Background Functional magnetic resonance imaging technique based on a manganese (Mn2+) tracer makes labeling the optic nerve in vivo possible.However studies on the optimal concentration and dynamic change after injection of Mn2+ are rare.Objective This study was designed to explore the time- and dose-dependent response for Mn2+-enhanced MRI of visual pathway after intravitreal injection of MnCl2.Methods Different concentrations of MnCl2(0.5,1,2,5,10,15,20,40mmol/L) with a volume of 25μl were intravitreally injected into the left eyes of 48 pigmented rabbits and were randomly divided into eight groups according to the drug concentrations.No reagent reg was injected into the right eyes as controls.MRI was performed at 4,6,8,12,24,48,96 and 168 hours after the administration of MnCl2 to examine the imaging of the optic nerve,chiasma,optic tract,lateral geniculate body and epithalamus.The signal-noise ratio of MRI in visual pathway was calculated and the optimal concentration and best imaging time after injection of MnCl2 were assessed.The use of the animals followed the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission.Results The imaging of the optical nerve in the left eyes was enhanced in comparison with the right eyes 24 hours after injection of 0.5-1 mmol/L MnCl2 with a significant difference in SNR value between these two groups (t=1.17,t=0.95,P>0.05).24 hours after the injection of 2 mmol/L MnCl2 into the left eyes,the SNR value of the optic nerve on the left side was higher than the right side t=8.43,P<0.05),but no image of lateral geniculate body and epithalamus was found in the left side compared to the right side (t=0.04,t=0.22,P>0.05).The strongest imaging signal in optical nerve was seen in 24 hours after the intravitreal injection of 10-40 mmol/L MnCl2 and decayed gradually from 24 to 168 hours with a transportation speed of (3.32±0.19) mm/h in rabbit visual pathway.SNR value of optic nerve showed a positive correlation with the concentrations of MnCl2 with the regression equation Y=77.786+2.467X(F=20.102,P=0.004,R2=0.770).Conclusion Manganese-enhanced MRI is a viable method for temporospatial visualization of optic never in the pigmented rabbits.The image intensity of MRI is associated with the dose of Mn2+.%背景 近年来基于Mn2+作为神经示踪剂的功能磁共振成像(MRI)技术使得活体示踪视神经成为可能,但其应用的最佳浓度及示踪视神经的动态过程的研究报道较少.目的 探讨不同浓度Mn2+在活体兔眼增强磁共振视神经示踪成像的量效和时效关系.方法 48只青紫兰兔经左侧眼球上方距角巩膜缘1～1.5mm处玻璃体腔内分别注入不同浓度的MnCl2溶液(0.5、1、2、5、10、15、20、40mmol/L)25μl,右眼不进行任何注射作为对照.分别于注射后4、6、8、12、24、48、96、168h用1.5T超导MRI对兔头颅进行扫描,观察兔眼玻璃体腔注射后视神经、视交叉、对侧视束、外侧膝状体和上丘视觉传导通路的MRI显像情况,计算出上述部位的信噪比(SNR),分析Mn2+作为MRI视路示踪剂的最佳有效浓度和最佳显像时间.结果 左眼玻璃体腔内注射0.5～1mmol/L MnCl2溶液后24h可见视神经显影较右眼视神经略增强,但双侧SNR值比较差异无统计学意义(t=1.17、t=0.95,P＞0.05).左眼玻璃体腔内注射2mmol/L的MnCl2 24h后,左侧视神经的SNR值明显高于右侧,差异有统计学意义(t=8.43,P＜0.05),但左侧外侧膝状体和上丘无明显强化显影,与右侧相比差异无统计学意义(t=0.04、t=0.22,P＞0.05).左眼玻璃体腔注射10~40mmol/L MnCl2 24h MRI视神经信号最强,此后随时间延长MRI信号逐渐减弱,168h后消失.视神经MRI图像的SNR值与玻璃体腔注入Mn2+浓度呈正相关,(Y=66.234+24.269 lnx,F=374.15,P=0.000,R2=0.984).Mn2+在视觉通路的转输速度为(3.32±0.19)mm/h.结论 兔玻璃体腔注射25μl 5~40mmol/L的MnCl2溶液24h,MRI能够清晰地显示整个视觉传导通路的信号增强,视路信号增强的程度呈MnCl2剂量依赖性并随着时间的延长呈现先增强后衰减的动态变化过程.
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