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). The results of a lung scan are
usually available in 1 day.
The radioactive tracer is
evenly distributed throughout the lungs during ventilation and
The perfusion scan is abnormal
but the ventilation scan is normal. Depending on the difference between the two
scans, a pulmonary embolism may be present.
Both the ventilation and
perfusion scans are abnormal. This can be caused by certain types of lung
disease, such as
pneumonia, COPD, or a pulmonary embolism.
Lung scan results can help your doctor determine the
likelihood that a pulmonary embolism is present. The results are generally
reported in one the following ways:
Normal. The results do not show any problem with
Low probability. The results show that the
likelihood of pulmonary embolism is low. Your doctor may feel that further
testing is needed.
Indeterminate or intermediate probability. The lung
scan results show there is a possibility of a pulmonary embolism. More tests,
such as angiogram or CT pulmonary angiogram, may be needed.
High probability. The results show that the
likelihood of a pulmonary embolism is high. No further diagnostic testing is
generally necessary. Your doctor will give you medicine to treat the pulmonary embolism.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
Pregnancy. A lung scan is not usually done
during pregnancy, because the radiation could damage the developing baby (fetus).
The inability to remain
still during the test.
The inability to breathe through the mask or
Medical conditions, such as
pulmonary edema or chronic obstructive pulmonary
disease (COPD), that involve the lungs or heart.