If your lungs seem to be giving you trouble and your doctor suspects a blood clot, you may have to brace for a pulmonary ventilation/perfusion (VQ) scan. Also called a radionuclide pulmonary scan, this nuclear medicine test examines the flow of air and blood as well as the blood supply in your lungs.
While it is mainly used to confirm the presence of a blood clot in your lungs (pulmonary embolus), the VQ scan also screens for abnormal circulation or shunts in lung vessels, lung inflammation or infections, chronic lung diseases, airway obstruction, pulmonary artery narrowing and any fluid buildup around or a collapsed area in the lungs.
The test itself is divided into two parts: the perfusion scan and the ventilation scan. During the perfusion scan, a nuclear medicine technologist injects a radionuclide dye into a vein in your arm or at the back of your hand. Then a special scanner locates the dye that circulates through your bloodstream and into your lungs, capturing images as you lie still on a table. Dye tends to accumulate where there is abnormal blood flow, which in turn could point to an artery blockage.
During the ventilation scan, you will be asked to breathe in a small dose of radioactive gas through a mask over your nose and mouth or a tube-like mouthpiece. While you do this, a special scanner takes pictures of your lungs. A complete VQ scan takes 30 to 60 minutes. Do note that you may need to get a chest X-ray a day or two before the test.