You may need a lung ventilation/perfusion (VQ) scan if you have signs or symptoms of a pulmonary embolism (PE). A PE is a sudden blockage in a lung artery. A blood clot usually causes the blockage.
Some blood clots that can cause a PE travel to the lungs from veins deep in the legs. This can cause pain and swelling in the affected limb.
Doctors use VQ scans to help find out whether a PE is causing these signs and symptoms. A VQ scan alone, however, won't confirm whether you have a PE. Your doctor also will consider other factors when making a diagnosis.
Doctors also use VQ scans to detect poor blood flow in the lungs' blood vessels, air trapping or uneven air distribution, and to examine the lungs before some types of surgery.