Fig. 1.—
Image analysis. a) Single regions of interest (ROI) in the lung section (indicated by white circles) were placed at a) A: 10; B: 30; C: 50; D: 70 E: 90% of the vertical lung height (normal subjects and subjects with primary pulmonary hypertension). b) Multiple ROI, examining perfusions at ∼10% of the vertical lung height (normal subjects only). c, d) Time/density curves were constructed for each ROI, with a gamma-variate fit to exclude re-circulation of contrast. CT: Hounsfield units.