1. A non-transitory computer readable medium programmed with steps comprising: receiving image data related to a region of interest of the subject; dividing the image data into sub-regions, wherein each sub-region is defined by having nerve fibers running in approximately a same direction; summing image intensities in the same direction of the nerve fibers for the sub-region; reducing a two-dimensional representation to a one-dimensional signal having peaks where the nerve fibers are located; and determining a nerve fiber count based on the peaks of the one-dimensional signal.