RF shimming strategy for an open 60-channel RF transmit 7T head coil for routine use on the single transmit mode

Abstract

Purpose: To develop and shim a 60-channel transmit 32-channel receive RF coil system for routine use in 7T neuro MRI based on the Tic-Tac-Toe antenna design. Methods: RF simulations were performed and used to optimize three non-subject-specific RF shim cases over three anatomically detailed head models: adult male, adult female, and child female. Dual-ROI and multi-ROI shimming strategies were developed. The coil was assembled and used to acquire in vivo B1+ maps and images on volunteers using the single transmit mode of the scanner. The coil is open in front of the face to allow for an open visual field and to encourage patient comfort. Results: The combination of 60 transmit channels enables more power efficiency and more degrees of freedom in RF shimming. The transmit array provides homogeneous B1+, with extended coverage into the temporal lobes and cerebellum when phase and amplitude shimming is performed and when a multi-ROI cost function is used. Safe levels of SAR are achieved. Conclusion: By using a non-subject specific RF shim case in single transmit (sTx) mode, this coil system allows for robust, routine neuroimaging at 7T.