Mixed-effects models,also called random-effects models,are a regression type of analysis which enables the analyst to not only describe the trend over time within each subject,but also to describe the variation among ...Mixed-effects models,also called random-effects models,are a regression type of analysis which enables the analyst to not only describe the trend over time within each subject,but also to describe the variation among different subjects.Nonlinear mixed-effects models provide a powerful and flexible tool for handling the unbalanced count data.In this paper,nonlinear mixed-effects models are used to analyze the failure data from a repairable system with multiple copies.By using this type of models,statistical inferences about the population and all copies can be made when accounting for copy-to-copy variance.Results of fitting nonlinear mixed-effects models to nine failure-data sets show that the nonlinear mixed-effects models provide a useful tool for analyzing the failure data from multi-copy repairable systems.展开更多
目的应用磁共振体素内不相干运动(intravoxel incoherent motion,IVIM)-扩散加权成像(diffusion-weighted imaging,DWI)序列联合定量非对称回波的最小二乘估算法迭代水脂分离序列(iterative decomposition of water and fat with echo a...目的应用磁共振体素内不相干运动(intravoxel incoherent motion,IVIM)-扩散加权成像(diffusion-weighted imaging,DWI)序列联合定量非对称回波的最小二乘估算法迭代水脂分离序列(iterative decomposition of water and fat with echo asymmetry and least squares estimation quantification sequence,IDEAL-IQ)测量早期活动性中轴型脊柱关节炎患者骶髂关节微循环灌注及脂肪含量变化,探讨其对早期活动性中轴型脊柱关节炎患者骶髂关节病变的临床诊断价值。方法37例早期活动性中轴型脊柱关节炎患者,均行磁共振常规T_(1)WI、T_(2)WI FSPD序列扫描,其中常规序列显示骶髂关节骨髓水肿为强直性脊柱炎阳性者29例为阳性组,强直性脊柱炎阴性者8例为阴性组,同期体检健康者20例为对照组;应用磁共振IVIM-DWI、IDEAL-IQ序列分别测量3组骶髂关节标准表观扩散系数(apparent diffusion coefficient,D_(stand))、慢速表观扩散系数(slow apparent diffusion coefficient,D_(slow))、快速表观扩散系数(fast apparent diffusion coefficient,D_(fast))、灌注分数(pseudo-diffusion coefficient,f)、骨髓脂肪分数(fat fraction,FF);绘制ROC曲线,评估磁共振IVIM-DWI、IDEAL-IQ序列D_(stand)、D_(slow)、D_(fast)、f、FF对早期活动性中轴型脊柱关节炎患者骶髂关节病变的诊断效能。结果IVIM-DWI序列显示,阳性组D_(stand)[(0.89±0.35)×10^(-3)mm^(2)/s]、D;[(0.95±0.27)×10^(-3)mm^(2)/s]、f(0.28±0.03)均高于阴性组[(0.61±0.12)×10^(-3)mm^(2)/s、(0.87±0.22)×10^(-3)mm^(2)/s、0.26±0.04]、对照组[(0.59±0.04)×10^(-3)mm^(2)/s、(0.73±0.17)×10^(-3)mm^(2)/s、0.25±0.02](P<0.05),阴性组均高于对照组(P<0.05);阳性组D;[(98.86±26.94)×10^(-3)mm^(2)/s]低于阴性组[(122.92±12.47)×10^(-3)mm^(2)/s]、对照组[(133.28±5.69)×10^(-3)mm^(2)/s](P<0.05),阴性组低于对照组(P<0.05);IDEAL-IQ序列显示,阳性组FF(38.38±13.99)低于阴性组(67.15±8.51)、对照组(62.38±8.44)(P<0.05),阴性组高于对照组(P<0.05)。D_(stand)、D_(slow)、D_(fast)、f、FF的最佳截断值分别为0.74×10^(-3)mm^(2)/s、0.67×10^(-3)mm^(2)/s、103.71×10^(-3)mm^(2)/s、0.27、57.71时,预测早期活动性中轴型脊柱关节炎患者骶髂关节病变的AUC分别为0.77(95%CI:0.65~0.86,P<0.001)、0.81(95%CI:0.70~0.89,P<0.001)、0.78(95%CI:0.67~0.87,P<0.001)、0.64(95%CI:0.52~0.75,P=0.037)、0.98(95%CI:0.91~0.99,P<0.001),灵敏度分别为65.52%、93.10%、55.17%、37.39%、96.55%,特异度分别为90.48%、61.90%、90.48%、88.10%、88.10%。结论磁共振IVIM-DWI、IDEAL-IQ序列可定量分析早期活动性中轴型脊柱关节炎患者骶髂关节微循环灌注及脂肪含量的变化,D_(stand)、D_(slow)、D_(fast)、FF对早期活动性中轴型脊柱关节炎患者骶髂关节病变有较高诊断价值。展开更多
文摘Mixed-effects models,also called random-effects models,are a regression type of analysis which enables the analyst to not only describe the trend over time within each subject,but also to describe the variation among different subjects.Nonlinear mixed-effects models provide a powerful and flexible tool for handling the unbalanced count data.In this paper,nonlinear mixed-effects models are used to analyze the failure data from a repairable system with multiple copies.By using this type of models,statistical inferences about the population and all copies can be made when accounting for copy-to-copy variance.Results of fitting nonlinear mixed-effects models to nine failure-data sets show that the nonlinear mixed-effects models provide a useful tool for analyzing the failure data from multi-copy repairable systems.
