Characterization of the R2*/R2 ratio of the BOLD laminar-specificity through biophysical simulations using realistic vascular architectures

GE-BOLD fMRI is the most used technique to measure functional hyperemia across cortical depth. GE-BOLD is sensitive towards all vascular contributions, while SE-BOLD increases the specificity towards small vessels– being more specific to neuronal activity. However, SE-BOLD fMRI measurements may not completely remove the macrovascular contribution. Using realistic vascular models, we simulated specific oxygenation states in different vascular compartments to characterize the GE-and SE-BOLD specificity across cortical depth quantified through the R2*/R2-ratio. Simulations show 1)similar ratio values at deeper layers indicating comparable specificity to microvessels for both sequences, 2)layer-fMRI SE-BOLD cannot completely eliminate the macrovascular contribution towards the pial surface.