Fig. 7.
(a) Regional perfusion estimated using the delayed input function model parameters (Q̇DIF) compared with the 13NN-saline reference method (Q̇REF). Data within each animal were mean-normalized, and are shown with distinct symbols. In all three groups, we found strong correlations between the two measurements, with regression lines not significantly different from the line of identity either in terms of slope or intercept. According to both techniques, perfusion was dependent on ROI gravitational position (p<0.001), with non-dependent regions (empty symbols) showing lower perfusion than middle (gray) or dependent regions (black). (b) Mean-normalized fractional blood volume (FB) was also correlated with Q̇REF, though the regression lines differed from the line of identity in terms of both slope and intercept for all three conditions. Of note, the positive intercepts in all groups imply the presence of a residual blood volume when perfusion is equal to zero. (c) Local lung delays (tROI) were inversely associated with Q̇REF in all groups, with regions of higher perfusion showing shorter delays. Curves show regression of tROI onto Q̇REF