1
|
Zhang B, Radder J, Giannakopoulos I, Grant A, Lagore R, Waks M, Tavaf N, Van de Moortele PF, Adriany G, Sadeghi-Tarakameh A, Eryaman Y, Lattanzi R, Uğurbil K. Performance of receive head arrays versus ultimate intrinsic SNR at 7 T and 10.5 T. Magn Reson Med 2024; 92:1219-1231. [PMID: 38649922 DOI: 10.1002/mrm.30108] [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: 12/19/2023] [Revised: 02/26/2024] [Accepted: 03/21/2024] [Indexed: 04/25/2024]
Abstract
PURPOSE We examined magnetic field dependent SNR gains and ability to capture them with multichannel receive arrays for human head imaging in going from 7 T, the most commonly used ultrahigh magnetic field (UHF) platform at the present, to 10.5 T, which represents the emerging new frontier of >10 T in UHFs. METHODS Electromagnetic (EM) models of 31-channel and 63-channel multichannel arrays built for 10.5 T were developed for 10.5 T and 7 T simulations. A 7 T version of the 63-channel array with an identical coil layout was also built. Array performance was evaluated in the EM model using a phantom mimicking the size and electrical properties of the human head and a digital human head model. Experimental data was obtained at 7 T and 10.5 T with the 63-channel array. Ultimate intrinsic SNR (uiSNR) was calculated for the two field strengths using a voxelized cloud of dipoles enclosing the phantom or the digital human head model as a reference to assess the performance of the two arrays and field depended SNR gains. RESULTS uiSNR calculations in both the phantom and the digital human head model demonstrated SNR gains at 10.5 T relative to 7 T of 2.6 centrally, ˜2 at the location corresponding to the edge of the brain, ˜1.4 at the periphery. The EM models demonstrated that, centrally, both arrays captured ˜90% of the uiSNR at 7 T, but only ˜65% at 10.5 T, leading only to ˜2-fold gain in array SNR in going from 7 to 10.5 T. This trend was also observed experimentally with the 63-channel array capturing a larger fraction of the uiSNR at 7 T compared to 10.5 T, although the percentage of uiSNR captured were slightly lower at both field strengths compared to EM simulation results. CONCLUSIONS Major uiSNR gains are predicted for human head imaging in going from 7 T to 10.5 T, ranging from ˜2-fold at locations corresponding to the edge of the brain to 2.6-fold at the center, corresponding to approximately quadratic increase with the magnetic field. Realistic 31- and 63-channel receive arrays, however, approach the central uiSNR at 7 T, but fail to do so at 10.5 T, suggesting that more coils and/or different type of coils will be needed at 10.5 T and higher magnetic fields.
Collapse
Affiliation(s)
- Bei Zhang
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, Texas, USA
| | - Jerahmie Radder
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Ilias Giannakopoulos
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA
| | - Andrea Grant
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Russell Lagore
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Matt Waks
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Nader Tavaf
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | | | - Gregor Adriany
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | | | - Yigitcan Eryaman
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA
| | - Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| |
Collapse
|
2
|
Özütemiz C, White M, Elvendahl W, Eryaman Y, Marjańska M, Metzger GJ, Patriat R, Kulesa J, Harel N, Watanabe Y, Grant A, Genovese G, Cayci Z. Use of a Commercial 7-T MRI Scanner for Clinical Brain Imaging: Indications, Protocols, Challenges, and Solutions-A Single-Center Experience. AJR Am J Roentgenol 2023; 221:788-804. [PMID: 37377363 PMCID: PMC10825876 DOI: 10.2214/ajr.23.29342] [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] [Indexed: 06/29/2023]
Abstract
The first commercially available 7-T MRI scanner (Magnetom Terra) was approved by the FDA in 2017 for clinical imaging of the brain and knee. After initial protocol development and sequence optimization efforts in volunteers, the 7-T system, in combination with an FDA-approved 1-channel transmit/32-channel receive array head coil, can now be routinely used for clinical brain MRI examinations. The ultrahigh field strength of 7-T MRI has the advantages of improved spatial resolution, increased SNR, and increased CNR but also introduces an array of new technical challenges. The purpose of this article is to describe an institutional experience with the use of the commercially available 7-T MRI scanner for routine clinical brain imaging. Specific clinical indications for which 7-T MRI may be useful for brain imaging include brain tumor evaluation with possible perfusion imaging and/or spectroscopy, radiotherapy planning; evaluation of multiple sclerosis and other demyelinating diseases, evaluation of Parkinson disease and guidance of deep brain stimulator placement, high-detail intracranial MRA and vessel wall imaging, evaluation of pituitary pathology, and evaluation of epilepsy. Detailed protocols, including sequence parameters, for these various indications are presented, and implementation challenges (including artifacts, safety, and side effects) and potential solutions are explored.
Collapse
Affiliation(s)
- Can Özütemiz
- Department of Radiology, University of Minnesota, 420 Delaware St SE, MMC 292, Minneapolis, MN 55455
| | - Matthew White
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
- Center for Clinical Imaging Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Wendy Elvendahl
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
- Center for Clinical Imaging Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Yigitcan Eryaman
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Małgorzata Marjańska
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Rémi Patriat
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Jeramy Kulesa
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Noam Harel
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Yoichi Watanabe
- Department of Radiation Oncology, University of Minnesota, Minneapolis, MN
| | - Andrea Grant
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Guglielmo Genovese
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| | - Zuzan Cayci
- Department of Radiology, University of Minnesota, 420 Delaware St SE, MMC 292, Minneapolis, MN 55455
- Center for Clinical Imaging Research, Department of Radiology, University of Minnesota, Minneapolis, MN
| |
Collapse
|
3
|
Gruber B, Stockmann JP, Mareyam A, Keil B, Bilgic B, Chang Y, Kazemivalipour E, Beckett AJ, Vu AT, Feinberg D, Wald LL. A 128-channel receive array for cortical brain imaging at 7 T. Magn Reson Med 2023; 90:2592-2607. [PMID: 37582214 PMCID: PMC10543549 DOI: 10.1002/mrm.29798] [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: 12/24/2022] [Revised: 06/27/2023] [Accepted: 06/28/2023] [Indexed: 08/17/2023]
Abstract
PURPOSE A 128-channel receive-only array for brain imaging at 7 T was simulated, designed, constructed, and tested within a high-performance head gradient designed for high-resolution functional imaging. METHODS The coil used a tight-fitting helmet geometry populated with 128 loop elements and preamplifiers to fit into a 39 cm diameter space inside a built-in gradient. The signal-to-noise ratio (SNR) and parallel imaging performance (1/g) were measured in vivo and simulated using electromagnetic modeling. The histogram of 1/g factors was analyzed to assess the range of performance. The array's performance was compared to the industry-standard 32-channel receive array and a 64-channel research array. RESULTS It was possible to construct the 128-channel array with body noise-dominated loops producing an average noise correlation of 5.4%. Measurements showed increased sensitivity compared with the 32-channel and 64-channel array through a combination of higher intrinsic SNR and g-factor improvements. For unaccelerated imaging, the 128-channel array showed SNR gains of 17.6% and 9.3% compared to the 32-channel and 64-channel array, respectively, at the center of the brain and 42% and 18% higher SNR in the peripheral brain regions including the cortex. For R = 5 accelerated imaging, these gains were 44.2% and 24.3% at the brain center and 86.7% and 48.7% in the cortex. The 1/g-factor histograms show both an improved mean and a tighter distribution by increasing the channel count, with both effects becoming more pronounced at higher accelerations. CONCLUSION The experimental results confirm that increasing the channel count to 128 channels is beneficial for 7T brain imaging, both for increasing SNR in peripheral brain regions and for accelerated imaging.
Collapse
Affiliation(s)
- Bernhard Gruber
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University Vienna, Austria
| | - Jason P. Stockmann
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
| | - Azma Mareyam
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
| | - Boris Keil
- Institute of Medical Physics and Radiation Protection, Department of Life Science Engineering, Mittelhessen University of Applied Sciences, Giessen, Germany
- Department of Diagnostic and Interventional Radiology, University Hospital Marburg, Philipps University of Marburg, Marburg, Germany
| | - Berkin Bilgic
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
| | - Yulin Chang
- Siemens Medical Solutions USA, Inc., Malvern, PA, USA
| | - Ehsan Kazemivalipour
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
| | - Alexander J.S. Beckett
- Advanced MRI Technologies, Sebastopol, CA, USA
- Helen Wills Institute for Neuroscience, University of California, Berkeley, CA, USA
| | - An T. Vu
- Radiology, University of California, San Francisco, CA, USA
- San Francisco Veteran Affairs Health Care System, San Francisco, CA, USA
| | - David Feinberg
- Advanced MRI Technologies, Sebastopol, CA, USA
- Helen Wills Institute for Neuroscience, University of California, Berkeley, CA, USA
| | - Lawrence L. Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
- Division of Health Sciences Technology, Harvard - Massachusetts Institute of Technology, Cambridge, MA, USA
| |
Collapse
|
4
|
Rios NL, Gilbert KM, Papp D, Cereza G, Foias A, Rangaprakash D, May MW, Guerin B, Wald LL, Keil B, Stockmann JP, Barry RL, Cohen-Adad J. An 8-channel Tx dipole and 20-channel Rx loop coil array for MRI of the cervical spinal cord at 7 Tesla. NMR IN BIOMEDICINE 2023; 36:e5002. [PMID: 37439129 PMCID: PMC10733907 DOI: 10.1002/nbm.5002] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Revised: 05/10/2023] [Accepted: 06/15/2023] [Indexed: 07/14/2023]
Abstract
The quality of cervical spinal cord images can be improved by the use of tailored radiofrequency (RF) coil solutions for ultrahigh field imaging; however, very few commercial and research 7-T RF coils currently exist for the spinal cord, and in particular, those with parallel transmission (pTx) capabilities. This work presents the design, testing, and validation of a pTx/Rx coil for the human neck and cervical/upper thoracic spinal cord. The pTx portion is composed of eight dipoles to ensure high homogeneity over this large region of the spinal cord. The Rx portion is made up of twenty semiadaptable overlapping loops to produce high signal-to-noise ratio (SNR) across the patient population. The coil housing is designed to facilitate patient positioning and comfort, while also being tight fitting to ensure high sensitivity. We demonstrate RF shimming capabilities to optimize B1 + uniformity, power efficiency, and/or specific absorption rate efficiency. B1 + homogeneity, SNR, and g-factor were evaluated in adult volunteers and demonstrated excellent performance from the occipital lobe down to the T4-T5 level. We compared the proposed coil with two state-of-the-art head and head/neck coils, confirming its superiority in the cervical and upper thoracic regions of the spinal cord. This coil solution therefore provides a convincing platform for producing the high image quality necessary for clinical and research scanning of the upper spinal cord.
Collapse
Affiliation(s)
- Nibardo Lopez Rios
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montréal, QC, Canada
| | - Kyle M. Gilbert
- Centre for Functional and Metabolic Mapping, The University of Western Ontario, London, ON, Canada
| | - Daniel Papp
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montréal, QC, Canada
| | - Gaspard Cereza
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montréal, QC, Canada
| | - Alexandru Foias
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montréal, QC, Canada
| | - D. Rangaprakash
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
| | - Markus W. May
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Bastien Guerin
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
| | - Lawrence L. Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
- Harvard-Massachusetts Institute of Technology Health Sciences & Technology, Cambridge, MA, USA
| | - Boris Keil
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Mittelhessen, Giessen, Germany
- Department of Diagnostic and Interventional Radiology, University Hospital Marburg, Philipps University of Marburg, Marburg, Germany
| | - Jason P. Stockmann
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
| | - Robert L. Barry
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
- Harvard-Massachusetts Institute of Technology Health Sciences & Technology, Cambridge, MA, USA
| | - Julien Cohen-Adad
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montréal, QC, Canada
- Functional Neuroimaging Unit, CRIUGM, Université de Montréal, Montreal, QC, Canada
- Mila – Quebec AI Institute, Montreal, QC, Canada
- Centre de recherche du CHU Sainte-Justine, Université de Montréal, Montréal, QC, Canada
| |
Collapse
|
5
|
Woo MK, DelaBarre L, Waks M, Lagore R, Kim J, Jungst S, Eryaman Y, Ugurbil K, Adriany G. A 32-Channel Sleeve Antenna Receiver Array for Human Head MRI Applications at 10.5 T. IEEE TRANSACTIONS ON MEDICAL IMAGING 2023; 42:2643-2652. [PMID: 37030782 DOI: 10.1109/tmi.2023.3261922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
For human brain magnetic resonance imaging (MRI), high channel count ( ≥ 32 ) radiofrequency receiver coil arrays are utilized to achieve maximum signal-to-noise ratio (SNR) and to accelerate parallel imaging techniques. With ultra-high field (UHF) MRI at 7 tesla (T) and higher, dipole antenna arrays have been shown to generate high SNR in the deep regions of the brain, however the array elements exhibit increased electromagnetic coupling with one another, making array construction more difficult with the increasing number of elements. Compared to a classical dipole antenna array, a sleeve antenna array incorporates the coaxial ground into the feed-point, resulting in a modified asymmetric antenna structure with improved intra-element decoupling. Here, we extended our previous 16-channel sleeve transceiver work and developed a 32-channel azimuthally arranged sleeve antenna receive-only array for 10.5 T human brain imaging. We experimentally compared the achievable SNR of the sleeve antenna array at 10.5 T to a more traditional 32-channel loop array bult onto a human head-shaped former. The results obtained with a head shaped phantom clearly demonstrated that peripheral intrinsic SNR can be significantly improved compared to a loop array with the same number of elements- except for the superior part of the phantom where sleeve antenna elements are not located.
