Compartmental models of cerebral blood flow. Analysis using the 81-keV and 31-keV photons of 133Xe.

The clearance of 133Xe from the cerebrum after intra-arterial injection was studied in the pig. A mathematical model, consisting of two exponential terms and a constant, was fitted to decay curves obtained for both the 81-keV and the 31-keV radiation of 133Xe. The corresponding exponential terms for the 31-keV and 81-keV curves were found to differ significantly, implying that the two-compartmental model, based on the paritition of the white and gray matter of the brain, is not adequate to describe the clearance process. Other studies have shown that cerebral blood flow is more heterogeneous than the two-compartment model suggests. The discrepancies found here are interpreted as due to the simplification of representing a multiexponential clearance process by means of a two-exponential model.