MR heating tests of MR critical implants

This article focuses on possible problems of MR heating tests for MR critical implants and gives some suggestions on how these problems could be mitigated. Critical implant length, MR heating tests in phantoms for 1.5T and 3.0T systems, whole-body averaged specific absorption rate provided by the MR system, and tissue damage assessment are briefly discussed. The U.S. Food and Drug Administration (FDA) is confronted with numerous MRI safety applications for implants. These MRI claims usually need to be supported by test results for force and torque, effects of the gradient fields, heating tests, and, in case of active implantable medical devices, by electromagnetic compatibility (EMC) test. For all types of implants, active and passive, heating tests are necessary to ensure the safety of the patient when exposed to the radio frequency field of the MR scanner. Unfortunately, there is currently misunderstanding about possible pitfalls in performing MR heating tests, in interpreting the results, and in assessing the measurement uncertainty. Most MR heating tests refer to the ASTM Standard F2182-02a (1), which is for passive implants only. Recent investigations revealed several problems associated with ASTM F218202a. Therefore, the ASTM Committee F04 on Medical and Surgical Materials and Devices, Sub-Committee F04.15 on Material Test Methods is currently revising F2182-02a. The suggestions outlined below summarize the FDA’s current knowledge of MR-induced heating for MR critical implants, which is based on numerous MR heating test reports submitted to the FDA. Research in this area is ongoing, and future results will show how testing of MR-critical implants need to be revised and properly performed. In this article, MR critical implants are defined as: