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Chen B, Dammann P, Jabbarli R, Sure U, Quick HH, Kraff O, Wrede KH. Safety and function of programmable ventriculo-peritoneal shunt valves: An in vitro 7 Tesla magnetic resonance imaging study. PLoS One 2023; 18:e0292666. [PMID: 37819939 PMCID: PMC10566673 DOI: 10.1371/journal.pone.0292666] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Accepted: 09/26/2023] [Indexed: 10/13/2023] Open
Abstract
OBJECTIVE The quantity of ultra-high field MRI neuroimaging studies has rapidly increased. This study tests function, safety, and image artifacts of two frequently implanted programmable ventriculo-peritoneal (VP) shunt valves in a 7T MRI system. METHODS All tests were performed using a whole-body 7T MRI system. Three proGAV 2.0 and 3 CODMAN CERTAS® Plus programmable VP-shunt valves were tested in three steps. 1) Deflection angle tests close to the bore opening at the location of a static magnetic field gradient of 3-5 T/m. 2) Valves were fixed on a spherical phantom in 3 positions (a. lateral, b. cranial, c. cranial with 22.5° tilt anteriorly) and assessed for keeping the programmed pressure setting and reprogrammability. 3) Valves were fixed on the phantom and positioned lateral in a radiofrequency head coil. MRI scans were performed for both models, including MPRAGE, GRE and SE sequences. RESULTS Deflection angles were moderate (13°, 14°, 13°) for the proGAV valves and close to critical (43°, 43°, 41°) for the CODMAN valves at the test location. Taking a scaling factor of 2-3 for the maximum spatial magnetic field gradient accessible to a patient within the magnet bore into account renders both valves MR unsafe regarding ferromagnetic attraction. The proGAV valves kept the pressure settings in all positions and were reprogrammable in positions a. and b. In position c., reprogrammability was lost. The CODMAN valves changed their pressure setting and reprogrammability was lost in all positions. MR image signal homogeneity was unaltered in the phantom center, artifacts limit the assessability of structures in close vicinity to the valves. CONCLUSION Both tested programmable VP-shunt valves are MR unsafe for 7T systems. Novel programming mechanisms using permanent magnets with sufficient magnetic coercivity or magnet-free mechanisms may allow the development of programmable VP-shunt valves that are conditional for 7T MR systems.
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Affiliation(s)
- Bixia Chen
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
- Department of Neurosurgery, University Hospital Essen, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
| | - Philipp Dammann
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
- Department of Neurosurgery, University Hospital Essen, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
| | - Ramazan Jabbarli
- Department of Neurosurgery, University Hospital Essen, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
| | - Ulrich Sure
- Department of Neurosurgery, University Hospital Essen, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
| | - Harald H. Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
| | - Oliver Kraff
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
| | - Karsten H. Wrede
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
- Department of Neurosurgery, University Hospital Essen, University Duisburg-Essen, Essen, North Rhine Westphalia, Germany
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Shaffer A, Weisbaum D, Naik A, Anderson A, Wszalek T, Cohen M, Sutton B, Webb A, Damon B, Arnold PM. Neurosurgical Implant Safety in 7 T MRI: A Scoping Review. J Magn Reson Imaging 2023; 57:661-669. [PMID: 36173367 DOI: 10.1002/jmri.28449] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Revised: 09/13/2022] [Accepted: 09/15/2022] [Indexed: 11/11/2022] Open
Abstract
The use of 7 Tesla (T) magnetic resonance imaging (MRI) is expanding across neurosurgical and neurologic specialties. However, few neurosurgical-related implants have been tested for safety at 7 T, limiting its use in patients with cranial fixation, shunt placements, and other implants. Implant safety can be determined via the American Society for Testing Materials International (ASTM) guidelines. To assess the current state of neurosurgical implant safety at 7 T, a systematic search was performed using PubMed, MEDLINE, Web of Knowledge, and citation matching. Studies written in English that included at least one neurosurgical implant and at least one safety outcome were included. Data were extracted for implant studied, implant composition, deflection angle, torque, temperature change, and ASTM guidelines followed. PRISMA reporting guidelines for scoping reviews were followed. Overall, 18 studies consisting of 45 unique implants were included. Implants included cranial fixation devices, aneurysm clips, spinal rods, pedicle screws, ventriculoperitoneal (VP) shunts, deep brain stimulation devices, and electroencephalogram (EEG) caps and electrodes. Cranial fixation devices, deep brain stimulation devices, spinal rods, and pedicle screws are likely 7 T MRI compatible based on outcomes reported. Aneurysm clips and EEG devices had variable safety outcomes. The VP shunts studied lost functionality after 7 T MRI exposure. We identified several implants that are likely compatible with 7 T MRI. Given the growth in 7 T imaging and expansion of the technology, neurosurgical implants should be constructed with the aforementioned considerations. Caution must be taken with all implants, especially aneurysm clips, programmable VP shunts, and EEG recording devices. It is also noteworthy that several implant testing reports did not report following ASTM standards. This scoping review seeks to concisely summarize all neurosurgical-related implants that have been tested for safety in 7 T MRI. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.
