Determination of oxygen extraction ratios by magnetic resonance imaging

The oxygen extraction ratio (OER) of a tissue describes the interplay betwe en oxygen delivery and consumption and, as such, directly reflects the viab ility and activity of any organ. It is shown that OER can be quantified usi ng a single magnetic resonance imaging observable, namely the relaxation ti me T-2 of venous blood draining from the tissue. This principle is applied to study local OER changes in the brain on visual stimulation in humans, un ambiguously demonstrating a mismatch between changes in blood flow and oxyg en metabolism on activation.