Abstract
The principal objective of the present study was to investigate the autoregulation mechanism of cerebral vascular and predication of BOLD fMRI response with BOLD vascular reactivity maps and calibration curve. By assuming no significant increase in CMRO2 during mild hypercapnia, we measure cerebral global hemodynamic changes induced by inhalation of graded CO2 (1-5%) gas mixture by utilizing blood oxygenation level dependent (BOLD) fMRI technique. In 3T MRI system, we used the global hypercapnia stimulation to modulate hemodynamic factors and estimated the change of cerebral vascular reactivity (CVR) by BOLD signal of human brain. In 11 healthy volunteers, T2* weighted gradient echo blip-EPI was applied for the mixed trial paradigm of alternating periods of inhalation graded CO2 for 1 min after air breathing for 2 min. The averaged BOLD signal changes of subjects are 1.36 ± 1.73% (mean±SD, 1%CO2) to 7.78 ± 3.68% (mean±SD, 5% CO2), with gender difference of female dominance in CO2 response. Lesion studies of brain tumor and post-operation showed the lack of autoregulation response, as demonstrated by graded CO2 study and CVR mapping. Inhalation of 5%CO2 during performing hand-clenching motor task, as compared to control with air breathing during motor task, can enhance the BOLD signal by 1.45± 1.43%(mean±SD) and spatial extension by a factor of 8-9. Established methodology of this work enhances investigation and visualization of dynamic coupling between CO2 and BOLD signal changes, which plays the key role in fMRI studies and pathophysiology of cerebral vascular diseases.