Images of the abdomen showing the distribution of the normalized index (NI). The images have been constructed from the 99mTc and 111In activity according to the NI equation in the Methods section. (Upper panels) Amount and distribution of edema in two animals after endotoxin infusion and 2.5 hours of mechanical ventilation with a PEEP of 5 cm H2O. (Lower panels) Edema in these animals after another 2.5 hours of either spontaneous breathing with a CPAP of 5 cm H2O or mechanical ventilation (MV) with a PEEP of 5 cm H2O. The red color indicates extravascular fluid. Note the larger increase in fluid in the animal on MV than on CPAP. The liver is shown in yellow in the upper part of the image.