Association Of Two-point Dixon Technique With Micro-CT In Dynamical Evaluation Of Bone Strength Of Osteoporosis Rats

Background and Objective: To investigate the regular alteration of bone strength and constitution of osteoporotic rats examined by two-point Dixon method and Micro-CT,comparing with bone biomechanical test and histopathology, so as to study the advantage of two means above.Materials and Methods: Forty 6-month old femal SD rats were randomly divided into ovariectomized group(OVX, n=20) and sham-operated group(SHAM, n=20). Bone marrow fat fraction(FF) were detected by two point Dixon method on 3 Tesla at the baseline and the 4th,8th,12 th week after operation. With rats killed by excessive anesthesia, the forth and fifth lumbar vertebrae were attained and prepared for: 1, Micro-CT scanning, bone mineral density(BMD), bone micro-architecture parameters and three-dimensional structural reconstruction; 2, bone biomechanical test; 3, HE staining.Results: Compared with those at baseline,FF value in OVX group was gradually increasing(P<0.05). The appearance of difference in FF was earlier than the changes of BMD(8th week, P<0.05) and synchronized with the alteration of trabecular separation(Tb.Sp), bone volume fraction(BVF) and structure model index(SMI). Trabecular thickness(Tb.Th) did not reveal statistical difference versus those at baseline until the 8th week, with trabecular number(Tb.N) no statistical difference. In the SHAM group, there were no significant differences in the subsequent FF and Micro-CT parameters(P>0.05). Bone marrow histology results showed that bone marrow adipocyte density increased significantly at the 4th week(P<0.05). At the end of the 12 th week, bone marrow adipocyte density and diameter,compared with those in SHAM group, increased by 55.1%, 32.6% respectively(P<0.01). Bone biomechanical features of the lumbar spine appeared statistical difference(P<0.05) at the 4th week in elestic modulus of OVX versus SHAM. Other parameters,including maximum failure load and failure strength changed significantly at the 8th week(P<0.05). In OVX group,FF showed a significantly negative correlation with BMD, BVF, break load, break stress, elastic modulus respectively,with a weaker negative correlation between FF and Tb.Th. FF was positively correlated with Tb.Sp, SMI, bone marrow adipocyte density and diameter.Conclusion:1 Two point Dixon technique and Micro-CT were able to quantitatively analyze the regularity of the changes of FF and bone microstructure in the process of OP.2 Combined with mechanical and histological results, it revealed that the increase of adipose tissue in bone marrow weakened bone strength and bone quality.3 FF changes detected by two point Dixon MR technique were earlier than those in BMD, and partially synchronized with the changes in the microarchitecture of trabecular bone.4 FF and bone microarchitecture parameters,with influence and independence in one another,had essential value in the changes of bone quality. Association of Dixon and Micro-CT might be comprehensive and accurate assessment tools of OP,and brought a new perspective in subsequent research.