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Yetisir F, Poser BA, Grant PE, Adalsteinsson E, Wald LL, Guerin B. Parallel transmission 2D RARE imaging at 7T with transmit field inhomogeneity mitigation and local SAR control. Magn Reson Imaging 2022; 93:87-96. [PMID: 35940379 PMCID: PMC9789791 DOI: 10.1016/j.mri.2022.08.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Revised: 07/15/2022] [Accepted: 08/02/2022] [Indexed: 12/26/2022]
Abstract
PURPOSE We develop and test a parallel transmit (pTx) pulse design framework to mitigate transmit field inhomogeneity with control of local specific absorption rate (SAR) in 2D rapid acquisition with relaxation enhancement (RARE) imaging at 7T. METHODS We design large flip angle RF pulses with explicit local SAR constraints by numerical simulation of the Bloch equations. Parallel computation and analytical expressions for the Jacobian and the Hessian matrices are employed to reduce pulse design time. The refocusing-excitation "spokes" pulse pairs are designed to satisfy the Carr-Purcell-Meiboom-Gill (CPMG) condition using a combined magnitude least squares-least squares approach. RESULTS In a simulated dataset, the proposed approach reduced peak local SAR by up to 56% for the same level of refocusing uniformity error and reduced refocusing uniformity error by up to 59% (from 32% to 7%) for the same level of peak local SAR compared to the circularly polarized birdcage mode of the pTx array. Using explicit local SAR constraints also reduced peak local SAR by up to 46% compared to an RF peak power constrained design. The excitation and refocusing uniformity error were reduced from 20%-33% to 4%-6% in single slice phantom experiments. Phantom experiments demonstrated good agreement between the simulated excitation and refocusing uniformity profiles and experimental image shading. CONCLUSION PTx-designed excitation and refocusing CPMG pulse pairs can mitigate transmit field inhomogeneity in the 2D RARE sequence. Moreover, local SAR can be decreased significantly using pTx, potentially leading to better slice coverage, enabling larger flip angles or faster imaging.
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Affiliation(s)
- Filiz Yetisir
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA.
| | - Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Universiteitssingel 40, 6229 ER Maastricht, the Netherlands
| | - P Ellen Grant
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA; Department of Pediatrics, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA; Department of Radiology, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA
| | - Elfar Adalsteinsson
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA; Institute for Medical Engineering and Science, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA
| | - Lawrence L Wald
- Department of Radiology, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, 77 MA Avenue, Cambridge, MA 02139, USA; Athinoula A. Martinos Center for Biomedical Imaging, MA General Hospital, 149 13th Street, Charlestown, MA 02129, USA
| | - Bastien Guerin
- Department of Radiology, Harvard Medical School, 25 Shattuck Street, Boston, MA 02115, USA; Athinoula A. Martinos Center for Biomedical Imaging, MA General Hospital, 149 13th Street, Charlestown, MA 02129, USA
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Becker M, Jouda M, Kolchinskaya A, Korvink JG. Deep regression with ensembles enables fast, first-order shimming in low-field NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 336:107151. [PMID: 35183922 DOI: 10.1016/j.jmr.2022.107151] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 01/21/2022] [Accepted: 01/24/2022] [Indexed: 06/14/2023]
Abstract
Shimming in the context of nuclear magnetic resonance aims to achieve a uniform magnetic field distribution, as perfect as possible, and is crucial for useful spectroscopy and imaging. Currently, shimming precedes most acquisition procedures in the laboratory, and this mostly semi-automatic procedure often needs to be repeated, which can be cumbersome and time-consuming. The paper investigates the feasibility of completely automating and accelerating the shimming procedure by applying deep learning (DL). We show that DL can relate measured spectral shape to shim current specifications and thus rapidly predict three shim currents simultaneously, given only four input spectra. Due to the lack of accessible data for developing shimming algorithms, we also introduce a database that served as our DL training set, and allows inference of changes to 1H NMR signals depending on shim offsets. In situ experiments of deep regression with ensembles demonstrate a high success rate in spectral quality improvement for random shim distortions over different neural architectures and chemical substances. This paper presents a proof-of-concept that machine learning can simplify and accelerate the shimming problem, either as a stand-alone method, or in combination with traditional shimming methods. Our database and code are publicly available.
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Affiliation(s)
- Moritz Becker
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology, Karlsruhe 76131, Germany
| | - Mazin Jouda
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology, Karlsruhe 76131, Germany
| | - Anastasiya Kolchinskaya
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology, Karlsruhe 76131, Germany
| | - Jan G Korvink
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology, Karlsruhe 76131, Germany.
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Shi Y, Clare S, Vannesjo SJ. Shim optimization with region of interest-specific Tikhonov regularization: Application to second-order slice-wise shimming of the brain. Magn Reson Med 2021; 87:1218-1230. [PMID: 34783374 DOI: 10.1002/mrm.28951] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 06/18/2021] [Accepted: 07/18/2021] [Indexed: 11/12/2022]
Abstract
PURPOSE Slice-wise shimming can improve field homogeneity, but suffers from large noise propagation in the shim calculation. Here, we propose a robust shim current optimization for higher-order dynamic shim updating, based on Tikhonov regularization with a variable regularization parameter, λ . THEORY AND METHODS: λ was selected for each slice separately in a fully automatic procedure based on a combination of boundary constraints and an L-curve search algorithm. Shimming performance was evaluated for second order slice-wise shimming of the brain at 7T, by simulation on a database of field maps from 143 subjects, and by direct measurements in 8 subjects. RESULTS Simulations yielded on average 36% reduction in the shim current norm for just 0.4 Hz increase in residual field SD as compared to unconstrained unregularized optimization. In vivo results yielded on average 34.0 Hz residual field SD as compared to 34.3 Hz with a constrained unregularized optimization, while simultaneously reducing the shim current norm to 2.8 A from 3.9 A. The proposed regularization also reduced the average step in the shim current between slices. CONCLUSION Slice-wise variable Tikhonov regularization yielded reduced current norm and current steps to a negligible cost in field inhomogeneity. The method holds promise to increase the robustness, and thereby the utility, of higher-order shim updating.
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Affiliation(s)
- Yuhang Shi
- Wellcome Centre for Integrative Neuroimaging, FMRIB, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Stuart Clare
- Wellcome Centre for Integrative Neuroimaging, FMRIB, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Signe Johanna Vannesjo
- Wellcome Centre for Integrative Neuroimaging, FMRIB, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
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Topping GJ, Hundshammer C, Nagel L, Grashei M, Aigner M, Skinner JG, Schulte RF, Schilling F. Acquisition strategies for spatially resolved magnetic resonance detection of hyperpolarized nuclei. MAGMA (NEW YORK, N.Y.) 2020; 33:221-256. [PMID: 31811491 PMCID: PMC7109201 DOI: 10.1007/s10334-019-00807-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 10/08/2019] [Accepted: 11/21/2019] [Indexed: 12/13/2022]
Abstract
Hyperpolarization is an emerging method in magnetic resonance imaging that allows nuclear spin polarization of gases or liquids to be temporarily enhanced by up to five or six orders of magnitude at clinically relevant field strengths and administered at high concentration to a subject at the time of measurement. This transient gain in signal has enabled the non-invasive detection and imaging of gas ventilation and diffusion in the lungs, perfusion in blood vessels and tissues, and metabolic conversion in cells, animals, and patients. The rapid development of this method is based on advances in polarizer technology, the availability of suitable probe isotopes and molecules, improved MRI hardware and pulse sequence development. Acquisition strategies for hyperpolarized nuclei are not yet standardized and are set up individually at most sites depending on the specific requirements of the probe, the object of interest, and the MRI hardware. This review provides a detailed introduction to spatially resolved detection of hyperpolarized nuclei and summarizes novel and previously established acquisition strategies for different key areas of application.
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Affiliation(s)
- Geoffrey J Topping
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Christian Hundshammer
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Luca Nagel
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Martin Grashei
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Maximilian Aigner
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Jason G Skinner
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | | | - Franz Schilling
- Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.
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Dorsch S, Mann P, Elter A, Runz A, Spindeldreier CK, Klüter S, Karger CP. Measurement of isocenter alignment accuracy and image distortion of an 0.35 T MR-Linac system. ACTA ACUST UNITED AC 2019; 64:205011. [DOI: 10.1088/1361-6560/ab4540] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Wilson M, Andronesi O, Barker PB, Bartha R, Bizzi A, Bolan PJ, Brindle KM, Choi IY, Cudalbu C, Dydak U, Emir UE, Gonzalez RG, Gruber S, Gruetter R, Gupta RK, Heerschap A, Henning A, Hetherington HP, Huppi PS, Hurd RE, Kantarci K, Kauppinen RA, Klomp DWJ, Kreis R, Kruiskamp MJ, Leach MO, Lin AP, Luijten PR, Marjańska M, Maudsley AA, Meyerhoff DJ, Mountford CE, Mullins PG, Murdoch JB, Nelson SJ, Noeske R, Öz G, Pan JW, Peet AC, Poptani H, Posse S, Ratai EM, Salibi N, Scheenen TWJ, Smith ICP, Soher BJ, Tkáč I, Vigneron DB, Howe FA. Methodological consensus on clinical proton MRS of the brain: Review and recommendations. Magn Reson Med 2019; 82:527-550. [PMID: 30919510 PMCID: PMC7179569 DOI: 10.1002/mrm.27742] [Citation(s) in RCA: 233] [Impact Index Per Article: 46.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 02/01/2019] [Accepted: 02/25/2019] [Indexed: 12/14/2022]
Abstract
Proton MRS (1 H MRS) provides noninvasive, quantitative metabolite profiles of tissue and has been shown to aid the clinical management of several brain diseases. Although most modern clinical MR scanners support MRS capabilities, routine use is largely restricted to specialized centers with good access to MR research support. Widespread adoption has been slow for several reasons, and technical challenges toward obtaining reliable good-quality results have been identified as a contributing factor. Considerable progress has been made by the research community to address many of these challenges, and in this paper a consensus is presented on deficiencies in widely available MRS methodology and validated improvements that are currently in routine use at several clinical research institutions. In particular, the localization error for the PRESS localization sequence was found to be unacceptably high at 3 T, and use of the semi-adiabatic localization by adiabatic selective refocusing sequence is a recommended solution. Incorporation of simulated metabolite basis sets into analysis routines is recommended for reliably capturing the full spectral detail available from short TE acquisitions. In addition, the importance of achieving a highly homogenous static magnetic field (B0 ) in the acquisition region is emphasized, and the limitations of current methods and hardware are discussed. Most recommendations require only software improvements, greatly enhancing the capabilities of clinical MRS on existing hardware. Implementation of these recommendations should strengthen current clinical applications and advance progress toward developing and validating new MRS biomarkers for clinical use.
