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A central issue of parallel RF transmission is the SAR management toensure patient safety. The additional degrees of freedom availablein parallel transmission hamper straight-forward SAR estimations asapplied for single channel transmission. As an alternative to the usually applied model-based SAR estimation, a new method has been proposed to estimate SAR from the acquired B1 maps. This B1-based SAR determination has been successfully tested for quadrature (single channel) excitation in vivo and non-quadrature (multi-channel) excitation in a phantom study. This study adapts B1-based SAR determination for non-quadrature excitation in vivo. To this goal, the local SAR inthighs and pelvis of a volunteer is investigated and compared withresults of corresponding FDTD simulations based on the same volunteer.

Fast and robust in vivo B1 mapping is an essential prerequisite forquantitative MRI or multi-element transmit applications like RF-shimming or accelerated multi-dimensional RF pulses. However, especially at higher field strength, the acquisition speed of current B1-mapping approaches is typically limited by SAR constraints, T1 relaxation times, or characteristic sequence properties, which makes a multi-transmit element B1 calibration scan rather time consuming. Moreover, existing B1 mapping approaches are typically prone to motion,since the flip angle is calculated from two or more acquisitions separated in time. In this work, a novel multi-slice B1 mapping approach dubbed DREAM (Dual Refocusing Echo Acquisition Mode) is proposed, which derives a 2D B1 map from a single, ultra-short acquisitionof about 130 ms duration, which is more than an order of magni- tudefaster than most existing B1 mapping techniques. Moreover, the transceive phase and B0 are delivered in addition and for free. The performance of the approach is demonstrated in vivo by B1 mapping experiments in the abdomen at 3T.