中文摘要：

干细胞在组织修复与再生医学中具有广阔的前景,但是干细胞体内移植后分布、活性、分化方向、作用机制等认知的缺乏成为制约干细胞治疗发展的主要瓶颈,因此,干细胞体内示踪技术的发展对于解决上述问题将起到至关重要的作用.目前利用磁性物质对干细胞进行标记后,结合磁共振成像技术（magnetic resonance imaging,MRI）可以实现体外无创、安全、持续、动态的示踪观察,示踪的效果取决于细胞内所携带磁性物质的含量、不同的磁性标记方式、细胞活性的维持.本文将对干细胞磁性标记的不同方式、磁性物质的胞内代谢及对干细胞的影响等研究进展进行系统综述,并结合现有的标记技术对如何提高干细胞磁性标记效率进行展望.

英文摘要：

Stem cells are cells with self-renewal and multiple differentiation direction characters. Variety of studies have shown that stem cells have broad prospects in tissue repair and regenerative medicine. However, some aspects of stem cells in vivo transplantation developed slowly, for instance, distribution, activity, differentiation direction and mechanism, which have restricted the development of stem cell therapy. Thus, exploring novel technologies for tracing stem cell in vivo will play a vital role in solving the above scientific problems. When stem cell are labeled magnetically, we can obtain a noninvasive, safe, sustained and dynamic tracing in vivo by combining with magnetic resonance imaging（MRI）. In addition, major factors influencing the efficiency of in vivo trace contain cellular content of magnetic material, the different methods for magnetic labeling and the maintenance of cell activity. Here, we review the recent progresses on different ways for magnetic labeling stem cell, the metabolism of magnetic substances and the impact on cell systematically. For magnetic labeling, one of the major aspects focuses on labelling stem cells with magnetic materials like superparamagnetic iron oxide nanoparticles（SPION）. Surface modification of SPION and exerting additional physical field when stem cell incubated with SPION both have enhanced label efficiency, however, it could not reflect the actual cellular activity in vivo which might bring out false-positive results by using this approach. Therefore, the use of reporter gene is developed, which could provide strong tissue contrast after stable transfection. However, whether the transfection alters stem cell properties remains to be proved. In addition, after SPION is uptaken by cells, the labeling efficiency will be decreased by a series intracellular degradation and metabolism, most particles is degraded by lysosomes into iron ions which could not provide effective MRI imaging. On the other hand, the cellular reactive oxygen species（ROS） level will