Tsafarov, Beatris

Background: Diffuse axonal brain injury (DABI) is a major component of traumatic brain injury, but the optimal timing of magnetic resonance imaging and histologic assessment after isolated DABI remains unclear. Because each method captures a different phase of injury, defining time-dependent diagnostic windows may improve experimental design and reduce animal use. Methods: Sixty-four Sprague-Dawley rats were randomized to moderate DABI or sham operation. Neurological Severity Score (NSS), 3 T diffusion tensor imaging (DTI), and histologic assessment were performed at early and late time points. Hippocampal fractional anisotropy (FA) was measured at 48 h and 1 month. β-amyloid precursor protein (β-APP) immunohistochemistry assessed acute axonal injury at 48 h, and hematoxylin and eosin (H&E) staining quantified hippocampal neuronal density at 1 month. Results: At 48 h, DABI rats had higher NSS, lower hippocampal FA, and greater β-APP-positive axonal accumulation than sham-operated rats. By 1 month, NSS and hippocampal FA no longer differed between groups, whereas hippocampal neuronal density remained significantly reduced in DABI rats, indicating persistent structural injury. Conclusions: In this rat model of isolated DABI, hippocampal FA and β-APP immunohistochemistry identified acute axonal pathology at 48 h, whereas conventional histology detected a persistent reduction in neuronal density at 1 month. These findings support a time-optimized diagnostic strategy using early DTI for noninvasive injury detection and late histology for long-term structural assessment.

Diffuse axonal brain injury (DAI) is a common, debilitating consequence of traumatic brain injury, yet its detection and severity grading remain challenging in clinical and experimental settings. This study evaluated the sensitivity of diffusion tensor imaging (DTI), histology, and neurological severity scoring (NSS) in assessing injury severity in a rat model of isolated DAI. A rotational injury model induced mild, moderate, or severe DAI in male and female rats. Neurological deficits were assessed 48 h after injury via NSS. Magnetic resonance imaging, including DTI metrics, such as fractional anisotropy (FA), relative anisotropy (RA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD), was performed prior to tissue collection. Histological analysis used beta amyloid precursor protein immunohistochemistry. Sensitivity and variability of each method were compared across brain regions and the whole brain. Histology was the most sensitive method, requiring very small groups to detect differences. Anisotropy-based MRI metrics, especially whole-brain FA and RA, showed strong correlations with histology and NSS and demonstrated high sensitivity with low variability. NSS identified injury but required larger group sizes. Diffusivity-based MRI metrics, particularly RD, were less sensitive and more variable. Whole-brain FA and RA were the most sensitive MRI measures of DAI severity and were comparable to histology in moderate and severe groups. These findings support combining NSS and anisotropy-based DTI for non-terminal DAI assessment in preclinical studies.

Traumatic brain injury (TBI) significantly contributes to death and disability worldwide. However, treatment options remain limited. Here, we focus on a specific pathology of TBI, diffuse axonal brain injury (DABI), which describes the process of the tearing of nerve fibers in the brain after blunt injury. Most protocols to study DABI do not incorporate a specific model for that type of pathology, limiting their ability to identify mechanisms and comorbidities of DABI. In this study, we developed a magnetic resonance imaging (MRI) protocol for DABI in a rat model using a 3-T clinical scanner. We compared the neuroimaging outcomes with histologic and neurologic assessments. In a sample size of 10 rats in the sham group and 10 rats in the DABI group, we established neurological severity scores before the intervention and at 48 h following DABI induction. After the neurological evaluation after DABI, all rats underwent MRI scans and were subsequently euthanized for histological evaluation. As expected, the neurological assessment showed a high sensitivity for DABI lesions indicated using the β-APP marker. Surprisingly, however, we found that the MRI method had greater sensitivity in assessing DABI lesions compared to histological methods. Out of the five MRI parameters with pathological changes in the DABI model, we found significant changes compared to sham rats in three parameters, and, as shown using comparative tests with other models, MRI was the most sensitive parameter, being even more sensitive than histology. We anticipate that this DABI protocol will have a significant impact on future TBI and DABI studies, advancing research on treatments specifically targeted towards improving patient quality of life and long-term outcomes.