Collapse
|
6
|
Nurzed B, Kuehne A, Aigner CS, Schmitter S, Niendorf T, Eigentler TW. Radiofrequency antenna concepts for human cardiac MR at 14.0 T. MAGMA (NEW YORK, N.Y.) 2023; 36:257-277. [PMID: 36920549 PMCID: PMC10140016 DOI: 10.1007/s10334-023-01075-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 02/23/2023] [Accepted: 02/27/2023] [Indexed: 04/28/2023]
Abstract
OBJECTIVE To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx). MATERIALS AND METHODS RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B1+) uniformity and efficiency in the heart of the human voxel model. B1+ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR10g) were examined at 7.0 T and 14.0 T. RESULTS At 14.0 T static pTx revealed a minimum B1+ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B1+ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B1+ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR10g < 5.25 W/kg. DISCUSSION MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.
Collapse
Affiliation(s)
- Bilguun Nurzed
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
| | | | | | | | - Thoralf Niendorf
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany.
- MRI.TOOLS GmbH, Berlin, Germany.
- Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
| | - Thomas Wilhelm Eigentler
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
- Chair of Medical Engineering, Technische Universität Berlin, Berlin, Germany
| |
Collapse
|
7
|
Rios NL, Gilbert KM, Papp D, Cereza G, Foias A, Rangaprakash D, May MW, Guerin B, Wald LL, Keil B, Stockmann JP, Barry RL, Cohen-Adad J. 8-channel Tx dipole and 20-channel Rx loop coil array for MRI of the cervical spinal cord at 7 Tesla. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.08.527664. [PMID: 36798276 PMCID: PMC9934596 DOI: 10.1101/2023.02.08.527664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The quality of cervical spinal cord images can be improved by the use of tailored radiofrequency coil solutions for ultra-high field imaging; however, very few commercial and research 7 Tesla radiofrequency coils currently exist for the spinal cord, and in particular those with parallel transmit capabilities. This work presents the design, testing and validation of a pTx/Rx coil for the human neck and cervical/upper-thoracic spinal cord. The pTx portion is composed of 8 dipoles to ensure high homogeneity over this large region of the spinal cord. The Rx portion is made of 20 semi-adaptable overlapping loops to produce high Signal-to-noise ratio (SNR) across the patient population. The coil housing is designed to facilitate patient positioning and comfort, while being tight fitting to ensure high sensitivity. We demonstrate RF shimming capabilities to optimize B 1 + uniformity, power efficiency and/or specific absorption rate (SAR) efficiency. B 1 + homogeneity, SNR and g-factor was evaluated in adult volunteers and demonstrated excellent performance from the occipital lobe down to the T4-T5 level. We compared the proposed coil with two state-of-the-art head and head/neck coils, confirming its superiority in the cervical and upper-thoracic regions of the spinal cord. This coil solution therefore provides a convincing platform for producing the high image quality necessary for clinical and research scanning of the upper spinal cord.
Collapse
Affiliation(s)
- Nibardo Lopez Rios
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montreal, QC, Canada
| | - Kyle M. Gilbert
- Centre for Functional and Metabolic Mapping, The University of Western Ontario, London, ON, Canada
| | - Daniel Papp
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montreal, QC, Canada
| | - Gaspard Cereza
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montreal, QC, Canada
| | - Alexandru Foias
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montreal, QC, Canada
| | - D. Rangaprakash
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
| | - Markus W. May
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
| | - Bastien Guerin
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
| | - Lawrence L. Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
- Harvard-Massachusetts Institute of Technology Health Sciences & Technology, Cambridge, MA, USA
| | - Boris Keil
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Mittelhessen, Giessen, Germany
- Department of Diagnostic and Interventional Radiology, University Hospital Marburg, Philipps University of Marburg, Marburg, Germany
| | - Jason P. Stockmann
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
| | - Robert L. Barry
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA
- Harvard Medical School, Boston, MA, USA
- Harvard-Massachusetts Institute of Technology Health Sciences & Technology, Cambridge, MA, USA
| | - Julien Cohen-Adad
- NeuroPoly Lab, Institute of Biomedical Engineering, Polytechnique Montréal, Montreal, QC, Canada
- Functional Neuroimaging Unit, CRIUGM, Université de Montréal, Montreal, QC, Canada
- Mila – Quebec AI Institute, Montreal, QC, Canada
- Centre de recherche du CHU Sainte-Justine, Université de Montréal, Montréal, QC, Canada
| |
Collapse
|
8
|
Novel materials in magnetic resonance imaging: high permittivity ceramics, metamaterials, metasurfaces and artificial dielectrics. MAGNETIC RESONANCE MATERIALS IN PHYSICS, BIOLOGY AND MEDICINE 2022; 35:875-894. [PMID: 35471464 PMCID: PMC9596558 DOI: 10.1007/s10334-022-01007-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 02/18/2022] [Accepted: 03/07/2022] [Indexed: 11/01/2022]
Abstract
AbstractThis article reviews recent developments in designing and testing new types of materials which can be: (i) placed around the body for in vivo imaging, (ii) be integrated into a conventional RF coil, or (iii) form the resonator itself. These materials can improve the quality of MRI scans for both in vivo and magnetic resonance microscopy applications. The methodological section covers the basic operation and design of two different types of materials, namely high permittivity materials constructed from ceramics and artificial dielectrics/metasurfaces formed by coupled conductive subunits, either in air or surrounded by dielectric material. Applications of high permittivity materials and metasurfaces placed next to the body to neuroimaging and extremity imaging at 7 T, body and neuroimaging at 3 T, and extremity imaging at 1.5 T are shown. Results using ceramic resonators for both high field in vivo imaging and magnetic resonance microscopy are also shown. The development of new materials to improve MR image quality remains an active area of research, but has not yet found significant use in clinical applications. This is mainly due to practical issues such as specific absorption rate modelling, accurate and reproducible placement, and acceptable size/weight of such materials. The most successful area has been simple “dielectric pads” for neuroimaging at 7 T which were initially developed somewhat as a stop-gap while parallel transmit technology was being developed, but have continued to be used at many sites. Some of these issues can potentially be overcome using much lighter metasurfaces and artificial dielectrics, which are just beginning to be assessed.
Collapse
|
9
|
Tao S, Zhou X, Westerhold EM, Middlebrooks EH, Lin C. Optimization of fast gray matter acquisition T1 inversion recovery (FGATIR) on 7T MRI for deep brain stimulation targeting. Neuroimage 2022; 252:119043. [PMID: 35235838 DOI: 10.1016/j.neuroimage.2022.119043] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 02/24/2022] [Accepted: 02/26/2022] [Indexed: 10/19/2022] Open
Abstract
Deep brain stimulation (DBS) is an increasingly utilized treatment for multiple neurological disorders. Continued improvements in DBS outcome are, in part, related to increasing ability to directly visualize stimulation targets by MRI. However, it is challenging to image DBS targets with conventional MRI techniques due to limited contrast. Fast Gray Matter Acquisition T1 Inversion Recovery (FGATIR) is a commonly used MRI sequence that improves visualization of several key DBS targets by suppressing white matter (WM) signal to better reveal deep-brain gray matter (GM) structures. Due to increased signal level at high field strength, application of FGATIR on 7T MRI may allow higher spatial resolution and better DBS targeting accuracy. However, successful utilization of FGATIR requires meticulous sequence optimization involving multiple parameters to maximize GM signal while suppressing WM. This is further complicated by the transmit RF field (B1+) inhomogeneity on 7T, which can cause severe contrast degradation. In this work, we introduce a systematic approach to optimize FGATIR and to improve visualization of thalamic DBS targets on 7T. FGATIR optimization is cast into a constrained optimization problem whose objective function and constraints are designed to maximize the GM-WM contrast-to-noise ratio (CNR) while accounting for B1+ inhomogeneity. This approach allows a systematic search for optimal parameters across the multi-dimensional parametric space while limiting the negative effect of B1+ variation. Bloch equation simulations were performed to solve the proposed optimization problem and to compare the sequence derived from this method against the sequence optimized without considering B1+ inhomogeneity. The results showed that this approach can improve GM-WM CNR in the presence of B1+ inhomogeneity, especially in some high relative B1+ areas where several key thalamic DBS targets are located. Additionally, in vivo images were acquired on a clinical 7T MRI to further validate this approach. Severe contrast degradation in the thalamus was observed when B1+ effect was not considered in sequence optimization, while the proposed approach yielded improved image contrast in the thalamus with key DBS targets well-defined. These results demonstrated that the proposed method allowed optimization of FGATIR on 7T to better visualize thalamic DBS targets, which may lead to improved DBS targeting accuracy as well as treatment outcome.
Collapse
Affiliation(s)
- Shengzhen Tao
- Department of Radiology, Mayo Clinic, Jacksonville, FL, USA.
| | - Xiangzhi Zhou
- Department of Radiology, Mayo Clinic, Jacksonville, FL, USA
| | | | | | - Chen Lin
- Department of Radiology, Mayo Clinic, Jacksonville, FL, USA
| |
Collapse
|
10
|
Hangel G, Niess E, Lazen P, Bednarik P, Bogner W, Strasser B. Emerging methods and applications of ultra-high field MR spectroscopic imaging in the human brain. Anal Biochem 2022; 638:114479. [PMID: 34838516 DOI: 10.1016/j.ab.2021.114479] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Revised: 10/15/2021] [Accepted: 11/16/2021] [Indexed: 12/21/2022]
Abstract
Magnetic Resonance Spectroscopic Imaging (MRSI) of the brain enables insights into the metabolic changes and fluxes in diseases such as tumors, multiple sclerosis, epilepsy, or hepatic encephalopathy, as well as insights into general brain functionality. However, the routine application of MRSI is mostly hampered by very low signal-to-noise ratios (SNR) due to the low concentrations of metabolites, about 10000 times lower than water. Furthermore, MRSI spectra have a dense information content with many overlapping metabolite resonances, especially for proton MRSI. MRI scanners at ultra-high field strengths, like 7 T or above, offer the opportunity to increase SNR, as well as the separation between resonances, thus promising to solve both challenges. Yet, MRSI at ultra-high field strengths is challenged by decreased B0- and B1-homogeneity, shorter T2 relaxation times, stronger chemical shift displacement errors, and aggravated lipid contamination. Therefore, to capitalize on the advantages of ultra-high field strengths, these challenges must be overcome. This review focuses on the challenges MRSI of the human brain faces at ultra-high field strength, as well as the possible applications to this date.
