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

PURPOSE: 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.

METHODS

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 + $$ {\mathrm{B}}_1^{+} $$ 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.

RESULTS

The availability of 60 transmit channels enables more control over B 1 + $$ {\mathrm{B}}_1^{+} $$ efficiency, specific absorption rate (SAR) efficiency, and B 1 + $$ {\mathrm{B}}_1^{+} $$ homogeneity using RF shimming. On the single transmit mode, the 2nd generation Tic Tac Toe RF coil system consistently provides homogeneous B 1 + $$ {\mathrm{B}}_1^{+} $$ field distribution with extended coverage into the temporal lobes, cerebellum, reaching all the way to C5-C6. Safe levels of SAR are also achieved.

CONCLUSION

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.