6.5 [standard deviation]). In untreated tumors, MR estimate of sO(2) and immunohistochemical analysis yielded correlated fractional hypoxic-necrotic areas (R(2) = 0.81). In tumors treated with antiangiogenic therapy, tumor MR estimate of sO(2) was decreased with respect to the healthy tissue (P< .001). CONCLUSION Results of this study suggest that the MR estimate of sO(2) is a reproducible estimate that could be used as an in vivo probe of hypoxia in brain tumors and as a sensitive reporter of the hypoxic effects of antiangiogenic therapies.
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Affiliation(s)
- Benjamin Lemasson
- INSERM, U836/Equipe 5, Neuroimagerie Fonctionnelle et Perfusion Cérébrale, Université Joseph Fourier-Site Santé de la Tronche, BP 170, Domaine de la Merci, 38042 Grenoble Cedex, France
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Wagner M, Magerkurth J, Volz S, Jurcoane A, Singer OC, Neumann‐Haefelin T, Zanella FE, Deichmann R, Hattingen E. T2′‐ and PASL‐based perfusion mapping at 3 Tesla: influence of oxygen‐ventilation on cerebral autoregulation. J Magn Reson Imaging 2012; 36:1347-52. [DOI: 10.1002/jmri.23777] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Accepted: 07/20/2012] [Indexed: 11/07/2022] Open
Affiliation(s)
- Marlies Wagner
- Institute of Neuroradiology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Jörg Magerkurth
- Institute of Neuroradiology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Steffen Volz
- Brain Imaging Center, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Alina Jurcoane
- Institute of Neuroradiology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Oliver C. Singer
- Department of Neurology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Tobias Neumann‐Haefelin
- Department of Neurology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Friedhelm E. Zanella
- Institute of Neuroradiology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Ralf Deichmann
- Brain Imaging Center, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
| | - Elke Hattingen
- Institute of Neuroradiology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany
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Hernando D, Vigen KK, Shimakawa A, Reeder SB. R*(2) mapping in the presence of macroscopic B₀ field variations. Magn Reson Med 2011; 68:830-40. [PMID: 22161866 DOI: 10.1002/mrm.23306] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Revised: 11/01/2011] [Accepted: 11/03/2011] [Indexed: 11/09/2022]
Abstract
R₂ mapping has important applications in MRI, including functional imaging, tracking of super-paramagnetic particles, and measurement of tissue iron levels. However, R₂ measurements can be confounded by several effects, particularly the presence of fat and macroscopic B₀ field variations. Fat introduces additional modulations in the signal. Macroscopic field variations introduce additional dephasing that results in accelerated signal decay. These effects produce systematic errors in the resulting R₂ maps and make the estimated R₂ values dependent on the acquisition parameters. In this study, we develop a complex-reconstruction, confounder-corrected R₂ mapping technique, which addresses the presence of fat and macroscopic field variations for both 2D and 3D acquisitions. This technique extends previous chemical shift-encoded methods for R₂, fat and water mapping by measuring and correcting for the effect of macroscopic field variations in the acquired signal. The proposed method is tested on several 2D and 3D phantom and in vivo liver, cardiac, and brain datasets.
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Affiliation(s)
- Diego Hernando
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
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An H, Liu Q, Eldeniz C, Lin W. Absolute oxygenation metabolism measurements using magnetic resonance imaging. Open Neuroimag J 2011; 5:120-35. [PMID: 22276084 PMCID: PMC3256581 DOI: 10.2174/1874440001105010120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2011] [Revised: 02/02/2011] [Accepted: 03/03/2011] [Indexed: 11/29/2022] Open
Abstract
Cerebral oxygen metabolism plays a critical role in maintaining normal function of the brain. It is the primary energy source to sustain neuronal functions. Abnormalities in oxygen metabolism occur in various neuro-pathologic conditions such as ischemic stroke, cerebral trauma, cancer, Alzheimer’s disease and shock. Therefore, the ability to quantitatively measure tissue oxygenation and oxygen metabolism is essential to the understanding of pathophysiology and treatment of various diseases. The focus of this review is to provide an introduction of various blood oxygenation level dependent (BOLD) contrast methods for absolute measurements of tissue oxygenation, including both magnitude and phase image based approaches. The advantages and disadvantages of each method are discussed.
