Figure 4.

(A)‐(D) show B₀ maps for different shimming approaches with a voxel in the occipital cortex. The best MRS shim volume of interest (VOI) homogeneity is reached with the localized MRS shim (B), however as a result, several parts of the brain are far off‐resonance. With a whole brain shim (C), the global field homogeneity is improved, at the cost of reduced homogeneity in the voxel. The achieved whole brain homogeneity that is used during water suppression when using HOS‐DLT is displayed in (D), during the MRS acquisition the linear shims are adjusted. The HOS‐DLT shim gives both good MRS VOI and whole brain homogeneity (note that B, C, D have the same scaling). (E) is the image without water suppression, used as denominator when calculating the water suppression ratio maps (F‐G). The result of large off‐resonance signals is seen in (F) where the water signal is not suppressed in large regions of the brain. With the HOS‐DLT shim, the extent of the water suppression is increased (G), reducing chance of stimulated echoes in the MRS data. An example of reduction of artificial signal from a poorly suppressed region is shown in time (H) and frequency (I) domain, where the 4.05 resonance of myo‐Inositol becomes visible only after suppression of the artifact