What Is Diffusion Tensor Imaging?
Diffusion tensor imaging (DTI) is a category of magnetic resonance imaging (MRI) that is utilized to understand the anatomical structure of the brain and the nervous system better. Diffusion is a process of transfer of molecules from a high-volume region to a low-volume region. The water molecules present in the body also tend to exhibit similar notions. Except that the direction of flow of these molecules need not be uniform. The molecules present in a tissue may diffuse in multiple directions, referred to as anisotropic diffusion.
The nerve cell is composed of two basic components - the cyton or cell body and the axon fiber. The DTI system works on the principle that water molecules move rapidly along the length of the nerve cell rather than perpendicular to it. This pathway is thought to provide less resistance to water molecules. Based on the anisotropic diffusion, it is easier to determine the nerve cell organization and the static anatomical layout of the brain that is not altered by the ongoing brain functions. This article aims to discuss the mechanism of action of the DTI technique and its extensive use in investigating peripheral nerve injuries.
What Is the Mechanism of Action of Diffusion Tensor Imaging?
The DTI technique, as previously discussed, works on the principle of diffusion of water molecules. Magnetic field gradients are delivered to bring about a directional phase shift in the water molecules. An intricate analysis of the diffusion is performed involving movement in multiple directions, with the help of a three-dimensional diffusion model referred to as the tensor. The tensor provides clear orientation of the nerve cell using two parameters -
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Fractional Anisotropy (FA): This parameter indicates the direction the diffusion is carried out. The value of FA is relatively higher when diffusion occurs along well-defined pathways such as the corpus callosum and lower in pathways that exhibit disrupted axonal structural integrity.
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Mean Diffusivity (MD): This parameter simply indicates the overall diffusive capability of the water molecules. Higher mean diffusivity indicates a higher amount of water content, implying that the resistance along the pathway of diffusion is the least.
Apart from the above two parameters, the DTI also provides the ADC (apparent diffusion coefficient of water), which is a vital parameter that measures the flow and distance a water molecule has covered during diffusion.
Where Is Diffusion Tensor Imaging Utilized?
The four aspects that widely utilize the DTI technique include:
1. Neurophysiology: Abnormal nerve disorders associated with nerve demyelination, such as multiple sclerosis, can be detected with the use of the DTI technique owing to its sensitivity to diffusion anisometry.
2. Brain Anatomy: The DTI technique enables one to attain information about the brain anatomy, which is otherwise not possible by using conventional MRI. Tracking down normal brain development as well as congenital (since birth) brain disorders becomes much simpler with the use of the DTI technique.
3. Neuropathology: Abnormal nerve disorders associated with nerve demyelination, such as multiple sclerosis can be detected with the use of the DTI technique owing to its sensitivity to diffusion anisometry.
4. Peripheral Nerve Injuries: Peripheral nerve injuries refer to damage incurred to the nerves of the upper or lower extremities. These injuries may be a result of direct trauma or non-traumatic cases. Nerve injury has a significant impact on one’s quality of life and hinders the day-to-day functionality of an individual. It may also present as temporary or permanent paralysis, irreversible muscular atrophy, or the formation of painful neuromas in many cases.
The DTI technique has shown promising results in detecting axonal or myelin-associated abnormalities in injured peripheral nerves, such as the wrist. It not only provides clarity on neuronal damage but is also non-invasive, making it a preferred option for several medical professionals globally. Apart from the injured state, the DTI tool can also be utilized to monitor the recovery phase of the nerve post-surgical intervention. It is a powerful tool to determine the success of the operated nerve or indicates the need for reoperation much earlier on compared to other conventional techniques. This allows the surgeon and the patient a second chance at saving the function of the concerned limb.
What Are the Limitations of the DTI Technique?
Although the DTI technique has proven its efficacy in determining the orientation of nerve fibers and early detection of peripheral nerve injuries, it also comes with its own set of limitations. The data obtained from the three-dimensional tensor model only pertains to a singular nerve fiber in a volumetric pixel. Thus, when the data involves multiple cross-linked fibers, it can turn out to be very confusing for the clinician. This can lead to a false or misdiagnosis of the situation at hand. Another drawback of the DTI technique is its inability to distinguish the axonal directionalities. This is because the DTI technique works on the principle of diffusion of water molecules.
Conclusion
The diffusion tensor imaging technique is extremely effective and has proven its vitality in the field of neuroscience on multiple occasions. The absolute non-invasive approach to obtain the desired result is one of the unique selling points of this imaging technique. Its utilization is gradually gaining popularity among medical professionals. One can expect to attain immense benefits from the growth and future advances in the field of diffusion imaging and analysis.