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Affiliation(s)
- Martin Wilson
- Centre for Human Brain Health and School of Psychology, University of Birmingham, Birmingham, England
| | - Ovidiu Andronesi
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Peter B Barker
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Robert Bartha
- Robarts Research Institute, University of Western Ontario, London, Canada
| | - Alberto Bizzi
- U.O. Neuroradiologia, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milano, Italy
| | - Patrick J Bolan
- Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Kevin M Brindle
- Department of Biochemistry, University of Cambridge, Cambridge, England
| | - In-Young Choi
- Department of Neurology, Hoglund Brain Imaging Center, University of Kansas Medical Center, Kansas City, Kansas
| | - Cristina Cudalbu
- Center for Biomedical Imaging, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | - Ulrike Dydak
- School of Health Sciences, Purdue University, West Lafayette, Indiana
| | - Uzay E Emir
- School of Health Sciences, Purdue University, West Lafayette, Indiana
| | - Ramon G Gonzalez
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Stephan Gruber
- High Field MR Center, Department of Biomedical imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Rolf Gruetter
- Laboratory for Functional and Metabolic Imaging, Center for Biomedical Imaging, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | - Rakesh K Gupta
- Fortis Memorial Research Institute, Gurugram, Haryana, India
| | - Arend Heerschap
- Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Anke Henning
- Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
| | | | - Petra S Huppi
- Department of Pediatrics, University of Geneva, Geneva, Switzerland
| | - Ralph E Hurd
- Stanford Radiological Sciences Lab, Stanford, California
| | - Kejal Kantarci
- Department of Radiology, Mayo Clinic, Rochester, Minnesota
| | - Risto A Kauppinen
- School of Psychological Science, University of Bristol, Bristol, England
| | | | - Roland Kreis
- Departments of Radiology and Biomedical Research, University of Bern, Bern, Switzerland
| | | | - Martin O Leach
- CRUK Cancer Imaging Centre, Institute of Cancer Research and Royal Marsden Hospital, London, England
| | - Alexander P Lin
- Center for Clinical Spectroscopy, Brigham and Women's Hospital, Harvard University Medical School, Boston, Massachusetts
| | | | - Małgorzata Marjańska
- Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | | | - Dieter J Meyerhoff
- DVA Medical Center and Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California
| | | | - Paul G Mullins
- Bangor Imaging Unit, School of Psychology, Bangor University, Bangor, Wales
| | | | - Sarah J Nelson
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California
| | | | - Gülin Öz
- Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Julie W Pan
- Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Andrew C Peet
- Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, England
| | - Harish Poptani
- Centre for Preclinical Imaging, Institute of Translational Medicine, University of Liverpool, Liverpool, England
| | - Stefan Posse
- Department of Neurology, University of New Mexico, Albuquerque, New Mexico
| | - Eva-Maria Ratai
- Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Nouha Salibi
- MR R&D, Siemens Healthineers, Malvern, Pennsylvania
| | - Tom W J Scheenen
- Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, the Netherlands
| | | | - Brian J Soher
- Department of Radiology, Duke University Medical Center, Durham, North Carolina
| | - Ivan Tkáč
- Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Daniel B Vigneron
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California
| | - Franklyn A Howe
- Molecular and Clinical Sciences, St George's University of London, London, England
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Allen SP, Feng X, Fielden SW, Meyer CH. Correcting image blur in spiral, retraced in/out (RIO) acquisitions using a maximized energy objective. Magn Reson Med 2018; 81:1806-1817. [PMID: 30421451 DOI: 10.1002/mrm.27541] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 08/27/2018] [Accepted: 08/28/2018] [Indexed: 12/22/2022]
Abstract
PURPOSE Images acquired with spiral k-space trajectories can suffer from off-resonance image blur. Previous work showed that averaging 2 images acquired with a retraced, in/out (RIO) trajectory self-corrects image blur so long as off-resonant spins accrue less than 1 half-cycle of relative phase over the readout. Practical scenarios frequently exceed this threshold. Here, we derive and characterize a more-robust off-resonance image blur correction method for RIO acquisitions. METHODS Phantom and human volunteer data were acquired using a RIO trajectory with readout durations ranging from 4 to 60 ms. The resulting images were deblurred using 3 candidate methods: conventional linear correction of the component images; semiautomatic deblurring of the component images using an established minimized phase objective function; and semiautomatic deblurring of the average of the component images using a maximized energy objective function, derived below. Deblurring errors were estimated relative to images acquired with 4 ms readouts. RESULTS All 3 methods converged to similar solutions in cases where less than 2 and 4 cycles of phase accrued over the readout in in vivo and phantom images, respectively (<13 ms readout at 3T). Above this threshold, the linear and minimized phase methods introduced several errors. The maximized energy function provided accurate deblurring so long as less than 6 and 10 cycles of phase accrued over the readout in in vivo and phantom images, respectively (<34 ms readout at 3T). CONCLUSION The maximized energy objective function can accurately deblur RIO acquisitions over a wide spectrum of off resonance frequencies.
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Affiliation(s)
- Steven P Allen
- Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia
| | - Xue Feng
- Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia
| | - Samuel W Fielden
- Department of Imaging Science and Innovation, Geisinger, Danville, Pennsylvania
| | - Craig H Meyer
- Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia.,Department of Radiology & Medical Imaging, University of Virginia, Charlottesville, Virginia
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Barry RL, Vannesjo SJ, By S, Gore JC, Smith SA. Spinal cord MRI at 7T. Neuroimage 2018; 168:437-451. [PMID: 28684332 PMCID: PMC5894871 DOI: 10.1016/j.neuroimage.2017.07.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Revised: 06/30/2017] [Accepted: 07/02/2017] [Indexed: 11/25/2022] Open
Abstract
Magnetic resonance imaging (MRI) of the human spinal cord at 7T has been demonstrated by a handful of research sites worldwide, and the spinal cord remains one of the areas in which higher fields and resolution could have high impact. The small diameter of the cord (∼1 cm) necessitates high spatial resolution to minimize partial volume effects between gray and white matter, and so MRI of the cord can greatly benefit from increased signal-to-noise ratio and contrasts at ultra-high field (UHF). Herein we review the current state of UHF spinal cord imaging. Technical challenges to successful UHF spinal cord MRI include radiofrequency (B1) nonuniformities and a general lack of optimized radiofrequency coils, amplified physiological noise, and an absence of methods for robust B0 shimming along the cord to mitigate image distortions and signal losses. Numerous solutions to address these challenges have been and are continuing to be explored, and include novel approaches for signal excitation and acquisition, dynamic shimming and specialized shim coils, and acquisitions with increased coverage or optimal slice angulations.
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Affiliation(s)
- Robert L Barry
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA.
