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Budé LMI, Steensma BR, Zivkovic I, Raaijmakers AJE. The coax monopole antenna: A flexible end-fed antenna for ultrahigh field transmit/receive arrays. Magn Reson Med 2024; 92:361-373. [PMID: 38376359 DOI: 10.1002/mrm.30036] [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: 08/01/2023] [Revised: 01/15/2024] [Accepted: 01/15/2024] [Indexed: 02/21/2024]
Abstract
PURPOSE The coax monopole antenna is presented for body imaging at 7 T. The antenna is fed at one end, eliminating the possibility of cable-coil coupling and simplifying cable routing. Additionally, its flexibility improves loading to the subject. METHODS Like the coax dipole antenna, an interruption in the shield of the coaxial cable allows the current to extend to the outside of the shield, generating a B1 + field. Matching is achieved using a single inductor at the distal side, and a cable trap enforces the desired antenna length. Finite difference time domain simulations are employed to optimize the design parameters. Phantom measurements are conducted to determine the antenna's B1 + efficiency and to find the S-parameters in straight and bent positions. Eight-channel simulations and measurements are performed for prostate imaging. RESULTS The optimal configuration is a length of 360 mm with a gap position of 40 mm. Simulation data show higher B1 + levels for the coax monopole (20% in the prostate), albeit with a 5% lower specific absorbance rate efficiency, compared to the fractionated dipole antenna. The S11 of the coax monopole exhibits remarkable robustness to loading changes. In vivo prostate imaging demonstrates B1 + levels of 10-14 μT with an input power of 8 × 800 W, which is comparable to the fractionated dipole antenna. High-quality images and acceptable coupling levels were achieved. CONCLUSION The coax monopole is a novel, flexible antenna for body imaging at 7 T. Its simple design incorporates a single inductor at the distal side to achieve matching, and one-sided feeding greatly simplifies cable routing.
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Affiliation(s)
- Lyanne M I Budé
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Bart R Steensma
- Division of Imaging and Oncology, UMC Utrecht, Utrecht, The Netherlands
| | - Irena Zivkovic
- Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Alexander J E Raaijmakers
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- Division of Imaging and Oncology, UMC Utrecht, Utrecht, The Netherlands
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2
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Schmidt S, He X, Metzger GJ. Universal modes: Calibration-free time-interleaved acquisition of modes. Magn Reson Med 2024; 92:43-56. [PMID: 38303151 PMCID: PMC11055664 DOI: 10.1002/mrm.30032] [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: 09/12/2023] [Revised: 12/11/2023] [Accepted: 01/15/2024] [Indexed: 02/03/2024]
Abstract
PURPOSE To introduce universal modes by applying the universal pulse concept to time-interleaved acquisition of modes (TIAMO), thereby achieving calibration-freeB 1 + $$ {B}_1^{+} $$ inhomogeneity mitigation for body imaging at ultra-high fields. METHODS Two databases of different RF arrays were used to demonstrate the feasibility of universal modes. The first comprised 31 cardiac in vivo data sets acquired at 7T while the second consisted of 6 simulated 10.5T pelvic data sets. Subject-specific solutions and universal modes were computed and subsequently evaluated alongside predefined default modes. For the cardiac database, subdivision into subpopulations was investigated. The optimization was performed using least-squares (LS) TIAMO and acquisition modes optimized for refocused echoes (AMORE). Finally, universal modes based on simulated pelvis data were applied in vivo at 10.5T. RESULTS In all studied cases, the universal modes yield improvements over the predefined default modes of up to 51% (cardiac) and 30% (pelvic) in terms of median excitation error when using two modes. The subpopulation-specific cardiac solutions revealed a further improvement of universal modes at the expense of increased errors when applied outside the appropriate subpopulation. Direct application of simulation-based universal modes in vivo resulted in up to a 14% reduction in excitation error compared to default modes and up to a 34% reduction in peak 10 g local specific absorption rate (SAR) compared to subject-specific solutions. CONCLUSIONS Universal modes are feasible for calibration-freeB 1 + $$ {B}_1^{+} $$ inhomogeneity mitigation at ultra-high fields. In addition, simulation-based solutions can be applied directly in vivo, eliminating the need for large in vivo databases.
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Affiliation(s)
- Simon Schmidt
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Gregory J. Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
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3
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Martinez Luque E, Liu Z, Sung D, Goldberg RM, Agarwal R, Bhattacharya A, Ahmed NS, Allen JW, Fleischer CC. An Update on MR Spectroscopy in Cancer Management: Advances in Instrumentation, Acquisition, and Analysis. Radiol Imaging Cancer 2024; 6:e230101. [PMID: 38578207 PMCID: PMC11148681 DOI: 10.1148/rycan.230101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 02/06/2024] [Accepted: 02/15/2024] [Indexed: 04/06/2024]
Abstract
MR spectroscopy (MRS) is a noninvasive imaging method enabling chemical and molecular profiling of tissues in a localized, multiplexed, and nonionizing manner. As metabolic reprogramming is a hallmark of cancer, MRS provides valuable metabolic and molecular information for cancer diagnosis, prognosis, treatment monitoring, and patient management. This review provides an update on the use of MRS for clinical cancer management. The first section includes an overview of the principles of MRS, current methods, and conventional metabolites of interest. The remainder of the review is focused on three key areas: advances in instrumentation, specifically ultrahigh-field-strength MRI scanners and hybrid systems; emerging methods for acquisition, including deuterium imaging, hyperpolarized carbon 13 MRI and MRS, chemical exchange saturation transfer, diffusion-weighted MRS, MR fingerprinting, and fast acquisition; and analysis aided by artificial intelligence. The review concludes with future recommendations to facilitate routine use of MRS in cancer management. Keywords: MR Spectroscopy, Spectroscopic Imaging, Molecular Imaging in Oncology, Metabolic Reprogramming, Clinical Cancer Management © RSNA, 2024.
