Investigation of BOLD signal dependence on cerebral blood flow and oxygen consumption: The deoxyhemoglobin dilution model

The relationship between blood oxygenation level-dependent (BOLD) MRI signa ls, cerebral blood flow (CBF), and oxygen consumption (CMRO2) in the physio logical steady state was investigated. A quantitative model, based on flow- dependent dilution of metabolically generated deoxyhemoglobin, was validate d by measuring BOLD signals and relative CBF simultaneously in the primary visual cortex (V1) of human subjects (N = 12) during graded hypercapnia at different levels of visual stimulation. BOLD and CBF responses to specific conditions were averaged across subjects and plotted as points in the BOLD- CBF plane, tracing out lines of constant CMRO2. The quantitative deoxyhemog lobin dilution model could be fit to these measured iso-CMRO2 contours with out significant (P less than or equal to 0.05) residual error and yielded M RI-based CMRO2 measurements that were in agreement with PET results for equ ivalent stimuli. BOLD and CBF data acquired during graded visual stimulatio n were then substituted into the model with constant parameters varied over plausible ranges. Relative changes in CBF and CMRO2 appeared to be coupled in an approximate ratio of similar to 2:1 for all realistic parameter sett ings. Magn Reson Med 42:849-863, 1999, (C) 1999 Wiley-Liss, Inc.