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Affiliation(s)
- Hongyu An
- Department of Radiology and Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, USA
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35
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Abstract
OBJECTIVE The purpose of this article is to review some of the basic principles of imaging and how metal-induced susceptibility artifacts originate in MR images. We will describe common ways to reduce or modify artifacts using readily available imaging techniques, and we will discuss some advanced methods to correct readout-direction and slice-direction artifacts. CONCLUSION The presence of metallic implants in MRI can cause substantial image artifacts, including signal loss, failure of fat suppression, geometric distortion, and bright pile-up artifacts. These cause large resonant frequency changes and failure of many MRI mechanisms. Careful parameter and pulse sequence selections can avoid or reduce artifacts, although more advanced imaging methods offer further imaging improvements.
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Finsterbusch J, Eippert F, Büchel C. Single, slice-specific z-shim gradient pulses improve T2*-weighted imaging of the spinal cord. Neuroimage 2011; 59:2307-15. [PMID: 21979381 DOI: 10.1016/j.neuroimage.2011.09.038] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Revised: 09/09/2011] [Accepted: 09/14/2011] [Indexed: 10/17/2022] Open
Abstract
T2*-weighted imaging of the spinal cord suffers from signal dropouts that hamper blood-oxygenation-level-dependent functional magnetic resonance imaging (fMRI). They are due to field inhomogeneities caused by the different magnetic susceptibilities of the vertebrae and the intervertebral disks that vary periodically along the cord and, thus, cannot be compensated appropriately with conventional (constant) shimming. In this study, a single, slice-specific gradient pulse ("z-shim") is applied in echo-planar imaging of axial sections in order to compensate for the corresponding through-slice signal dephasing without affecting the acquisition time, i.e. the temporal resolution. Based on a reference acquisition sampling a range of compensation moments, the value yielding the maximum signal amplitude within the spinal cord is determined for each slice. Severe N/2 ghosting for larger compensation moments is avoided by applying the gradient pulse after the corresponding reference echoes. Furthermore, first-order flow compensation in the slice direction of both the slice-selection and the z-shim gradient pulse considerably reduces signal fluctuations in the cerebro-spinal fluid surrounding the spinal cord, i.e. would minimize ringing artifacts in fMRI. Phantom and in vivo experiments show the necessity to use slice-specific compensation moments in the presence of local susceptibility differences. Measurements performed in a group of 24 healthy volunteers at 3T demonstrate that this approach improves T2*-weighted imaging of axial sections of the cervical spinal cord by (i) increasing the signal intensity (overall by about 20%) and (ii) reducing signal intensity variations along the cord (by about 80%). Thus, it may help to improve the feasibility and reliability of fMRI of the spinal cord.
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Affiliation(s)
- Jürgen Finsterbusch
- Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
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37
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Sigovan M, Hamoudeh M, Al Faraj A, Charpigny D, Fessi H, Canet-Soulas E. Positive contrast with therapeutic iron nanoparticles at 4.7 T. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2011; 24:259-65. [DOI: 10.1007/s10334-011-0258-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 04/13/2011] [Accepted: 05/06/2011] [Indexed: 01/24/2023]
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Christen T, Lemasson B, Pannetier N, Farion R, Segebarth C, Rémy C, Barbier EL. Evaluation of a quantitative blood oxygenation level-dependent (qBOLD) approach to map local blood oxygen saturation. NMR IN BIOMEDICINE 2011; 24:393-403. [PMID: 20960585 DOI: 10.1002/nbm.1603] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 06/11/2010] [Accepted: 07/15/2010] [Indexed: 05/30/2023]
Abstract
Blood oxygen saturation (SO(2)) is a promising parameter for the assessment of brain tissue viability in numerous pathologies. Quantitative blood oxygenation level-dependent (qBOLD)-like approaches allow the estimation of SO(2) by modelling the contribution of deoxyhaemoglobin to the MR signal decay. These methods require a high signal-to-noise ratio to obtain accurate maps through fitting procedures. In this article, we present a version of the qBOLD method at long TE taking into account separate estimates of T(2), total blood volume fraction (BV(f)) and magnetic field inhomogeneities. Our approach was applied to the brains of 13 healthy rats under normoxia, hyperoxia and hypoxia. MR estimates of local SO(2) (MR_LSO(2)) were compared with measurements obtained from blood gas analysis. A very good correlation (R(2) = 0.89) was found between brain MR_LSO(2) and sagittal sinus SO(2).