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Affiliation(s)
- Eva Martinez Luque
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Zexuan Liu
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Dongsuk Sung
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Rachel M. Goldberg
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Rishab Agarwal
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Aditya Bhattacharya
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Nadine S. Ahmed
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Jason W. Allen
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
| | - Candace C. Fleischer
- From the Departments of Radiology and Imaging Sciences (E.M.L., Z.L.,
D.S., J.W.A., C.C.F.) and Neurology (J.W.A.), Emory University School of
Medicine, Atlanta, Ga; Department of Biomedical Engineering (E.M.L., Z.L., D.S.,
J.W.A., C.C.F.), Georgia Institute of Technology and Emory University, Atlanta,
Ga; College of Arts and Sciences, Emory University, Atlanta, Ga (R.M.G.); and
College of Business (R.A.) and College of Sciences (A.B., N.S.A.), Georgia
Institute of Technology, Atlanta, Georgia
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Williams SN, McElhinney P, Gunamony S. Ultra-high field MRI: parallel-transmit arrays and RF pulse design. Phys Med Biol 2023; 68. [PMID: 36410046 DOI: 10.1088/1361-6560/aca4b7] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Accepted: 11/21/2022] [Indexed: 11/22/2022]
Abstract
This paper reviews the field of multiple or parallel radiofrequency (RF) transmission for magnetic resonance imaging (MRI). Currently the use of ultra-high field (UHF) MRI at 7 tesla and above is gaining popularity, yet faces challenges with non-uniformity of the RF field and higher RF power deposition. Since its introduction in the early 2000s, parallel transmission (pTx) has been recognized as a powerful tool for accelerating spatially selective RF pulses and combating the challenges associated with RF inhomogeneity at UHF. We provide a survey of the types of dedicated RF coils used commonly for pTx and the important modeling of the coil behavior by electromagnetic (EM) field simulations. We also discuss the additional safety considerations involved with pTx such as the specific absorption rate (SAR) and how to manage them. We then describe the application of pTx with RF pulse design, including a practical guide to popular methods. Finally, we conclude with a description of the current and future prospects for pTx, particularly its potential for routine clinical use.
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Affiliation(s)
- Sydney N Williams
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom
| | - Paul McElhinney
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom
| | - Shajan Gunamony
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom.,MR CoilTech Limited, Glasgow, United Kingdom
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5
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Odehnalová E, Valíková L, Caluori G, Kulík T, Římalová V, Jadczyk T, Dražanová E, Pavlova I, Pešl M, Kubeš V, Stárek Z. Comparison of gross pathology inspection and 9.4 T magnetic resonance imaging in the evaluation of radiofrequency ablation lesions in the left ventricle of the swine heart. Front Physiol 2022; 13:834328. [PMID: 36338496 PMCID: PMC9626654 DOI: 10.3389/fphys.2022.834328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Accepted: 10/03/2022] [Indexed: 11/15/2022] Open
Abstract
Aims: Gross pathology inspection (patho) is the gold standard for the morphological evaluation of focal myocardial pathology. Examination with 9.4 T magnetic resonance imaging (MRI) is a new method for very accurate display of myocardial pathology. The aim of this study was to demonstrate that lesions can be measured on high-resolution MRI images with the same accuracy as on pathological sections and compare these two methods for the evaluation of radiofrequency (RF) ablation lesion dimensions in swine heart tissue during animal experiment. Methods: Ten pigs underwent radiofrequency ablations in the left ventricle during animal experiment. After animal euthanasia, hearts were explanted, flushed with ice-cold cardioplegic solution to relax the whole myocardium, fixed in 10% formaldehyde and scanned with a 9.4 T magnetic resonance system. Anatomical images were processed using ImageJ software. Subsequently, the hearts were sliced, slices were photographed and measured in ImageJ software. Different dimensions and volumes were compared. Results: The results of both methods were statistically compared. Depth by MRI was 8.771 ± 2.595 mm and by patho 9.008 ± 2.823 mm; p = 0.198. Width was 10.802 ± 2.724 mm by MRI and 11.125 ± 2.801 mm by patho; p = 0.049. Estuary was 2.006 ± 0.867 mm by MRI and 2.001 ± 0.872 mm by patho; p = 0.953. The depth at the maximum diameter was 4.734 ± 1.532 mm on MRI and 4.783 ± 1.648 mm from the patho; p = 0.858. The volumes of the lesions calculated using a formula were 315.973 ± 257.673 mm3 for MRI and 355.726 ± 255.860 mm3 for patho; p = 0.104. Volume directly measured from MRI with the “point-by-point” method was 671.702 ± 362.299 mm3. Conclusion: Measurements obtained from gross pathology inspection and MRI are fully comparable. The advantage of MRI is that it is a non-destructive method enabling repeated measurements in all possible anatomical projections.
