Zoomed functional imaging in the human brain at 7 tesla with simultaneous high spatial and high temporal resolution

Functional neuroimaging in the human brain using noninvasive magnetic resonance methods has the potential of providing highly resolved maps of neuronal activation. Decreasing the voxel size and obtaining simultaneously high temporal resolution is a major challenge and is mainly limited by sensitivity. Here, signal-to-noise gains at high magnetic fields (7 Tesla) and an optimized surface coil setup are combined with a novel approach for zoomed functional imaging in the visual cortex. For echoplanar imaging, the acquisition time and segmentation was shortened fourfold by using a reduced field-of-view. An adiabatic outer-volume suppression method, BISTRO, was used to obliterate signal outside the area-of-interest achieving effective suppression even for inhomogeneous B₁-fields. A single-shot acquisition was performed at submillimeter resolution in the human brain, while simultaneously maintaining a high temporal resolution of 125 ms. Functional studies with and without field-of-view reduction were performed. Activation and percent change maps were compared with respect to spatial extent, t values and percentage changes of the BOLD contrast. The detection of functional activation was found to be equal within the inter-series variability for the two acquisition schemes. Thus, single-trial BOLD responses were detected for the first time robustly at a 500 × 500 μm² in plane and 250 ms temporal resolution, significantly expanding the possibilities of event-related functional imaging in the human brain. The magnetization transfer effect induced by the outer-volume suppression pulses was investigated and found to be increased during neuronal activity.