Collapse
Affiliation(s)
- Gilbert Hangel
- High Field MR Centre, Department of Medical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria; Department of Neurosurgery, Medical University of Vienna, Austria
| | - Eva Niess
- High Field MR Centre, Department of Medical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria
| | - Philipp Lazen
- High Field MR Centre, Department of Medical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria
| | - Petr Bednarik
- High Field MR Centre, Department of Medical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria
| | - Wolfgang Bogner
- High Field MR Centre, Department of Medical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria
| | - Bernhard Strasser
- High Field MR Centre, Department of Medical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria.
| |
Collapse
|
11
|
Ineichen BV, Beck ES, Piccirelli M, Reich DS. New Prospects for Ultra-High-Field Magnetic Resonance Imaging in Multiple Sclerosis. Invest Radiol 2021; 56:773-784. [PMID: 34120128 PMCID: PMC8505164 DOI: 10.1097/rli.0000000000000804] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Revised: 05/09/2021] [Accepted: 05/09/2021] [Indexed: 11/26/2022]
Abstract
ABSTRACT There is growing interest in imaging multiple sclerosis (MS) through the ultra-high-field (UHF) lens, which currently means a static magnetic field strength of 7 T or higher. Because of higher signal-to-noise ratio and enhanced susceptibility effects, UHF magnetic resonance imaging improves conspicuity of MS pathological hallmarks, among them cortical demyelination and the central vein sign. This could, in turn, improve confidence in MS diagnosis and might also facilitate therapeutic monitoring of MS patients. Furthermore, UHF imaging offers unique insight into iron-related pathology, leptomeningeal inflammation, and spinal cord pathologies in neuroinflammation. Yet, limitations such as the longer scanning times to achieve improved resolution and incipient safety data on implanted medical devices need to be considered. In this review, we discuss applications of UHF imaging in MS, its advantages and limitations, and practical aspects of UHF in the clinical setting.
Collapse
Affiliation(s)
- Benjamin V. Ineichen
- From the Translational Neuroradiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD
- Department of Neuroradiology, Clinical Neuroscience Center, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Erin S. Beck
- From the Translational Neuroradiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD
| | - Marco Piccirelli
- Department of Neuroradiology, Clinical Neuroscience Center, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Daniel S. Reich
- From the Translational Neuroradiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD
| |
Collapse
|
12
|
Abstract
Especially after the launch of 7 T, the ultrahigh magnetic field (UHF) imaging community achieved critically important strides in our understanding of the physics of radiofrequency interactions in the human body, which in turn has led to solutions for the challenges posed by such UHFs. As a result, the originally obtained poor image quality has progressed to the high-quality and high-resolution images obtained at 7 T and now at 10.5 T in the human torso. Despite these tremendous advances, work still remains to further improve the image quality and fully capitalize on the potential advantages UHF has to offer.
Collapse
|
13
|
Woo MK, Delabarre L, Waks M, Lee J, Lagore RL, Jungst S, Grant A, Eryaman Y, Ugurbil K, Adriany G. Comparison of 16-Channel Asymmetric Sleeve Antenna and Dipole Antenna Transceiver Arrays at 10.5 Tesla MRI. IEEE TRANSACTIONS ON MEDICAL IMAGING 2021; 40:1147-1156. [PMID: 33360987 PMCID: PMC8078892 DOI: 10.1109/tmi.2020.3047354] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Multi-element transmit arrays with low peak 10 g specific absorption rate (SAR) and high SAR efficiency (defined as ( [Formula: see text]SAR [Formula: see text] are essential for ultra-high field (UHF) magnetic resonance imaging (MRI) applications. Recently, the adaptation of dipole antennas used as MRI coil elements in multi-channel arrays has provided the community with a technological solution capable of producing uniform images and low SAR efficiency at these high field strengths. However, human head-sized arrays consisting of dipole elements have a practical limitation to the number of channels that can be used due to radiofrequency (RF) coupling between the antenna elements, as well as, the coaxial cables necessary to connect them. Here we suggest an asymmetric sleeve antenna as an alternative to the dipole antenna. When used in an array as MRI coil elements, the asymmetric sleeve antenna can generate reduced peak 10 g SAR and improved SAR efficiency. To demonstrate the advantages of an array consisting of our suggested design, we compared various performance metrics produced by 16-channel arrays of asymmetric sleeve antennas and dipole antennas with the same dimensions. Comparison data were produced on a phantom in electromagnetic (EM) simulations and verified with experiments at 10.5 Tesla (T). The results produced by the 16-channel asymmetric sleeve antenna array demonstrated 28 % lower peak 10 g SAR and 18.6 % higher SAR efficiency when compared to the 16-channel dipole antenna array.
Collapse
|
14
|
Tavaf N, Lagore RL, Jungst S, Gunamony S, Radder J, Grant A, Moeller S, Auerbach E, Ugurbil K, Adriany G, Van de Moortele PF. A self-decoupled 32-channel receive array for human-brain MRI at 10.5 T. Magn Reson Med 2021; 86:1759-1772. [PMID: 33780032 DOI: 10.1002/mrm.28788] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 03/02/2021] [Accepted: 03/07/2021] [Indexed: 11/10/2022]
Abstract
PURPOSE Receive array layout, noise mitigation, and B0 field strength are crucial contributors to SNR and parallel-imaging performance. Here, we investigate SNR and parallel-imaging gains at 10.5 T compared with 7 T using 32-channel receive arrays at both fields. METHODS A self-decoupled 32-channel receive array for human brain imaging at 10.5 T (10.5T-32Rx), consisting of 31 loops and one cloverleaf element, was co-designed and built in tandem with a 16-channel dual-row loop transmitter. Novel receive array design and self-decoupling techniques were implemented. Parallel imaging performance, in terms of SNR and noise amplification (g-factor), of the 10.5T-32Rx was compared with the performance of an industry-standard 32-channel receiver at 7 T (7T-32Rx) through experimental phantom measurements. RESULTS Compared with the 7T-32Rx, the 10.5T-32Rx provided 1.46 times the central SNR and 2.08 times the peripheral SNR. Minimum inverse g-factor value of the 10.5T-32Rx (min[1/g] = 0.56) was 51% higher than that of the 7T-32Rx (min[1/g] = 0.37) with R = 4 × 4 2D acceleration, resulting in significantly enhanced parallel-imaging performance at 10.5 T compared with 7 T. The g-factor values of 10.5 T-32 Rx were on par with those of a 64-channel receiver at 7 T (eg, 1.8 vs 1.9, respectively, with R = 4 × 4 axial acceleration). CONCLUSION Experimental measurements demonstrated effective self-decoupling of the receive array as well as substantial gains in SNR and parallel-imaging performance at 10.5 T compared with 7 T.
Collapse
Affiliation(s)
- Nader Tavaf
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Russell L Lagore
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Steve Jungst
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Shajan Gunamony
- Center for Cognitive Neuroimaging, University of Glasgow, Glasgow, Scotland
| | - Jerahmie Radder
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Andrea Grant
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Steen Moeller
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Edward Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Kamil Ugurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | | |
Collapse
|
15
|
Arshad M, Qureshi M, Inam O, Omer H. Transfer learning in deep neural network-based receiver coil sensitivity map estimation. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2021; 34:717-728. [PMID: 33772694 DOI: 10.1007/s10334-021-00919-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Revised: 03/07/2021] [Accepted: 03/09/2021] [Indexed: 11/30/2022]
Abstract
INTRODUCTION The success of parallel Magnetic Resonance Imaging algorithms like SENSitivity Encoding (SENSE) depends on an accurate estimation of the receiver coil sensitivity maps. Deep learning-based receiver coil sensitivity map estimation depends upon the size of training dataset and generalization capabilities of the trained neural network. When there is a mismatch between the training and testing datasets, retraining of the neural networks is required from a scratch which is costly and time consuming. MATERIALS AND METHODS A transfer learning approach, i.e., end-to-end fine-tuning is proposed to address the data scarcity and generalization problems of deep learning-based receiver coil sensitivity map estimation. First, generalization capabilities of a pre-trained U-Net (initially trained on 1.5T receiver coil sensitivity maps) are thoroughly assessed for 3T receiver coil sensitivity map estimation. Later, end-to-end fine-tuning is performed on the pre-trained U-Net to estimate the 3T receiver coil sensitivity maps. RESULT AND CONCLUSION Peak Signal-to-Noise Ratio, Root Mean Square Error and central line profiles (of the SENSE reconstructed images) show a successful SENSE reconstruction by utilizing the receiver coil sensitivity maps estimated by the proposed method.
Collapse
Affiliation(s)
- Madiha Arshad
- Medical Image Processing Research Group (MIPRG), Department of Electrical and Computer Engineering, COMSATS University, Islamabad, Pakistan.
| | - Mahmood Qureshi
- Medical Image Processing Research Group (MIPRG), Department of Electrical and Computer Engineering, COMSATS University, Islamabad, Pakistan
| | - Omair Inam
- Medical Image Processing Research Group (MIPRG), Department of Electrical and Computer Engineering, COMSATS University, Islamabad, Pakistan
| | - Hammad Omer
- Medical Image Processing Research Group (MIPRG), Department of Electrical and Computer Engineering, COMSATS University, Islamabad, Pakistan
| |
Collapse
|
16
|
Viessmann O, Polimeni JR. High-resolution fMRI at 7 Tesla: challenges, promises and recent developments for individual-focused fMRI studies. Curr Opin Behav Sci 2021; 40:96-104. [PMID: 33816717 DOI: 10.1016/j.cobeha.2021.01.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Limited detection power has been a bottleneck for subject-specific functional MRI (fMRI) studies, however the higher signal-to-noise ratio afforded by ultra-high magnetic fields (≥ 7 Tesla) provides levels of sensitivity and resolution needed to study individual subjects. What may be surprising is that higher imaging resolution may provide both higher specificity and sensitivity due to reductions in partial volume effects and reduced physiological noise. However, challenges remain to ensure high data quality and to reduce variability in ultra-high field fMRI. We discuss session-specific biases including those caused by factors related to instrumentation, anatomy, and physiology-which can translate into variability across sessions-and how to minimize these to help ultra-high field fMRI reach its full potential for individual-focused studies.
Collapse
Affiliation(s)
- Olivia Viessmann
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.,Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Jonathan R Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA.,Department of Radiology, Harvard Medical School, Boston, MA, USA.,Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA
| |
Collapse
|
17
|
Yacoub E, Grier MD, Auerbach EJ, Lagore RL, Harel N, Adriany G, Zilverstand A, Hayden BY, Heilbronner SR, Uğurbil K, Zimmermann J. Ultra-high field (10.5 T) resting state fMRI in the macaque. Neuroimage 2020; 223:117349. [PMID: 32898683 PMCID: PMC7745777 DOI: 10.1016/j.neuroimage.2020.117349] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 08/20/2020] [Accepted: 08/31/2020] [Indexed: 01/02/2023] Open
Abstract
Resting state functional connectivity refers to the temporal correlations between spontaneous hemodynamic signals obtained using functional magnetic resonance imaging. This technique has demonstrated that the structure and dynamics of identifiable networks are altered in psychiatric and neurological disease states. Thus, resting state network organizations can be used as a diagnostic, or prognostic recovery indicator. However, much about the physiological basis of this technique is unknown. Thus, providing a translational bridge to an optimal animal model, the macaque, in which invasive circuit manipulations are possible, is of utmost importance. Current approaches to resting state measurements in macaques face unique challenges associated with signal-to-noise, the need for contrast agents limiting translatability, and within-subject designs. These limitations can, in principle, be overcome through ultra-high magnetic fields. However, imaging at magnetic fields above 7T has yet to be adapted for fMRI in macaques. Here, we demonstrate that the combination of high channel count transmitter and receiver arrays, optimized pulse sequences, and careful anesthesia regimens, allows for detailed single-subject resting state analysis at high resolutions using a 10.5 Tesla scanner. In this study, we uncover thirty spatially detailed resting state components that are highly robust across individual macaques and closely resemble the quality and findings of connectomes from large human datasets. This detailed map of the rsfMRI 'macaque connectome' will be the basis for future neurobiological circuit manipulation work, providing valuable biological insights into human connectomics.
