From the Guidelines
CT pulmonary angiography (CTPA) is the preferred test for diagnosing pulmonary emboli, not a standard CT chest with contrast or CT angio chest. CTPA uses specific timing and injection protocols designed to optimally visualize the pulmonary arteries when they are filled with contrast, allowing for direct visualization of filling defects caused by clots. The contrast injection is timed precisely to opacify the pulmonary arteries at the moment of image acquisition. Standard CT chest with contrast, while useful for many thoracic conditions, uses different timing and contrast protocols that may not adequately highlight the pulmonary vasculature for embolism detection. CTPA offers high sensitivity and specificity for detecting pulmonary emboli, particularly in the main, lobar, and segmental pulmonary arteries, as supported by the 2019 ESC guidelines 1.
The test requires approximately 100-150 mL of iodinated contrast media administered at a rapid rate, so kidney function should be assessed beforehand, and patients should be adequately hydrated to minimize contrast-induced nephropathy risk. The American College of Physicians also recommends using CTPA in patients with a high pretest probability of PE 1. Furthermore, the 2022 update of the ACR Appropriateness Criteria for suspected pulmonary embolism continues to support the use of CTPA as the primary diagnostic modality 1.
Some key points to consider when choosing between CTPA and other imaging modalities include:
- CTPA has high sensitivity and specificity for detecting pulmonary emboli
- CTPA is the preferred test for diagnosing pulmonary emboli in patients with a high pretest probability of PE
- CTPA requires careful consideration of kidney function and hydration status due to the use of iodinated contrast media
- Other imaging modalities, such as ventilation-perfusion scans and MR angiography, may be useful in certain clinical scenarios, but CTPA remains the primary diagnostic modality for suspected pulmonary embolism.
From the Research
Diagnostic Tests for Pulmonary Emboli
- CT pulmonary angiography (CTPA) is considered the imaging test of first choice for diagnosing pulmonary embolism, with high sensitivity and specificity 2.
- The detection rate of pulmonary emboli with CT angiography using a low-dose protocol (80 kVp) is comparable to that of a standard protocol (120 kVp) in patients weighing less than 100 kg 3.
- Reducing the scan range in CT-PA can substantially decrease radiation dose while maintaining diagnostic accuracy for detecting pulmonary embolism 4.
Comparison of Diagnostic Tests
- A meta-analysis of 12 studies found that CT pulmonary angiography has an overall sensitivity of 74.1% and specificity of 89.5% for detecting pulmonary emboli 5.
- Pulmonary angiography is considered a safe procedure with modern contrast media and technique, with a low complication rate of 1.4% 6.