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A ventilation–perfusion (VQ) scan is a nuclear medicine scan that uses radioactive material (radiopharmaceutical) to examine airflow (ventilation) and blood flow (perfusion) in the lungs.
The aim of the scan is to look for evidence of any blood clot in the lungs, called pulmonary embolism (PE).
A VQ scan is carried out in two parts. In the first part, radioactive material is breathed in and pictures or images are taken to look at the airflow in the lungs. In the second part, a different radioactive material is injected into a vein in the arm, and more images taken to see the blood flow in the lungs.
(See Nuclear Medicine for further general information).
Your doctor would refer you for this scan if the doctor suspects you might have a blood clot in your lung. A blood clot in the lung can sometimes be fatal, particularly if left untreated. The most common early symptoms are shortness of breath and a sharp pain when you breathe in.
Blood clots in the lungs often come from a clot in the leg called a deep vein thrombosis. A VQ scan will determine if a blood clot has travelled from your leg to your lung.
There is no preparation for a VQ scan other than having a recent chest X-ray examination. Your referring doctor will discuss this with you. You should continue to take your normal medications.
You will need to keep still while the images are being taken, so they are not blurred. If you feel you will not be able to stay still for approximately 3–15 minutes (this is the time of each scan and depends on the type of scan), please advise your doctor or the nuclear medicine staff where you are having the scan.
If you are severely claustrophobic, please advise the department when you make your appointment. The gamma camera is to be placed close to you to acquire the images (see Nuclear Medicine – What is a Gamma Camera?).
If you are or think you might be pregnant, and/or breast-feeding, you must inform the doctor who is referring you for the VQ scan and also the radiology staff where you are having the VQ scan.
Women who are breast-feeding need to make special preparations for after the scan. This will involve stopping breast-feeding for approximately 24 hours. This is due to the radioactivity in your breast milk after the scan injection. You should discuss this with your referring doctor or with the nuclear medicine practice where you will be having the test. You might need to have bottles of formula or previously expressed breast milk available.
The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has recommendations about breast-feeding and close contact with children after nuclear medicine tests.
VQ scans can be carried out if you are pregnant. Usually only the injected radiopharmaceutical is used and the dose of radioactivity is reduced to minimise the radiation to the developing foetus (unborn baby).
The scan is carried out in two parts:
You will be given a small dose of radioactive material (radiopharmaceutical) to breathe in through a nebuliser for a few minutes, with guidance from the nuclear medicine technologist who is carrying out the scan. A nebuliser is a small machine that changes liquid into an aerosol (or mist), which is breathed in, usually through a tube-like mouthpiece or a special mask that fits over your nose and mouth.
You will then lie down on a table and images of your lungs will be taken at several different angles by a gamma camera. This is a special nuclear medicine camera that identifies where the radioactive material has gone to in the lungs.
The nuclear medicine technologist will then inject a different radiopharmaceutical into a vein in your arm. A second set of images of your lungs will be taken.
The entire imaging process will take 30–60 minutes. While the images are taken, you will be asked to breathe gently and to keep still, otherwise the images will be blurry and might need to be repeated. The medical radiation technologist will ensure that you are comfortable throughout the whole process.
The radiopharmaceuticals you received will be eliminated from your body within 24 hours of the scan. Part of the radioactive material will pass out of your body through your urine and the rest of the radioactive material will completely decay away (or disappear).
There are no after effects from a VQ scan. The radioactive material used in a VQ scan is not known to interfere with any food or medications you might be taking.
If you are breast-feeding, see the ‘How do I prepare’ section for more information about special precautions you need to take.
A VQ scan takes approximately 30 minutes – 1 hour to complete.
There are minimal risks involved in the VQ scan.
Allergic reactions to the radiopharmaceuticals are rare and will be treated as needed.
The test involves exposure to ionising radiation (see Radiation Risk of Medical Imaging in Adults and Children).
If you are pregnant, the test can still be carried out after consultation with the nuclear medicine specialist. A reduced dose of radioactive material will be given, so that it will not affect your foetus (your unborn baby).
If you are breast-feeding, it is advised that you stop breast-feeding for the 24 hours after the scan. This is so that your baby is not unnecessarily exposed to radiation. During this time, your milk can be expressed, but it need not be discarded. It can be stored in the fridge and can be used to feed your baby 24 hours after the VQ scan.
The benefits of a VQ scan are:
The VQ scan is carried out by a nuclear medicine technologist. The images taken by the technologist are reviewed by a nuclear medicine specialist doctor who provides a written report to the doctor who referred you for the VQ scan.
Most large public and private hospitals and private radiology or nuclear medicine practices have nuclear medicine facilities where VQ scans are carried out.
The time that it takes your doctor to receive a written report on the test you have had will vary, depending on:
Please feel free to ask the private practice, clinic or hospital where you are having your test or procedure when your doctor is likely to have the written report.
It is important that you discuss the results with the doctor who referred you, either in person or on the telephone, so that they can explain what the results mean for you.
Page last modified on 26/7/2017.
RANZCR® is not aware that any person intends to act or rely upon the opinions, advices or information contained in this publication or of the manner in which it might be possible to do so. It issues no invitation to any person to act or rely upon such opinions, advices or information or any of them and it accepts no responsibility for any of them.
RANZCR® intends by this statement to exclude liability for any such opinions, advices or information. The content of this publication is not intended as a substitute for medical advice. It is designed to support, not replace, the relationship that exists between a patient and his/her doctor. Some of the tests and procedures included in this publication may not be available at all radiology providers.
RANZCR® recommends that any specific questions regarding any procedure be discussed with a person's family doctor or medical specialist. Whilst every effort is made to ensure the accuracy of the information contained in this publication, RANZCR®, its Board, officers and employees assume no responsibility for its content, use, or interpretation. Each person should rely on their own inquires before making decisions that touch their own interests.