Which imaging modality is preferred for the initial evaluation of suspected pulmonary embolism?

CT pulmonary angiography is the preferred imaging modality for the initial evaluation of suspected pulmonary embolism due to its high sensitivity and specificity for detecting clots in the pulmonary arteries. This imaging technique utilizes contrast-enhanced computed tomography to visualize the blood vessels in the lungs, allowing for rapid and accurate identification of emboli.

Moreover, CT pulmonary angiography is quick and widely available, making it a practical choice in emergency settings where timely diagnosis is critical. It can also be performed with a relatively low risk of complications, which is essential for patients who are often in a precarious health state due to potential respiratory compromise.

In contrast, X-rays do not have the sensitivity to detect pulmonary embolism since they primarily assess the lung structure and can appear normal even in the presence of significant embolic events. MRI is generally reserved for specific situations, like evaluating patients with contraindications to CT or those requiring additional information about cardiac structures. Ultrasound is primarily used for venous assessments, particularly in the diagnosis of deep vein thrombosis, but is not the first-line imaging for pulmonary embolism itself.