Collapse
Affiliation(s)
- Essa Yacoub
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States; Center for Neuroengineering, University of Minnesota, Minneapolis, MN 55455, United States
| | - Mark D Grier
- Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, United States
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States
| | - Russell L Lagore
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States
| | - Noam Harel
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States; Department of Neurosurgery, University of Minnesota, Minneapolis, MN 55455, United States
| | - Gregor Adriany
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States; Center for Neuroengineering, University of Minnesota, Minneapolis, MN 55455, United States
| | - Anna Zilverstand
- Department of Psychiatry, University of Minnesota, Minneapolis, MN 55455, United States
| | - Benjamin Y Hayden
- Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, United States; Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States; Center for Neuroengineering, University of Minnesota, Minneapolis, MN 55455, United States; Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, United States
| | - Sarah R Heilbronner
- Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, United States; Center for Neuroengineering, University of Minnesota, Minneapolis, MN 55455, United States
| | - Kamil Uğurbil
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States; Center for Neuroengineering, University of Minnesota, Minneapolis, MN 55455, United States
| | - Jan Zimmermann
- Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, United States; Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455, United States; Center for Neuroengineering, University of Minnesota, Minneapolis, MN 55455, United States; Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, United States.
| |
Collapse
|
18
|
Hennig J, Kiviniemi V, Riemenschneider B, Barghoorn A, Akin B, Wang F, LeVan P. 15 Years MR-encephalography. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2020; 34:85-108. [PMID: 33079327 PMCID: PMC7910380 DOI: 10.1007/s10334-020-00891-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 09/02/2020] [Accepted: 09/29/2020] [Indexed: 02/07/2023]
Abstract
Objective This review article gives an account of the development of the MR-encephalography (MREG) method, which started as a mere ‘Gedankenexperiment’ in 2005 and gradually developed into a method for ultrafast measurement of physiological activities in the brain. After going through different approaches covering k-space with radial, rosette, and concentric shell trajectories we have settled on a stack-of-spiral trajectory, which allows full brain coverage with (nominal) 3 mm isotropic resolution in 100 ms. The very high acceleration factor is facilitated by the near-isotropic k-space coverage, which allows high acceleration in all three spatial dimensions. Methods The methodological section covers the basic sequence design as well as recent advances in image reconstruction including the targeted reconstruction, which allows real-time feedback applications, and—most recently—the time-domain principal component reconstruction (tPCR), which applies a principal component analysis of the acquired time domain data as a sparsifying transformation to improve reconstruction speed as well as quality. Applications Although the BOLD-response is rather slow, the high speed acquisition of MREG allows separation of BOLD-effects from cardiac and breathing related pulsatility. The increased sensitivity enables direct detection of the dynamic variability of resting state networks as well as localization of single interictal events in epilepsy patients. A separate and highly intriguing application is aimed at the investigation of the glymphatic system by assessment of the spatiotemporal patterns of cardiac and breathing related pulsatility. Discussion MREG has been developed to push the speed limits of fMRI. Compared to multiband-EPI this allows considerably faster acquisition at the cost of reduced image quality and spatial resolution.
Collapse
Affiliation(s)
- Juergen Hennig
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany. .,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany.
| | - Vesa Kiviniemi
- Oulu Functional NeuroImaging Group, Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland
| | - Bruno Riemenschneider
- Department of Radiology, Center for Biomedical Imaging, New York University Grossman School of Medicine, New York, NY, USA
| | - Antonia Barghoorn
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany.,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Burak Akin
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany.,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Fei Wang
- Department of Radiology, Medical Physics, Faculty of Medicine, Medical Center University of Freiburg, University of Freiburg, Freiburg, Germany.,Center for Basics in NeuroModulation (NeuroModulBasics), Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Pierre LeVan
- Departments of Radiology and Paediatrics, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada
| |
Collapse
|
19
|
Grant A, Metzger GJ, Van de Moortele PF, Adriany G, Olman C, Zhang L, Koopermeiners J, Eryaman Y, Koeritzer M, Adams ME, Henry TR, Uğurbil K. 10.5 T MRI static field effects on human cognitive, vestibular, and physiological function. Magn Reson Imaging 2020; 73:163-176. [PMID: 32822819 DOI: 10.1016/j.mri.2020.08.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Revised: 07/21/2020] [Accepted: 08/14/2020] [Indexed: 01/18/2023]
Abstract
PURPOSE To perform a pilot study to quantitatively assess cognitive, vestibular, and physiological function during and after exposure to a magnetic resonance imaging (MRI) system with a static field strength of 10.5 Tesla at multiple time scales. METHODS A total of 29 subjects were exposed to a 10.5 T MRI field and underwent vestibular, cognitive, and physiological testing before, during, and after exposure; for 26 subjects, testing and exposure were repeated within 2-4 weeks of the first visit. Subjects also reported sensory perceptions after each exposure. Comparisons were made between short and long term time points in the study with respect to the parameters measured in the study; short term comparison included pre-vs-isocenter and pre-vs-post (1-24 h), while long term compared pre-exposures 2-4 weeks apart. RESULTS Of the 79 comparisons, 73 parameters were unchanged or had small improvements after magnet exposure. The exceptions to this included lower scores on short term (i.e. same day) executive function testing, greater isocenter spontaneous eye movement during visit 1 (relative to pre-exposure), increased number of abnormalities on videonystagmography visit 2 versus visit 1 and a mix of small increases (short term visit 2) and decreases (short term visit 1) in blood pressure. In addition, more subjects reported metallic taste at 10.5 T in comparison to similar data obtained in previous studies at 7 T and 9.4 T. CONCLUSION Initial results of 10.5 T static field exposure indicate that 1) cognitive performance is not compromised at isocenter, 2) subjects experience increased eye movement at isocenter, and 3) subjects experience small changes in vital signs but no field-induced increase in blood pressure. While small but significant differences were found in some comparisons, none were identified as compromising subject safety. A modified testing protocol informed by these results was devised with the goal of permitting increased enrollment while providing continued monitoring to evaluate field effects.
Collapse
Affiliation(s)
- Andrea Grant
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States.
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States
| | | | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States
| | - Cheryl Olman
- Department of Psychology, University of Minnesota, Minneapolis, MN, United States
| | - Lin Zhang
- School of Public Health Biostatistics, University of Minnesota, Minneapolis, MN, United States
| | - Joseph Koopermeiners
- School of Public Health Biostatistics, University of Minnesota, Minneapolis, MN, United States
| | - Yiğitcan Eryaman
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States
| | - Margaret Koeritzer
- M Health Fairview, Department of Audiology, Minneapolis, MN, United States
| | - Meredith E Adams
- Department of Otolaryngology, Head and Neck Surgery, University of Minnesota, Minneapolis, MN, United States
| | - Thomas R Henry
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States; Department of Neurology, University of Minnesota, Minneapolis, MN, United States
| | - Kamil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States
| |
Collapse
|
20
|
Del Bosque R, Cui J, Ogier S, Cheshkov S, Dimitrov IE, Malloy C, Wright SM, McDougall M. A 32-channel receive array coil for bilateral breast imaging and spectroscopy at 7T. Magn Reson Med 2020; 85:551-559. [PMID: 32820540 DOI: 10.1002/mrm.28425] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 06/19/2020] [Accepted: 06/22/2020] [Indexed: 11/09/2022]
Abstract
PURPOSE This work describes the construction and evaluation of a bilateral 32-channel receive array for breast imaging at 7T. METHODS The receive array consisted of 32 receive coils, placed on two 3D-printed hemispherical formers. Each side of the receive array consisted of 16 receive loops, each loop having a corresponding detachable board with match/tune capacitors, active detuning circuitry, and a balun. Coil performance was evaluated on homogeneous canola oil phantoms using a Philips Achieva 7T system. Array coil performance was compared with a bilateral forced current excitation volume coil in transmit/receive mode and with a previously reported 16-channel unilateral coil with a similar design. RESULTS The 32-channel array had an increase in average SNR throughout both phantoms by a factor of five as compared with the volume coil, with SNR increases up to 10 times along the periphery and three times in the center. Noise measurements showed low interelement noise correlation (average: 5.4%; maximum: 16.8%). Geometry factor maps were acquired for various acceleration factors and showed mean geometry factors <1.2, for combined acceleration factors of up to six. CONCLUSIONS The improvements achieved demonstrate the clear potential for use in dynamic contrast-enhanced or diffusion-weighted MR studies, while maintaining diagnostically relevant spatial and temporal resolutions.
Collapse
Affiliation(s)
- Romina Del Bosque
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA
| | - Jiaming Cui
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| | - Stephen Ogier
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| | - Sergey Cheshkov
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Center for Brain Health, University of Texas at Dallas, Dallas, Texas, USA
| | - Ivan E Dimitrov
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Philips Healthcare, Gainesville, Florida, USA
| | - Craig Malloy
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Steven M Wright
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA.,Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| | - Mary McDougall
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA.,Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| |
Collapse
|
21
|
Han S, Liao C, Manhard MK, Park DJ, Bilgic B, Fair MJ, Wang F, Blazejewska AI, Grissom WA, Polimeni JR, Setsompop K. Accelerated spin-echo functional MRI using multisection excitation by simultaneous spin-echo interleaving (MESSI) with complex-encoded generalized slice dithered enhanced resolution (cgSlider) simultaneous multislice echo-planar imaging. Magn Reson Med 2020; 84:206-220. [PMID: 31840295 PMCID: PMC7083698 DOI: 10.1002/mrm.28108] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 10/29/2019] [Accepted: 11/14/2019] [Indexed: 12/14/2022]
Abstract
PURPOSE Spin-echo functional MRI (SE-fMRI) has the potential to improve spatial specificity when compared with gradient-echo fMRI. However, high spatiotemporal resolution SE-fMRI with large slice-coverage is challenging as SE-fMRI requires a long echo time to generate blood oxygenation level-dependent (BOLD) contrast, leading to long repetition times. The aim of this work is to develop an acquisition method that enhances the slice-coverage of SE-fMRI at high spatiotemporal resolution. THEORY AND METHODS An acquisition scheme was developed entitled multisection excitation by simultaneous spin-echo interleaving (MESSI) with complex-encoded generalized slice dithered enhanced resolution (cgSlider). MESSI uses the dead-time during the long echo time by interleaving the excitation and readout of 2 slices to enable 2× slice-acceleration, while cgSlider uses the stable temporal background phase in SE-fMRI to encode/decode 2 adjacent slices simultaneously with a "phase-constrained" reconstruction method. The proposed cgSlider-MESSI was also combined with simultaneous multislice (SMS) to achieve further slice-acceleration. This combined approach was used to achieve 1.5-mm isotropic whole-brain SE-fMRI with a temporal resolution of 1.5 s and was evaluated using sensory stimulation and breath-hold tasks at 3T. RESULTS Compared with conventional SE-SMS, cgSlider-MESSI-SMS provides 4-fold increase in slice-coverage for the same repetition time, with comparable temporal signal-to-noise ratio. Corresponding fMRI activation from cgSlider-MESSI-SMS for both fMRI tasks were consistent with those from conventional SE-SMS. Overall, cgSlider-MESSI-SMS achieved a 32× encoding-acceleration by combining Rinplane × MB × cgSlider × MESSI = 4 × 2 × 2 × 2. CONCLUSION High-quality, high-resolution whole-brain SE-fMRI was acquired at a short repetition time using cgSlider-MESSI-SMS. This method should be beneficial for high spatiotemporal resolution SE-fMRI studies requiring whole-brain coverage.
Collapse
Affiliation(s)
- SoHyun Han
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Congyu Liao
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Mary Kate Manhard
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Daniel Joseph Park
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
| | - Berkin Bilgic
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Merlin J. Fair
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - Fuyixue Wang
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Medical Engineering & Medical Physics, Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts
| | - Anna I. Blazejewska
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
| | - William A. Grissom
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
| | - Jonathan R. Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts
| | - Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts
- Department of Radiology, Harvard Medical School, Boston, Massachusetts
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts
| |
Collapse
|
22
|
Oros-Peusquens AM, Loução R, Abbas Z, Gras V, Zimmermann M, Shah NJ. A Single-Scan, Rapid Whole-Brain Protocol for Quantitative Water Content Mapping With Neurobiological Implications. Front Neurol 2019; 10:1333. [PMID: 31920951 PMCID: PMC6934004 DOI: 10.3389/fneur.2019.01333] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 12/02/2019] [Indexed: 12/16/2022] Open
Abstract
Water concentration is tightly regulated in the healthy human brain and changes only slightly with age and gender in healthy subjects. Consequently, changes in water content are important for the characterization of disease. MRI can be used to measure changes in brain water content, but as these changes are usually in the low percentage range, highly accurate and precise methods are required for detection. The method proposed here is based on a long-TR (10 s) multiple-echo gradient-echo measurement with an acquisition time of 7:21 min. Using such a long TR ensures that there is no T1 weighting, meaning that the image intensity at zero echo time is only proportional to the water content, the transmit field, and to the receive field. The receive and transmit corrections, which are increasingly large at higher field strengths and for highly segmented coil arrays, are multiplicative and can be approached heuristically using a bias field correction. The method was tested on 21 healthy volunteers at 3T field strength. Calibration using cerebral-spinal fluid values (~100% water content) resulted in mean values and standard deviations of the water content distribution in white matter and gray matter of 69.1% (1.7%) and 83.7% (1.2%), respectively. Measured distributions were coil-independent, as seen by using either a 12-channel receiver coil or a 32-channel receiver coil. In a test-retest investigation using 12 scans on one volunteer, the variation in the mean value of water content for different tissue types was ~0.3% and the mean voxel variability was ~1%. Robustness against reduced SNR was assessed by comparing results for 5 additional volunteers at 1.5T and 3T. Furthermore, water content distribution in gray matter is investigated and regional contrast reported for the first time. Clinical applicability is illustrated with data from one stroke patient and one brain tumor patient. It is anticipated that this fast, stable, easy-to-use, high-quality mapping method will facilitate routine quantitative MR imaging of water content.
