When is CT angiography preferred for suspected pulmonary embolism, and what are its limitations?

• A. Preferred when the patient is hemodynamically stable; high sensitivity and specificity but involves radiation and contrast
• B. Preferred when the patient is unstable and in shock
• C. Not useful in PE diagnosis
• D. Only used after ventilation-perfusion scan

Answer: (A)

The test is about when CT angiography is the best imaging option for suspected pulmonary embolism and what limits its use.

CT pulmonary angiography is the preferred choice in patients who are hemodynamically stable because it can quickly and directly visualize clots within the pulmonary arteries with high sensitivity and specificity. This accuracy helps confirm PE or rule it out, and it also lets you see other chest conditions that might mimic PE, all in one study.

However, there are important limits to keep in mind. CT angiography uses iodinated contrast, which raises the risk of contrast-induced nephropathy in patients with kidney dysfunction and can provoke allergic reactions in those with contrast allergies. It also involves ionizing radiation, which is a consideration for cumulative exposure and is particularly relevant in young patients or pregnancy. Transporting a stable patient to the CT scanner takes time, but moving a patient who is unstable or in shock to CT is generally not feasible and can delay life-saving treatment; in such cases, bedside assessment (and sometimes alternative imaging like a ventilation-perfusion scan or ultrasound) plus clinical judgment guide management. Subsegmental emboli can be missed on CT, and very small clots may not be detected despite a high pretest probability.

So the best answer reflects that CT angiography is favored in stable patients for its accuracy, while acknowledging its radiation and contrast-related limitations and the impracticality in unstable patients.