Miot-Noirault E, Akoka S, Hoffschir D, Pontvert D, Gaboriaud G, Alapetite C, Fetissof F, Le Pape A
Laboratoire de Biophysique Cellulaire et RMN, Tours, France.
AJNR Am J Neuroradiol. 1996 May;17(5):907-12.
To investigate the MR T2 relaxation time and histologic changes after a single-fraction 25-Gy dose of radiation to the brain of pigs.
The right hemisphere of 10 Meishan pigs was irradiated with a single dose of 25 GY at the 90% isodose, using a 12-MeV electron beam. T2 relaxation time was measured within three regions of interest in the brain: those that had received 90%, 70%, and 40% of the total dose, respectively. T2 kinetics over time was compared with histologic studies.
Brain T2 values were noted to increase within the irradiated areas. T2 kinetics were analyzed in three phases: an immediate transient phase and two long-lasting phases. These two long-lasting phases were correlated with the detection of ventricular compression and necrosis, respectively. The T2 increase within the 90% region of interest was 19%, 22%, and 26% for phases I, II, and III, respectively. T2 measurements within other regions of interest were not significant.
Although our results suggest a dose threshold for T2 variations, brain T2 values increased after irradiation at a level at which disease could not be seen on conventional MR images. This illustrates the value of using conventional MR imaging in a quantitative manner to assess molecular tissue abnormalities at earlier stages of developing diseases.
研究单次25 Gy剂量辐射猪脑后的磁共振T2弛豫时间及组织学变化。
使用12 MeV电子束，在90%等剂量线处对10只梅山猪的右半球进行单次25 Gy剂量的照射。在脑内三个感兴趣区域测量T2弛豫时间，分别为接受总剂量90%、70%和40%的区域。将T2随时间的动力学变化与组织学研究结果进行比较。
照射区域内脑T2值升高。T2动力学变化分为三个阶段：一个即时短暂阶段和两个持续较长时间的阶段。这两个持续较长时间的阶段分别与脑室受压和坏死的检测相关。在90%感兴趣区域内，T2值在I期、II期和III期分别升高了19%、22%和26%。其他感兴趣区域的T2测量值无显著变化。
尽管我们的结果提示了T2变化的剂量阈值，但在常规磁共振图像上未见病变的辐射剂量水平下，照射后脑T2值仍升高。这说明了以定量方式使用常规磁共振成像来评估疾病发展早期分子组织异常的价值。
