After suspecting a pulmonary embolus, what is the next recommended test after an X-ray?

A helical CT pulmonary angiogram is the preferred next step in the diagnostic process after suspecting a pulmonary embolus, following an initial X-ray. This imaging technique is specifically designed to visualize blood vessels in the lungs and can quickly and effectively detect blockages in the pulmonary arteries caused by emboli. The helical CT scan provides high-resolution images and rapid acquisition times, making it a vital tool in acute settings where time is crucial, such as with suspected pulmonary embolism.

In comparison, while a standard CT scan is useful for various conditions, it does not provide the same detailed view of the pulmonary arteries that a helical CT pulmonary angiogram does. Pulmonary function tests assess lung function and are not directly diagnostic for pulmonary embolism. A chest MRI, although useful for certain types of lung pathology, is not standard for evaluating suspected pulmonary embolism due to the longer acquisition time and less availability in emergency situations. Hence, the helical CT pulmonary angiogram stands out as the optimal choice in this scenario.