目的：研究光磁双模态分子探针Gd-DO3A-ethylthiourea-fluorescein isothiocyanate（Gd-DO3A-EA-FITC）在脑组织间隙（interstitial space, ISS）成像分析中的应用价值。方法：24只SD雄性大鼠随机分为磁示踪组(6只)、荧光示踪组(6只)和光磁示踪组(12只)，光磁示踪组随机分为磁示踪亚组(6只)和荧光示踪亚组(6只)。分别在大鼠尾状核区注入磁示踪剂钆-二乙三胺五乙酸(gadoliniumdiethylene triamine pentaacetic acid, Gd-DTPA)、光示踪剂异硫氰酸荧光素(fluorescein isothiocyanate, FITC)和光磁双模态分子探针Gd-DO3A-EA-FITC，应用磁共振成像(magnetic resonance imaging, MRI)检测示踪剂在脑ISS中的扩散和分布，利用自主研发的脑ISS图像处理系统测量Gd-DO3A-EA-FITC和Gd-DTPA在脑ISS内的扩散系数、清除率、体积分数和半衰期等扩散参数。注射示踪剂2 h后，利用激光扫描共聚焦显微镜(laser scanning confocal microscope, LSCM)对离体脑切片进行荧光信号的采集，并对比分析斜矢状位切片中示踪剂扩散分布的最大面积。结果：Gd-DTPA和Gd-DO3A-EA-FITC在鼠脑内的平均扩散系数分别为(3.31±0.11)×10-4 mm2/s和(3.37±0.15)×10-4 mm2/s (t=0.942，P=0.360)，清除率分别为(3.04±0.37) mmol/L和(2.90±0.51) mmol/L (t=0.640，P=0.531)，体积分数分别为17.18%±0.14%和17.31%±0.15% (t=1.961，P=0.068)，半衰期分别为(86.58±3.31) min和(84.61±2.38) min (t=1.412，P=0.177)，扩散分布最大面积分别为(22.71±1.00) mm2和(23.25±0.68) mm2 (t=1.100，P=0.297)，两者的各项扩散参数差异均无统计学意义。FITC和Gd-DO3A-EA-FITC在鼠脑内扩散分布最大面积分别为(22.10±1.29) mm2和(22.61±1.16) mm2 (t=0.713，P=0.492)，两者差异无统计学意义，Gd-DO3A-EA-FITC的扩散面积略大于FITC。结论：Gd-DO3A-EA-FITC与传统的Gd-DTPA的成像结果相同，可用于ISS的测量。

Objective： To investigate the application of the optical magnetic bimodal molecular probe Gd-DO3A-ethylthiouret-fluorescein isothiocyanate (Gd-DO3A-EAFITC) in brain tissue imaging and brain interstitial space (ISS). Methods: In the study, 24 male SD rats were randomly divided into 3 groups, including magnetic probe group (n=6), optical probe group (n=6) and optical magnetic bimodal probe group (n=12), then the optical magnetic bimodal probe group was divided equally into magnetic probe subgroup (n=6) and optical probe subgroup (n=6). Referencing the brain stereotaxic atlas, the coronal globus pallidus as center level, the probes including gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA), fluorescein isothiocyanate (FITC) and Gd-DO3A-EA-FITC of 2 μL (10 mmol/L) were injected into the caudate nucleus respectively, magnetic resonance imaging (MRI) was performed in the magnetic probe group and magnetic probe subgroup to image the dynamic diffusion and distribution of the probes in the brain ISS, a self-developed brain ISS image processing system was used to measure the diffusion coefficient, clearance, volume fraction and half-time in these two groups. Laser scanning confocal microscope (LSCM) was performed in vitro in the optical probe group and optical probe subgroup for fluorescence imaging at the time points 2 hours after the injection of the probe, and the distribution in the oblique sagittal slice was compared with the result of the first two groups. Results: For the magnetic probe group and magnetic probe subgroup, there were the same imaging results between the probes of Gd-DTPA and Gd-DO3A-EA-FITC. The diffusion parameters of Gd-DTPA and GdDO3A-EA-FITC were as follows: the average diffusion coefficients ［(3.31±0.11)×10-4 mm2/s vs. (3.37±0.15)×10-4 mm2/s, t=0.942, P=0.360］, the clearance ［(3.04±0.37) mmol/L vs. (2.90±0.51) mmol/L, t=0.640, P=0.531］, the volume fractions (17.18%±0.14% vs. 17.31%±0.15%, t=1.961, P=0.068), the half-time ［(86.58±3.31) min vs. (84.61±2.38) min, t=1.412, P=0.177］, the diffusion areas ［(23.25±0.68) mm2 vs. (22.71±1.00) mm2, t=1.100, P=0.297］. The statistical analysis of each brain was made by t test, and the diffusion parameters were not statistically significant. Moreover, for the optical probe group and optical probe subgroup, the diffusion area of Gd-DO3A-EA-FITC ［(22.61±1.16) mm2］ was slightly larger than that of FITC ［(22.10±1.29) mm2］, the statistical analysis of each brain was made by t test, and the diffusion parameters were not statistically significant (t=0.713, P=0.492). Conclusion: Gd-DO3AEA-FITC shows the same imaging results as the traditional GD-DTPA, and it can be used in measuring brain ISS.