Collapse
Affiliation(s)
| | - Ricardo Loução
- Institute of Neurosciences and Medicine 4 (INM-4), Forschungszentrum Jülich, Jülich, Germany
| | - Zaheer Abbas
- Institute of Neurosciences and Medicine 4 (INM-4), Forschungszentrum Jülich, Jülich, Germany
| | - Vincent Gras
- Institute of Neurosciences and Medicine 4 (INM-4), Forschungszentrum Jülich, Jülich, Germany
| | - Markus Zimmermann
- Institute of Neurosciences and Medicine 4 (INM-4), Forschungszentrum Jülich, Jülich, Germany
| | - N J Shah
- Institute of Neurosciences and Medicine 4 (INM-4), Forschungszentrum Jülich, Jülich, Germany.,Institute of Neurosciences and Medicine 11 (INM-11), JARA, Forschungszentrum Jülich, Jülich, Germany.,JARA - BRAIN - Translational Medicine, Aachen, Germany.,Department of Neurology, RWTH Aachen University, Aachen, Germany
| |
Collapse
|
23
|
He X, Ertürk MA, Grant A, Wu X, Lagore RL, DelaBarre L, Eryaman Y, Adriany G, Auerbach EJ, Van de Moortele PF, Uğurbil K, Metzger GJ. First in-vivo human imaging at 10.5T: Imaging the body at 447 MHz. Magn Reson Med 2019; 84:289-303. [PMID: 31846121 DOI: 10.1002/mrm.28131] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 11/25/2019] [Accepted: 11/26/2019] [Indexed: 01/31/2023]
Abstract
PURPOSE To investigate the feasibility of imaging the human torso and to evaluate the performance of several radiofrequency (RF) management strategies at 10.5T. METHODS Healthy volunteers were imaged on a 10.5T whole-body scanner in multiple target anatomies, including the prostate, hip, kidney, liver, and heart. Phase-only shimming and spoke pulses were used to demonstrate their performance in managing the B 1 + inhomogeneity present at 447 MHz. Imaging protocols included both qualitative and quantitative acquisitions to show the feasibility of imaging with different contrasts. RESULTS High-quality images were acquired and demonstrated excellent overall contrast and signal-to-noise ratio. The experimental results matched well with predictions and suggested good translational capabilities of the RF management strategies previously developed at 7T. Phase-only shimming provided increased efficiency, but showed pronounced limitations in homogeneity, demonstrating the need for the increased degrees of freedom made possible through single- and multispoke RF pulse design. CONCLUSION The first in-vivo human imaging was successfully performed at 10.5T using previously developed RF management strategies. Further improvement in RF coils, transmit chain, and full integration of parallel transmit functionality are needed to fully realize the benefits of 10.5T.
Collapse
Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Andrea Grant
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Russell L Lagore
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Lance DelaBarre
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Yiğitcan Eryaman
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Eddie J Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | | | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| |
Collapse
|
24
|
Chieh SW, Kaveh M, Akçakaya M, Moeller S. Self-calibrated interpolation of non-Cartesian data with GRAPPA in parallel imaging. Magn Reson Med 2019; 83:1837-1850. [PMID: 31722128 DOI: 10.1002/mrm.28033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 08/20/2019] [Accepted: 09/17/2019] [Indexed: 12/22/2022]
Abstract
PURPOSE To develop a non-Cartesian k-space reconstruction method using self-calibrated region-specific interpolation kernels for highly accelerated acquisitions. METHODS In conventional non-Cartesian GRAPPA with through-time GRAPPA (TT-GRAPPA), the use of region-specific interpolation kernels has demonstrated improved reconstruction quality in dynamic imaging for highly accelerated acquisitions. However, TT-GRAPPA requires the acquisition of a large number of separate calibration scans. To reduce the overall imaging time, we propose Self-calibrated Interpolation of Non-Cartesian data with GRAPPA (SING) to self-calibrate region-specific interpolation kernels from dynamic undersampled measurements. The SING method synthesizes calibration data to adapt to the distinct shape of each region-specific interpolation kernel geometry, and uses a novel local k-space regularization through an extension of TT-GRAPPA. This calibration approach is used to reconstruct non-Cartesian images at high acceleration rates while mitigating noise amplification. The reconstruction quality of SING is compared with conjugate-gradient SENSE and TT-GRAPPA in numerical phantoms and in vivo cine data sets. RESULTS In both numerical phantom and in vivo cine data sets, SING offers visually and quantitatively similar reconstruction quality to TT-GRAPPA, and provides improved reconstruction quality over conjugate-gradient SENSE. Furthermore, temporal fidelity in SING and TT-GRAPPA is similar for the same acceleration rates. G-factor evaluation over the heart shows that SING and TT-GRAPPA provide similar noise amplification at moderate and high rates. CONCLUSION The proposed SING reconstruction enables significant improvement of acquisition efficiency for calibration data, while matching the reconstruction performance of TT-GRAPPA.
Collapse
Affiliation(s)
- Seng-Wei Chieh
- Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota
| | - Mostafa Kaveh
- Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota
| | - Mehmet Akçakaya
- Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota.,Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| | - Steen Moeller
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
| |
Collapse
|
25
|
Kim KN, Hernandez D, Seo JH, Noh Y, Han Y, Ryu YC, Chung JY. Quantitative assessment of phased array coils with different numbers of receiving channels in terms of signal-to-noise ratio and spatial noise variation in magnetic resonance imaging. PLoS One 2019; 14:e0219407. [PMID: 31276549 PMCID: PMC6611621 DOI: 10.1371/journal.pone.0219407] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 06/21/2019] [Indexed: 11/19/2022] Open
Abstract
The neuroimaging of humans using 7T magnetic resonance imaging (MRI) has been conducted using phased array (PA) coils with different numbers of receiving channels. PA coils with a high number of channels may offer parallel imaging (PI) with a high reduction (R)-factor, which is enabled via under-sampling and coil geometry (g) factor, increasing the radiofrequency signal sensitivity provided by a small coil. The goals of this study were to assess and validate the coil performance of PA coils with different numbers of receiver (Rx)-channels in and to propose the coil selection guidelines by visualizing 7T brain images. The combined magnetic flux density (||B1||) distributions of four configurations of PA coils—4-, 8-, 12-, and 16-channel Rx-only mode under the local transmit (Tx) mode of birdcage coils—were evaluated using electromagnetic (EM) calculations. These four configurations of PA coils and a local Tx coil were designed and built for a 7T MRI experiment. For 7T brain imaging experiments, all PA coils with (w/) and without (w/o) R-factors were compared in terms of signal-to-noise ratio (SNR) and spatial noise variation (SNV). EM simulation results clearly demonstrated that PA coils with a high number of Rx channels showed more homogeneously distributed ||B1|| fields than a PA coils with a low number of Rx coils. The results of this study demonstrate that a collection of smaller surface coils can contribute to high RF signal sensitivity in terms of the anatomical coverage of the brain and may facilitate PI. With further improvement in coil technology, researchers and clinicians will be provided with PA coils with different numbers of channels, which can ensure the optimum SNR and PI benefits for 7T brain MR imaging.
Collapse
Affiliation(s)
- Kyoung-Nam Kim
- Department of Biomedical Engineering, Gachon University, Incheon, Korea
| | - Daniel Hernandez
- Department of Biomedical Engineering, Gachon University, Incheon, Korea
| | - Jeung-Hoon Seo
- Neuroscience Research Institute, Gachon University, Incheon, Korea
| | - Young Noh
- Department of Neurology, Gachon University Gil Medical Center, Incheon, Korea
| | - Yeji Han
- Department of Biomedical Engineering, Gachon University, Incheon, Korea
| | - Yeun Chul Ryu
- Neuroscience Research Institute, Gachon University, Incheon, Korea
| | - Jun-Young Chung
- Department of Neuroscience, College of Medicine, Gachon University, Incheon, Korea
- * E-mail:
| |
Collapse
|
26
|
Erturk MA, Li X, Van de Moortele PF, Ugurbil K, Metzger GJ. Evolution of UHF Body Imaging in the Human Torso at 7T: Technology, Applications, and Future Directions. Top Magn Reson Imaging 2019; 28:101-124. [PMID: 31188271 PMCID: PMC6587233 DOI: 10.1097/rmr.0000000000000202] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
Abstract
The potential value of ultrahigh field (UHF) magnetic resonance imaging (MRI) and spectroscopy to biomedical research and in clinical applications drives the development of technologies to overcome its many challenges. The increased difficulties of imaging the human torso compared with the head include its overall size, the dimensions and location of its anatomic targets, the increased prevalence and magnitude of physiologic effects, the limited availability of tailored RF coils, and the necessary transmit chain hardware. Tackling these issues involves addressing notoriously inhomogeneous transmit B1 (B1) fields, limitations in peak B1, larger spatial variations of the static magnetic field B0, and patient safety issues related to implants and local RF power deposition. However, as research institutions and vendors continue to innovate, the potential gains are beginning to be realized. Solutions overcoming the unique challenges associated with imaging the human torso are reviewed as are current studies capitalizing on the benefits of UHF in several anatomies and applications. As the field progresses, strategies associated with the RF system architecture, calibration methods, RF pulse optimization, and power monitoring need to be further integrated into the MRI systems making what are currently complex processes more streamlined. Meanwhile, the UHF MRI community must seize the opportunity to build upon what have been so far proof of principle and feasibility studies and begin to further explore the true impact in both research and the clinic.
Collapse
Affiliation(s)
- M Arcan Erturk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | | | | | | | | |
Collapse
|
27
|
Atefi SR, Serano P, Poulsen C, Angelone LM, Bonmassar G. Numerical and Experimental Analysis of Radiofrequency-Induced Heating Versus Lead Conductivity During EEG-MRI at 3 T. IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY 2019; 61:852-859. [PMID: 31210669 PMCID: PMC6579539 DOI: 10.1109/temc.2018.2840050] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
This study investigates radiofrequency (RF)-induced heating in a head model with a 256-channel electroencephalogram (EEG) cap during magnetic resonance imaging (MRI). Nine computational models were implemented each with different EEG lead electrical conductivity, ranging from 1 to 5.8 × 107 S/m. The peak values of specific absorption rate (SAR) averaged over different volumes were calculated for each lead conductivity. Experimental measurements were also performed at 3-T MRI with a Gracilaria Lichenoides (GL) phantom with and without a low-conductive EEG lead cap ("InkNet"). The simulation results showed that SAR was a nonlinear function of the EEG lead conductivity. The experimental results were in line with the numerical simulations. Specifically, there was a ΔT of 1.7 °C in the GL phantom without leads compared to ΔT of 1.8 °C calculated with the simulations. Additionally, there was a ΔT of 1.5 °C in the GL phantom with the InkNet compared to a ΔT of 1.7 °C in the simulations with a cap of similar conductivity. The results showed that SAR is affected by specific location, number of electrodes, and the volume of tissue considered. As such, SAR averaged over the whole head, or even SAR averaged over volumes of 1 or 0.1 g, may conceal significant heating effects and local analysis of RF heating (in terms of peak SAR and temperature) is needed.