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Affiliation(s)
- Eva Odehnalová
- Interventional Cardiac Electrophysiology Group, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
| | - Lucia Valíková
- Interventional Cardiac Electrophysiology Group, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
| | - Guido Caluori
- Interventional Cardiac Electrophysiology Group, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
- Nanotechnology, CEITEC Masaryk University, Brno, Czech
- IHU LIRYC, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Pessac, France
- University Bordeaux, INSERM, Cardiothoracic Research Center of Bordeaux, Pessac, France
| | - Tomáš Kulík
- Interventional Cardiac Electrophysiology Group, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
- 1st Department of Internal Medicine—Cardioangiology, St. Anne’s University Hospital Brno, Brno, Czech
| | - Veronika Římalová
- Biostatistics, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
| | - Tomasz Jadczyk
- Interventional Cardiac Electrophysiology Group, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
- Division of Cardiology and Structural Heart Diseases, Medical University of Silesia, Katowice, Poland
| | - Eva Dražanová
- Institute of Scientific Instruments of the Czech Academy of Sciences, Brno, Czech
| | - Iveta Pavlova
- Institute of Scientific Instruments of the Czech Academy of Sciences, Brno, Czech
| | - Martin Pešl
- Interventional Cardiac Electrophysiology Group, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
- Nanotechnology, CEITEC Masaryk University, Brno, Czech
- Department of Biology, Faculty of Medicine Masaryk University Brno, Brno, Czech
| | - Václav Kubeš
- Department of Pathology, University Hospital Brno, Brno, Czech
| | - Zdeněk Stárek
- Interventional Cardiac Electrophysiology Group, International Clinical Research Center, St. Anne’s University Hospital Brno, Brno, Czech
- 1st Department of Internal Medicine—Cardioangiology, St. Anne’s University Hospital Brno, Brno, Czech
- *Correspondence: Zdeněk Stárek,
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Orzada S, Akash S, Fiedler TM, Kratzer FJ, Ladd ME. An investigation into the dependence of virtual observation point‐based specific absorption rate calculation complexity on number of channels. Magn Reson Med 2022; 89:469-476. [DOI: 10.1002/mrm.29434] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 07/13/2022] [Accepted: 08/10/2022] [Indexed: 11/11/2022]
Affiliation(s)
- Stephan Orzada
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
- Erwin L. Hahn Institute for MRI University Duisburg‐Essen Essen Germany
- Radiation Oncology University Hospital Heidelberg Heidelberg Germany
| | - Safi Akash
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Thomas M. Fiedler
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Fabian J. Kratzer
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Mark E. Ladd
- Medical Physics in Radiology German Cancer Research Center (DKFZ) Heidelberg Germany
- Erwin L. Hahn Institute for MRI University Duisburg‐Essen Essen Germany
- Faculty of Physics and Astronomy Heidelberg University Heidelberg Germany
- Faculty of Medicine Heidelberg University Heidelberg Germany
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7
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He X, Schmidt S, Zbýň Š, Haluptzok T, Moeller S, Metzger GJ. Improved TSE imaging at ultrahigh field using nonlocalized efficiency RF shimming and acquisition modes optimized for refocused echoes (AMORE). Magn Reson Med 2022; 88:1702-1719. [PMID: 35692053 PMCID: PMC9339473 DOI: 10.1002/mrm.29318] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 05/07/2022] [Accepted: 05/10/2022] [Indexed: 11/06/2022]
Abstract
Purpose To develop and evaluate a novel RF shimming optimization strategy tailored to improve the transmit efficiency in turbo spin echo imaging when performing time‐interleaved acquisition of modes (TIAMO) at ultrahigh fields. Theory and Methods A nonlocalized efficiency shimming cost function is proposed and extended to perform TIAMO using acquisition modes optimized for refocused echoes (AMORE). The nonlocalized efficiency shimming was demonstrated in brain and knee imaging at 7 Tesla. Phantom and in vivo torso imaging studies were performed to compare the performance between AMORE and previously proposed TIAMO mode optimizations with and without localized constraints in turbo spin echo and gradient echo acquisitions. Results The proposed nonlocalized efficiency RF shimming produced a circularly polarized‐like field with fewer signal dropouts in the brain and knee. For larger targets, AMORE was used and required a significantly lower transmitter voltage to produce a similar contrast to existing TIAMO mode design approaches for turbo spin echo as well as gradient echo acquisitions. In vivo, AMORE effectively reduced signal dropout in the interior torso while providing more uniform contrast with reduced transmit power. A local constraint further improved performance for a target region while maintaining performance in the larger FOV. Conclusion AMORE based on the presented nonlocalized efficiency shimming cost function demonstrated improved contrast and SNR uniformity as well as increased transmit efficiency for both gradient echo and turbo spin echo acquisitions. Click here for author‐reader discussions
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Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Simon Schmidt
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Štefan Zbýň
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Tobey Haluptzok
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Steen Moeller
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
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8
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Tenbergen CJA, Metzger GJ, Scheenen TWJ. Ultra-high-field MR in Prostate cancer: Feasibility and Potential. MAGNETIC RESONANCE MATERIALS IN PHYSICS, BIOLOGY AND MEDICINE 2022; 35:631-644. [PMID: 35579785 PMCID: PMC9113077 DOI: 10.1007/s10334-022-01013-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 03/31/2022] [Accepted: 04/07/2022] [Indexed: 02/07/2023]
Abstract
Multiparametric MRI of the prostate at clinical magnetic field strengths (1.5/3 Tesla) has emerged as a reliable noninvasive imaging modality for identifying clinically significant cancer, enabling selective sampling of high-risk regions with MRI-targeted biopsies, and enabling minimally invasive focal treatment options. With increased sensitivity and spectral resolution, ultra-high-field (UHF) MRI (≥ 7 Tesla) holds the promise of imaging and spectroscopy of the prostate with unprecedented detail. However, exploiting the advantages of ultra-high magnetic field is challenging due to inhomogeneity of the radiofrequency field and high local specific absorption rates, raising local heating in the body as a safety concern. In this work, we review various coil designs and acquisition strategies to overcome these challenges and demonstrate the potential of UHF MRI in anatomical, functional and metabolic imaging of the prostate and pelvic lymph nodes. When difficulties with power deposition of many refocusing pulses are overcome and the full potential of metabolic spectroscopic imaging is used, UHF MR(S)I may aid in a better understanding of the development and progression of local prostate cancer. Together with large field-of-view and low-flip-angle anatomical 3D imaging, 7 T MRI can be used in its full strength to characterize different tumor stages and help explain the onset and spatial distribution of metastatic spread.
