A lung scan is a nuclear scanning test that is most commonly used to detect a blood clot that is preventing normal blood flow to part of a lung (pulmonary embolism).
Two types of lung scans are usually done together:
Ventilation scan. During a ventilation scan, a radioactive tracer gas or mist is inhaled into the lungs. Pictures from this scan can show areas of the lungs that are not receiving enough air or that retain too much air. Areas of the lung that retain too much air show up as bright or "hot" spots on the pictures. Areas that are not receiving enough air show up as dark or "cold" spots.
Perfusion scan. During a perfusion scan, a radioactive tracer substance is injected into a vein in the arm. It travels through the bloodstream and into the lungs. Pictures from this scan can show areas of the lungs that are not receiving enough blood. The tracer is absorbed evenly in areas of the lung where the blood flow is normal. These areas show up with the tracer distributed evenly. Areas that are not receiving enough blood show up as cold spots.
If the lungs are working normally, blood flow on a perfusion scan matches air flow on a ventilation scan. A mismatch between the ventilation and perfusion scans may mean a pulmonary embolism.
Ventilation and perfusion scans can be done separately or together to diagnose certain lung diseases. If both scans are done, the test is called a V/Q scan. The ventilation scan usually is done first.
Why It Is Done
A lung scan is done to:
- Find a blood clot that is preventing normal blood flow (perfusion) to part of a lung (pulmonary embolism).
- Check the flow of blood (perfusion) or air (ventilation) through the lungs.
- See which parts of the lungs are working and which are damaged. This is often done before lung surgery to remove parts of the lung.