Multi-projection magnetic resonance inverse imaging of the human visuomotor system

Using highly parallel radiofrequency (RF) detection, magnetic resonance inverse imaging (InI) can achieve 100ms temporal resolution with whole brain coverage. This is achieved by trading off partition encoding steps and thus spatial resolution for a higher acquisition rate. The reduced spatial information is estimated by solving under-determined inverse problems using RF coil sensitivity information. Here we propose multi projection inverse imaging (mInI) to combine different projection images to improve the spatial resolution of InI. Specifically, coronal, sagittal, and transverse projection images were acquired from different runs of the fMRI acquisitions using a 32-channel head coil array. Simulations show that mInI improves the quality of the instantaneous image reconstruction significantly. Going from one projection to three projections, the spatial resolution quantified by the full width at half maximum of the point-spread function (PSF) is improved from 2.6 pixels to 1.4 pixels (4mm nominal resolution per pixel). Considering the shape of the PSF, the effective spatial resolution is improved from 16.9 pixels to 4.7 pixels. In vivo fMRI experiments using a two-choice reaction time tasks show visual and sensorimotor cortical activities spatially consistent with typical EPI data, yet mInI offers 100ms temporal resolution with the whole brain coverage. The mInI data with three projections revealed that the sensorimotor cortex was activated 700ms after the visual cortex. mInI can be applied to BOLD-contrast fMRI experiments to characterize the dynamics of the activated brain areas with a high spatiotemporal resolution. ► Inverse imaging (InI) achieves fast sampling rate using an RF coil array. ► The lower spatial resolution of InI is due to solving ill-posed inverse problem. ► Multi-projection InI (mInI) combines projections to improve spatial resolution. ► mInI has more homogeneous and higher spatial resolution than InI with TR=10Hz.