Marguerite Wieckowska

Changes in neuronal activity are accompanied by an increase in glucose and oxygen demand, reflected by focal changes in cerebral blood flow (CBF), cerebral blood volume (CBV), blood oxygenation and metabolism of associated brain areas. These changes can be used to produce functional maps of brain operations, and alterations in cerebral hemodynamics are commonly associated with cerebrovascular disease. An accurate, non-invasive and accessible method to measure CBF values can thus be a helpful tool to study normal brain and to diagnose or assess the extent of various disorders.

Positron emission tomography (PET) provides quantitative measurement of CBF in vivo, and has been long used to study cerebral hemodynamics. However, this technique suffers a number of important limitations. Magnetic resonance imaging (MRI) appears like a convenient alternative to PET, in light of the development of functional MRI (fMRI) in 1991, which allows the imaging of hemodynamic changes in the brain with high temporal resolution.

The goal of this study is to validate the CBF fMRI measurements against PET, the current gold standard, under identical conditions. We therefore use PET to quantitatively measure activation-induced local changes in CBF in the visual cortex of 10 healthy normal volunteers during a simple visual stimulation paradigm, and compare these values to those measured in fMRI experiments using the same subjects and activation protocol. We also use PET to validate fMRI measures of global changes in CBF, which are obtained using mild hypercapnia conditions.