From the Guidelines
A chest CT angiogram (CTA) should be ordered in patients with a high pretest probability of pulmonary embolism (PE) or when a patient presents with unexplained dyspnea, chest pain, tachycardia, or hypoxemia, especially with risk factors such as immobility, recent surgery, cancer, pregnancy, or hormone therapy, as recommended by the American College of Physicians 1.
Key Considerations
- The Wells or PERC criteria can help determine pre-test probability of PE, guiding the decision to order a CTA 1.
- For patients with low or intermediate pretest probability of PE, a high-sensitivity d-dimer measurement should be obtained as the initial diagnostic test, and imaging studies should not be used as the initial test 1.
- Age-adjusted d-dimer thresholds (age × 10 ng/mL) should be used in patients older than 50 years to determine whether imaging is warranted 1.
- CTA is the preferred method of diagnosis when available and there is no contraindication to radiographic contrast dye, as it provides rapid, detailed vascular imaging that allows for prompt diagnosis and treatment of potentially life-threatening conditions 1.
Important Details
- Before ordering a CTA, ensure the patient can receive intravenous contrast by checking renal function with creatinine levels and assessing for contrast allergies.
- If contrast is contraindicated, consider alternative imaging like ventilation-perfusion scanning for PE or MRI for aortic pathology.
- The clinical significance of isolated sub-segmental PE on CT angiography is questionable, and the decision to treat should be made on an individual basis, taking into account the clinical probability and the bleeding risk 1.
From the Research
Indications for Chest CT Angiogram
- Chest CT angiogram is indicated for patients with suspected pulmonary embolism (PE) 2, 3, 4, 5
- It is also used to diagnose aortic dissection, which is another potentially life-threatening cause of chest pain 5
- The decision to order a chest CT angiogram should be based on risk stratification algorithms, such as the simplified Geneva Score (sGS) in combination with D-dimer blood tests 4
Diagnostic Criteria
- CT pulmonary angiography is used to evaluate patients with suspected PE, and it can detect both partial and complete intraluminal filling defects 2
- The affected artery may be enlarged in acute pulmonary embolism, and partial filling defects are often centrally located 2
- Chronic pulmonary embolism can manifest as complete occlusive disease in vessels that are smaller than adjacent patent vessels, and it can also cause evidence of recanalization, webs or flaps, and partial filling defects that form obtuse angles with the vessel wall 2
Imaging Protocols
- CT pulmonary angiography can be performed with a low volume of contrast medium (20 ml) and still provide diagnostic image quality 6
- The use of high-concentration contrast medium (Iomeprol 400 mgI/ml) and a high iodine delivery rate (1.2 mgI/s) can help to improve image quality 6
- The diagnostic performance of CT pulmonary angiography can be affected by factors such as massive PE, pleuro-pulmonary abnormalities, and image noise 6
Clinical Decision Making
- The radiologist should determine the quality of the CT pulmonary angiographic study and whether PE is present 2
- If the quality of the study is poor, the radiologist should identify which pulmonary arteries have been rendered indeterminate and whether additional imaging is necessary 2
- The clinical importance of small isolated clots detected by CT pulmonary angiography is uncertain, and the most realistic scenario to measure efficacy of pulmonary CT angiography may be assessment of patient outcome 3