"Lung VQ scan", also called "Lung Ventilation-Perfusion scintigraphy" uses ventilation & perfusion scintigraphies to evaluate pulmonary function. The Ventilation study records the broncho-pulmonary distribution of an inhaled radioactive aerosol within the lungs, whereas Pulmonary perfusion scintigraphy records arterial blood flow within the lungs. This test is mainly performed to look for pulmonary embolism, apart from other indications such as quantifying differential pulmonary function before pulmonary surgery in lung cancer and evaluation of lung transplant etc. Pulmonary embolism is a medical emergency where a blood clot gets caught in one of the lungs' arteries and blocks the normal flow of blood. Depending on the size and number of the clots, this can be a serious problem.