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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.

Overview

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.

Outlook

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.




Other Names for Lung Ventilation/Perfusion Scans

Lung ventilation/perfusion scans also are called VQ scans, pulmonary ventilation/perfusion scans, and nuclear medicine tests.




Who Needs a Lung Ventilation/Perfusion Scan?

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.

Signs and symptoms of a PE include chest pain, trouble breathing, rapid breathing, coughing, and coughing up blood. An irregular heartbeat called an arrhythmia (ah-RITH-me-ah) also may suggest a PE.

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.




What To Expect Before a Lung Ventilation/Perfusion Scan?

A lung ventilation/perfusion (VQ) scan may be done during an emergency to help diagnose or rule out a pulmonary embolism (PE). A PE is a sudden blockage in a lung artery. This serious condition can cause low blood oxygen levels, damage to the lungs, or even death.

If your VQ scan isn't done during an emergency, your doctor will tell you how to prepare for the test. Most people don't need to take any special steps to prepare for a VQ scan.

Your doctor may ask you to wear clothing that has no metal hooks or snaps. These materials can block the scanner's view. Or, you may be asked to wear a hospital gown for the test.

Tell your doctor whether you're pregnant or may be pregnant. If possible, you should avoid radiation exposure during pregnancy, as it may harm the fetus.

You and your doctor will decide whether the benefits of a VQ scan outweigh the small risk to the fetus, or whether another test might be better.

If you're breastfeeding, ask your doctor how long you should wait after the test before you breastfeed. The radioisotopes used for VQ scans can pass through your breast milk to your baby.

You may want to prepare for the scan by pumping and saving milk for 24 to 48 hours in advance. You can bottle-feed your baby in the hours after the VQ scan.




What To Expect During a Lung Ventilation/Perfusion Scan

Lung ventilation/perfusion (VQ) scans are done at radiology clinics or hospitals.

For the test, you lie on a table for about 1 hour and have two types of scans: ventilation and perfusion. The ventilation scan shows the pattern of air flow in your lungs. The perfusion scan shows the pattern of blood flow in your lungs.

You must lie very still during the tests or the pictures may blur. If you're having trouble staying still, your doctor may give you medicine to help you relax.

Both scans use radioisotopes (a low-risk radioactive substance). This substance releases energy inside your body. Special scanners outside of your body use the energy to create images of air and blood flow in your lungs.

The radioisotopes used in VQ scans can cause an allergic reaction, including itching and hives. Medicines can relieve these symptoms.

Ventilation

For this scan, you lie on a table that moves under the arm of the scanner. You wear a breathing mask over your nose and mouth and inhale a small amount of radioisotope gas mixed with oxygen.

As you breathe, the scanner takes pictures that show air going into your lungs. You'll need to hold your breath for a few seconds at the start of each picture.

The scan is painless, and each picture takes only a few minutes. However, wearing the mask can make some people feel anxious. If this happens, your doctor may give you medicine to help you relax.

Perfusion

For this scan, a small amount of radioisotope is injected into a vein in your arm. The scanner then takes pictures of blood flow through your lungs.

The scan itself doesn't hurt, but you may feel some discomfort from the radioisotope injection.




What To Expect After a Lung Ventilation/Perfusion Scan

Most people can return to their normal activities right after a lung ventilation/perfusion (VQ) scan.

If you got medicine to help you relax during the scan, your doctor will tell you when you can return to your normal activities. The medicine may make you tired, so you'll need someone to drive you home.

You may have a bruise on your arm where the radioisotopes were injected. You'll need to drink plenty of fluids to flush the radioisotopes out of your body. Your doctor can advise you about how much fluid to drink.

If you're breastfeeding, ask your doctor how long you should wait after the test before you breastfeed. The radioisotopes used for VQ scans can pass through your breast milk to your baby.

You may want to prepare for the scan by pumping and saving milk for 24 to 48 in advance. You can bottle-feed your baby in the hours after the VQ scan.




What Does a Lung Ventilation/Perfusion Scan Show?

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.




What Are the Risks of a Lung Ventilation/Perfusion Scan?

Lung ventilation/perfusion (VQ) scans involve little risk for most people. The radioisotopes used for both tests expose you to a small amount of radiation. 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.

Although rare, the radioisotopes may cause an allergic reaction.

Radiation

The radiation from a VQ scan leaves your body after a few days. Exposure to radiation is associated with a risk of cancer. However, it's not known whether the amount of radiation from a VQ scan increases your risk for cancer.

You and your doctor will decide whether the benefits of a VQ scan outweigh the possible risks. Your doctor also will try to avoid ordering multiple VQ scans for you over a short period.

If you're pregnant or breastfeeding, talk with your doctor about the risk of radiation to your baby. He or she will consider whether another test can be used instead.

Allergic Reaction

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




Links to Other Information About Lung Ventilation/Perfusion Scans

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July 25, 2014 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.