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Affiliation(s)
- Annabelle Shaffer
- Carle Illinois College of Medicine, University of Illinois Urbana Champaign, Urbana, Illinois, USA
| | - David Weisbaum
- Department of Neurosurgery, Carle Foundation Hospital, Urbana, Illinois, USA
| | - Anant Naik
- Carle Illinois College of Medicine, University of Illinois Urbana Champaign, Urbana, Illinois, USA
| | - Aaron Anderson
- Carle Illinois Advanced Imaging Center, Urbana, Illinois, USA.,Beckman Institute for Advanced Science & Technology, University of Illinois Urbana Champaign, Urbana, Illinois, USA
| | - Tracey Wszalek
- Carle Illinois Advanced Imaging Center, Urbana, Illinois, USA.,Beckman Institute for Advanced Science & Technology, University of Illinois Urbana Champaign, Urbana, Illinois, USA
| | - Mark Cohen
- Carle Illinois College of Medicine, University of Illinois Urbana Champaign, Urbana, Illinois, USA
| | - Brad Sutton
- Carle Illinois Advanced Imaging Center, Urbana, Illinois, USA.,Beckman Institute for Advanced Science & Technology, University of Illinois Urbana Champaign, Urbana, Illinois, USA
| | - Andrew Webb
- Carle Illinois Advanced Imaging Center, Urbana, Illinois, USA.,Beckman Institute for Advanced Science & Technology, University of Illinois Urbana Champaign, Urbana, Illinois, USA.,Leiden University Medical Center, Leiden, Netherlands
| | - Bruce Damon
- Carle Illinois Advanced Imaging Center, Urbana, Illinois, USA.,Beckman Institute for Advanced Science & Technology, University of Illinois Urbana Champaign, Urbana, Illinois, USA
| | - Paul M Arnold
- Carle Illinois College of Medicine, University of Illinois Urbana Champaign, Urbana, Illinois, USA.,Department of Neurosurgery, Carle Foundation Hospital, Urbana, Illinois, USA
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3
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McCarthy L, Verma G, Hangel G, Neal A, Moffat BA, Stockmann JP, Andronesi OC, Balchandani P, Hadjipanayis CG. Application of 7T MRS to High-Grade Gliomas. AJNR Am J Neuroradiol 2022; 43:1378-1395. [PMID: 35618424 PMCID: PMC9575545 DOI: 10.3174/ajnr.a7502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 02/11/2022] [Indexed: 01/26/2023]
Abstract
MRS, including single-voxel spectroscopy and MR spectroscopic imaging, captures metabolites in high-grade gliomas. Emerging evidence indicates that 7T MRS may be more sensitive to aberrant metabolic activity than lower-field strength MRS. However, the literature on the use of 7T MRS to visualize high-grade gliomas has not been summarized. We aimed to identify metabolic information provided by 7T MRS, optimal spectroscopic sequences, and areas for improvement in and new applications for 7T MRS. Literature was found on PubMed using "high-grade glioma," "malignant glioma," "glioblastoma," "anaplastic astrocytoma," "7T," "MR spectroscopy," and "MR spectroscopic imaging." 7T MRS offers higher SNR, modestly improved spatial resolution, and better resolution of overlapping resonances. 7T MRS also yields reduced Cramér-Rao lower bound values. These features help to quantify D-2-hydroxyglutarate in isocitrate dehydrogenase 1 and 2 gliomas and to isolate variable glutamate, increased glutamine, and increased glycine with higher sensitivity and specificity. 7T MRS may better characterize tumor infiltration and treatment effect in high-grade gliomas, though further study is necessary. 7T MRS will benefit from increased sample size; reductions in field inhomogeneity, specific absorption rate, and acquisition time; and advanced editing techniques. These findings suggest that 7T MRS may advance understanding of high-grade glioma metabolism, with reduced Cramér-Rao lower bound values and better measurement of smaller metabolite signals. Nevertheless, 7T is not widely used clinically, and technical improvements are necessary. 7T MRS isolates metabolites that may be valuable therapeutic targets in high-grade gliomas, potentially resulting in wider ranging neuro-oncologic applications.
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Affiliation(s)
- L McCarthy
- From the Department of Neurosurgery (L.M., C.G.H.), Icahn School of Medicine at Mount Sinai, Mount Sinai Health System, New York, New York
| | - G Verma
- BioMedical Engineering and Imaging Institute (G.V., P.B.), Icahn School of Medicine at Mount Sinai, New York, New York
| | - G Hangel
- Department of Neurosurgery (G.H.)
- High-field MR Center (G.H.), Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria
| | - A Neal
- Department of Medicine (A.N.), Royal Melbourne Hospital, University of Melbourne, Melbourne, Australia
- Department of Neurology (A.N.), Royal Melbourne Hospital, Melbourne, Australia
| | - B A Moffat
- The Melbourne Brain Centre Imaging Unit (B.A.M.), Department of Radiology, The University of Melbourne, Melbourne, Australia
| | - J P Stockmann
- A. A. Martinos Center for Biomedical Imaging (J.P.S., O.C.A.), Massachusetts General Hospital, Charlestown, Massachusetts
- Harvard Medical School (J.P.S., O.C.A.), Boston, Massachusetts
| | - O C Andronesi
- A. A. Martinos Center for Biomedical Imaging (J.P.S., O.C.A.), Massachusetts General Hospital, Charlestown, Massachusetts
- Harvard Medical School (J.P.S., O.C.A.), Boston, Massachusetts
| | - P Balchandani
- BioMedical Engineering and Imaging Institute (G.V., P.B.), Icahn School of Medicine at Mount Sinai, New York, New York
| | - C G Hadjipanayis
- From the Department of Neurosurgery (L.M., C.G.H.), Icahn School of Medicine at Mount Sinai, Mount Sinai Health System, New York, New York
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Abstract
After introduction of the first human 7 tesla (7T) system in 1999, 7T MR systems have been employed as one of the most advanced platforms for human MR research for more than 20 years. Currently, two 7T MR models are approved for clinical use in the U.S.A. The approval facilitated introduction of the 7T system, summing up to around 100 worldwide. The approval in Japan is much awaited. As a clinical MR scanner, the 7T MR system is drawing attention in terms of safety.Several large-sized studies on bioeffects have been reported for vertigo, dizziness, motion disturbances, nausea, and others. Such effects might also be found in MR workers and researchers. Frequency and severity of reported bioeffects will be presented and discussed, including their variances. The high resonance frequency and shorter RF wavelength of 7T increase the concern about the safety. Homogeneous RF pulse excitation is difficult even for the brain, and a multi-channel parallel transmit (pTx) system is considered mandatory. However, pTx may create a hot spot, which makes the estimation of specific absorption rate (SAR) to be difficult. The stronger magnetic field of 7T causes a large force of displacement and heating on metallic implants or devices, and the scan of patients with them should not be conducted at 7T. However, there are some opinions that such patients might be scanned even at 7T, if certain criteria are met. This article provides a brief review on the effect of the static magnetic field on humans (MR subjects, workers, and researchers) and neurons, in addition to scan sound, SAR, and metal implants and devices. Understanding and avoiding adverse effects will contribute to the reduction in safety risks and the prevention of incidents.
