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Perera Molligoda Arachchige AS, Teixeira de Castro Gonçalves Ortega AC, Catapano F, Politi LS, Hoff MN. From strength to precision: A systematic review exploring the clinical utility of 7-Tesla magnetic resonance imaging in abdominal imaging. World J Radiol 2024; 16:20-31. [PMID: 38312348 PMCID: PMC10835428 DOI: 10.4329/wjr.v16.i1.20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 12/06/2023] [Accepted: 12/25/2023] [Indexed: 01/23/2024] Open
Abstract
BACKGROUND After approval for clinical use in 2017 early investigations of ultra-high-field abdominal magnetic resonance imaging (MRI) have demonstrated the feasibility as well as diagnostic capabilities of liver, kidney, and prostate MRI at 7-Tesla. However, the elevation of the field strength to 7-Tesla not only brought advantages to abdominal MRI but also presented considerable challenges and drawbacks, primarily stemming from heightened artifacts and limitations in Specific Absorption Rate, etc. Furthermore, evidence in the literature is relatively scarce concerning human studies in comparison to phantom/animal studies which necessitates an investigation into the evidence so far in humans and summarizing all relevant evidence. AIM To offer a comprehensive overview of current literature on clinical abdominal 7T MRI that emphasizes current trends, details relevant challenges, and provides a concise set of potential solutions. METHODS This systematic review adheres to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A PubMed search, utilizing Medical Subject Headings terms such as "7-Tesla" and organ-specific terms, was conducted for articles published between January 1, 1985, and July 25, 2023. Eligibility criteria included studies exploring 7T MRI for imaging human abdominal organs, encompassing various study types (in-vivo/ex-vivo, method development, reviews/meta-analyses). Exclusion criteria involved animal studies and those lacking extractable data. Study selection involved initial identification via title/abstract, followed by a full-text review by two researchers, with discrepancies resolved through discussion. Data extraction covered publication details, study design, population, sample size, 7T MRI protocol, image characteristics, endpoints, and conclusions. RESULTS The systematic review included a total of 21 studies. The distribution of clinical 7T abdominal imaging studies revealed a predominant focus on the prostate (n = 8), followed by the kidney (n = 6) and the hepatobiliary system (n = 5). Studies on these organs, and in the pancreas, demonstrated clear advantages at 7T. However, small bowel studies showed no significant improvements compared to traditional MRI at 1.5T. The majority of studies evaluated originated from Germany (n = 10), followed by the Netherlands (n = 5), the United States (n = 5), Austria (n = 2), the United Kingdom (n = 1), and Italy (n = 1). CONCLUSION Further increase of abdominal clinical MRI field strength to 7T demonstrated high imaging potential, yet also limitations mainly due to the inhomogeneous radiofrequency (RF) excitation field relative to lower field strengths. Hence, further optimization of dedicated RF coil elements and pulse sequences are expected to better optimize clinical imaging at high magnetic field strength.
