Department of Diagnostic Radiology and Nuclear Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
J Neurotrauma. 2011 Oct;28(10):2091-102. doi: 10.1089/neu.2010.1739. Epub 2011 Sep 29.
Understanding tissue alterations at an early stage following traumatic brain injury (TBI) is critical for injury management and limiting severe consequences from secondary injury. We investigated the early microstructural and metabolic profiles using in vivo diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy ((1)H MRS) at 2 and 4 h following a controlled cortical impact injury in the rat brain using a 7.0 Tesla animal MRI system and compared profiles to baseline. Significant decrease in mean diffusivity (MD) and increased fractional anisotropy (FA) was found near the impact site (hippocampus and bilateral thalamus; p<0.05) immediately following TBI, suggesting cytotoxic edema. Although the DTI parameters largely normalized on the contralateral side by 4 h, a large inter-individual variation was observed with a trend towards recovery of MD and FA in the ipsilateral hippocampus and a sustained elevation of FA in the ipsilateral thalamus (p<0.05). Significant reduction in metabolite to total creatine ratios of N-acetylaspartate (NAA, p=0.0002), glutamate (p=0.0006), myo-inositol (Ins, p=0.04), phosphocholine and glycerophosphocholine (PCh+GPC, p=0.03), and taurine (Tau, p=0.009) were observed ipsilateral to the injury as early as 2 h, while glutamine concentration increased marginally (p=0.07). These metabolic alterations remained sustained over 4 h after TBI. Significant reductions of Ins (p=0.024) and Tau (p=0.013) and marginal reduction of NAA (p=0.06) were also observed on the contralateral side at 4 h after TBI. Overall our findings suggest significant microstructural and metabolic alterations as early as 2 h following injury. The tendency towards normalization at 4 h from the DTI data and no further metabolic changes at 4 h from MRS suggest an optimal temporal window of about 3 h for interventions that might limit secondary damage to the brain. Results indicate that early assessment of TBI patients using DTI and MRS may provide valuable information on the available treatment window to limit secondary brain damage.
了解创伤性脑损伤（TBI）后早期的组织改变对于损伤管理和限制继发性损伤的严重后果至关重要。我们使用 7.0T 动物 MRI 系统，在大鼠大脑中进行了受控皮质撞击损伤后 2 和 4 小时，通过体内扩散张量成像（DTI）和质子磁共振波谱（1H MRS）研究了早期的微观结构和代谢特征，并将特征与基线进行了比较。TBI 后立即在撞击部位（海马体和双侧丘脑）附近发现平均扩散系数（MD）显著降低，各向异性分数（FA）增加（p<0.05），表明存在细胞毒性水肿。尽管 DTI 参数在 4 小时时在对侧基本正常化，但观察到个体间差异很大，同侧海马体的 MD 和 FA 有恢复的趋势，同侧丘脑的 FA 持续升高（p<0.05）。损伤对侧的 N-乙酰天冬氨酸（NAA，p=0.0002）、谷氨酸（p=0.0006）、肌醇（Ins，p=0.04）、磷酸胆碱和甘油磷酸胆碱（PCh+GPC，p=0.03）和牛磺酸（Tau，p=0.009）的代谢物与总肌酸比显著降低，在损伤侧最早可在 2 小时观察到，而谷氨酰胺浓度略有增加（p=0.07）。这些代谢改变在 TBI 后 4 小时仍持续存在。在 TBI 后 4 小时，损伤对侧的 Ins（p=0.024）和 Tau（p=0.013）显著降低，NAA 略有降低（p=0.06）。总的来说，我们的发现表明，在损伤后 2 小时内就出现了明显的微观结构和代谢改变。从 DTI 数据来看，4 小时时的正常化趋势和从 MRS 来看没有进一步的代谢变化表明，大约 3 小时是干预的最佳时间窗口，这可能会限制对大脑的继发性损伤。结果表明，使用 DTI 和 MRS 对 TBI 患者进行早期评估可能提供有关限制继发性脑损伤的可用治疗窗口的有价值的信息。
