==Severity==
Severity of pulmonary embolism is determined by the level of the embolism along the pulmonary arterial tree, as well as how many such vessels are involved, and how much of the area is covered in each vessel.
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File:Computed tomograph of pulmonary vessels.jpg|Pulmonary arterial tree levels
File:SegandSubsegPE.png|Segmental and subsegmental pulmonary emboli on both sides
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