| | - S Johanna Vannesjo
- Oxford Centre for Functional MRI of the Brain (FMRIB), Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Samantha By
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | - John C Gore
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Seth A Smith
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
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Shi Y, Vannesjo SJ, Miller KL, Clare S. Template-based field map prediction for rapid whole brain B 0 shimming. Magn Reson Med 2017; 80:171-180. [PMID: 29193340 PMCID: PMC5900895 DOI: 10.1002/mrm.27020] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 10/29/2017] [Accepted: 10/30/2017] [Indexed: 11/21/2022]
Abstract
Purpose In typical MRI protocols, time is spent acquiring a field map to calculate the shim settings for best image quality. We propose a fast template‐based field map prediction method that yields near‐optimal shims without measuring the field. Methods The template‐based prediction method uses prior knowledge of the B0 distribution in the human brain, based on a large database of field maps acquired from different subjects, together with subject‐specific structural information from a quick localizer scan. The shimming performance of using the template‐based prediction is evaluated in comparison to a range of potential fast shimming methods. Results Static B0 shimming based on predicted field maps performed almost as well as shimming based on individually measured field maps. In experimental evaluations at 7 T, the proposed approach yielded a residual field standard deviation in the brain of on average 59 Hz, compared with 50 Hz using measured field maps and 176 Hz using no subject‐specific shim. Conclusions This work demonstrates that shimming based on predicted field maps is feasible. The field map prediction accuracy could potentially be further improved by generating the template from a subset of subjects, based on parameters such as head rotation and body mass index. Magn Reson Med 80:171–180, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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Affiliation(s)
- Yuhang Shi
- Wellcome Centre for Integrative Neuroimaging, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - S Johanna Vannesjo
- Wellcome Centre for Integrative Neuroimaging, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Karla L Miller
- Wellcome Centre for Integrative Neuroimaging, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
| | - Stuart Clare
- Wellcome Centre for Integrative Neuroimaging, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
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Nassirpour S, Chang P, Fillmer A, Henning A. A comparison of optimization algorithms for localized in vivo B 0 shimming. Magn Reson Med 2017; 79:1145-1156. [PMID: 28543722 DOI: 10.1002/mrm.26758] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Revised: 04/05/2017] [Accepted: 04/29/2017] [Indexed: 01/06/2023]
Abstract
PURPOSE To compare several different optimization algorithms currently used for localized in vivo B0 shimming, and to introduce a novel, fast, and robust constrained regularized algorithm (ConsTru) for this purpose. METHODS Ten different optimization algorithms (including samples from both generic and dedicated least-squares solvers, and a novel constrained regularized inversion method) were implemented and compared for shimming in five different shimming volumes on 66 in vivo data sets from both 7 T and 9.4 T. The best algorithm was chosen to perform single-voxel spectroscopy at 9.4 T in the frontal cortex of the brain on 10 volunteers. RESULTS The results of the performance tests proved that the shimming algorithm is prone to unstable solutions if it depends on the value of a starting point, and is not regularized to handle ill-conditioned problems. The ConsTru algorithm proved to be the most robust, fast, and efficient algorithm among all of the chosen algorithms. It enabled acquisition of spectra of reproducible high quality in the frontal cortex at 9.4 T. CONCLUSIONS For localized in vivo B0 shimming, the use of a dedicated linear least-squares solver instead of a generic nonlinear one is highly recommended. Among all of the linear solvers, the constrained regularized method (ConsTru) was found to be both fast and most robust. Magn Reson Med 79:1145-1156, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Sahar Nassirpour
- Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,IMPRS for Cognitive and Systems Neuroscience, Eberhard-Karls University of Tuebingen, Germany
| | - Paul Chang
- Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,IMPRS for Cognitive and Systems Neuroscience, Eberhard-Karls University of Tuebingen, Germany
| | | | - Anke Henning
- Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,Institute for Biomedical Engineering, UZH and ETH Zürich, Zürich, Switzerland
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Chang P, Nassirpour S, Henning A. Modeling real shim fields for very high degree (and order) B 0 shimming of the human brain at 9.4 T. Magn Reson Med 2017; 79:529-540. [PMID: 28321902 DOI: 10.1002/mrm.26658] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 02/06/2017] [Accepted: 02/06/2017] [Indexed: 01/07/2023]
Abstract
PURPOSE To describe the process of calibrating a B0 shim system using high-degree (or high order) spherical harmonic models of the measured shim fields, to provide a method that considers amplitude dependency of these models, and to show the advantage of very high-degree B0 shimming for whole-brain and single-slice applications at 9.4 Tesla (T). METHODS An insert shim with up to fourth and partial fifth/sixth degree (order) spherical harmonics was used with a Siemens 9.4T scanner. Each shim field was measured and modeled as input for the shimming algorithm. Optimal shim currents can therefore be calculated in a single iteration. A range of shim currents was used in the modeling to account for possible amplitude nonlinearities. The modeled shim fields were used to compare different degrees of whole-brain B0 shimming on healthy subjects. RESULTS The ideal shim fields did not correctly shim the subject brains. However, using the modeled shim fields improved the B0 homogeneity from 55.1 (second degree) to 44.68 Hz (partial fifth/sixth degree) on the whole brains of 9 healthy volunteers, with a total applied current of 0.77 and 6.8 A, respectively. CONCLUSIONS The necessity of calibrating the shim system was shown. Better B0 homogeneity drastically reduces signal dropout and distortions for echo-planar imaging, and significantly improves the linewidths of MR spectroscopy imaging. Magn Reson Med 79:529-540, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Paul Chang
- Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,IMPRS for Cognitive and Systems Neuroscience, Eberhard-Karls University of Tuebingen, Germany
| | - Sahar Nassirpour
- Max Planck Institute for Biological Cybernetics, Tuebingen, Germany.,IMPRS for Cognitive and Systems Neuroscience, Eberhard-Karls University of Tuebingen, Germany
| | - Anke Henning
- Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
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12
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Niranjan A, Christie IN, Solomon SG, Wells JA, Lythgoe MF. fMRI mapping of the visual system in the mouse brain with interleaved snapshot GE-EPI. Neuroimage 2016; 139:337-345. [PMID: 27296012 PMCID: PMC4988789 DOI: 10.1016/j.neuroimage.2016.06.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 06/01/2016] [Accepted: 06/09/2016] [Indexed: 12/01/2022] Open
Abstract
The use of functional magnetic resonance imaging (fMRI) in mice is increasingly prevalent, providing a means to non-invasively characterise functional abnormalities associated with genetic models of human diseases. The predominant stimulus used in task-based fMRI in the mouse is electrical stimulation of the paw. Task-based fMRI in mice using visual stimuli remains underexplored, despite visual stimuli being common in human fMRI studies. In this study, we map the mouse brain visual system with BOLD measurements at 9.4T using flashing light stimuli with medetomidine anaesthesia. BOLD responses were observed in the lateral geniculate nucleus, the superior colliculus and the primary visual area of the cortex, and were modulated by the flashing frequency, diffuse vs focussed light and stimulus context. Negative BOLD responses were measured in the visual cortex at 10Hz flashing frequency; but turned positive below 5Hz. In addition, the use of interleaved snapshot GE-EPI improved fMRI image quality without diminishing the temporal contrast-noise-ratio. Taken together, this work demonstrates a novel methodological protocol in which the mouse brain visual system can be non-invasively investigated using BOLD fMRI.
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Affiliation(s)
- Arun Niranjan
- UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK
| | - Isabel N Christie
- UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK; Centre for Cardiovascular and Metabolic Neuroscience, Department of Neuroscience, Physiology & Pharmacology, University College London, London, UK
| | - Samuel G Solomon
- Department of Experimental Psychology, University College London, London, UK
| | - Jack A Wells
- UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK
| | - Mark F Lythgoe
- UCL Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, UK
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13
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Mitrea BG, Krafft AJ, Song R, Loeffler RB, Hillenbrand CM. Paired self-compensated spin-lock preparation for improved T1ρ quantification. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 268:49-57. [PMID: 27161095 DOI: 10.1016/j.jmr.2016.04.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Revised: 04/28/2016] [Accepted: 04/29/2016] [Indexed: 06/05/2023]
Abstract
PURPOSE Spin-lock (SL) imaging allows quantification of the spin-lattice relaxation time in the rotating frame (T1ρ). B0 and B1 inhomogeneities impact T1ρ quantification because the preparatory block in SL imaging is sensitive to the field heterogeneities. Here, a modified preparatory block (PSC-SL) is proposed that attempts to alleviate SL sensitivity to field inhomogeneities in scenarios where existing approaches fail, i.e. high SL frequencies. METHODS Computer simulations, phantom and in vivo experiments were used to determine the effect of field inhomogeneities on T1ρ quantification. Existing SL preparations were compared with PSC-SL in different conditions to assess the advantages and disadvantages of each method. RESULTS Phantom experiments and computer modeling demonstrate that PSC-SL provides superior T1ρ quantification at high SL frequencies in situations where the existing SL preparation methods fail. This result has been confirmed in pre-clinical neuro and body imaging at 7T. CONCLUSION PSC-SL complements existing methods by increasing the accuracy of T1ρ quantification at high spin-lock frequencies when large field inhomogeneities are present. A-priory information about the experimental conditions such, as field distribution and spinlock frequency are useful for selecting an appropriate spin-lock preparation for specific applications.
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Affiliation(s)
- Bogdan G Mitrea
- Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Axel J Krafft
- Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Ruitian Song
- Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Ralf B Loeffler
- Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Claudia M Hillenbrand
- Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, TN, USA.
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14
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Song K, Bao Q, Chen F, Huang C, Feng J, Liu C. Gradient shimming based on regularized estimation for B(0)-field and shim functions. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 268:1-9. [PMID: 27131476 DOI: 10.1016/j.jmr.2016.04.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Revised: 04/13/2016] [Accepted: 04/15/2016] [Indexed: 06/05/2023]
Abstract
Mapping B0-field and shim functions spatially is a crucial step in the gradient shimming. The conventional estimation method used in the phase difference imaging technique takes no account for noise and T2(∗) effects, and is prone to create noisy and distorted field maps. This paper describes a new gradient shimming based on the regularized estimation for B0-field and shim functions. Based on a statistical model, the B0-field and shim function maps are estimated by a Penalized Maximum Likelihood method that minimizes two regularized least-squares cost functions, respectively. The first cost function of B0-field exploits the two facts that the noise in the phase difference measurements is Gaussian and the B0-field maps tend to be smooth. And the other one adds an additional fact that each shim function corresponds to a given spherical harmonic of the magnetic field. Significant improvements in the quality of field mapping and in the final shimming results are demonstrated through computer simulations as well as experiments, especially when the magnetic field homogeneity is poor.
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Affiliation(s)
- Kan Song
- State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Center for Magnetic Resonance, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Qingjia Bao
- State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Center for Magnetic Resonance, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China.
| | - Fang Chen
- State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Center for Magnetic Resonance, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
| | - Chongyang Huang
- State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Center for Magnetic Resonance, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
| | - Jiwen Feng
- State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Center for Magnetic Resonance, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
| | - Chaoyang Liu
- State Key Laboratory of Magnetic Resonance and Atomic Molecular Physics, Wuhan Center for Magnetic Resonance, Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China.
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15
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Ratai EM, Gilberto González R. Clinical magnetic resonance spectroscopy of the central nervous system. HANDBOOK OF CLINICAL NEUROLOGY 2016; 135:93-116. [PMID: 27432661 DOI: 10.1016/b978-0-444-53485-9.00005-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Proton magnetic resonance spectroscopy (1H MRS) is a noninvasive imaging technique that can easily be added to the conventional magnetic resonance (MR) imaging sequences. Using MRS one can directly compare spectra from pathologic or abnormal tissue and normal tissue. Metabolic changes arising from pathology that can be visualized by MRS may not be apparent from anatomy that can be visualized by conventional MR imaging. In addition, metabolic changes may precede anatomic changes. Thus, MRS is used for diagnostics, to observe disease progression, monitor therapeutic treatments, and to understand the pathogenesis of diseases. MRS may have an important impact on patient management. The purpose of this chapter is to provide practical guidance in the clinical application of MRS of the brain. This chapter provides an overview of MRS-detectable metabolites and their significance. In addition some specific current clinical applications of MRS will be discussed, including brain tumors, inborn errors of metabolism, leukodystrophies, ischemia, epilepsy, and neurodegenerative diseases. The chapter concludes with technical considerations and challenges of clinical MRS.
