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What Is a Lung Ventilation/Perfusion Scan?

A lung ventilation/perfusion scan, or VQ scan, is a test that measures air and blood flow in your lungs. A VQ scan most often is used to help diagnose or rule out a pulmonary embolism (PULL-mun-ary EM-bo-lizm), or 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. PE is a serious condition that can cause low blood oxygen levels, damage to the lungs, or even death.

A VQ scan also can detect poor blood flow in the lungs' blood vessels and uneven air distribution, and it can provide pictures that help doctors prepare for some types of lung surgery.


A VQ scan involves two types of scans: ventilation and perfusion. The ventilation scan shows where air flows in your lungs. The perfusion scan shows where blood flows in your lungs.

Both scans use radioisotopes (a low-risk radioactive substance). For the ventilation scan, you inhale a small amount of radioisotope gas. For the perfusion scan, the radioisotopes are injected into a vein in your arm.

Radioisotopes release energy inside your body. Special scanners outside of your body use the energy to create images of air and blood flow patterns in your lungs.


VQ scans involve little pain or risk for most people. During the perfusion scan, you may feel some discomfort when the radioisotopes are injected. You also may have a bruise at the injection site after the test.

The amount of radiation in the radioisotopes used for both tests is very small. The amount of radiation in the gas and injection together are about the same as the amount a person is naturally exposed to in 1 year.

Very rarely, the radioisotopes used in VQ scans can cause an allergic reaction. Hives or a rash may result. Medicines can relieve this reaction.

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Last Updated: July 25, 2014