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Duan S, Wu X, Shi J, Li W, Dong Q, Xin SX. Study of the radiofrequency-induced heating inside the human head with dental implants at 7 T. Bioelectromagnetics 2024; 45:82-93. [PMID: 37860924 DOI: 10.1002/bem.22490] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2023] [Revised: 08/28/2023] [Accepted: 10/09/2023] [Indexed: 10/21/2023]
Abstract
Conductive dental implants are commonly used in restorative therapy to replace missing teeth in patients. Ensuring the radiofrequency (RF) safety of these patients is crucial when performing 7 T magnetic resonance scans of their heads. This study aimed to investigate RF-induced heating inside the human head with dental implants at 7 T. Dental implants and their attachments were fabricated and integrated into an anatomical head model, creating different measurement configurations (MCs). Numerical simulations were conducted using a 7 T transmit coil loaded with the anatomical head model, both with and without dental implants. The maximum temperatures inside the head for various MCs were computed using the maximum permissible input powers (MPIPs) obtained without dental implants and compared with published limits. Additionally, the MPIPs with dental implants were calculated for scenarios where the temperature limits were exceeded. The maximum temperatures observed inside the head ranged from 38.4°C to 39.6°C. The MPIPs in the presence of dental implants were 81.9%-97.3% of the MPIPs in the absence of dental implants for scenarios that exceeded the regulatory limit. RF-induced heating effect of the dental implants was not significant. The safe scanning condition in terms of RF exposure was achievable for patients with dental implants. For patients with conductive dental implants of unknown configuration, it is recommended to reduce the input power by 18.1% of MPIP without dental implants to ensure RF safety.
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Affiliation(s)
- Song Duan
- Department of Radiation Oncology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, Guangdong, China
| | - Xiuxiu Wu
- Department of Radiation Oncology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, Guangdong, China
| | - Juntian Shi
- Department of Radiation Oncology, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, Guangdong, China
| | - Wenhui Li
- Department of Dentistry, Air Force Hospital of Southern Theater Command of PLA, Guangzhou, Guangdong, China
| | - Qingshan Dong
- Department of Stomatology, General Hospital of Central Theater Command of PLA, WuHan, China
| | - Sherman Xuegang Xin
- Biophysics and Medical Imaging Lab, School of Medicine, South China University of Technology, Guangzhou, Guangdong, China
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2
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Jacobs P, Fagan AJ. The effect of frequency (64-498 MHz) on specific absorption rate adjacent to metallic orthopedic screws in MRI: A numerical simulation study. Med Phys 2024; 51:1074-1082. [PMID: 38116822 PMCID: PMC10922637 DOI: 10.1002/mp.16902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Revised: 11/04/2023] [Accepted: 12/04/2023] [Indexed: 12/21/2023] Open
Abstract
BACKGROUND The imaging of patients with implanted electrically-conductive devices via magnetic resonance imaging at ultra-high fields is hampered by uncertainties relating to the potential for inducing tissue heating adjacent to the implant due to coupling of energy from the incident electromagnetic field into the implant. Existing data in the peer-reviewed literature of comparisons across field strengths of tissue heating and its surrogate, the specific absorption rate (SAR), is scarce and contradictory, leading to further doubts pertaining to the safety of imaging patients with such devices. PURPOSE The radiofrequency-induced SAR adjacent to orthopedic screws of varying length and at frequencies of 64 to 498 MHz was investigated via full-wave electromagnetic simulations, to provide an accurate comparison of SAR across MRI field strengths. METHODS Dipole antennas were used for RF transmission to achieve a uniform electric field tangential to the screws located 120 mm above the antenna midpoints, embedded in a bone-mimicking material. The input power to the antennas was constrained to achieve the following targets without the screw present: (i) E = 100 V/m, (ii) B1 + = 2 μT, and (iii) global-average-SAR = 3.2 W/kg. Simulations were performed with a spatial resolution of 0.2 mm in the volume surrounding the screws, resulting in 76-137 MCells, noting the maximum 1 g-averaged SAR value in each case. Simulations were repeated at 128 and 297 MHz for screws embedded in muscle tissue. RESULTS The peak SAR, occurring at the resonant screw length, substantially increased as the frequency decreased when the input power to the dipole antenna was constrained to achieve constant electric field in background tissue at the screws' locations. A similar pattern was observed when constraining input power to achieve constant B1 + and global-average-SAR. The dielectric properties of the tissue in which the screws were embedded dominated the SAR comparisons between 297 and 128 MHz. CONCLUSIONS The study design allowed for a direct comparison to be performed of SAR across frequencies and implant lengths without the confounding effect of variable incident electric field. Lower frequencies produced substantially larger SAR values for implants approaching the resonant length for the worst-case uniform incident electric field along the screws' length. The data may inform risk-benefit assessments for imaging patients with orthopedic implants at the new clinical field strength of 7 Tesla.
