QCT骨密度测量的质量控制及意义

目的目前国内对QCT骨密度测量的质量控制研究较少，本文介绍了QCT骨密度测量的准确度、精密度试验方法和意义。方法使用东芝CT机自带体模和软件为测量工具，测量四川大学华西骨质疏松研究中心等研制的QCT骨体模（称四川体模）的骨密度值。四川体模固定于15cm深的水浴中模拟人体腰椎，东芝体模置于水浴容器与扫描床面之间，按照人腰椎QCT骨密度测量相同的条件和方法进行操作，每日1次对测量体模连续测量25日，计算SD和CV，分别以25次测量125d25次测量／1d基线作3m的shewhart图。结果测量四川体模从小到大三管骨密度分别的准确度误差为-60．4％、-39．1％和-13．6％，其分别的校正系数为2．69、1．64、1．15，相关系数为0．9966，回归方程Y=35．6＋0．958X（X为测量骨密度，Y为校正后骨密度）。本型QCT机骨密度测量的25次／1d及25次，25d精密度误差分别为1．25～5．54％和1．98～7．87％。25次125d的精密度误差要大于25次，d，显示机器一日内精密度误差变化小，随时间延长其变化增大。以25次125d的结果为基线绘制的shewhart图优于25次/d。结论一切QCT骨密度测量都应进行质量控制，准确度必须予以校正，精密度试验应在此基础上进行。这样结果才真实、科学、可靠并具有可比性。

Significance and quality control of bone densitometry by QCT

Objective To introduce QCT and its significance, accuracy and precision in bone marrow density(BMD)measurement.Methods The BMD of the QCT bone phantom made by the West-China Osteoporosis Study Center of Sichuan University (Sichuan phantom) was tested using the bone phantom and software coming with a Toshiba CT machine.The Sichuan phantom was put 15 cm under the water simulating human vertebrae and the Toshiba phantom between the water container and the scanning table.Measurement was conducted once daily for 25 days under the same condition as that for human being.SD and CV were calculated and Shewhart chart was plotted.Results The accuracy errors of the three sections measured from large to small in the Sichuan phantom were -60.4%,-39.1% and -13.6%,their correction coefficients were 2.69,1.64,1.15,and the relative coefficient were 0.9966;the regression equation was Y=35.6 0.958X.Precision error of the 25 times/one day and 25times/25days in bone densitometry by this QCT was 1.25%-5.54% and 1.98%-7.87% respectively.Thus the variation of precision error was small in one day,but increased with the time.Polt baseline of shewhart chart of 25times/25days is better than that of the 25times/one day.Conclusions Quality control is necessary in all BMD measurement by QCT.The accuracy errors must be corrected followed by precision experiment to ensure a true,scientific and reliable result.