M. Thuen, A. Kristoffersen, T. R. Vandberg, T. E. Singstad, O. Haraldseth, C. Brekken Department of Circulation and Medical Imaging, Norwegian University for Science and Technology, Trondheim, Norway, Department of Medical Imaging, St. Olavs Hospital HF, Trondheim, Norway Introduction: Diffusion tensor imaging (DTI) is an increasingly important non-invasive clinical imaging technique. Since fast echo planar imaging technique (EPI) is sensitive to geometrical distortions because of susceptibility effects, most animal studies have so far have used a standard spin echo DTI sequence. With a spin-echo DTI sequence, acquisition times can be long, up to several hours, and most experiments have therefore been carried out ex vivo. Here, we have developed a protocol for in vivo imaging of the optic nerve in rats using fast echo planar diffusion tensor imaging (EPIDTI). The results are confirmed with manganese-enhanced MRI (MEMRI), where the calcium analogue manganese, which is taken up and transported along axons, give contrast in MRI because of its paramagnetic properties (1).