Can a computed tomography (CT) chest angiogram be ordered for a pregnant patient?

CT Chest Angiogram in Pregnancy: Safety and Recommendations

CT chest angiogram can be performed in pregnant patients when clinically indicated, but ventilation-perfusion (V/Q) scanning is preferred as the first-line imaging modality for suspected pulmonary embolism due to lower maternal breast radiation exposure.

Radiation Safety Considerations

Fetal Radiation Exposure

• The fetal radiation dose from CT chest angiogram is approximately 0.3 mGy 1
• This is well below the danger threshold for fetal injury, which is considered to be 50 mSv (50,000 mGy) 1
• All radiological tests used for pulmonary embolism diagnosis fall significantly below this threshold 1

Maternal Radiation Exposure

• CT chest angiogram delivers approximately 7 mGy to maternal tissues 1
• The primary concern with CT chest angiography in pregnant women is the higher radiation dose to maternal breast tissue compared to V/Q scanning 1
• This higher breast radiation exposure results in a small but significant increase in lifetime risk of breast cancer 1

Imaging Algorithm for Suspected Pulmonary Embolism in Pregnancy

1. First-line approach: V/Q scanning when available

   • Preferred over CT due to lower maternal breast radiation exposure 1
   • Diagnostic yield in pregnancy is approximately 80% 1
   • Ventilation scan may be unnecessary if chest X-ray is normal, further limiting radiation exposure 1

2. When to use CT chest angiogram:

   • When V/Q scanning is not available 1
   • In patients with abnormal chest radiographs 1
   • When immediate diagnosis is critical in hemodynamically unstable patients 1

3. Additional considerations:

   • D-dimer testing may be used, but has limited utility as levels physiologically increase throughout pregnancy 1
   • Lower-limb compression ultrasound may be performed if D-dimer is abnormal, as proximal DVT warrants anticoagulation and makes thoracic imaging unnecessary 1

Documentation and Communication

• Document radiation dose to the mother in medical records, particularly if the fetus is in the field of view 1
• Discuss risks and benefits with the patient, emphasizing that:
  • The risk of missing a potentially fatal diagnosis outweighs radiation concerns 1
  • Erroneously diagnosing PE also carries risks of unnecessary anticoagulation 1

Key Principles to Remember

• Follow the ALARA principle: "As Low As Reasonably Achievable" for radiation exposure 1
• The decision to perform imaging should aim for diagnostic certainty rather than avoiding radiation at all costs 1
• Conventional pulmonary angiography carries significantly higher radiation exposure (2.2-3.7 mSv) and should be avoided during pregnancy 1

Common Pitfalls to Avoid

• Delaying necessary imaging due to unfounded radiation concerns
• Using conventional pulmonary angiography instead of CT or V/Q scanning
• Failing to consider alternative diagnoses for dyspnea in pregnancy
• Not documenting radiation exposure in medical records
• Overlooking the availability of V/Q scanning as a preferred first option

In conclusion, while V/Q scanning is preferred when available, CT chest angiogram remains a safe and valuable diagnostic tool for pregnant patients when clinically indicated, with radiation doses well below thresholds of concern for fetal injury.