Abstract #0454

Buxton R, Leontiev O

The coupling ratio n of the fractional changes in CBF and CMRO2 during neural activation can be measured reproducibly with a calibrated BOLD technique. However, the estimated value of n varies from approximately 2-5 depending on the method of choosing a region of interest (ROI) for averaging, suggesting the presence of a strong bias due to voxel selection. A possible explanation of the source of the bias is the inclusion of venous structures when either a BOLD-localizer or a V1 retinotopic map is used for constructing the ROI. Given these biases, a functional flow localizer is recommended.