文摘目的应用磁共振体素内不相干运动(intravoxel incoherent motion,IVIM)-扩散加权成像(diffusion-weighted imaging,DWI)序列联合定量非对称回波的最小二乘估算法迭代水脂分离序列(iterative decomposition of water and fat with echo asymmetry and least squares estimation quantification sequence,IDEAL-IQ)测量早期活动性中轴型脊柱关节炎患者骶髂关节微循环灌注及脂肪含量变化,探讨其对早期活动性中轴型脊柱关节炎患者骶髂关节病变的临床诊断价值。方法37例早期活动性中轴型脊柱关节炎患者,均行磁共振常规T_(1)WI、T_(2)WI FSPD序列扫描,其中常规序列显示骶髂关节骨髓水肿为强直性脊柱炎阳性者29例为阳性组,强直性脊柱炎阴性者8例为阴性组,同期体检健康者20例为对照组;应用磁共振IVIM-DWI、IDEAL-IQ序列分别测量3组骶髂关节标准表观扩散系数(apparent diffusion coefficient,D_(stand))、慢速表观扩散系数(slow apparent diffusion coefficient,D_(slow))、快速表观扩散系数(fast apparent diffusion coefficient,D_(fast))、灌注分数(pseudo-diffusion coefficient,f)、骨髓脂肪分数(fat fraction,FF);绘制ROC曲线,评估磁共振IVIM-DWI、IDEAL-IQ序列D_(stand)、D_(slow)、D_(fast)、f、FF对早期活动性中轴型脊柱关节炎患者骶髂关节病变的诊断效能。结果IVIM-DWI序列显示,阳性组D_(stand)[(0.89±0.35)×10^(-3)mm^(2)/s]、D;[(0.95±0.27)×10^(-3)mm^(2)/s]、f(0.28±0.03)均高于阴性组[(0.61±0.12)×10^(-3)mm^(2)/s、(0.87±0.22)×10^(-3)mm^(2)/s、0.26±0.04]、对照组[(0.59±0.04)×10^(-3)mm^(2)/s、(0.73±0.17)×10^(-3)mm^(2)/s、0.25±0.02](P<0.05),阴性组均高于对照组(P<0.05);阳性组D;[(98.86±26.94)×10^(-3)mm^(2)/s]低于阴性组[(122.92±12.47)×10^(-3)mm^(2)/s]、对照组[(133.28±5.69)×10^(-3)mm^(2)/s](P<0.05),阴性组低于对照组(P<0.05);IDEAL-IQ序列显示,阳性组FF(38.38±13.99)低于阴性组(67.15±8.51)、对照组(62.38±8.44)(P<0.05),阴性组高于对照组(P<0.05)。D_(stand)、D_(slow)、D_(fast)、f、FF的最佳截断值分别为0.74×10^(-3)mm^(2)/s、0.67×10^(-3)mm^(2)/s、103.71×10^(-3)mm^(2)/s、0.27、57.71时,预测早期活动性中轴型脊柱关节炎患者骶髂关节病变的AUC分别为0.77(95%CI:0.65~0.86,P<0.001)、0.81(95%CI:0.70~0.89,P<0.001)、0.78(95%CI:0.67~0.87,P<0.001)、0.64(95%CI:0.52~0.75,P=0.037)、0.98(95%CI:0.91~0.99,P<0.001),灵敏度分别为65.52%、93.10%、55.17%、37.39%、96.55%,特异度分别为90.48%、61.90%、90.48%、88.10%、88.10%。结论磁共振IVIM-DWI、IDEAL-IQ序列可定量分析早期活动性中轴型脊柱关节炎患者骶髂关节微循环灌注及脂肪含量的变化,D_(stand)、D_(slow)、D_(fast)、FF对早期活动性中轴型脊柱关节炎患者骶髂关节病变有较高诊断价值。
