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
Two types of lung scans are usually done
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
- 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.