VQ Scan

A VQ scan is an imaging test that evaluates how well air and blood flow through your lungs. Healthcare providers most commonly use it to detect a blood clot in your lungs. They may also use it to diagnose certain types of pulmonary hypertension (high blood pressure in your lungs) and to check your lung function:

• After a lung transplant
• Before surgery to remove all or part of your lung
• During treatment for COPD (chronic obstructive pulmonary disease) or other lung conditions to determine how well the treatment is working

A VQ scan is a two-part, noninvasive test. The “V” stands for ventilation, or air flow in and out of your lungs. The “Q” stands for quantity of perfusion, or blood flow to the small blood vessels in your lungs. You might also hear this test called a ventilation-perfusion scan, a lung scan or lung scintigraphy.

Unlike CT scans, VQ scans don’t use contrast dye. So, they’re safe for people who can’t use contrast due to allergies or renal insufficiency. VQ scans do use a small amount of radiation.

How does a VQ scan work?

A healthcare provider performs a VQ scan in two parts. These happen one right after another on the same day. For the first part (ventilation), your provider will have you breathe in a small amount of radioactive particles (tracer).

Think of the tracer like bright tags attached to parts of the air. Your provider uses a special camera — similar to an X-ray or a CT camera — to take pictures of your lungs. The bright tags of the tracer make the air flowing into your lungs show up on the images.

For the second part (perfusion), your provider will give you an injection of a similar tracer. This time, the bright tags flow through your blood vessels. Your provider will use the same camera to get pictures of the blood flow in your lungs.

Preparation

You don’t need to do anything specific to prepare for a VQ scan. But you should tell your provider:

• If you’re pregnant or think you might be: Your provider might suggest a different form of imaging to reduce the risk of radiation exposure to the fetus.
• If you’re breastfeeding: Your provider might give you instructions on how to feed your baby on the day of the test or following the procedure. This reduces the risk of exposing your baby to radiation in your milk.
• If you don’t think you can sit or lie still for several minutes at a time: Movement can blur the images, and your provider won’t be able to use them.

Before you get a VQ scan, you’ll get a chest X-ray. This can be anywhere from one to 24 hours before your scan. This gives your provider more information to help them understand the scan results.

What happens during a VQ scan?

You’ll start with the ventilation scan. During this part:

1. You might change into a hospital gown.
2. Your provider will help you put on a device that you’ll breathe from. It might be a mask or a mouthpiece with a clip over your nose.
3. Your provider will attach the mask or mouthpiece to a machine with a hose. They’ll add the tracer to the hose.
4. You’ll either lie on a table or sit in a chair to take pictures. If you’re lying on a table, it’ll slide into a machine that looks like a cylinder. If you’re in a chair, your provider will position you in front of the camera.
5. You’ll breathe in through the mask or mouthpiece while the camera takes pictures.
6. Your provider will reposition your body during the test to get the pictures they need.
7. Your provider will have you remove the mask or mouthpiece. They may take pictures for another minute or two after that.

In most cases, you’ll move to the perfusion scan immediately after the ventilation scan. The two are very similar and have many of the same steps. Instead of breathing in the radioactive tracer, your provider will inject the tracer into your vein using an IV.

How long does a VQ scan take?

A VQ scan takes between 30 and 60 minutes in total. Each test takes about 15 minutes. Yours may take more or less time depending on prep time and whether your provider is getting the images they need.

After the test

After a VQ scan, the tracer will leave your lungs as you breathe in fresh air. The injected tracer will lose its radioactivity and leave the rest of your body through your pee and poop in a few hours or days. If you’re breastfeeding, check with your provider about how to safely feed your baby for the day or two following the scan.

Possible risks and side effects

The risks of having a VQ scan are minimal. They include:

• Exposure to radiation: VQ scans expose you to a small amount of radiation. This leaves your body within a few hours to days of the scan.
• Inability to shield from radiation: While VQ scans only expose you to a small amount of radiation, there’s no way to shield a fetus from it. If you’re pregnant, your provider may recommend a CT scan instead. A provider can use a shield during a CT scan to reduce the fetus’ exposure to radiation.
• Allergic reaction: These are rare and usually mild.
• Discomfort: The needle stick to inject the tracer or staying still for several minutes may be uncomfortable.

What do the results look like?

You’ll usually know the results of a VQ scan within 24 hours. If the results are abnormal, it means something is preventing your lungs from working properly. If the sets of pictures from the two parts of the scan don’t match, it could mean you have a pulmonary embolism (PE).

When should I call my doctor?

Talk to your healthcare provider if you have any questions about the test or its results.

What’s the difference between a CT scan and a VQ scan?

CT scans and VQ scans both take pictures of your lungs to help diagnose issues like blood clots. A CT scan uses a camera that takes pictures of a contrast dye in your body. A provider looks at the pictures to identify issues.

A VQ scan uses a camera that takes pictures of radioactive particles in your body. A provider can look at one set of pictures or compare the two to understand how your lungs are working. It exposes you to less radiation than a CT scan.