WATER DIFFUSION IN OPTIC & TRIGEMINAL NERVE AFTER CARDIAC ARREST

水的表观扩散系数（ADC） 在灰色和白色物质中，在全球 缺血 然而，缺血对水扩散及其 神经中各向异性是未知的。 本研究的目的是 测量水在视神经和三叉神经的扩散及其各向异性 大鼠心脏骤停后的神经。 方法：心脏骤停， 通过静脉注射在麻醉的Sprague-Dawley大鼠（n=7）中诱导 氯化钾 核心温度维持在3711！C通过 暖空气循环 MRI弥散测量在 GE CSI 2 T光谱仪在心脏骤停前和20、40、60和 心脏骤停后90分钟。 为了研究各向异性 扩散，并且由于神经与Z大致对齐， 方向，ADC值平行（//）和垂直（^）于 应用扩散梯度获得神经的长度 分别沿沿着Z和X（或Y）。 结果与结论：ADC（//） 在视神经中，ADC（^）分别下降了44%和46%， 90 min时，三叉神经分别减少24%和26 心脏骤停后，相对于心脏骤停前的ADC。 有趣的是，接近最小ADC的速率比 大脑皮层 这是符合缓慢下降的 心脏骤停后白色物质相对于灰质的ADC值。 尽管ADC的绝对减小，但各向异性{ADC（f）/ADC（f）} 在心脏骤停后的90分钟内， 对于视神经和三叉神经，保持在~2.9。 因此，我们认为， 扩散各向异性的变化将不会在急性 缺血期。

Introduction: The apparent diffusion coefficient (ADC) of water in gray and white matter decreases significantly (~35%) after global ischemia. However, the effects of ischemia on water diffusion and its anisotropy in nerve are unknown. The purpose of this study was to measure water diffusion and its anisotropy in the optic and trigeminal nerve after cardiac arrest in the rat. Methods: Cardiac arrest was induced in anesthetized Sprague-Dawley rats (n=7) by an i.v. injection of potassium chloride. Core temperature was maintained at 3711!C by warm air circulation. MRI diffusion measurements were performed on a GE CSI 2 T spectrometer prior to cardiac arrest and at 20, 40, 60, and 90 min after cardiac arrest. In order to investigate anisotropic diffusion and since the nerves are in approximate alignment with the Z direction, the ADC values parallel (//) and perpendicular (^) to the length of the nerve were obtained with the diffusion gradients applied along Z and X (or Y), respectively. Results and Conclusion: ADC(//) and ADC(^) decreased by 44 and 46%, respectively, in the optic nerve, and by 24 and 26%, respectively, in the trigeminal nerve at 90 min post cardiac arrest, relative to the ADCs prior to cardiac arrest. Interestingly, the rate of approach to the minimum ADC was slower than in the cortex. This is in agreement with the slower decrease of the ADC in white matter relative to gray matter after cardiac arrest. Despite the absolute reductions in ADC, anisotropy {ADC(//)/ADC(^)} was preserved throughout the 90 min after cardiac arrest and it remained at ~2.9 for both the optic and trigeminal nerves. Therefore, changes in diffusional anisotropy would not be expected at the acute stage of ischemia.