A lung perfusion scan is a nuclear medicine test that produces a picture of blood flow to the lungs. A lung ventilation scan measures the ability of the lungs to take in air and uses radiopharmaceuticals to produce a picture of how air is distributed in the lungs.
Lung perfusion scans and lung ventilation scans are usually performed in the same session. They are done to detect pulmonary embolisms, determine how much blood is flowing to lungs, determine which areas of the lungs are capable of ventilation, and assess how well the lungs are functioning after surgery. These tests are called by different names, including perfusion lung scan, aerosol lung scan, radionucleotide ventilation lung scan, ventilation lung scan, xenon lung scan, ventilation/perfusion scanning (VPS), pulmonary scintiphotography, or, most commonly, V/Q scan.
The amount of radioactivity a person is exposed to during these tests is very low and is not harmful. However, if the patient has had other recent radionuclear tests, it may be necessary to wait until other radiopharmaceuticals have been cleared from the body so that they do not interfere with these tests.
In a lung perfusion scan, a small amount of the protein labeled with a radioisotope is injected into the patient's hand or arm vein. The patient is positioned under a special camera that can detect radioactive material, and a series of photographs are made of the chest. When these images are projected onto a screen (oscilloscope), they show how the radioactive protein has been distributed by the blood vessels running through the lungs.
In a lung ventilation scan, a mask is placed over the nose and mouth, and the patient is asked to inhale and exhale a combination of air and radioactive gas. Pictures are then taken that show the distribution of the gas in the lungs. Each test takes 15-30 minutes.
There is little preparation needed for these tests. The patient may eat and drink normally before the procedure. Tests to check for pulmonary embolism are often performed on an emergency basis.
No special aftercare is needed. The patient may resume normal activities immediately.
There are practically no risks associated with these tests.
Normal results in both tests show an even distribution of radioactive material in all parts of the lungs.
In the lung perfusion scan, an absence of radioactive marker material suggests decreased blood flow to that part of the lung, and possibly a pulmonary embolism. However, pneumonia, emphysema, or lung tumors can create readings on the lung perfusion scan that falsely suggest a pulmonary embolism is present.
In the lung ventilation scan, absence of marker material when the lung perfusion scan for the area is normal suggests lung disease.
Certain combinations of abnormalities in lung perfusion and ventilation scans suggest pulmonary embolism.