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Affiliation(s)
- Carlijn J A Tenbergen
- Department of Medical Imaging, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, The Netherlands.
| | - Gregory J Metzger
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, USA
| | - Tom W J Scheenen
- Department of Medical Imaging, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, The Netherlands
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany
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9
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Dietrich S, Aigner CS, Mayer J, Kolbitsch C, Schulz-Menger J, Schaeffter T, Schmitter S. Motion-compensated fat-water imaging for 3D cardiac MRI at ultra-high fields. Magn Reson Med 2022; 87:2621-2636. [PMID: 35092090 DOI: 10.1002/mrm.29144] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2021] [Revised: 11/23/2021] [Accepted: 12/14/2021] [Indexed: 12/16/2022]
Abstract
PURPOSE Respiratory motion-compensated (MC) 3D cardiac fat-water imaging at 7T. METHODS Free-breathing bipolar 3D triple-echo gradient-recalled-echo (GRE) data with radial phase-encoding (RPE) trajectory were acquired in 11 healthy volunteers (7M\4F, 21-35 years, mean: 30 years) with a wide range of body mass index (BMI; 19.9-34.0 kg/m2 ) and volunteer tailored B 1 + shimming. The bipolar-corrected triple-echo GRE-RPE data were binned into different respiratory phases (self-navigation) and were used for the estimation of non-rigid motion vector fields (MF) and respiratory resolved (RR) maps of the main magnetic field deviations (ΔB0 ). RR ΔB0 maps and MC ΔB0 maps were compared to a reference respiratory phase to assess respiration-induced changes. Subsequently, cardiac binned fat-water images were obtained using a model-based, respiratory motion-corrected image reconstruction. RESULTS The 3D cardiac fat-water imaging at 7T was successfully demonstrated. Local respiration-induced frequency shifts in MC ΔB0 maps are small compared to the chemical shifts used in the multi-peak model. Compared to the reference exhale ΔB0 map these changes are in the order of 10 Hz on average. Cardiac binned MC fat-water reconstruction reduced respiration induced blurring in the fat-water images, and flow artifacts are reduced in the end-diastolic fat-water separated images. CONCLUSION This work demonstrates the feasibility of 3D fat-water imaging at UHF for the entire human heart despite spatial and temporal B 1 + and B0 variations, as well as respiratory and cardiac motion.
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Affiliation(s)
- Sebastian Dietrich
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | | | - Johannes Mayer
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Christoph Kolbitsch
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Jeanette Schulz-Menger
- Experimental and Clinical Research Center, A Joint Cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine and HELIOS Hospital Berlin Buch, Berlin, Germany.,DZHK (German Center for Cardiovascular Research), Partner Site Berlin, Berlin, Germany.,Helios Clinics Berlin-Buch Department of Cardiology and Nephrology, Berlin, Germany
| | - Tobias Schaeffter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.,Department of Medical Engineering, Technische Universität Berlin, Germany
| | - Sebastian Schmitter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.,Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
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Destruel A, Jin J, Weber E, Li M, Engstrom C, Liu F, Crozier S. Integrated Multi-Modal Antenna With Coupled Radiating Structures (I-MARS) for 7T pTx Body MRI. IEEE TRANSACTIONS ON MEDICAL IMAGING 2022; 41:39-51. [PMID: 34370662 DOI: 10.1109/tmi.2021.3103654] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
One of the main challenges in ultra-high field whole body MRI relates to the uniformity and efficiency of the radiofrequency field. Although recent advances in the design of RF coils have demonstrated that dipole antennas have a current distribution ideally suited to 7T MRI, they are limited by low isolation and poor robustness to loading changes. Multi-layered and self-decoupled loop coils have demonstrated improved RF performance in these areas at lower field MRI but have not been adapted to dipole designs. In this work, we introduce a novel type of RF antenna consisting of integrated multi-modal antenna with coupled radiating structures (I-MARS), which use layered conductors and dielectric substrates to allow dipole and transmission line modes to co-exist on the same compact dipole-shaped structure. The proposed antenna was optimally designed for 7T MRI and compared with existing dipole antennas using numerical simulations, which showed that I-MARS had similar B1 over specific absorption rate efficiency and superior isolation and stability. Subsequently, a prototype pTx coil array was built and tested in vivo on healthy volunteers at 7T. The articulated, modular construction of the I-MARS coil array allowed it to be readily conformed across multiple body regions (hip, knee, shoulder, lumbar spine and prostate), without requiring modification of the tuning and matching of the antennas. Using RF shimming, uniform and efficient excitation was successfully achieved in the acquisition of high-resolution MR images.
