Managing Patients With Unlabeled Passive Implants on MR Systems Operating Below 1.5 T.

The standard of care for managing a patient with an implant is to identify the item and to assess the relative safety of scanning the patient. Because the 1.5 T MR system is the most prevalent scanner in the world and 3 T is the highest field strength in widespread use, implants typically have "MR Conditional" (i.e., an item with demonstrated safety in the MR environment within defined conditions) labeling at 1.5 and/or 3 T only. This presents challenges for a facility that has a scanner operating at a field strength below 1.5 T when encountering a patient with an implant, because scanning the patient is considered "off-label." In this case, the supervising physician is responsible for deciding whether to scan the patient based on the risks associated with the implant and the benefit of magnetic resonance imaging (MRI). For a passive implant, the MRI safety-related concerns are static magnetic field interactions (i.e., force and torque) and radiofrequency (RF) field-induced heating. The worldwide utilization of scanners operating below 1.5 T combined with the increasing incidence of patients with implants that need MRI creates circumstances that include patients potentially being subjected to unsafe imaging conditions or being denied access to MRI because physicians often lack the knowledge to perform an assessment of risk vs. benefit. Thus, physicians must have a complete understanding of the MRI-related safety issues that impact passive implants when managing patients with these products on scanners operating below 1.5 T. This monograph provides an overview of the various clinical MR systems operating below 1.5 T and discusses the MRI-related factors that influence safety for passive implants. Suggestions are provided for the management of patients with passive implants labeled MR Conditional at 1.5 and/or 3 T, referred to scanners operating below 1.5 T. The purpose of this information is to empower supervising physicians with the essential knowledge to perform MRI exams confidently and safely in patients with passive implants. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 3.

Benefits of Using Magnetic Resonance Imaging During Breast Tissue Expansion: Literature Review and Case Series.

Breast cancer results in up to 1.6 million new candidates for yearly breast reconstruction (BR) surgery. Two-stage breast reconstruction surgery with the use of a tissue expander (TE) is a common approach to reconstructing the breast after mastectomy. However, a common disadvantage encountered with the traditional breast TE is the magnetic injection port, which has been reported to cause injuries in patients undergoing magnetic resonance (MR) imaging. Therefore this type of breast TE is labeled "MR unsafe." Recent technological advances have incorporated radio-frequency identification (RFID) technology in the TE to allow for the location of the injection port without magnetic components, resulting in an MR-conditional TE. This paper aims to review the information regarding the safety profile of TEs with magnetic ports and to gather distinct clinical scenarios in which an MR-conditional TE benefits the patient during the BR process. A literature review ranging from 2018 to 2022 was performed with the search terms: "tissue expander" OR "breast tissue expander" AND "magnetic resonance imaging" OR "MRI." Additionally, a case series was collected from each of the authors' practices. The literature search yielded 13 recent peer-reviewed papers, and 6 distinct clinical scenarios were compiled and discussed. Most clinicians find MRI examinations to be the state-of-art diagnostic imaging modality. However, due to the preexisting risks associated with TEs with magnetic ports, the MRI labeling classification should be considered when deciding which TE is the most appropriate for the patient requiring MRI examinations.

ACR guidance document on MR safe practices: Updates and critical information 2019.

The need for a guidance document on MR safe practices arose from a growing awareness of the MR environment's potential risks and adverse event reports involving patients, equipment, and personnel. Initially published in 2002, the American College of Radiology White Paper on MR Safety established de facto industry standards for safe and responsible practices in clinical and research MR environments. The most recent version addresses new sources of risk of adverse events, increases awareness of dynamic MR environments, and recommends that those responsible for MR medical director safety undergo annual MR safety training. With regular updates to these guidelines, the latest MR safety concerns can be accounted for to ensure a safer MR environment where dangers are minimized. Level of Evidence: 1 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2020;51:331-338.

Breast Tissue Expander With Radiofrequency Identification Port: Assessment of MRI Issues.

