Computational Assessment of the Deposited Power and the Temperature Increase around Two Coupled Implanted Leads Inside a 1.5 T MRI Scanner

A specific method for the estimation of the induced power at the tip by an active implantable medical device (AIMD) during an MRI scan is not defined in ISO/TS 10974:2018 for the cases of devices with multiple leads or the presence of abandoned and retained leads, where coupling between two leads could take place. Therefore, the aim of this work is to evaluate a numerical method, similar to Tier 3 of ISO/TS 10974:2018, for the estimation of the deposited power at the tips of two coupled implanted leads. Specifically, the proposed methodology applies the same parameters as the standard Tier 3 process. However, these parameters are calculated for each implant in the presence of its neighbors in order to include the coupling between them. Numerical electromagnetic simulations were performed, in which a pair of generic implant leads was excited and placed at various positions relative to each other. The deposited power at the tips of the pair was analyzed based on the standard Tier 3 approach, and the results show that this could overestimate the induced power by more than 6 dB. Therefore, a modified Tier 3 numerical method for the estimation of the deposited power at their tips is proposed, which can produce a reliable calculation. This method was confirmed by evaluating various configurations of the two leads excited by orthogonal electrical fields, and also its uncertainty budget was developed. Finally, the method was repeated for different properties of the generic implants and the surrounding tissue, as well as for a pair of realistic implants and in vivo implantation trajectories.