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Sadeghi-Tarakameh A, Jungst S, Lanagan M, DelaBarre L, Wu X, Adriany G, Metzger GJ, Van de Moortele PF, Ugurbil K, Atalar E, Eryaman Y. A nine-channel transmit/receive array for spine imaging at 10.5 T: Introduction to a nonuniform dielectric substrate antenna. Magn Reson Med 2021; 87:2074-2088. [PMID: 34825735 DOI: 10.1002/mrm.29096] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 11/04/2021] [Accepted: 11/05/2021] [Indexed: 12/17/2022]
Abstract
PURPOSE The purpose of this study is to introduce a new antenna element with improved transmit performance, named the nonuniform dielectric substrate (NODES) antenna, for building transmit arrays at ultrahigh-field. METHODS We optimized a dipole antenna at 10.5 Tesla by maximizing the B 1 + -SAR efficiency in a phantom for a human spine target. The optimization parameters included permittivity variation in the substrate, substrate thickness, antenna length, and conductor geometry. We conducted electromagnetic simulations as well as phantom experiments to compare the transmit/receive performance of the proposed NODES antenna design with existing coil elements from the literature. RESULTS Single NODES element showed up to 18% and 30% higher B 1 + -SAR efficiency than the fractionated dipole and loop elements, respectively. The new element is substantially shorter than a commonly used dipole, which enables z-stacked array formation; it is additionally capable of providing a relatively uniform current distribution along its conductors. The nine-channel transmit/receive NODES array achieved 7.5% higher B 1 + homogeneity than a loop array with the same number of elements. Excitation with the NODES array resulted in 33% lower peak 10g-averaged SAR and required 34% lower input power than the loop array for the target anatomy of the spine. CONCLUSION In this study, we introduced a new RF coil element: the NODES antenna. NODES antenna outperformed the widely used loop and dipole elements and may provide improved transmit/receive performance for future ultrahigh field MRI applications.
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Affiliation(s)
- Alireza Sadeghi-Tarakameh
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA.,Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey.,National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey
| | - Steve Jungst
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Mike Lanagan
- Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, USA
| | - Lance DelaBarre
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Xiaoping Wu
- 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
| | - Gregory J Metzger
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | | | - Kamil Ugurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Ergin Atalar
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey.,National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey
| | - Yigitcan Eryaman
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
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12
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Abstract
Especially after the launch of 7 T, the ultrahigh magnetic field (UHF) imaging community achieved critically important strides in our understanding of the physics of radiofrequency interactions in the human body, which in turn has led to solutions for the challenges posed by such UHFs. As a result, the originally obtained poor image quality has progressed to the high-quality and high-resolution images obtained at 7 T and now at 10.5 T in the human torso. Despite these tremendous advances, work still remains to further improve the image quality and fully capitalize on the potential advantages UHF has to offer.
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13
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Terekhov M, Elabyad IA, Schreiber LM. Global optimization of default phases for parallel transmit coils for ultra-high-field cardiac MRI. PLoS One 2021; 16:e0255341. [PMID: 34358243 PMCID: PMC8346258 DOI: 10.1371/journal.pone.0255341] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 07/14/2021] [Indexed: 11/19/2022] Open
Abstract
The development of novel multiple-element transmit-receive arrays is an essential factor for improving B1+ field homogeneity in cardiac MRI at ultra-high magnetic field strength (B0 > = 7.0T). One of the key steps in the design and fine-tuning of such arrays during the development process is finding the default driving phases for individual coil elements providing the best possible homogeneity of the combined B1+-field that is achievable without (or before) subject-specific B1+-adjustment in the scanner. This task is often solved by time-consuming (brute-force) or by limited efficiency optimization methods. In this work, we propose a robust technique to find phase vectors providing optimization of the B1-homogeneity in the default setup of multiple-element transceiver arrays. The key point of the described method is the pre-selection of starting vectors for the iterative solver-based search to maximize the probability of finding a global extremum for a cost function optimizing the homogeneity of a shaped B1+-field. This strategy allows for (i) drastic reduction of the computation time in comparison to a brute-force method and (ii) finding phase vectors providing a combined B1+-field with homogeneity characteristics superior to the one provided by the random-multi-start optimization approach. The method was efficiently used for optimizing the default phase settings in the in-house-built 8Tx/16Rx arrays designed for cMRI in pigs at 7T.
