MR弛豫技术与双能X线吸收法评价大鼠骨质疏松的比较研究

Comparison between MR relaxometry techniques and dual-energy X-ray absorptiometry in evaluation of osteoporotic postmenopausal rats

目的探讨MR弛豫技术及参数与双能X线吸收法（DXA）对诊断大鼠骨质疏松模型的优劣。方法雌性3月龄大鼠30只，按完全随机化方法分为对照组和去势骨质疏松造模组（每组15只）。30只大鼠造模前及造模12周后分别行DXA测量，测量参数包括全身骨量（BMC）、全身骨密度（BMD）、左侧股骨骨密度（Hbmdl）；造模成型后，在MR1．5T成像系统下完成：（1）多回波快速梯度脉冲序列，分别以不同回波间隔测量T2^＊；（2）多回波快速SE序列测量T2图（T2map）；（3）SE序列测量T1map；（4）用两样本t检验分析对照组和实验组间各指标参数的差别，用Fisher检验筛选对骨质疏松作用有统计学意义的指标。最后分别提取2组大鼠的股骨做病理组织学检查。结果（1）病理组织学证实骨质疏松组造模成型；（2）成模后对照组、骨质疏松组间DXA的参数（BMC、BMD、Hbmdl）经Fisher检验，筛选出BMD为判别指标，其判别正确率为86．7％；（3）对照组和骨质疏松组之间所测得的2组MR弛豫数据值[T2＊1000、横向弛豫率（R2^＊）1000、T2^＊500、R2^＊。500、T2^＊400、R2^＊400、T2^＊300、R2‘300、T2’200、R2’200、T2’100、R2’100、T2map、R2map、T1map]作两样本t检验，t值分别为6．20、4．79、5．18、5．22、5．59、4．37、6．14、5．12、5．09、4．99、5．57、4．84、4．07、2．98、6，75，除R2mapP=0．07以外，其余P值均〈0．01，差异有统计学意义；（4）对A、B2组MR弛豫和双能DXA的17个参数（T2^＊1000，T2‘500，T2‘400，L‘300，T2‘200，T2。100，T2map，R2‘1000，R2’500，R2^＊400，R2^＊300，R2’200，R2‘100，T1map，BMC，BMD，Hbmdl）经Fisher检验，17个参数中T2map和T1map2个指标对骨质疏松的表达较佳，其判别正确率为100％。结论MR的T2map是骨质疏松的较佳判别指标，在MR弛豫技术的运用中，磁场的稳定性是重要的；而MR弛豫技术与DXA结合可更精确地诊断骨质疏松的程度。

Objective To evaluate MR relaxometry techniques and dual-energy X-ray absorptiometry （DXA） for the diagnosis of osteoporotic diseases in rats. Methods Thirty 3-month-old female rats were randomly divided （using completely randomized grouping method ） into two groups （each contained 15 rats）. Animals in group A without osteoporotic castration were included as normal controls, whereas osteoporotic castration was created in each animal in group B. Three parameters （BMC, BMD, Hbmdl） was measured for both groups by DXA at two time points, one immediately before the castration and another at the 12 th week after the castration. Then animals from the control group and the osteoporotic group went through the following three diagnostic procedures using a 1.5 T MR system： （ 1 ） A fast multi echo gradient echo （MEGRE） pulse train sequence with different inter-echo intervals （1000, 500, 400, 300, 200, 100） to obtain the T2 ＊ value. （2） A multi-echo fast spin echo sequence to obtain the T2 map. （3） A conventional spin-echo （CSE） sequence to obtain the T1 map. The statistical difference between group A and group B was tested by t-test to analyze parameters. And, the most significant parameter for diagnosis of osteoporotic diseases was picked out from all parameters by Fisher Sequential discriminant analysis. At the end of experiments, animals were killed and histopathological examination was performed on the femurs of animals from both control and osteoporotic groups. Results （ 1 ） Histopathological examination confirmed the presence of osteoporosis in all animals in group B. （2） BMD was picked out from 3 DXA parameters （BMC, BMD,Hbmdl） by fisher stepwise discriminant analysis, and its discriminant rates was 87. 6%. （3） All 2-sample t-test results（t =6.20, 4.79, 5. 18, 5.22, 5.59, 4.37, 6. 14, 5.12, 5.09, 4.99, 5.57, 4. 84, 4. 07, 2.98, 6. 75 individually） for MR relaxometry parameters （ T2 ＊ 1000, R2 ＊ 1000, T2 ＊ 500, R2 ＊ 500,T2^＊400, R2 ＊ 400,T2 ＊ 300,R2 ＊ 300,T2 ＊ 200, R2 ＊ 200,T2 ＊ 100,R2 ＊ 100, T2map, R2map, Tlmap） showed statistically significant differences between groups A and B （P =0. 01 for T2 ＊ map, P =0. 00 for all other parameters） except the R2map （P = 0. 07 ）. （4） Using fisher stepwise discrimination method in the analysis of 14 parameters of MR relaxometry techniques and 3 parameters of dual X-ray absorptiometry（ T2 ＊ 1000 ,T2 ＊ 500 ,T2 ＊ 400 ,T2 ＊ 300 ,T2 ＊ 200, T2 ＊ 100, T2map, R2 ＊ 1000, R2 ＊ 500, R2 ＊ 400, R2 ＊ 300, R2 ＊ 200, R2 ＊ 100, T1 map, BMC, BMD, Hbmdl ）, we found that the most significant difference was from the T2 map and T1 map. Conclusions The MR relaxometry parameter-T2 map in the present study is shown to be appropriate parameter for the diagnosis of osteoporotic diseases, and stability of magnetic field plays an important role in this process. It would be the optimal method to make a diagnosis of osteoporotic diseases with both MR relaxometry and DXA technological means.