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Affiliation(s)
- Eva-Maria Ratai
- Division of Neuroradiology, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, and Athinoula A. Martinos Center for Biomedical Imaging, Boston, MA, USA.
| | - R Gilberto González
- Division of Neuroradiology, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, and Athinoula A. Martinos Center for Biomedical Imaging, Boston, MA, USA
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16
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Liu G, Qu X, Cai S, Zhang Z, Chen Z, Cai C, Chen Z. Fast 3D gradient shimming by only 2×2 pixels in XY plane for NMR-solution samples. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 248:13-18. [PMID: 25290504 DOI: 10.1016/j.jmr.2014.09.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Revised: 09/06/2014] [Accepted: 09/08/2014] [Indexed: 06/03/2023]
Abstract
Shimming is an essential process for most NMR experiments, and time saving in this process is desired. Here we propose a fast 3D gradient shimming with a low resolution of only 2×2 pixels in the XY plane, and the number of pixels in the Z direction remains unchanged. The proposed pulse sequences employ the selective excitation and the convection compensation. Consequently, the fast 3D gradient shimming adapts to a wide range of samples on regular NMR spectrometers.
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Affiliation(s)
- Guangcao Liu
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, Fujian 361005, China
| | - Xiaobo Qu
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, Fujian 361005, China
| | - Shuhui Cai
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, Fujian 361005, China
| | - Zhiyong Zhang
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, Fujian 361005, China
| | - Zhiwei Chen
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, Fujian 361005, China
| | - Congbo Cai
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, Fujian 361005, China
| | - Zhong Chen
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen, Fujian 361005, China.
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17
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Fillmer A, Kirchner T, Cameron D, Henning A. Constrained image-based B0 shimming accounting for "local minimum traps" in the optimization and field inhomogeneities outside the region of interest. Magn Reson Med 2014; 73:1370-80. [PMID: 24715495 DOI: 10.1002/mrm.25248] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 03/17/2014] [Accepted: 03/19/2014] [Indexed: 01/09/2023]
Abstract
PURPOSE To improve B0 shimming for applications in high- and ultrahigh-field magnetic resonance imaging and magnetic resonance spectroscopy. METHODS An existing image-based constrained B0 shimming algorithm was enhanced using two techniques: (1) A region of less interest was introduced to control B0 field inhomogeneities in the vicinity of the region of interest; (2) multiple sets of starting values were used for the fitting routine, to avoid "getting trapped" in a local minimum of the optimization function. The influence of constraints during the fitting procedure, due to hardware limitations, on the B0 shim result was investigated. The performance of this algorithm was compared to other B0 shim algorithms for typical shim problems in head and body applications at 3T and 7T. RESULTS Utilization of a weighted region of less interest lead to a significant gain in B0 homogeneity adjacent to the region of interest. The loss of B0 quality due to the enlarged total shim volume within the region of interest remained minimal, allowing for improved artifact reduction in magnetic resonance spectroscopic imaging. Multiple sets of starting values and consideration of shim field constraints led to an additional gain in B0 shim quality. CONCLUSION The proposed algorithm allows for more flexible control of B0 inhomogeneities and, hence, enables gains in image and spectral quality for MR applications. RO1AR050597
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Affiliation(s)
- Ariane Fillmer
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
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18
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Cheng JS, Gao PP, Zhou IY, Chan RW, Chan Q, Mak HK, Khong PL, Wu EX. Resting-state fMRI using passband balanced steady-state free precession. PLoS One 2014; 9:e91075. [PMID: 24622278 PMCID: PMC3951283 DOI: 10.1371/journal.pone.0091075] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Accepted: 02/09/2014] [Indexed: 11/28/2022] Open
Abstract
OBJECTIVE Resting-state functional MRI (rsfMRI) has been increasingly used for understanding brain functional architecture. To date, most rsfMRI studies have exploited blood oxygenation level-dependent (BOLD) contrast using gradient-echo (GE) echo planar imaging (EPI), which can suffer from image distortion and signal dropout due to magnetic susceptibility and inherent long echo time. In this study, the feasibility of passband balanced steady-state free precession (bSSFP) imaging for distortion-free and high-resolution rsfMRI was investigated. METHODS rsfMRI was performed in humans at 3 T and in rats at 7 T using bSSFP with short repetition time (TR = 4/2.5 ms respectively) in comparison with conventional GE-EPI. Resting-state networks (RSNs) were detected using independent component analysis. RESULTS AND SIGNIFICANCE RSNs derived from bSSFP images were shown to be spatially and spectrally comparable to those derived from GE-EPI images with considerable intra- and inter-subject reproducibility. High-resolution bSSFP images corresponded well to the anatomical images, with RSNs exquisitely co-localized to the gray matter. Furthermore, RSNs at areas of severe susceptibility such as human anterior prefrontal cortex and rat piriform cortex were proved accessible. These findings demonstrated for the first time that passband bSSFP approach can be a promising alternative to GE-EPI for rsfMRI. It offers distortion-free and high-resolution RSNs and is potentially suited for high field studies.
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Affiliation(s)
- Joe S. Cheng
- Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
| | - Patrick P. Gao
- Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
| | - Iris Y. Zhou
- Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
| | - Russell W. Chan
- Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
| | | | - Henry K. Mak
- Diagnostic Radiology, The University of Hong Kong, Hong Kong SAR, China
| | - Pek L. Khong
- Diagnostic Radiology, The University of Hong Kong, Hong Kong SAR, China
| | - Ed X. Wu
- Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
- Department of Anatomy, The University of Hong Kong, Hong Kong SAR, China
- Department of Medicine, The University of Hong Kong, Hong Kong SAR, China
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19
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Abstract
Magnetic resonance spectroscopy (MRS) is indicated in the imaging protocol of the patient with epilepsy to screen for metabolic derangements such as inborn errors of metabolism and to characterize masses that may be equivocal on conventional magnetic resonance imaging for dysplasia versus neoplasia. Single-voxel MRS with echo time of 35 milliseconds may be used for this purpose as a quick screening tool in the epilepsy imaging protocol. MRS is useful in the evaluation of both focal and generalized epilepsy.
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20
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Dula AN, Smith SA, Gore JC. Application of chemical exchange saturation transfer (CEST) MRI for endogenous contrast at 7 Tesla. J Neuroimaging 2013; 23:526-32. [PMID: 23402307 PMCID: PMC3659199 DOI: 10.1111/j.1552-6569.2012.00751.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Revised: 07/05/2012] [Accepted: 07/23/2012] [Indexed: 01/31/2023] Open
Abstract
Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) indirectly images exchangeable solute protons resonating at frequencies different than bulk water. These solute protons are selectively saturated using low bandwidth RF irradiation and saturation is transferred to bulk water protons via chemical exchange, resulting in an attenuation of the measured water proton signal. CEST MRI is an advanced MRI technique with wide application potential due to the ability to examine complex molecular contributions. CEST MRI at high field (7 Tesla [7 T]) will improve the overall results due to increase in signal, T1 relaxation time, and chemical shift dispersion. Increased field strength translates to enhanced quantification of the metabolite of interest, allowing more fundamental studies on underlying pathophysiology. CEST contrast is affected by several tissue properties, such as the concentrations of exchange partners and their rate of proton exchange, whose effects have been examined and explored in this review. We have highlighted the background of CEST MRI, typical implementation strategy, and complications at 7 T.
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Affiliation(s)
- Adrienne N. Dula
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN 37232, U.S.A
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232, U.S.A
| | - Seth A. Smith
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN 37232, U.S.A
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232, U.S.A
| | - John C. Gore
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN 37232, U.S.A
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232, U.S.A
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21
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Finsterbusch J, Sprenger C, Büchel C. Combined T2*-weighted measurements of the human brain and cervical spinal cord with a dynamic shim update. Neuroimage 2013; 79:153-61. [PMID: 23603283 DOI: 10.1016/j.neuroimage.2013.04.021] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2012] [Revised: 02/21/2013] [Accepted: 04/04/2013] [Indexed: 10/26/2022] Open
Abstract
Important functions of the central nervous system such as sensory processing and motor execution, involve the spinal cord. Recent advances in human functional MRI have allowed to investigate spinal cord neuronal processes using the blood-oxygenation-level-dependent (BOLD) contrast. However, to assess the functional connectivity between the brain and the spinal cord, functional MRI measurements covering both regions in the same experiment are required. Unfortunately, the ideal MRI setup differs considerably for the brain and the spinal cord with respect to resolution, field-of-view, relevant receive coils, and, in particular, shim adjustments required to minimize distortion artifacts. Here, these issues are addressed for combined T2*-weighted MRI measurements of the human brain and the cervical spinal cord by using adapted parameter settings (field-of-view, in-plane resolution, slice thickness, and receiver bandwidth) for each region, a dynamic receive coil element selection where for each slice only the elements with significant signal contributions are considered, and, most importantly, the implementation of a dynamic update of the frequency and the linear shims in order to provide shim settings individually adapted to the brain and spinal cord subvolume. The feasibility of this setup for combined measurements is demonstrated in healthy volunteers at 3T. Although geometric distortions are slightly more pronounced and the temporal signal-to-noise ratio is lower as compared to measurements focusing to the brain or spinal cord only, the overall image quality can be expected to be sufficient for combined functional MRI experiments. Thus, the presented approach could help to unravel the functional coupling between the brain and 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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22
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Kachramanoglou C, De Vita E, Thomas DL, Wheeler-Kingshott CAM, Balteau E, Carlstedt T, Choi D, Thompson AJ, Ciccarelli O. Metabolic changes in the spinal cord after brachial plexus root re-implantation. Neurorehabil Neural Repair 2012; 27:118-24. [PMID: 22961264 PMCID: PMC4107801 DOI: 10.1177/1545968312457825] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Objective. To investigate metabolic changes within the spinal cord using
proton magnetic resonance spectroscopy (1H-MRS) and determine their
relationship with clinical function in patients with complete brachial plexus avulsion who
underwent reimplantation of the ventral roots. Methods. Single-voxel
1H-MRS of the cord between C1 and C3 was performed in 10 patients with normal
spinal cord on MRI, who underwent reimplantation of C5 to T1 ventral roots on average 5.5
years earlier, and 19 healthy controls. The ratios of the concentrations of the following
main metabolites, with respect to total creatine levels, were obtained: total
N-acetyl-aspartate, choline-containing compounds, creatine and phosphocreatine (Cr), and
myo-inositol (m-Ins). Patient disability was assessed using upper limb scales. Differences
in metabolite concentration ratios and their correlations with disability were
investigated. Results. Patients showed increased m-Ins/Cr ratio compared
with controls, which was associated with the level of function of the affected arm and
time from injury. Conclusions. The finding of increased m-Ins/Cr in
patients suggests that reactive gliosis, perhaps in response to the degeneration of
avulsed fibers, may occur in the spinal cord above the site of injury and be relevant to
motor dysfunction. However, this pathological process appears to diminish with time. These
insights underline the need to integrate metabolic imaging with structural and functional
magnetic resonance imaging to obtain a complete view of spinal cord plasticity. Last, this
study provides the first steps toward identifying markers to serve as outcome measures for
trials comparing strategies of plexus repair following avulsion injury.
