Diseases & Conditions A - Z
powered by Talix

What is a VQ Scan?


A pulmonary ventilation/perfusion scan is a series of two lung scans. The scans are either performed together or one after the other, but are often referred to as one procedure.

One of the scans is called a VQ scan, which stands for ventilation quotient. This scan measures how well air is able to flow through your lungs. The other scan is called a perfusion scan, which shows where blood flows in your lungs.

Both scans involve the use of a low-risk radioactive substance that can be traced by a special type of scanner. The substance will show up in the scanned image and can tell your doctor information about how well your lungs are working. The substance will gather at areas of abnormal blood or airflow, which may indicate a blockage in the lung.

Why is the scan ordered?

A VQ scan is used most frequently to screen for a pulmonary embolus, which is also known as a blood clot in the lungs. Symptoms of pulmonary embolus may include:

  • rapid heart rate
  • trouble breathing
  • decreased oxygen saturation levels
  • chest pain

This scan may also be used to screen for other lung conditions, or to test the lung function in people with lung disease. The VQ scan may be used to screen for or test lung function related to the following conditions:

  • lung infections or inflammation, such as bronchitis, pneumonia, or pneumonitis
  • chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) or emphysema
  • pulmonary effusion, which occurs when fluid collects around the lungs
  • pulmonary artery narrowing
  • atelectasis, which is a collapsed area in the lung
  • airway obstruction, which can be caused by a tumor

Preparing for the test

Your doctor will explain the procedure of the VQ scan to you, as well as the risks associated with the test. You will be asked to sign a consent form after the possible risks have been explained to you and you’ve had a chance to ask any questions.

Before the test, you should tell your doctor about any known allergies you have, particularly to contrast dyes or latex. This will make sure your doctor and the rest of the medical staff are prepared for the possibility of an allergic reaction during the test.

It’s also important that you tell your doctor if you are pregnant or breastfeeding. The contrast dye used may be passed on to the fetus or through breast milk.

You should inform your doctor if you have had a test that included the use of radioactive materials — called a nuclear test — in the past 48 hours. If you have, there may be radioactive dye remaining in your body, which can affect the results of the test.

You should try to wear loose fitting clothing without metal fasteners to the test, or you may be asked to change into a patient gown. It’ll also necessary to remove any metal jewelry, including piercings, so you may wish to also avoid wearing jewelry to the test. Generally, there is no special dietary preparation, such as fasting, before the scan.

You may also be asked to have an X-ray of your chest done 24 to 48 hours before your test.

What happens during the test

For the entire scan, which takes about 45 minutes, you’ll be asked to lie down on an examination table. For the perfusion scan, a technician will set up an intravenous (IV) line. Radionuclide dye will be introduced into your bloodstream through a needle, usually using a vein on the inside of your elbow or on the back of your hand. This dye usually contains small amounts of radioactive technetium. You may feel mild to moderate pain from the IV or a pricking sensation.

When the dye has been injected, the technician will remove the IV and you will then be moved under a special scanner. This scanner will detect the dye and look at how it flows into your lungs via your bloodstream.

You will need to lie still while the images are being captured. However, the technician may ask you to move positions to get pictures from different angles.

For the VQ scan, you will be given a mouthpiece while you are still lying underneath the scanner. You will be asked to breathe through the mouthpiece, which contains a gas with a radioactive substance, usually radioactive xenon or technetium.

The scanner will take images of your lungs while you are breathing in the gas. You should try not to swallow this gas. It could interfere with the images that need to be taken of the lungs. You may be asked to hold your breath to capture certain images.

When the technician has taken all the necessary pictures, the mouthpiece will be removed, and you will be able to leave the scanner. And your breathing will gradually remove the gas from your lungs.

What are the risks?

There is a low risk associated with a VQ scan. The amount of radiation a person is exposed to in this process is roughly equal to the amount they are naturally exposed to in a year, according to the National Heart, Lung, and Blood Institute.

However, problems can arise due to the radioactive substances and the insertion of the IV. Possible risks include:

  • excessive bleeding at the IV site
  • infection at the IV site
  • allergic reaction to the radioactive dye  

After the test

You may be monitored for a short time after the test to check for any allergic reactions. Someone will also check the IV site for redness and swelling. You may feel slightly dizzy from lying down during the test.

It is important that you drink plenty of fluids after your test to help flush the radioactive substances from your body. If you notice any redness, swelling, or pain at the IV site once you return home, notify your doctor as this may be sign of an infection.

You can eat and drink as usual, unless your doctor says otherwise. Also, avoid having any other nuclear procedures for the next 24 to 48 hours.

Content licensed from:

Written by: Janelle Martel
Medically reviewed on: Jun 07, 2016: Deborah Weatherspoon, PhD, MSN, CRNA, COI

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
Symptom Search
Enter your symptoms in our Symptom Checker to find out possible causes of your symptoms. Go.
Drug Interaction Checker
Enter any list of prescription drugs and see how they interact with each other and with other substances. Go.
Pill Identifier
Enter its color and shape information, and this tool helps you identify it. Go.
Drugs A-Z
Find information on drug interactions, side effects, and more. Go.