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 your vein. You are placed on a movable table that is under the arm of a scanner. The machine scans your lungs as blood flows through them to find the location of the radioactive particles.

During the ventilation scan, you breathe in radioactive gas through a mask while you are sitting or lying on a table under the scanner arm.

How to prepare for the test

You do not need to stop eating (fast), eat a special diet, or take any medications before the test.

A chest x-ray is usually done before or after 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 part of the scan.

The mask used during the ventilation scan may make you feel nervous about being in a small space (claustrophobia). You must lie still during the scan.

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 done to detect a pulmonary embolus. It is also used to:

• Detect abnormal circulation (shunts) in the blood vessels of the lungs (pulmonary vessels)
• Test lung function in people with advanced pulmonary disease, such as COPD

Normal Values

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 evenly.

What abnormal results mean

If the lungs take up lower-than-normal amounts of radioisotope during a ventilation or perfusion scan, it may be due to:

• Airway obstruction
• A problem with blood flow (such as occlusion of the pulmonary arteries)
• Damage from chronic smoking or COPD
• Pneumonia
• Pneumonitis
• Pulmonary embolus
• Reduced breathing and ventilation ability

What the risks are

Risks are about the same as for x-rays (radiation) and needle pricks.

No radiation is released from the scanner. Instead, it detects radiation and converts it into an image.

There is a small exposure to radiation from the radioisotope. The radioisotopes used during scans are short-lived. All of the radiation leaves 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 where the needle is inserted. 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. This 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, especially in people with lung disease. Other tests may be needed 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.

Patz EF, Coleman RE. Nuclear Medicine Techniques. In: Mason RJ, Murray J, Broaddus VC, Nadel J, eds. Textbook of Respiratory Medicine. 3rd ed. Philadelphia, Pa: Saunders Elsevier; 2005: chap 21.