Ventilation-Perfusion Scanning (V/Q Scanning)

Ventilation-perfusion scanning is most often used to detect the presence of blood clots in the lung (these are sometimes referred to by the healthcare team as pulmonary emboli). Chronic blood clots in the lungs may be a cause of PH. Although the presence of blood clots does not make the diagnosis of PH certain, it can make significant differences to the decision making for future investigations and treatment of PH.

The ventilation-perfusion scan is conducted in two parts, one to measure breathing (ventilation) and the other to measure blood flow (perfusion) in all areas of the lung.

In the ventilation part, the patient inhales a radioactive gas mixture through a mask placed over the nose and mouth while sitting or lying on a table beneath the arm of the scanning device. The scanner then scans the lungs to detect the location of the radioactive particles (radioisotopes) as air flows through the lungs. The radiation dose used in this test is very low.

For the perfusion part of the test, a small intravenous line is placed in the forearm, through which an injection of a radioactive substance (radioisotope) is given. The individual then lies down on the moveable table that is positioned under the arm of the scanning device. The device then scans the lungs to detect the location of the radioactive particles as the blood flows through the lungs.

The ventilation-perfusion scanning test produces a series of scans showing the lungs from various positions and angles which helps tell the doctor about the ‘evenness’ of airflow and blood flow to the lungs, abnormalities in these can help point to the possibility of blood clots.

A specialist radiologist examines the resulting scans. In general, results are interpreted as low, medium or high probability (or likelihood) of pulmonary emboli (clots in the lung). One of the more common types of PH occurs in people who have developed recurrent blood clots in their lungs over a long period of time.