Correction for the presence of intravascular oxygen-15 in the steady-state technique for measuring regional oxygen extraction ratio in the brain: 1. Description of the method.

The oxygen-15 steady-state inhalation technique provides quantitative values of regional cerebral blood flow, fractional oxygen extraction, and oxygen utilisation. These last two, however, have been found to be higher than those reported using arteriovenous difference techniques. On theoretical grounds, this overestimation is due to the signal from nonextracted intravascular oxygen-15. In this paper, a method is presented to correct for this intravascular component utilising a measurement of regional cerebral blood volume. The statistical penalty imposed as a result of this correction is defined.