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Affiliation(s)
| | | | - Federica Catapano
- Department of Biomedical Sciences, Humanitas University, Pieve Emanuele 20072, Milan, Italy
- IRCCS Humanitas Research Hospital, Rozzano 20089, Milan, Italy
| | - Letterio S Politi
- Department of Biomedical Sciences, Humanitas University, Pieve Emanuele 20072, Milan, Italy
- Department of Neuroradiology, IRCCS Humanitas Research Hospital, Rozzano 20089, Milan, Italy
| | - Michael N Hoff
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA 94143, United States
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Renal imaging at 5 T versus 3 T: a comparison study. Insights Imaging 2022; 13:155. [PMID: 36153471 PMCID: PMC9509503 DOI: 10.1186/s13244-022-01290-9] [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: 04/20/2022] [Accepted: 08/24/2022] [Indexed: 11/10/2022] Open
Abstract
Background Recently, a whole-body 5 T MRI scanner was developed to open the door of abdominal imaging at high-field strength. This prospective study aimed to evaluate the feasibility of renal imaging at 5 T and compare the image quality, potential artifacts, and contrast ratios with 3 T. Methods Forty healthy volunteers underwent MRI examination both at 3 T and 5 T. MRI sequences included T1-weighted gradient-echo (GRE), T2-weighted fast spin echo, diffusion-weighted imaging, and multi-echo GRE T2* mapping. Image quality and presence of artifacts were assessed for all sequences using four-point scales. For anatomical imaging, the signal-to-noise ratio (SNR) and contrast ratio (CR) of abdomen organ tissues were calculated. Besides, for functional imaging, the contrast-to-noise ratio of cortex/medulla was calculated. Wilcoxon signed rank-sum test was used to compare the visual evaluation scores and quantitative measurements between 3 and 5 T images. Results Compared to 3 T examination, T1-weighted sequence at 5 T showed significantly better image quality with higher conspicuity of the renal veins and arteries, and comparable artifacts. Image quality was comparable between both field strengths on T2-weighted images, whereas a significantly higher level of artifacts was observed at 5 T. Besides, 5 T MRI contributed to higher SNR and CR for abdomen organ tissues. For functional imaging, 5 T MRI showed improved corticomedullar discrimination. There was no significant difference between apparent diffusion coefficient of renal at 3 T and 5 T, while 5 T MRI resulted in significantly shorter T2* values in both cortex and medulla. Conclusions 5 T MRI provides anatomical and functional images of the kidney with sufficient image quality.
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Platt T, Ladd ME, Paech D. 7 Tesla and Beyond: Advanced Methods and Clinical Applications in Magnetic Resonance Imaging. Invest Radiol 2021; 56:705-725. [PMID: 34510098 PMCID: PMC8505159 DOI: 10.1097/rli.0000000000000820] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 08/07/2021] [Accepted: 08/07/2021] [Indexed: 12/15/2022]
Abstract
ABSTRACT Ultrahigh magnetic fields offer significantly higher signal-to-noise ratio, and several magnetic resonance applications additionally benefit from a higher contrast-to-noise ratio, with static magnetic field strengths of B0 ≥ 7 T currently being referred to as ultrahigh fields (UHFs). The advantages of UHF can be used to resolve structures more precisely or to visualize physiological/pathophysiological effects that would be difficult or even impossible to detect at lower field strengths. However, with these advantages also come challenges, such as inhomogeneities applying standard radiofrequency excitation techniques, higher energy deposition in the human body, and enhanced B0 field inhomogeneities. The advantages but also the challenges of UHF as well as promising advanced methodological developments and clinical applications that particularly benefit from UHF are discussed in this review article.
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Affiliation(s)
- Tanja Platt
- From the Medical Physics in Radiology, German Cancer Research Center (DKFZ)
| | - Mark E. Ladd
- From the Medical Physics in Radiology, German Cancer Research Center (DKFZ)
- Faculty of Physics and Astronomy
- Faculty of Medicine, University of Heidelberg, Heidelberg
- Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen
| | - Daniel Paech
- Division of Radiology, German Cancer Research Center (DKFZ), Heidelberg
- Clinic for Neuroradiology, University of Bonn, Bonn, Germany
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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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Paez A, Gu C, Cao Z. Robust RF shimming and small-tip-angle multispoke pulse design with finite-difference regularization. Magn Reson Med 2021; 86:1472-1481. [PMID: 33934406 DOI: 10.1002/mrm.28820] [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: 05/20/2020] [Revised: 03/29/2021] [Accepted: 04/07/2021] [Indexed: 01/07/2023]
Abstract
PURPOSE A new regularizer is proposed for the magnitude least-squares optimization algorithm, to ensure robust parallel transmit RF shimming and small-tip-angle multispoke pulse designs for ultrahigh-field MRI. METHODS A finite-difference regularization term is activated as an additional regularizer in the iterative magnitude-least-squares based pulse design algorithm when an unwanted flip angle null distribution is detected. Both simulated and experimental B 1 + maps from different transmit arrays and different human subjects at 7 T were used to evaluate the proposed algorithm. The algorithm was further demonstrated in experiment with dynamic multislice RF shimming for a single-shot gradient-echo EPI for human functional MRI at 7 T. RESULTS The proposed finite-difference regularizer effectively prevented excitation null to be formed for RF shimming and small-tip-angle multispoke pulses, and improved the latter with a monotonic trade-off relationship between flip angle error and RF power. The proposed algorithm was demonstrated to be effective with several head-array geometries by simulation and with a commercial head array with 12 healthy human subjects by experiment. During a functional MRI scan at 7 T with dynamic RF shimming, the proposed algorithm ensured high image SNR throughout the human brain, compared with near-complete local signal loss by the conventional magnitude-least-squares algorithm. CONCLUSION Using finite-difference regularization to avoid unwanted solutions, the robustness of RF shimming and small-tip-angle multispoke pulse design algorithms are improved, with better flip angle homogeneity and a monotonic trade-off relationship between flip angle error and RF power.
