A Transmission Line Model for the Evaluation of MRI RF-Induced Fields on Active Implantable Medical Devices

Self Cite

During MR scans, abandoned leads from active implantable medical devices (AIMDs) can experience excessive heating at the lead tip, depending on the type of termination applied to the proximal contacts (proximal end treatment). The influence of different proximal end treatments (ie, [1] freely exposed in the tissue, [2] terminated with metal in contact with the tissue, or [3] capped with plastic, and thereby fully insulated, on the RF-induced lead-tip heating) are studied. A technique to ensure that MR Conditional AIMD leads remain MR Conditional even when abandoned is recommended. Methods: Abandoned leads from three MR Conditional AIMDs ([1] a sacral neuromodulation system, [2] a cardiac rhythm management pacemaker system, and [3]a deep brain stimulator system) were investigated in this study. The computational lead models (ie, the transfer functions) for different proximal end treatments were measured and used to assess the in vivo lead-tip heating for four virtual human models (FATS, Duke, Ella, and Billie) and compared with the lead-tip heating of the complete MR Conditional AIMD system. Result: The average and maximum lead-tip heating for abandoned leads proximally capped with metal is always lower than that from the complete AIMD system. Abandoned leads proximally insulated could lead to an average in vivo temperature rise up to 3.5 times higher than that from the complete AIMD system. Conclusion: For the three investigated AIMDs under 1.5T MR scanning, our results indicate that RF-induced lead-tip heating of abandoned leads strongly depends on the proximal lead termination. A metallic cap applied to the proximal termination of the tested leads could significantly reduce the RF-induced lead-tip heating.

Section: Transfer Function Measurement Resultsmentioning

confidence: 98%

Magnetic resonance conditionality of abandoned leads from active implantable medical devices at 1.5 T

Wang

Guo

et al. 2021

Self Cite

“…The RF‐induced heating for an implantable system can be assessed using the transmission line theorem, where the tissue itself acts as the return ground. Therefore, for different lead structures, the return ground is unchanged.…”

Section: Resultsmentioning

confidence: 99%

“…To address these questions we applied in this paper a rigorous method to develop the equivalent medium for accurate transfer function assessment. The entire AIMD lead was modeled as a transmission line where the two ends were terminated with a tip and an implantable pulse generator (IPG) impedance . The method to determine the equivalent medium is described in detail.…”

Section: Introductionmentioning

confidence: 99%

On the development of equivalent medium for active implantable device radiofrequency safety assessment

Wang

Liu

et al. 2019

Self Cite

Purpose: To develop the equivalent medium theorem that can be used to perform accurate evaluation of implantable device safety under MRI exposure. Methods: Numerical methods were used to determine the equivalent medium parameters along clinically relevant trajectories inside a human body model. Additionally, numerical and experimental investigations were performed using both a computational human body model and an inhomogeneous phantom to demonstrate the effectiveness of the method. Results: The equivalent medium parameters, which are determined from a simplified lead configuration, are independent of the lead types and lead design parameters and only depend on the lead trajectories. Experimental investigations using an inhomogeneous phantom showed excellent agreement between the computational predicted values and the direct measured temperature rises indicating the effectiveness and accuracy of this method. Conclusion: For the models based on multiple patient trajectories studied, it demonstrates that the equivalent medium theorem is valid for leads of different types and designs, as long as the lead trajectories are determined. K E Y W O R D S active implantable medical device (AIMD), equivalent medium, radiofrequency (RF) heating, transfer function | 1175

“…6 A detailed theoretical analysis of the problem was conducted by calculating the specific absorption rate around the electrode and the rise in temperature using the bioheat equation. 7 Moreover, theoretical models in the form of transfer function [8][9][10][11][12] or distributed circuit element model 9,13 have been proposed to analyze the problem and predict the temperature rise.…”

Section: Introductionmentioning

confidence: 99%

Wireless control of induced radiofrequency currents in active implantable medical devices during MRI

Açıkel

Silemek

Atalar

2019

Purpose To introduce a prototype active implantable medical device (AIMD) for which the induced radiofrequency currents can be controlled wirelessly. Methods The modified transmission line method is used to formulate how the lead‐case impedance of an AIMD affects the temperature rise around the electrode. A prototype AIMD is designed with the aim of controlling the unwanted temperature rise around its electrode during an MRI examination by altering the impedance between the lead and the case of the implant. MRI experiments were conducted with this prototype implant, which also has a built‐in temperature sensor at its electrode. During the experiment, the implant’s lead‐case impedance was controlled using Bluetooth communication with a remote computer, and the lead tip temperature was recorded. Results Ten different lead‐case impedance values and their corresponding tip temperature rises were examined during MRI experiments. The experimental results confirmed that the tip temperature rise can be controlled by varying the lead‐case impedance wirelessly. Conclusion The feedback from the temperature at the AIMD tip, together with variable lead‐case impedance, enables control of the safety profile of the AIMD during an MRI examination.