This study aims to evaluate the impact of insulation defects on the radio frequency-induced heating of stents under a 1.5T MRI environment. Sim4Life simulations were conducted using a birdcage coil and an ASTM phantom to calculate the 1g averaged SAR and temperature rise, while experimental validations were performed using the MITS Coils system with fiber optic temperature sensors. This study compares the RF-induced heating from intact stents and stents with different coating layer defects. Results indicate that localized insulation failure enhances localized heating. These findings suggest that insulation integrity is a critical parameter for the MRI safety assessment of implants.

This study evaluates the safety of using stereoelectroencephalography (SEEG) electrodes during radiofrequency (RF) ablation. A commercially available electrodes driven by a commercially available $\mathbf{R F}$ generator were used to determine the safety region using porcine brain tissue. Fiber-optic sensors recorded temperature variations at multiple distance to establish the safety region for different power levels and time durations. Results show linear temperature increase when the input voltages are in the range of 50 V to 70 V and nonlinear rapid heating with impedance surge when the input voltage exceeds 70 V. Stable and controlled ablation was successfully achieved below 70 V, and providing experimental evidence for the safe operating parameters of SEEG electrodes in neurosurgical applications.

This study investigates the RF-induced heating of tibial nail implants during MRI using thermal simulations. Results show that surgical state, bone adhesives, implant characteristics, and anatomical variability strongly influence temperature rise. Heating was most pronounced in surgical models with 50 mm adhesives and in cases with synovial fluid due to high conductivity, while variations were also observed with nail length across different human models. In many scenarios, rises in temperature exceeded $6^{\circ} \mathrm{C}$, raising safety concerns for post-operative MRI in patients with implants.

This study shows temperature rises of dual leads verses single lead AIMD system under a same RF exposure level. It investigates the relationship between the temperature rises of dual leads and their spacing in a magnetic resonance imaging (MRI) environment. It also explores the potential safety hazards that smaller spaced dual leads may pose in the human body. The temperature rises of the dual leads with different spacings of 3mm, 8mm and 13mm were measured under different pathways. The experimental results show that the temperature rises of the dual lead remains the same as the distance increases compared to a single lead.

PURPOSE:This study presents an in-silico assessment of RF-induced heating of orthopedic implants during various stages of bone fracture healing, namely surgery, scar, and healed phases, under 1.5 T and 3.0 T MRI. METHODS:Computational human models Duke, Ella, and Fats were used to develop the stages of bone fracture healing. These models reflect clinically relevant conditions and also include assessment of the surgery model with the presence of tissue adhesive and its leakage. Two types of orthopedic implants are analyzed: (a) a tibial nail system embedded within bone, and (b) a reverse shoulder arthroplasty (RSA) implant located partially in bone and muscle. RESULTS:Results demonstrate variations in RF-induced heating across stages of bone fracture healing and anatomical models, indicating that localized tissue properties, location of the implantation as well as the presence of tissue adhesive significantly influence RF-induced heating. CONCLUSION:The findings highlight the importance of (a) integrating clinically relevant in silico models to evaluate the safety of patients undergoing MRI scans which are not included in the current testing standards for passive implantable medical devices, and (b) accurate labeling of orthopedic implants for testing in an MRI environment.

This roadmap provides a comprehensive and forward-looking perspective on the individualized application and safety of non-ionizing radiation (NIR) dosimetry in diagnostic and therapeutic medicine. Covering a wide range of frequencies, i.e., from low-frequency to terahertz, this document provides an overview of the current state of the art and anticipates future research needs in selected key topics of NIR-based medical applications. It also emphasizes the importance of personalized dosimetry, rigorous safety evaluation, and interdisciplinary collaboration to ensure safe and effective integration of NIR technologies in modern therapy and diagnosis.

PURPOSE:Emissions generated during magnetic resonance imaging (MRI)-including gradient coil induced electric fields and radiofrequency coil induced heating near nerve fiber-may alter neural activation inside patients. This study investigates the combined effects of these emissions on vagus nerve activation in the presence of cuff electrodes. METHODS:Electromagnetic, thermal, and neurophysiological simulations were performed to quantify activation thresholds under MRI-induced fields. The study examined the impact of gradient field exposure and RF-induced heating, particularly for the trapezoidal waveform of the gradient coil with short pulse duration. RESULTS:The results indicate that the presence of the cuff electrode significantly reduces the activation threshold under gradient field exposure, while RF-induced heating further decreases the threshold for stimulations with short pulse durations. In some scenarios, the reduced neuron activation threshold can be lower than peripheral nerve stimulation limits defined in IEC 60601-2-33. CONCLUSION:These findings indicate the potential risk of unintended vagus nerve stimulation in MRI environments, emphasizing the need for safety considerations in patients with implantable vagus nerve stimulators.

