Measurement of Liver Stiffness Using Shear Wave Elastography in a Rat Model: Factors Impacting Stiffness Measurement with Multiple- and Single-Tracking-Location Techniques

The clinical use of elastography for monitoring fibrosis progression is challenged by the subtle changes in liver stiffness associated with early-stage fibrosis and the comparatively large variance in stiffness estimates provided by elastography. Single-tracking-location (STL) shear wave elasticity imaging (SWEI) is an ultrasound elastography technique previously found to provide improved estimate precision compared with multiple-tracking-location (MTL) SWEI. Because of the improved precision, it is reasonable to expect that STL-SWEI would provide improved ability to differentiate liver fibrosis stage compared with MTL-SWEI. However, this expectation has not been previously challenged rigorously. In this work, the performance of STL- and MTL-SWEI in the setting of a rat model of liver fibrosis is characterized, and the advantages of STL-SWEI in staging fibrosis are explored. The purpose of this study was to determine what advantages, if any, arise from using STL-SWEI instead of MTL-SWEI in the characterization of fibrotic liver. Thus, the ability of STL-SWEI to differentiate livers at various METAVIR fibrosis scores, for ex vivo postmortem measurements, is explored. In addition, we examined the effect of the common confounding factor of fluid versus solid boundary conditions in SWEI experiments. Sprague-Dawley rats were treated with carbon tetrachloride over several weeks to produce liver disease of varying severity. STL and MTL stiffness measurements were performed ex vivo and compared with the METAVIR scores from histological analysis and the duration of treatment. A strong association was observed between liver stiffness and weeks of treatment with the liver toxin carbon tetrachloride. Direct comparison of STL- and MTL-SWEI measurements revealed no significant difference in ability to differentiate fibrosis stages based on SWEI mean values. However, image interquartile range was greatly improved in the case of STL-SWEI, compared with MTL-SWEI, at small beam spacing.     

实时剪切波弹性成像技术评估跟腱急性闭合性损伤

目的 探讨采用实时剪切波弹性成像（SWE）技术根据跟腱硬度评价急性跟腱闭合性损伤的临床价值。方法 对49例跟腱急性闭合性损伤患者行高频超声及实时SWE检查,获得患侧和健侧跟腱的杨氏模量值和剪切波速度（SWV）,比较完全断裂跟腱、不完全断裂跟腱与正常侧跟腱的差异。结果 经手术证实跟腱完全断裂患者36例,高频超声均诊断正确;经MRI证实,跟腱不完全断裂13例,其中超声正确诊断10例,漏诊3例。跟腱完全断裂组、跟腱部分断裂组和正常跟腱组跟腱杨氏模量值分别为（130.02±24.64） kPa、（281.08±84.36） kPa和（546.51±48.52） kPa,SWV分别为（6.23±1.04） m/s、（9.05±0.97） m/s和（14.33±1.41） m/s,3组间总体差异和两两比较差异均有统计学意义（P均<0.05）。结论 超声弹性成像可以作为高频超声诊断跟腱急性闭合性损伤的有效补充。     

超极速脉搏波技术在代谢综合征病人动脉粥样硬化中的应用价值

目的探讨超极速脉搏波( ufPWV)技术在代谢综合征( MS)病人动脉粥样硬化中的应用价值。方法回顾性选取 2021年 1月至 2021年 12月秦皇岛市第四医院 MS病人 150例作为病例组,根据颈动脉内 -中膜厚度( IMT)将病例组分为 MSⅠ组: IMT正常( <1.0 mm)病人 50例; MSⅡ组: IMT增厚( 1.5 mm>IMT≥1.0 mm)病人 50例; MSⅢ组:有斑块( IMT厚度 ≥1.5 mm)病人 50例;另选取同期健康体检者 50例作为对照组。采用 ufPWV技术检测并比较四组颈动脉脉搏波指标［收缩起始时脉搏波传导速度( PWV-BS)、收缩结束时脉搏波传导速度( PWV-ES)］并采用受试者操作特征( ROC)曲线分析上述指标对动脉粥样硬化的诊断价值。结果病例组 PWV-BS、PWV-ES高于对照组(,6.85±2.14比 4.93±1.60、10.86±3.65比 6.34±2.11,均 P<0.001); MSⅢ组 PWV-BS、PWV-ES>MSⅡ组>MSⅠ组( 8.08±1.81比 6.78±1.46比 5.69±1.24、12.80±2.39比 10.87±2.04比 8.91±1.66,均 P< 0.001); PWV-BS、PWV-ES与身体质量指数( BMI)、舒张压( DBP)、收缩压( SBP)、总胆固醇( TC)、三酰甘油( TG)、低密度脂蛋白胆固醇(LDL-C)、空腹血糖( FBG)、空腹胰岛素( FINS)呈正相关,与高密度脂蛋白胆固醇(HDL-C)呈负相关(P<0.05); PWV-BS、 PWV-ES高水平的 MS病人发生动脉粥样硬化的风险分别是低水平病人的 2.303倍、 1.962倍, 95%CI分别为( 1.70,3.12)、(1.50,2.58);当PWV-BS>6.20 m/s时, MS病人发生动脉粥样硬化的 AUC为 0.75;PWV-ES>10.21 m/s时,诊断 MS病人发生动脉粥样硬化的 AUC为 0.77;两者联合诊断 MS病人发生动脉粥样硬化的 AUC为 0.92,95%CI为( 0.86,0.96)灵敏度为 87.00%,特异度为86.00%,优于两者单独诊断。结论 ufPWV技术定量指标 PWV-BS、PWV-ES与 MS临床病情密切合诊断动脉粥样硬化的价值较为可靠,可为临床采取针对性防治措施提供有效指导。     

A simple and robust estimator for linear regression models with strictly exogenous instruments

In this paper, I investigate the estimation of linear regression models with strictly exogenous instruments under minimal identifying assumptions. I introduce a uniformly (in the data‐generating process) consistent estimator under nearly minimal identifying assumptions. The proposed estimator, called the integrated instrumental variables (IIV) estimator, is a simple weighted least‐squares estimator. It does not require the choice of a bandwidth or tuning parameter, or the selection of a finite set of instruments. Thus, the estimator is extremely simple to implement. Monte Carlo evidence supports the theoretical claims and suggests that the IIV estimator is a robust complement to optimal instrumental variables in finite samples. In an application with quarterly UK data, the IIV estimator estimates a positive and significant elasticity of intertemporal substitution and an equally sensible estimate for its reciprocal, in sharp contrast to instrumental variables methods that fail to identify these parameters.     

An Iterative Thresholding Method for the Minimum Compliance Problem

In this paper, we propose a simple energy decaying iterative thresholdingalgorithm to solve the two-phase minimum compliance problem. The material domain is implicitly represented by its characteristic function, and the problem is formulated into a minimization problem by the principle of minimum complementaryenergy. We prove that the energy is decreasing in each iteration. Two effective continuation schemes are proposed to avoid trapping into the local minimum. Numericalresults on 2D isotropic linear material demonstrate the effectiveness of the proposedmethods.