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Affiliation(s)
- Adrian Paez
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.,Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Chunming Gu
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.,Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - Zhipeng Cao
- Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.,Department of Radiology, Vanderbilt University Medical Center, Nashville, Tennessee, USA
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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.
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Affiliation(s)
- M Arcan Erturk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
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Ladd ME, Bachert P, Meyerspeer M, Moser E, Nagel AM, Norris DG, Schmitter S, Speck O, Straub S, Zaiss M. Pros and cons of ultra-high-field MRI/MRS for human application. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2018; 109:1-50. [PMID: 30527132 DOI: 10.1016/j.pnmrs.2018.06.001] [Citation(s) in RCA: 275] [Impact Index Per Article: 45.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 06/06/2018] [Accepted: 06/07/2018] [Indexed: 05/08/2023]
Abstract
Magnetic resonance imaging and spectroscopic techniques are widely used in humans both for clinical diagnostic applications and in basic research areas such as cognitive neuroimaging. In recent years, new human MR systems have become available operating at static magnetic fields of 7 T or higher (≥300 MHz proton frequency). Imaging human-sized objects at such high frequencies presents several challenges including non-uniform radiofrequency fields, enhanced susceptibility artifacts, and higher radiofrequency energy deposition in the tissue. On the other side of the scale are gains in signal-to-noise or contrast-to-noise ratio that allow finer structures to be visualized and smaller physiological effects to be detected. This review presents an overview of some of the latest methodological developments in human ultra-high field MRI/MRS as well as associated clinical and scientific applications. Emphasis is given to techniques that particularly benefit from the changing physical characteristics at high magnetic fields, including susceptibility-weighted imaging and phase-contrast techniques, imaging with X-nuclei, MR spectroscopy, CEST imaging, as well as functional MRI. In addition, more general methodological developments such as parallel transmission and motion correction will be discussed that are required to leverage the full potential of higher magnetic fields, and an overview of relevant physiological considerations of human high magnetic field exposure is provided.
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Affiliation(s)
- Mark E Ladd
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Medicine, University of Heidelberg, Heidelberg, Germany; Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany; Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
| | - Peter Bachert
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany.
| | - Martin Meyerspeer
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; MR Center of Excellence, Medical University of Vienna, Vienna, Austria.
| | - Ewald Moser
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; MR Center of Excellence, Medical University of Vienna, Vienna, Austria.
| | - Armin M Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
| | - David G Norris
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands; Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
| | - Sebastian Schmitter
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.
| | - Oliver Speck
- Department of Biomedical Magnetic Resonance, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany; German Center for Neurodegenerative Diseases, Magdeburg, Germany; Center for Behavioural Brain Sciences, Magdeburg, Germany; Leibniz Institute for Neurobiology, Magdeburg, Germany.
| | - Sina Straub
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
| | - Moritz Zaiss
- High-Field Magnetic Resonance Center, Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany.
