On the SAR Averaging Nature of Parallel Excitation Pulses and Its Impact on Conservative Worst-Case Analysis

Stefanie Buchenau¹, Martin Haas¹, Jrgen Hennig¹, Maxim Zaitsev¹

To assure patient safety during parallel excitation experiments, monitoring of the RF pulses is necessary. If no additional hardware is available that measures RF phases a common approach is a conservative worst-case analysis that assumes absolutely constructive interference of the electric fields. This work shows that due to the varying phase settings during a parallel excitation pulse, worst-case SAR that may occur for single time steps is averaged over the pulse duration. This still holds true if the designed RF pulse is erroneously executed. Therefore conservative worst-case analysis overestimates SAR and it is possible to relax RF power limits that are based on this worst-case analysis.