鼻咽癌放射治疗后放射性脑损伤急性反应早期的1H-MR波谱研究

1H-MRS study on radiation-induced injury of the brain in early acute reaction stage after nasopharyngeal carcinoma radiotherapy

目的评价1H- MR波谱(1H- MRS)对鼻咽癌放射治疗(简称放疗)后放射性脑损伤急性反应早期的诊断价值。方法对18例已被病理证实且为首次行放疗的鼻咽癌患者进行前瞻性研究,于不同时间段对其双侧颞叶(共72个部位,颞叶前后部各为36处)进行常规MR和1H MRS成像,成像时间为放疗前和放疗后接受放射剂量20Gy、40Gy及60Gy时,成像序列为轴面SET1WI、T2WI、T2液体衰减反转恢复序列(T2FLAIR)、三维扰相稳态梯度恢复采集T1序列(3D- SPGRT1)。以序列T2FLAIR或3D -SPGRT1为波谱成像的定位图,采用点分辨法进行多体素及单体素波谱成像,观察不同时间段颞叶各部位谱线的形态学改变及各代谢物间比值的变化。结果放疗后,双侧颞叶在常规MRI均未见明显信号改变,而在1H MRS成像上,双侧颞叶前部谱线形态均有不同程度的改变,而颞叶后部无明显改变,表现为局部N乙酰天门冬氨酸(NAA)峰和胆碱(Cho)峰降低,Cho/肌酸(Cr)、NAA/Cr及NAA/Cho比值在不同时间段均有下降;在接受放射剂量20Gy时,颞叶前叶有20处,占所有颞前叶的比例为56%(20/36);40Gy时有22处,占61%(22/36);60Gy时有13处,占36%(13/36)。而谱线为NAA与Cho峰倒置在20Gy时,颞叶前叶有4处,占11%(4/36);40Gy时,有10处,占28%(10/36);60Gy时为23处,占64%(23/36)。与接受射线剂量呈明显正相关,不同剂量其同一比值差异有统计学意义(P<0.05)。结论1H MRS可在组织细胞代谢水平发现鼻咽癌放疗后急性反应早期的放射性脑损伤。

Objective To evaluate the diagnostic value of in vivo ^1H-MRS in the hyper acute reaction stage of radiation-induced brain injury after nasopharyngeal carcinoma radiotherapy. Methods Eighteen patientswith nasopharyngeal carcinoma accepted radiotherapy for the first time. Bilateral temporal lobes in all cases were examined by conventional MRI and ^1 H-MRS before and after radiotherapy with radiation dose of 20 Gy, 40 Gy, and 60 Gy, respectively. MR image was performed with T1 -weighted gradient- and spin-echo, T2-weighted spin-echo, fluid-attenuated inversion-recovery, and point resolution spectroscopy. The change of the spectroscopic morphology and the ratios of the metabelites were observed. Results There were no changes of signal in the temporal lobes with conventional MRI, but the peak height of NAA and Cho decreased obviously in the anterior half of the temporal lobes with ^1H-MRS after radiotherapy. The post-radiotherapy changes of different metabolic peak in the anterior temporal lobes presented as two types ： one type was that Cho and NAA peak were of the same height simultaneously. There were 20 locations （56%） of the 36 reaching the peak when accepting 20 Gy, 22 （61%） when accepting 40 Gy, and 13 （36%） when accepting 60 Gy, respectively. The other type was that Cho peak became the highest, whereas NAA peak was obviously lower and decreased to be the second highest. There were 4 locations （ 11% ） of the 36 reaching the peak when accepting 20 Gy, 10 （28%） when accepting 40 Gy, and 23 （ 64% ） when accepting 60 Gy, respectively. The ratio of Cho/Cr, NAA/Cr, and NAA/Cho decreased in the same position too. In addition, there was positive correlation between the ratios of the metabolites and the dose of radiotherapy. Conclusion ^1H-MRS can be used to diagnose the radiationinduced injury of the brain in early acute reaction stage after nasopharyngeal carcinoma radiotherapy through reflecting histiocytic metabolism, and provide objective basis for pathology development and cellular metabolism study, also it can provide feasible projects for the clinic.