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Figure 6a.   Stripe sign. Pulmonary angiography showed no pulmonary embolism. (a) Chest radiograph shows no area of increased opacity in the right midlung zone. The right midlung demonstrated normal findings on a xenon-133 ventilation scan. (b) Posterior (left) and right posterior oblique (right) images from a perfusion scan demonstrate a possible perfusion mismatch in the apical segment of the right lower lobe (posterior image) and a peripheral rim of increased activity, or stripe sign (arrows on right posterior oblique image). The stripe sign indicates a very low probability that this lesion was caused by pulmonary embolism.