Tests and studies: Lung ventilation/perfusion scan
Pulmonary ventilation/perfusion scan
Definition
A pulmonary ventilation/perfusion scan is a pair of nuclear scan tests. These tests use inhaled and injected radioactive material (radioisotopes) to measure breathing (ventilation) and circulation (perfusion) in all areas of the lungs.
Alternative Names
V/Q scan; Ventilation/perfusion scan; Lung ventilation/perfusion scan
How the Test is Performed
A pulmonary ventilation/perfusion scan is actually two tests. These tests may be performed separately or together.
During the perfusion scan, a health care provider injects radioactive albumin into the patient's vein. The patient is immediately placed on a movable table that is under the arm of a scanner. The machine scans the patient's lungs as blood flows through them to detect the location of the radioactive particles.
The ventilation scan is performed by scanning the lungs while the person inhales radioactive gas. With a mask over the nose and mouth, the patient breathes the gas while sitting or lying on the table beneath the scanner arm.
How to Prepare for the Test
You do not need to fast, eat a special diet, or take any medications before the test.
A chest x-ray is usually performed prior to or following a ventilation and perfusion scan.
You will sign a consent form and wear a hospital gown or comfortable clothing that does not have metal fasteners.
How the Test Will Feel
The table may feel hard or cold. You may feel a sharp prick while the material is injected into the vein for the perfusion portion of the scan. The mask used during the ventilation scan may give you a claustrophobic feeling. You must lie still during scanning.
The radioisotope injection usually does not cause discomfort.
Why the Test is Performed
The ventilation scan is used to see how well air reaches all parts of the lungs. The perfusion scan measures the blood supply through the lungs.
A ventilation and perfusion scan is most often performed to detect a pulmonary embolus. It is also used to evaluate lung function in people with advanced pulmonary disease, such as COPD, and to detect abnormal circulation (shunts) in the pulmonary blood vessels.
Normal Results
The health care provider should take a ventilation and perfusion scan and then evaluate it with a chest x-ray. All parts of both lungs should take up the radioisotope uniformly.
What Abnormal Results Mean
A decreased uptake of radioisotope during a perfusion scan indicates a problem with blood flow, including occlusion of the pulmonary arteries. A localized decrease in perfusion scan uptake (particularly when the ventilation scan is normal) may indicate pulmonary embolus. Larger areas of decreased perfusion scan uptake may indicate a condition such as pneumonitis.
A decreased uptake of radioisotope during a ventilation scan may indicate reduced breathing and ventilation ability or airway obstruction. A decreased ventilation uptake (plus x-ray evidence of consolidation) may indicate pneumonia. Larger areas of poor uptake may indicate damage from chronic smoking or COPD.
Risks
Risks are about the same as for x-rays (radiation) and needle pricks.
No radiation is emitted from the scanner. Instead, it detects radiation and converts it to a visible image. There is a small exposure to radiation from the radioisotope. The radioisotopes used during scans are short-lived, with almost all radiation leaving the body in a few days. However, as with any radiation exposure, caution is advised for pregnant or breast-feeding women.
There is a slight risk for infection or bleeding at the site of the needle insertion. The risk with perfusion scan is the same as with inserting an intravenous needle for any other purpose.
In rare cases, a person may develop an allergy to the radioisotope, which may include a serious anaphylactic reaction.
Considerations
A pulmonary ventilation and perfusion scan may be a lower-risk alternative to pulmonary angiography for evaluating disorders of the lung blood supply.
This test may not provide an absolute diagnosis, particularly in people with underlying lung disease. Other tests may be necessary to confirm or rule out the findings of a pulmonary ventilation and perfusion scan.
References
Piccini JP, Nilsson K. The Osler Medical Handbook. 2nd ed. Philadelphia, Pa:Saunders; 2006.
Behrman RE, Kliegman RM, Jenson HB. Nelson Textbook of Pediatrics. 17th ed. Philadelphia, Pa:Saunders, 2003.
