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

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.