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Affiliation(s)
- Tomohisa Okada
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Thai Akasaka
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Dinh Hd Thuy
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Tadashi Isa
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
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5
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Reiss S, Lottner T, Ozen AC, Polei S, Bitzer A, Bock M. Analysis of the RF Excitation of Endovascular Stents in Small Gap and Overlap Scenarios Using an Electro-Optical E-field Sensor. IEEE Trans Biomed Eng 2021; 68:783-792. [DOI: 10.1109/tbme.2020.3009869] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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6
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Niendorf T, Beenakker JWM, Langner S, Erb-Eigner K, Bach Cuadra M, Beller E, Millward JM, Niendorf TM, Stachs O. Ophthalmic Magnetic Resonance Imaging: Where Are We (Heading To)? Curr Eye Res 2021; 46:1251-1270. [PMID: 33535828 DOI: 10.1080/02713683.2021.1874021] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Magnetic resonance imaging of the eye and orbit (MReye) is a cross-domain research field, combining (bio)physics, (bio)engineering, physiology, data sciences and ophthalmology. A growing number of reports document technical innovations of MReye and promote their application in preclinical research and clinical science. Realizing the progress and promises, this review outlines current trends in MReye. Examples of MReye strategies and their clinical relevance are demonstrated. Frontier applications in ocular oncology, refractive surgery, ocular muscle disorders and orbital inflammation are presented and their implications for explorations into ophthalmic diseases are provided. Substantial progress in anatomically detailed, high-spatial resolution MReye of the eye, orbit and optic nerve is demonstrated. Recent developments in MReye of ocular tumors are explored, and its value for personalized eye models derived from machine learning in the treatment planning of uveal melanoma and evaluation of retinoblastoma is highlighted. The potential of MReye for monitoring drug distribution and for improving treatment management and the assessment of individual responses is discussed. To open a window into the eye and into (patho)physiological processes that in the past have been largely inaccessible, advances in MReye at ultrahigh magnetic field strengths are discussed. A concluding section ventures a glance beyond the horizon and explores future directions of MReye across multiple scales, including in vivo electrolyte mapping of sodium and other nuclei. This review underscores the need for the (bio)medical imaging and ophthalmic communities to expand efforts to find solutions to the remaining unsolved problems and technical obstacles of MReye, with the objective to transfer methodological advancements driven by MR physics into genuine clinical value.
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Affiliation(s)
- Thoralf Niendorf
- MRI.TOOLS GmbH, Berlin, Germany.,Berlin Ultrahigh Field Facility, Max Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Jan-Willem M Beenakker
- Department of Ophthalmology and Department of Radiology, Leiden University Medical Centre, Leiden, The Netherlands
| | - Sönke Langner
- Institute of Diagnostic and Interventional Radiology, Pediatric Radiology and Neuroradiology, Rostock University Medical Center, Rostock, Germany
| | - Katharina Erb-Eigner
- Department of Radiology, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität Zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Meritxell Bach Cuadra
- Center for Biomedical Imaging (CIBM), Lausanne, Switzerland.,Department of Radiology, Lausanne University and University Hospital, Lausanne, Switzerland
| | - Ebba Beller
- Institute of Diagnostic and Interventional Radiology, Pediatric Radiology and Neuroradiology, Rostock University Medical Center, Rostock, Germany
| | - Jason M Millward
- Berlin Ultrahigh Field Facility, Max Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | | | - Oliver Stachs
- Department Life, Light & Matter, University Rostock, Rostock, Germany.,Department of Ophthalmology, Rostock University Medical Center, Rostock, Germany
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7
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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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8
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Fagan AJ, Amrami KK, Welker KM, Frick MA, Felmlee JP, Watson RE. Magnetic Resonance Safety in the 7T Environment. Magn Reson Imaging Clin N Am 2020; 28:573-582. [PMID: 33040997 DOI: 10.1016/j.mric.2020.07.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The arrival of 7T MR imaging into the clinic represents a significant step-change in MR technology. This article describes safety concerns associated with imaging at 7T, including the increased magnetic forces on magnetic objects at 7T and the interaction of the 300 MHz (Larmor) radiofrequency energy with tissue in the body. A dedicated multidisciplinary 7T Safety team should develop safety policies and procedures to address these safety challenges and keep abreast of best practice in the field. The off-label imaging of implanted devices is discussed, and also the need for staff training to deal with complexities of patient handling and image interpretation.
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Affiliation(s)
- Andrew J Fagan
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA.
| | - Kimberly K Amrami
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Kirk M Welker
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Matthew A Frick
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Joel P Felmlee
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Robert E Watson
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
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9
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Winter L, Silemek B, Petzold J, Pfeiffer H, Hoffmann W, Seifert F, Ittermann B. Parallel transmission medical implant safety testbed: Real‐time mitigation of RF induced tip heating using time‐domain E‐field sensors. Magn Reson Med 2020; 84:3468-3484. [DOI: 10.1002/mrm.28379] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 05/19/2020] [Accepted: 05/22/2020] [Indexed: 12/15/2022]
Affiliation(s)
- Lukas Winter
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Berk Silemek
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Johannes Petzold
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Harald Pfeiffer
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Werner Hoffmann
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Frank Seifert
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Bernd Ittermann
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
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10
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Image Artifact Management for Clinical Magnetic Resonance Imaging on a 7 T Scanner Using Single-Channel Radiofrequency Transmit Mode. Invest Radiol 2020; 54:781-791. [PMID: 31503079 DOI: 10.1097/rli.0000000000000598] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVES The aim of this work was to devise mitigation strategies for addressing a range of image artifacts on a clinical 7 T magnetic resonance imaging scanner using the regulatory-approved single-channel radiofrequency transmit mode and vendor-supplied radiofrequency coils to facilitate clinical scanning within reasonable scan times. MATERIALS AND METHODS Optimized imaging sequence protocols were developed for routine musculoskeletal knee and neurological imaging. Sources of severe image nonuniformities were identified, and mitigation strategies were devised. A range of custom-made high permittivity dielectric pads were used to compensate for B1 and B1 inhomogeneities, and also for magnetic susceptibility-induced signal dropouts particularly in the basal regions of the temporal lobes and in the cerebellum. RESULTS Significant improvements in image uniformity were obtained using dielectric pads in the knee and brain. A combination of small voxels, reduced field of view B0 shimming, and high in-plane parallel imaging factors helped to minimize signal loss in areas of high susceptibility-induced field distortions. The high inherent signal-to-noise ratio at 7 T allowed for high receiver bandwidths and thin slices to minimize chemical shift artifacts. Intermittent artifacts due to radiofrequency inversion pulse limitations (power, bandwidth) were minimized with dielectric pads. A patient with 2 implanted metallic cranial fixation devices located within the radiofrequency transmit field was successfully imaged, with minimal image geometric distortions. CONCLUSIONS Challenges relating to severe image artifacts at 7 T using single-channel radiofrequency transmit functionality in the knee and brain were overcome using the approaches described in this article. The resultant high diagnostic image quality paves the way for incorporation of this technology into the routine clinical workflow. Further developmental efforts are required to expand the range of applications to other anatomical areas, and to expand the evidence- and knowledge-base relating to the safety of scanning patients with implanted metallic devices.
