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%.