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

To develop an radiofrequency (RF) shimming approach for operating the 2nd Generation Tic Tac Toe RF coil system (60 transmit channels integrated with 32-channel receive insert) for routine use in 7T neuro MRI on the single transmit mode.

RF simulations were performed and used to develop non-subject-specific RF shim cases over three anatomically detailed head models: adult male, adult female, and child female. Multi-ROI shimming strategies were developed and implemented. $B_1^{+}$ maps and in vivo images were acquired on the single transmit mode of a 7T scanner using the RF shim cases derived from the computer simulations.

The availability of 60 transmit channels enables more control over $B_1^{+}$ efficiency, specific absorption rate (SAR) efficiency, and $B_1^{+}$ homogeneity using RF shimming. On the single transmit mode, the 2nd generation Tic Tac Toe RF coil system consistently provides homogeneous $B_1^{+}$ field distribution with extended coverage into the temporal lobes, cerebellum, reaching all the way to C5-C6. Safe levels of SAR are also achieved.

By using a non-subject specific RF shimming approach derived from computer simulations, the 2nd generation Tic Tac Toe RF coil system allows for robust, routine neuroimaging (>1750 in vivo scanning sessions over the past 28 months) at 7T in single transmit mode.