Pulmonary ventilation/perfusion scan

Pulmonary ventilation/perfusion scan
Intervention Type	Diagnostic Procedure ;
Medicine System	Western Conventional ;

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A ventilation/perfusion scan (otherwise known as V/Q scan or lung scintigraphy) is a study which shows whether an area of the lung is being ventilated with oxygen and perfused with blood. In the setting of a pulmonary embolism (PE), perfusion can be obstructed due to the formation of a clot. The ventilation/perfusion scan is less commonly used due to the more widespread availability of computed tomography (CT) technology, however it may be useful in patients who have an allergy to iodinated contrast. It may also be useful in pregnant patients in an attempt to minimize radiation exposure. The diagnostic value of the results of the V/Q scan is improved when combined with the clinical pretest probability of PE. A high probability scan coupled with a high clinical pretest probability of PE is diagnostic for PE, while a normal scan regardless of the clinical pretest probability excludes PE. For the majority of the cases of suspected PE, however, the ventilation/perfusion scan does not establish the diagnosis nor exclude PE and further tests are required.

How the Test is Performed

When a ventilation/perfusion scan is performed, it consists of two parts, a ventilation scan and a perfusion scan. The ventilation scan involves breathing a radioisotope gas through a face-mask, then being positioned at a scanning table. The lungs are scanned by the device, which picks up the distribution pattern of the inhaled radioisotope in the lungs. The perfusion scan involves injection of radioisotope solution into a vein, via an intravenous (IV) cannula. The lungs are scanned; this time the distribution of blood flow in the blood vessels of the lungs (pulmonary arteries) is detected.