定量CT与DXA测量近段股骨面积骨密度及T值的比较研究

Comparison between QCT-derived and DXA-derived areal bone mineral density and Tscores at the proximal femur

目的研究定量CT(QCT)测量近段股骨面积骨密度准确性和可重复性,并对QCT和DXA近段股骨测量结果及T值进行比较性研究。方法来自前瞻性城乡流病研究(PURE)项目的 103名女性和49名男性同一天进行髋关节QCT和DXA扫描。对观察者间及观察者内CTXA测量结果进行分析,为了减小QCT和DXA因体模不同造成的误差,用Mindways回归方程对QCT测量结果进行换算,并运用Bland-Altman分析及线性回归分析比较CTXA和DXA结果的差异和相关性。结果 QCT全髋关节(TH)与股骨颈(FN)的面积骨密度均低于DXA测量结果,分别为21.0%和17.8%。而QCT测量值用Mindways回归方程换算后,减小了与DXA测量结果的差异。FN及TH的观察者内及观察者间CTXA测量误差分别为0.070和0.024 g/cm2及0.030和0.012 g/cm2,与DXA重复测量误差相近。经过Mindways校准方程换算后,Bland-Altman分析显示CTXA和DXA的TH的偏倚为-0.002(SD=0.05)g/cm2,而FN为-0.005(SD=0.06)g/cm2。CTXA测量女性近段股骨的T值与DXA的T值相关性很好,FN的R2=0.809,TH的R2=0.883。结论 CTXA测量的髋关节a BMD与DXA的测量的准确性相近,经过合适的调整,CTXA能够得出类似DXA的a BMD,对于老年女性其获得的全髋关节的T值与DXA结果相关性很好,从而能够用于诊断骨质疏松。

Objective To study the precision and the reproduction of quantitative computed tomography （QCT） in measuring the areal bone mineral density of the proximal femur, and to compare the T score results between QCT measurement and DXA measurement. Methods Both hip QCT and DXA were performed on the same day in 103 females and 49 males recruited from the Prospective Urban Rural Epidemiology （PURE） study. The inter- and intra-observer variations of CTXA measurement were assessed. In order to reduce the bias from the model, the results were recalculated using a Midways equation, and the difference and correlation between CTXA and DXA results were analyzed using Bland-Altman analysis and linear regression analysis. Results QCT-derived aBMD from the total hip （TH） and the femoral neck （FN） was lower than the DXA-derived aBMD at the both sites by 21.0% and 17.8% , respectively. The interand intra-observer variations of CTXA were 0. 07 and 0. 024 g/cm^2 in FN, and 0. 03 and 0. 012 g/cm^2 in TH, respectively, which were comparable to the DXA inter-scan variations. Bland-Altman analysis showed that the bias of TH and FN was - 0. 002 （ SD = 0.05） g/cm^2 and - 0. 005 （ SD = 0. 06） g/cm^2 , respectively. The CTXA- derived T scores were highly correlated with DXA-derived T scores in females. And R2 values were 0. 809 for FN and 0. 883 for TH, respectively. Conclusion CTXA shows good agreement with DXA in the measurement of aBMD at the proximal femur after suitable adjustment. The T score obtained from QCT is well correlated with that from DXA. Therefore QCT can be used for the diagnosis of osteoporosis.