This scan is used to check the blood supply to the lung tissue. Any factor that reduces the blood supply to the lung tissue will be seen as a perfusion defect in the scan. One of the most common uses is to confirm or rule out pulmonary embolism in patients who develop acute respiratory symptoms following surgery or prolonged immobilization. Lung perfusion scans are usually performed in these cases along with lung ventilation scans, but in most centers, due to the lack of a suitable radiopharmaceutical for lung ventilation scans, perfusion scans alone and their comparison with plain lung radiographs have acceptable diagnostic accuracy. . Another application is to quantify the amount of perfusion in each of the lobes or segments of the lung, which is of considerable importance before surgery to remove part of the lung. This scan does not require any special preparation and the imaging is done immediately after the injection.