Ventilation/perfusion scan

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A ventilation/perfusion scan, also called a V/Q scan, is a medical test to measure the circulation of air and blood within a patient's lungs. The ventilation part of the test evaluates the ability of air to reach all parts of the lungs, while the perfusion part measures how well the blood circulates within the lungs. This test is most commonly done in order to check for the presence of a blood clot or abnormal blood flow inside the lungs (pulmonary embolism), although computed tomography angiography is now more commonly used for this purpose. A V/Q scan may also be performed in the case of serious lung disorders such as COPD or pneumonia.

[edit] Procedure

The ventilation and perfusion segments of a V/Q scan may be performed separately or together.

In the ventilation phase of the test, a gaseous radioisotope tracer containing krypton or technetium is inhaled by the patient through a mask that covers the nose and mouth. The perfusion phase of the test involves the intravenous injection of radioactive albumin. The patient lies beneath a scanner which allows the movement of the radioactive agents to be visualised.

[edit] Significance of results

Decreased uptake of the inhaled radioisotope may indicate the impaired ability to breathe, airway obstruction, or possible pneumonia.

Decreased circulation of the injected albumin indicates a problem with blood flow into or within the lungs. A localised area of decreased uptake suggests a pulmonary embolus or blood clot in the lungs. This is especially true if the ventilation part of the V/Q scan is normal.

[edit] Risks

Although this test uses radioactive materials, the tracers involved have short half-lifes which limit the total amount of radiation exposure. This test should be administered with caution to women who are pregnant or breastfeeding.