Lung Ventilation/Perfusion Scan

A lung ventilation/perfusion test, commonly referred to as a VQ test, is carried out to test the function of the lungs. The test measures the blood and airflow in the lungs and is most commonly used if a doctor suspects that a patient has suffered a pulmonary embolism. A pulmonary embolism (PE) is a blood clot, which breaks away and travels up to the lungs. A PE can be fatal because it blocks blood flow and causes the oxygen levels in the blood to decrease.

Overview of the Lung Ventilation/Perfusion Scan test

The VQ test involves two parts: the ventilation test and the perfusion test. The ventilation scan displays airflow and the movement of air in the lungs, while the perfusion scan displays blood flow in the lungs. The VQ test can display abnormalities in the lungs, which may not be visible on other types of test or scan.

The scans use radioisotopes to highlight air and blood flow. The radioisotopes cause the body to release energy, which enables special scanners to generate detailed images of the lungs.


The lung ventilation/perfusion test is a safe procedure and does not usually cause any problems for patients, as the amount of radiation used is very small (the equivalent to how much a person is exposed to naturally over the course of one year) and side-effects are very rare. Occasionally, people feel mild pain when the radioisotope is injected for the perfusion part of the test and there may be bruising around the site of the injection; but any discomfort should wear off very quickly.

In rare cases, people have allergic reactions to the radioisotopes, but doctors can easily treat this with medication.

The ventilation/perfusion test may also be known by the following names:

  • The VQ test.
  • Pulmonary ventilation/ perfusion test.
  • Nuclear medicine tests.

Who would need a lung ventilation/perfusion test?

You may be advised to have a ventilation/perfusion test if you have symptoms of pulmonary embolism. A pulmonary embolism occurs when a blood clot breaks away and travels up to the lungs, blocking the supply of blood to the lungs. Symptoms of pulmonary embolism include:

  • Chest pain (which may suddenly get worse, especially when you breathe in).
  • Difficulty breathing (this can come on slowly or quickly).
  • Coughing up blood.
  • Increased heart rate.
  • Collapsing.

A pulmonary embolism can be fatal and it should be treated as a medical emergency. If doctors suspect that a PE is causing a patient’s symptoms, they will carry out a VQ test. The test results will not be sufficient to diagnose PE but they will help doctors to reach a firm diagnosis. Doctors may also use a VQ scan to investigate blood flow in the lungs or examine the lungs before surgery is carried out.

Before the lung ventilation/perfusion test

Before the test your doctor will explain what is going to happen and how the test works. There is usually no preparation needed prior to the test but you will be advised to avoid wearing clothing with metal fastenings. If you are pregnant it is very important that you tell your doctor before the test, as radiation can be harmful to unborn babies. If you are pregnant your doctor will talk to you about the test and decide if the benefits of having the test outweigh the risks. If they decide against doing a VQ they will recommend an alternative test.

If you are breastfeeding it is advisable to wait a while after the test until you next breastfeed, as the radioisotopes can be passed to a baby through the breast milk. Your doctor will be able to advise you on this matter or you can express and store some milk before the test.

What does the procedure involve?

The VQ test is carried out at a Nuclear Medicine Department and can be performed as an inpatient or outpatient procedure. The test is in two parts but it only requires one visit to the Nuclear Medicine Department.

Part 1 - the ventilation scan

The ventilation scan is used to examine airflow in the lungs and is a very simple procedure. You will be asked to sit down and inhale some gas through a mouthpiece, which is invisible and has no taste. The gas contains a very small sum of radiation, which enables doctors to see your lungs in detail.

After you have inhaled the gas you will be asked to lie down and images of your lungs will be taken using a gamma camera. You will not need to take your clothes off for the test, but you will be asked to remove any clothing with metal fastenings and jewellery and also to take loose change out of your pockets. Images of your lungs will be taken for around 20 minutes. You will not feel any pain during this period and you will be asked to relax and breathe normally, though you may also be asked to hold your breath at certain times.

