Sub-millimeter fMRI at 1.5 tesla: Correlation of high resolution with low resolution measurements

Functional magnetic resonance imaging of the visual cortex with an in‐plane resolution of 0.4 × 0.4 mm2 was performed using a simple visual stimulus resulting in clear maps of activation. A collapsing filter was used to compare these high‐resolution images with low‐resolution images collected during the same session. A good correspondence between the high‐ and low‐resolution functional maps was found with respect to the center of localization of activation. However, only 20% of the size of activated areas in the low‐resolution experiment was observed at high resolution, which was partly caused by the difference in signal‐to‐noise ratio. The high‐resolution images produce signal changes much higher than the low‐resolution images due to reduced partial volume effects. Additionally, the high‐resolution functional maps were compared with detailed anatomical and venous information. The activated areas were predominantly observed at venous vessels within the sulci with a diameter on the order of the pixel size. J. Magn. Reson. Imaging 1999;9:475–482. © 1999 Wiley‐Liss, Inc.