What initial imaging modality is considered the gold standard for diagnosing pulmonary embolism?

The gold standard for diagnosing pulmonary embolism is pulmonary angiography. This imaging modality involves the direct visualization of the pulmonary arteries and allows for the detection of blood clots within these vessels. Pulmonary angiography provides high accuracy and detail, making it the definitive test for confirming the presence of a pulmonary embolism.

While other imaging modalities, such as a helical CT scan, are frequently used due to their convenience and speed, they do not possess the same level of diagnostic accuracy as pulmonary angiography. The CT scan is often used as a first-line investigation because of its quick acquisition time and ability to visualize the lungs and vasculature simultaneously, but pulmonary angiography remains the top choice when absolute confirmation is necessary.

Chest X-ray and ultrasound play limited roles in the diagnosis of pulmonary embolism. Chest X-rays are useful for excluding other conditions but are not diagnostic for pulmonary embolism. Ultrasound may be employed to evaluate for deep vein thrombosis, which can be a source of emboli, but it does not visualize the pulmonary vasculature directly.

Thus, while helical CT scans are commonly used in clinical practice due to their efficacy and rapid results, pulmonary angiography is the definitive gold standard when it comes to directly diagnosing pulmonary