A Graphic Approach to Compartmental Slippage

The variance of rCBF data estimated from simulation of random influences or from retest procedures provides some insight into the general stability of the two-compartment model for noninvasive xenon 133 studies. In an actual patient study, however, it is not very informative with regard to the reliability of individual results. Determination of the accuracy of individual measurements is of special interest under conditions which may cause compartmental slippage (Reivich 1969; Waltz et al. 1972). As shown by Illif et al. (1975), Bruce et al. (1975), and Heiss et al. (1976), this may occur in most cerebrovascular disorders. Therefore, a graphic method for assessing this individual accuracy with particular reference to compartmental slippage was developed. Its properties are demonstrated in an exemplary rCBF measurement before and after extra-intracranial bypass surgery.