Is a CT (Computed Tomography) chest angiogram the same as a CTPA (Computed Tomography Pulmonary Angiogram)?

CT Chest Angiogram vs. CTPA: Understanding the Difference

A CT chest angiogram and CTPA (CT Pulmonary Angiogram) are not the same, though they are related imaging techniques with distinct timing of contrast enhancement and specific vascular targets. 1

Key Differences

• Contrast Timing and Target Vessels:

  • CT Chest Angiogram (CTA Chest): Contrast enhancement is timed for the aorta and its branches, primarily evaluating the systemic circulation 1
  • CTPA (CTA Pulmonary Arteries): Contrast timing is specifically optimized for evaluation of the pulmonary arteries 1

• Clinical Applications:

  • CTA Chest: Better for identifying systemic arterial supply to structures in the chest, including potential systemic supply to pulmonary arteriovenous malformations (PAVMs) 1
  • CTPA: Specifically designed for evaluating pulmonary vasculature and is the primary imaging modality for suspected pulmonary embolism 1

Technical Considerations

• Both techniques:

  • Utilize intravenous contrast
  • Offer high spatial resolution
  • Can detect vascular abnormalities 1
  • Require proper timing of contrast administration 1

• Protocol Differences:

  • The primary difference is in the timing of image acquisition relative to contrast injection 1
  • CTPA protocols are specifically optimized to capture images when contrast is maximally concentrated in the pulmonary arteries 1
  • CTA chest protocols are timed to optimize visualization of the aorta and its branches 1

Clinical Implications

• For Pulmonary Embolism:

  • CTPA is the preferred and standard imaging modality 1
  • CTPA has largely replaced conventional pulmonary angiography as the gold standard 2, 3

• For Pulmonary Arteriovenous Malformations:

  • Both techniques can be useful but with different strengths
  • CTPA may be more sensitive for correlating PAVM grade with contrast-enhanced echocardiography findings 1
  • CTA chest may better identify systemic arterial supply to PAVMs 1

Potential Pitfalls

• Air Embolism Risk: Both techniques carry a small risk of air embolism in patients with certain conditions like PAVM; proper precautions should be taken 1

• Diagnostic Limitations:

  • Standard CTA chest may miss some pulmonary vascular findings that would be visible on CTPA 4, 5
  • Conversely, CTPA may not optimally evaluate solid organs, serosal surfaces, and lymph nodes compared to standard portal venous phase CT 5

Bottom Line

When ordering these studies, clinicians should specify whether they need a CTPA (for suspected pulmonary embolism or primary pulmonary vascular disease) or a CTA chest (for evaluation of the aorta and its branches) to ensure the appropriate contrast timing protocol is used for the clinical question at hand 1.