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Affiliation(s)
- Maxim Terekhov
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center, University Hospital Wuerzburg, Wuerzburg, Germany
- * E-mail:
| | - Ibrahim A. Elabyad
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Laura M. Schreiber
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center, University Hospital Wuerzburg, Wuerzburg, Germany
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14
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Reiter T, Lohr D, Hock M, Ankenbrand MJ, Stefanescu MR, Kosmala A, Kaspar M, Juchem C, Terekhov M, Schreiber LM. On the way to routine cardiac MRI at 7 Tesla - a pilot study on consecutive 84 examinations. PLoS One 2021; 16:e0252797. [PMID: 34297720 PMCID: PMC8301632 DOI: 10.1371/journal.pone.0252797] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 05/23/2021] [Indexed: 11/29/2022] Open
Abstract
INTRODUCTION Cardiac magnetic resonance (CMR) at ultrahigh field (UHF) offers the potential of high resolution and fast image acquisition. Both technical and physiological challenges associated with CMR at 7T require specific hardware and pulse sequences. This study aimed to assess the current status and existing, publicly available technology regarding the potential of a clinical application of 7T CMR. METHODS Using a 7T MRI scanner and a commercially available radiofrequency coil, a total of 84 CMR examinations on 72 healthy volunteers (32 males, age 19-70 years, weight 50-103 kg) were obtained. Both electrocardiographic and acoustic triggering were employed. The data were analyzed regarding the diagnostic image quality and the influence of patient and hardware dependent factors. 50 complete short axis stacks and 35 four chamber CINE views were used for left ventricular (LV) and right ventricular (RV), mono-planar LV function, and RV fractional area change (FAC). Twenty-seven data sets included aortic flow measurements that were used to calculate stroke volumes. Subjective acceptance was obtained from all volunteers with a standardized questionnaire. RESULTS Functional analysis showed good functions of LV (mean EF 56%), RV (mean EF 59%) and RV FAC (mean FAC 52%). Flow measurements showed congruent results with both ECG and ACT triggering. No significant influence of experimental parameters on the image quality of the LV was detected. Small fractions of 5.4% of LV and 2.5% of RV segments showed a non-diagnostic image quality. The nominal flip angle significantly influenced the RV image quality. CONCLUSION The results demonstrate that already now a commercially available 7T MRI system, without major methods developments, allows for a solid morphological and functional analysis similar to the clinically established CMR routine approach. This opens the door towards combing routine CMR in patients with development of advanced 7T technology.
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Affiliation(s)
- Theresa Reiter
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
- Department of Internal Medicine I, Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - David Lohr
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Michael Hock
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Markus Johannes Ankenbrand
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Maria Roxana Stefanescu
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Aleksander Kosmala
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
- Department of Radiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Mathias Kaspar
- Department of Health Services Research, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Christoph Juchem
- Departments of Biomedical Engineering and Radiology, Columbia University, New York, New York, United States of America
| | - Maxim Terekhov
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Laura Maria Schreiber
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
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15
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Orzada S, Fiedler TM, Quick HH, Ladd ME. Post-processing algorithms for specific absorption rate compression. Magn Reson Med 2021; 86:2853-2861. [PMID: 34216047 DOI: 10.1002/mrm.28909] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 05/19/2021] [Accepted: 06/10/2021] [Indexed: 11/06/2022]
Abstract
PURPOSE Compression of local specific absorption rate (SAR) matrices is essential for enabling SAR monitoring and efficient pulse calculation in parallel transmission. Improvements in compression result in lower error margin and/or lower number of virtual observation points (VOPs). The purpose of this work is to introduce two algorithms for post-processing of already compressed VOP sets. One calculates individual overestimation matrices for the VOPs to reduce overestimation, the other identifies redundant VOPs. METHODS The first algorithm was evaluated for VOP sets calculated for three different transmit arrays with either 8 or 16 channels. For each array, two different overestimation matrices were used to generate the VOP sets. Each post-processed VOP set was evaluated using one million random excitation vectors and the results compared to the VOP set before post-processing. The second algorithm was evaluated by utilizing the same random excitation vectors and comparing the results after removal of the redundant VOPs with the results before removal to verify that these were identical. RESULTS The first algorithm reduced the mean overestimation by up to four fifths compared to the original set, while keeping the number of VOPs constant. The second algorithm decreased the number of VOPs generated by a compression with Eichfelder and Gebhardt's algorithm by more than 40% in 40% of the investigated cases and by more than 20% in 73% of the investigated cases. CONCLUSION Two post-processing algorithms are presented that enhance previously compressed VOP sets by improving the accuracy per number of VOPs.
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Affiliation(s)
- Stephan Orzada
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.,Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany.,Faculty of Medicine, University of Heidelberg, Heidelberg, Germany
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16
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He X, Auerbach EJ, Garwood M, Kobayashi N, Wu X, Metzger GJ. Parallel transmit optimized 3D composite adiabatic spectral-spatial pulse for spectroscopy. Magn Reson Med 2021; 86:17-32. [PMID: 33497006 PMCID: PMC8545499 DOI: 10.1002/mrm.28682] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 12/22/2020] [Accepted: 12/23/2020] [Indexed: 01/05/2023]
Abstract
PURPOSE To develop a 3D composite adiabatic spectral-spatial pulse for refocusing in spin-echo spectroscopy acquisitions and to compare its performance against standard acquisition methods. METHODS A 3D composite adiabatic pulse was designed by modulating a train of parallel transmit-optimized 2D subpulses with an adiabatic envelope. The spatial and spectral profiles were simulated and validated by experiments to demonstrate the feasibility of the design in both single and double spin-echo spectroscopy acquisitions. Phantom and in vivo studies were performed to evaluate the pulse performance and compared with semi-LASER with respect to localization performance, sequence timing, signal suppression, and specific absorption rate. RESULTS Simultaneous 2D spatial localization with water and lipid suppression was achieved with the designed refocusing pulse, allowing high-quality spectra to be acquired with shorter minimum TE/TR, reduced SAR, as well as adaptation to spatially varying B0 and B 1 + field inhomogeneities in both prostate and brain studies. CONCLUSION The proposed composite pulse can serve as a more SAR efficient alternative to conventional localization methods such as semi-LASER at ultrahigh field for spin echo-based spectroscopy studies. Subpulse parallel-transmit optimization provides the flexibility to manage the tradeoff among multiple design criteria to accommodate different field strengths and applications.
