Ventilation-Perfusion Scan for Suspected Pulmonary Embolism

Diagnostic Approach

The American College of Radiology recommends a ventilation-perfusion (V/Q) scan as the first-line imaging test for patients with suspected pulmonary embolism who cannot receive intravenous contrast 1
For patients with suspected pulmonary embolism, begin with clinical probability assessment and D-dimer testing, and if low clinical probability and negative D-dimer, PE can be safely excluded without imaging 2
If intermediate/high probability or positive D-dimer, proceed to imaging, with V/Q scan being a recommended option 2

A normal V/Q scan has high negative predictive value confirmed by outcome studies, making it a reliable test for excluding pulmonary embolism 3
Perfusion imaging alone can sometimes be performed in certain protocols, offering an alternative when ventilation imaging is not feasible 1
MR Angiography without contrast may be considered in specialized centers with expertise, although limited evidence is available for its use in PE diagnosis 4

The American College of Radiology suggests that V/Q scanning is particularly useful in patients with chronic kidney disease, as it avoids the risk of contrast-induced nephropathy 1
In patients with contrast allergy, V/Q scan is the primary alternative to CTPA, providing a safe diagnostic option 1