| Objective: Via implanting radioactive particles 125I at bilateral lamina of thoracic vertebra in rabbits for excessive radiation,this study established spinal cord radiation injury rabbit animal model to observe the status of spinal cord injury with pathology results.By general observation and MRI scanning at different time points,the ADC and FA of radiated sites in animal models were obtained,and the feasibility of these two values in evaluating spinal cord radiation injury of rabbits was investigated.Method: 1.A total of 12 CV New Zealand rabbits were fed and observed,and DTI image sequences of 1.5T magnetic resonance were applied to scan the brains and spinal cords in rabbits respectively.By Functool software,the normal ADC and FA in rabbit central nervous system were acquired in order to study their characteristics and patterns.Then based on rabbit anatomical features,appropriate segments of spinal cord were identified for experiment and observation.2.By random sampling,5-6 0.8m Ci125I particles were implanted at bilateral lamina above the 10 th thoracic vertebra in 8 rabbits in order to establish 125I plesioradiotherapy animal model.Dose distribution was planned before particle implantation,and exposure dose of spinal cord achieved 100（±5%）Gy based on the calculation of TPS,a treatment planning system.3.MRI scanning on the 10 th thoracic vertebra horizontal observation area was conducted before particle implantation,2w,4w,6w,8w,10 w,12w,4m,5m and 6m after implantation.T2 WI and DTI sequences were scanned respectively,and then the ADC and FA values of radioactive particle 125I in spinal cord were obtained.4.All rabbits were sacrificed 6m after particle implantation.Spinal cord tissues from observation area were extracted for pathological observation;HE staining as well as immunohistochemical staining of NF200 and CD31 were applied to detect spinal cord injuries.Result: 1.The average ADC and FA of rabbit brain were 0.87±0.09×10-3mm2/s and 0.23±0.09 respectively;the average ADC and FA of cervical cord were 1.06±0.16×10-3mm2/s and 0.55±0.08 respectively;the average ADC and FA of thoracic cord were 1.14±0.12×10-3mm2/s and 0.57±0.06;the average ADC and FA of lumbar cord were 1.22±0.13×10-3mm2/s and 0.61±0.06 respectively;the average ADC and FA of spinal cord of the 10 th thoracic vertebra were 0.589±0.039 and 1.149± 0.082× 10-3 mm2/s.2.By pathological observation from HE staining,part of the neurons in spinal gray matter with effective 125I radiation was injured or disappeared.Blood vessel endothelium was positive by CD31 staining.NF200 positive staining or expression was observed in neuron,nervous axon and nerve fiber bundle alignment area of white matter.3.ADC value of spinal cord tissue with effective radiation elevated gradually one month after radioactive particle implantation,and the value during observation period was higher than that before particle implantation（p<0.01）.However,FA value of above area 4 months after 125I implantation was lower than that before implantation.Conclusion: 1.The implantation of radioactive particle 125I（D90=100Gy）besides spinal canal was able to induce radioactive injuries in spinal cord;2.The observation of ADC and FA values from DTI sequence under certain conditions was able to discover the injuries in spinal cord;3.DTI sequence of magnetic resonance was a potentially effective method in detecting radioactive injuries in spinal cord. |
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