Lung Disease & Respiratory Health Center
Lung Scan
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). See a picture of a
lung scan 
.
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 indicate 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.
How To Prepare
Before your lung scan, tell your doctor if:
- You are or might be pregnant.
- You are breast-feeding. Use formula (discard your breast milk) for 1 to 2 days after the scan until the radioactive tracer has been eliminated from your body.
A chest X-ray is usually done the same day either before or after the lung scan.
You may be asked to sign a consent form
before the test. Talk to your doctor about any concerns you have regarding the
need for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form
(What is a PDF document?).
WebMD Medical Reference from Healthwise
