Fig 4.

Cerebrovascular reserve (CVR) percentage augmentation maps calculated with BOLD and arterial spin-labeling (ASL), as well as a BTR map overlaid on a T1-weighted anatomic image. Images are all from the same subject (a 32-year-old woman with unilateral left MCA stenosis and multiple TIAs). The white grid overlay represents the MR thermometry VOI derived from multivoxel spectroscopy analysis using the water-NAA chemical shift difference. Images are displayed in the radiologic convention. Impaired cerebrovascular reserve in the left hemisphere is present in both BOLD and ASL, with a greater severity of impairment in arterial spin-labeling, likely related to tag decay and residual delay sensitivity despite the use of 10 separate, in-line postlabel delays of varying duration. The BTR map demonstrates an asymmetric thermal response, with less brain cooling following vasodilatory stimulus in the diseased left hemisphere, indicated by reduced (ie, less negative) BTR values and corresponding primarily to the areas of greatest impairment in the anterior and posterior MCA borderzone territories. Maximal (most negative) BTRs are noted in the regions spatially concordant with the greatest hemodynamic augmentation (blue regions) in the right parietal lobe. Adapted from Fleischer et al.⁸⁰