Imaging Recommendations for Suspected Pulmonary Embolism

Primary Imaging Recommendation

The American College of Physicians recommends CT pulmonary angiography (CTPA) as the imaging modality of choice for suspected pulmonary embolism, with ventilation-perfusion scans reserved for patients who have contraindications to CTPA or when CTPA is unavailable 1
CTPA should be obtained in all patients with high pretest probability of pulmonary embolism, and in patients with low or intermediate pretest probability who have elevated D-dimer levels 1
The British Thoracic Society guidelines designate CTPA as the recommended initial lung imaging modality for non-massive pulmonary embolism 2, 3, 4

Patients with a good quality negative CTPA do not require further investigation or treatment for pulmonary embolism 2, 3, 4
Clinical outcome studies demonstrate it is safe to withhold anticoagulation when pulmonary embolism is excluded on CTPA, with subsequent pulmonary embolism occurring in only 1.1% of patients at 3 months 2, 3, 4, 6
CTPA is clearly superior in specificity to ventilation-perfusion isotope scanning and allows quantitative assessment that correlates well with clinical severity 2, 6

CTPA enables direct visualization of intravascular thrombus, webs, bands, and vessel occlusion while simultaneously evaluating alternative diagnoses when pulmonary embolism is excluded 2, 6, 7
Dual-energy CT techniques improve detection through perfusion mapping and can rescue suboptimal contrast studies using monoenergetic images 7

V/Q scanning should be used only when CTPA is unavailable or contraindicated, such as contrast allergy or renal insufficiency 1
MRA has limited utility for acute pulmonary embolism diagnosis, with sensitivity of only 78% in adequate studies 7
Echocardiography will reliably diagnose clinically massive pulmonary embolism and should be performed within 1 hour in massive pulmonary embolism 3, 4

Imaging should be performed within 1 hour in massive pulmonary embolism, and ideally within 24 hours in non-massive pulmonary embolism 3, 4

A small proportion of examinations will be technically unsatisfactory; quality control is critical for reliable interpretation 2, 6
Subsegmental clot may be less reliably detected than proximal clot, though most patients with subsegmental pulmonary embolism also have more proximal clot that can be identified 2, 6