Experimental and numerical evaluations of simultaneously excitable Eigenmodes in a 20-channel transmit RF array for 7 Tesla human MRI

The Eigenmodes of a 20-channel Tic-Tac-Toe RF array are presented and analyzed. The Eigenmodes were calculated for each excitation level in Z (static magnetic field) direction, resulting in 4 modes per level and 20 in total. FDTD simulations and in-vivo experiments were performed. Quadrature mode is the most efficient, and generally excites the center of the brain; Anti-quadrature mode excites the head periphery; and the Zero-phase mode excites the cerebellum. Up to 5 modes can be excited simultaneously which can potentially result in a homogenous B1+ pattern and low levels of Average/peak SAR.