What type of Computed Tomography (CT) is ordered to rule out Pulmonary Embolism (PE)?

From the Guidelines

To rule out pulmonary embolism (PE), a CT pulmonary angiogram (CTPA) is the preferred imaging study. This recommendation is based on the evidence from the American College of Physicians [ 1 ], which suggests that CTPA is the most appropriate imaging test for patients with a high pretest probability of PE. The use of CTPA has been shown to have a high sensitivity and specificity for detecting PE, and it is able to identify alternative diagnoses that may explain the patient's symptoms [ 1 ].

Key Points to Consider

• CTPA uses intravenous contrast material to visualize the pulmonary arteries and detect filling defects caused by blood clots.
• The procedure typically takes about 15-30 minutes to complete, with the actual scanning time being only a few minutes.
• Patients will need to have an IV placed for contrast administration and may be asked to hold their breath briefly during the scan.
• CTPA has largely replaced ventilation-perfusion (V/Q) scans as the first-line imaging test for suspected PE due to its higher sensitivity and specificity.
• Patients with impaired kidney function may require special consideration regarding contrast use, and those with severe contrast allergies may need pre-medication or alternative imaging approaches.

Clinical Considerations

• The clinical probability of PE should be assessed using validated clinical prediction rules, such as the Wells rule or the Geneva rule [ 1 ].
• Patients with a low or intermediate pretest probability of PE may undergo a high-sensitivity d-dimer measurement as the initial diagnostic test [ 1 ].
• The use of age-adjusted d-dimer thresholds may be considered in patients older than 50 years [ 1 ].

Recent Guidelines

• The American College of Radiology Appropriateness Criteria recommend CTPA as the preferred imaging study for suspected PE [ 1 ].
• The European Society of Cardiology guidelines also recommend CTPA as the first-line imaging test for suspected PE [ 1 ].

From the Research

Computed Tomography for Pulmonary Embolism

• Computed Tomography Pulmonary Angiography (CTPA) is the imaging test of first choice to rule out Pulmonary Embolism (PE) 2, 3, 4.
• CTPA has been shown to have a high sensitivity and specificity for the diagnosis of pulmonary embolism 2, 3, 5.
• The presence or absence of pulmonary embolism can be determined with sufficient certainty without the need for additional imaging tests after a negative CTPA 2, 3, 5.

Alternative Imaging Modalities

• Ventilation-perfusion scintigraphy is reserved for patients with a stringent contraindication for CTPA 2.
• Compression ultrasonography is reserved for patients with concomitant symptomatic deep vein thrombosis 2.
• Magnetic Resonance Pulmonary Angiography is not a suitable alternative for CTPA 2.
• Single Photon Emission Tomography (SPECT) V/Q scanning offers a nuclear medicine modality that is an alternative to CTPA in at least some patients with suspected pulmonary embolism at a fraction of the risk of radiation exposure 3.

Diagnostic Algorithms

• Diagnostic algorithms using CTPA or V/Q scanning have proven to be comparably safe to exclude the diagnosis of pulmonary embolism 3, 5.
• Excluding low-risk patients for pulmonary embolism as defined by clinical scoring systems and D-dimer testing would enhance the yield of diagnostic testing 3, 5.
• CTPA is the most reliable test for diagnosis of pulmonary embolism, but diagnostic algorithms using V/Q scanning may be preferred in some patient populations 3.