Dr. Maria Cabanes-Sempere
ZMT Zurich MedTech AG

Certification of active medical implants for use in magnetic resonance imaging (MRI) machines requires the testing of immunity with respect to radiofrequency voltages induced into the active electronics of the implant. Test procedures and conditions are specified by the International Organization for Standardization ISO/TS 10974:2017: “Assessment of the Safety of Magnetic Resonance Imaging for Patients with an Active Implantable Medical Device”.

The testing of immunity (malfunction) is typically performed on the bench using an injection circuitry. However, the injection test voltage must be determined under real exposure conditions as they would occur in real human inside MRI. For implant and tissue heating Tier 3 of ISO/TS10974 has been the path of choice in the past 5 years. For induced voltage testing this path was unavailable due to the lack of suitable voltage probes.

We have developed an optical differential voltage probe to be used in electromagnetically hostile environments like magnetic resonance imaging that is able to deliver the full complex-valued voltage signal with a dynamic range of 120 dB and a frequency range from 100 kHz to 1 GHz and with a total measurement uncertainty of 1.14 dB. This novel optical voltage probe enables the testing of the safety of active medical implants exposed to radio frequency fields in MRI according to Tier 3 of ISO/TS 10974:2017 significantly mitigating the conservativeness of alternative test approaches.