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Zhou IY, Cheung MM, Lau C, Chan KC, Wu EX. Balanced steady-state free precession fMRI with intravascular susceptibility contrast agent. Magn Reson Med 2011; 68:65-73. [PMID: 22127794 DOI: 10.1002/mrm.23202] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Revised: 08/03/2011] [Accepted: 08/11/2011] [Indexed: 11/07/2022]
Abstract
One major challenge in echo planar imaging-based functional MRI (fMRI) is the susceptibility-induced image distortion. In this study, a new cerebral blood volume-weighted fMRI technique using distortion-free balanced steady-state free precession (bSSFP) sequence was proposed and its feasibility was investigated in rat brain at 7 Tesla. After administration of intravascular susceptibility contrast agent (monocrystalline iron oxide nanoparticle [MION] at 15 mg/kg), unilateral visual stimulation was presented using a block-design paradigm. With repetition time/echo time = 3.8/1.9 ms and α = 18°, bSSFP fMRI was performed and compared with the conventional cerebral blood volume-weighted fMRI using post-MION gradient echo and spin echo echo planar imaging. The results showed that post-MION bSSFP fMRI provides comparable sensitivity but with no severe image distortion and signal dropout. Robust negative responses were observed during stimulation and activation patterns were in excellent agreement with known neuroanatomy. Furthermore, the post-MION bSSFP signal was observed to decrease significantly during hypercapnia challenge, indicating its sensitivity to cerebral blood volume changes. These findings demonstrated that post-MION bSSFP fMRI is a promising alternative to conventional cerebral blood volume-weighted fMRI. This technique is particularly suited for fMRI investigation of animal models at high field.
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Affiliation(s)
- Iris Y Zhou
- Laboratory of Biomedical Imaging and Signal Processing, Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
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24
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Abstract
Dynamic slice-wise shimming improves B0 field homogeneity by updating shim coil currents for every slice in a multislice acquisition, producing better field homogeneity over a volume than can be obtained by a single static global shim. The first aim of this work was to evaluate the performance of slice-wise field-map-based second-order dynamic shimming in a human high-field 7 T clinical scanner vis-à-vis image based second order static global shimming. Another goal was to characterize eddy currents induced by second and third order shim switching. A final aim was to compare global and dynamic shimming through shim orders to elucidate the relative benefits of going to higher orders and to dynamic shim updating from a static shimming regime. An external hardware module was used to store and dynamically update slice-optimized shim values during multislice data acquisition. High-bandwidth multislice gradient echo scans with B0 field mapping and low-bandwidth single-shot echo planar scans were performed on phantoms and humans using second-order dynamic and static global shims. For the measurement of second and third order shim induced eddy currents, step response temporal phase changes of individual shims were measured and fit to shim harmonics spatially and to multiexponential decay functions temporally. Finally, an order-wise field-map-based comparison was performed with first, second and third order global static shimming, first and second order dynamic shimming, as well as combined second or third order global and first order dynamic shim. Dynamic shimming considerably improved B0 homogeneity compared to static global shimming both in phantoms and in human subjects, reducing image distortion and signal dropout. The unshielded second and third order shims generated strong B0 and self and cross-term eddy fields, with multiple time constants ranging from milliseconds to seconds. Field homogeneity improved with increasing order of shim, with dynamic shimming performing better than global shimming. Hybrid global and dynamic shimming approach yielded field homogeneity better than global static shims but worse than dynamic shims.
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25
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Cheng JY, Santos JM, Pauly JM. Fast concomitant gradient field and field inhomogeneity correction for spiral cardiac imaging. Magn Reson Med 2011; 66:390-401. [PMID: 21384423 DOI: 10.1002/mrm.22802] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 12/01/2010] [Accepted: 12/10/2010] [Indexed: 11/09/2022]
Abstract
Non-Cartesian imaging provides many advantages in terms of flexibility, functionality, and speed. However, a major drawback to these imaging methods is off-resonance distortion artifacts. These artifacts manifest as blurring in spiral imaging. Common techniques that remove the off-resonance field inhomogeneity distortion effects are not sufficient, because the high order concomitant gradient fields are nontrivial for common imaging conditions, such as imaging 5 cm off isocenter in an 1.5 T scanner. Previous correction algorithms are either slow or do not take into account the known effects of concomitant gradient fields along with the field inhomogeneities. To ease the correction, the distortion effects are modeled as a non-stationary convolution problem. In this work, two fast and accurate postgridding algorithms are presented and analyzed. These methods account for both the concomitant field effects and the field inhomogeneities. One algorithm operates in the frequency domain and the other in the spatial domain. To take advantage of their speed and accuracy, the algorithms are applied to a real-time cardiac study and a high-resolution cardiac study. Both of the presented algorithms provide for a practical solution to the off-resonance problem in spiral imaging.
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Affiliation(s)
- Joseph Y Cheng
- Department of Electrical Engineering, Magnetic Resonance Systems Research Laboratory, Stanford University, Stanford, California 94305-9510, USA.
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Hu P, Stoeck CT, Smink J, Peters DC, Ngo L, Goddu B, Kissinger KV, Goepfert LA, Chan J, Hauser TH, Rofsky NM, Manning WJ, Nezafat R. Noncontrast SSFP pulmonary vein magnetic resonance angiography: impact of off-resonance and flow. J Magn Reson Imaging 2011; 32:1255-61. [PMID: 21031533 DOI: 10.1002/jmri.22356] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
PURPOSE To investigate pulmonary vein (PV) off-resonance and blood flow as causes of signal void artifacts in noncontrast steady-state-free-precession (SSFP) PV magnetic resonance angiography (MRA). MATERIALS AND METHODS PV blood off-resonance was measured on 11 healthy adult subjects and 10 atrial fibrillation (AF) patients. Noncontrast PV MRA was performed using a 3D slab-selective SSFP sequence at 1.5T on seven healthy subjects with signal profile shifts of 0-125 Hz. The time-resolved blood flow velocity of the PVs was measured on five healthy subjects. The impact of flow was studied on six healthy subjects, on whom SSFP PV MRA was acquired twice with the electrocardiogram (ECG) trigger delay corresponding to low and high flow, respectively. RESULTS The PV off-resonances were 97 ± 27 Hz, 65 ± 20 Hz, 74 ± 25 Hz, and 52 ± 17 Hz for right inferior, left inferior, right superior, and left superior PVs, respectively, on healthy subjects, and 74 ± 20 Hz, 38 ± 9 Hz, 51 ± 20 Hz, and 28 ± 11 Hz on AF patients (P<0.01 for all). The off-resonance caused severe signal voids in the PVs. Signal acquired during mid-diastole with high PV flow caused additional signal voids in the left atrium, which was reduced by setting the ECG trigger delay to late-diastole. CONCLUSION PV off-resonance and flow causes signal void artifacts in noncontrast 3D slab-selective SSFP PV MRA.
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Affiliation(s)
- Peng Hu
- Department of Medicine (Cardiology Division), Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA
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27
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Yang S, Kim H, Ghim MO, Lee BU, Kim DH. Local in vivo shimming using adaptive passive shim positioning. Magn Reson Imaging 2011; 29:401-7. [PMID: 21216551 DOI: 10.1016/j.mri.2010.10.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2009] [Revised: 10/15/2010] [Accepted: 10/23/2010] [Indexed: 12/01/2022]
Abstract
A subject-specific local in vivo passive shimming method, focusing on the prefrontal and temporal regions, is proposed. The aim of the investigation is to show that subject variability exists in optimal passive shimming and that the proposed method can be effectively used to overcome these differences. A shimming structure capable of adjusting the position of the passive shims to within a millimeter resolution is built. The optimal shim positions for each individual subject are computed from obtained field map using a convex optimization algorithm. Passive shim experiments at predetermined fixed shim positions vs. individually adjusted shim positions were performed and compared. The results show that intersubject variability exists in the optimal shim positions and that the location-sensitive method proposed can be useful for improving main field homogeneity in vivo.