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9
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Niendorf T, Paul K, Oezerdem C, Graessl A, Klix S, Huelnhagen T, Hezel F, Rieger J, Waiczies H, Frahm J, Nagel AM, Oberacker E, Winter L. W(h)ither human cardiac and body magnetic resonance at ultrahigh fields? technical advances, practical considerations, applications, and clinical opportunities. NMR IN BIOMEDICINE 2016; 29:1173-97. [PMID: 25706103 DOI: 10.1002/nbm.3268] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 12/26/2014] [Accepted: 01/13/2015] [Indexed: 05/12/2023]
Abstract
The objective of this study was to document and review advances and groundbreaking progress in cardiac and body MR at ultrahigh fields (UHF, B0 ≥ 7.0 T) with the goal to attract talent, clinical adopters, collaborations and resources to the biomedical and diagnostic imaging communities. This review surveys traits, advantages and challenges of cardiac and body MR at 7.0 T. The considerations run the gamut from technical advances to clinical opportunities. Key concepts, emerging technologies, practical considerations, frontier applications and future directions of UHF body and cardiac MR are provided. Examples of UHF cardiac and body imaging strategies are demonstrated. Their added value over the kindred counterparts at lower fields is explored along with an outline of research promises. The achievements of cardiac and body UHF-MR are powerful motivators and enablers, since extra speed, signal and imaging capabilities may be invested to overcome the fundamental constraints that continue to hamper traditional cardiac and body MR applications. If practical obstacles, concomitant physics effects and technical impediments can be overcome in equal measure, sophisticated cardiac and body UHF-MR will help to open the door to new MRI and MRS approaches for basic research and clinical science, with the lessons learned at 7.0 T being transferred into broad clinical use including diagnostics and therapy guiding at lower fields. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Thoralf Niendorf
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Berlin, Germany
| | - Katharina Paul
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Celal Oezerdem
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Andreas Graessl
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Sabrina Klix
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Till Huelnhagen
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | | | | | - Jens Frahm
- Biomedizinische NMR Forschungs GmbH, am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Göttingen, Germany
| | - Armin M Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Eva Oberacker
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
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de Boer A, Hoogduin JM, Blankestijn PJ, Li X, Luijten PR, Metzger GJ, Raaijmakers AJE, Umutlu L, Visser F, Leiner T. 7 T renal MRI: challenges and promises. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2016; 29:417-33. [PMID: 27008461 PMCID: PMC4891364 DOI: 10.1007/s10334-016-0538-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Revised: 02/02/2016] [Accepted: 02/15/2016] [Indexed: 01/07/2023]
Abstract
The progression to 7 Tesla (7 T) magnetic resonance imaging (MRI) yields promises of substantial increase in signal-to-noise (SNR) ratio. This increase can be traded off to increase image spatial resolution or to decrease acquisition time. However, renal 7 T MRI remains challenging due to inhomogeneity of the radiofrequency field and due to specific absorption rate (SAR) constraints. A number of studies has been published in the field of renal 7 T imaging. While the focus initially was on anatomic imaging and renal MR angiography, later studies have explored renal functional imaging. Although anatomic imaging remains somewhat limited by inhomogeneous excitation and SAR constraints, functional imaging results are promising. The increased SNR at 7 T has been particularly advantageous for blood oxygen level-dependent and arterial spin labelling MRI, as well as sodium MR imaging, thanks to changes in field-strength-dependent magnetic properties. Here, we provide an overview of the currently available literature on renal 7 T MRI. In addition, we provide a brief overview of challenges and opportunities in renal 7 T MR imaging.
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Affiliation(s)
- Anneloes de Boer
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
| | - Johannes M Hoogduin
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands.
| | - Peter J Blankestijn
- Department of Nephrology, University Medical Centre Utrecht, Utrecht, The Netherlands
| | - Xiufeng Li
- Department of Radiology, Centre for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Peter R Luijten
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
| | - Gregory J Metzger
- Department of Radiology, Centre for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Alexander J E Raaijmakers
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
| | - Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Fredy Visser
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands.,Philips Healthcare, Best, The Netherlands
| | - Tim Leiner
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
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Abstract
Since the introduction of 4 T human systems in three academic laboratories circa 1990, rapid progress in imaging and spectroscopy studies in humans at 4 T and animal model systems at 9.4 T have led 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 demonstrated the existence of significant advantages in SNR and biological information content at these ultrahigh fields, as well as the presence of numerous challenges. Primary difference from lower fields is the deviation from the near field regime; at the frequencies corresponding to hydrogen resonance conditions at ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image nonuniformities for a given sample-coil configuration because of interferences. These nonuniformities were considered detrimental to the progress of imaging at high field strengths. However, they are advantageous for parallel imaging for signal reception and parallel 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, 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.
