Dynamic B0 shimming at 7 Tesla

Abstract

Increased main field (B0) strength in MRI leads to increased signal levels but also causes higher field inhomogeneity (delta-B0). This thesis presents the implementation and evaluation of ‘Dynamic Shimming’, an advanced field shimming (correction) technique, on a high field human 7 Tesla clinical scanner. In this technique, the shim settings are changed during the acquisition of data from individual sub-volumes leading to better optimized field homogeneity compared to conventional static global shimming. Phantom and invivo experiments have been performed comparing the two shimming techniques. Dynamic shimming was seen to produce lower residual delta- B0 , image distortion and signal losses that static global shimming. In addition, a novel software based prospective method of eddy field compensation applied to higher order shim induced eddy currents has been developed and implemented. The method is shown to significantly reduced eddy fields and related artifacts in dynamic shimming.