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FIGURE 4. Graphs of base-to-apex longitudinal perfusion gradient expressed as first derivative or spatial slope of relative activity (vertical axis) at each tomographic slice from base-to-apex (horizontal axis) at rest (blue diamonds) and with dipyridamole stress (red Xs) with +2 SD and –2 SD limits of 50 reference subjects at rest (blue dashes) and after diypridamole (red dashes) for the same 3 clinical examples illustrated in Figures 2 and 3. Slope units are changes in relative activity per slice from base to apex. For the healthy control person (A), the base-to-apex longitudinal perfusion gradient at rest and during dipyridamole stress and the rest-to-stress change are both within 2 SD of 50 healthy control subjects. For the person with the severe stress-induced perfusion defect (B), the longitudinal perfusion gradient at rest and stress and the rest-to-stress change are all outside 2 SD of healthy reference subjects. For the person with the minimal perfusion abnormality (C), the longitudinal perfusion gradient and its rest-to-stress change are outside 2 SD limits of healthy reference subjects even though there is no clinically significant localized regional stress-induced perfusion defect.
