A lung perfusion scan is a medical imaging scan conducted to assess the quality of bloodflow to the lungs. It is usually performed in concert with a lung ventilation scan, looking at how much air enters the lungs, and the two tests may be known together as a V/Q scan. The purpose of such scans is to look for areas where blood or air are not circulating within the lungs, indicating a pulmonary embolism or other respiratory problem is present. The tests are done on an outpatient basis in an imaging clinic or hospital.
For a lung perfusion scan, the patient is injected with a small amount of a short-lived radioactive tracer material. The patient lies flat and still on a table and an imaging machine takes a series of pictures to follow the tracer as it flows through the blood in the lungs. Cold spots on the scan indicate areas where the supply of blood is inadequate, suggestive of a problem with the lungs. Once the scan is done, the patient can usually go home immediately, and the tracer will naturally be eliminated from the body over the course of several days.
In a V/Q test, a ventilation scan is done first, with the patient inhaling a mixture of oxygen and radioactive gas. Once the patient's lungs are cleared, the lung perfusion scan can be performed. The results of both scans are compared and should be identical, showing healthy blood perfusion to the lungs and thorough oxygen circulation. Cold spots on the scans are a cause for concern. In addition, an X-ray may be taken of the lungs to use as a basis for comparison and study, depending on why the patient is having the scans done in the first place.
Risks associated with a lung perfusion scan are low. The radioactive isotope is provided in a very small dosage and should not expose the patient to the risk of disease or other complications. Infections at the injection site are a potential risk, but a very small one as long as hospital personnel use safe injection technique. In some cases, patients develop allergies to the tracer dyes used, in which case they can be at risk of an allergic reaction in future scans. People with a history of bad reactions during medical imaging studies with radioactive substances, and people with egg allergies, should alert their care providers before a lung perfusion scan.