Cerebral blood flow, blood volume, and oxygen metabolism dynamics in human visual and motor cortex as measured by whole-brain multi-modal magnetic resonance imaging

The development of neuroimaging methods to characterize flow-metabolism coupling is crucial for understanding mechanisms that subserve oxygen delivery. Functional magnetic resonance imaging (fMRI) using blood-oxygenation-level-dependent (BOLD) contrast reflects composite changes in cerebral blood volume (CBV), cerebral blood flow (CBF), and the cerebral metabolic rate of oxygen consumption (CMRO2). However, it is difficult to separate these parameters from the composite BOLD signal, thereby hampering MR-based flow-metabolism coupling studies. Here, a novel, noninvasive CBV-weighted MRI approach (VASO-FLAIR with 3D GRASE (GRadient-And-Spin-Echo)) is used in conjunction with CBF-weighted and BOLD fMRI in healthy volunteers (n = 7) performing simultaneous visual (8Hz flashing-checkerboard) and motor (1Hz unilateral joystick) tasks. This approach allows for CBV, CBF, and CMRO2 to be estimated, yielding (mean +/- s.d.): Delta CBF = 63% +/- 12%, Delta CBV= 17% +/- 7%, and Delta CMRO2 = 13% +/- 11% in the visual cortex, and Delta CBF = 46% +/- 11%, Delta CBV = 8% +/- 3%, and Delta CMRO2 = 12% +/- 13% in the motor cortex. Following the visual and motor tasks, the BOLD signal became more negative (P = 0.003) and persisted longer (P = 0.006) in the visual cortex compared with the motor cortex, whereas CBV and CBF returned to baseline earlier and equivalently. The proposed whole-brain technique should be useful for assessing regional discrepancies in hemodynamic reactivity without the use of intravascular contrast agents. Journal of Cerebral Blood Flow & Metabolism (2009) 29, 1856-1866; doi:10.1038/jcbfm.2009.107; published online 5 August 2009