From the Guidelines
Yes, CT with contrast can show if there is a PE, but CT pulmonary angiography (CTPA) is the preferred imaging modality for evaluating patients suspected of having acute PE. According to the most recent evidence from 1 and 1, CTPA is highly accurate for detecting PE, with sensitivity around 83-100% and specificity of 89-97%. Although conventional CT with contrast material (not performed as dedicated CTPA) is generally not indicated in the routine workup of acute chest pain thought to be secondary to acute PE, it should be acknowledged that incidental PE can be accurately diagnosed on routine chest CT with contrast, as noted in 1.
The key to accurate diagnosis is the use of intravenous contrast material to highlight the pulmonary arteries, allowing radiologists to detect blood clots that obstruct blood flow. The contrast agent appears bright white on the images, while clots appear as dark filling defects within the contrast-enhanced vessels. For optimal results, the timing of the contrast injection is crucial to ensure maximum opacification of the pulmonary arteries when the images are acquired.
Some important considerations include:
- Patients with kidney problems may require special consideration before receiving contrast due to the risk of contrast-induced nephropathy.
- Those with severe contrast allergies may need premedication or alternative testing approaches.
- CTPA is the major diagnostic modality currently used for diagnosing PE, as stated in 1 and 1.
- The diagnosis of PE is challenging due to the nonspecific nature of the clinical presentation, and clinical scoring algorithms, D-dimer testing, and specialized CT angiography are often used to aid in diagnosis, as discussed in 1.
Overall, while CT with contrast can be used to diagnose PE, CTPA is the preferred imaging modality due to its high accuracy and ability to provide detailed images of the lungs, heart, and major blood vessels.
From the Research
CT with Contrast and Pulmonary Embolism Diagnosis
- CT with contrast is a commonly used diagnostic tool for detecting pulmonary embolism (PE) 2, 3, 4.
- The sensitivity and specificity of CT with contrast in diagnosing PE have been reported to be high, with values ranging from 65% to 100% and 82% to 98%, respectively 3, 4.
- A study published in 2006 found that CT, if positive, provides reliable confirmation of the presence of PE, and if negative, effectively rules out clinically significant PE 2.
- Another study published in 1995 found that electron-beam CT is a sensitive and specific noninvasive method for the diagnosis of PE, with a prospective sensitivity of 65% and specificity of 97% 3.
- A comparison of CT scan and ventilation-perfusion (V-P) scan in detecting PE found that CT scan had a higher sensitivity and specificity than V-P scan, especially for central and peripheral PE combined 4.
Comparison with Other Diagnostic Tools
- A study published in 2024 compared three diagnostic strategies for suspicion of PE, including planar ventilation-perfusion scan (V/Q), CT pulmonary angiography (CTPA), and single photon emission CT ventilation-perfusion scan (SPECT V/Q) 5.
- Another study published in 2013 compared the diagnostic accuracy of V/Q SPECT and CTPA for PE, and found that V/Q SPECT had a higher sensitivity and specificity than CTPA 6.
- The area under the receiver operator characteristic (ROC) curve for V/Q SPECT, planar imaging, and CTPA were 0.898,0.838, and 0.877, respectively, indicating that V/Q SPECT is superior to V/Q planar scan and CTPA in the diagnosis of PE 6.
Diagnostic Accuracy
- The diagnostic accuracy of CT with contrast in detecting PE is high, with a sensitivity and specificity of 77% to 81% and 91% to 98%, respectively 4.
- The use of CT with contrast can help to rule out clinically significant PE, especially in patients with a low probability of PE 2.
- The combination of CT with contrast and other diagnostic tools, such as V/Q SPECT, can improve the diagnostic accuracy of PE 6.