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Denic A, Macura SI, Mishra P, Gamez JD, Rodriguez M, Pirko I. MRI in rodent models of brain disorders. Neurotherapeutics 2011; 8:3-18. [PMID: 21274681 PMCID: PMC3075741 DOI: 10.1007/s13311-010-0002-4] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Magnetic resonance imaging (MRI) is a well-established tool in clinical practice and research on human neurological disorders. Translational MRI research utilizing rodent models of central nervous system (CNS) diseases is becoming popular with the increased availability of dedicated small animal MRI systems. Projects utilizing this technology typically fall into one of two categories: 1) true "pre-clinical" studies involving the use of MRI as a noninvasive disease monitoring tool which serves as a biomarker for selected aspects of the disease and 2) studies investigating the pathomechanism of known human MRI findings in CNS disease models. Most small animal MRI systems operate at 4.7-11.7 Tesla field strengths. Although the higher field strength clearly results in a higher signal-to-noise ratio, which enables higher resolution acquisition, a variety of artifacts and limitations related to the specific absorption rate represent significant challenges in these experiments. In addition to standard T1-, T2-, and T2*-weighted MRI methods, all of the currently available advanced MRI techniques have been utilized in experimental animals, including diffusion, perfusion, and susceptibility weighted imaging, functional magnetic resonance imaging, chemical shift imaging, heteronuclear imaging, and (1)H or (31)P MR spectroscopy. Selected MRI techniques are also exclusively utilized in experimental research, including manganese-enhanced MRI, and cell-specific/molecular imaging techniques utilizing negative contrast materials. In this review, we describe technical and practical aspects of small animal MRI and provide examples of different MRI techniques in anatomical imaging and tract tracing as well as several models of neurological disorders, including inflammatory, neurodegenerative, vascular, and traumatic brain and spinal cord injury models, and neoplastic diseases.
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Affiliation(s)
- Aleksandar Denic
- Department of Neuroscience, Mayo Clinic, Rochester, Minnesota 55905 USA
| | - Slobodan I. Macura
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota 55905 USA
| | - Prasanna Mishra
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota 55905 USA
| | - Jeffrey D. Gamez
- Department of Neurology, Mayo Clinic, 200 First St. SW, Rochester, Minnesota 55905 USA
| | - Moses Rodriguez
- Department of Neurology, Mayo Clinic, 200 First St. SW, Rochester, Minnesota 55905 USA
| | - Istvan Pirko
- Department of Neurology, Mayo Clinic, 200 First St. SW, Rochester, Minnesota 55905 USA
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Zhang Y, Guo Y, Ragin AB, Lewandowski RJ, Yang GY, Nijm GM, Sahakian AV, Omary RA, Larson AC. MR imaging to assess immediate response to irreversible electroporation for targeted ablation of liver tissues: preclinical feasibility studies in a rodent model. Radiology 2010; 256:424-32. [PMID: 20656834 DOI: 10.1148/radiol.10091955] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
PURPOSE To test the hypothesis that magnetic resonance (MR) imaging measurements can be used to immediately detect treated tissue regions after irreversible electroporation (IRE) ablation procedures in rodent liver tissues. MATERIALS AND METHODS All experiments received institutional animal care and use committee approval. In four rats for preliminary studies and 18 rats for formal assessment, MR imaging-compatible electrodes were inserted into the liver and MR imaging-monitored IRE procedures were performed at one of three electrode voltages (1000, 1500, or 2500 V), with T1- and T2-weighted images acquired before and immediately after application of the IRE pulses. MR imaging measurements were compared with both finite element modeling (FEM)-anticipated ablation zones and histologically confirmed ablation zones at necropsy. Intraclass and Spearman correlation coefficients were calculated for statistical comparisons. RESULTS MR imaging measurements permitted immediate depiction of IRE ablation zones that were hypointense on T1-weighted images and hyperintense on T2-weighted images. MR imaging-based measurements demonstrated excellent consistency with FEM-anticipated ablation zones (r > 0.90 and P < .001 for both T1- and T2-weighted images). MR imaging measurements were also highly correlated with histologically confirmed ablation zone measurements (rho > 0.90 and P < .001 for both T1- and T2-weighted images). CONCLUSION MR imaging permits immediate depiction of ablated tissue zones for monitoring of IRE ablation procedures. These measurements could potentially be used during treatment to elicit repeat application of IRE pulses or adjustments to electrode positions to ensure complete treatment of targeted lesions.