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Affiliation(s)
- Sejung Yang
- Department of Electronics Engineering, Ewha Womans University, Seoul, 120-750, Korea
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28
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Landman BA, Huang AJ, Gifford A, Vikram DS, Lim IAL, Farrell JAD, Bogovic JA, Hua J, Chen M, Jarso S, Smith SA, Joel S, Mori S, Pekar JJ, Barker PB, Prince JL, van Zijl PCM. Multi-parametric neuroimaging reproducibility: a 3-T resource study. Neuroimage 2010; 54:2854-66. [PMID: 21094686 DOI: 10.1016/j.neuroimage.2010.11.047] [Citation(s) in RCA: 192] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 11/11/2010] [Accepted: 11/12/2010] [Indexed: 11/25/2022] Open
Abstract
Modern MRI image processing methods have yielded quantitative, morphometric, functional, and structural assessments of the human brain. These analyses typically exploit carefully optimized protocols for specific imaging targets. Algorithm investigators have several excellent public data resources to use to test, develop, and optimize their methods. Recently, there has been an increasing focus on combining MRI protocols in multi-parametric studies. Notably, these have included innovative approaches for fusing connectivity inferences with functional and/or anatomical characterizations. Yet, validation of the reproducibility of these interesting and novel methods has been severely hampered by the limited availability of appropriate multi-parametric data. We present an imaging protocol optimized to include state-of-the-art assessment of brain function, structure, micro-architecture, and quantitative parameters within a clinically feasible 60-min protocol on a 3-T MRI scanner. We present scan-rescan reproducibility of these imaging contrasts based on 21 healthy volunteers (11 M/10 F, 22-61 years old). The cortical gray matter, cortical white matter, ventricular cerebrospinal fluid, thalamus, putamen, caudate, cerebellar gray matter, cerebellar white matter, and brainstem were identified with mean volume-wise reproducibility of 3.5%. We tabulate the mean intensity, variability, and reproducibility of each contrast in a region of interest approach, which is essential for prospective study planning and retrospective power analysis considerations. Anatomy was highly consistent on structural acquisition (~1-5% variability), while variation on diffusion and several other quantitative scans was higher (~<10%). Some sequences are particularly variable in specific structures (ASL exhibited variation of 28% in the cerebral white matter) or in thin structures (quantitative T2 varied by up to 73% in the caudate) due, in large part, to variability in automated ROI placement. The richness of the joint distribution of intensities across imaging methods can be best assessed within the context of a particular analysis approach as opposed to a summary table. As such, all imaging data and analysis routines have been made publicly and freely available. This effort provides the neuroimaging community with a resource for optimization of algorithms that exploit the diversity of modern MRI modalities. Additionally, it establishes a baseline for continuing development and optimization of multi-parametric imaging protocols.
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Affiliation(s)
- Bennett A Landman
- Department of Electrical Engineering, Vanderbilt University, Nashville, TN 37235-1679, USA.
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29
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Yeung DK, Fong KY, Chan QC, King AD. Chemical shift imaging in the head and neck at 3T: Initial results. J Magn Reson Imaging 2010; 32:1248-54. [DOI: 10.1002/jmri.22365] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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30
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Chow AM, Zhou IY, Fan SJ, Chan KW, Chan KC, Wu EX. Metabolic changes in visual cortex of neonatal monocular enucleated rat: a proton magnetic resonance spectroscopy study. Int J Dev Neurosci 2010; 29:25-30. [DOI: 10.1016/j.ijdevneu.2010.10.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2010] [Revised: 08/30/2010] [Accepted: 10/01/2010] [Indexed: 01/14/2023] Open
Affiliation(s)
- April M. Chow
- Laboratory of Biomedical Imaging and Signal ProcessingThe University of Hong KongPokfulamHong Kong SARChina
- Department of Electrical and Electronic EngineeringThe University of Hong KongPokfulamHong Kong SARChina
| | - Iris Y. Zhou
- Laboratory of Biomedical Imaging and Signal ProcessingThe University of Hong KongPokfulamHong Kong SARChina
- Department of Electrical and Electronic EngineeringThe University of Hong KongPokfulamHong Kong SARChina
| | - Shu Juan Fan
- Laboratory of Biomedical Imaging and Signal ProcessingThe University of Hong KongPokfulamHong Kong SARChina
- Department of Electrical and Electronic EngineeringThe University of Hong KongPokfulamHong Kong SARChina
| | - Kannie W.Y. Chan
- Laboratory of Biomedical Imaging and Signal ProcessingThe University of Hong KongPokfulamHong Kong SARChina
- Department of Electrical and Electronic EngineeringThe University of Hong KongPokfulamHong Kong SARChina
| | - Kevin C. Chan
- Laboratory of Biomedical Imaging and Signal ProcessingThe University of Hong KongPokfulamHong Kong SARChina
- Department of Electrical and Electronic EngineeringThe University of Hong KongPokfulamHong Kong SARChina
| | - Ed X. Wu
- Laboratory of Biomedical Imaging and Signal ProcessingThe University of Hong KongPokfulamHong Kong SARChina
- Department of Electrical and Electronic EngineeringThe University of Hong KongPokfulamHong Kong SARChina
- Department of AnatomyThe University of Hong KongPokfulamHong Kong SARChina
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31
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Leitman DI, Wolf DH, Loughead J, Valdez JN, Kohler CG, Brensinger C, Elliott MA, Turetsky BI, Gur RE, Gur RC. Ventrolateral prefrontal cortex and the effects of task demand context on facial affect appraisal in schizophrenia. Soc Cogn Affect Neurosci 2010; 6:66-73. [PMID: 20212004 DOI: 10.1093/scan/nsq018] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Schizophrenia patients display impaired performance and brain activity during facial affect recognition. These impairments may reflect stimulus-driven perceptual decrements and evaluative processing abnormalities. We differentiated these two processes by contrasting responses to identical stimuli presented under different contexts. Seventeen healthy controls and 16 schizophrenia patients performed an fMRI facial affect detection task. Subjects identified an affective target presented amongst foils of differing emotions. We hypothesized that targeting affiliative emotions (happiness, sadness) would create a task demand context distinct from that generated when targeting threat emotions (anger, fear). We compared affiliative foil stimuli within a congruent affiliative context with identical stimuli presented in an incongruent threat context. Threat foils were analysed in the same manner. Controls activated right orbitofrontal cortex (OFC)/ventrolateral prefrontal cortex (VLPFC) more to affiliative foils in threat contexts than to identical stimuli within affiliative contexts. Patients displayed reduced OFC/VLPFC activation to all foils, and no activation modulation by context. This lack of context modulation coincided with a 2-fold decrement in foil detection efficiency. Task demands produce contextual effects during facial affective processing in regions activated during affect evaluation. In schizophrenia, reduced modulation of OFC/VLPFC by context coupled with reduced behavioural efficiency suggests impaired ventral prefrontal control mechanisms that optimize affective appraisal.
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Affiliation(s)
- David I Leitman
- Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
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32
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Zhang Y, Li S, Shen J. Automatic high-order shimming using parallel columns mapping (PACMAP). Magn Reson Med 2010; 62:1073-9. [PMID: 19645006 DOI: 10.1002/mrm.22077] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
This work presents a new automatic high-order shimming method that maps the B(0) field using a group of parallel columns. We found that a pair of four columns in two separate slices could determine an optimal correction field comprising the spherical harmonic terms up to the third-order. The technique of multiple stimulated echoes was incorporated into the method, allowing the use of at least eight shots to accomplish field mapping. The shim currents were first determined in the logic frame by assuming that the slices were in axial planes, and then uniquely converted into the physical frame where the slices could be at any oblique angle, by using a spherical harmonics rotation transformation. This method thus works regardless of slice orientation. It was demonstrated on a 3T scanner equipped with a complete set of second-order harmonic shim coils. Both phantom and in vivo experiments showed that this newly introduced high-order shimming method is an effective and efficient way to reduce field inhomogeneity for a region of imaging slices.
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Affiliation(s)
- Yan Zhang
- Spectroscopy Core Facility, National Institute of Mental Health (NIMH), National Institutes of Health, Bethesda, Maryland 20892-1527, USA
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33
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Kubach MR, Bornstedt A, Hombach V, Merkle N, Schär M, Spiess J, Nienhaus GU, Rasche V. Cardiac phase-specific shimming (CPSS) for SSFP MR cine imaging at 3 T. Phys Med Biol 2009; 54:N467-78. [DOI: 10.1088/0031-9155/54/20/n01] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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34
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Kim M, Gillen J, Landman BA, Zhou J, van Zijl PCM. Water saturation shift referencing (WASSR) for chemical exchange saturation transfer (CEST) experiments. Magn Reson Med 2009; 61:1441-50. [PMID: 19358232 DOI: 10.1002/mrm.21873] [Citation(s) in RCA: 509] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Chemical exchange saturation transfer (CEST) is a contrast mechanism that exploits exchange-based magnetization transfer (MT) between solute and water protons. CEST effects compete with direct water saturation and conventional MT processes, and generally can only be quantified through an asymmetry analysis of the water saturation spectrum (Z-spectrum) with respect to the water frequency, a process that is exquisitely sensitive to magnetic field inhomogeneities. Here it is shown that direct water saturation imaging allows measurement of the absolute water frequency in each voxel, allowing proper centering of Z-spectra on a voxel-by-voxel basis independently of spatial B(0) field variations. Optimal acquisition parameters for this "water saturation shift referencing" (WASSR) approach were estimated using Monte Carlo simulations and later confirmed experimentally. The optimal ratio of the WASSR sweep width to the linewidth of the direct saturation curve was found to be 3.3-4.0, requiring a sampling of 16-32 points. The frequency error was smaller than 1 Hz at signal-to-noise ratios of 40 or higher. The WASSR method was applied to study glycogen, where the chemical shift difference between the hydroxyl (OH) protons and bulk water protons at 3T is so small (0.75-1.25 ppm) that the CEST spectrum is inconclusive without proper referencing.
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Affiliation(s)
- Mina Kim
- Russell H. Morgan Department of Radiology and Radiological Sciences, Neurology Section, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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35
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Lee J, Lustig M, Kim DH, Pauly JM. Improved shim method based on the minimization of the maximum off-resonance frequency for balanced steady-state free precession (bSSFP). Magn Reson Med 2009; 61:1500-6. [PMID: 19319895 DOI: 10.1002/mrm.21800] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In this work, a shim method that minimizes the maximum off-resonance frequency (min-max shim) in balanced steady-state free precession (bSSFP) is tested for brain imaging at 3T with constant and linear shim terms. The method demonstrates improvement of spatial coverage and banding artifact reduction over standard least-squares shimming. In addition, a new method (modified min-max shim) is introduced. This method reduces boundary band regions where the artifact is inevitable due to the excessive off-resonance frequency distribution. In comparison to standard least-squares shimming, the min-max based shim method either eliminates or reduces the size of banding artifacts. The method can be used to increase the signal-to-noise ratio (SNR) in bSSFP imaging or to increase the functional contrast in bSSFP functional MRI (fMRI) by allowing a longer usable repetition time (TR).
