RespiratoryTier 2Topic

Imaging - CT pulmonary angiography (CTPA)

Role

CT with IV contrast timed to opacify the pulmonary arteries - the first-line definitive imaging test for suspected pulmonary embolism
Has largely replaced V/Q scanning as first-line in most settings given wider availability, higher specificity, and the ability to identify an alternate diagnosis

Technique

The contrast bolus is timed to peak pulmonary arterial opacification; a filling defect within the opacified vessel represents thrombus

Who to scan

Use a validated pre-test probability tool (Wells score) + D-dimer to select patients for CTPA, avoiding unnecessary imaging in low pre-test probability with a negative D-dimer
CTPA also identifies RV strain (an indirect marker of severity) and alternate diagnoses (pneumonia, malignancy) when PE is excluded

Practicalities and PERC

Requires adequate renal function for contrast, and is technically more limited in pregnancy (though still used, weighed against V/Q scanning)
PERC rule can avoid testing altogether in very low-risk patients

Findings

Pulmonary embolism, right heart strain, deep vein thrombosis

A negative CTPA

A technically adequate negative CTPA safely excludes clinically significant PE

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