Spanning spatial scales with functional imaging in the human brain; initial experiences at 10.5 Tesla

Abstract

One of the most important new frontiers in the effort to improve the spatial resolution and accuracy of imaging of human brain activity is the recent development of greater than 10 Tesla magnetic fields. Here we present initial results for 10.5 Tesla Blood Oxygenation Level Dependent (BOLD) based functional brain imaging (fMRI) of the human brain acquired with previously unavailable or difficult to attain spatial resolutions and functional contrast. We present data obtained with nominal isotropic resolutions ranging from 0.65 to 0.35 mm for partial brain coverage for stimulus evoked responses, and 0.75 mm for whole brain coverage to capture the spontaneous fluctuations that are the source of functional connectivity measures. The increasingly higher nominal resolutions (i.e. smaller voxel volumes and dimensions) employed in image acquisition were shown to correspond to real gains in resolution using image reconstruction methods developed to minimize blurring. Existence of supralinear gains in stimulus-evoked percent signal change and major improvements in statistical significance were evident relative to 7 Tesla, the most advanced commercially available ultrahigh magnetic field platform currently employed in human brain studies. These results were feasible due to gains in intrinsic signal-to-noise ratio, BOLD contrast, and image acceleration provided by the uniquely high magnetic field of 10.5 Tesla, and the use of novel high channel count arrays to capture these gains. The results provide a preview of the potential that will be available in the new era of greater than 10 Tesla human functional imaging, particularly for mesoscale functional organizations and connectivity.