OBJECTIVE. Breast tissue expanders with magnetic ports are MRI unsafe, preventing patients from benefiting from the diagnostic capabilities of MRI. A tissue expander was recently developed with a radiofrequency identification (RFID) port used for needle location and expansion that may be acceptable for a patient undergoing MRI. The purpose of this investigation was to evaluate MRI issues using standardized techniques and well-accepted methods for this tissue expander with RFID port. MATERIALS AND METHODS. The breast tissue expander with RFID port (Motiva Flora Tissue Expander, Establishment Labs) was assessed for magnetic field interactions (translational attraction and torque, 3 T), MRI-related heating (1.5 T/64 MHz and 3 T/128 MHz), artifacts (3 T), and functional changes associated with different MRI conditions (1.5 T/64 MHz and 3 T/128 MHz). RESULTS. Magnetic field interactions were minor (deflection angle of 2° and no torque) and thus will not pose a risk. At 1.5 T/64 MHz and 3 T/128 MHz, the highest temperature elevations (1.7°C and 1.9°C, respectively) were physiologically inconsequential. The tissue expander with RFID port exhibited relatively small artifacts on MRI. Exposures of the tissue expander with RFID port to different MRI conditions did not impact the ability to localize the RFID port or to read the electronic serial number. CONCLUSION. The findings indicated that this tissue expander with RFID port is "MR Conditional" for a patient referred for MRI at 1.5 T or 3 T. Importantly, the relatively small artifact associated with this implant offers potential advantages for patients undergoing MRI compared with tissue expanders that have magnetic ports that create substantial signal losses and distortions on MR images.

Evaluation of MRI Issues for a New Wirelessly Powered, Spinal Cord Stimulation Lead With Receiver.

OBJECTIVE. MRI is an imaging modality frequently ordered for patients with neuromodulation systems implanted for spinal cord stimulation. The purpose of this investigation was to evaluate MRI safety issues (magnetic field interactions, MRI-related heating, functional disturbances, and artifacts) for a new wirelessly powered lead with receiver used for SCS. MATERIALS AND METHODS. Lead samples underwent in vitro evaluation for MRI safety issues using standardized techniques. Magnetic field interactions (i.e., translational attraction and torque) and artifacts were tested at 3 T. MRI-related heating was performed at 1.5 T/64 MHz and 3 T/128 MHz using two different methods: numerical simulations with analytical modeling and physical testing. Possible functional disturbances were evaluated under exposures to 1.5-T/64-MHz and 3-T/128-MHz MRI conditions. RESULTS. The lead exhibited minor magnetic field interactions (22° deflection angle, no torque) at 3 T. The highest temperature change recorded at 1.5 T/64 MHz and 3 T/128 MHz was 3.8°C and 11.3°C, respectively. Exposures to MRI conditions did not damage or alter the functional aspects of the leads. The maximum artifact size seen on a gradient-echo pulse sequence extended approximately 10 mm relative to the size of the lead. CONCLUSION. The MRI tests performed on patients with the new lead with receiver revealed no substantial concerns with respect to the conditions that we provide in the safety guidelines that were based on the results of this investigation. Therefore, MRI examinations will result in acceptable heating when conducted at appropriate whole-body-averaged specific absorption rate levels (i.e., 2.0 W/kg at 1.5 T/64 MHz and 0.3 W/kg at 3 T/128 MHz, corresponding to adjusted temperature rises of 3.6°C and 1.2°C, respectively). Therefore, patients with this wirelessly powered lead and receiver implanted can safely undergo MRI examinations under specific conditions.

MRI Evaluation of an Atrial-Anchored Transcatheter Mitral Valve Replacement Implant.

OBJECTIVE. A medical implant that is made from metal must undergo proper MRI testing to ensure patient safety. The purpose of this investigation was to assess issues with MRI with a newly developed atrial-anchored transcatheter mitral valve replacement (TMVR) implant. MATERIALS AND METHODS. The atrial-anchored TMVR implant underwent an in vitro evaluation for MRI safety issues using standardized techniques and well-accepted methods. Magnetic field interactions including translational attraction and torque and artifacts were tested at 3 T. MRI-related heating was assessed at 1.5 T/64 MHz and 3 T/128 MHz using numeric simulations with analytical modeling and experimental testing. RESULTS. The atrial-anchored TMVR implant exhibited minor magnetic field interactions (9° deflection angle and no torque) at 3 T. The findings from the numeric simulations with analytical modeling were used to guide the placement of the implant in the phantom for the heating test and to identify the position on the implant that would result in the highest temperature rise. The highest temperature elevations recorded for the TMVR implant obtained on MRI at 1.5 T/64 MHz and 3 T/128 MHz were 2.7°C and 2.4°C, respectively. The maximum artifact size seen on a gradient echo pulse sequence extended approximately 5 mm relative to the size of the implant. CONCLUSION. The results of the tests performed on the atrial-anchored TMVR implant revealed no substantial concerns with respect to the conditions used in this investigation. Therefore, a patient with this new implant can safely undergo MRI by following the specific conditions defined by this study. The implant was deemed MR Conditional.

Safety Considerations of 7-T MRI in Clinical Practice.

