What is the role of a VQ scan or CT angiogram when pulmonary embolism is suspected?

The role of a VQ scan (ventilation-perfusion scan) or CT angiogram in the context of suspected pulmonary embolism is primarily to detect blood clots in the lungs. Both imaging modalities are essential diagnostic tools for evaluating patients who exhibit signs and symptoms indicative of pulmonary embolism.

A VQ scan works by assessing the distribution of air (ventilation) and blood (perfusion) in the lungs. When a blood clot obstructs blood flow in a particular area, the scan will show decreased perfusion in that area while ventilation remains normal, thereby indicating a potential embolism. On the other hand, a CT angiogram provides a detailed cross-sectional image of the blood vessels, allowing for direct visualization of any clots present in the pulmonary arteries.

These imaging techniques are critical in making timely and accurate diagnoses of pulmonary embolism, which is essential for initiating appropriate treatment to prevent further complications. In comparison to other options, measuring cardiac output, assessing pulmonary artery pressure, or monitoring oxygen saturation do not directly inform the presence of clots and, therefore, do not serve the primary diagnostic purpose that VQ scans and CT angiograms fulfill in this specific scenario.