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Affiliation(s)
- Jongho Lee
- Advanced MRI, Laboratory for Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
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36
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Balteau E, Hutton C, Weiskopf N. Improved shimming for fMRI specifically optimizing the local BOLD sensitivity. Neuroimage 2009; 49:327-36. [PMID: 19682587 PMCID: PMC2775904 DOI: 10.1016/j.neuroimage.2009.08.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2009] [Revised: 06/22/2009] [Accepted: 08/05/2009] [Indexed: 11/29/2022] Open
Abstract
In functional MRI, magnetic field inhomogeneities due to air-tissue susceptibility differences may lead to severe signal dropouts and geometric distortions in echo-planar images. Therefore, the inhomogeneities in the field are routinely minimized by shimming prior to imaging. However in fMRI, the Blood Oxygen Level Dependent (BOLD) effect is the measure of interest, so the BOLD sensitivity (BS) should be optimized rather than the magnetic field homogeneity. The analytical expression for an estimate of the BOLD sensitivity has been recently developed, allowing for the computation of BOLD sensitivity maps from echo-planar images and field maps. This report describes a novel shimming procedure that optimizes the local BOLD sensitivity over a region of interest. The method is applied in vivo and compared to a standard global shimming procedure. A breath-holding experiment was carried out and demonstrated that the BS-based shimming significantly improved the detection of activation in a target region of interest, the medial orbitofrontal cortex.
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Affiliation(s)
- Evelyne Balteau
- Cyclotron Research Centre, Liège University, Liège, Belgium.
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37
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In vivo diffusion tensor imaging of thoracic and cervical rat spinal cord at 7 T. Magn Reson Imaging 2009; 27:1236-41. [PMID: 19520537 DOI: 10.1016/j.mri.2009.05.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2008] [Revised: 02/17/2009] [Accepted: 05/06/2009] [Indexed: 11/20/2022]
Abstract
In vivo diffusion tensor imaging (DTI) of rat cervical and thoracic spinal cord was performed using a three-element phased array coil at 7 T. The magnetic field was shimmed over the spinal cord in real time using an in-house developed automatic algorithm. Echo planar imaging (EPI)-based diffusion-weighted images (DWIs) were acquired with 21 gradient encoding directions. The DWIs were tensor encoded, and diffusion tensor metrics, fractional anisotropy (FA), mean diffusivity (MD), longitudinal diffusivity (lambda(0)) and transverse diffusivity (lambda( perpendicular)) were determined for both white matter (WM) and gray matter (GM). The results on six normal rats indicated no significant differences in the diffusion tensor metrics between thoracic and cervical regions. However, the DTI-derived metrics in cervical spinal cord from our study are somewhat different from the published results in rats. The possible reasons for these differences are suggested.
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38
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Abstract
In this chapter, the basic principles of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) (Sects. 2.2, 2.3, and 2.4), the technical components of the MRI scanner (Sect. 2.5), and the basics of contrast agents and the application thereof (Sect. 2.6) are described. Furthermore, flow phenomena and MR angiography (Sect. 2.7) as well as diffusion and tensor imaging (Sect. 2.7) are elucidated.
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39
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Loughead J, Gur RC, Elliott M, Gur RE. Neural circuitry for accurate identification of facial emotions. Brain Res 2007; 1194:37-44. [PMID: 18191116 DOI: 10.1016/j.brainres.2007.10.105] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2007] [Revised: 10/31/2007] [Accepted: 10/31/2007] [Indexed: 10/22/2022]
Abstract
Converging studies have revealed neural circuits for emotion processing, yet none has related activation to identification accuracy. We report a hybrid (block and event-related) fMRI study in 17 healthy adults, which permitted performance-based analysis. As in earlier studies, blocked analysis of the facial emotion identification task showed activation of amygdala, fusiform, thalamus, inferior and midfrontal regions. However, an event-related analysis of target stimuli demonstrated time locked activation associated with correct identification of happy, sad, angry and fearful faces. Overall, correct detection of angry and fearful faces was associated with greater activation compared to incorrect responses, especially in the amygdala and fusiform gyrus. The opposite was observed for happy and sad faces, where greater thalamic and midfrontal activation portended incorrect responses. Results indicate that the fusiform cortex and amygdala respond differentially in the four target conditions (happy, sad, angry and fearful) along the dimension of threat-relatedness.
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Affiliation(s)
- James Loughead
- Department of Psychiatry, University of Pennsylvania, Philadelphia, PA 19104, USA.
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40
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Hammond KE, Lupo JM, Xu D, Metcalf M, Kelley DAC, Pelletier D, Chang SM, Mukherjee P, Vigneron DB, Nelson SJ. Development of a robust method for generating 7.0 T multichannel phase images of the brain with application to normal volunteers and patients with neurological diseases. Neuroimage 2007; 39:1682-92. [PMID: 18096412 DOI: 10.1016/j.neuroimage.2007.10.037] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Revised: 10/22/2007] [Accepted: 10/30/2007] [Indexed: 02/06/2023] Open
Abstract
The increased susceptibility effects and high signal-to-noise ratio at 7.0 T enable imaging of the brain using the phase of the magnetic resonance signal. This study describes and evaluates a robust method for calculating phase images from gradient-recalled echo (GRE) scans. The GRE scans were acquired at 7.0 T using an eight-channel receive coil at spatial resolutions up to 0.195 x 0.260 x 2.00 mm. The entire 7.0 T protocol took less than 10 min. Data were acquired from forty-seven subjects including clinical patients with multiple sclerosis (MS) or brain tumors. The phase images were post-processed using a fully automated phase unwrapping algorithm that combined the data from the different channels. The technique was used to create the first phase images of MS patients at any field strength and the first phase images of brain tumor patients above 1.5 T. The clinical images showed novel contrast in MS plaques and depicted microhemorrhages and abnormal vasculature in brain tumors with unsurpassed resolution and contrast.
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Affiliation(s)
- Kathryn E Hammond
- University of California San Francisco/Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA 94158-2532, USA.
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41
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Yeo DTB, Chenevert TL, Fessler JA, Kim B. Zero and first-order phase shift correction for field map estimation with dual-echo GRE using bipolar gradients. Magn Reson Imaging 2007; 25:1263-71. [PMID: 17442524 PMCID: PMC2795570 DOI: 10.1016/j.mri.2007.02.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2006] [Revised: 02/09/2007] [Accepted: 02/10/2007] [Indexed: 10/23/2022]
Abstract
A simple phase error correction technique used for field map estimation with a generally available dual-echo gradient-echo (GRE) sequence is presented. Magnetic field inhomogeneity maps estimated using two separate GRE volume acquisitions at different echo times are prone to dynamic motion errors between acquisitions. By using the dual-echo sequence, the data are collected during two back-to-back readout gradients in opposite polarity after a single radio frequency pulse, and interecho motion artifacts and alignment errors in field map estimation can be factored out. Residual phase error from the asymmetric readout pulses is modeled as an affine term in the readout direction. Results from phantom and human data suggest that the first-order phase correction term stays constant over time and, hence, can be applied to different data acquired with the same protocol over time. The zero-order phase correction term may change with time and is estimated empirically for different scans.
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Affiliation(s)
- Desmond T. B. Yeo
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, USA
| | - Thomas L. Chenevert
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Jeffrey A. Fessler
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, USA
| | - Boklye Kim
- Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
- *Corresponding author. Basic Radiological Sciences Division, Department of Radiology, University of Michigan Medical School, 109 Zina Pitcher Place, AC51 BSRB, MI 48109-2200, USA. Tel.: +1-734-763-5692; Fax: +1-734-615-1471. Email address: (Boklye Kim)
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42
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Sica CT, Meyer CH. Concomitant gradient field effects in balanced steady-state free precession. Magn Reson Med 2007; 57:721-30. [PMID: 17390357 DOI: 10.1002/mrm.21183] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Linear magnetic field gradients spatially encode the image information in MRI. Concomitant gradients are undesired magnetic fields that accompany the desired gradients and occur as an unavoidable consequence of Maxwell's equations. These concomitant gradients result in undesired phase accumulation during MRI scans. Balanced steady-state free precession (bSSFP) is a rapid imaging method that is known to suffer from signal dropout from off-resonance phase accrual. In this work it is shown that concomitant gradient phase accrual can induce signal dropout in bSSFP. The spatial variation of the concomitant phase is explored and shown to be a function of gradient strength, slice orientation, phase-encoding (PE) direction, distance from isocenter, and main field strength. The effect on the imaging signal level was simulated and then verified in phantom and in vivo experiments. The nearest signal-loss artifacts occurred in scans that were offset from isocenter along the z direction with a transverse readout. Methods for eliminating these artifacts, such as applying compensatory frequency or shim offsets, are demonstrated. Concomitant gradient artifacts can occur at 1.5T, particularly in high-resolution scans or with additional main field inhomogeneity. These artifacts will occur closer to isocenter at field strengths below 1.5T because concomitant gradients are inversely proportional to the main field strength.
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Affiliation(s)
- Christopher T Sica
- Engineering Physics Program, University of Virginia, Charlottesville, Virginia 22908, USA
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43
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Hetherington HP, Chu WJ, Gonen O, Pan JW. Robust fully automated shimming of the human brain for high-field 1H spectroscopic imaging. Magn Reson Med 2006; 56:26-33. [PMID: 16767750 DOI: 10.1002/mrm.20941] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Although a variety of methods have been proposed to provide automated adjustment of shim homogeneity, these methods typically fail or require large numbers of iterations in vivo when applied to regions with poor homogeneity, such as the temporal lobe. These limitations are largely due to 1) the limited accuracy of single evolution time measurements when full B0 mapping studies are used, and 2) inaccuracies arising from projection-based methods when the projections pass through regions where the inhomogeneity exceeds the order of the fitted parameters. To overcome these limitations we developed a novel B0 mapping method using multiple evolution times with a novel unwrapping scheme in combination with a user-defined ROI selection tool. We used these methods at 4T on 10 control subjects to obtain high-resolution spectroscopic images of glutamate from the bilateral hippocampi.
