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.
How To Prepare
Before your lung scan, tell your
You are or might be pregnant.
are breast-feeding. The radioactive tracer used in this test can get into your breast milk. Do not breast-feed your baby for 1 or 2 days after this test. During this time, you can give your baby breast milk you stored before the test, or you can give formula. Discard the breast milk you pump for the 1 or 2 days after the test.
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?).
need to remove any jewelry that might interfere with the scan. You may need to
take off all or most of your clothes, depending on which area is being examined
(you may be allowed to keep on your underwear if it does not interfere with the
test). You will be given a cloth or paper covering to use during the
During the scan, you will either lie on your back with the
scanning camera positioned over or under your chest, or you will sit with the camera
positioned next to your chest. The camera does not produce any radiation, so
you are not exposed to any more radiation while the scan is being
For the ventilation scan, a mask
will be placed over your mouth and nose. Or you may have a nose clip on your
nose and a tube in your mouth that you use for breathing. You will inhale the
tracer gas or mist through the mask or tube by taking a deep breath and then
holding it. The camera will scan for radiation released by the tracer and
produce pictures as the tracer moves through your lungs. You may be asked to
breathe the gas in and out through your mouth for several minutes. You may then
be asked to hold your breath for short periods (about 10 seconds) and to change
positions so your lungs can be viewed from other angles. The camera may move to
take pictures from different angles. You need to remain very still during the
scans to avoid blurring the pictures.
Afterward, the radioactive
gas or mist will clear from your lungs as you breathe.
ventilation scan takes about 15 to 30 minutes.
For the perfusion scan, the
technologist cleans the site on your arm where the radioactive tracer will be
injected. A small amount of the radioactive tracer is then injected.
After the radioactive tracer is injected, the camera will scan for
radiation released by the tracer and produce pictures as the tracer moves
through your lungs. The
camera may be repositioned around your chest to get different views. You need to
remain very still during the scans to avoid blurring the pictures.
The perfusion scan takes about 5 to 10 minutes.
How It Feels
You may find that breathing through the
mask during the ventilation scan is uncomfortable, especially if you feel very
short of breath. But you will be given plenty of oxygen through the
You may feel nothing at all from the needle puncture when the
tracer is injected, or you may feel a brief sting or pinch as the needle goes
through the skin. Otherwise, a lung scan is usually painless. You may find it
hard to remain still during the scan. Ask for a pillow or blanket to make
yourself as comfortable as possible before the scan begins.
Allergic reactions to the radioactive
tracer are very rare. Most of the tracer will be eliminated from your body (through
your urine or stool) within a day, so be sure to promptly flush the toilet and
thoroughly wash your hands with soap and water. The amount of radiation is so
small that it is not a risk for people to come in contact with you following
Occasionally, some soreness or swelling may develop at
the injection site. These symptoms can usually be relieved by applying moist,
warm compresses to your arm.
There is always a slight risk of
damage to cells or tissue from being exposed to any radiation, including the
low level of radiation released by the radioactive tracer used for this test.
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.
What To Think About
Checking for a blood clot in your leg (deep venous thrombosis) can help your doctor decide if you are at high risk
for having a pulmonary embolism. After a medical history and physical
examination are done to establish your risk level (pretest probability) for
deep leg vein thrombosis, an
ultrasound is usually done. Your pretest probability
and initial ultrasound results will help your doctor determine the most
appropriate follow-up tests to see whether you have a pulmonary embolism.
For more information, see the topic
scan results are sometimes investigated further using pulmonary angiography or
computed tomography scanning technique called CT
pulmonary angiography, or CTPA. Pulmonary angiography is an
X-ray test that uses
contrast material injected into the bloodstream to
evaluate the blood flow through the arteries leading to the lungs (pulmonary
arteries). Many medical centers or doctors now use CTPA as their first choice
for evaluating a pulmonary embolus rather than a lung scan because CT has
become more available. For more information, see the
Angiogram of the Lung and
CT Scan of the Body.
Lung scan results for
people who have a long-term (chronic) lung disease, such as
emphysema or chronic obstructive pulmonary disease
(COPD), may be hard to interpret. For this reason, other tests, such as CT
angiogram, may be done.
The results of a combined (ventilation and perfusion) lung scan,
often called a V/Q scan, may be hard to interpret. These results should be
interpreted along with a person's symptoms and the results of other tests, such
as a physical exam, lab tests, and a chest X-ray.
Other Works Consulted
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
How this information was developed to help you make better health decisions.