Whole-brain BOLD Responses to Graded Hypoxic Challenges at 7T, 9.4T, and 15.2T: Implications for Ultrahigh-Field BOLD-DSC MRI

Motivation: To address quantification challenges in susceptibility-based CBV measurements using BOLD-DSC. Goal(s): Examine blood and tissue ΔR2* responses to varying blood oxygen saturation changes and magnetic field strengths. Approach: Whole-brain BOLD responses were evaluated using 5-second hypoxic challenges (0%, 5%, and 10% O2) in anesthetized mice at ultrahigh field strengths of 7T, 9.4T and 15.2T. Results: CBV values showed dependency on hypoxic stimulus doses and magnetic field strengths, with higher susceptibility yielding greater CBV values. Normalizing regional CBV to white matter values mitigated the variability from susceptibility contrasts within the same field strength. Impact: We investigated hypoxia-induced blood and tissue ΔR2* responses across varying ΔY levels and field strengths, alongside CBV assessments. This study provides biophysical insights into field-dependent BOLD signals at ultrahigh fields and addresses challenges in quantification of susceptibility-based CBV measurements.