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Kraff O, Fischer A, Nagel AM, Mönninghoff C, Ladd ME. MRI at 7 Tesla and above: demonstrated and potential capabilities. J Magn Reson Imaging 2014; 41:13-33. [PMID: 24478137 DOI: 10.1002/jmri.24573] [Citation(s) in RCA: 129] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Accepted: 01/03/2014] [Indexed: 12/29/2022] Open
Abstract
With more than 40 installed MR systems worldwide operating at 7 Tesla or higher, ultra-high-field (UHF) imaging has been established as a platform for clinically oriented research in recent years. Along with technical developments that, in part, have also been successfully transferred to lower field strengths, MR imaging and spectroscopy at UHF have demonstrated capabilities and potentials for clinical diagnostics in a variety of studies. In terms of applications, this overview article focuses on already achieved advantages for in vivo imaging, i.e., in imaging the brain and joints of the musculoskeletal system, but also considers developments in body imaging, which is particularly challenging. Furthermore, new applications for clinical diagnostics such as X-nuclei imaging and spectroscopy, which only really become feasible at ultra-high magnetic fields, will be presented.
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Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
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14
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Regatte RR. Why buy an expensive ($7 million) 7T MRI system for biomedical research? J Magn Reson Imaging 2013; 40:280-2. [PMID: 24123421 DOI: 10.1002/jmri.24444] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 09/11/2013] [Indexed: 12/26/2022] Open
Affiliation(s)
- Ravinder R Regatte
- Quantitative Multinuclear Musculoskeletal Imaging Group (QMMIG), Center for Biomedical Imaging, Department of Radiology, New York University Langone Medical Center, New York, NY, USA
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15
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Seven-Tesla MRI of the female pelvis. Eur Radiol 2013; 23:2364-73. [PMID: 23645332 DOI: 10.1007/s00330-013-2868-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Revised: 03/15/2013] [Accepted: 03/29/2013] [Indexed: 01/01/2023]
Abstract
OBJECTIVES The aim of this study was to investigate the feasibility of 7-T contrast-enhanced MR imaging of the female pelvis. METHODS Ten healthy female volunteers were examined on a 7-T whole-body MR system utilising a custom-built eight-channel transmit/receive radiofrequency body coil. The examination protocol included (1) T1-weighted fat-saturated 2D spoiled gradient echo (FLASH), (2) dynamic T1-weighted fat-saturated 3D FLASH, and (3) T2-weighted TSE sequences. For qualitative image analysis pelvic anatomy, uterine zonal anatomy and image impairment due to artefacts was assessed using a five-point scale. For quantitative analysis contrast ratios between the junctional zone and myometrium were obtained for T2-weighted MRI. RESULTS Two-dimensional FLASH MRI offered the best overall image quality (meancontrast-enhanced 4.9) and highest tissue contrast (meancontrast-enhanced 4.7). T2-weighted TSE imaging provided a moderate to high conspicuity of the uterine zonal anatomy with mean scores ranging from 3.5 for endometrium to 4.65 for myometrium. Overall image impairment was rated strongest for T2-weighted MRI (2.9) and least for 2D FLASH MRI (mean 4.2). CONCLUSION This study demonstrated the feasibility of 7-T T1-weighted MRI of the female pelvis and current constraints associated with T2-weighted MRI. KEY POINTS • Dynamic contrast-enhanced female pelvis MR imaging at 7 T is feasible. • Unenhanced T1-weighted MRI offers inherent hyperintense delineation of pelvic arterial vasculature. • Two-dimensional FLASH MRI provided best overall image quality and least artefact impairment.