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Affiliation(s)
- Hoby P Hetherington
- Department of Radiology, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA.
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Abstract
The discrete Fourier transform (FT) is a conventional method for spatial reconstruction of chemical shifting imaging (CSI) data. Due to point spread function (PSF) effects, FT reconstruction leads to intervoxel signal leakage (Gibbs ringing). Spectral localization by imaging (SLIM) reconstruction was previously proposed to overcome this intervoxel signal contamination. However, the existence of magnetic field inhomogeneities creates an additional source of intervoxel signal leakage. It is demonstrated herein that even small field inhomogeneities substantially amplify intervoxel signal leakage in both FT and SLIM reconstruction approaches. A new CSI data acquisition strategy and reconstruction algorithm (natural linewidth (NL) CSI) is presented that eliminates effects of magnetic field inhomogeneity-induced intervoxel signal leakage and intravoxel phase dispersion on acquired data. The approach is based on acquired CSI data, high-resolution images, and magnetic field maps. The data are reconstructed based on the imaged object structure (as in the SLIM approach) and a reconstruction matrix that takes into account the inhomogeneous field distribution inside anatomically homogeneous compartments. Phantom and in vivo results show that the new method allows field inhomogeneity effects from the acquired MR signal to be removed so that the signal decay is determined only by the "natural" R2 relaxation rate constant (hence the term "natural linewidth" CSI).
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Affiliation(s)
- Adil Bashir
- Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri 63110, USA
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Zhao Y, Anderson AW, Gore JC. Computer simulation studies of the effects of dynamic shimming on susceptibility artifacts in EPI at high field. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2005; 173:10-22. [PMID: 15705507 DOI: 10.1016/j.jmr.2004.11.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2004] [Revised: 11/01/2004] [Indexed: 05/24/2023]
Abstract
Dynamic shimming in multi-slice imaging aims to achieve optimal magnetic field homogeneity by updating the shim coil currents for each slice in real time. Dynamic shimming may reduce the signal loss and geometric distortion caused by magnetic susceptibility variations between tissues and is likely to be valuable for fast T2*-sensitive imaging techniques like EPI. A computer simulation of dynamic shimming using real image data has been developed to demonstrate the effectiveness of higher order dynamic shimming for echo planar imaging at high magnetic field, and to investigate the potential benefits of different orders of shim coil. Geometric distortions and signal intensities for different degrees of dynamic shimming were simulated and the results are compared with the images obtained with a conventional shimming technique. These results demonstrate the effectiveness, necessity and difficulty of high order dynamic shimming.
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Affiliation(s)
- Yansong Zhao
- Department of Electrical Engineering, Yale University, New Haven, CT 06520, USA.
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Miyasaka N, Takahashi K, Hetherington HP. Fully automated shim mapping method for spectroscopic imaging of the mouse brain at 9.4 T. Magn Reson Med 2005; 55:198-202. [PMID: 16270332 DOI: 10.1002/mrm.20731] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
For spectroscopic imaging studies of the mouse brain, it is critical to obtain optimal B(0) homogeneity over a large region of interest (ROI). In this paper, a fully automated shimming method for mouse brain at 9.4 T, based on B(0) mapping, is described. B(0) maps were obtained using a multislice gradient echo sequence with multiple phase evolution time delays with a novel unwrapping scheme. The unwrapping method allows phase maps with large bandwidths (+/-1 kHz) but with high resolution (0.3 Hz/ degrees ) to be acquired in a single acquisition, thereby minimizing the number of iterations required. The SD of the B(0) over the ROI (8 x 5 x 1 mm) was less than 10 Hz after shimming. Application of this method to the in vivo mouse brain allowed reproducible, high-quality spectroscopic data to be collected with 1-microl voxels.
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Affiliation(s)
- Naoyuki Miyasaka
- Department of Radiology, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA.
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Pelchat ML, Johnson A, Chan R, Valdez J, Ragland JD. Images of desire: food-craving activation during fMRI. Neuroimage 2004; 23:1486-93. [PMID: 15589112 DOI: 10.1016/j.neuroimage.2004.08.023] [Citation(s) in RCA: 376] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2004] [Revised: 08/12/2004] [Accepted: 08/18/2004] [Indexed: 11/22/2022] Open
Abstract
Food craving (defined as an intense desire to eat a specific food) is of interest because it is extremely common and because it influences obesity or nutritional status. It has also been suggested that food craving may be the evolutionary source for cravings of all kinds including cravings for drugs and alcohol. Yet, little is known about the functional neuroanatomy of food craving. We report here the first functional magnetic resonance imaging (fMRI) study to explicitly examine food craving. A two-part technique was used to produce the food cravings. Threshold was reduced through a diet manipulation (monotonous diet) and cravings were triggered during blood oxygenation level-dependent (BOLD) fMRI sessions by having subjects imagine the sensory properties of favorite foods (a cue-induction technique). Subjects were also asked to imagine the monotonous diet (which they did not crave). Diet condition had an activating effect on both behavioral (reports of craving) and fMRI measures. Craving-related changes in fMRI signal were identified in the hippocampus, insula, and caudate, three areas reported to be involved in drug craving. Thus, this work supports the common substrate hypothesis for food and drug cravings.
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Chen Z, Li SS, Yang J, Letizia D, Shen J. Measurement and automatic correction of high-order B0 inhomogeneity in the rat brain at 11.7 Tesla. Magn Reson Imaging 2004; 22:835-42. [PMID: 15234452 DOI: 10.1016/j.mri.2004.01.062] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2003] [Accepted: 01/30/2004] [Indexed: 11/24/2022]
Abstract
In vivo B(0) inhomogeneity in the rat brain at 11.7 Tesla was measured and decomposed up to the fourth-order spherical harmonic terms using an automatic slice shimming routine derived from the FLATNESS method. In vivo shimming of horizontal slices showed that significant improvement in the T(2)*-weighted echo-planar imaging was achieved after correction of all first-, second- and third-order in-slice shims. For localized proton spectroscopy, reproducible, high quality data were obtained after correcting all first- and second-order shims. The measured high-order in vivo B(0) inhomogeneity in terms of spherical harmonic terms should provide a useful guide for designing shims to meet in vivo requirements.
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Affiliation(s)
- Zhengguang Chen
- Molecular Imaging Branch, NIMH, National Institute of Health, Bethesda, MD 20892, USA
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Klassen LM, Menon RS. Robust automated shimming technique using arbitrary mapping acquisition parameters (RASTAMAP). Magn Reson Med 2004; 51:881-7. [PMID: 15122668 DOI: 10.1002/mrm.20094] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Quantitative MRI techniques as well as methods such as blood oxygen level-dependent (BOLD) imaging and in vivo spectroscopy require stringent optimization of magnetic field homogeneity, particularly when using high main magnetic fields. Automated shimming approaches require a method of measuring the main magnetic field, B(0), followed by adjusting the currents in resistive shim coils to maximize homogeneity. A robust automated shimming technique using arbitrary mapping acquisition parameters (RASTAMAP) using a 3D multiecho gradient echo sequence that measures B(0) with high precision was developed. Inherent compensation and postprocessing methods enable removal of artifacts due to hardware timing errors, gradient propagation delays, gradient amplifier asymmetry, and eddy currents. This allows field maps to be generated for any field of view, bandwidth, resolution, or acquisition orientation without custom tuning of sequence parameters. Field maps of an aqueous phantom show +/- 1 Hz variation with altered acquisition orientations and bandwidths. Subsequent fitting of measured shim coil field maps allows calculation of shim currents to produce optimum field homogeneity.
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Affiliation(s)
- L Martyn Klassen
- Laboratory for Functional Magnetic Resonance Research, Robarts Research Institute, London, Ontario, Canada
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Gunning-Dixon FM, Gur RC, Perkins AC, Schroeder L, Turner T, Turetsky BI, Chan RM, Loughead JW, Alsop DC, Maldjian J, Gur RE. Age-related differences in brain activation during emotional face processing. Neurobiol Aging 2003; 24:285-95. [PMID: 12498962 DOI: 10.1016/s0197-4580(02)00099-4] [Citation(s) in RCA: 209] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Advancing age is associated with significant declines on neurobehavioral tasks that demand substantial mental effort. Functional imaging studies of mental abilities indicate that older adults faced with cognitive challenges tend to activate more regions, particularly frontal, than their younger counterparts, and that this recruitment of additional regions may reflect an attempt to compensate for inefficiency in cortical networks. The neural basis of emotion processing in aging has received little attention, and the goal of the present study was to use functional magnetic resonance imaging (fMRI) to examine the influence of age on facial emotion processing and activation in cortical and limbic regions. Participants (eight old and eight young adults) viewed facial displays of happiness, sadness, anger, fear, disgust, and neutrality in alternating blocks of emotion and age discrimination. We predicted that in response to an emotion discrimination task, older adults would demonstrate increased use of frontal regions relative to younger adults, perhaps combined with diminished use of regions recruited by younger adults, such as temporo-limbic regions. During the emotion discrimination task, young participants activated, visual, frontal and limbic regions, whereas older participants activated parietal, temporal and frontal regions. A direct comparison between emotion and age discrimination revealed that while younger adults activated the amygdala and surrounding temporo-limbic regions, older adults activated left frontal regions. The results of this study suggest that older adults may rely on different cortical networks to perceive emotional facial expressions than do their younger counterparts.
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Affiliation(s)
- Faith M Gunning-Dixon
- Department of Psychiatry and Radiology, Section of Neuropsychiatry, University of Pennsylvania, Philadelphia, PA 19104, USA.
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