Figure 5b. Triple matched defect in the right midlung zone. Pulmonary angiography showed no pulmonary embolism. (a) Portable chest radiograph shows an area of increased opacity in the right midlung. The right lung base is not well visualized. (b) Posterior single-breath (left) and equilibrium (right) images from a xenon-133 ventilation scan show a ventilation defect in the right midlung zone. (c) Posterior (left) and right posterior oblique (right) images from a perfusion scan show a perfusion defect in the right midlung zone in the apical segment of the right lower lobe (arrows).