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Umutlu L, Theysohn N, Maderwald S, Johst S, Lauenstein TC, Moenninghoff C, Goericke SL, Dammann P, Wrede KH, Ladd ME, Forsting M, Schlamann M. 7 Tesla MPRAGE imaging of the intracranial arterial vasculature: nonenhanced versus contrast-enhanced. Acad Radiol 2013; 20:628-34. [PMID: 23473725 DOI: 10.1016/j.acra.2012.12.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 12/05/2012] [Accepted: 12/06/2012] [Indexed: 11/27/2022]
Abstract
PURPOSE To intraindividually compare the delineation of intracranial arterial vasculature in nonenhanced versus contrast-enhanced magnetization prepared rapid gradient echo (MPRAGE) imaging at 7 Tesla (T). MATERIALS AND METHODS Sixteen subjects were examined on a 7 T whole-body magnetic resonance system (Magnetom 7T) equipped with a 32-channel transmit/receive head coil. MPRAGE imaging was performed pre- and postcontrast after the application of 0.1 mmol/kg bodyweight gadobutrol. For qualitative analysis, the delineation of the intracranial arteries, overall image quality, and image impairment were assessed in the nonenhanced and contrast-enhanced datasets using a 5-point scale (5 = excellent to 1 = nondiagnostic). Additionally, contrast ratios (CR) of the middle cerebral artery in correlation to surrounding gray matter in nonenhanced and postcontrast images were obtained. For statistical analysis a Wilcoxon signed-rank test was applied. RESULTS Nonenhanced MPRAGE imaging offered an excellent delineation of the central vessel segments of the anterior circulation (mean anterior circulation 4.6) and a moderate- to high-quality assessment of the vessels of the posterior circulation (mean posterior circulation 3.9). Vessel delineation was improved in all assessed segments in the contrast-enhanced datasets, except for the cavernous segment of the internal carotid artery. Quantitative analysis revealed a mild, nonsignificant increase in CR mean values of the M1 segment (CRnonenhanced 0.67; CRcontrast-enhanced 0.69). CONCLUSION Our results demonstrate the high diagnostic value of nonenhanced 7 T MPRAGE imaging for the assessment of the intracranial arterial vasculature, with improved assessment of the peripheral segments because of the application of a contrast agent.
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Umutlu L, Maderwald S, Kinner S, Kraff O, Bitz AK, Orzada S, Johst S, Wrede K, Forsting M, Ladd ME, Lauenstein TC, Quick HH. First-pass contrast-enhanced renal MRA at 7 Tesla: initial results. Eur Radiol 2012; 23:1059-66. [PMID: 23064714 DOI: 10.1007/s00330-012-2666-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Revised: 08/28/2012] [Accepted: 09/08/2012] [Indexed: 10/27/2022]
Abstract
OBJECTIVE The aim of this study was to assess the feasibility of first-pass contrast-enhanced renal MR angiography (MRA) at 7 T. METHODS In vivo first-pass contrast-enhanced high-field examinations were obtained in eight healthy subjects on a 7-T whole-body MRI. A custom-built body transmit/receive radiofrequency (RF) coil and RF system suitable for RF shimming were used for image acquisition. For dynamic imaging, gadobutrol was injected intravenously and coronal unenhanced, arterial and venous data sets using a T1-weighted spoiled gradient-echo sequence were obtained. Qualitative image analysis and assessment of artefact impairment were performed by two senior radiologists using a five-point scale (5 = excellent, 1 = non-diagnostic). SNR and CNR of the perirenal abdominal aorta and both main renal arteries were assessed. RESULTS Qualitative image evaluation revealed overall high-quality delineation of all assessed segments of the unenhanced arterial vasculature (meanunenhanced 4.13). Nevertheless, the application of contrast agent revealed an improvement in vessel delineation of all the vessel segments assessed, confirmed by qualitative (meanunenhanced 4.13 to meancontrast-enhanced 4.85) and quantitative analysis (SNR meanunenhanced 64.3 to meancontrast-enhanced 98.4). CONCLUSION This study demonstrates the feasibility and current constraints of ultra-high-field contrast-enhanced renal MRA relative to unenhanced MRA.
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Affiliation(s)
- L Umutlu
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Arendahls Wiese 199, 45141 Essen, Germany.
