Evaluation of E-Field Distributions in Parallel Transmit Systems by Time-Domain Optical Electric-Field Sensors

Frank Seifert¹, Tomasz Dawid Lindel¹, Peter Ullmann²

Ensuring RF safety is crucial for parallel transmit MRI. During parallel transmission the E-field distributions inside and outside the body exhibit a complex time evolution which cannot be covered by calorimetric SAR measurements. We introduce an optical electric field sensor (OEFS) to map non-stationary E-fields during parallel transmit MRI. We tested a customized OEFS system for certain static phase settings of a 4-channel transmit array. Our measurements confirmed a pathologic single hot-spot SAR-distribution as expected from FDTD simulations. In conclusion, the featured OEFS is an appropriate tool to identify possible safety issues of parallel transmit technologies.