Blood clots. A blood clot that floats into the lung interferes with blood flow to that segment. A lung perfusion scan with will show a hole (no blood flow) behind the clot.
Several reasons. Perfusion lung scan in most adults is used to localize perfusion defects possible caused by pulmonary embolism or to differentiate consolidation in lungs in association with ventilation scan in differentiating air space disease (pneumonia, atelectasis) from pulmonary embolism. Sometimes congenital deficiency in lung perfusion related to congenital heart disease or pulmonary hypoplasia is documented.
A radionuclide. Pulmonary perfusion scan is usually performed in conjunction with a radionuclide ventilation scan, in order to find areas of the lung which are ventilated but not perfused, which would mean a pulmonary embolism, or lung clot, in a patient with the appropriate history. Other uses include: quantitating pulmonary blood flow in surgical planning, or determining the size of a cardiac shunt.
Pulmonary embolism. The v/q scan is a nuclear medicine study that is primarily used to evaluate for possible pulmonary embolism or to evaluate resolution of previously known pulmonary embolism. It involves imaging perfusion of the lungs by the blood and imaging ventilation of the lungs by air. A tiny amount of radiation is put into the blood to allow this, and a tiny amount into the air.
Lung V-Q scan. Ventilation scanning involves the patient breathing in a radiotracer while perfusion scanning involves injecting the radiotracer through an iv. The procedure is done usually to evaluate the presence of absence of a pulmonary embolism (usually a blood clot) and involves comparing the radiotracer's presence in the alveoli vs. Its presence in the lung circulation.
Blood vs air. The perfusion scan images blood perfusion of the lungs. The ventilation scan is used to image ventilation by air of the lungs. Generally, both are performed together to see how well lung perfusion (blood) matches lung ventilation (air).