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Umutlu L, Forsting M, Ladd ME. Ultrahigh-field magnetic resonance imaging: the clinical potential for anatomy, pathogenesis, diagnosis and treatment planning in neck and spine disease. Neuroimaging Clin N Am 2012; 22:363-71, xii. [PMID: 22548937 DOI: 10.1016/j.nic.2012.02.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An increase of the magnetic field strength to ultrahigh-field yields advantageous as well as disadvantageous changes in physical effects. The beneficial increase in signal/noise ratio can be leveraged into higher spatiotemporal resolution, and an exacerbation of artifacts can impede ultrahigh-field imaging. With the successful introduction of intracranial and musculoskeletal imaging at 7 T, recent advances in coil design have created opportunities for further applications of ultrahigh-field magnetic resonance (MR) imaging in other parts of the body. Initial studies in 7 T neck and spine MR imaging have revealed promising insights and new challenges, demanding further research and methodological optimization.
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Affiliation(s)
- Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, D-45122 Essen, Germany.
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Moser E, Stahlberg F, Ladd ME, Trattnig S. 7-T MR--from research to clinical applications? NMR IN BIOMEDICINE 2012; 25:695-716. [PMID: 22102481 DOI: 10.1002/nbm.1794] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Revised: 08/25/2011] [Accepted: 08/31/2011] [Indexed: 05/31/2023]
Abstract
Over 20,000 MR systems are currently installed worldwide and, although the majority operate at magnetic fields of 1.5 T and below (i.e. about 70%), experience with 3-T (in high-field clinical diagnostic imaging and research) and 7-T (research only) human MR scanners points to a future in functional and metabolic MR diagnostics. Complementary to previous studies, this review attempts to provide an overview of ultrahigh-field MR research with special emphasis on emerging clinical applications at 7 T. We provide a short summary of the technical development and the current status of installed MR systems. The advantages and challenges of ultrahigh-field MRI and MRS are discussed with special emphasis on radiofrequency inhomogeneity, relaxation times, signal-to-noise improvements, susceptibility effects, chemical shifts, specific absorption rate and other safety issues. In terms of applications, we focus on the topics most likely to gain significantly from 7-T MR, i.e. brain imaging and spectroscopy and musculoskeletal imaging, but also body imaging, which is particularly challenging. Examples are given to demonstrate the advantages of susceptibility-weighted imaging, time-of-flight MR angiography, high-resolution functional MRI, (1)H and (31)P MRSI in the human brain, sodium and functional imaging of cartilage and the first results (and artefacts) using an eight-channel body array, suggesting future areas of research that should be intensified in order to fully explore the potential of 7-T MR systems for use in clinical diagnosis.
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Affiliation(s)
- Ewald Moser
- Centre for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
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Snyder CJ, Delabarre L, Moeller S, Tian J, Akgun C, Van de Moortele PF, Bolan PJ, Ugurbil K, Vaughan JT, Metzger GJ. Comparison between eight- and sixteen-channel TEM transceive arrays for body imaging at 7 T. Magn Reson Med 2011; 67:954-64. [PMID: 22102483 DOI: 10.1002/mrm.23070] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Revised: 06/02/2011] [Accepted: 06/06/2011] [Indexed: 11/05/2022]
Abstract
Eight- and sixteen-channel transceive stripline/TEM body arrays were compared at 7 T (297 MHz) both in simulation and experiment. Despite previous demonstrations of similar arrays for use in body applications, a quantitative comparison of the two configurations has not been undertaken to date. Results were obtained on a male pelvis for assessing transmit, signal to noise ratio, and parallel imaging performance and to evaluate local power deposition versus transmit B(1) (B(1) (+) ). All measurements and simulations were conducted after performing local B(1) (+) phase shimming in the region of the prostate. Despite the additional challenges of decoupling immediately adjacent coils, the sixteen-channel array demonstrated improved or nearly equivalent performance to the eight-channel array based on the evaluation criteria. Experimentally, transmit performance and signal to noise ratio were 22% higher for the sixteen-channel array while significantly increased reduction factors were achievable in the left-right direction for parallel imaging. Finite difference time domain simulations demonstrated similar results with respect to transmit and parallel imaging performance, however, a higher transmit efficiency advantage of 33% was predicted. Simulations at both 3 and 7 T verified the expected parallel imaging improvements with increasing field strength and showed that, for a specific B(1) (+) shimming strategy used, the sixteen-channel array exhibited lower local and global specific absorption rate for a given B(1) (+) .
