Measurement of specific absorption rate for clinical EPR at 1200 MHz

The specific absorption rate (SAR) has been measured experimentally at 1200 MHz under the conditions and in the configuration used for in vivo electron paramagnetic resonance (EPR) spectroscopy of human subjects. The measurement of SAR was based on an analysis of the time dependence of the temperature of a model tissue (isolated bovine skeletal muscle) placed adjacent to the surface loop of the EPR resonator. The measured SAR in the tissue at the position that should have the greatest density of microwaves, directly under the wire of the loop, was 3.7±1.2 W/kg at 100 mW incident radio-frequency power to a surface loop resonator with an efficiency of about 0.1 mT/W^1/2. This is substantially below the recommended limit in the relevant regulation for extremities. The method of measurement of SAR used in this study can be adapted for other resonators and other types of clinical applications of EPR spectroscopy and imaging.