VQ Scan

What is a VQ Scan?


Ventilation/perfusion lung scans, also known as a V/Q scan, is used to examine the circulation of air and blood within a patient’s lungs. The scan requires the use of two nuclear tests. This means that two medical isotopes are used to detect the flow of breathing (ventilation) and blood circulation (perfusion) in the lungs. Having these scans performed will require that a patient either inhale or have injected radioactive material (isotopes) so that ventilation and perfusion can be detected and analyzed on the scans.

Why is the V/Q Scan performed?

Typically, the V/Q scan is done to test for the presence of blood clots or other abnormalities in ventilation and circulation in the lung area. It is also commonly used in the presentation of chronic obstructive pulmonary disease (COPD) or pneumonia. There are some cases in which a V/Q scan would be contraindicated, such as in the case of a patient presenting with kidney failure. In this situation, health care professionals would opt for a computed topography with radiocontrast instead.

The Procedure


As mentioned, the test involves the use of two scans. However, health care professional typically will include a chest x-ray either before or after the scans. This is done so that they can comparatively examine the scans and to detect other causes to the lung disease(s) they are testing. A common question is whether one needs to fast the night before a V/Q scan. Unlike other tests, the V/Q and chest x-ray scans do not require that an individual fast or consume a special diet prior to the tests.


vq scan


The perfusion portion of the scan requires an injection of radioactive isotopes. You can expect this to be about as painful as getting a shot or having blood drawn at the doctor’s office. Radioactive albumin is the material that is injected into a vein.  As is usual with all tests involving a scan, patients will be asked to lay with their back on a table. This table may not be comfortable given the nature of the scan and may be very cold and hard. Each hospital will have different equipment available and it is recommended to ask prior to the scan so that you are not shocked by the feeling and can prepare yourself appropriately. With the perfusion scan, the table is movable and is placed directly beneath the scanner. The scanner will take snapshots of the way blood flows through your lungs and find the radioactive particles.


The ventilation scan tends to be described as the scarier of the two scans. This is for two reasons. First the scan requires an individual to remain in a small space for the duration of the scan. This might not be ideal of those who are claustrophobic. The second is that this portion entails the patient inhaling special gasses that are detected by the scan. Prior to the scan a health care professional will place a mask for the duration of the scan so that the gaseous radionuclide’s are constantly flowing through your lungs. The inability to move and having a mask over your face is often the most uncomfortable part of the procedure. It is vital to stay still during this portion of the scan and thus requires much concentration on the part of the patient. If you have any concerns about this portion it is recommended to talk with your health care provider prior to beginning the scan. They are experienced in methods on distracting yourself from the situation at hand and are likely to be able to provide multiple suggestions for getting you comfortably through the test.



Results are separated into four categories: normal, low probability, intermediate probability, and high probability. The results indicate the likelihood of having a perfusion (circulation) deficit with an indicated ventilation deficit. Decreased circulation may indicate issues with blood flow into or out of the lungs, which may be indicative of a pulmonary embolus (a blockage of an artery or vein of the lung that has resulted from a substance that travelled from another part of the body). Decreased ventilation may indicate inability to breathe properly, airway obstruction, or even pneumonia.


Normal results indicate that there is no deficit in perfusion and thus indicates no diagnosis for impaired ventilation or perfusion.


A low probability outcome indicates that there is a perfusion and ventilation deficit. While results might not be expected for the average individual, given that there was a deficit in both ventilation/perfusion it indicates that the individual has a ratio that differs from the greater population. This would result in no diagnosis of lung disease.


Intermediate probability indicates that there is a perfusion deficit related to parenchymal abnormality indicated on chest x-ray. Parenchyma refers to the functional components of an organ. In the case of a chest x-ray examining the lungs it refers to the alveolar tissue (respiratory bronchioles, alveolar ducts, and terminal bronchioles), the sites in which lung exchange occurs.  While this category is not good, it cannot be diagnostic and thus will require further testing, as is the same with a low probability result.


Finally, high probability is the category of most concern. It indicates that there are multiple sites in which perfusion is noted as deficient, however, these deficiencies occur with normal ventilation. A typical diagnosis of this would be pulmonary thromboembolism (indicating a high likelihood of a blood clot from the lower extremities being dislodged and causing difficulty in perfusion of the lungs).

Radioactive Material Risk


There is always some concern for individuals undergoing testing involving radioactive material. However, in the case of a VQ scan the amount of radioactive material exposure is so small that it is not significant medically. V/Q scans are even used in pregnant women by decreasing the dose of radioactive substance. Luckily, these isotopes have a short life span and are generally completed removed from the body in a few days. In women breastfeeding, it is recommended to refrain from breastfeeding for at least 24 hours after administration of the medical isotopes. Another risk factor is the development of an allergy to the isotope. This is extremely rare, however, something to discuss with your health care professional to ensure they are prepared for the consequences were such an event to occur.

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