CT Pulmonary Angiography

Aka: CT Pulmonary Angiography, Pulmonary Artery CTA, Pulmonary Artery CT Angiogram, CT Angiogram for Pulmonary Embolism

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II. Indications

  1. Pulmonary Embolism Evaluation

III. Efficacy: CT Chest Pulmonary Angiogram (Helical and Ultrafast, multidetector)

  1. Test Sensitivity: 83-86% (much higher for central emboli)
  2. Test Specificity: 93-96% (much higher for central emboli)

IV. Findings: Pulmonary Embolism

  1. Approach
    1. Decrease image brightness and contrast
    2. Trace each pulmonary artery from the hilum/saddle
      1. Use axial view
      2. Follow vessels in four passes for each of the main lung lobes (RUL, RLL, LUL, LLL)
      3. Trace any possible arterial filling defect back to its central source (confirm not in pulmonary vein)
  2. Filling Defect within pulmonary vasculature (axial view)
    1. Grey thrombus is surrounded by a thin rim of bright IV contrast
    2. False Positive filling defect with low flow in pulmonary veins
      1. Trace back each possible filling defect into central vessels to distinguish pulmonary vein from artery
  3. Pulmonary Infarct
    1. Wedge or dome shaped Lung Consolidation (Hampton's Hump)

V. Findings: Associated Right Heart Strain

  1. Precautions
    1. CT Chest is thought to overestimate right heart strain
    2. Cardiac POCUS is preferred to evaluate for acute right heart strain
  2. Ventricular septum may bow into left side (severe, saddle embolism)
  3. Prominent hepatic vasculature with IV contrast enhancement
    1. Hepatic congestion as a complication for acute Right Heart Failure
  4. Right ventricle dilation
    1. Right ventricle should be smaller than left ventricle (in the absence of chronic right heart or lung disease)
    2. Right Ventricle diameter to Left Ventricle Diameter Ratio (axial views) >1.5
      1. Associated with increased risk of ICU admission and death in hemodynamically stable patients
      2. Ghaye (2006) RadioGraphics 26:23-39 +PMID:16418240 [PubMed]

VI. Precautions: Factors that degrade CT Quality (lower sensitivity)

  1. Increased Respiratory Rate
    1. Hides small basilar pulmonary emboli
  2. Obesity
    1. Obscures general pulmonary vasculature
  3. Decreased Cardiac Output

VII. Disadvantages

  1. CT-associated Radiation Exposure (5-10 mSv)
  2. Breast tissue irradiation in younger women may be most significant risk from CT Chest
  3. Difficult to use if patient severely dyspneic
    1. Patient must hold breath for 15 to 30 seconds
  4. Misses small peripheral emboli
    1. However these may be clinically insignificant

VIII. References

  1. Stein (2006) N Engl J Med 354(22): 2317-27 +PMID:16738268 [PubMed]
  2. Tubbs and Janicki (2025) Emergency Chest CT, Mastering Emergency Imaging, CCME, accessed 5/13/2026

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