Fig. (6).

Gradient-echo BOLD vs. arterial CBV-based fMRI responses to visual stimulation in isoflurane-anesthetized cats at 9.4 T [30]. Images and functional maps illustrate results from one of seven animals. A: gradient-echo BOLD fMRI with TE = 20 ms (without MT). To determine arterial CBV changes, only pixels which are active in BOLD fMRI were selected. Then, intercepts were calculated from gradientecho BOLD data acquired at 3 different MT levels. B & C: intercept maps. Since negative intercepts (purple) are likely due to a reduction of the MT-insensitive CSF volume, only positive intercepts (red/yellow) were converted to ΔCBV_a values for quantification, shown in C. Clearly, the highest CBV_a change is located at the middle of the cortex indicated by white arrows. D: T1-weighted anatomic image showing gray and white matter contrast. The visual cortex indicated by green contours has a myelin-rich hyperintense band at the middle of the cortex (white arrows), indicating layer 4. E: average cortical depth profiles of GE BOLD fMRI (without MT) and ΔCBV_a obtained from quadrangular ROIs in area 18 (illustrated by red outlines in D). Approximate cortical layer locations were determined by the relative distances of those layers in area 18 [48]. Error bars: SEM (n = 7).