Subtracting this result from the water fraction leaves the percentage of the ROI which is lung parenchyma. We have used the scanning protocol and analysis described above to characterize and visualize pulmonary blood flow distribution under various conditions, including alterations in body posture, lung volume, and with the imposition of artificially created pulmonary emboli. Transverse images are shown looking along the feet to head axis with the spine down. The sagittal image sequence is shown with the spine to the left in each cross section, and moving from right to left in the subject. The coronal image sequence represents moving from dorsal to ventral regions of the lung, with the right side of the animal shown on the viewer's left in each coronal slice.
Higher perfusion is seen in the gravity dependent regions of the supine lung.
However, when the animal is flipped to the prone posture this gradient does not reverse, but disappears, demonstrating important non-gravitational determinants of perfusion. In a separate experiment, depicted in figure 4, we simulated a pulmonary embolus by inflating a balloon catheter in the pulmonary vasculature. The balloon is also shown in cross section in the lower middle panel as identified via theplane's intersection with the oblique section in the lower left panel. Parenchymal time-intensity curves of the sampled regions are shown in the figure. The color coded image of regional blood flow clearly shows an abnormal loss of flow, allowing for easy embolus localization by visual inspection of the color coded images.