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.
How To Prepare
Before your lung scan, tell your doctor if:
- You are or might be pregnant.
- You 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.
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?).
How It Is Done
You will 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 test.
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 done.
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.
The 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 mask.
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 the test.
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 perfusion.
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 your lungs.
- 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 tube.
- 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. To learn more, see the topic Doppler Ultrasound.
- Uncertain perfusion scan results are sometimes investigated further using pulmonary angiography or a newer 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.
- 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.
|Anne C. Poinier, MD - Internal Medicine|
|Myo Min Han, MD - Nuclear Medicine|
|Last Revised||October 1, 2012|
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