BACKGROUND AND PURPOSE:: METHODS:: RESULTS:: VR was significantly lower in normal white matter than gray matter (P < .05) and in tumors compared to the normal, contralateral brain (P < 0.002). The area of abnormal VR (1103 ± 659 mm) was significantly greater (P = .019) than the enhancement (543 ± 530 mm), but significantly smaller (P = .0011) than the FLAIR abnormality (2363 ± 1232 mm). However, the variability in the areas of gadolinium contrast enhancement versus VR abnormality indicates that the contrast mechanism elicited by BH (caused by abnormal arteriolar smooth muscles) appears to be fundamentally different from the contrast mechanism of gadolinium enhancement (caused by the presence of “leaky” gap junctions). CONCLUSIONS