Measurement of relative cerebral blood volume using BOLD contrast and mild hypoxic hypoxia.

Relative cerebral blood volume (CBV) was estimated using a mild hypoxic challenge in humans, combined with BOLD contrast gradient-echo imaging at 3 T. Subjects breathed 16% inspired oxygen, eliciting mild arterial desaturation. The fractional BOLD signal change induced by mild hypoxia is expected to be proportional to CBV under conditions in which there are negligible changes in cerebral perfusion. By comparing the regional BOLD signal changes arising with the transition between normoxia and mild hypoxia, we calculated CBV ratios of 1.5 ± 0.2 (mean ± S.D.) for cortical gray matter to white matter and 1.0 ± 0.3 for cortical gray matter to deep gray matter.