Part 2 - the perfusion scan

Once the ventilation test has been carried out the perfusion test will be conducted. Sometimes the test is done straightaway, but it can take some time for the lungs to clear, so it may be done around 3-4 hours after.

The perfusion test involves having a small sum of radioisotope injected into your arm. This should be painless but if you are scared of needles or worried about the injection talk to your nurse. The radioactive material enables doctors to see clear images of your lungs. The gamma camera will be used to capture images of your lungs and this will take around 20 minutes. Once the perfusion test is over you will be free to leave. Side-effects are very rare but if you experience any it is important that you seek medical help.

After the scan

The scan should not be painful and you should be able to resume normal activities after the test. If you have been given medication to help you to relax during the test, your doctor will advise you to wait a while until the effects of the drugs have worn off.

You may feel very mild pain and experience bruising in your arm where the needle was injected; however, this should wear off very quickly. Afterwards your doctor will advise you to drink plenty of fluid to flush out the radioisotopes.
If you are breastfeeding your doctor will advise you when it is safe to feed your baby, although it may be a good idea to express some milk before the test.

What does a lung ventilation/perfusion test show?

A lung ventilation/perfusion test displays the movement of air and blood around the lungs. If the test results show full flow of blood and air to the lungs, this indicates a normal result.

If the results show that airflow is normal but the supply of blood is abnormal, this may indicate a pulmonary embolism (PE), which blocks the supply of blood to the lungs. The outcome of the scan will also indicate your risk of PE. Further tests (including chest X-rays and physical examinations) will be carried out to reach a firm diagnosis of whether or not you have had a pulmonary embolism.

If the scan results show low blood supply to certain areas of the lungs, this may indicate harm to the lungs caused by other conditions, such as chronic obstructive pulmonary disease (COPD).

Are there any risks associated with the lung ventilation/perfusion test?

VQ tests carry a very low risk and the amount of radiation used is very small and equates to the same amount of radiation a person would naturally be exposed to during the course of a year. Exposure to radiation is linked with an increased risk of cancer, but the increase is very slight and doctors will always weigh the risks against the benefits before advising a patient to have a VQ test.

If you are pregnant or breastfeeding, you should tell your doctor before the test is carried out. Radiation can harm unborn and very young babies and your doctor may advise you to have a different type of test.

There is a risk of allergic reaction to the radioisotope, but this is very rare.

Key notes about lung ventilation/perfusion tests

  • A lung ventilation/perfusion test examines air and blood flow in the lungs.
  • The test is most commonly used to diagnose pulmonary embolism, a condition which happens when a blood clot blocks the flow of blood to the lungs.
  • A VQ test will usually be ordered if a patient has symptoms associated with a pulmonary embolism. The test can also be used to examine a patient’s lungs before surgery.
  • Usually, no preparation is required before a VQ test, although patients are advised to avoid wearing clothing with metal hooks or fastenings, such as zips.
  • Tell your doctor if you are pregnant or you think you may be pregnant before you have the test, as radiation can harm unborn babies.
  • The test is carried out in 2 parts: the ventilation test is carried out first, followed by the perfusion test. The ventilation test involves breathing in gas containing a small dose of radiation through a mouthpiece. Images will then be taken of your lungs with a camera and the pictures will be analysed by specially trained doctors. The perfusion test involves having an injection of radioisotope and the test allows doctors to see blood flow in your lungs.
  • Both tests use radioisotopes but the amount of radiation is very small.
  • Most people can resume normal activities immediately after the scan. However, if you have taken medicine to help you relax, you will need to wait for this to wear off as it may make you drowsy.
  • If you are breastfeeding it may be a good idea to express some milk before you have the test. Alternatively, your doctor will be able to advise you when you can feed again.
  • The results of the test will show doctors how air and blood are flowing around the lungs. If airflow is normal but the blood supply is not, this may indicate that you have had a pulmonary embolism.
  • VQ tests are generally very safe and carry very low risks.


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