Pulmonary ventilation/perfusion scan

Alternative names
V/Q scan; Ventilation/perfusion scan; Lung ventilation/perfusion scan

Definition

A pulmonary ventilation/perfusion scan is a pair of nuclear scan tests that use inhaled and injected radioactive material (radioisotopes) to measure breathing (ventilation) and circulation (perfusion) in all areas of the lungs.

How the test is performed

A pulmonary ventilation/perfusion scan is actually two tests that may be performed separately or together.

The perfusion scan is performed by injecting radioactive albumin into a vein. The patient is immediately placed on a movable table that is positioned under the arm of a scanner. The 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. A mask is placed over the nose and mouth, and the patient is asked to breathe the gas while sitting or lying on the table beneath the arm of the scanner.

How to prepare for the test

No special diet, medications, or fasting are necessary before the test.

A chest X-ray is usually performed prior to or following a ventilation and perfusion scan.

The patient usually signs a consent form and is asked to wear a hospital gown or comfortable clothing without metal fasteners.

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 the test will feel

The table may feel hard and/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 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 evaluate the ability of air to reach all portions of the lungs. The perfusion scan measures the supply of blood 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 the presence of shunts (abnormal circulation) in the pulmonary blood vessels.

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.

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 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 damage from chronic smoking or COPD.

What the risks are

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.

There is a slight risk for infection or bleeding at the site of the needle insertion. 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.

Special 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.

Johns Hopkins patient information

Last revised: December 3, 2012
by Gevorg A. Poghosian, Ph.D.

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