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Respiratory system scintigraphy 1. Lung anatomy and physiology 2. Lung Ventilation Imaging Radioactivity and its dynamic change in lung can be imaged with radioactive detection equipment during the radioactive gas is inhaled and exhaled. Parameters of lung ventilation function can be calculated. 2.1. Radiopharmaceuticals 133Xe 81mKr Radio-aerosols 3. Lung Perfusion Imaging Particles with diameter greater than 10μm is injected intravenously and these particles could not pass lung capillary bed because of the diameter of capillary is less than 8μm. So these particles are blocked in capillary bed. The distribution of these particles in lung is proportional to the blood flow in pulmonary artery. 3.1. Radiopharmaceuticals 99mTc-MAA (Macroaggregated Albumin) 3.2. Clinical Indications Assessing the probability of acute or chronic pulmonary thromboembolic disease; establishing the presence of chronic, unresolved pulmonary emboli; Quantifying differential pulmonary function; Evaluating lung transplants; Evaluating the effects of congenital heart/lung disease; Confirming the presence of bronchopleural fistulae; Evaluating the effects of chronic pulmonary parenchymal disorders such as cystic fibrosis. 3.3. 2.5 Clinical Usage 3.3.1. Diagnosis of Pulmonary Embolism Ventilation and perfusion to broncho-pulmonary segments are matched in a healthy individual. In pulmonary embolic disease, segmental reduction in perfusion occurs with maintenance of normal ventilation. This leads to the mismatch of perfusion and ventilation in the broncho-pulmonary segment. Pulmonary embolism typically causes multiple, wedgeshaped, bilateral perfusion defects. Perfusion lung scintigraphy has an extremely high sensitivity in the diagnosis of pulmonary embolism , since a normal lung scan virtually excludes the diagnosis. Since the scan "sees" a absent perfusion but not the embolus, it is not completely specific. Criteria for the size and number of unmatched perfusion defects create a "probability" factor in four classes. Normal Perfusion - Less than 1% chance. Low Probability - Matched Defects less than 10-30% chance (studies vary). High Probability - Unmatched Defects, probability 90%. Intermediate Probability - Outside other groups, probability 10-90%. 3.3.2. Evaluation of the Severity of Pulmonary Embolism Perfusion lung scintigraphy is the best technique for evaluating the severity of embolism. This can be achieved by simply counting the number of unperfused lung segments on all six views obtained with the gamma camera, thus obtaining a reliable index of severity of the disease. 3.3.3. Evaluation of Chronic Obstructive Pulmonary Disease Chronic bronchitis causes a patchy, non-segmental decrease of perfusion in the lung parenchyma. Defects may be located everywhere in the lungs, although they appear more frequently in the lower regions, especially in exacerbations. A quite recent application of perfusion lung scintigraphy is in evaluating the inhomogeneity of pulmonary emphysema when considering surgical intervention to reduce lung volume. Aerosols are more suitable for evaluating ventilation in COPD. (孙晓光)