Collapse
Affiliation(s)
- Seyed Reza Atefi
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129 USA, and also with the University of Boras 50190, Boras Sweden
| | - Peter Serano
- Division of Biomedical Physics, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, MD 11401 USA
| | | | - Leonardo M Angelone
- Division of Biomedical Physics, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, MD 11401 USA
| | - Giorgio Bonmassar
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129 USA
| |
Collapse
|
28
|
Uğurbil K, Auerbach E, Moeller S, Grant A, Wu X, Van de Moortele PF, Olman C, DelaBarre L, Schillak S, Radder J, Lagore R, Adriany G. Brain imaging with improved acceleration and SNR at 7 Tesla obtained with 64-channel receive array. Magn Reson Med 2019; 82:495-509. [PMID: 30803023 DOI: 10.1002/mrm.27695] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 12/28/2018] [Accepted: 01/25/2019] [Indexed: 12/27/2022]
Abstract
PURPOSE Despite the clear synergy between high channel counts in a receive array and magnetic fields ≥ 7 Tesla, to date such systems have been restricted to a maximum of 32 channels. Here, we examine SNR gains at 7 Tesla in unaccelerated and accelerated images with a 64-receive channel (64Rx) RF coil. METHODS A 64Rx coil was built using circular loops tiled in 2 separable sections of a close-fitting form; custom designed preamplifier boards were integrated into each coil element. A 16-channel transmitter arranged in 2 rows along the z-axis was employed. The performance of the 64Rx array was experimentally compared to that of an industry-standard 32-channel receive (32Rx) array for SNR in unaccelerated images and for noise amplification under parallel imaging. RESULTS SNR gains were observed in the periphery but not in the center of the brain in unaccelerated imaging compared to the 32Rx coil. With either 1D or 2D undersampling of k-space, or with slice acceleration together with 1D undersampling of k-space, significant reductions in g-factor noise were observed throughout the brain, yielding effective gains in SNR in the entire brain compared to the 32Rx coil. Task-based FMRI data with 12-fold 2D (slice and phase-encode) acceleration yielded excellent quality functional maps with the 64Rx coil but was significantly beyond the capabilities of the 32Rx coil. CONCLUSION The results confirm the expectations from modeling studies and demonstrate that whole-brain studies with up to 16-fold, 2D acceleration would be feasible with the 64Rx coil.
Collapse
Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Edward Auerbach
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Steen Moeller
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Andrea Grant
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Xiaoping Wu
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | | | - Cheryl Olman
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Lance DelaBarre
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | | | - Jerahmie Radder
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Russell Lagore
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| | - Gregor Adriany
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota
| |
Collapse
|
29
|
Hu J, Li M, Dai Y, Geng C, Tong B, Zhou Z, Liang X, Yang W, Zhang B. Combining SENSE and reduced field-of-view for high-resolution diffusion weighted magnetic resonance imaging. Biomed Eng Online 2018; 17:77. [PMID: 29903023 PMCID: PMC6003092 DOI: 10.1186/s12938-018-0511-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Accepted: 06/05/2018] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND In diffusion-weighted magnetic resonance imaging (DWI) using single-shot echo planar imaging (ss-EPI), both reduced field-of-view (FOV) excitation and sensitivity encoding (SENSE) alone can increase in-plane resolution to some degree. However, when the two techniques are combined to further increase resolution without pronounced geometric distortion, the resulted images are often corrupted by high level of noise and artifact due to the numerical restriction in SENSE. Hence, this study is aimed to provide a reconstruction method to deal with this problem. METHODS The proposed reconstruction method was developed and implemented to deal with the high level of noise and artifact in the combination of reduced FOV imaging and traditional SENSE, in which all the imaging data were considered jointly by incorporating the motion induced phase variations among excitations. The in vivo human spine diffusion images from ten subjects were acquired at 1.5 T and reconstructed using the proposed method, and compared with SENSE magnitude average results for a range of reduction factors in reduced FOV. These images were evaluated by two radiologists using visual scores (considering distortion, noise and artifact levels) from 1 to 10. RESULTS The proposed method was able to reconstruct images with greatly reduced noise and artifact compared to SENSE magnitude average. The mean g-factors were maintained close to 1 along with enhanced signal-to-noise ratio efficiency. The image quality scores of the proposed method were significantly higher (P < 0.01) than SENSE magnitude average for all the evaluated reduction factors. CONCLUSION The proposed method can improve the combination of SENSE and reduced FOV for high-resolution ss-EPI DWI with reduced noise and artifact.
Collapse
Affiliation(s)
- Jisu Hu
- Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, Jiangsu, China
| | - Ming Li
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, 321 Zhongshan Road, Nanjing, Jiangsu, China
| | - Yakang Dai
- Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, Jiangsu, China
| | - Chen Geng
- Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, Jiangsu, China
| | - Baotong Tong
- Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, Jiangsu, China
| | - Zhiyong Zhou
- Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou, Jiangsu, China
| | - Xue Liang
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, 321 Zhongshan Road, Nanjing, Jiangsu, China
| | - Wen Yang
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, 321 Zhongshan Road, Nanjing, Jiangsu, China
| | - Bing Zhang
- Department of Radiology, Affiliated Drum Tower Hospital of Nanjing University Medical School, 321 Zhongshan Road, Nanjing, Jiangsu, China.
| |
Collapse
|
30
|
Brunheim S, Gratz M, Johst S, Bitz AK, Fiedler TM, Ladd ME, Quick HH, Orzada S. Fast and accurate multi-channel B1+ mapping based on the TIAMO technique for 7T UHF body MRI. Magn Reson Med 2018; 79:2652-2664. [PMID: 28994132 DOI: 10.1002/mrm.26925] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 08/21/2017] [Accepted: 08/26/2017] [Indexed: 01/11/2023]
Abstract
PURPOSE Current methods for mitigation of transmit field B1+ inhomogeneities at ultrahigh field (UHF) MRI by multi-channel radiofrequency (RF) shimming rely on accurate B1+ mapping. This can be time consuming when many RF channels have to be mapped for in vivo body MRI, where the B1 maps should ideally be acquired within a single breath-hold. Therefore, a new B1+ mapping technique (B1TIAMO) is proposed. METHODS The performance of this technique is validated against an established method (DREAM) in phantom measurements for a cylindrical head phantom with an 8-channel transmit/receive (Tx/Rx) array. Furthermore, measurements for a 32-channel Tx/Rx remote array are conducted in a large body phantom and the |B1+| map reliability is validated against simulations of the transmit RF field distribution. Finally, in vivo results of this new mapping technique for human abdomen are presented. RESULTS For the head phantom (8-channel Tx/Rx coil), the single |B1+| comparison between B1 TIAMO, the direct DREAM measurements, and simulation data showed good agreement with 10-19% difference. For the large body phantom (32-channel Tx/Rx coil), B1TIAMO matched the RF field simulations well. CONCLUSION The results demonstrate the potential to acquire 32 accurate single-channel B1+ maps for large field-of-view body imaging within only a single breath-hold of 16 s at 7T UHF MRI. Magn Reson Med 79:2652-2664, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Sascha Brunheim
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Marcel Gratz
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Sören Johst
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
| | - Andreas K Bitz
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, FH Aachen-University of Applied Sciences, Aachen, Germany
| | - Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Mark E Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stephan Orzada
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany
| |
Collapse
|
31
|
Hangel G, Strasser B, Považan M, Heckova E, Hingerl L, Boubela R, Gruber S, Trattnig S, Bogner W. Ultra-high resolution brain metabolite mapping at 7 T by short-TR Hadamard-encoded FID-MRSI. Neuroimage 2018; 168:199-210. [DOI: 10.1016/j.neuroimage.2016.10.043] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 10/24/2016] [Accepted: 10/26/2016] [Indexed: 10/20/2022] Open
|
32
|
Poser BA, Setsompop K. Pulse sequences and parallel imaging for high spatiotemporal resolution MRI at ultra-high field. Neuroimage 2018; 168:101-118. [PMID: 28392492 PMCID: PMC5630499 DOI: 10.1016/j.neuroimage.2017.04.006] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 04/01/2017] [Accepted: 04/03/2017] [Indexed: 12/18/2022] Open
Abstract
The SNR and CNR benefits of ultra-high field (UHF) have helped push the envelope of achievable spatial resolution in MRI. For applications based on susceptibility contrast where there is a large CNR gain, high quality sub-millimeter resolution imaging is now being routinely performed, particularly in fMRI and phase imaging/QSM. This has enabled the study of structure and function of very fine-scale structures in the brain. UHF has also helped push the spatial resolution of many other MRI applications as will be outlined in this review. However, this push in resolution comes at a cost of a large encoding burden leading to very lengthy scans. Developments in parallel imaging with controlled aliasing and the move away from 2D slice-by-slice imaging to much more SNR-efficient simultaneous multi-slice (SMS) and 3D acquisitions have helped address this issue. In particular, these developments have revolutionized the efficiency of UHF MRI to enable high spatiotemporal resolution imaging at an order of magnitude faster acquisition. In addition to describing the main approaches to these techniques, this review will also outline important key practical considerations in using these methods in practice. Furthermore, new RF pulse design to tackle the B1+ and SAR issues of UHF and the increased SAR and power requirement of SMS RF pulses will also be touched upon. Finally, an outlook into new developments of smart encoding in more dimensions, particularly through using better temporal/across-contrast encoding and reconstruction will be described. Just as controlled aliasing fully exploits spatial encoding in parallel imaging to provide large multiplicative gains in accelerations, the complimentary use of these new approaches in temporal and across-contrast encoding are expected to provide exciting opportunities for further large gains in efficiency to further push the spatiotemporal resolution of MRI.
Collapse
Affiliation(s)
- Benedikt A Poser
- Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands.
| | - Kawin Setsompop
- Department of Radiology, Harvard Medical School, Boston, MA, USA; Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
| |
Collapse
|
33
|
|
34
|
Trattnig S, Springer E, Bogner W, Hangel G, Strasser B, Dymerska B, Cardoso PL, Robinson SD. Key clinical benefits of neuroimaging at 7T. Neuroimage 2018; 168:477-489. [PMID: 27851995 PMCID: PMC5832016 DOI: 10.1016/j.neuroimage.2016.11.031] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 10/06/2016] [Accepted: 11/12/2016] [Indexed: 01/15/2023] Open
Abstract
The growing interest in ultra-high field MRI, with more than 35.000 MR examinations already performed at 7T, is related to improved clinical results with regard to morphological as well as functional and metabolic capabilities. Since the signal-to-noise ratio increases with the field strength of the MR scanner, the most evident application at 7T is to gain higher spatial resolution in the brain compared to 3T. Of specific clinical interest for neuro applications is the cerebral cortex at 7T, for the detection of changes in cortical structure, like the visualization of cortical microinfarcts and cortical plaques in Multiple Sclerosis. In imaging of the hippocampus, even subfields of the internal hippocampal anatomy and pathology may be visualized with excellent spatial resolution. Using Susceptibility Weighted Imaging, the plaque-vessel relationship and iron accumulations in Multiple Sclerosis can be visualized, which may provide a prognostic factor of disease. Vascular imaging is a highly promising field for 7T which is dealt with in a separate dedicated article in this special issue. The static and dynamic blood oxygenation level-dependent contrast also increases with the field strength, which significantly improves the accuracy of pre-surgical evaluation of vital brain areas before tumor removal. Improvement in acquisition and hardware technology have also resulted in an increasing number of MR spectroscopic imaging studies in patients at 7T. More recent parallel imaging and short-TR acquisition approaches have overcome the limitations of scan time and spatial resolution, thereby allowing imaging matrix sizes of up to 128×128. The benefits of these acquisition approaches for investigation of brain tumors and Multiple Sclerosis have been shown recently. Together, these possibilities demonstrate the feasibility and advantages of conducting routine diagnostic imaging and clinical research at 7T.
