Quantitative evaluation of micro-structural damage of vulnerable areas in rats with diffuse axonal injury with 7.0T MRI

Abstract

Objective To observe the spatiotemporal characteristics of the micro-structural injury in a rat model of diffuse axonal injury (DAI) and quantitatively assess the axonal injury severity in the vulnerable areas. Methods The 7.0 T MRI was performed in rats in DAI group (n =20) and control group ( n = 15 ) to synthesize the diffusion tensor imaging ( DTI) parameter map and calculate the parameter value of the vulnerable areas. Immunohistochemistry was used to detect β-APP expression in the vulnerable areas and the IPP software to quantitatively assess the axonal injury severity. Results Compared with the control group, FA and AD maps showed local signal defection or reduction in the corpus callosum and their values decreased significantly in the brain stem and corpus callosum in the DAI group (P ＜0.01 ). The integrated optical density (IOD) value of the vulnerable areas in the DAI group was significantly higher than that of the control group ( P ＜ 0. 01 ) , with the highest level in the brain stem (P＜0.05). The normalized FA, AD and ADC in the vulnerable areas were correlated negatively with the IOD (P ＜ 0.05). Conclusion DTI can detect invisible micro-structural injury in the vulnerable areas and quantitatively assess the axonal injury severity in vivo in the early stage. Key words: Diffuse axonal injury; Diffusion tensor imaging; Immunohistochemistry; Integrated optical density; Region of interest