SAR and Temperature Changes in the Leg Due to an RF Decoupling Coil at Frequencies Between 64 and 213 MHz

Specific absorption rate (SAR) due to a butterfly surface coil in a realistic model of the leg was calculated for frequencies 64 ≤ ν ≤ 213 MHz. The resulting temperature distribution and temperature changes (ΔT) were found using the bioheat transfer equation. To compare results at different frequencies, the minimum B‐field within the coil's footprint in the plane parallel to the coil but displaced 50 mm from it was kept constant. To achieve the same minimum B‐field as that associated with operation at 64 MHz that was compliant with safety guidelines (peak SAR in 1 cm3of tissue of 2.3 W/kg), it was predicted that SAR would exceed recommended levels when ν ≥ 149 MHz. The corresponding maximum ΔT at 64, 128, and 213 MHz were 0.3, 1.3, and 5.0°C, respectively. J. Magn. Reson. Imaging 2000;12:68–74. © 2000 Wiley‐Liss, Inc.