Pulmonary Ventilation/Perfusion Scan
A pulmonary ventilation/perfusion scan is a series of two scans that measure how well air and blood are able to flow through your lungs (ventilation scan), as well as the blood supply through the lungs (perfusion scan). The scans are either performed together or one after the other, but are often discussed as one scan: the pulmonary ventilation/perfusion scan.
During a pulmonary ventilation/perfusion scan, a radioactive dye is injected into your veins. This dye will show up on a special type of scanner, and will give your doctor information about how well your lungs are working. The dye will gather at areas of abnormal blood flow, which may indicate a blockage in the lung artery.
This test may also be called a V/Q scan or a radionuclide pulmonary scan.
Why Is the Test Ordered?
A pulmonary ventilation/perfusion scan is used most frequently to screen for pulmonary embolus, which is also known as a blood clot in the lungs. Symptoms of pulmonary embolus include rapid heart rate, trouble breathing, decreased oxygen saturation levels, and chest pain.
This scan may also be used to screen for other lung conditions, or to test the lung function in individuals with lung disease. The pulmonary ventilation/perfusion scan may be used to screen for or test lung function in:
- lung infections or inflammation, such as bronchitis, pneumonia, or pneumonitis
- chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) or emphysema
- pulmonary effusion, which occurs when fluid collects around the lungs
- pulmonary artery narrowing
- atelectasis, which is a collapsed area in the lung
- airway obstruction, which can be caused by a tumor
Preparing for the Test
Your doctor will explain the procedure of the pulmonary ventilation/perfusion scan to you, as well as the risks associated with the test. You will be asked to sign a consent form after this information has been explained to you and after you have had the chance to ask any questions you may have.
Before the test, you should tell your doctor about any known allergies you have, particularly to contrast dyes or latex. This will alert your doctor to the possibility of an allergic reaction during the test, so the medical staff is prepared. It is also important that you tell your doctor if you are pregnant or breastfeeding, because the contrast dye used may be passed on to the fetus or through breast milk.
Finally, you should inform your doctor if you have had a nuclear test in the past 48 hours. This is because there may be radioactive dye remaining in your body, which can change the results of the test.
You should try to wear loose-fitting clothing without metal fasteners to the test. You will be asked to remove any metal jewelry, so you may wish to also avoid wearing jewelry to the test.
You may be asked to have an X-ray of your chest done 24 to 48 hours before your test.
What Happens During the Test
For this test, you will be asked to lie down on an examination table. Then, a technician will set up an intravenous (IV) line. This IV line will inject the radionuclide dye into your bloodstream, usually through a vein on the inside of your elbow or on the back of your hand. You may feel mild to moderate pain from the IV, which may feel like a pricking sensation.
When the radionuclide dye has been injected, the technician will remove the IV and you will then be moved under a special scanner. This scanner will detect the dye and look at how the radioactive substance flows into your lungs via your bloodstream. You will need to lie still while the images are being captured. However, the technician may ask you at times to move positions to take certain pictures.
For the next part of the test, you will be given a mouthpiece while you are still sitting or lying underneath the scanner. You will be asked to breathe through the mouthpiece, which contains a gas with a radioactive substance. The scanner will take images of your lungs while you are breathing in the gas.
You may be asked to hold your breath to capture certain images. When the technician has taken all the necessary pictures, the mouthpiece will be removed, and you will be able to leave the scanner.
It is important that you drink plenty of fluids after your test to help flush the radioactive substances from your body.
What Are the Risks?
There is a low risk associated with a pulmonary ventilation/perfusion scan. However, problems can arise due to the radioactive substances and the insertion of the IV. Possible risks include:
- excessive bleeding at the IV site
- infection at the IV site
- allergic reaction to the radioactive dye (rare)