Multi-Modal Magnetic Resonance Imaging Alterations in Two Rat Models of Mild Neurotrauma

Abstract

Magnetic resonance imaging (MRI) is increasingly used in the assessment of the severity and progression of neurotrauma. We evaluated temporal and regional changes after mild fluid percussion (FPI) and controlled cortical impact (CCI) injury using T2-weighted-imaging (T2WI) and diffusion-weighted imaging (DWI) MRI over 7 days. Region of interest analysis of brain areas distant to the injury site (such as the hippocampus, retrosplenial and piriform cortices, and the thalamus) was undertaken. In the hippocampus of CCI animals, we found a slow increase (51%) in apparent diffusion coefficients (ADC) over 72 h, which returned to control values. The hippocampal T2 values in the CCI animals were elevated by 18% over the 7-day time course compared to control, indicative of edema formation. Histological analysis supported the lack of overt cellular loss in most brain regions after mild CCI injury. FPI animals showed a generalized decrease in hippocampal ADC values over the first 72 h, which then returned to sham levels, with decreased T2 values over the same period, which remained depressed at 7 days. Histological assessment of FPI animals revealed numerous shrunken cells in the hippocampus and thalamus, but other regions showed little damage. Increased immunohistochemical staining for microglia and astroglia at 7 days post-injury was greater in FPI animals within the affected brain regions. In summary, traumatic brain injury is less severe in mild CCI than FPI, based on the temporal events assessed with MRI.

Multi-Modal Magnetic Resonance Imaging in the Acute and Sub-Acute Phase of Mild Traumatic Brain Injury: Can We See the Difference?

“…58 Although a recent study presenting bidirectional changes in FA of mTBI patients raised the possibility of spatial factors contributing to alterations in FA, 59 our data support rather the significance of temporal factors: both FA and MD changed significantly in a relatively short period, and no bidirectional changes were detected. The rapid consolidation of MD hypothetically may be associated with the recovery process from edema, because edema is thought to pass over in a similar pace after mTBI.…”

A prospective diffusion tensor imaging study in mild traumatic brain injury

“…Although myelin only accounts for approximately 13% of total water in white matter compartments, a reduction in this percentage would theoretically also decrease diffusivity perpendicular to the axon. 30 At a more basic level, there may be qualitative differences in neuropathologic processes among appropriately diagnosed mTBI patients as illustrated by a recent study 34 comparing the fluid percussion (FPI) and cortical impact (CCI) injury models. Injured animals from both groups differed from shams in terms of T2 values and apparent diffusion coefficients (ADC), but in opposite directions.…”

MRI Characterization of Progressive Brain Alterations After Experimental Traumatic Brain Injury: Region Specific Tissue Damage, Hemodynamic Changes and Axonal Injury

“…For example, the hyperintensity in T 2 weighted images has been used to show edema, neuronal loss or, the consequence of tissue atrophy and partial volume effect. The hippocampal T 2 relaxation time has been reported to increase during the first 7 days after TBI induced by controlled cortical impact (Obenaus et al, 2007). A 3 month follow-up showed enlarged ventricles, cisterns, and that the necrotic tissue in the primary contusion site was absorbed and replaced by cerebrospinal fluid (Iwamoto et al, 1997).…”

“…A 3 month follow-up showed enlarged ventricles, cisterns, and that the necrotic tissue in the primary contusion site was absorbed and replaced by cerebrospinal fluid (Iwamoto et al, 1997). Diffusion weighted imaging has shown decreased apparent water diffusion (ADC) acutely (<24 hours) after TBI followed by increased diffusion days or weeks after TBI (Albensi et al, 2000;Obenaus et al, 2007;Onyszchuk et al, 2007;Van Putten et al, 2005;Vink et al, 2001). Histological studies in rat models have verified these aforementioned MRI findings and the robust cellular loss and cavity formation in the primary cortical contusion site during the early weeks post-injury, the degeneration has been found to be selective for certain cell types and brain regions (Conti et al, 1998;Cortez, McIntosh, Noble 1989a;Hallam et al, 2004;Raghupathi et al, 2002;Rink et al, 1995;Sato et al, 2001) and it has been demonstrated to go on up to 1 year (Bramlett et al, 1997;Pierce et al, 1998;Smith et al, 1997).…”