64 MHz RF Exposure System for Testing of Implanted Medical Devices in MRI Applications

Currently whole-body transmit RF coils are the most common RF environment for testing. These RF exposure systems designed for testing of devices are commercially available and currently used in a clinical setting; however, even though head-only transmit/receive (TX/RCV) coils are available on MRI scanners, there is not a validated head-only RF exexposure system available for either 64 or 128 MHz. Testing of active implantable medical devices (AIMDs) is guided by the requirements described in ISO 10974:2018(E). Determining the effects radiofrequency (RF) fields have on AIMDS in an MRI system are of paramount importance. Implanted medical devices in the head and neck experience a different local electric field when being imaged head-only exexposure system. This is a significant difference in local electric field when exposed to a head-only transmit coil versus being exposed to a whole-body transmit coil. To adequately evaluate the safety of these devices in that environment, head-only RF exposure systems are needed. In this paper we summarize the steps in developing and validating a head-only RF exexposure system that is properly tuned to 64 MHz and matched to 50 Ω for the testing of implanted medical devices. These steps include the methods for simulating and developing a head-only RF exexposure system.