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Affiliation(s)
- Xiaoxuan He
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Edward J. Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Michael Garwood
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Naoharu Kobayashi
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Xiaoping Wu
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
| | - Gregory J. Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States
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17
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Fiedler TM, Orzada S, Flöser M, Rietsch SHG, Quick HH, Ladd ME, Bitz AK. Performance analysis of integrated RF microstrip transmit antenna arrays with high channel count for body imaging at 7 T. NMR IN BIOMEDICINE 2021; 34:e4515. [PMID: 33942938 DOI: 10.1002/nbm.4515] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 02/18/2021] [Accepted: 03/09/2021] [Indexed: 05/12/2023]
Abstract
The aim of the current study was to investigate the performance of integrated RF transmit arrays with high channel count consisting of meander microstrip antennas for body imaging at 7 T and to optimize the position and number of transmit elements. RF simulations using multiring antenna arrays placed behind the bore liner were performed for realistic exposure conditions for body imaging. Simulations were performed for arrays with as few as eight elements and for arrays with high channel counts of up to 48 elements. The B1+ field was evaluated regarding the degrees of freedom for RF shimming in the abdomen. Worst-case specific absorption rate (SARwc ), SAR overestimation in the matrix compression, the number of virtual observation points (VOPs) and SAR efficiency were evaluated. Constrained RF shimming was performed in differently oriented regions of interest in the body, and the deviation from a target B1+ field was evaluated. Results show that integrated multiring arrays are able to generate homogeneous B1+ field distributions for large FOVs, especially for coronal/sagittal slices, and thus enable body imaging at 7 T with a clinical workflow; however, a low duty cycle or a high SAR is required to achieve homogeneous B1+ distributions and to exploit the full potential. In conclusion, integrated arrays allow for high element counts that have high degrees of freedom for the pulse optimization but also produce high SARwc , which reduces the SAR accuracy in the VOP compression for low-SAR protocols, leading to a potential reduction in array performance. Smaller SAR overestimations can increase SAR accuracy, but lead to a high number of VOPs, which increases the computational cost for VOP evaluation and makes online SAR monitoring or pulse optimization challenging. Arrays with interleaved rings showed the best results in the study.
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Affiliation(s)
- Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Stephan Orzada
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Martina Flöser
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Stefan H G Rietsch
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany
- Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany
- Faculty of Medicine, University of Heidelberg, Heidelberg, 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
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18
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Orzada S, Fiedler TM, Quick HH, Ladd ME. Local SAR compression algorithm with improved compression, speed, and flexibility. Magn Reson Med 2021; 86:561-568. [PMID: 33634530 DOI: 10.1002/mrm.28739] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 01/12/2021] [Accepted: 01/28/2021] [Indexed: 01/07/2023]
Abstract
PURPOSE Local specific absorption rate (SAR) compression algorithms are essential for enabling online SAR monitoring in parallel transmission. A better compression resulting in a lower number of virtual observation points improves speed of SAR calculation for online supervision and pulse design. METHOD An iterative expansion of an existing algorithm presented by Lee et al is proposed in this work. The original algorithm is used within a loop, making use of the virtual observation points from the previous iteration as the starting subvolume, while decreasing the overestimation with each iteration. This algorithm is evaluated on the SAR matrices of three different simulated arrays. RESULT The number of virtual observation points is approximately halved with the new algorithm, while at the same time the compression time is reduced with speed-up factors of up to 2.5. CONCLUSION The new algorithm improves the original algorithm in terms of compression rate and speed.
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Affiliation(s)
- Stephan Orzada
- Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany
| | - Thomas M Fiedler
- Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany.,Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany.,Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany.,Faculty of Medicine, University of Heidelberg, Heidelberg, Germany
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19
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Fagan AJ, Bitz AK, Björkman-Burtscher IM, Collins CM, Kimbrell V, Raaijmakers AJ. 7T MR Safety. J Magn Reson Imaging 2021; 53:333-346. [PMID: 32830900 PMCID: PMC8170917 DOI: 10.1002/jmri.27319] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 07/21/2020] [Accepted: 07/22/2020] [Indexed: 12/11/2022] Open
Abstract
Magnetic resonance imaging and spectroscopy (MRI/MRS) at 7T represents an exciting advance in MR technology, with intriguing possibilities to enhance image spatial, spectral, and contrast resolution. To ensure the safe use of this technology while still harnessing its potential, clinical staff and researchers need to be cognizant of some safety concerns arising from the increased magnetic field strength and higher Larmor frequency. The higher static magnetic fields give rise to enhanced transient bioeffects and an increased risk of adverse incidents related to electrically conductive implants. Many technical challenges remain and the continuing rapid pace of development of 7T MRI/MRS is likely to present further challenges to ensuring safety of this technology in the years ahead. The recent regulatory clearance for clinical diagnostic imaging at 7T will likely increase the installed base of 7T systems, particularly in hospital environments with little prior ultrahigh-field MR experience. Informed risk/benefit analyses will be required, particularly where implant manufacturer-published 7T safety guidelines for implants are unavailable. On behalf of the International Society for Magnetic Resonance in Medicine, the aim of this article is to provide a reference document to assist institutions developing local institutional policies and procedures that are specific to the safe operation of 7T MRI/MRS. Details of current 7T technology and the physics underpinning its functionality are reviewed, with the aim of supporting efforts to expand the use of 7T MRI/MRS in both research and clinical environments. Current gaps in knowledge are also identified, where additional research and development are required. Level of Evidence 5 Technical Efficacy 2 J. MAGN. RESON. IMAGING 2021;53:333-346.
