What to Know About a VQ Scan

Medically Reviewed by Dan Brennan, MD on June 29, 2021

A VQ scan is short for Lung or Pulmonary Ventilation (V) and Perfusion (Q) Scans. It’s an imaging test that measures air and blood flow in your lungs. Your doctor may request this test, and below you’ll find more on what to expect.  

How Does a VQ Scan Work?

The VQ scan is a nuclear scan. It measures airflow, called ventilation, and blood flow, called perfusion, in your lungs. The V and Q make up a math equation that helps doctors calculate the air and blood flow. 

The scan uses a special x-ray scanner outside of your body. It takes pictures of the air and blood flow patterns in your lungs. 

This scan is mostly used to help doctors diagnose a blood clot in your lungs. This is called a pulmonary embolism. Your doctor also may request this test to check out your lungs before a certain surgery. 

How Is a VQ Scan Performed?

A VQ scan uses nuclear radiology to scan your lungs. The procedure turns a very small amount of radioactive substance into the examination to scan your airflow. 

These scans are done in hospitals or radiology clinics. You don’t have to prepare for a VQ scan. Your doctor may ask you to take a chest x-ray prior. The test will take you an hour or so. 

You will need to hold your breath before each scan. Holding for a few minutes will help you stay still as the scanner moves over your lungs taking pictures. 

For the airflow test ventilation, right before the VQ scan happens you’ll have to wear a mask over your nose and mouth that lets you breathe in small amounts of the radioisotope gas and oxygen. For the perfusion scan for the blood flow test, the doctor will inject a small amount of radioisotope into your vein. 

Then, the VQ scanner will pick up the radioisotope energy in your body. That energy will be used to make pictures of your lungs. 

Why Is a VQ Scan Done?

Your doctor will recommend a VQ scan if they want to measure your blood supply throughout your lungs. Conditions like abnormal circulation, or shunts, in your pulmonary blood vessels and COPD can be diagnosed or further looked into after this kind of scan. 

Most likely, your doctor will recommend this type of imaging scan if they are concerned about a pulmonary embolism. 

Symptoms of pulmonary embolism include: 

  • Shortness of breath
  • Chest pain that worsened by breathing in 
  • Bloody cough
  • Leg pain or swelling
  • Pain in your back
  • Excessive sweating
  • Lightheadedness, dizziness, or passing out
  • Blue lips or nails

What the Results Mean

After the scan is done, you’ll either get a normal result or an abnormal result. Your doctor will be able to help you figure out the next steps depending on your results. 

Normal result. If both of your lungs work well and your air and blood flow is working properly, you’ll get a normal result. Both lungs should look and work the same. 

Abnormal results. If you get a scan back that shows your lungs aren’t getting the right amount of air or blood pumping through them, then it’ll come back abnormal. This could mean that you have any of the following conditions: 

Your doctor will look at the results and diagnose your underlying condition that’s affecting your lung VQ scan. 

Conditions That Can Affect a VQ Scan

VQ scans have little risk to them. You may feel a little pain at the injection site for your perfusion, but this will only be because of the needle. There are rare cases where a VQ scan can cause reactions or may not be suitable for some individuals. 

Allergic reaction. Very rarely, you may be allergic to the radioisotope that’s breathed in or injected. However, this can be treated quickly. 

Pregnancy. The test uses very small amounts of radiation that’s inhaled and injected into your body. This test is not recommended for women who are pregnant or want to become pregnant. Radiation from the test can seep into your breast milk. This can be harmful to your baby. 

Reaction to needle prick. There is a small chance that you could get an infection or bruising at the injection site of the radioisotope. This risk is very rare and will depend on how your body responds to intravenous needles.

Show Sources


American Lung Association: “Pulmonary Embolism Symptoms and Diagnosis.”

Harvard Health Publishing: “Ventilation-Perfusion Scan or V-Q Scan.”

National Heart, Lung, and Blood Institute: "Lung VQ Scan."

Stanford Health Care: “Ventilation-perfusion Scan (V/Q Scan).”

UCLA Health: “Lung Ventilation/Perfusion Scan.”

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