**1. Introduction**

Magnetic resonance imaging (MRI) is the best imaging technique for the evaluation of the neurologic system due to the ability to diagnose central nervous system (CNS) diseases in both humans and animals, especially diseases affecting cerebral white matter (CWM), providing in vivo markers for disease severity or response to therapy and shedding light on progression and recovery processes. The broad spectrum of magnetic resonance contrast mechanisms makes MRI one of the most important and widely used imaging tool for diagnosis in the CNS. However, one of the disadvantages of conventional MRI is that it does not allow the visualization of the cerebral White matter constituent fiber tracts and their connectivity in the brain in vivo [1].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Previously, the anatomy of the cerebral white matter tracts could only be studied by postmortem dissection or through invasive methods, and said methods could only reveal a few tracts in vivo (neurosurgery) and no tracts could be observed in vivo via conventional imaging studies [1–6].

Diffusion tensor tractography (DTT) is a useful noninvasive imaging technique that can identify and represent fiber tracts of the cerebral white matter and their connections in the brain in vivo [1]; also, it can give us information that cannot be achieved by conventional anatomical MRI or histology. In addition to displaying specific cerebral white matter fiber tracts, this technique can also improve the quantification of diffusion characteristics within these fibers [1, 7–9].

DTT provides a three-dimensional representation of diffusion tensor imaging (DTI), and data can be displayed on a colored map obtained from information on the directionality of the movement of water molecules along the main fiber tracts of cerebral white matter [1].

#### **1.1. Diffusion tensor imaging**

DTI uses the property of the water diffusion anisotropy in axonal fibers allowing the analysis and tracking of said fibers in the brain [1, 4, 10, 11].

DTI permits the exploration of microstructural tissue features through the observation of water molecular diffusion, thus furnishing information about the anatomy, microstructural features, and damage of the main brain bundles, useful in several pathological animal models. DTIbased tractography permits the virtual reconstruction of the white matter fiber bundles invivo, following the principal diffusion direction [12, 13].

This technique is commonly used in human medicine to study the anatomy and maturation of the normal, aging brain, but it also can be used to help diagnose neurological conditions, including brain ischemia, multiple sclerosis, diffuse axonal injury, epilepsy, metabolic disorders, certain mental illnesses, and brain tumors, as well as establish a prognosis for patients with these conditions [14, 15]. Though DTI has been extensively used to investigate brains of the dogs ex vivo [11]; there is only one report of the in vivo use of DTT to study cerebral white matter fiber tracts in dogs [1].

The ability to trace cerebral white matter fibers in the dog generates a number of opportunities for potential clinical applications, and has both diagnostic and prognostic [1].