Transcutaneous electrical nerve stimulation (TENS) is a widely used modality for pain relief and neuromuscular rehabilitation. However, the presence of implantable orthopedic devices can significantly distort the surrounding electric field, potentially leading to unintended neuronal activation. This study examines the influence of such implants on nerve stimulation during TENS therapy through a combination of numerical modeling and experimental validation. Electromagnetic simulations and neurophysiological modeling using NEURON, based on an anatomically accurate human body model, demonstrate pronounced electric field distortions at the edges of implantable devices, resulting in a lowered activation threshold for adjacent neurons. These findings are corroborated by phantom experiments, which show substantial alterations in electric field distribution in the presence of orthopedic plates and screws. The results suggest that TENS application should maintain a safe distance from implantable devices to minimize the risk of inadvertent nerve activation.

This study investigates the thermal risks associated with electrosurgical units (ESUs) in patients with metallic orthopedic implants. Using a combination of phantom-based experiments and computational simulations, we evaluated the effects of implant presence and electrode configuration on localized heating. Gel phantom experiments were conducted under three conditions: without implants, with a titanium rod, and with a metallic plate positioned between ESU electrodes. Voltage and temperature changes were recorded across ESU power settings at 20 W, 30 W, and 40 W. These results were validated using COMSOL simulations. To assess clinical relevance, human body simulations with the Duke model in Sim4Life were performed at 40 W, 80 W, and 120 W, evaluating the impact of implant proximity and dispersive electrode placement. Results showed strong agreement between experimental and simulation data. Significant temperature increases were observed near implants, especially at higher power settings or with short distance between implant and ESU electrode, the maximum temperature increase could achieve 11.6 °C at the implant device when the device is 3 cm away from active electrode. This is about 4 times higher than that from the scenario without any implants. ESU electrode placement can also influence heating patterns. These findings highlight the importance of surgical configuration and implant positioning in minimizing thermal risks during electrosurgical procedures.

Magnetic resonance imaging (MRI) safety for active implantable medical devices (AIMDs) can be compromised by radiofrequency-induced heating and voltage rectification, both of which are affected by the impedance of the implantable pulse generator (ZIPG). However, the influence of ZIPG on these safety mechanisms has not been systematically characterized. This article applied the transfer function (TF) approach to quantify how varying ZIPG values impact AIMD heating and voltage behavior. A mock implantable pulse generator (IPG) and a commercially available lead were tested across five impedance configurations using TF measurements and electromagnetic simulations with anatomically realistic human models. The results showed that voltage TFs maintained consistent shapes, but exhibited linearly increased (up to 50%) magnitudes with higher ZIPG, indicating a greater risk of voltage rectification and potential device malfunction. In contrast, heating TFs remained stable when the ratio of lead characteristic impedance to ZIPG was small. These findings demonstrate that IPG impedance can significantly influence AIMD responses in MRI environments and underscore the need for individualized evaluation of IPG interchangeability to ensure safe clinical use.

PURPOSE:To assess the RF-induced heating of orthopedic implants in a 5T whole-body MRI system through electromagnetic simulations and experimental validation, with the goal of ensuring patient safety in ultra-high field (UHF) MRI. METHODS:Numerical and experimental studies were conducted to evaluate RF-induced heating in five titanium screws (4-12 cm) inside a 60-cm wide 5T whole-body MRI scanner using the standard ASTM phantom. The temperature rise over 15 min was determined through full-wave electromagnetic simulations and direct measurements. The Finite Difference Time Domain (FDTD) method was used to quantify the 1 g mass-averaged specific absorption rate (pSAR1g) in 10 clinically relevant plate-and-screw configurations implanted in the Duke and Ella human body models at three anatomical locations: humerus, femur, and tibia. RESULTS:In the phantom study, the 6 cm screw exhibited the highest SAR and temperature rise, demonstrating a resonance effect at 5T. However, in human body models, the worst-case implant lengths shifted to 7-11 cm, highlighting the influence of tissue heterogeneity on resonance conditions. SAR values were also affected by the implant's position within the RF coil. The strong agreement between simulations and measurements validates the computational approach. CONCLUSION:This study systematically evaluates RF-induced heating in orthopedic implants within the newly approved 5T whole-body MRI, demonstrating that implant length, positioning, and surrounding media significantly impact heating risks. The findings highlight the necessity for updated MRI safety guidelines at UHF strengths, as implant safety conditions at 5T systems may differ from those at 1.5 and 3T MRI systems.