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Affiliation(s)
- Andrew J. Fagan
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - Andreas K. Bitz
- Faculty of Electrical Engineering and Information Technology, FH Aachen - University of Applied Sciences, Aachen, Germany
| | - Isabella M. Björkman-Burtscher
- Department of Radiology, University of Gothenburg, Sahlgrenska Academy, Sahlgrenska University Hospital, Gothenburg, Sweden
| | - Christopher M. Collins
- Center for Advanced Imaging Innovation and Research, NYU Langone Medical Center, New York, New York, USA
| | - Vera Kimbrell
- Department of Radiology, Brigham and Women’s Hospital, Boston, Massachusetts, USA
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20
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Dietrich S, Aigner CS, Kolbitsch C, Mayer J, Ludwig J, Schmidt S, Schaeffter T, Schmitter S. 3D Free-breathing multichannel absolute B 1 + Mapping in the human body at 7T. Magn Reson Med 2020; 85:2552-2567. [PMID: 33283915 DOI: 10.1002/mrm.28602] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 10/23/2020] [Accepted: 10/25/2020] [Indexed: 12/13/2022]
Abstract
PURPOSE To introduce and investigate a method for free-breathing three-dimensional (3D) B 1 + mapping of the human body at ultrahigh field (UHF), which can be used to generate homogenous flip angle (FA) distributions in the human body at UHF. METHODS A 3D relative B 1 + mapping sequence with a radial phase-encoding (RPE) k-space trajectory was developed and applied in 11 healthy subjects at 7T. An RPE-based actual flip angle mapping method was applied with a dedicated B 1 + shim setting to calibrate the relative B 1 + maps yielding absolute B 1 + maps of the individual transmit channels. The method was evaluated in a motion phantom and by multidimensional in vivo measurements. Additionally, 3D gradient echo scans with and without static phase-only B 1 + shims were used to qualitatively validate B 1 + shim predictions. RESULTS The phantom validation revealed good agreement for B 1 + maps between dynamic measurement and static reference acquisition. The proposed 3D method was successfully validated in vivo by comparing magnitude and phase distributions with a 2D Cartesian reference. 3D B 1 + maps free from visible motion artifacts were successfully acquired for 11 subjects with body mass indexes ranging from 19 kg/m2 to 34 kg/m2 . 3D respiration-resolved absolute B 1 + maps indicated FA differences between inhalation and exhalation up to 15% for one channel and up to 24% for combined channels for shallow breathing. CONCLUSION The proposed method provides respiration-resolved absolute 3D B 1 + maps of the human body at UHF, which enables the investigation and development of 3D B 1 + shimming and parallel transmission methods to further enhance body imaging at UHF.
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Affiliation(s)
- Sebastian Dietrich
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Christoph S Aigner
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Christoph Kolbitsch
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Johannes Mayer
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Juliane Ludwig
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Simon Schmidt
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Tobias Schaeffter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Department of Medical Engineering, Technische Universität Berlin, Berlin, Germany
| | - Sebastian Schmitter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
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21
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Ibrahim ESH, Arpinar VE, Muftuler LT, Stojanovska J, Nencka AS, Koch KM. Cardiac functional magnetic resonance imaging at 7T: Image quality optimization and ultra-high field capabilities. World J Radiol 2020; 12:231-246. [PMID: 33240463 PMCID: PMC7653183 DOI: 10.4329/wjr.v12.i10.231] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 09/27/2020] [Accepted: 10/14/2020] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND 7T cardiac magnetic resonance imaging (MRI) introduces several advantages, as well as some limitations, compared to lower-field imaging. The capabilities of ultra-high field (UHF) MRI have not been fully exploited in cardiac functional imaging.
AIM To optimize 7T cardiac MRI functional imaging without the need for conducting B1 shimming or subject-specific tuning, which improves scan efficiency. In this study, we provide results from phantom and in vivo scans using a multi-channel transceiver modular coil.
METHODS We investigated the effects of adding a dielectric pad at different locations next to the imaged region of interest on improving image quality in subjects with different body habitus. We also investigated the effects of adjusting the imaging flip angle in cine and tagging sequences on improving image quality, B1 field homogeneity, signal-to-noise ratio (SNR), blood-myocardium contrast-to-noise ratio (CNR), and tagging persistence throughout the cardiac cycle.
RESULTS The results showed the capability of achieving improved image quality with high spatial resolution (0.75 mm × 0.75 mm × 2 mm), high temporal resolution (20 ms), and increased tagging persistence (for up to 1200 ms cardiac cycle duration) at 7T cardiac MRI after adjusting scan set-up and imaging parameters. Adjusting the imaging flip angle was essential for achieving optimal SNR and myocardium-to-blood CNR. Placing a dielectric pad at the anterior left position of the chest resulted in improved B1 homogeneity compared to other positions, especially in subjects with small chest size.
CONCLUSION Improved regional and global cardiac functional imaging can be achieved at 7T MRI through simple scan set-up adjustment and imaging parameter optimization, which would allow for more streamlined and efficient UHF cardiac MRI.
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Affiliation(s)
- El-Sayed H Ibrahim
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - V Emre Arpinar
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - L Tugan Muftuler
- Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Jadranka Stojanovska
- Department of Radiology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Andrew S Nencka
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Kevin M Koch
- Department of Radiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
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Ibrahim ESH, Arpinar VE, Muftuler LT, Stojanovska J, Nencka AS, Koch KM. Cardiac functional magnetic resonance imaging at 7T: Image quality optimization and ultra-high field capabilities. World J Radiol 2020. [DOI: 10.4329/wjr.v12.i10.229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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23
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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.
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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
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24
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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.
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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
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