Real-time Motion and B0 correction for LASER MRSI using EPI volumetric navigators

A method is presented to correct the effects of motion and motion-related B0 perturbations on spectroscopic imaging in real-time through the use of a volumetric navigator (vNav). It is demonstrated that for an axial slice, lifting the chin significantly disrupts the B0 homogeneity in the zero-order (frequency), first-order Y (coronal) axis, and in the second-order ZY term. This vNav is able to measure and correct in real time both head pose and zero- to first-order B0 inhomogeneities. The vNav has been validated in six volunteers who deliberately lifted and then dropped their chin during the scan. These scans show that motion correction alone is not enough to recover the spectral quality. By applying real-time shim adjustments, spectral quality was fully recovered to line widths under 0.08 ppm and SNR to within acceptable limits in five out of six subjects. In the sixth subject 83% of the spectra within the VOI were recovered, compared to the worst case non-shim corrected scan where none of the voxels fell within these quality bounds. It is shown that the use of a vNav comes at no additional cost to the scan time or spectral SNR.