中文摘要：

目的使用超顺磁性氧化铁（SPIO）纳米粒子对神经干细胞进行体外标记，并在体外及活体移植后对标记细胞进行MRI示踪。方法实验动物包括13只SD大鼠。联合应用SPIO及多聚左旋赖氨酸（PLL）通过受体介导的内吞作用标记神经干细胞，对标记细胞分别进行普鲁士蓝染色、电子显微镜观察、体外MRI示踪及活体移植后体内MRI示踪。体外1．5T及4．7TMR扫描对象分为5组，分别为5×10^5个标记后培养1d的细胞、5×10^5个相同时期未标记的细胞、提取标记细胞后的含铁培养基、相应的无铁培养基及蒸馏水。扫描序列包括轴面T1WI、T2WI及T2·WI，并在4．7TMR仪上测量标记细胞的弛豫率R2及R2＊的变化。结果（1）该方法标记神经干细胞的有效率为100％，普鲁士蓝染色证实了每个标记细胞胞质内有多少不等的蓝染铁颗粒。（2）体外1．5T及4．7T MRI显示，标记细胞同未标记细胞相比，T1WI信号强度平均上升分别为20．53％及24．06％，T2WI信号强度平均下降分别为40．78％及50．66％，T2＊WI信号强度平均下降46．57％及53．70％。1．5T MRI上标记细胞的信号改变在T2WI与T2·WI之间差异无统计学意义（F=3．06，P〉0．05），而T2WI及T2·WI与T1WI之间差异均有统计学意义（F=6．5，P〈0．05）。（3）4．7T MRI测量未标记细胞和标记细胞的T2分别为516ms及77ms，其弛豫率R2分别为1．94s^-1及12．98s^-1；T2·分别为109ms及22．9ms，其弛豫率R2＊分别为9．17s^-1及43．67s^-1。（4）标记细胞活体移植1周后行1．5TMR检查，见移植部位在T2WI及T2＊WI上呈显著低信号，而对照侧未见低信号。结论该方法标记神经干细胞简单高效，标记细胞弛豫率R2及R2＊明显提高，并能采用1．5TMRI对标记细胞进行活体内外示踪研究。

英文摘要：

Objective To label neural stem cells with superparamagnetic iron oxide （SPIO） and track labeled cells with MRI in vitro and in vivo after implantation. Methods 13 SD rats were used for the study. Rat neural stem cells were labeled with SPIO combined with PLL by the mean of receptor-mediated endocytosis. Prussian blue staining and electron microscopy were conducted to identify the iron particles in these neural stem cells, and SPIO-labeled cells were tracked with 1.5 T and 4. 7T MRI in vivo and in vitro after implantation. The subjects were divided into five groups, including 5×10^5 labeled cells,5×10^5 unlabeled cells, cell culture medium with SPIO, cell culture medium without SPIO and distilled water. MRI scanning sequences included TIWI, T2WI and T2 ＊ WI. R2 and R2 ＊ relaxation rate of labeled cells were calculated. Results （ 1 ） Neural stem cells could be labeled with SPIO and labeling efficiency was 100%, Prussian blue staining showed numerous blue-stained iron particles in the cytoplasm. （2） The average percentage change of signal intensity of labeled cells on TIWI in 1.5 T and 4.7 T MRI was 20.53% and 24.06% respectively, on T2WI was 40. 78% and 50. 66% respectively, and on T2 ＊ WI was 46. 57% and 53.70% respectively. The signal intensity had no significant difference between T2WI and T2 ＊ WI in 1.5 T MRI, however the signal intensity had significant difference between T2WI or T2 ＊ WI and TIWI. （3） T2 of unlabeled cells and labeled cells in 4. 7 T MRI were 516 ms and 77 ms respectively, Ra were 1.94 s-1 and 12.98 s^-1 respectively; and T2＊ were 109 ms and 22.9 ms, R2＊ were 9.17 s^-1 and 43.67 s^-1 respectively. （4） Remarkable low signal area on T2WI and T2＊ WI was seen in the left brain implanted with labeled cells one week ago, however no signal change in the right brain implanted with unlabeled cells. Conclusion Neural stem cells can be labeled effectively with SPIO; R2 and R2＊ of labeled cells were increased obviously; MRI can be used to track labeled cells in vitr