What to Know About a VQ Scan

Medically Reviewed by Melinda Ratini, MS, DO on August 05, 2023
4 min read

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.  

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. 

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 your breath 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. 

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 and you are not able to take a computed tomography pulmonary arteriography (CTPA) test.

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

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. 

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. Make sure your doctor knows if you may be pregnant.  There is a slight risk from the radiation to both you and your baby. Your breast tissue is more sensitive to radiation when you are pregnant, and this test causes a very slight increase in breast cancer risk. Your baby will also get a small dose of radiation which can also cause a small increase in cancer risk for them in the future. The test will only be done if it is medically needed and these risks are outweighed by the benefits of finding and treating a possible life-threatening condition like a blood clot in your lung.

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.