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11
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Abstract
BACKGROUND It can be expected that the number of 7 T MRI systems for clinical use will increase in the future. On the other hand, almost no medical implant has been labeled MR conditional for 7 T, so far, leaving the question of implant safety unanswered to the MR operator. METHODS In principle, the same interactions between magnetizable and electric conductive material apply at 7 T as known at lower magnetic field strengths. However, there are a few important differences that need to be taken into account to perform a profound risk-benefit analysis. After a more general introduction of technical differences between 3 and 7 T systems, the article will focus mainly on safety assessments with regard to interactions between implant and radiofrequency (RF) transmit fields. In addition, strategies to ensure access at 7 T will be discussed. RESULTS OF PRACTICAL RELEVANCE Besides hazards due to the magnetic force which can be up to 2.3 times stronger at 7 T compared to 3 T, increased risks of RF-induced tissue heating are the most critical aspects. The resonant-length of an implant at 7 T is about 5 cm. Other than at 3 T, MR systems at 7 T are less standardized. Especially with regard to the RF transmit coil and transmission methods used, substantial differences need to be expected. Hence, it is important to critically question published safety assessments of implants and to have a thorough discussion about how this relates to the individual exposure scenario. For nonmagnetic implants without a dedicated 7 T safety evaluation, but which are 3 T MR conditional and have a certain minimum distance to the RF transmit coil, a consensus recommendation from the national network German Ultrahigh Field Imaging (GUFI) may be helpful.
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Affiliation(s)
- O Kraff
- Erwin L. Hahn Institute for MR Imaging, Universität Duisburg-Essen, Kokereiallee 7, 45141, Essen, Deutschland.
| | - H H Quick
- Erwin L. Hahn Institute for MR Imaging, Universität Duisburg-Essen, Kokereiallee 7, 45141, Essen, Deutschland.,Hochfeld- und Hybride MR-Bildgebung, Universitätsklinikum Essen, Essen, Deutschland
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12
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Blackwell J, Oluniran G, Tuohy B, Destrade M, Kraśny MJ, Colgan N. Experimental assessment of clinical MRI-induced global SAR distributions in head phantoms. Phys Med 2019; 66:113-118. [PMID: 31593874 DOI: 10.1016/j.ejmp.2019.09.242] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2019] [Revised: 09/05/2019] [Accepted: 09/28/2019] [Indexed: 01/18/2023] Open
Abstract
OBJECTIVE Accurate estimation of SAR is critical to safeguarding vulnerable patients who require an MRI procedure. The increased static field strength and RF duty cycle capabilities in modern MRI scanners mean that systems can easily exceed safe SAR levels for patients. Advisory protocols routinely used to establish quality assurance protocols are not required to advise on the testing of MRI SAR levels and is not routinely measured in annual medical physics quality assurance checks. This study aims to develop a head phantom and protocol that can independently verify global SAR for MRI clinical scanners. METHODS A four-channel birdcage head coil was used for RF transmission and signal reception. Proton resonance shift thermometry was used to estimate SAR. The SAR estimates were verified by comparing results against two other independent measures, then applied to a further four scanners at field strengths of 1.5 T and 3 T. RESULTS Scanner output SAR values ranged from 0.42 to 1.52 W/kg. Percentage SAR differences between independently estimated values and those calculated by the scanners differed by 0-2.3%. CONCLUSION We have developed a quality assurance protocol to independently verify the SAR output of MRI scanners.
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Affiliation(s)
- J Blackwell
- School of Physics, National University of Ireland Galway, Galway, Ireland; School of Mathematics, Statistics and Applied Mathematics, National University of Ireland Galway, Galway, Ireland.
| | - G Oluniran
- School of Physics, National University of Ireland Galway, Galway, Ireland
| | - B Tuohy
- Medical Physics and Bioengineering, Galway University Hospital, Galway, Ireland
| | - M Destrade
- School of Mathematics, Statistics and Applied Mathematics, National University of Ireland Galway, Galway, Ireland
| | - M J Kraśny
- School of Physics, National University of Ireland Galway, Galway, Ireland
| | - N Colgan
- School of Physics, National University of Ireland Galway, Galway, Ireland
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13
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Noureddine Y, Kraff O, Ladd ME, Wrede K, Chen B, Quick HH, Schaefers G, Bitz AK. Radiofrequency induced heating around aneurysm clips using a generic birdcage head coil at 7 Tesla under consideration of the minimum distance to decouple multiple aneurysm clips. Magn Reson Med 2019; 82:1859-1875. [DOI: 10.1002/mrm.27835] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Revised: 05/08/2019] [Accepted: 05/10/2019] [Indexed: 12/13/2022]
Affiliation(s)
- Yacine Noureddine
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg‐Essen Essen Germany
- MR:comp GmbH, MR Safety Testing Laboratory Gelsenkirchen Germany
| | - Oliver Kraff
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg‐Essen Essen Germany
| | - Mark E. Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg‐Essen Essen Germany
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ) Heidelberg Germany
- Faculty of Physics and Astronomy and Faculty of Medicine University of Heidelberg Heidelberg Germany
| | - Karsten Wrede
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg‐Essen Essen Germany
- Department of Neurosurgery University Hospital Essen Essen Germany
| | - Bixia Chen
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg‐Essen Essen Germany
- Department of Neurosurgery University Hospital Essen Essen Germany
| | - Harald H. Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg‐Essen Essen Germany
- High Field and Hybrid MR, University Hospital Essen Essen Germany
| | - Gregor Schaefers
- MR:comp GmbH, MR Safety Testing Laboratory Gelsenkirchen Germany
- MRI‐STaR – Magnetic Resonance Institute for Safety, Technology and Research GmbH Gelsenkirchen Germany
| | - Andreas K. Bitz
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ) Heidelberg Germany
- Faculty of Electrical Engineering and Information Technology FH Aachen University of Applied Sciences Aachen NRW Germany
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Abstract
Radiofrequency (RF) coils are an essential part of the magnetic resonance (MR) system. To exploit the inherently higher signal-to-noise ratio at ultrahigh magnetic fields (UHF), research sites were forced to build up expertise in RF coil development, as the number of commercially available RF coils were limited. In addition, an integrated transmit body RF coil, which is well-established at MR systems of lower field strength, is still missing at UHF due to technical and physical constraints. This review article provides a brief recapitulation of RF characteristics and RF coils in general to introduce terminology and RF-related parameters, and will then provide an extensive overview of current state-of-the-art RF coils used for MRI from head to toe at 7 Tesla. Finally, a section on RF safety will briefly discuss challenges in performing a safety assessment for custom-designed RF coils, and issues arising from the interaction of the RF field and potentially implanted medical devices.
