Spiral CT of pulmonary embolism: technical considerations and interpretive pitfalls

The diagnostic work-up of pulmonary embolism has been recently modified by the introduction of spiral computed tomography (CT), which enables noninvasive depiction of endoluminal clots in second-to fourth-division pulmonary arteries. If this technique is currently considered a powerful imaging alternative for the detection of acute central emboli, it is mainly related to the possibility to obtain a uniform and high degree of arterial enhancement of pulmonary arteries down to 2-3 mm in diameter. Minimal experience in spiral CT angiography is necessary to achieve this goal and requires familiarity with both data acquisition and contrast medium injection. A number of interpretive pitfalls exist in assessing spiral CT images, and certain caveats have to be heeded. However, it is important to keep in mind that their recognition becomes less and less problematic as the radiologist gains experience with spiral CT of the pulmonary vasculature. Therefore, the purpose of this article is to review the diagnostic approach to pulmonary embolism with spiral CT, with special emphasis on protocol parameters and scan interpretation.