Study On Rabbit Model Of Bone Marrow Adiposis Induced By Quantitative Radiotherapy Based On Magnetic Resonance Q-dixon And Histo Sequences

Objective:The purpose of this study was to establish a rabbit model of lumbar bone marrow steatosis induced by 6mvx ray irradiation,and to explore the feasibility and diagnostic value of HISTO sequence and Q-dixon sequence in quantifying bone marrow proton density fat fraction（FF）of rabbit lumbar bone marrow.Materials and methods:1.39 New Zealand white rabbits were randomly divided into control group（n=4）,experimental group（n=30）and pre experiment（n=5）to study the tolerance of New Zealand white rabbits to 6MV X-ray radiation dose.At the same time,the experimental group was divided into 2gy dose group（n=6）,4Gy dose group（n=6）,6gy dose group（n=6）,8Gy dose group（n=6）and 10GY dose group（n=6）according to the different doses of radiotherapy.The rabbits were slowly injected with 3%Pentobarbital Sodium through ear vein.After the corneal reflex was dull,the pain reflex disappeared,the muscle tension decreased and the breathing remained stable,the rabbits were placed on the linear accelerator treatment bed in prone position.Methods:the medical linear accelerator of MEDA,Sweden,was used.6MV high-energy X-ray was used to irradiate the lumbar spine,thoracic spine and other areas.In the experimental group,2gy,4Gy,6gy,8Gy and 10GY dose groups were given 2gy,4Gy,6gy,8Gy and 10GY single dose irradiation respectively.All the animals in the experimental group were only irradiated once,while the rabbits in the control group were fed normally without intervention.2.The rabbits in the experimental group and the control group were selected for MRI scanning every week.Siemens 3.0T prism MRI and special rabbit coil were used to scan and collect the sagittal images of lumbar vertebrae in experimental group and control group.Including t1-vibe sequence,Q-dixon sequence and HISTO sequence.After scanning,7 lumbar vertebrae were separated one by one with bone biting forceps.L5 and L6 vertebrae were examined by pathology.The area of fat vacuoles in bone marrow was quantified by Image J software.The remaining five lumbar bone marrow tissues were taken out and sent to Guangxi test and analysis research center to quantify the fresh lumbar vertebra fat content（FLVFC）by acid hydrolysis method.FF_Histo value and FF_Q-dixonvalue were obtained automatically and manually through the post-processing software of syngo.via workstation.The FF_Q-dixonvalue of each vertebral body was measured three times,and the average value was taken as the result.3.Spss24.0 statistical software（IBM,USA）was used for data analysis.All data were tested for normality by Shapiro Wilk method,and the data in the experimental group conformed to normal distribution;Paired t-test was used to compare the FF_Histo values of L5 and L6vertebrae obtained from HISTO sequences of all experimental animals;Random block design was used to compare the Q-dixon values of L4,L5 and L6 vertebrae in all experimental animals.The relationship among the fat content（FLVFC）,FF_Q-dixon value,FF_Histo value and the area of fat vacuoles in fresh lumbar bone marrow was studied by person correlation.The correlation coefficient r>0.700 was highly correlated.Results:1.The results of pathological sections of lumbar vertebrae in white rabbits showed that the changes of lumbar bone marrow obtained by different doses of irradiation were similar,and the degree of fatty bone marrow increased with the increase of irradiation dose.On the15th day after radiotherapy,the degree of lumbar bone marrow adiposis in each group reached the maximum.With the increase of radiation dose,he staining microscope observed that the area of bone marrow fat vacuoles was larger and larger,and the shape of vacuoles changed irregularly.2.There was no significant difference in FF_Histo value between L5and L6（t=1.227,P=0.232）.The FF_Q-dixon value of lumbar spine based on Q-dixon sequence had no significant difference among the three vertebrae L4,L5 and L6（F=0.038,P=0.962）.3.There was a high correlation between FF_Histo value and FF_Q-dixon value（r=0.942,P<0.001）;There was a high correlation between FF_Histo value and FLVFC（r=0.706,P<0.001）;There was no correlation between FF_Histo value and bone marrow fat vacuole area（r=0.173,P=0.418）;There was a high correlation between FF_Q-dixon and FLVFC（r=0.758,P<0.001）;There was no correlation between FF_Q-dixon value and bone marrow fat vacuole area（r=0.131,P=0.542）;There was no correlation between bone marrow fat vacuole area and FLVFC（r=0.091,P=0.671）.Conclusion:1.In this study,we successfully established the rabbit model of lumbar bone marrow steatosis by 6MV X-ray irradiation of bone marrow,and provided reference value for the follow-up related research.2.This study found that there was no significant difference in the fat content of multiple lumbar vertebrae,which is expected to be used to evaluate the whole lumbar steatosis by measuring the fat content of a single vertebral body.3.This study found that the calculation of fat area in pathological section is based on the number of fat cells in the tissue,not the actual triglyceride content,which cannot be used as the reference standard of MRI.4.This study confirmed that Q-dixon and HISTO sequences can accurately quantify the fat content of lumbar bone marrow,and effectively and accurately evaluate the changes of bone marrow in cancer patients during radiotherapy.Q-dixon and HISTO sequences can be used to evaluate the changes of bone marrow steatosis in cancer patients during radiotherapy.