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Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
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15
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Niendorf T, Schulz-Menger J, Paul K, Huelnhagen T, Ferrari VA, Hodge R. High Field Cardiac Magnetic Resonance Imaging: A Case for Ultrahigh Field Cardiac Magnetic Resonance. Circ Cardiovasc Imaging 2019; 10:CIRCIMAGING.116.005460. [PMID: 28611118 DOI: 10.1161/circimaging.116.005460] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Thoralf Niendorf
- From the Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (T.N., K.P., T.H., R.H.); DZHK (German Centre for Cardiovascular Research), partner site Berlin (T.N., J.S.-M.); Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (J.S.-M.); Department for Cardiology and Nephrology, HELIOS Clinic Berlin-Buch, Germany (J.S.-M.); and Division of Cardiovascular Medicine and Penn Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (V.A.F.).
| | - Jeanette Schulz-Menger
- From the Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (T.N., K.P., T.H., R.H.); DZHK (German Centre for Cardiovascular Research), partner site Berlin (T.N., J.S.-M.); Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (J.S.-M.); Department for Cardiology and Nephrology, HELIOS Clinic Berlin-Buch, Germany (J.S.-M.); and Division of Cardiovascular Medicine and Penn Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (V.A.F.)
| | - Katharina Paul
- From the Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (T.N., K.P., T.H., R.H.); DZHK (German Centre for Cardiovascular Research), partner site Berlin (T.N., J.S.-M.); Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (J.S.-M.); Department for Cardiology and Nephrology, HELIOS Clinic Berlin-Buch, Germany (J.S.-M.); and Division of Cardiovascular Medicine and Penn Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (V.A.F.)
| | - Till Huelnhagen
- From the Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (T.N., K.P., T.H., R.H.); DZHK (German Centre for Cardiovascular Research), partner site Berlin (T.N., J.S.-M.); Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (J.S.-M.); Department for Cardiology and Nephrology, HELIOS Clinic Berlin-Buch, Germany (J.S.-M.); and Division of Cardiovascular Medicine and Penn Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (V.A.F.)
| | - Victor A Ferrari
- From the Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (T.N., K.P., T.H., R.H.); DZHK (German Centre for Cardiovascular Research), partner site Berlin (T.N., J.S.-M.); Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (J.S.-M.); Department for Cardiology and Nephrology, HELIOS Clinic Berlin-Buch, Germany (J.S.-M.); and Division of Cardiovascular Medicine and Penn Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (V.A.F.)
| | - Russell Hodge
- From the Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (T.N., K.P., T.H., R.H.); DZHK (German Centre for Cardiovascular Research), partner site Berlin (T.N., J.S.-M.); Working Group on Cardiovascular Magnetic Resonance, Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany (J.S.-M.); Department for Cardiology and Nephrology, HELIOS Clinic Berlin-Buch, Germany (J.S.-M.); and Division of Cardiovascular Medicine and Penn Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (V.A.F.)
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16
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De Cocker LJ, Lindenholz A, Zwanenburg JJ, van der Kolk AG, Zwartbol M, Luijten PR, Hendrikse J. Clinical vascular imaging in the brain at 7T. Neuroimage 2018; 168:452-458. [PMID: 27867089 PMCID: PMC5862656 DOI: 10.1016/j.neuroimage.2016.11.044] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2016] [Revised: 09/30/2016] [Accepted: 11/16/2016] [Indexed: 01/23/2023] Open
Abstract
Stroke and related cerebrovascular diseases are a major cause of mortality and disability. Even at standard-field-strengths (1.5T), MRI is by far the most sensitive imaging technique to detect acute brain infarctions and to characterize incidental cerebrovascular lesions, such as white matter hyperintensities, lacunes and microbleeds. Arterial time-of-flight (TOF) MR angiography (MRA) can depict luminal narrowing or occlusion of the major brain feeding arteries, and this without the need for contrast administration. Compared to 1.5T MRA, the use of high-field strength (3T) and even more so ultra-high-field strengths (7T), enables the visualization of the lumen of much smaller intracranial vessels, while adding a contrast agent to TOF MRA at 7T may enable the visualization of even more distal arteries in addition to veins and venules. Moreover, with 3T and 7T, the arterial vessel walls beyond the circle of Willis become visible with high-resolution vessel wall imaging. In addition, with 7T MRI, the brain parenchyma can now be visualized on a submillimeter scale. As a result, high-resolution imaging studies of the brain and its blood supply at 7T have generated new concepts of different cerebrovascular diseases. In the current article, we will discuss emerging clinical applications and future directions of vascular imaging in the brain at 7T MRI.
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Affiliation(s)
- Laurens Jl De Cocker
- Department of Radiology, University Medical Center Utrecht, The Netherlands; Department of Radiology, Kliniek Sint-Jan, Brussels, Belgium.
