Brain Blood Flow and Velocity

OBJECTIVE: Because transcranial Doppler sonography (TCD) is unable to measure arterial diameter, it remains unproven whether the changes in cerebral blood velocity it measures are representative of changes in cerebral blood flow (CBF). Our study was designed to compare velocity changes with flow changes measured by two magnetic resonance imaging (MRI) techniques, perfusion MRI and arterial spin labeling (ASL), using flavanol-rich cocoa to induce CBF changes in healthy volunteers. METHODS: We enrolled 20 healthy volunteers aged 62 to 80 years (mean, 73 years). Each was studied at baseline and after drinking standardized servings of cocoa for 7 to 14 days. RESULTS: Changes in middle cerebral artery (MCA) flow by TCD were significantly correlated with changes in perfusion assessed by gadolinium-enhanced MRI (r = 0.63; P < .03). Measurements with ASL showed a stronger correlation with borderline significance. CONCLUSIONS: Changes in flow velocity in the MCA associated with drinking cocoa were highly correlated with changes in CBF measured by the two MRI techniques using the tracer gadolinium and ASL. These results validate Doppler measurements of CBF velocity as representative assessments of CBF.