The in vivo autoradiographic measurement of regional cerebral blood flow using stable xenon and computerized tomography: the effect of tissue heterogeneity and computerized tomography noise.

We have studied the effect of brain tissue (gray matter-white matter) heterogeneity and computerized tomography (CT) noise on the accuracy of xenon CT measurements of regional cerebral blood flow (rCBF) based upon "autoradiographic" and multiple-scan washin protocols. The results of our mathematical analysis indicate that both protocols are associated with a variety of measurement errors that lead to unacceptable and, to a large extent, unpredictable uncertainties in calculated values of rCBF. Brain tissue heterogeneity and high volumetric flow rates may--even in the absence of movement artifact and CT noise--lead to measurement errors in excess of 20%. Moreover, CT noise is additive in regard to these errors, and constitutes the most confounding variable of all.