CT pulmonary angiography (CTPA) is a medical diagnostic test that employs computed tomography to obtain an image of the pulmonary arteries. CTPA was introduced in the 1990s as an alternative to ventilation/perfusion scanning, which relies on radionuclide imaging of the blood vessels of the lung. Because of its minimally invasive nature and high sensitivity and specificity, CTPA has evolved into the first line imaging study for the evaluation of suspected pulmonary embolism. Images are acquired using a breathhold technique during the pulmonary arterial enhancement phase following intravenous contrast material injection, with pulmonary embolism appearing as a filling defect in the otherwise densely opacified pulmonary artery.

Initial experience with single detector helical scanners showed high sensitivity for evaluation of the proximal pulmonary vascular tree (which includes the segmental branches) with sensitivities and specificities both well above 90%. However, the technique has been much less accurate for peripheral (subsegmental) branches, with sensitivities and specificities probably in the range of 60 to 70%. The advent of multi-detector CT (4-, 8-, 16-, and 64-slice) scanners has provided increased spatial resolution with decreased scan time (decreasing motion artifact), as well the ability to perform multiplanar image reformation. Image acquisition is routinely under 10 seconds for 64-MDCT. This technology has resulted in exquisitely detailed evaluation of the entire pulmonary vascular tree, with improved detection of peripheral pulmonary embolism.