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Affiliation(s)
- Yue Zhang
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA
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Jung KJ, Peng H, Zhao T, Avidan G, Behrmann M. Recovery of signal loss due to an in-plane susceptibility gradient in the gradient echo EPI through acquisition of extended phase-encoding lines. Magn Reson Imaging 2010; 28:777-83. [PMID: 20456891 DOI: 10.1016/j.mri.2010.03.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Revised: 01/20/2010] [Accepted: 03/05/2010] [Indexed: 11/25/2022]
Abstract
In gradient echo imaging the in-plane susceptibility gradient causes an echo shift which results in signal loss. The loss of signal becomes more severe in gradient echo EPI, due to the low amplitude of the gradient which is applied in the phase-encoding direction during a long echo train. As the readout gradient amplitude is set to be very high in gradient echo EPI, the echo shift in the readout direction is negligible compared to that in the phase-encoding direction. Traditionally, a z-shimming technique has been applied to the phase-encoding direction of gradient echo EPI to restore the lost signal. This technique, however, requires a significant increase of scan time, as is also the case with the through-plane z-shimming technique. A new approach that allows one to restore the lost signal is to acquire additional phase-encoding lines beyond the regular phase-encoding range. The extension of the phase-encoding lines prior to the regular phase-encoding range exploits the delay time for optimum echo time of the BOLD sensitivity. Therefore, scan time is increased only for the extended phase-encoding lines posterior to the regular phase-encoding range. This technique has been confirmed experimentally by imaging human subject's heads at 3T.
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Affiliation(s)
- Kwan-Jin Jung
- Brain Imaging Research Center, University of Pittsburgh, Pittsburgh, PA 15203, USA.
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Franconi F, Chapon C, Le Jeune JJ, Richomme P, Lemaire L. Susceptibility gradient quantization by MRI signal response mapping (SIRMA) to dephaser. Med Phys 2010; 37:877-84. [PMID: 20229897 DOI: 10.1118/1.3298019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Susceptibility effects are a very efficient source of contrast in magnetic resonance imaging. However, detection is hampered by the fact the induced contrast is negative. In this work, the SIgnal Response MApping (SIRMA) to dephaser method is proposed to map susceptibility gradient to improve visualization. METHODS In conventional gradient echo acquisitions, the echo formation of susceptibility affected spins is shifted in k-space, the shift being proportional to the susceptibility gradient. Susceptibility gradients map can be produced by measuring this induced shifts. The SIRMA method measures these shifts from a series of dephased images collected with additional incremental dephasers. These additional dephasers correspond either to a slice refocusing gradient offset or to a reconstruction window off-centering. The signal intensity profile as a function of the additional dephaser was determined on a pixel-by-pixel basis from the ensemble of dephased images. Susceptibility affected voxels presented a signal response profile maximum shifted compared to nonaffected voxels ones. Shift magnitude and sign were measured for each pixel to determine susceptibility gradients and produce a susceptibility gradient map. RESULTS In vitro experiments demonstrated the ability of the method to map gradient inhomogeneities induced by a cylinder. Quantization accuracy was evaluated comparing SIRMA images and simulations performed on the well-characterized air filled cylinder model. Performances of the SIRMA method, evaluated in vitro on cylinders filled with various superparamagnetic iron oxide SPIO concentrations, showed limited influence of acquisition parameters. Robustness of the method was then assessed in vivo after an infusion of SPIO-loaded nanocapsules into the rat brain using a convection-enhanced drug delivery approach. The region of massive susceptibility gradient induced by the SPIO-loaded nanocapsules was clearly delineated on SIRMA maps and images were compared to T2* weighted images, Susceptibility Gradient Map (SGM), and histological Perl's staining slice. The potential for quantitative evaluation of SPIO distribution volume was demonstrated. CONCLUSIONS The proposed method is a promising technique for a wide range of applications especially in molecular or cellular imaging with respect to its quantitative nature and its computational simplicity.
