Local tissue temperature increase of a generic implant compared to the basic restrictions defined in safety guidelines

The objective of this study was to investigate if persons with implantable medical devices are intrinsically protected by the current electromagnetic safety guidelines. For inter-laboratory comparisons, the U.S. Food and Drug Administration has defined a generic implant as consisting of an insulated wire with noninsulated tips, simulating active implants composed of a metallic case, and insulated wires with electric contacts at the tip. In this study, we determined the amplitude of the uniform electric fields induced in body tissues that cause a local increase in the tissue temperature by 1 °C in the presence of this generic implant for a wide range of frequencies and wire lengths. The field amplitudes were compared to the basic restrictions of the current exposure guidelines for both occupational and uncontrolled exposure. Results showed that a 1 °C temperature increase in the tissues around the tips of the generic implant can be reached for field strengths much smaller than 1% of those in the basic restrictions. The simulated results were validated by experimental evaluations. The impact of perfusion was investigated and was found to lead to a reduction in the local temperature peak by only 1.6-3 times. Additional simulations inside an inhomogeneous anatomical model were performed to ascertain whether similar heating as in the generic model was observed. The significant temperature elevations due to the presence of a generic implant indicate that demonstrating compliance with the basic restrictions might not be sufficient for persons with implants. Special considerations may be required, especially in the case of novel, emerging technologies that feature strong near-fields at frequencies below 10 MHz (e.g., wireless power-transfer systems).