Figure 2. Cartoon depicting diffusion of water molecules in two alternative environments. (a) In a region of high cellularity the translational motion of individual water molecules is considerably impeded. (b) In an area with substantial cell loss such as occurs with necrosis and/or apoptosis the translational motion of water molecules is relatively unimpeded. The degree of restriction of molecular translational motion is manifest as contrast differences on a diffusion weighted image and can be quantified. Cartoon courtesy of Dr P Murphy, Pfizer, Inc.