Figure 2. Example of image processing. A transverse section of the thorax in an anesthetized subject breathing spontaneously (#4), with the surrounding rib cage removed through processing (top). The heart and right hemidiaphragm are clearly visible. The section after the heart and abdominal contents have been removed, leaving an image of predominantly the lung (middle). The outline of the lung in gray, with areas of atelectasis defined by application of a density threshold (see text for details) shown in white (bottom).