Peter Herman1,2, Basavaraju G. Sanganahalli1, Daniel Coman1, Fahmeed Hyder1,3
1Department of Diagnostic Radiology, Yale University, New Haven, CT, United States; 2Institute of Human Physiology, Semmelweis University, Budapest, Hungary; 3Department of Biomedical Engineering, Yale University, New Haven, CT, United States
Oxygen consumption has become an important measure of brain function and can be measured by multi-modal measurement of BOLD, blood flow and volume. While discharge hematocrit is unchanged, the tube hematocrit in microvessels (Hctmicro) can decrease during activation because it depends on velocities of RBC and plasma. We combined laser-Doppler and fMRI measurements of RBC and plasma velocities to estimate Hctmicro. Our results show that Hctmicro decrease, corresponding to reduced blood viscosity, needs to be included in functional hyperemic response of the BOLD signal, as without it δCMRO2 can be underestimated by as much as 30%.