Field-dependent Regional BOLD Responses to Varied Transient Hypoxic Stimuli in Mice

Motivation: Heterogenous BOLD responses are expected across brain regions due to different baseline blood volumes. However, there are very few experimental data to show regional differences of ΔR2*. Goal(s): To determine regional ΔR2* by graded hypoxia and to elucidate field dependency of regional ΔR2* to transient hypoxic stimuli. Approach: Three hypoxic conditions (90%N2, 95%N2, 100%N2) were administered to anesthetized mice in two different magnetic field strengths of 9.4T and 15.2T. Results: The peak ΔR2* map revealed heterogenous BOLD responses across regions. Field-dependent ΔR2* ratio to 15.2T to 9.4T is close to the ratio of the magnetic field strengths. Impact: We quantitatively determined regional BOLD responses in whole brain to hypoxia, which is dependent on baseline blood volume. Our result can serve as reference data for normalizing sensitivity of BOLD responses evoked by neuronal activity or vascular stimuli across regions.