| | - Arjen Lindenholz
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Jaco Jm Zwanenburg
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | | | - Maarten Zwartbol
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Peter R Luijten
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Jeroen Hendrikse
- Department of Radiology, University Medical Center Utrecht, The Netherlands
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Kording F, Ruprecht C, Schoennagel B, Fehrs K, Yamamura J, Adam G, Goebel J, Nassenstein K, Maderwald S, Quick H, Kraff O. Doppler ultrasound triggering for cardiac MRI at 7T. Magn Reson Med 2017; 80:239-247. [DOI: 10.1002/mrm.27032] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 10/09/2017] [Accepted: 11/13/2017] [Indexed: 01/31/2023]
Affiliation(s)
- F. Kording
- Department of Diagnostic and Interventional Radiology and Nuclear Medicine; University Medical Center Hamburg-Eppendorf; Hamburg Germany
| | - C. Ruprecht
- Department of Diagnostic and Interventional Radiology and Nuclear Medicine; University Medical Center Hamburg-Eppendorf; Hamburg Germany
| | - B. Schoennagel
- Department of Diagnostic and Interventional Radiology and Nuclear Medicine; University Medical Center Hamburg-Eppendorf; Hamburg Germany
| | - K. Fehrs
- Department of Diagnostic and Interventional Radiology and Nuclear Medicine; University Medical Center Hamburg-Eppendorf; Hamburg Germany
| | - J. Yamamura
- Department of Diagnostic and Interventional Radiology and Nuclear Medicine; University Medical Center Hamburg-Eppendorf; Hamburg Germany
| | - G. Adam
- Department of Diagnostic and Interventional Radiology and Nuclear Medicine; University Medical Center Hamburg-Eppendorf; Hamburg Germany
| | - J. Goebel
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology; University Hospital, University Duisburg-Essen; Essen Germany
| | - K. Nassenstein
- Department of Diagnostic and Interventional Radiology and Neuroradiology; University Hospital, University Duisburg-Essen; Essen Germany
| | - S. Maderwald
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
| | - H.H. Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- High Field and Hybrid MR Imaging; University Hospital, University Duisburg-Essen; Essen Germany
| | - O. Kraff
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
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18
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Grochowski C, Staśkiewicz G. Ultra high field TOF-MRA: A method to visualize small cerebral vessels. 7T TOF-MRA sequence parameters on different MRI scanners - Literature review. Neurol Neurochir Pol 2017; 51:411-418. [PMID: 28774679 DOI: 10.1016/j.pjnns.2017.06.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Revised: 05/02/2017] [Accepted: 06/30/2017] [Indexed: 11/26/2022]
Abstract
INTRODUCTION Time-of-flight (TOF) angiography is a technique allowing to visualize the blood flow in vessels. 7T ToF-MRA is able to visualize the whole Circle of Willis including small perforating branches without any known side effects as opposed to usually used DSA and CTA with high exposition to the radiation and high doses of contrast as far as CTA is concerned. AIM The aim of this review is to describe ultra-high field ToF-MRA and present different protocol data depending on the scanner used in the study. MATERIALS AND METHODS PubMed, Embase, Ovid, Google Scholar databases were searched. Selection of studies for this systematic review included 7T magnetic resonance angiography studies. We searched for type of head coil used in various studies, flip angle, echo time, repetition time, field-of-view (FOV), number of slices per slab, matrix, voxel size and acquisition time. DISCUSSION Visualization for the small perforating vessels of the Circle of Willis, that are not fully visualized using low-field-strength MRA is improving with increasing magnetic field strength, which has been proved by several studies. CONCLUSION Ultra-high filed ToF-MRA has found to be a superior method in depicting cerebral microvasculature. 7T ToF-MRA seems to be a reliable method for visualization of arteries up to the second order cerebral arteries and has a potential to replace DSA.
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Affiliation(s)
- Cezary Grochowski
- Neurosurgery and Pediatric Neurosurgery Department in Lublin, Medical University of Lublin, Poland.
| | - Grzegorz Staśkiewicz
- Department of Anatomy in Lublin ul. Jaczewskiego 4 (Collegium Anatomicum), Lublin 20-090, Poland
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19
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Kraff O, Quick HH. 7T: Physics, safety, and potential clinical applications. J Magn Reson Imaging 2017; 46:1573-1589. [DOI: 10.1002/jmri.25723] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 03/17/2017] [Indexed: 12/19/2022] Open
Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for MR Imaging; University of Duisburg-Essen; Essen Germany
| | - Harald H. Quick
- Erwin L. Hahn Institute for MR Imaging; University of Duisburg-Essen; Essen Germany
- High Field and Hybrid MR Imaging; University Hospital Essen; Essen Germany
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20
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Fiedler TM, Ladd ME, Bitz AK. SAR Simulations & Safety. Neuroimage 2017; 168:33-58. [PMID: 28336426 DOI: 10.1016/j.neuroimage.2017.03.035] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Revised: 02/28/2017] [Accepted: 03/16/2017] [Indexed: 01/19/2023] Open
Abstract
At ultra-high fields, the assessment of radiofrequency (RF) safety presents several new challenges compared to low-field systems. Multi-channel RF transmit coils in combination with parallel transmit techniques produce time-dependent and spatially varying power loss densities in the tissue. Further, in ultra-high-field systems, localized field effects can be more pronounced due to a transition from the quasi stationary to the electromagnetic field regime. Consequently, local information on the RF field is required for reliable RF safety assessment as well as for monitoring of RF exposure during MR examinations. Numerical RF and thermal simulations for realistic exposure scenarios with anatomical body models are currently the only practical way to obtain the requisite local information on magnetic and electric field distributions as well as tissue temperature. In this article, safety regulations and the fundamental characteristics of RF field distributions in ultra-high-field systems are reviewed. Numerical methods for computation of RF fields as well as typical requirements for the analysis of realistic multi-channel RF exposure scenarios including anatomical body models are highlighted. In recent years, computation of the local tissue temperature has become of increasing interest, since a more accurate safety assessment is expected because temperature is directly related to tissue damage. Regarding thermal simulation, bio-heat transfer models and approaches for taking into account the physiological response of the human body to RF exposure are discussed. In addition, suitable methods are presented to validate calculated RF and thermal results with measurements. Finally, the concept of generalized simulation-based specific absorption rate (SAR) matrix models is discussed. These models can be incorporated into local SAR monitoring in multi-channel MR systems and allow the design of RF pulses under constraints for local SAR.
