Miot E, Hoffschir D, Pontvert D, Gaboriaud G, Alapetite C, Masse R, Fetissof F, Le Pape A, Akoka S
Laboratoire de Biophysique Cellulaire et RMN/INSERM U316, Tours, France.
Int J Radiat Oncol Biol Phys. 1995 Apr 30;32(1):121-8. doi: 10.1016/0360-3016(94)00413-F.
Using magnetic resonance (MR) and isotopic imaging to investigate the cerebral alterations after highdose single-fraction irradiation on a pig model. We assessed the nuclear magnetic resonance (NMR) relaxation times as early markers of radiation injury to the healthy brain.
A total of 17 animals was studied; 15 irradiated and 2 unirradiated controls. Pigs were irradiated with a 12 MeV electron beam at a rate of 2 Gy/min. Ten animals received 40 Gy at the 90% isodose, five animals received 60 Gy, and two animals were unirradiated. The follow-up intervals ranged from 2 days to 6 months. T1-weighted scans, T2-weighted scans, and scintigrams were performed on all animals to study neurological abnormalities, cerebral blood flow, and blood-brain barrier (BBB) integrity. T1 and T2 relaxation times were measured in selected regions of interest (ROIs) within the irradiated and contralateral hemispheres. A ratio T1 after irradiation/T1 before irradiation, and a ratio T2 after irradiation/T2 before irradiation, were calculated, pooled for each dose group, and followed as a function of time after irradiation.
Scintigraphy visualized the brain perfusion defect and BBB disruption in all irradiated brains. The ratio T2 after irradiation/T2 before irradiation was proportional to the effective dose received. The T2 ratio kinetics could be analyzed in three phases:an immediate and transient phase, two long-lasting phases, which preceded compression of the irradiated lateral ventricle, and edema and necrosis at later stages of radiation injury, respectively. The magnetic resonance imaging (MRI) observations correlated well with histological analysis.
The results show that quantitative imaging is a sensitive in vivo method for early detection of cerebral radiation injury. The reliability and dose dependence of T2 relaxation time may offer new opportunities to detect and understand brain pathophysiology after high-dose single-fraction irradiation.
利用磁共振（MR）和同位素成像技术，在猪模型上研究单次大剂量照射后脑的变化。我们评估了核磁共振（NMR）弛豫时间，将其作为健康脑辐射损伤的早期标志物。
共研究了17只动物，其中15只接受照射，2只为未照射的对照。猪以2 Gy/分钟的速率接受12 MeV电子束照射。10只动物在90%等剂量线处接受40 Gy照射，5只动物接受60 Gy照射，2只动物未接受照射。随访时间间隔为2天至6个月。对所有动物进行T1加权扫描、T2加权扫描和闪烁扫描，以研究神经功能异常、脑血流量和血脑屏障（BBB）完整性。在照射侧和对侧半球的选定感兴趣区域（ROI）测量T1和T2弛豫时间。计算照射后T1/照射前T1以及照射后T2/照射前T2的比值，按剂量组汇总，并跟踪其作为照射后时间的函数变化。
闪烁扫描显示所有照射脑均存在脑灌注缺损和BBB破坏。照射后T2/照射前T2的比值与所接受的有效剂量成正比。T2比值动力学可分为三个阶段：一个即时且短暂的阶段，两个持续较长时间的阶段，分别先于照射侧脑室受压以及辐射损伤后期的水肿和坏死。磁共振成像（MRI）观察结果与组织学分析相关性良好。
结果表明，定量成像在体内是早期检测脑辐射损伤的一种敏感方法。T2弛豫时间的可靠性和剂量依赖性可能为检测和理解单次大剂量照射后脑的病理生理学提供新的机会。