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Affiliation(s)
- F Franconi
- Plateforme d'Ingénierie et d'Analyses Moléculaires, Université d'Angers, 45045 Angers, France.
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Baudrexel S, Volz S, Preibisch C, Klein JC, Steinmetz H, Hilker R, Deichmann R. Rapid single-scan T2*-mapping using exponential excitation pulses and image-based correction for linear background gradients. Magn Reson Med 2009; 62:263-8. [PMID: 19353655 DOI: 10.1002/mrm.21971] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A method for fast quantitative T(2)* mapping based on multiple gradient-echo (multi-GE) imaging with correction for static magnetic field inhomogeneities is described, using an exponential excitation pulse. Field gradient maps are obtained from the phase information and modulus data are subsequently corrected, allowing for simple monoexponential T(2)* fitting. Echoes with long echo times suffering from major signal losses due to field inhomogeneities are excluded from the analysis. The acquisition time for a matrix size of 256 x 256, 1 mm in-plane resolution, and 2 mm slice thickness amounts to 15 s per slice. An additional correction for in-plane field gradients further improves accuracy. Phantom experiments show that the method provides accurate T(2)* values for field gradients up to 200 microT/m; for gradients up to 300 microT/m errors do not exceed 15%. In vivo T(2)* values acquired on healthy volunteers at 3T are in excellent agreement with results from the literature.
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Affiliation(s)
- Simon Baudrexel
- Department of Neurology, University Hospital, Goethe University Frankfurt am Main, Frankfurt am Main, Germany.
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Lu W, Pauly KB, Gold GE, Pauly JM, Hargreaves BA. SEMAC: Slice Encoding for Metal Artifact Correction in MRI. Magn Reson Med 2009; 62:66-76. [PMID: 19267347 DOI: 10.1002/mrm.21967] [Citation(s) in RCA: 277] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Magnetic resonance imaging (MRI) near metallic implants remains an unmet need because of severe artifacts, which mainly stem from large metal-induced field inhomogeneities. This work addresses MRI near metallic implants with an innovative imaging technique called "Slice Encoding for Metal Artifact Correction" (SEMAC). The SEMAC technique corrects metal artifacts via robust encoding of each excited slice against metal-induced field inhomogeneities. The robust slice encoding is achieved by extending a view-angle-tilting (VAT) spin-echo sequence with additional z-phase encoding. Although the VAT compensation gradient suppresses most in-plane distortions, the z-phase encoding fully resolves distorted excitation profiles that cause through-plane distortions. By positioning all spins in a region-of-interest to their actual spatial locations, the through-plane distortions can be corrected by summing up the resolved spins in each voxel. The SEMAC technique does not require additional hardware and can be deployed to the large installed base of whole-body MRI systems. The efficacy of the SEMAC technique in eliminating metal-induced distortions with feasible scan times is validated in phantom and in vivo spine and knee studies.
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Affiliation(s)
- Wenmiao Lu
- Department of Radiology, Stanford University, Stanford, CA 94305-5488, USA.
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45
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Webb AG, Neuberger T, Park EJ, Smith N. Temperature mapping near the surface of ultrasound transducers using susceptibility- compensated magnetic resonance imaging. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2009; 56:1145-1150. [PMID: 19574122 DOI: 10.1109/tuffc.2009.1156] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Magnetic resonance imaging (MRI)-based temperature mapping very close to the surface of an ultrasound transducer is not possible due to the large magnetic susceptibility- induced image artifacts that arise from the materials used in transducer construction. Here, it is shown in phantoms that "susceptibility-compensated" MRI sequences can be used to measure thermal increases approximately 1 mm from the surface of a 4-element cymbal array transducer, which has been used widely for noninvasive transdermal drug delivery. The estimated temperatures agree well with those measured using thermocouples.