This study explores the influence of cuff electrode design, including variations in diameter and wrapping angle, on implantable medical device RF-induced heating under MRI procedure. Numerical and experimental studies were performed to evaluate the heating variation due to these factors inside the ASTM phantom. The results highlight that electrode design can significantly impact heating. It was observed that electrodes with smaller diameters and smaller wrapping angles can have higher RF-induced heating. It was also observed that the electrode designs will not change the shape of the device model. These findings provide critical insights for efficient and safer designs for cuff electrode.

This article presents a novel lead-specific validation method for magnetic resonance radiofrequency safety evaluations on active implantable medical devices (AIMDs). The proposed method designs a set of optimized validation pathways for the specific AIMD lead which achieve 1) high temperature rise or high induced voltages during the validation measurements with 2) minimally correlated electric fields along the pathways inside a electric field generating phantom box. The novel strategy 1) calculates the heating, or the induced voltage, for 603 preselected pathways and ranks these pathways based on temperature rise or voltage values and 2) performs matrix operations on these pathways to select pathways with minimally correlated tangential electric fields to each other. Two commercially available AIMDs were used to demonstrate the effectiveness of this novel strategy. Consequently, the strategy potentially provides a better transfer function validation for AIMD leads in terms of accuracy and completion.

In this article, a novel implementation of combined radiofrequency (RF) and gradient injection network was developed to enhance magnetic resonance imaging (MRI) safety testing. This network enables both separate and simultaneous injections of RF and gradient pulses, providing a more accurate simulation of real-world MRI environments. Using the proposed setup, several commercially available medical devices were tested under varying conditions. The results revealed that some devices exhibited significantly different rectification responses under combined injections, including increased rectified RF pulses in the presence of gradients, which in some cases led to device failure. The setup was validated for compliance with safety standards and represents a significant advancement in comprehensive device testing. This capability is critical for ensuring the safety of active implantable medical devices during MRI procedures.

PURPOSE:This study investigates the impact of lower limb amputation on radiofrequency (RF)-induced heating of active and passive implantable medical devices (AIMDs and PIMDs) in a 1.5 T MRI environment. METHODS:High-resolution anatomical models representing various body types and levels of amputation (below-knee and above-knee) were explored in the study. Full-wave electromagnetic simulations were used to assess specific absorption rate (SAR) near modular hip prostheses. The RF-induced lead-tip heating for a clinically relevant peripheral nerve stimulation (PNS) device was evaluated following ISO 10974. Results were normalized using whole-body SAR and averaged B1+rms. Experimental validation was performed using an anatomically inspired leg phantom with embedded metallic implants. RESULTS:SAR near passive implants increased with implant length and was influenced by the level of amputation. In general, more extensive amputations resulted in reduced SAR due to alterations in tissue geometry. For active implantable medical devices (AIMDs), temperature rise also decreased with greater amputation extent; however, localized heating effects were intensified near the amputation site. Phantom simulation results were in strong agreement with experimental measurements, supporting the accuracy of the modeling approach. CONCLUSION:Limb amputation significantly alters RF field distribution, affecting RF-induced heating near both active and passive implants. These results highlight the need for amputation-specific safety assessments during MRI to ensure accurate evaluation of heating risks and implant compatibility in amputee patients.

