Simultaneous Excitation of Distinct Electromagnetic Modes Using a Tx Array

Yujuan Zhao¹, Sossena Wood¹, Tiejun Zhao², Narayanan Krishnamurthy¹, Tamer S. Ibrahim¹

The inhomogeneous distribution of the magnetic field B1+ at ultrahigh field imaging (≥7T MRI) is a significant challenge for the RF coil design. In this work, a new excitation paradigm is presented utilizing 20-channel Tic-Tac-Toe (TTT) based RF transmit array design where the 20 elements are combined into 5 different groups in order to excite 20 distinct modes with longitudinal spatial selectivity. Any 5 of these modes can be simultaneously excited. The optimization shimming method has been used to find a uniform excitation pattern under SAR constraints. The results are successfully tested on a 7T MRI scanner using phantoms and in-vivo (7 human subjects.)