PURPOSE: Blood oxygen-level dependent (BOLD) functional MRI signals depend on changes in deoxyhemoglobin content, which is associated with baseline cerebral blood volume (CBV) and blood oxygen saturation change. To accurately interpret activation-induced BOLD responses and quantify perfusion values by BOLD dynamic susceptibility contrast (BOLD-DSC) with transient hypoxia, it is critical to assess Δ METHODS: Whole-brain BOLD responses were examined using 5-s graded hypoxic challenges with 10%, 5%, and 0% O RESULTS: Substantial heterogeneity in hypoxia-induced Δ CONCLUSIONS: Our investigations provide biophysical insights into the BOLD contrast mechanism at ultrahigh fields, and address quantification issues in susceptibility-based CBV measurements.