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Affiliation(s)
- Thomas M Fiedler
- 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
| | - 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, 52066 Aachen, Germany
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21
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Noureddine Y, Kraff O, Ladd ME, Wrede KH, Chen B, Quick HH, Schaefers G, Bitz AK. In vitro and in silico assessment of RF-induced heating around intracranial aneurysm clips at 7 Tesla. Magn Reson Med 2017; 79:568-581. [DOI: 10.1002/mrm.26650] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 01/11/2017] [Accepted: 01/26/2017] [Indexed: 11/12/2022]
Affiliation(s)
- Yacine Noureddine
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- MR:comp GmbH, MR Safety Testing Laboratory; Gelsenkirchen Germany
| | - Oliver Kraff
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
| | - Mark E. Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- Division of Medical Physics in Radiology (E020); German Cancer Research Center (DKFZ); Heidelberg Germany
| | - Karsten H. Wrede
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- Department of Neurosurgery; University Hospital Essen; Essen Germany
| | - Bixia Chen
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- Department of Neurosurgery; University Hospital Essen; Essen Germany
| | - Harald H. Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- High Field and Hybrid MR Imaging; University Hospital Essen; Essen Germany
| | - Gregor Schaefers
- MR:comp GmbH, MR Safety Testing Laboratory; Gelsenkirchen Germany
- MRI-STaR-Magnetic Resonance Institute for Safety, Technology and Research GmbH; Gelsenkirchen Germany
| | - Andreas K. Bitz
- Erwin L. Hahn Institute for Magnetic Resonance Imaging; University Duisburg-Essen; Essen Germany
- Division of Medical Physics in Radiology (E020); German Cancer Research Center (DKFZ); Heidelberg Germany
- Faculty of Electrical Engineering and Information Technology; FH Aachen-University of Applied Sciences; Aachen NRW Germany
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22
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Kabil J, Belguerras L, Trattnig S, Pasquier C, Felblinger J, Missoffe A. A Review of Numerical Simulation and Analytical Modeling for Medical Devices Safety in MRI. Yearb Med Inform 2016:152-158. [PMID: 27830244 DOI: 10.15265/iy-2016-016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
OBJECTIVES To review past and present challenges and ongoing trends in numerical simulation for MRI (Magnetic Resonance Imaging) safety evaluation of medical devices. METHODS A wide literature review on numerical and analytical simulation on simple or complex medical devices in MRI electromagnetic fields shows the evolutions through time and a growing concern for MRI safety over the years. Major issues and achievements are described, as well as current trends and perspectives in this research field. RESULTS Numerical simulation of medical devices is constantly evolving, supported by calculation methods now well-established. Implants with simple geometry can often be simulated in a computational human model, but one issue remaining today is the experimental validation of these human models. A great concern is to assess RF heating on implants too complex to be traditionally simulated, like pacemaker leads. Thus, ongoing researches focus on alternative hybrids methods, both numerical and experimental, with for example a transfer function method. For the static field and gradient fields, analytical models can be used for dimensioning simple implants shapes, but limited for complex geometries that cannot be studied with simplifying assumptions. CONCLUSIONS Numerical simulation is an essential tool for MRI safety testing of medical devices. The main issues remain the accuracy of simulations compared to real life and the studies of complex devices; but as the research field is constantly evolving, some promising ideas are now under investigation to take up the challenges.
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Affiliation(s)
| | | | | | | | - J Felblinger
- Jacques Felblinger, Ph.D, Prof., Laboratoire IADI (UL-INSERM U947), CHRU Nancy Brabois, Rue du Morvan, 54511 Vandoeuvre Cedex, France, Tel: + 33 3 83 15 49 76, E-Mail:
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Oberacker E, Paul K, Huelnhagen T, Oezerdem C, Winter L, Pohlmann A, Boehmert L, Stachs O, Heufelder J, Weber A, Rehak M, Seibel I, Niendorf T. Magnetic resonance safety and compatibility of tantalum markers used in proton beam therapy for intraocular tumors: A 7.0 Tesla study. Magn Reson Med 2016; 78:1533-1546. [DOI: 10.1002/mrm.26534] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2016] [Revised: 09/29/2016] [Accepted: 10/07/2016] [Indexed: 12/13/2022]
Affiliation(s)
- Eva Oberacker
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
| | - Katharina Paul
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
| | - Till Huelnhagen
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
| | - Celal Oezerdem
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
| | - Andreas Pohlmann
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
| | - Laura Boehmert
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
| | - Oliver Stachs
- Department of Ophthalmology; University of Rostock; Rostock Germany
| | - Jens Heufelder
- Charité-Universitätsmedizin Berlin, BerlinProtonen am HZB; Berlin Germany
| | - Andreas Weber
- Charité-Universitätsmedizin Berlin, BerlinProtonen am HZB; Berlin Germany
| | - Matus Rehak
- Charité-Universitätsmedizin Berlin, Klinik für Augenheilkunde Campus Benjamin Franklin; Berlin Germany
| | - Ira Seibel
- Charité-Universitätsmedizin Berlin, Klinik für Augenheilkunde Campus Benjamin Franklin; Berlin Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
- Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association; Berlin Germany
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24
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Chen B, Schoemberg T, Kraff O, Dammann P, Bitz AK, Schlamann M, Quick HH, Ladd ME, Sure U, Wrede KH. Cranial fixation plates in cerebral magnetic resonance imaging: a 3 and 7 Tesla in vivo image quality study. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2016; 29:389-98. [DOI: 10.1007/s10334-016-0548-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Revised: 03/02/2016] [Accepted: 03/10/2016] [Indexed: 01/26/2023]
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25
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Wrede KH, Matsushige T, Goericke SL, Chen B, Umutlu L, Quick HH, Ladd ME, Johst S, Forsting M, Sure U, Schlamann M. Non-enhanced magnetic resonance imaging of unruptured intracranial aneurysms at 7 Tesla: Comparison with digital subtraction angiography. Eur Radiol 2016; 27:354-364. [DOI: 10.1007/s00330-016-4323-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 03/02/2016] [Accepted: 03/05/2016] [Indexed: 11/25/2022]
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26
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Experience with magnetic resonance imaging of human subjects with passive implants and tattoos at 7 T: a retrospective study. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2015; 28:577-90. [DOI: 10.1007/s10334-015-0499-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2015] [Revised: 07/25/2015] [Accepted: 08/19/2015] [Indexed: 10/23/2022]
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27
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Non-Enhanced MR Imaging of Cerebral Arteriovenous Malformations at 7 Tesla. Eur Radiol 2015; 26:829-39. [DOI: 10.1007/s00330-015-3875-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Revised: 05/21/2015] [Accepted: 06/03/2015] [Indexed: 10/23/2022]
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28
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Dharmadhikari S, James JR, Nyenhuis J, Bansal N. Evaluation of radiofrequency safety by high temperature resolution MR thermometry using a paramagnetic lanthanide complex. Magn Reson Med 2015; 75:2121-9. [DOI: 10.1002/mrm.25792] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 05/05/2015] [Accepted: 05/06/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Shalmali Dharmadhikari
- School of Health Sciences, Purdue University; West Lafayette Indiana USA
- Department of Radiology and Imaging Sciences; Indiana University School of Medicine; Indianapolis Indiana USA
| | - Judy R. James
- Department of Radiology; Mayo Clinic, Scottsdale; Arizona USA
| | - John Nyenhuis
- Department of Electrical and Computer Engineering; Purdue University; West Lafayette Indiana USA
| | - Navin Bansal
- Department of Radiology and Imaging Sciences; Indiana University School of Medicine; Indianapolis Indiana USA
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Winter L, Oberacker E, Özerdem C, Ji Y, von Knobelsdorff-Brenkenhoff F, Weidemann G, Ittermann B, Seifert F, Niendorf T. On the RF heating of coronary stents at 7.0 Tesla MRI. Magn Reson Med 2014; 74:999-1010. [PMID: 25293952 DOI: 10.1002/mrm.25483] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Revised: 09/11/2014] [Accepted: 09/11/2014] [Indexed: 12/16/2022]
Abstract
PURPOSE Examine radiofrequency (RF) induced heating of coronary stents at 7.0 Tesla (T) to derive an analytical approach which supports RF heating assessment of arbitrary stent geometries and RF coils. METHODS Simulations are performed to detail electromagnetic fields (EMF), local specific absorption rates (SAR) and temperature changes. For validation E-field measurements and RF heating experiments are conducted. To progress to clinical setups RF coils tailored for cardiac MRI at 7.0T and coronary stents are incorporated into EMF simulations using a human voxel model. RESULTS Our simulations of coronary stents at 297 MHz were confirmed by E-field and temperature measurements. An analytical solution which describes SAR(1g tissue voxel) induced by an arbitrary coronary stent interfering with E-fields generated by an arbitrary RF coil was derived. The analytical approach yielded a conservative estimation of induced SAR(1g tissue voxel) maxima without the need for integrating the stent into EMF simulations of the human voxel model. CONCLUSION The proposed analytical approach can be applied for any patient, coronary stent type, RF coil configuration and RF transmission regime. The generalized approach is of value for RF heating assessment of other passive electrically conductive implants and provides a novel design criterion for RF coils.