Although 7-T MRI has recently received approval for use in clinical patient care, there are distinct safety issues associated with this relatively high magnetic field. Forces on metallic implants and radiofrequency power deposition and heating are safety considerations at 7 T. Patient bioeffects such as vertigo, dizziness, false feelings of motion, nausea, nystagmus, magnetophosphenes, and electrogustatory effects are more common and potentially more pronounced at 7 T than at lower field strengths. Herein the authors review safety issues associated with 7-T MRI. The rationale for safety concerns at this field strength are discussed as well as potential approaches to mitigate risk to patients and health care professionals.

Evaluation of Magnetic Resonance Imaging Safety and Imaging Issues Associated with the Occlusion Balloon Used during Fetoscopic Endoluminal Tracheal Occlusion.

INTRODUCTION: Congenital diaphragmatic hernias can be successfully treated by fetoscopic tracheal occlusion (FETO), a minimally invasive procedure that may improve postnatal survival. The endoluminal balloon utilized for FETO contains a metallic component that may pose possible risks for the fetus and mother related to the use of magnetic resonance imaging (MRI). The objective of this study is to evaluate MRI-related imaging and safety issues (magnetic field interactions, heating, and artifacts) for the occlusion balloon used in FETO. MATERIALS AND METHODS: Using well-established techniques, tests were performed to assess magnetic field interactions (translational attraction and torque) and MRI-related heating and artifacts that occurred when exposing the occlusion balloon typically used for FETO (Goldbal2, Balt, www.balt.fr) to a 3-T magnet. MRI-related heating was determined by placing the occlusion balloon in a gelled-saline-filled, head-torso phantom and conducting MRI at relatively high, whole-body-averaged specific absorption rate (2.9 W/kg) for 15 min. Artifacts were measured in association with the use of T1-weighted, spin-echo and gradient-echo pulse sequences. RESULTS: The balloon displayed minor magnetic field interactions and physiologically inconsequential heating (highest temperature rise: 0.1°C above background). Artifacts extended approximately 10 mm from the occlusion balloon on the gradient-echo pulse sequence, suggesting that anatomy located at a position greater than this distance may be visualized on MRI. DISCUSSION: In this paper, we demonstrate that the risks of performing MRI at 3 T or less in a patient who has this occlusion balloon in place are acceptable (or MR conditional, using current terminology).

Assessment of MRI issues at 1.5 T for the Temperature Logger Implant.

PURPOSE: The Temperature Logger Implant is a newly developed device that is capable of providing data for animal studies on thermoregulatory function, hibernation, hypothermia, and general health. During research, it may be necessary to conduct a magnetic resonance imaging (MRI) examination on an animal with this device implanted to assess anatomical changes or other conditions. Notably, this new device was specially designed to be unaffected by the electromagnetic fields used for MRI. Therefore, to verify that there would be no problems related to MRI, the purpose of this investigation was to evaluate MRI-related issues for the Temperature Logger Implant. METHODS: Tests were performed on the Temperature Logger Implant using well-accepted techniques to evaluate magnetic field interactions (translational attraction and torque, 1.5 T), MRI-related heating (whole body averaged specific absorption rate, 2.9 W/kg), artifacts (T1-weighted, spin echo and gradient echo pulse sequences), and functional changes related to exposure to eight different imaging conditions. RESULTS: Magnetic field interactions were relatively low (deflection angle 4°, no torque) and heating was minor (highest temperature rise, > 1.1 °C) indicating that these factors will not pose a hazard to an animal. The largest artifact (gradient echo pulse sequence) extended 10 mm from the size and shape of the Temperature Logger Implant. Exposure to the eight different conditions at 1.5 T/ 64 MHz did not alter or damage the operational aspects of the device. CONCLUSIONS: The findings demonstrated that MRI can be performed safely on an animal with this new Temperature Logger Implant and, thus, this device is deemed "MR Conditional" (i.e., using current labeling terminology), according to the conditions used in this investigation.

In Vitro Magnetic Resonance Imaging Evaluation of Fragmented, Open-Coil, Percutaneous Peripheral Nerve Stimulation Leads.

