Current contribution of diffusion tensor imaging in the evaluation of diffuse axonal injury

Abstract

Traumatic brain injury (TBI) is the number one cause of death and morbidity among young adults. Moreover, survivors are frequently left with functional disabilities during the most productive years of their lives. One main aspect of TBI pathology is diffuse axonal injury, which is increasingly recognized due to its presence in 40% to 50% of all cases that require hospital admission. Diffuse axonal injury is defined as widespread axonal damage and is characterized by complete axotomy and secondary reactions due to overall axonopathy. These changes can be seen in neuroimaging studies as hemorrhagic focal areas and diffuse edema. However, the diffuse axonal injury findings are frequently under-recognized in conventional neuroimaging studies. In such scenarios, diffuse tensor imaging (DTI) plays an important role because it provides further information on white matter integrity that is not obtained with standard magnetic resonance imaging sequences. Extensive reviews concerning the physics of DTI and its use in the context of TBI patients have been published, but these issues are still hazy for many allied-health professionals. Herein, we aim to review the current contribution of diverse state-of-the-art DTI analytical methods to the understanding of diffuse axonal injury pathophysiology and prognosis, to serve as a quick reference for those interested in planning new studies and who are involved in the care of TBI victims. For this purpose, a comprehensive search in Pubmed was performed using the following keywords: "traumatic brain injury", "diffuse axonal injury", and "diffusion tensor imaging".

Diagnostic Problems in Diffuse Axonal Injury

“…DTI provides improved evaluation of the integrity of the white matter of the brain by virtue of its ability to image water diffusion characteristics, which are estimated through various DTI parameters, including fractional anisotropy, mean diffusivity, and tract volume [31,32]. In addition, DTI has been shown to have higher sensitivity for the detection of DAI lesions than that of conventional brain MRI [9,[33][34][35][36]. Furthermore, diffusion tensor tractography, which is a derivative of DTI, enables three-dimensional (3-D) visualization and estimation of specific neural tracts [9,[36][37][38].…”

“…In addition, DTI has been shown to have higher sensitivity for the detection of DAI lesions than that of conventional brain MRI [9,[33][34][35][36]. Furthermore, diffusion tensor tractography, which is a derivative of DTI, enables three-dimensional (3-D) visualization and estimation of specific neural tracts [9,[36][37][38]. The advantage of diffusion tensor tractography over DTI is that the characteristics of an entire neural tract can be determined by examining the tract's parameters and analyzing the reconstructed 3-D configuration of the tract [9,[36][37][38].…”

“…Furthermore, diffusion tensor tractography, which is a derivative of DTI, enables three-dimensional (3-D) visualization and estimation of specific neural tracts [9,[36][37][38]. The advantage of diffusion tensor tractography over DTI is that the characteristics of an entire neural tract can be determined by examining the tract's parameters and analyzing the reconstructed 3-D configuration of the tract [9,[36][37][38]. As a result, it can be used to produce detailed 3-D reconstructed imagery of neural tracts, providing marked improvements in detecting the site and extent of DAIs within the examined tracts [9,[36][37][38].…”

“…The advantage of diffusion tensor tractography over DTI is that the characteristics of an entire neural tract can be determined by examining the tract's parameters and analyzing the reconstructed 3-D configuration of the tract [9,[36][37][38]. As a result, it can be used to produce detailed 3-D reconstructed imagery of neural tracts, providing marked improvements in detecting the site and extent of DAIs within the examined tracts [9,[36][37][38]. DTT abnormality by previous head trauma, concurrent neurological disease, aging, or artifact of DTT should be ruled out [25] (Figure 2).…”

“…DAI is characterized histologically by widespread damage to axons, mainly in areas at the border between the cortical gray and white matters such as in the corpus callosum, brainstem, and cerebellum [3,7,8]. DAI is diagnosed in 40%-50% of patients admitted to hospital for traumatic brain injury (TBI), and is closely associated with loss of consciousness (LOC) and a poor outcome after head trauma [8,9].…”