What is the primary use of a V/Q scan in a clinical setting?

The primary use of a V/Q scan, or ventilation-perfusion scan, is to help diagnose pulmonary embolism. This imaging technique involves two components: the first part evaluates ventilation, assessing the airflow in the lungs, while the second part evaluates perfusion, which assesses blood flow. In cases of pulmonary embolism, there is often a mismatch between ventilation and perfusion; for example, areas of the lung may be well-ventilated but poorly perfused due to an obstruction in the blood vessels caused by an embolus. This characteristic mismatch is key for clinicians to identify and evaluate the presence of pulmonary embolism, making the V/Q scan an essential tool in the diagnosis of this life-threatening condition.

The other options, while related to lung assessments, do not align with the primary indication for a V/Q scan. Measuring lung capacity typically involves spirometry or other pulmonary function tests, and assessing lung infections usually requires different imaging methods or laboratory tests. Evaluating lung cancer can involve various imaging modalities like CT scans or PET scans, which provide more detailed information about tumors. Thus, the specific application of a V/Q scan in diagnosing pulmonary embolism is what makes it the correct choice.