Fig. 6. Bivariate distribution of mean normalized regional perfusion for a typical animal. Height of surface over the x–y plane in the surface plot represents the fraction of voxels containing the respective combination of mean normalized regional perfusion before (control) and after pulmonary embolism (PE). Note the large number of regions with very low perfusion after PE corresponding to a wide range of regional perfusion values before embolism. The dashed and continuous lines are the projections of the frequency distribution of relative perfusion in the relative frequency versus perfusion control and relative frequency versus perfusion PE planes, respectively.