A lung ventilation/perfusion (VQ) scan shows how well air and blood are flowing through your lungs. Normal results show full air and blood flow to all parts of your lungs.
If air flow is normal but blood flow isn't, you may have a pulmonary embolism (PE). A PE is a sudden blockage in a lung artery. The blockage usually is caused by a blood clot that travels to the lung from a vein in the leg.
The results of the scan show whether you're at high, medium, or low risk for a PE. However, a VQ scan alone won't confirm whether you have a PE. A scan showing low blood flow in spots may reflect other lung problems, such as lung damage from COPD (chronic obstructive pulmonary disease).
Your doctor uses the VQ scan results—along with results from a physical exam, chest x ray, and other tests—to make a diagnosis.