Correction of B0 induced slice profile distortion using parallel transmit

Introduction: With the advent of parallel transmit (PTx), there has been much interest in creating complex spatially localised excitations. The algorithms which calculate the requisite pulses [1,2] require an estimate of the B1 field produced by each coil, and also a map of the B0 (off resonance) field, since this distorts the excited magnetisation profiles. In fact spatially localized excitations are a core feature of virtually every MRI acquisition, usually in the form of a slice or slab, and these too suffer from off resonance particularly at higher field strengths. The resulting distortions are often not apparent because imaging is usually in the plane of the slice/slab . A special case is pre-saturation, for which slab bending is directly visualized when the saturation band intersects the imaging plane. Distortion is most severe when selection gradients are weak, e.g. when selecting thick slabs or for delivering high-power pre-saturation pulses, and when considering a large field of view, over which it is difficult to achieve a good B0 shim. In this work we have explored the possibility of correcting for B0 induced slice profile distortion using parallel transmission.