Evaluation of cerebral radiation injury using MRI and Proton MRS

脑坏死是辐照后中枢神经系统最严重的副作用。我们研究了磁化转移成像（MTI）和质子磁共振波谱（proton - mrs）在早期检测正常猫脑放射性坏死中的作用。使用12 mev电子束，在猫右脑半球1.5*2.0 cm顶点门静脉处照射单次60 Gy剂量。使用1.5 T MR成像单元获得MR图像和质子- mrs。冠状快速自旋回波成像，TR=3000 msec，有效TE=88 msec。以TR=600 msec和TE=4 msec进行2D-GRASS成像，每隔50 msec用共振磁化传递脉冲评估磁化传递比（MTR）。利用点分辨光谱脉冲序列在目标体积（10*10*10mm3）上获得质子- mrs。重复时间为2000 ms，回声时间为136 ms。在照射后3.5至4.5个月，所有猫的T2-WI显示异常高的MR信号强度。质子谱显示，与对侧未照射的脑区相比，所有猫脑区含胆碱化合物/肌酸-磷酸肌酸比值明显增加，n-乙酰天冬氨酸/肌酸-磷酸肌酸比值呈下降趋势。这些变化发生的时间至少比磁共振图像上发现的异常早一个月。MTI也比常规MR图像更早显示辐照区异常低的MTR。镜下检查显示T2-WI高信号区为脱髓鞘，包含侧腹坏死。我们推测，就在辐射坏死之前，由于膜合成受到干扰和/或膜降解加速，细胞膜动力学发生了变化。体内质子- mrs和MTI可能是检测辐射损伤的潜在工具，即使传统的T2图像显示没有信号变化。少

Brain necrosis is the most serious side effect in the central nervous system after irradiation. We investigated the usefulness of magnetization transfer imaging (MTI) and proton magnetic resonance spectroscopy (Proton-MRS) for the early detection of cerebral radiation necrosis in the normal brain of cats.A single 60 Gy dose was irradiated with a 1.5*2.0 cm vertex portal in the right cerebral hemisphere of the cat, using a 12-MeV electron beam. MR images and Proton-MRS were obtained, using a 1.5 T MR imaging unit. Coronal fast spin-echo imaging was performed with TR=3000 msec and effective TE=88 msec. 2D-GRASS imaging was per-formed with TR=600 msec and TE=4 msec and every 50 msec off resonance magnetization transfer pulses were used for evaluate magnetization transfer ratio (MTR). Proton-MRS were obtained from a volume (10*10*10mm3) of interest by using point resolved spectroscopy pulse sequence. Repetition time and echo time were 2000 ms and 136 ms, respectively.Irradiated white matte … More r revealed an abnormally high MR signal intensity on T2-WI in all cats 3.5 to 4.5 months after irradiation. Proton spectra in the affected region showed an apparent increase of the choline-containing com-pounds/creatine-phosphocreatine ratio and a trend of a decreasing N-acetylaspartate/creatine-phosphocreatine ratio compared with the contralateral non-irradiated brain in all cats. These changes occurred at least one month earlier than abnormalities detected on MR images. MTI also showed abnormally low MTR at the irradiated area earlier than conventional MR images. Microscopic examinations revealed the regions of high signal intensity on T2-WI were demyelination and contained flank necrosis.We speculate that, just before radiation necrosis, cell membrane kinetics was changed as membrane synthesis was disturbed and/or membrane degradation was accelerated. In vivo Proton-MRS and MTI could be a potential tool for detecting radiation injury, even when conventional T2 image shows no signal change. Less