Improving measurement of functional connectivity through decreasing partial volume effects at 7 T

Several applications of fMRI at high field have taken advantage of the increased BOLD contrast to increase spatial resolution, but the potential benefits of higher fields for detecting and analyzing functional connectivity have largely been unexplored. We measured the influence of spatial resolution at 7 T on estimates of functional connectivity through decreased partial volume averaging. Ten subjects were imaged at 7 T with a range of spatial resolutions (1×1×2 mm to 3×3×2 mm) during performance of a finger tapping task and in the resting state. We found that resting state correlations within the sensory-motor system increase as voxel dimensions decreased from 3×3×2 mm to 1×1×2 mm, whereas connectivity to other brain regions was unaffected. This improvement occurred even as overall signal to noise ratios decrease. Our data suggest that this increase may be due to decreased partial volume averaging, and that functional connectivity within the primary seed region is heterogeneous on the scale of single voxels.