比较双能X线吸收测量仪与显微CT显示不同时期去卵巢大鼠胫骨骨量和微结构的特点

目的 应用和比较双能X线吸收测量仪(DXA)与显微CT(μCT)观察不同时期去卵巢(OVX)大鼠胫骨骨量及骨微结构的改变特点.方法 40只7个月龄SD大鼠以简单随机抽样方法分为OVX组和假手术(SHAM)组,每组20只,于手术后3周及15周分别处死10只.处死后剥离左侧胫骨行DXA扫描,从胫骨近端开始将胫骨按其长度等分为7个感兴趣区(ROI1～7),计算获得各区域及总体骨密度值.然后将胫骨以4%多聚甲醛固定24 h,10%蔗糖溶液洗涤后行μCT扫描,选取距生长板远端2.5 mm、层厚0.4 mm骨组织为皮质骨感兴趣区域,选取距生长板远端0.7 mm、层厚1.2 mm骨组织为松质骨感兴趣区域行三维重组.获取二维最大密度投射图像及三维结构图像,并对感兴趣区的皮质骨和松质骨进行定量分析.所得结果以独立样本t检验进行比较.结果 3周时,OVX组大鼠胫骨ROI1区骨密度为(0.2346±0.0280)g/cm2,显著低于SHAM组(0.2660±0.0199)g/cm2,(P＜0.05);15周时,OVX组大鼠胫骨ROI1区及ROI2区骨密度分别为(0.2527±0.0161)及(0.1862±0.0052)g/cm2,较SHAM组(0.2793±0.0229)及(0.1986±0.0102)g/cm2有明显下降(P值均＜0.01).3周时,OVX组大鼠骨皮质骨面积、骨髓腔面积、截面总面积、截面惯性矩分别为(0.4306±0.1308)、(10.31±1.98)、(10.74±2.05)mm2和(4.101±0.726)mm4,均明显高于SHAM组(0.3138±0.0621)、(8.44±1.25)、(8.75±1.26)mm2和(3.485±0.373)mm4(P值均＜0.05).至15周时,除皮质骨平均厚度OVX组大鼠为(0.0235±0.0024)mm,低于SHAM组(0.0285±0.0052)mm外(P＜0.05),其余各参数差异均无统计学意义.15周OVX组大鼠左侧胫骨骨丢失敏感区域内皮质骨平均厚度和皮质骨面积为(0.0235±0.0024)mm及(0.2528±0.0367)mm2,较3周OVX组大鼠(0.0377±0.0098)mm及(0.4306±0.1308)mm2有明显下降(P值均＜0.05).SHAM组,15周大鼠骨内径周长、骨外径周长和截面惯性矩分别为(13.38±0.54)、(13.59±0.56)mm和(4.096±0.364)mm4,与3周大鼠(12.41±0.74)、(12.63±0.75)mm和(3.485±0.373)mm4相比差异有统计学意义(P值均＜0.05).3周时,OVX组大鼠体积骨密度、组织骨密度、骨体积分数和骨小梁数量分别为(288.2±48.2)、(604.5±45.3)mg/mm3和(25.1±5.1)%、(6.04±2.94)mm-1,显著低于SHAM组(408.4±51.6)、(686.7±40.0)mg/mm3和(33.6±4.1)%、(9.85±2.83)mm-1(P值均＜0.05),结构模型指数、骨小梁间隔则分别为3.09±0.27及(0.186±0.129)mm,明显高于SHAM组2.63±0.21及(0.078±0.038)mm(P值分别＜0.01和＜0.05).至15周时,OVX组体积骨密度、骨体积分数、骨小梁数量、结构模型指数和骨小梁间隔分别为(271.2±50.9)mg/mm3、(21.6±5.2)%、(3.21±1.92)mm-1、3.11±0.36、(0.370±0.215)mm与SHAM组(389.8±77.0)mg/mm3、(30.9±6.0)%、(7.44±3.53)mm-1、2.58±0.36、(0.141±0.104)mm的差异均有统计学意义(P值均＜0.01),但组织骨密度差别消失.15周OVX组大鼠组织骨密度、骨小梁厚度、骨小梁数量、骨小梁间隔分别为(691.0±36.7)mg/mm3、(0.040±0.009)mm、(3.21±1.92)mm-1、(0.370±0.215)mm较3周OVX大鼠(604.5±45.3)mg/mm3、(0.030±0.002)mm、(6.04±2.94)mm-1、(0.186±0.129)mm差异有统计学意义(P值均＜0.05).结论 DXA是一种应用广泛的骨密度测量方法,但可能无法及时准确地反映出大鼠去卵巢后骨量的变化.μCT是研究骨密度和骨微结构细微改变的较合适的方法.

