兔早期放射性脑损伤:1H-MRS与病理对照研究

目的 建立新西兰兔早期放射性脑损伤模型,观察MRS各指标的变化,并与病理组织学改变进行对照.方法 将27只均接受单次大剂量25 Gy全脑照射后的成年新西兰兔随机均分为9组,设照射前、照射后1～8周共9个观察点,行单体素1 H-MRS.在每个观察时间点于MR扫描结束后处死该组动物,观察病理学改变,并与MRS改变结合分析.结果 胆碱/肌酸(Cho/Cr)比值的变化趋势为先上升后明显下降:照射前为1.52±0.28,照射后4周为3.20士0.72,照射后8周为2.04±0.05；N-乙酰天门冬氨酸(NAA)/Cr比值的变化趋势为逐渐下降:照射前为1.97±0.25,照射后8周为1.28±0.05.Cho/NAA比值呈持续上升,照射前为1.19±0.15,照射后8周为2.04士0.78.照射后2周,组织病理学开始发现小血管充血和血管内皮细胞肿胀；照射后4周脑室周围白质和胼胝体出现神经元肿胀,胞浆水肿,星形胶质细胞和小胶质细胞增生,并见脱髓鞘改变.结论 新西兰兔早期放射性脑损伤模型 MRS各观察指标的变化与病理组织学改变密切相关；MRS可以作为早期检测放射性脑损伤的影像学手段.

Acute brain radiation injury of rabbits: A control study on proton MRS findings and histopathological changes

Objective To establish radiation induced brain injury rabbit models for observing ¹H-MRS changes and probing on the correlation between MRS findings and histopathological changes. Methods Twenty-seven adult New Zealand white rabbits were randomly divided into 9 groups (each n=3). The rabbit brains were irradiated with a single dose of 25 Gy. The observation posts included pre-radiation and 1 to 8 weeks after radiation. Each group underwent single-voxel ¹H-MRS, after the completion of image acquisition, the animals were sacrificed, and histological specimens were obtained. Pathological changes were analyzed combined with MRS changes. Results The metabolic ratios of choline/creatine (Cho/Cr) increased first and then decreased obviously. Cho/Cr was 1.52±0.28 pre-radiation, 3.20±0.72 at 4 weeks, and 2.04±0.05 at 8 weeks after radiation. The metabolic ratios of N-acetyl aspartate (NAA)/Cr showed significant decrease tendency, which decreased to 1.28±0.05 8 weeks after radiation from pre-radiation value of 1.97±0.25. The metabolic ratios of Cho/NAA showed significant increase after irradiation, which increased to 2.04±0.78 at 8 weeks after radiation, while the value was 1.19±0.15 pre-irradiation. After irradiation, vascular changes included telangiectasias and thrombosis, which appeared 2 weeks after irradiation in the histology samples. From 4 weeks after irradiation, ueuron swelling, cytoplasm edema, astrocytosis and microglia hyperplasia could be observed, and demyelination were observed in the white matter and corpus callosum. Conclusion The changes of MRS index are closely related with histopathological findings of acute brain radiation injury of rabbits. MRS can be used as an imaging method for early diagnosis of radiation brain injury.