Degraded Water Suppression in 1H-MRS Due to Shimming; a Visualisation Method and a Comparison of Shimming Methods

sa Carlsson^1,2, Maria Ljungberg^1,2, Gran Starck^1,2, Eva Forssell-Aronsson^1,2

Shimming and water suppression are necessary to receive qualitative 1H-spectra. However, the global effects of locally optimised shim gradients might make the water suppression spatially selective and hence pose a risk of spurious echo artifacts. A method that visualise the spatially complex regions of unsuppressed water signal was designed and the impact of different shimming methods were compared. Even a large VOI, in a homogeneous region and linear shims resulted in a water suppression that did not cover the whole head. Higher order shims, a small VOI in a susceptibility influenced region left more than half of the head unsuppressed.