The analysis of bone mass and microarchitecture in ovariectomized rat by dual energy X-ray absorptiometry and microCT

Objective To observe and compare the changes of bone mass and microarchitecture in ovariectomized rat left tibia by dual energy X-ray absorptiometry(DXA)and microCT(μCT).Methods Forty seven-month-old SD rats were randomly divided into ovariectomized(OVX)and sham-operated(SHAM)groups,twenty in each group.After killed at 3 weeks and 15 weeks post-surgery,DXA scanning were performed in the left tibia in vitro.The images of left tibia were divided into seven isometric regions of interest(ROI1-7).When analysis finished,bone density(BD)of each ROI and the total bone were determined.The samples were fixed by 4% paraformaldehyde and then placed in the specimen holder filled with deionized water.The sensitive regions for bone mass changes were selected for scanning by Fluro.After scanning,the regions involving 0.4mm slice thickness and 2.5mm distance far end from tibial growth plate were selected as the ROI of cortical bone analysis.The regions selected as ROI of cancellous analysis,were involved in 1.2mm slice thickness and 0.7mm distance at the far end from tibial growth plate.After three dimension reconstruction.2D images of the maximum intensity projection and pictures of 3D microarchitecture were obtained.and BD and microarchitectural parameters were quantitatively identified.All data was statistically processed with SPSS for Windows.Results At the 3rd week,BD of ROI1 in rat left tibia in OVX(0.2346±0.0280)g/cm2 was much lower than that(0.2660±0.01990)g/cm2 in SHAM(P＜0.05).While at the 15th week,BD of ROI1(0.2527±0.0161)and ROI2(0.1862±0.0052)g/cm2 in OVX were both lower than SHAM(0.2793±0.0229)and(0.1986±0.0102)g/cm2 respectively,P＜0.01 for both).Compared wim SHAM ratcortical area(Ct-Ar)=(0.3138±0.0621)mm2,marrow area(Ma-Ar)=(8.44±1.25)mm2,total area(T-Ar)=(8.75±1.26)mm2,moment of inertia(Mm)=(3.485±0.373)mm4],there were significant increases in Ct-Ar(0.4306±0.1308)mm2,Ma-Ar(10.31±1.98)mm2,T-Ar(10.74±2.05)mm2,and Mm(4.101±0.726)mm4 in OVX mice at the 3rd week(P＜0.05 for all).While at the 15th week,only cortical thickness(Ct-Th)(0.0235±0.0024)mm showed a decrease in OVX group(P＜0.05).In OVX group,Ct-Th(0.0235±0.0024)mm and Ct-Ar(0.2528±0.0367)mm at 15 weeks were lower than thatCt-Th=(0.0377±0.0098)mm,Ct-Ar=(0.4306±0.1308)mm2 at 3 weeks(P＜0.01 for both)].In SHAM group,inner perimeter(In-Pm)(13.38±0.54)mm,outer perimeter(Ot-Pm)(13.59±0.56)mm and Mm(4.096±0.364)mm4 at 15 weeks were higher than thatIn-Pm=(12.41±0.74)mm,Ot-Pm=(12.63±0.75)mm,Mm=(3.485±0.373)mm4 at 3 weeks(P＜0.01 for all)].OVX rats had much lower volume BD(vBD)(288.2±48.2)mg/mm3,tissue BD(tBD)(604.5±45.3)mg/mm3,bone volume fraction(BVF)(25.1±5.1)%,and trabecular mumeer(Tb-N)(6.04±2.94)mm-1(P＜0.01 for all),but higher structure model index(SMI)3.09±0.27 and trabecular separation(Tb-Sp)(0.186±0.129)mm than SHAM 2.63±0.21 and(0.078±0.038)mm respectively at the 3rd week(P＜0.01 and P＜0.05 respectively).At the 15th week,vBD(271.2±50.9)mg/mm3,BVF(21.6±5.2)%and Tb-N (3.21±1.92)mm-1 in OVX were still lower than SHAMvBD=(389.8±77.0)mg/mm3,BVF=(30.9±6.0)%,Tb-N=(7.44±3.53)mm-1 respectively(P＜0.01 for all)],SMI 3.11±0.36 and Tb-Sp(0.370±0.215)mm in OVX were also higher than SHAM 2.58±0.36 and(0.141±0.104)mm(P＜0.01 for both),but no significant difference of tBD could be found.In OVX group.the scores of tBD(691.0±36.7)mg/mm,Tb-Th(0.040±0.009)mm,Tb-N(3.21±1.92)mm-1,Tb-Sp(0.370±0.215)mm in the 15th week were higher than thattBD=(604.5±45.3)mg/mm,Tb-Th=(0.030±0.002)mm,Tb-N=(6.04±2.94)mm-1,Tb-Sp=(0.186±0.129)mm respectively]in the 3rd week (P＜0.05 for all),while there were no differences between the 3rd and the 15th week in SHAM group.Conclusions DXA is weak in detecting the tiny changes of BD though it is convenient and non-invasive.μCT is suitable to detect the changes of bone mass and microarchitecture.