Calculation of heating of passive implants by the RF electromagnetic field in MRI

The in-vitro and in-vivo temperature rises during MRI for a sample passive implant in the form of a metal rod of 8 mm diameter and 118 mm length in the right humerus were calculated with FDTD and the heat equation. The temperature rise in a phantom test was calculated for a background medium with electric properties specified in ASTM F2182-09 and for a medium with electrical properties of the cancellous bone that surrounds the implant. Scaled to local background SAR, in-vitro rises are greater for the bone. For a patient in the MRI coil with landmark in the torso and a whole body SAR of 2 W/kg, the calculated temperature rise after six minutes of RF power deposition was 1.3°C for 64 MHz and 2.4°C for 128 MHz. The numerical methods presented here could be extended to determine the temperature rises that would occur in the phantom and in the patient for other implants.