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Affiliation(s)
- Lukas Winter
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Eva Oberacker
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Celal Özerdem
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Yiyi Ji
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Florian von Knobelsdorff-Brenkenhoff
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany.,Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Gerd Weidemann
- Physikalisch Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Bernd Ittermann
- Physikalisch Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Frank Seifert
- Physikalisch Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany.,Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
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Wrede KH, Johst S, Dammann P, Özkan N, Mönninghoff C, Kraemer M, Maderwald S, Ladd ME, Sure U, Umutlu L, Schlamann M. Improved cerebral time-of-flight magnetic resonance angiography at 7 Tesla--feasibility study and preliminary results using optimized venous saturation pulses. PLoS One 2014; 9:e106697. [PMID: 25232868 PMCID: PMC4169393 DOI: 10.1371/journal.pone.0106697] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Accepted: 08/07/2014] [Indexed: 11/24/2022] Open
Abstract
Purpose Conventional saturation pulses cannot be used for 7 Tesla ultra-high-resolution time-of-flight magnetic resonance angiography (TOF MRA) due to specific absorption rate (SAR) limitations. We overcome these limitations by utilizing low flip angle, variable rate selective excitation (VERSE) algorithm saturation pulses. Material and Methods Twenty-five neurosurgical patients (male n = 8, female n = 17; average age 49.64 years; range 26–70 years) with different intracranial vascular pathologies were enrolled in this trial. All patients were examined with a 7 Tesla (Magnetom 7 T, Siemens) whole body scanner system utilizing a dedicated 32-channel head coil. For venous saturation pulses a 35° flip angle was applied. Two neuroradiologists evaluated the delineation of arterial vessels in the Circle of Willis, delineation of vascular pathologies, presence of artifacts, vessel-tissue contrast and overall image quality of TOF MRA scans in consensus on a five-point scale. Normalized signal intensities in the confluence of venous sinuses, M1 segment of left middle cerebral artery and adjacent gray matter were measured and vessel-tissue contrasts were calculated. Results Ratings for the majority of patients ranged between good and excellent for most of the evaluated features. Venous saturation was sufficient for all cases with minor artifacts in arteriovenous malformations and arteriovenous fistulas. Quantitative signal intensity measurements showed high vessel-tissue contrast for confluence of venous sinuses, M1 segment of left middle cerebral artery and adjacent gray matter. Conclusion The use of novel low flip angle VERSE algorithm pulses for saturation of venous vessels can overcome SAR limitations in 7 Tesla ultra-high-resolution TOF MRA. Our protocol is suitable for clinical application with excellent image quality for delineation of various intracranial vascular pathologies.
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Affiliation(s)
- Karsten H. Wrede
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Neurosurgery, University Hospital Essen, Essen, Germany
- * E-mail:
| | - Sören Johst
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Philipp Dammann
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Neurosurgery, University Hospital Essen, Essen, Germany
| | - Neriman Özkan
- Department of Neurosurgery, University Hospital Essen, Essen, Germany
| | - Christoph Mönninghoff
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Markus Kraemer
- Department of Neurology, Alfried Krupp von Bohlen und Halbach Hospital, Essen, Germany
| | - Stefan Maderwald
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Mark E. Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
- Division of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Ulrich Sure
- Department of Neurosurgery, University Hospital Essen, Essen, Germany
| | - Lale Umutlu
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Marc Schlamann
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
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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: 126] [Impact Index Per Article: 12.6] [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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Zhao W, Cohen-Adad J, Polimeni JR, Keil B, Guerin B, Setsompop K, Serano P, Mareyam A, Hoecht P, Wald LL. Nineteen-channel receive array and four-channel transmit array coil for cervical spinal cord imaging at 7T. Magn Reson Med 2013; 72:291-300. [PMID: 23963998 DOI: 10.1002/mrm.24911] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 06/12/2013] [Accepted: 07/15/2013] [Indexed: 11/10/2022]
Abstract
PURPOSE To design and validate a radiofrequency (RF) array coil for cervical spinal cord imaging at 7T. METHODS A 19-channel receive array with a four-channel transmit array was developed on a close-fitting coil former at 7T. Transmit efficiency and specific absorption rate were evaluated in a B1 (+) mapping study and an electromagnetic model. Receive signal-to-noise ratio (SNR) and noise amplification for parallel imaging were evaluated and compared with a commercial 3T 19-channel head-neck array and a 7T four-channel spine array. The performance of the array was qualitatively demonstrated in human volunteers using high-resolution imaging (down to 300 μm in-plane). RESULTS The transmit and receive arrays showed good bench performance. The SNR was approximately 4.2-fold higher in the 7T receive array at the location of the cord with respect to the 3T coil. The g-factor results showed an additional acceleration was possible with the 7T array. In vivo imaging was feasible and showed high SNR and tissue contrast. CONCLUSION The highly parallel transmit and receive arrays were demonstrated to be fit for spinal cord imaging at 7T. The high sensitivity of the receive coil combined with ultra-high field will likely improve investigations of microstructure and tissue segmentation in the healthy and pathological spinal cord.
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Affiliation(s)
- Wei Zhao
- A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA; Harvard Medical School, Boston, Massachusetts, USA
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