Definition This study demonstrates the distribution of the air a person breathes into the lung, known as ventilation. This test, along with a complementary test known as a pulmonary perfusion scan, is vital to diagnosing a blood clot in the lungs, or pulmonary embolism.
Who is a candidate for the test? A pulmonary ventilation scan is performed on a person who is suspected of having blood clots in the lungs or other breathing difficulties. This test is normally done together with a pulmonary perfusion scan.
How is the test performed? Before the pulmonary ventilation scan, a chest x-ray is taken.
For the pulmonary ventilation scan, the person is usually asked to sit upright. If the person is unable to sit, he or she can lie flat on his or her back on a table. Before the scan begins, the technologist will rehearse the very special breathing manoeuvres that the person will need to do to ensure a satisfactory scan. The person is asked to breathe in a radioactive gas, such as xenon-133 or krypton-81. The gas gives off gamma rays, which can be detected by a "gamma camera" that is positioned over the chest. A computer then generates pictures that can be interpreted by a doctor.
The person will breathe the gas in and out through either a tight fitting mask or a mouthpiece with a nose clamp. The test usually takes about 40 minutes.
What is involved in preparation for the test? The person undergoing the scan will undress from the waist up and will put on an examination gown. All jewellery and metal objects will be removed because these may interfere with the examination.
The person will also be given complete breathing instructions and is usually asked to practice the breathing manoeuvres before the examination begins. The success of the examination depends on the person's ability to perform these breathing manoeuvres.
What do the test results mean? An abnormal scan can result from many different disease processes in the lung, such as pneumonia or emphysema. However, the test is usually ordered to rule out a blood clot in the lungs, or pulmonary embolism. Although the test is not 100% accurate, a doctor can usually make a diagnosis based on the results of the pulmonary ventilation scan and the pulmonary perfusion scan.
Author: James Compton, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/06/2005 Contributors Potential conflict of interest information for reviewers available on request
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