OBJECTIVE: Percutaneous peripheral nerve stimulation (PNS) is an FDA-cleared pain treatment. Occasionally, fragments of the lead (MicroLead, SPR Therapeutics, LLC, Cleveland, OH, USA) may be retained following lead removal. Since the lead is metallic, there are associated magnetic resonance imaging (MRI) risks. Therefore, the objective of this investigation was to evaluate MRI-related issues (i.e., magnetic field interactions, heating, and artifacts) for various lead fragments. METHODS: Testing was conducted using standardized techniques on lead fragments of different lengths (i.e., 50, 75, and 100% of maximum possible fragment length of 12.7 cm) to determine MRI-related problems. Magnetic field interactions (i.e., translational attraction and torque) and artifacts were tested for the longest lead fragment at 3 Tesla. MRI-related heating was evaluated at 1.5 Tesla/64 MHz and 3 Tesla/128 MHz with each lead fragment placed in a gelled-saline filled phantom. Temperatures were recorded on the lead fragments while using relatively high RF power levels. Artifacts were evaluated using T1-weighted, spin echo, and gradient echo (GRE) pulse sequences. RESULTS: The longest lead fragment produced only minor magnetic field interactions. For the lead fragments evaluated, physiologically inconsequential MRI-related heating occurred at 1.5 Tesla/64 MHz while under certain 3 Tesla/128 MHz conditions, excessive temperature elevations may occur. Artifacts extended approximately 7 mm from the lead fragment on the GRE pulse sequence, suggesting that anatomy located at a position greater than this distance may be visualized on MRI. CONCLUSIONS: MRI may be performed safely in patients with retained lead fragments at 1.5 Tesla using the specific conditions of this study (i.e., MR Conditional). Due to possible excessive temperature rises at 3 Tesla, performing MRI at that field strength is currently inadvisable.

Standardized MR terminology and reporting of implants and devices as recommended by the American College of Radiology Subcommittee on MR Safety.

Considerable confusion exists among the magnetic resonance (MR) imaging user community as to how to determine whether a patient with a metal implanted device can be safely imaged in an MR imaging unit. Although there has been progress by the device manufacturers in specifying device behavior in a magnetic field, and some MR imaging manufacturers provide maps of the "spatial gradients," there remains significant confusion because of the lack of standardized terminology and reporting guidelines. The American College of Radiology, through its Subcommittee on MR Safety, has proposed standardized terminology that will contribute to greater safety and understanding for screening metal implants and/or devices prior to MR imaging.

MR system operator: recommended minimum requirements for performing MRI in human subjects in a research setting.

This article is intended to provide guidelines for the minimum level of safety and operational knowledge that an MR system operator should exhibit in order to safely perform an MR procedure in a human subject in a research setting. This article represents the position of the International Society for Magnetic Resonance in Medicine (ISMRM) regarding this important topic and was developed by members of this society's MR Safety Committee.

Evaluation of magnetic resonance imaging issues for implantable microfabricated magnetic actuators.

The mechanical robustness of microfabricated torsional magnetic actuators in withstanding the strong static fields (7 T) and time-varying field gradients (17 T/m) produced by an MR system was studied in this investigation. The static and dynamic mechanical characteristics of 30 devices were quantitatively measured before and after exposure to both strong uniform and non-uniform magnetic fields. The results showed no statistically significant change in both the static and dynamic mechanical performance, which mitigate concerns about the mechanical stability of these devices in association with MR systems under the conditions used for this assessment. The MR-induced heating was also measured in a 3-T/128-MHz MR system. The results showed a minimal increase (1.6 °C) in temperature due to the presence of the magnetic microactuator array. Finally, the size of the MR-image artifacts created by the magnetic microdevices were quantified. The signal loss caused by the devices was approximately four times greater than the size of the device.

Assessment of MRI issues at 7 T for 28 implants and other objects.

OBJECTIVE: Metallic implants are currently a contraindication for volunteer subjects and patients referred for 7-T examinations because of concerns related to magnetic field interactions and MRI-related heating. Artifacts may also be problematic. Therefore, the purpose of this investigation was to evaluate these MRI issues for 28 implants and other objects in association with a 7-T MR system. MATERIALS AND METHODS: Tests were performed at 7 T using standardized procedures to evaluate magnetic field interactions (translational attraction and torque) for all 28 items. MRI-related heating and artifacts were assessed using spin-echo and gradient-echo pulse sequences, respectively, for two aneurysm clips located within a transmit-receive head radiofrequency coil. RESULTS: Eight of the 28 items showed magnetic field interactions at levels that could pose risks to human subjects. The two aneurysm clips exhibited heating, but the temperature rise did not exceed 1°C. Artifacts were dependent on the material and dimensions of each aneurysm clip. CONCLUSION: These findings show that certain implants and objects may be acceptable for human subjects undergoing MRI examinations at 7 T, whereas others may involve possible risks. This information has important implications for individuals referred for MRI examinations at 7 T.

