Purpose With the progression of brain tissue aging, the transport and drainage characteristics of metabolites and secretory products for neurons in extracellular space occurs irreversible change. This paper aims to investigate and quantify MR tracer diffusion characteristics in cerebral interstitial fluid of elderly SD rats. Materials and Methods MR contrast agent Gd-DTPA was injected into the caudate nucleus of two groups of rats including 8 in experimental group (15-17 month old) and 15 in control group (7-10 month old). MR scan was performed at 0.25 h, 0.5 h, 1 h, 2 h, 3 h and 4 h to observe the dynamic distribution in the caudate and measure the diffusion and clearance rate. Results There was no statistically significant difference in diffusion rate and D* between control group with (3.32±0.70)×10-4 mm2/s and experimental group with (3.25±0.46)×10-4 mm2/s (t=1.739, P>0.05). The clearance rate k' was significantly different between control group (0.62±0.12)×10-4/s and experimental group (0.29±0.08)×10-4/s (t=11.602, P<0.05). Conclusion The degeneration of aging brain tissue changes the composition of extracellular space resulting in decreased speed of ISF clearance. This may cause accumulation of metabolites which eventually triggers a variety of age-related diseases.%目的随着脑组织衰老的进展，神经细胞代谢及分泌产物在脑细胞外间隙（ECS）转运及引流特性发生不可逆性改变，本研究通过 MR 示踪剂在 ECS 内扩散的特征反映老年 SD 大鼠脑组织间液流动的改变，并通过软件计算将其量化。材料与方法分别选择实验组老年 SD 大鼠（15~17个月）8只及对照组正常成年 SD 大鼠（7~10个月）15只，尾状核注射 MR 示踪剂钆喷酸葡胺，分别于0.25 h、0.5 h、1 h、2 h、3 h、4 h 进行 MRI 扫描，观察造影剂在尾状核的动态分布，并测量造影剂的扩散及清除速率。结果实验组 SD 大鼠的示踪剂在 ECS 内的扩散率 D*为（3.25±0.46）×10-4 mm2/s，与对照组的（3.32±0.70）×10-4 mm2/s 比较，差异无统计学意义（t=1.739， P>0.05）；但实验组尾状核区的示踪剂清除速率 k'为（0.29±0.08）×10-4/s，较对照组的（0.62±0.12）×10-4/s 明显减低，差异有统计学意义（t=11.602，P<0.05）。结论SD 大鼠脑衰老组织的退行性改变引起 ECS 结构等变化，使脑组织间液清除减慢，这可能与代谢产物蓄积并最终诱发多种老年性疾病有密切的关系。
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