整合磁共振成像和光学成像的优势，采用双模态成像活体动态观察内皮祖细胞（EPCs）移植后靶向归巢到血管内皮损伤局部的生物学过程。

利用化学法合成负载磁共振显影剂SPIO和近红外染料Cy7.5的PEG-PEI纳米载体建立裸大鼠颈动脉内膜损伤模型，随机分为空载体对照组（PEG-PEI组）和实验组（PEG-PEI-SPIO组），体外分别通过动态光散射实验检测其纳米粒子的粒径、电位，CCK-8实验和Annexin V流式实验检测其细胞毒性；体内借助磁共振成像和活体荧光成像动态观察大鼠EPCs尾静脉移植后靶向归巢到血管内皮损伤局部的过程，两组间比较采用t检验。

动态光散射实验表明：当N/P = 12时，PEG-PEI-SPIO纳米粒子与质粒复合后的粒径为（129.61±1.05）nm，表面电位为2.41 mV；电镜检测结果发现：复合后的纳米粒子呈现形态一致的圆形，SPIO位于复合体系中心，复合体系的粒径在（130.06 ±1.21）nm；CCK-8实验和Annexin V流式实验表明：当N/P = 12时，PEG-PEI组与PEG-PEI-SPIO组纳米载体的增殖毒性和凋亡毒性差异无统计学意义；普鲁士蓝染色显示：PEG-PEI-SPIO纳米粒子可被EPCs吞至细胞质中。活体荧光显像结果显示：Cy7.5标记的EPCs能够在移植后2 d内归巢到血管内皮损伤处（高荧光信号强度）；磁共振显像结果显示：SPIO标记的EPCs移植后2 d内到达损伤部位血管内皮下（MRI T₂强度下降）。

纳米载体PEG-PEI-SPIO具有很好的质粒复合功能、稳定的形态学特征、低细胞毒性以及良好的活体可视化功能，可有效整合磁共振成像和光学成像在空间分辨率、敏感性、特异性以及定量分析等各方面的优势，活体示踪EPCs在体移植后的靶向归巢过程，对活体评价干细胞移植疗效，优化移植策略提供客观指标和理论指导。

Integrated magnetic resonance and optical imaging to create dynamically dual-modality imaging to observe the biological process of endothelial progenitor cells (EPCs) homing to the local vascular endothelial injury after transplanted.

Chemically synthesized PEG-PEI nanocarriers loaded with magnetic resonance imaging agent SPIO and near-infrared dye Cy7.5 were randomly divided into an empty carrier control group (PEG-PEI group) and an experimental group (PEG-PEI-SPIO group) ; The particle size and potential of the nanoparticles were measured by dynamic light scattering experiment in vitro, CCK-8 experiment and Annexin V flow cytometry; A nude rat carotid artery intima injury model was established, and the tail vein of EPCs was dynamically observed by magnetic resonance imaging and intravital fluorescence imaging After transplantation, the process of homing to the local vascular endothelial injury is targeted. t test was used for comparison between two groups.

Dynamic light scattering experiments show that the particle size of PEG-PEI-SPIO nanoparticles is 129.6 nm, and the surface potential is 2.4 mV when N/P = 12; electron microscopy Results show that the composite nanoparticles has circles shape, SPIO is located in the center of the composite system, and the particle size of the composite system is about 130 nm; CCK- 8 experiment and Annexin V flow cytometry experiment show that when N/P = 12, compared to the nanocarrier PEG-PEI control group, the proliferation toxicity and apoptosis toxicity of PEG-PEI-SPIO nanocarriers has no statistic differences; Prussian blue staining shows that PEG-PEI-SPIO nanoparticles can be endothelialized into the cytoplasm. In vivo fluorescence imaging Results showed that Cy7.5-labeled EPCs home to the vascular endothelial injury within 2 days after transplantation (increased fluorescence signal intensity) ; MRI Results showed that SPIO-labeled EPCs reached the sub-endothelium injury location within 2 days after transplantation (the intensity of MRI T₂ decreased) .

PEG-PEI nanocarrier can effectively integrate the advantages of magnetic resonance imaging and optical imaging in terms of spatial resolution, sensitivity, specificity, and quantitative analysis. Tracking of EPCs' targeted homing process with nanocarrier can be used for the in vivo evaluation of transplantation effect and optimizing transplantation strategy, which provides objective indicators and theoretical guidance for stem cell therapy.