Collapse
Affiliation(s)
- Siegfried Trattnig
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria; Christian Doppler Laboratory for Clinical Molecular MRI, Vienna, Austria.
| | - Elisabeth Springer
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria; Christian Doppler Laboratory for Clinical Molecular MRI, Vienna, Austria.
| | - Wolfgang Bogner
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria.
| | - Gilbert Hangel
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria.
| | - Bernhard Strasser
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria.
| | - Barbara Dymerska
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria.
| | - Pedro Lima Cardoso
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria.
| | - Simon Daniel Robinson
- High Field MR Center, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090, Vienna, Austria.
| |
Collapse
|
35
|
Uğurbil K. Imaging at ultrahigh magnetic fields: History, challenges, and solutions. Neuroimage 2018; 168:7-32. [PMID: 28698108 PMCID: PMC5758441 DOI: 10.1016/j.neuroimage.2017.07.007] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 07/05/2017] [Accepted: 07/07/2017] [Indexed: 01/06/2023] Open
Abstract
Following early efforts in applying nuclear magnetic resonance (NMR) spectroscopy to study biological processes in intact systems, and particularly since the introduction of 4 T human scanners circa 1990, rapid progress was made in imaging and spectroscopy studies of humans at 4 T and animal models at 9.4 T, leading to the introduction of 7 T and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has provided numerous technological solutions to challenges posed at these ultrahigh fields, and demonstrated the existence of significant advantages in signal-to-noise ratio and biological information content. Primary difference from lower fields is the deviation from the near field regime at the radiofrequencies (RF) corresponding to hydrogen resonance conditions. At such ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image non-uniformities for a given sample-coil configuration because of destructive and constructive interferences. These non-uniformities were initially considered detrimental to progress of imaging at high field strengths. However, they are advantageous for parallel imaging in signal reception and transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies and improvements in instrumentation and imaging methods, today ultrahigh fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques.
Collapse
Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota Medical School, Minneapolis, MN 55455, USA.
| |
Collapse
|
36
|
Paška J, Cloos MA, Wiggins GC. A rigid, stand-off hybrid dipole, and birdcage coil array for 7 T body imaging. Magn Reson Med 2017; 80:822-832. [PMID: 29250833 DOI: 10.1002/mrm.27048] [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: 07/07/2017] [Revised: 10/23/2017] [Accepted: 11/24/2017] [Indexed: 11/11/2022]
Abstract
PURPOSE To design a robust and patient friendly radiofrequency coil array (8-channel transmit and 16-channel receive) for cross-sectional body imaging at 7 T, and to improve our understanding of the combination of dipole and loop like elements for ultra high field strengths. METHODS The hybrid coil array was optimized in eletromagnetic simulations. Considered array candidates were the dipole, loop and birdcage array. The winning design was constructed and the signal-to-noise (SNR) was compared to a close fitting array at 3 T. Transmit and receive properties for different body sizes were assessed, and multi-parametric maps were acquired with the Plug-and-Play MRF method. RESULTS The winning design consists of a dipole array for transceive combined with a birdcage array for receive only. The central SNR improved by a factor of 3 as compared to a 3 T system with a local receive array. A transmit efficiency between 2.4 and 3.9 μT/kW, a specific absorption rate efficiency of 0.25 to 0.53 μT/W/kg, and a high SNR was achieved in the center for the targeted patient population. CONCLUSION The constructed coil array is easy to handle, safe, and patient friendly, allowing further development of abdominal imaging at 7 T. Quantitative MRI in the abdomen is possible with Plug-and-Play MRF using the designed coil array. Magn Reson Med 80:822-832, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Jan Paška
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York, USA
| | - Martijn A Cloos
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York, USA
| | - Graham C Wiggins
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York, USA
| |
Collapse
|
37
|
Haemer GG, Vaidya M, Collins CM, Sodickson DK, Wiggins GC, Lattanzi R. Approaching ultimate intrinsic specific absorption rate in radiofrequency shimming using high-permittivity materials at 7 Tesla. Magn Reson Med 2017; 80:391-399. [PMID: 29193307 DOI: 10.1002/mrm.27022] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Revised: 10/18/2017] [Accepted: 10/31/2017] [Indexed: 11/07/2022]
Abstract
PURPOSE The aim of this study was to evaluate the effect of integrated high-permittivity materials (HPMs) on excitation homogeneity and global specific absorption rate (SAR) for transmit arrays at 7T. METHODS A rapid electrodynamic simulation framework was used to calculate L-curves associated with excitation of a uniform 2D profile in a dielectric sphere. We used ultimate intrinsic SAR as an absolute performance reference to compare different transmit arrays in the presence and absence of a layer of HPM. We investigated the optimal permittivity for the HPM as a function of its thickness, the sample size, and the number of array elements. RESULTS Adding a layer of HPM can improve the performance of a 24-element array to match that of a 48-element array without HPM, whereas a 48-element array with HPM can perform as well as a 64-element array without HPM. Optimal relative permittivity values changed based on sample and coil geometry, but were always within a range obtainable with readily available materials (εr = 100-200). CONCLUSION Integration of HPMs could be a practical method to improve RF shimming performance, alternative to increasing the number of coils. The proposed simulation framework could be used to explore the design of novel transmit arrays for head imaging at ultra-high field strength. Magn Reson Med 80:391-399, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Gillian G Haemer
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA
| | - Manushka Vaidya
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA
| | - Christopher M Collins
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA
| | - Daniel K Sodickson
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA
| | - Graham C Wiggins
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA
| | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA
| |
Collapse
|
38
|
Rispoli JV, Wilcox MD, By S, Wright SM, McDougall MP. Effects of coplanar shielding for high field MRI. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2017; 2016:6250-6253. [PMID: 28269680 DOI: 10.1109/embc.2016.7592157] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
This work investigates the efficacy of "coplanar shielding," in which copper shields are oriented concentric and coplanar to the RF coils rather than implemented as a full ground plane behind them. Following FDTD simulations to determine optimal shielding parameters, two coil geometries were constructed: a circular loop surface coil and a half-volume five-element receive array. Each was evaluated using bench measurements with and without coplanar shielding. Imaging, including accelerated SENSE imaging, was performed with the shielded and unshielded receive arrays on a whole-body 7T scanner. Results from modeled and fabricated coils showed good agreement with improvements in Q factors for all cases. Imaging showed substantial improvements in SNR and g-factors for the coplanar shielded array.
Collapse
|
39
|
Ivanov D, Gardumi A, Haast RA, Pfeuffer J, Poser BA, Uludağ K. Comparison of 3 T and 7 T ASL techniques for concurrent functional perfusion and BOLD studies. Neuroimage 2017; 156:363-376. [DOI: 10.1016/j.neuroimage.2017.05.038] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 05/17/2017] [Accepted: 05/17/2017] [Indexed: 02/04/2023] Open
|
40
|
Henning A. Proton and multinuclear magnetic resonance spectroscopy in the human brain at ultra-high field strength: A review. Neuroimage 2017; 168:181-198. [PMID: 28712992 DOI: 10.1016/j.neuroimage.2017.07.017] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 06/27/2017] [Accepted: 07/10/2017] [Indexed: 12/11/2022] Open
Abstract
Magnetic Resonance Spectroscopy (MRS) allows for a non-invasive and non-ionizing determination of in vivo tissue concentrations and metabolic turn-over rates of more than 20 metabolites and compounds in the central nervous system of humans. The aim of this review is to give a comprehensive overview about the advantages, challenges and advances of ultra-high field MRS with regard to methodological development, discoveries and applications from its beginnings around 15 years ago up to the current state. The review is limited to human brain and spinal cord application at field strength of 7T and 9.4T and includes all relevant nuclei (1H, 31P, 13C).
Collapse
Affiliation(s)
- Anke Henning
- Max Plank Institute for Biological Cybernetics, Tübingen, Germany; Institute of Physics, Ernst-Moritz-Arndt University, Greifswald, Germany.
| |
Collapse
|
41
|
Bilgic B, Ye H, Wald LL, Setsompop K. Simultaneous Time Interleaved MultiSlice (STIMS) for Rapid Susceptibility Weighted acquisition. Neuroimage 2017; 155:577-586. [PMID: 28435102 DOI: 10.1016/j.neuroimage.2017.04.036] [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: 01/23/2017] [Revised: 04/14/2017] [Accepted: 04/15/2017] [Indexed: 01/30/2023] Open
Abstract
T2* weighted 3D Gradient Echo (GRE) acquisition is the main sequence used for Susceptibility Weighted Imaging (SWI) and Quantitative Susceptibility Mapping (QSM). These applications require a long echo time (TE) to build up phase contrast, requiring a long repetition time (TR), and leading to excessively lengthy scans. The long TE acquisition creates a significant amount of unused time within each TR, which can be utilized for either multi-echo sampling or additional image encoding with the echo-shift technique. The latter leads to significant saving in acquisition time while retaining the desired phase and T2* contrast. In this work, we introduce the Simultaneous Time Interleaved MultiSlice (STIMS) echo-shift technique, which mitigates slab boundary artifacts by interleaving comb-shaped slice groups with Simultaneous MultiSlice (SMS) excitation. This enjoys the same SNR benefit of 3D signal averaging as previously introduced multi-slab version, where each slab group is sub-resolved with kz phase encoding. Further, we combine SMS echo-shift with Compressed Sensing (CS) Wave acceleration, which enhances Wave-CAIPI acquisition/reconstruction with random undersampling and sparsity prior. STIMS and CS-Wave combination thus yields up to 45-fold acceleration over conventional full encoding, allowing a 15sec full-brain acquisition with 1.5 mm isotropic resolution at long TE of 39 ms at 3T. In addition to utilizing empty sequence time due to long TE, STIMS is a general concept that could exploit gaps due to e.g. inversion modules in magnetization-prepared rapid gradient-echo (MPRAGE) and fluid attenuated inversion recovery (FLAIR) sequences.
Collapse
Affiliation(s)
- Berkin Bilgic
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA.
| | - Huihui Ye
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, Zhejiang, China; Center for Brain Imaging Science and Technology, Key Laboratory for Biomedical Engineering of Ministry of Education, College of Biomedical Engineering & Instrument Science, Zhejiang University, Hangzhou, Zhejiang, China
| | - Lawrence L Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA; Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, USA
| | - Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA; Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, USA
| |
Collapse
|
42
|
Diffusion MRI of the human brain at ultra-high field (UHF): A review. Neuroimage 2017; 168:172-180. [PMID: 28428047 DOI: 10.1016/j.neuroimage.2017.04.037] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Revised: 04/14/2017] [Accepted: 04/15/2017] [Indexed: 11/20/2022] Open
Abstract
The continued drive towards MRI scanners operating at increasingly higher main magnetic fields is primarily motivated by the maxim that more teslas mean more signal and lead to better images. This promise of increased signal, which cannot easily be achieved in other ways, encourages efforts to overcome the inextricable technical challenges which accompany this endeavor. Unlike for many applications, however, diffusion imaging is not currently able to directly reap these potential signal gains - at the time of writing it seems fair to say that, for matched gradient and RF hardware, the majority of diffusion images acquired at 7T, while comparable in quality to those achievable at 3T, do not demonstrate a clear advantage over what can be obtained at lower field. This does not mean that diffusion imaging at UHF is not a worthwhile pursuit - but more a reflection of the fact that the associated challenges are manifold - and converting the potential of higher field strengths into 'better' diffusion imaging is by no means a straightforward task. This article attempts to summarize the specific reasons that make diffusion imaging at UHF more complicated than one might expect, and to highlight the range of developments that have already been made which have enabled diffusion images of excellent quality to be acquired at 7T.
Collapse
|
43
|
Saito K, Tajima Y, Harada TL. Diffusion-weighted imaging of the liver: Current applications. World J Radiol 2016; 8:857-867. [PMID: 27928467 PMCID: PMC5120245 DOI: 10.4329/wjr.v8.i11.857] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Revised: 08/10/2016] [Accepted: 10/24/2016] [Indexed: 02/06/2023] Open
Abstract
Diffusion-weighted imaging (DWI) of the liver can be performed using most commercially available machines and is currently accepted in routine sequence. This sequence has some potential as an imaging biomarker for fibrosis, tumor detection/characterization, and following/predicting therapy. To improve reliability including accuracy and reproducibility, researchers have validated this new technique in terms of image acquisition, data sampling, and analysis. The added value of DWI in contrast-enhanced magnetic resonance imaging was established in the detection of malignant liver lesions. However, some limitations remain in terms of lesion characterization and fibrosis detection. Furthermore, the methodologies of image acquisition and data analysis have been inconsistent. Therefore, researchers should make every effort to not only improve accuracy and reproducibility but also standardize imaging parameters.
