When your physician requests a lung scan, two procedures and scans will be performed – a ventilation and a perfusion scan. During a ventilation scan, a radioactive gas is inhaled, while a radioactive tracer is injected into the bloodstream in the case of the perfusion scan. A gamma camera is used for imaging to keep track of the radioactive material in the breathing passages and blood vessels. The camera records these images so that your doctor can see which parts of the lungs are receiving air and blood sufficiently or not.
A ventilation–perfusion (VQ) scan is a nuclear medicine scan that uses a radioactive compound (radiopharmaceutical) to examine airflow (ventilation) and blood flow (perfusion) in the lungs. Lung scans are mainly used for diagnosing pulmonary emboli (blood clots in the lungs).
Although a spiral CT is normally the first choice in investigating pulmonary emboli, there are a few exceptions:
When having a ventilation lung scan, you will be asked to be seated and to breathe in and out through a mouthpiece connected to a nebulizing system. You will then be asked to follow certain instructions as you inhale and exhale, breathing in a combination of air and radioactive gas. After about 10 minutes you will be taken to the gamma camera room where images will be recorded of the pattern of ventilation. After the ventilation scan a perfusion scan follows immediately where you will be injected with a small amount of radioactive material in a vein before a second set of images will be obtained reflecting blood flow or perfusion to the lungs. The whole procedure takes about an hour.