Electrocardiogram-triggered, higher order, projection-based B₀ shimming allows for fast and reproducible shim convergence in spinal cord ¹H MRS

¹H MRS allows insight into the chemical composition of the central nervous system. However, as a result of technical challenges, it has rarely been applied to the spinal cord. In particular, the strong susceptibility changes around the spinal cord and the pulsatile flow of the cerebrospinal fluid lead to distinct B₀ field distortions which often considerably degrade the spectral quality. Hence, B₀ shimming is one of the main challenges in ¹H MRS of the spinal cord. Electrocardiogram (ECG)-triggered, higher order, projection-based B₀ shimming was introduced and compared with both conventional projection-based B₀ shimming and B₀ shimming based on ECG-triggered, three-dimensional B₀ field mapping. The linewidth of the unsuppressed water peak was used to evaluate the reproducibility and the potential improvement to B₀ homogeneity. The use of ECG-triggered projection-based B₀ shimming in combination with ECG triggering during preparation phases and triggering during acquisition of the spectra is the most robust method and thus helps to improve the spectral quality for MRS of the spinal cord.