Collapse
|
44
|
T Vu A, Jamison K, Glasser MF, Smith SM, Coalson T, Moeller S, Auerbach EJ, Uğurbil K, Yacoub E. Tradeoffs in pushing the spatial resolution of fMRI for the 7T Human Connectome Project. Neuroimage 2016; 154:23-32. [PMID: 27894889 DOI: 10.1016/j.neuroimage.2016.11.049] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 11/07/2016] [Accepted: 11/19/2016] [Indexed: 11/28/2022] Open
Abstract
Whole-brain functional magnetic resonance imaging (fMRI), in conjunction with multiband acceleration, has played an important role in mapping the functional connectivity throughout the entire brain with both high temporal and spatial resolution. Ultrahigh magnetic field strengths (7T and above) allow functional imaging with even higher functional contrast-to-noise ratios for improved spatial resolution and specificity compared to traditional field strengths (1.5T and 3T). High-resolution 7T fMRI, however, has primarily been constrained to smaller brain regions given the amount of time it takes to acquire the number of slices necessary for high resolution whole brain imaging. Here we evaluate a range of whole-brain high-resolution resting state fMRI protocols (0.9, 1.25, 1.5, 1.6 and 2mm isotropic voxels) at 7T, obtained with both in-plane and slice acceleration parallel imaging techniques to maintain the temporal resolution and brain coverage typically acquired at 3T. Using the processing pipeline developed by the Human Connectome Project, we demonstrate that high resolution images acquired at 7T provide increased functional contrast to noise ratios with significantly less partial volume effects and more distinct spatial features, potentially allowing for robust individual subject parcellations and descriptions of fine-scaled patterns, such as visuotopic organization.
Collapse
Affiliation(s)
- An T Vu
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA; Helen Wills Institute for Neuroscience, University of California, Berkeley, CA, USA; Advanced MRI Technologies, Sebastopol, CA, USA.
| | - Keith Jamison
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Matthew F Glasser
- Washington University School of Medicine, Washington University, St. Louis, MO, USA
| | - Stephen M Smith
- FMRIB (Oxford Centre for Functional MRI of the Brain), Oxford University, Oxford, UK
| | - Timothy Coalson
- Washington University School of Medicine, Washington University, St. Louis, MO, USA
| | - Steen Moeller
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Edward J Auerbach
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Kamil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Essa Yacoub
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| |
Collapse
|
45
|
Padormo F, Beqiri A, Hajnal JV, Malik SJ. Parallel transmission for ultrahigh-field imaging. NMR IN BIOMEDICINE 2016; 29:1145-61. [PMID: 25989904 PMCID: PMC4995736 DOI: 10.1002/nbm.3313] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Revised: 03/27/2015] [Accepted: 03/29/2015] [Indexed: 05/24/2023]
Abstract
The development of MRI systems operating at or above 7 T has provided researchers with a new window into the human body, yielding improved imaging speed, resolution and signal-to-noise ratio. In order to fully realise the potential of ultrahigh-field MRI, a range of technical hurdles must be overcome. The non-uniformity of the transmit field is one of such issues, as it leads to non-uniform images with spatially varying contrast. Parallel transmission (i.e. the use of multiple independent transmission channels) provides previously unavailable degrees of freedom that allow full spatial and temporal control of the radiofrequency (RF) fields. This review discusses the many ways in which these degrees of freedom can be used, ranging from making more uniform transmit fields to the design of subject-tailored RF pulses for both uniform excitation and spatial selection, and also the control of the specific absorption rate. © 2015 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.
Collapse
Affiliation(s)
- Francesco Padormo
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Arian Beqiri
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Joseph V Hajnal
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
- Centre for the Developing Brain, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| | - Shaihan J Malik
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St Thomas' Hospital, London, UK
| |
Collapse
|
46
|
Setsompop K, Feinberg DA, Polimeni JR. Rapid brain MRI acquisition techniques at ultra-high fields. NMR IN BIOMEDICINE 2016; 29:1198-221. [PMID: 26835884 PMCID: PMC5245168 DOI: 10.1002/nbm.3478] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 11/28/2015] [Accepted: 12/02/2015] [Indexed: 05/04/2023]
Abstract
Ultra-high-field MRI provides large increases in signal-to-noise ratio (SNR) as well as enhancement of several contrast mechanisms in both structural and functional imaging. Combined, these gains result in a substantial boost in contrast-to-noise ratio that can be exploited for higher-spatial-resolution imaging to extract finer-scale information about the brain. With increased spatial resolution, however, there is a concurrent increased image-encoding burden that can cause unacceptably long scan times for structural imaging and slow temporal sampling of the hemodynamic response in functional MRI - particularly when whole-brain imaging is desired. To address this issue, new directions of imaging technology development - such as the move from conventional 2D slice-by-slice imaging to more efficient simultaneous multislice (SMS) or multiband imaging (which can be viewed as "pseudo-3D" encoding) as well as full 3D imaging - have provided dramatic improvements in acquisition speed. Such imaging paradigms provide higher SNR efficiency as well as improved encoding efficiency. Moreover, SMS and 3D imaging can make better use of coil sensitivity information in multichannel receiver arrays used for parallel imaging acquisitions through controlled aliasing in multiple spatial directions. This has enabled unprecedented acceleration factors of an order of magnitude or higher in these imaging acquisition schemes, with low image artifact levels and high SNR. Here we review the latest developments of SMS and 3D imaging methods and related technologies at ultra-high field for rapid high-resolution functional and structural imaging of the brain. Copyright © 2016 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- Kawin Setsompop
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - David A. Feinberg
- Helen Wills Institute for Neuroscience, University of California, Berkeley, CA, USA
- Advanced MRI Technologies, Sebastopol, CA, USA
| | - Jonathan R. Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
| |
Collapse
|
47
|
Strasser B, Považan M, Hangel G, Hingerl L, Chmelik M, Gruber S, Trattnig S, Bogner W. (2 + 1)D-CAIPIRINHA accelerated MR spectroscopic imaging of the brain at 7T. Magn Reson Med 2016; 78:429-440. [PMID: 27548836 PMCID: PMC5535010 DOI: 10.1002/mrm.26386] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Revised: 07/25/2016] [Accepted: 07/27/2016] [Indexed: 12/15/2022]
Abstract
Purpose To compare a new parallel imaging (PI) method for multislice proton magnetic resonance spectroscopic imaging (1H‐MRSI), termed (2 + 1)D‐CAIPIRINHA, with two standard PI methods: 2D‐GRAPPA and 2D‐CAIPIRINHA at 7 Tesla (T). Methods (2 + 1)D‐CAIPIRINHA is a combination of 2D‐CAIPIRINHA and slice‐CAIPIRINHA. Eight healthy volunteers were measured on a 7T MR scanner using a 32‐channel head coil. The best undersampling patterns were estimated for all three PI methods. The artifact powers, g‐factors, Cramér–Rao lower bounds (CRLB), and root mean square errors (RMSE) were compared quantitatively among the three PI methods. Metabolic maps and spectra were compared qualitatively. Results (2 + 1)D‐CAIPIRINHA allows acceleration in three spatial dimensions in contrast to 2D‐GRAPPA and 2D‐CAIPIRINHA. Thus, this sequence significantly decreased the RMSE of the metabolic maps by 12.1 and 6.9%, on average, for 4 < R < 11, compared with 2D‐GRAPPA and 2D‐CAIPIRINHA, respectively. The artifact power was 22.6 and 8.4% lower, and the CRLB were 3.4 and 0.6% lower, respectively. Conclusion (2 + 1)‐CAIPIRINHA can be implemented for multislice MRSI in the brain, enabling higher accelerations than possible with two‐dimensional (2D) parallel imaging methods. An eight‐fold acceleration was still feasible in vivo with negligible PI artifacts with lipid decontamination, thus decreasing the measurement time from 120 to 15 min for a 64 × 64 × 4 matrix. Magn Reson Med 78:429–440, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- B Strasser
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - M Považan
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.,Christian Doppler Laboratory for Clinical Molecular MR Imaging, Medical University of Vienna, Vienna, Austria
| | - G Hangel
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - L Hingerl
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - M Chmelik
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.,Christian Doppler Laboratory for Clinical Molecular MR Imaging, Medical University of Vienna, Vienna, Austria
| | - S Gruber
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - S Trattnig
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.,Christian Doppler Laboratory for Clinical Molecular MR Imaging, Medical University of Vienna, Vienna, Austria
| | - W Bogner
- MRCE, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
48
|
Schmidt R, Webb A. Improvements in RF Shimming in High Field MRI Using High Permittivity Materials With Low Order Pre-Fractal Geometries. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:1837-1844. [PMID: 26890643 DOI: 10.1109/tmi.2016.2531120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Ultra-high field MRI is an area of great interest for clinical research and basic science due to the increased signal-to-noise, spatial resolution and magnetic-susceptibility-based contrast. However, the fact that the electromagnetic wavelength in tissue is comparable to the relevant body dimensions means that the uniformity of the excitation field is much poorer than at lower field strengths. In addition to techniques such as transmit arrays, one simple but effective method to counteract this effect is to use high permittivity "pads". Very high permittivities enable thinner, flexible pads to be used, but the limiting factor is wavelength effects within the pads themselves, which can lead to image artifacts. So far, all studies have used simple continuous rectangular/circular pad geometries. In this work we investigate how the wavelength effects can be partially mitigated utilizing shaped pad with holes. Several arrangements have been simulated, including low order pre-fractal geometries, which maintain the overall coverage of the pad, but can provide better image homogeneity in the region of interest or higher sensitivity depending on the setup. Experimental data in the form of in vivo human images at 7T were acquired to validate the simulation results.
Collapse
|
49
|
Budinger TF, Bird MD, Frydman L, Long JR, Mareci TH, Rooney WD, Rosen B, Schenck JF, Schepkin VD, Sherry AD, Sodickson DK, Springer CS, Thulborn KR, Uğurbil K, Wald LL. Toward 20 T magnetic resonance for human brain studies: opportunities for discovery and neuroscience rationale. MAGMA (NEW YORK, N.Y.) 2016; 29:617-39. [PMID: 27194154 PMCID: PMC5538368 DOI: 10.1007/s10334-016-0561-4] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Revised: 04/06/2016] [Accepted: 04/11/2016] [Indexed: 12/16/2022]
Abstract
An initiative to design and build magnetic resonance imaging (MRI) and spectroscopy (MRS) instruments at 14 T and beyond to 20 T has been underway since 2012. This initiative has been supported by 22 interested participants from the USA and Europe, of which 15 are authors of this review. Advances in high temperature superconductor materials, advances in cryocooling engineering, prospects for non-persistent mode stable magnets, and experiences gained from large-bore, high-field magnet engineering for the nuclear fusion endeavors support the feasibility of a human brain MRI and MRS system with 1 ppm homogeneity over at least a 16-cm diameter volume and a bore size of 68 cm. Twelve neuroscience opportunities are presented as well as an analysis of the biophysical and physiological effects to be investigated before exposing human subjects to the high fields of 14 T and beyond.
Collapse
Affiliation(s)
- Thomas F Budinger
- Lawrence Berkeley National Laboratory, University of California, Berkeley, CA, USA.
| | - Mark D Bird
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - Lucio Frydman
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
- Weizmann Institute, Rehovot, Israel
| | - Joanna R Long
- McKnight Brain Institute, University of Florida, Gainesville, FL, USA
| | - Thomas H Mareci
- McKnight Brain Institute, University of Florida, Gainesville, FL, USA
| | | | - Bruce Rosen
- Massachusetts General Hospital, Harvard Medical School, Harvard, MA, USA
| | - John F Schenck
- General Electric Corporate Research, Schenectady, NY, USA
| | - Victor D Schepkin
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - A Dean Sherry
- University of Texas Southwestern Medical Center, Dallas, TX, USA
| | | | | | | | | | - Lawrence L Wald
- Massachusetts General Hospital, Harvard Medical School, Harvard, MA, USA
| |
Collapse
|
50
|
Gilbert KM, Gati JS, Barker K, Everling S, Menon RS. Optimized parallel transmit and receive radiofrequency coil for ultrahigh-field MRI of monkeys. Neuroimage 2016; 125:153-161. [DOI: 10.1016/j.neuroimage.2015.10.048] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Revised: 10/08/2015] [Accepted: 10/19/2015] [Indexed: 12/14/2022] Open
|