Figure 27a. Lung algorithm artifact in a 70-year-old woman with dyspnea. (a) CT scan obtained with an edge-enhancing algorithm shows a lung algorithm artifact that mimics acute pulmonary embolism (arrows). This finding is seen when viewed with mediastinal or pulmonary embolism-specific windows and manifests as a bright ring around pulmonary arteries, particularly if associated with a flow artifact. (b) CT scan obtained with the standard algorithm does not demonstrate this artifact. No embolism was present.