Volume parcellation for improved dynamic shimming

Abstract

The need for a homogeneous magnetic field in magnetic resonance imaging is well established, especially at high static magnetic field strengths where susceptibility-induced image distortions and signal losses become excessively large. Dynamic shim updating, where the optimal set of shim currents is applied for each slice during a multi-slice acquisition, has been shown to improve magnetic field homogeneity to a greater extent than conventional global shimming. Here, in an initial feasibility study, we show via simulation that improved efficacy of shimming can be achieved by using the novel parcellated dynamic shimming method. The results of these simulations indicate that parcellated dynamic shimming based on just linear shim terms can perform approximately as well as slice-based dynamic shimming with up to third-order shim terms. This work shows that the effective magnetic field inhomogeneity can be further reduced if shimming and image data acquisition are sequentially performed over a series of compact, cuboidal sub-volumes rather than planes. Further work is needed to develop an imaging approach that can be used for the optimal implementation of parcellated dynamic shimming.