lung ventilation-perfusion scan

A lung ventilation/perfusion scan, or VQ scan, is a test that measures air and blood flow in the lungs.

This test most often is used to help diagnose or rule out a pulmonary embolism, or PE. A PE is a blood clot that travels to the lungs and blocks blood flow. This results in low blood oxygen levels, damage to the lungs, or even death.

The scan also can detect poor blood flow in the lungs' blood vessels and 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.

Who needs a lung ventilation-perfusion scan?

People who have signs or symptoms of a pulmonary embolism (PE) may need lung ventilation/perfusion (VQ) scans. A PE occurs when a blood clot travels to the lungs and blocks blood flow. Signs and symptoms of PE include chest pain, trouble breathing, rapid breathing, coughing, coughing up blood, and a rapid heart rate. Some clots travel to the lungs from veins deep in the legs. This can cause pain and swelling in the affected limb(s).

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 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 and to examine the lungs before some types of surgery.

Before a lung ventilation-perfusion scan

Most people don't need to prepare for a lung ventilation/perfusion (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 unnecessary radiation exposure during pregnancy. This is because of the concern that radiation 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 breast-feeding, ask your doctor how long you should wait after the test before you breast-feed. The radioisotopes used for VQ scans can be passed to your baby through your breast milk.

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.

During a lung ventilation-perfusion scan

A lung ventilation/perfusion (VQ) scan is done at a radiology clinic.

You will lie on a table for about 1 hour and have 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.

You must lie very still for 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 to your lungs.

The radioisotopes used in VQ scans can cause an allergic reaction, including itching and hives. If this happens, your doctor will give you medicine to relieve the symptoms.

Ventilation

For this scan, you lie on an open 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 member of the health care team will inject a small amount of radioisotope 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 when the radioisotopes are injected.

After a lung ventilation-perfusion scan

Most people can return to their normal routines 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 routine. 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 will 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 breast-feeding, ask your doctor how long you should wait after the test before you breast-feed. The radioisotopes used for VQ scans can be passed to your baby through your breast milk.

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?

A lung ventilation/perfusion (VQ) scan shows how well air and blood are flowing through your lungs. Normal results will 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). PE occurs when a blood clot travels to the lungs and blocks blood flow.

The results of the scan will show whether you're at high, medium, or low risk for PE. However, a VQ scan alone won't confirm whether you have PE. A scan showing low blood flow in spots may reflect other lung problems, such as lung damage from chronic obstructive pulmonary disease (COPD).

Your doctor will use the VQ scan results along with results from a physical exam, chest X-ray, and other tests to make a diagnosis.

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 the radioisotopes used in VQ scans leaves the 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 puts you at higher risk than the amount of radiation you're naturally exposed to.

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

If you're pregnant or breast-feeding, talk to your doctor about the risk of radiation related to this test. He or she will consider whether another test can be used instead.