An alternative method for determination of low-frequency specific absorption rate patterns in homogeneous phantoms.

We propose a new application of voltage gradient measurements to determine specific absorption rate (SAR) at low frequencies where quasi-static electromagnetic conditions apply. This method, which we call the voltage gradient method, relies on direct measurement of the voltage field rather than measurement of the electric field or thermal transients. The voltage gradient method is fast and can be implemented with voltmeters of moderate cost. We tested the voltage gradient method using normal saline, in a phantom with simple geometry, and a sine wave voltage source at 5, 10, 20 and 50 kHz. Compared to the SAR measured thermally in the same phantom, the voltage gradient method produced almost identical curves when normalized. When the results of the voltage gradient method were scaled to the same power level used for the thermal SAR, the agreement was compatible with typical thermal SAR accuracy.