Which test is considered the most definitive for diagnosing pulmonary embolism?

The pulmonary angiogram is considered the most definitive test for diagnosing pulmonary embolism because it directly visualizes the pulmonary arteries and can identify the presence of clots within them. This procedure involves injecting a contrast material into the pulmonary arteries and taking X-ray images, allowing for a clear and accurate assessment of blood flow and blockages.

Other diagnostic methods, such as a CT scan, are highly effective and commonly used due to their non-invasive nature and rapid results, but they may not be as definitive as a pulmonary angiogram in all cases. An echocardiogram can provide useful information about the heart's function and may show signs of right heart strain or other indirect indicators of pulmonary embolism, but it does not directly visualize the embolism itself. Ultrasound can be useful for detecting deep vein thrombosis, a precursor to pulmonary embolism, but it does not assess the pulmonary vasculature directly.

In summary, while other imaging modalities play important roles in the diagnosis of pulmonary embolism, the pulmonary angiogram remains the gold standard due to its specificity and ability to confirm the diagnosis with direct evidence.