Abstract #0463

Zhao F, Wang P, Hendrich K, Kim S

Comparative sizes of vessels which dilate in response to neural activation were determined by calculation of relative baseline and functional vessel-size-indices (VSI). Baseline signal changes induced by MION (monocrystalline iron oxide nanoparticles) injection and functional signal changes before and after MION injection were simultaneously measured in the same cat by echo planar imaging with vessel-size-independent gradient-echo and vessel-size-dependent spin-echo techniques. In most of the cortex, functional VSI is larger than baseline VSI, suggesting that functional vasodilation occurs in vessels larger than capillaries.