A method for detecting the presence of various transmissible spongiform encephalopathy (TSE) in mammals is provided. Steps include taking a magnetic resonance imaging (MRI) image of the brain of the mammal, selecting a section within the image, determining a measurement of a first brain structure in the section, and determining a measurement of a second brain structure in the section. The ratio of the measurements is calculated and used to determine the probability that the mammal has a TSE. Areas and/or volumes of the first and second brain structures may be used. In one embodiment, the image section is sagittal or axial. An embodiment uses the lateral ventricle or frontal lobe as the first brain structure, and the cerebrum as the second brain structure. The method of determining the areas and volumes of the brain structures is provided. MRIs that can be used along with the MRI parameters are provided.