Alternate Names: Scan - lung ventilation/perfusion; V/Q scan
How Performed: This is actually 2 tests that may be performed separately or together.
The perfusion scan is performed by injecting radioactive albumin (99m Tc macroaggregated albumin) into a vein. You are immediately placed on a movable table that is positioned under the arm of the scanner. Your lungs are scanned to detect the location of the radioactive particles as blood flows through the lungs.
The ventilation scan is performed by scanning the lungs while having the person inhale radioactive gas (air mixed with 133 xenon or 99m Tc DTPA aerosol). A mask is placed over the nose and mouth and you are asked to breathe the gas while sitting or lying on the table beneath the arm of the scanner.
How To Prepare: No diets, medications, or fasting are necessary before the test.
A chest X-ray may be performed prior to or following a ventilation and perfusion scan.
You must sign a consent form. You are asked to wear a hospital gown or comfortable clothing without metal fasteners. Remove jewelry and dentures before the scan.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:
How It Feels: The table may be hard or cold. There may be a sharp prick during injection of material into the vein for the perfusion portion of the scan. The mask used during the ventilation scan may give some persons a claustrophobic feeling. You must lie still during scanning.
You will not feel the radioisotope.
Risks: Risks are essentially the same as for X-rays (radiation) and needle pricks.
There is a small exposure to radiation from the radioisotope. The radioisotopes used during scans are short lived, with almost all radiation gone in a few days. However, as with any radiation exposure, caution is advised during pregnancy or if a woman is breastfeeding. No radiation is emitted from the scanner; it detects radiation and converts it to a visible image.
Any time a needle is placed in the body there is a slight risk for infection or bleeding. The risk with perfusion scan is no different than for placement of an intravenous needle for any other purpose.
It is extremely rare, but a person may develop an allergy to the radioisotope, which may include a serious anaphylactic reaction.
Why Performed: The ventilation scan is used to evaluate the ability to aerate all portions of the lungs. The perfusion scan measures the supply of blood through the lungs.
A ventilation and perfusion scan is performed to detect pulmonary embolus. It is also used to evaluate lung function in people with pulmonary disease such as COPD, to locate and evaluate growths before and after treatment, and to detect conditions such as lung infections and lung collapse. It may be used to evaluate the extent of burn inhalation injury.
Normal Values: A ventilation and perfusion scan should be correlated with a chest X-ray. There should be uniform uptake of radioisotope in all portions of the lungs with equal distribution in both lungs.
Abnormal Results: A decreased uptake of radioisotope during a perfusion scan indicates a problem with blood flow, including occlusion of the pulmonary arteries. A localized decreased in perfusion scan uptake (particularly when 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 chronic smoking or COPD.
Cost:
Special Considerations: A pulmonary ventilation and perfusion scan may be a lower-risk alternative to pulmonary angiography for some people to evaluate 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.
