Content Map Terms

Lung VQ Scan

Test Overview

A lung scan is a type of nuclear scanning test. It is most often used to find a pulmonary embolism. This is a blood clot that prevents normal blood flow in the lung.

Two types of lung scans are usually done together:

  • Ventilation scan. During this scan, you inhale a radioactive tracer gas or mist. Pictures from this scan can show areas of the lungs that aren't getting enough air or that hold too much air.
  • Perfusion scan. During this scan, a radioactive tracer is injected into a vein in your arm. It travels through your blood and into the lungs. Pictures from this scan can show areas of the lungs that aren't getting enough blood.

If the lungs are working as they should, the results of the two scans will match. If the scan results don't match, you may have a blood clot in the lung.

Ventilation and perfusion scans can be done on their own or together. If both scans are done, the test is called a V/Q scan. The ventilation scan usually is done first.

Why It Is Done

A lung scan is done to:

  • Find a blood clot that is preventing normal blood flow to part of a lung.
  • Check the flow of blood or air through the lungs.
  • See which parts of the lungs are working and which are damaged. This is often done before lung surgery to remove parts of the lung.

How To Prepare

Before your lung scan, tell your doctor if:

  • You are or might be pregnant.
  • You are breastfeeding. The radioactive tracer used in this test can get into your breast milk. Do not breastfeed your baby for 1 or 2 days after this test. During this time, you can give your baby breast milk you stored before the test, or you can give formula. Don't use the breast milk you pump for the 1 or 2 days after the test. Throw it out.

A chest X-ray is usually done the same day, either before or after the lung scan.

You may be asked to sign a consent form.

Talk to your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form .

How It Is Done

You will need to take off any jewellery that might interfere with the scan. You may need to take off all or most of your clothes, depending on which area is being examined. You will be given a cloth or paper covering to use during the test.

During the scan, you might lie on your back with the scanning camera over or under your chest. Or you might sit with the camera next to your chest. The camera does not produce any radiation.

Ventilation scan

For the ventilation scan, a mask will be placed over your mouth and nose. Or you may have a nose clip on your nose and a tube in your mouth that you use for breathing. You will take a deep breath and hold it.

The camera will take pictures as the tracer moves through your lungs.

You may be asked to breathe the gas in and out through your mouth for several minutes. You may then be asked to hold your breath for short periods (about 10 seconds) and to change positions. This is done so your lungs can be viewed from other angles. The camera may move to take pictures from different angles. You need to stay very still during the scans to avoid blurring the pictures.

Afterward, the radioactive gas or mist will clear from your lungs as you breathe.

The ventilation scan takes about 15 to 30 minutes.

Perfusion scan

For the perfusion scan, a small amount of the radioactive tracer is injected into your arm.

After the tracer is injected, the camera will take pictures as the tracer moves through your lungs. The camera may be repositioned around your chest to get different views. You need to stay very still during the scans to avoid blurring the pictures.

The perfusion scan takes about 5 to 10 minutes.

How It Feels

Breathing through the mask during the ventilation scan may be uncomfortable, especially if you feel very short of breath. But you will be given plenty of oxygen through the mask.

If you have a perfusion scan, you may feel nothing at all from the needle, or you may feel a brief sting or pinch. Otherwise, a lung scan is usually painless.

You may find it hard to stay still. Ask for a pillow or blanket to make yourself as comfortable as possible before the scan begins.


Allergic reactions to the radioactive tracer are very rare.

Some people have soreness or swelling at the injection site. A moist, warm compress applied to the arm may help.

Anytime you're exposed to radiation, there's a small chance of damage to cells or tissue. That's the case even with the low-level radioactive tracer used for this test. But the chance of damage is very low compared with the benefits of the test.

Most of the tracer will leave your body through your urine or stool within a day. So be sure to flush the toilet right after you use it, and wash your hands well with soap and water. The amount of radiation in the tracer is very small. This means it isn't a risk for people to be around you after the test.


A lung scan is a type of nuclear scanning test. It is most often used to find a pulmonary embolism. This is a blood clot that prevents normal blood flow in the lung.

The results of a lung scan are usually ready in 1 day.

Lung scan


The radioactive tracer is evenly distributed throughout the lungs during ventilation and perfusion.


The ventilation scan is abnormal, but the perfusion scan is normal. This may mean abnormal airways in all or parts of the lung. It may be a sign of chronic obstructive pulmonary disease (COPD) or asthma.

The perfusion scan is abnormal, but the ventilation scan is normal. Depending on the difference between the two scans, it may be a sign of a pulmonary embolism.

Both the ventilation and perfusion scans are abnormal. This can be caused by certain types of lung disease, such as pneumonia or COPD, or by a pulmonary embolism.

Lung scan results can help your doctor find out how likely it is that you have a blood clot in your lung (pulmonary embolism). The results are most often reported in one the following ways:

  • Normal. The results do not show any problem with your lungs.
  • Low probability. The results show that the likelihood of a blood clot is low. Your doctor may feel that you need more tests.
  • Indeterminate or intermediate probability. The lung scan results show it is possible that you have a blood clot. More tests may be needed.
  • High probability. The results show a high likelihood of a blood clot. Your doctor will give you medicine to treat the clot.

What Affects the Test

You may not be able to have the test, or the results may not be helpful, if:

  • You are pregnant. The radiation from a lung scan could harm the baby.
  • You're not able to stay still during the test.
  • You're not able to breathe through the mask or tube.
  • You have a medical condition that involves the lungs or heart, such as pulmonary edema or chronic obstructive pulmonary disease (COPD).

What To Think About

  • Checking for a blood clot in your leg (deep venous thrombosis) can help your doctor decide if you are at high risk for having one in your lung. The doctor will ask about your medical history and do a physical examination to learn your risk level for deep leg vein thrombosis. Then an ultrasound is usually done. Your pretest probability and ultrasound results will help your doctor decide which follow-up tests you need. To learn more, see the topic Doppler Ultrasound.
  • If your perfusion scan results are unclear, your doctor may want to do more tests. Pulmonary angiography is an X-ray test that uses contrast material injected into the bloodstream to check the blood flow leading to the lungs. Many medical centres and doctors now use a newer CT scanning technique called CT pulmonary angiography, or CTPA.


Current as of:
September 23, 2020

Author: Healthwise Staff
Medical Review:
Anne C. Poinier MD - Internal Medicine
Adam Husney MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
Myo Min Han MD - Nuclear Medicine