Magnetic resonance imaging (MRI) is a widely used diagnostic tool with millions of scans performed annually. However, the presence of active implantable medical devices (AIMDs), such as neurostimulators, can pose significant safety risks due to interactions of AIMDs and the MRI's electromagnetic fields. Specifically, radiofrequency (RF)-induced heating can lead to device malfunction or tissue damage. To address these risks, this study introduces a novel automated scaling and validation test system to evaluate the safety of AIMDs during MRI scans. The system streamlines the process of positioning AIMDs along various trajectories and measuring RF-induced heating, significantly reducing manual intervention and potential errors. Results demonstrate enhanced efficiency and reliability in AIMD model validation, with a high correlation between predicted and measured results. By automating the validation process, this system has the potential to improve patient safety, reduce costs, and expand the use of MRI for patients with AIMDs.

Existing methods for evaluating radiofrequency (RF)-induced heating typically assess active implantable medical devices (AIMDs) in isolation, without accounting for interactions with surrounding passive implants. This oversight can lead to under- or overestimation of heating in clinical scenarios involving multiple implants. This article presents an efficient approach for assessing RF-induced heating of AIMDs in a magnetic resonance imaging (MRI) environment when other implantable medical devices are present. The method leverages the transfer function approach to evaluate heating effects. To demonstrate its effectiveness, in vitro simulations and experiments were conducted using a cervical plate at various configurations. RF-induced heating within a human body model was then analyzed for an AIMD with and without nearby implantable devices. The results show that RF-induced heating at the lead tip varied by up to 36.7%, depending on the type and location of nearby passive implants. These findings highlight the critical need to incorporate multi-implant interactions into RF safety assessments to achieve more accurate and clinically relevant predictions.

Objective.Implanted devices exposed to time-varying magnetic fields in clinical environments-such as magnetic resonance imaging (MRI) and transcranial magnetic stimulation (TMS)-may induce unintended interactions with surrounding neural tissue. These interactions can lead to inadvertent nerve stimulation; however, the underlying mechanisms governing magnetic field-implant-neuron coupling remain poorly understood and require further investigation.Approach.We developed a biophysical model integrated with analytical calculations to quantify the influence of implanted objects on magnetically induced electric fields. To assess the physiological impact of these distortions, we constructed a multi-compartment model of a myelinated axon and evaluated its response to a single magnetic pulse across varying intensities. Activation thresholds were determined, and the underlying ion channel dynamics were further analyzed to elucidate the mechanisms of neural excitation induced by the altered field.Main results.The presence of the implant significantly altered the spatial distribution of the magnetically induced electric field, leading to indirect activation of nearby axons. Key factors such as implant-axon distance, implant size, and geometry critically influenced the extent of field distortion and the threshold required for neural activation. Variations in magnetic field intensity affected both the timing and location of axonal activation. Notably, high-intensity stimulation resulted in accelerated initiation of action potentials due to implant-induced electric field distortions. These intensity-dependent effects also modulated ion channel dynamics, further shaping the neural response.Significance.This study establishes foundational principles governing the interaction between externally applied time-varying magnetic fields, implanted devices, and surrounding neural tissue. It highlights essential safety considerations for MRI and TMS procedures, particularly when implants are located within regions subject to stimulation. The analytical framework developed herein offers a versatile tool for predicting electromagnetic effects across diverse implant types and clinical scenarios, supporting both improved device design and informed regulatory guidance.

PURPOSE:To understand the impact of lead winding near the Implantable Pulse Generator (IPG) on Active Implantable Medical Device (AIMD) transfer function (TF) models and RF-induced heating inside human body during Magnetic Resonance Imaging (MRI) scan at 1.5 T for safety considerations. METHODS:Three AIMD systems: a Cardiac Rhythm Management (CRM), a Spinal Cord Stimulator (SCS), and a Deep Brain Stimulator (DBS) are used in the study. TF models were developed for various winding configurations and validated in accordance with ISO/TS 10974. Heating predictions using human body models were evaluated inside three anatomical human models. RESULTS:Results reveal significant variations in TF robustness and heating behavior across different systems and winding configurations. The CRM system demonstrated the highest TF robustness, whereas the SCS system showed the maximum variation. It was observed that the RF-induced heating was lower for CRM and DBS systems with winding, whereas for the SCS system, the RF-induced heating would be higher with different winding patterns. These findings emphasize the need for tailored MRI safety assessments for AIMDs, particularly for systems with thin lead insulation. CONCLUSION:The study highlights the importance of considering AIMD lead properties and patient-specific winding configurations in MRI safety evaluation.