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Affiliation(s)
- Andrew G Webb
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
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Meng Y, Lei H. A single-scan T2* mapping method based on two gradient-echo images with compensation for macroscopic field inhomogeneity. Magn Reson Med 2009; 60:1388-95. [PMID: 19025905 DOI: 10.1002/mrm.21731] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
T2*-weighted imaging (T2*WI) and quantitative T2* mapping with conventional gradient-echo acquisition are often hindered by severe signal loss induced by macroscopic field inhomogeneity. Various z-shimming approaches have been developed for T2*WI/T2* mapping in which the effects of macroscopic field inhomogeneity are suppressed while the sensitivity of T2*-related signal intensity to alterations in the microscopic susceptibility is maintained. However, this is often done at the cost of significantly increased imaging time. In this work, a fast T2* mapping method with compensation for macroscopic field inhomogeneity was developed. A proton density-weighted image and a composite T2*-weighted image, both of which were essentially free from macroscopic field inhomogeneity-induced signal loss, were used for the T2* calculation. The composite T2*-weighted image was reconstructed from a number of gradient-echo images acquired with successively incremented z-shimming compensation. Because acquisition of the two images and z-shimming compensation were realized in a single scan, the total acquisition time for obtaining a T2* map with the proposed method is the same as the time taken for a conventional multiecho gradient-echo imaging sequence without compensation. The performance and efficiency of the proposed method were demonstrated and evaluated at 4.7 T.
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Affiliation(s)
- Yuguang Meng
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
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Marshall H, Hajnal JV, Warren JE, Wise RJ, Larkman DJ. An efficient automated z-shim based method to correct through-slice signal loss in EPI at 3T. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2009; 22:187-200. [DOI: 10.1007/s10334-009-0164-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Revised: 12/23/2008] [Accepted: 01/12/2009] [Indexed: 11/30/2022]
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48
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Sutton BP, Ouyang C, Karampinos DC, Miller GA. Current trends and challenges in MRI acquisitions to investigate brain function. Int J Psychophysiol 2009; 73:33-42. [PMID: 19236896 DOI: 10.1016/j.ijpsycho.2008.12.020] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Revised: 12/08/2008] [Accepted: 12/23/2008] [Indexed: 11/19/2022]
Abstract
Functional magnetic resonance imaging (fMRI) studies using the blood oxygenation level dependent (BOLD) response have become a widely used tool for noninvasive assessment of functional organization of the brain. Yet the technique is still fairly new, with many significant challenges remaining. Capitalizing on additional contrast mechanisms available with MRI, several other functional imaging techniques have been developed that potentially provide improved quantification or specificity of neuronal function. This article reviews the challenges and the current state of the art in MRI-based methods of imaging cognitive function.
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Affiliation(s)
- Bradley P Sutton
- Bioengineering Department, University of Illinois at Urbana-Champaign, 3120 DCL, 1304 W Springfield Avenue, Urbana, IL 61801 United States.
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Deng W, Yang C, Alagappan V, Wald LL, Boada FE, Stenger VA. Simultaneous z-shim method for reducing susceptibility artifacts with multiple transmitters. Magn Reson Med 2009; 61:255-9. [PMID: 19165881 PMCID: PMC2714643 DOI: 10.1002/mrm.21870] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Accepted: 10/01/2008] [Indexed: 11/10/2022]
Abstract
The signal loss susceptibility artifact is a major limitation in gradient-echo MRI applications. Various methods, including z-shim techniques and multidimensional tailored radio frequency (RF) pulses, have been proposed to mitigate the through-plane signal loss artifact, which is dominant in axial slices above the sinus region. Unfortunately, z-shim techniques require multiple steps and multidimensional RF methods are complex, with long pulse lengths. Parallel transmission methods were recently shown to be promising for improving B1 inhomogeneity and reducing the specific absorption rate. In this work, a novel method using time-shifted slice-select RF pulses is presented for reducing the through-plane signal loss artifact in parallel transmission applications. A simultaneous z-shim is obtained by concurrently applying unique time-shifted pulses on each transmitter. The method is shown to reduce the signal loss susceptibility artifact in gradient-echo images using a four-channel parallel transmission system at 3T.
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Affiliation(s)
- Weiran Deng
- UH-QMC Magnetic Resonance Research Center, Department of Medicine, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 96813-2427, USA.
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Chung JY, Yoon HW, Kim YB, Park HW, Cho ZH. Susceptibility compensated fMRI study using a tailored RF echo planar imaging sequence. J Magn Reson Imaging 2009; 29:221-8. [DOI: 10.1002/jmri.21397] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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