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Affiliation(s)
- Paul Jacobs
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - Andrew J Fagan
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
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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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Tsutsui S, Matsuda T, Takeda K, Sasaki M, Kubo Y, Setta K, Fujiwara S, Chida K, Ogasawara K. Assessment of Heating on Titanium Alloy Cerebral Aneurysm Clips during 7T MRI. AJNR Am J Neuroradiol 2022; 43:972-977. [PMID: 35738672 DOI: 10.3174/ajnr.a7561] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 05/06/2022] [Indexed: 12/15/2022]
Abstract
BACKGROUND AND PURPOSE Patients with cerebral aneurysms often undergo MR imaging after microsurgical clipping. Ultra-high-field MR imaging at 7T may provide high diagnostic capability in such clinical situations. However, titanium alloy clips have safety issues such as adverse interactions with static magnetic fields and radiofrequency-induced heating during 7T MR imaging. The purpose of this study was to quantitatively assess temperature increases on various types of titanium alloy aneurysm clips during 7T MR imaging. MATERIALS AND METHODS Five types of titanium alloy aneurysm clips were tested, including combinations of short, long, straight, angled, and fenestrated types. Each clip was set in a phantom filled with gelled saline mixed with polyacrylic acid and underwent 7T MR imaging with 3D T1WI with a spoiled gradient recalled acquisition in the steady-state technique. Temperature was chronologically measured at the tips of the clip blade and head, angled part of the clip, and 5 mm from the tip of the clip head using MR imaging-compatible fiber-optic thermometers. RESULTS Temperature increases at all locations for right-angled and short straight clips were <1°C. Temperature increases at the angled part for the 45° angled clip and the tip of the clip head for the straight fenestrated clip were >1°C. Temperature increases at all locations for the long straight clip were >2°C. CONCLUSIONS Temperature increases on the right-angled and short straight clips remained below the regulatory limit during 7T MR imaging, but temperature increases on the 45° angled, straight fenestrated, and long straight clips exceeded this limit.
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Affiliation(s)
- S Tsutsui
- From the Department of Neurosurgery (S.T., Y.K., K.S., S.F., K.C., K.O.)
| | - T Matsuda
- Division of Ultrahigh Field MRI (T.M., K.T., M.S.), Institute for Biomedical Sciences, Iwate Medical University School of Medicine, Morioka, Japan
| | - K Takeda
- Division of Ultrahigh Field MRI (T.M., K.T., M.S.), Institute for Biomedical Sciences, Iwate Medical University School of Medicine, Morioka, Japan
| | - M Sasaki
- Division of Ultrahigh Field MRI (T.M., K.T., M.S.), Institute for Biomedical Sciences, Iwate Medical University School of Medicine, Morioka, Japan
| | - Y Kubo
- From the Department of Neurosurgery (S.T., Y.K., K.S., S.F., K.C., K.O.)
| | - K Setta
- From the Department of Neurosurgery (S.T., Y.K., K.S., S.F., K.C., K.O.)
| | - S Fujiwara
- From the Department of Neurosurgery (S.T., Y.K., K.S., S.F., K.C., K.O.)
| | - K Chida
- From the Department of Neurosurgery (S.T., Y.K., K.S., S.F., K.C., K.O.)
| | - K Ogasawara
- From the Department of Neurosurgery (S.T., Y.K., K.S., S.F., K.C., K.O.)
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5
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Tang M, Yamamoto T. Progress in Understanding Radiofrequency Heating and Burn Injuries for Safer MR Imaging. Magn Reson Med Sci 2022; 22:7-25. [PMID: 35228437 PMCID: PMC9849420 DOI: 10.2463/mrms.rev.2021-0047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
RF electromagnetic wave exposure during MRI scans induces heat and occasionally causes burn injuries to patients. Among all the types of physical injuries that have occurred during MRI examinations, RF burn injuries are the most common ones. The number of RF burn injuries increases as the static magnetic field of MRI systems increases because higher RFs lead to higher heating. The commonly believed mechanisms of RF burn injuries are the formation of a conductive loop by the patient's posture or cables, such as an electrocardiogram lead; however, the mechanisms of RF burn injuries that occur at the contact points, such as the bore wall and the elbow, remain unclear. A comprehensive understanding of RF heating is needed to address effective countermeasures against all RF burn injuries for safe MRI examinations. In this review, we summarize the occurrence of RF burn injury cases by categorizing RF burn injuries reported worldwide in recent decades. Safety standards and regulations governing RF heating that occurs during MRI examinations are presented, along with their theoretical and physiological backgrounds. The experimental assessment techniques for RF heating are then reviewed, and the development of numerical simulation techniques is explained. In addition, a comprehensive theoretical interpretation of RF burn injuries is presented. By including the results of recent experimental and numerical simulation studies on RF heating, this review describes the progress achieved in understanding RF heating from the standpoint of MRI burn injury prevention.
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Affiliation(s)
- Minghui Tang
- Department of Diagnostic Imaging, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, Hokkaido, Japan
| | - Toru Yamamoto
- Division of Biomedical Engineering and Science, Faculty of Health Sciences, Hokkaido University, Sapporo, Hokkaido, Japan,Corresponding author: Faculty of Health Sciences, Hokkaido University, Kita 12 Nishi 5, Kita-ku, Sapporo, Hokkaido 060-0812, Japan. Phone: +81-11-706-3412, Fax: +81-11-706-4916, E-mail:
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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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Winter L, Seifert F, Zilberti L, Murbach M, Ittermann B. MRI‐Related Heating of Implants and Devices: A Review. J Magn Reson Imaging 2020; 53:1646-1665. [DOI: 10.1002/jmri.27194] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 04/29/2020] [Accepted: 04/30/2020] [Indexed: 12/11/2022] Open
Affiliation(s)
- Lukas Winter
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Frank Seifert
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Luca Zilberti
- Istituto Nazionale di Ricerca Metrologica Torino Italy
| | - Manuel Murbach
- ZMT Zurich MedTech AG Zurich Switzerland
- Institute for Molecular Instrumentation and Imaging (i3M) Universidad Politécnica de Valencia (UPV) Valencia Spain
| | - Bernd Ittermann
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
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