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Affiliation(s)
- C J Snyder
- Department of Radiology, University of Minnesota, Minneapolis, MN, USA
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Umutlu L, Bitz AK, Maderwald S, Orzada S, Kinner S, Kraff O, Brote I, Ladd SC, Schroeder T, Forsting M, Antoch G, Ladd ME, Quick HH, Lauenstein TC. Contrast-enhanced ultra-high-field liver MRI: a feasibility trial. Eur J Radiol 2011; 82:760-7. [PMID: 21862273 DOI: 10.1016/j.ejrad.2011.07.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Accepted: 07/22/2011] [Indexed: 11/30/2022]
Abstract
The aim of this study was to investigate the feasibility of dynamic contrast-enhanced 7 T MRI of the liver using an eight-channel radiofrequency (RF) transmit/receive body-coil. 16 healthy subjects were examined on a 7 T MR system utilizing a custom-built eight-channel RF body-coil suitable for RF-shimming. The following data were acquired: (1) steady state free precession imaging, (2) T2w turbo spin echo imaging, (3) T1w in and opposed-phase imaging, (4) T1w 3D FLASH images pre-contrast and in arterial, portal-venous and venous phase and (5) a fat-saturated pre- and post-contrast 2D FLASH sequence. Visual evaluation of (1) the delineation of liver vasculature, (2) the overall image quality, and (3) artifact presence and consequent image impairment was performed. SNR of the liver parenchyma was measured for the contrast-enhanced 2D and 3D FLASH sequences. For statistical analysis, a Wilcoxon-Rank Test was used. Best delineation of non-enhanced liver vasculature and overall image quality was found for 2D FLASH MRI, with only slight improvement in vessel conspicuity after the application of contrast media. T2-weighted TSE imaging remained strongly impaired, falling short of diagnostic relevance and precluding a clinical application. Our results demonstrate the feasibility and diagnostic potential of dedicated contrast-enhanced 7 T liver MRI as well as the potential for non-contrast-enhanced angiographic application.
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Affiliation(s)
- Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Germany.
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Martin C, Frauenrath T, Ozerdem C, Renz W, Niendorf T. Development and evaluation of a small and mobile Magneto Alert Sensor (MALSE) to support safety requirements for magnetic resonance imaging. Eur Radiol 2011; 21:2187-92. [PMID: 21647823 DOI: 10.1007/s00330-011-2153-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2011] [Revised: 04/15/2011] [Accepted: 04/25/2011] [Indexed: 11/27/2022]
Abstract
OBJECTIVE The purpose of this study is to (i) design a small and mobile Magnetic field ALert SEnsor (MALSE), (ii) to carefully evaluate its sensors to their consistency of activation/deactivation and sensitivity to magnetic fields, and (iii) to demonstrate the applicability of MALSE in 1.5 T, 3.0 T and 7.0 T MR fringe field environments. METHODS MALSE comprises a set of reed sensors, which activate in response to their exposure to a magnetic field. The activation/deactivation of reed sensors was examined by moving them in/out of the fringe field generated by 7TMR. RESULTS The consistency with which individual reed sensors would activate at the same field strength was found to be 100% for the setup used. All of the reed switches investigated required a substantial drop in ambient magnetic field strength before they deactivated. CONCLUSIONS MALSE is a simple concept for alerting MRI staff to a ferromagnetic object being brought into fringe magnetic fields which exceeds MALSEs activation magnetic field. MALSE can easily be attached to ferromagnetic objects within the vicinity of a scanner, thus creating a barrier for hazardous situations induced by ferromagnetic parts which should not enter the vicinity of an MR-system to occur.
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Affiliation(s)
- Conrad Martin
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany.
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