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Purpose: Neurovascular MRI suffers from a rapid drop in B1+ into the neckwhen using transmit head coils at 7T. One solution to improving B1+ magnitudein the major feeding arteries in the neck is to use custom RF shims on paralleltransmit (pTx) head coils. However, calculating such shims requires robustmulti-channel B1+ maps in both the head and the neck, which is challenging dueto low RF penetration into the neck, limited dynamic range of multi-channel B1+mapping techniques, and B0 sensitivity. We therefore sought a robustlarge-dynamic-range pTx field mapping protocol, and tested whether RF shimmingcan improve carotid artery B1+ in practice.  Methods: A pipeline is presented that combines B1+ mapping data acquiredusing circularly polarized (CP-) and CP2-mode RF shims at multiple voltages.The pipeline was evaluated by comparing the predicted and measured B1+ formultiple random transmit shims, and by assessing the ability of RF shimming toincrease the B1+ in the carotid arteries.  Results: The proposed method achieved good agreement between predicted andmeasured B1+ in both the head and the neck. The B1+ magnitude in the carotidarteries can be increased by 42% using tailored RF shims or by 37% usinguniversal RF shims, while also improving the RF homogeneity compared to CPmode.  Conclusion: B1+ in the neck can be increased using RF shims calculated frommulti-channel B1+ maps in both the head and the neck. This can be achievedusing universal phase-only RF shims, facilitating easy implementation inexisting sequences.

Head-and-neck multi-channel B1+ mapping and carotid arteries RF shimming using a parallel transmit head coil