Figure 4a. Chronic pulmonary embolism in a 62-year-old woman. (a) Unenhanced thin-section (1-mm collimation) CT scan obtained at the level of the right inferior pulmonary vein shows calcified thrombi (arrows) in the right middle and lower lobe arteries. (b) CT scan (lung window) obtained at the level of the basal portion of the left lung shows mosaic areas of hypoperfusion (large arrows). Note also the nodular branching structure (small arrow), a finding that suggests bronchiolitis.