Influence of cerebrospinal fluid on specific absorption rate generated by 300 MHz MRI transmit array

We investigated how cerebrospinal fluid (CSF) simulated as a single electrically connected object and variation of the geometry of an anatomical human head model influence the transmit and safety excitation efficiencies of a 7T magnetic resonance imaging transmit array. A dual-row array was excited in circularly polarized (CP) and radiofrequency (RF) shimming modes. In both excitation modes, CSF partially shielded the brain from the array RF field. It resulted in decreases of both transmit and safety excitation efficiencies. A smaller head size resulted in larger transmit and safety excitation efficiencies for the CP excitation mode.