MRI-based temperature and SAR mapping with a new dual-coil solenoid/birdcage heating/measurement system

We describe an MRI-based method for mapping temperature and specific absorption rate (SAR) using a solenoid coil and a birdcage coil for heating and imaging of a weakly conductive dielectric sample, respectively. The accuracy and the quality of SAR/temperature mapping are enhanced by separating the heating and imaging RF coils. 50 W of RF power is applied to the solenoid coil to heat the conductive agar-gel phantom for 120 sec. Maps of temperature increase were acquired with an MRI-based method. The MR-based measurements were in good agreement with fiber optic measurements. Finally, the dual-coil heating system was simulated using the finite difference time domain (FDTD) method. The distribution of numerically-calculated and experimentally-acquired SAR were also in good agreement.