B1+ Shimming in 1H RS-COKE Spectroscopic Imaging in the Human Brain at 7T

Motivation: 7T MRI is adversely affected by inhomogeneity in the B1 transmit field. In MRSI applications, this can manifest as spatial variability in water-suppression and signal excitation, which may adversely affect quantification. Goal(s): To use B1+ shimming to decrease the inhomogeneity of the transmit field and improve water suppression and metabolite quantification in RS-COKE MRSI. Approach: B1+ shim weights for all RF pulses were optimised using magnitude least-squares and data compared with a circularly polarised mode acquisition. Results: Metabolite quantification showed greater consistency, lower error estimates and improved water-suppression efficiency, in some subjects, when B1+ shimming was applied to the RS-COKE MRSI sequence. Impact: The use of B1+ shimming in RS-COKE MRSI improves the quantification of metabolite concentrations in some subjects. This increased robustness will allow for its application to patient populations in future clinical research.