MRI conditional safety of mixed systems: Study of the impact of active implant medical device impedance on the radiofrequency-induced lead heating

Abstract

Purpose: The aim of this paper is to study the impact of pulse generator small impedance variations on the overall radiofrequency (RF)-induced heating of a cardiac rhythm management (CRM) lead in a 1.5 T MR system.

Methods: An analysis was conducted on two CRM pacing leads with different structural designs. The leads were connected to three CRM devices belonging to different technological platforms: two pacemakers and a cardiac resynchronization therapy defibrillator (CRT-D). All pulse generators had a small (< $5\%$ ) RF input impedance compared to the overall system (pulse generator and lead) impedance. In addition, two Dummy load devices with an input impedance that is not negligible compared to the lead impedance were also studied. The implantable systems were studied in terms of RF deposited power at the lead electrodes, which is proportional to the RF-induced heating.

Results: Results show that both leads behave very similarly in terms of RF deposited power for the same in-vivo tangential E-field excitation when mounting any of the pulse generators; reported differences are well below the combined uncertainty $(k=1)$ . On the other hand, both Dummy load devices resulted in a RF deposited power which differs from the other pulse generators by values larger than the combined uncertainty.

Conclusion: The results of our experimental analysis show that different pulse generators would not change the RF-induced heating behavior of a given lead, provided that the pulse generator impedances are small (in our study less than 5%) compared to the overall system impedance.

Keywords: MRI; RF-induced lead heating; active implant medical device; cardiac implantable electronic device; implantable pulse generator; tier 3.