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FIG 8. Schematic representations of the diffusion signal intensity in vasogenic edema and pseudonormalization in cortex affected by PRES. By definition, the slope of the signal intensity is plotted on the ADC map, and the magnitude of the signal intensity at b = 1,000 s/mm2 is plotted on the diffusion-weighted image.
A, Vasogenic edema. Because water is highly mobile in areas of vasogenic edema, the slope of the signal intensity is steeper and the ADC values are higher, as shown in Figure 1G–I. At b = 1000 s/mm2, the magnitude of the diffusion signal intensity is either normal or below normal, as shown in Figure 1D–F.
B, Pseudonormalization. The net diffusion signal intensity results from averaging of a cytotoxic component, which has restricted water motion and therefore has a shallow slope, and a vasogenic component, with a steep slope. The net diffusion signal intensity line is parallel to the normal case but higher in magnitude. Because the slopes are parallel, ADC values are isointense or normal in the areas of pseudonormalization, as shown in Figure 6D. Because the magnitude is higher at b = 1000 s/mm2, the DWI signal intensity is high, as shown in Figure 6C.
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