Evaluation of magnetic resonance imaging issues for a wirelessly powered lead used for epidural, spinal cord stimulation.

OBJECTIVE: The objective of this investigation was to evaluate magnetic resonance imaging (MRI) issues (magnetic field interactions, MRI-related heating, and artifacts) for a wirelessly powered lead used for spinal cord stimulation (SCS). MATERIALS AND METHODS: A newly developed, wirelessly powered lead (Freedom-4, Stimwave Technologies Inc., Scottsdale, AZ, USA) underwent evaluation for magnetic field interactions (translational attraction and torque) at 3 Tesla, MRI-related heating at 1.5 Tesla/64 MHz and 3 Tesla/128 MHz, and artifacts at 3 Tesla using standardized techniques. MRI-related heating tests were conducted by placing the lead in a gelled-saline-filled phantom and performing MRI procedures using relatively high levels of radiofrequency energy. Artifacts were characterized using T1-weighted, spin echo (SE), and gradient echo (GRE) pulse sequences. RESULTS: The lead exhibited minor magnetic field interactions (2 degree deflection angle and no torque). Heating was not substantial under 1.5 Tesla/64 MHz (highest temperature change, 2.3°C) and 3 Tesla/128 MHz (highest temperature change, 2.2°C) MRI conditions. Artifacts were moderate in size relative to the size and shape of the lead. CONCLUSIONS: These findings demonstrated that it is acceptable for a patient with this wirelessly powered lead used for SCS to undergo MRI under the conditions utilized in this investigation and according to other necessary guidelines. Artifacts seen on magnetic resonance images may pose possible problems if the area of interest is in the same area or close to this lead.

Low-intensity focused ultrasound pulsation device used during magnetic resonance imaging: evaluation of magnetic resonance imaging-related heating at 3 Tesla/128 MHz.

OBJECTIVE: The objective of this study was to determine magnetic resonance imaging (MRI)-related heating for a low-intensity focused ultrasound pulsation (LIFUP) device used during MRI performed at 3 T/128 MHz. MATERIALS AND METHODS: A special phantom was constructed to mimic the thermal properties of the human brain, and a piece of human temporal bone (skull) was embedded on top. Four fluoroptic thermometry probes, placed above and below the skull, were used to measure temperature changes during MRI (3 T/128 MHz; scanner-reported head average specific absorption rate 1.1-2 W/kg) with and without concurrent LIFUP sonication. LIFUP sonication was applied using a focused ultrasound device (BXPulsar 1001, Brainsonix, Inc., Los Angeles, CA, USA) at a derated spatial-peak temporal-average intensity of 3870 mW/cm(2) . RESULTS: MRI performed at relatively high specific absorption rate (SAR) caused a slight elevation in temperature (≤0.6°C). Concurrent use of MRI at a medium-strength SAR and LIFUP sonication resulted in maximum temperature rise of 3.1°C after 8 min of continuous use. CONCLUSIONS: Under the specific conditions utilized for this investigation, LIFUP sonication does not appear to present significant heating risks when used concurrently with MRI. This information has important implications for the use of the LIFUP sonication in human subjects undergoing MRI at 3 T/128 MHz.

Computational and experimental studies of an orthopedic implant: MRI-related heating at 1.5-T/64-MHz and 3-T/128-MHz.

PURPOSE: To use numerical modeling to predict the worst-case of magnetic resonance imaging (MRI)-induced heating of an orthopedic implant of different sizes under 1.5-T/64-MHz and 3-T/128-MHz conditions and to apply the experimental test to validate the numerical results for worst-case heating. MATERIALS AND METHODS: Investigations of specific absorption rate (SAR) and the temperature rise of an orthopedic implant of different sizes within a standard phantom were accomplished by numerical finite-difference time-domain modeling and experimental measurements. MRI-related heating experiments were performed using standardized techniques at 1.5-T/64-MHz and 3-T/128-MHz. RESULTS: The numerical modeling results indicated that the induced energy deposition is almost linearly related to the dimension of the orthopedic implant when it is less than 100 mm for 1.5-T/64-MHz and 3-T/128-MHz conditions. At 3-T/128-MHz, when the dimension is greater than 100 mm, the linear relation does not exist, which suggests a wavelength effect at higher frequency. Higher temperature rises occurred at 1.5-T/64-MHz MRI than at 3-T/128-MHz for both numerical modeling and experimental studies. CONCLUSION: The numerical technique predicted which device size had maximum heating and its location. Temperature rise data agreed well with thermal simulation results. The presented method proved to be suitable to assess MRI-induced heating of complex medical implants.