Effect of lesion boundary conditions on axial strain elastograms: a parametric study

Ultrasound elastography produces strain images of compliant tissues under quasi-static compression. When a material is compressed, there are several parameters that affect the stress-distribution and, hence, the strain distribution in the material. The state of bonding of an inclusion to the background material is a critical parameter. Heretofore, in the field of elastography, the inclusion was considered to be firmly bonded to the background material and analytical solutions were derived for the elasticity problem involving simple geometries like circular inclusion (for two dimensional [2D]) and spherical inclusion (three dimensional [3D]). Under these conditions, simple analytical expressions relating the strain contrast to the modulus contrast were derived. However, it is known that the state of bonding of some tumors to their surrounding tissues depends on the type of the lesion. For example, benign lesions of the breast are known to be loosely bonded to the surrounding tissue, while malignant breast lesions are firmly bonded. In this study, we perform a parametric study using finite element modeling (FEM) to investigate the validity of the analytical expression relating the strain contrast to the modulus contrast, when the state of bonding at the inclusion/background interface spans a large dynamic range. The results suggest that estimated modulus contrast using the analytical expression is sensitive to the region-of-interest within the inclusion that is considered in the computation of the strain contrast. By considering the inclusion region lying along the axis of lateral symmetry instead of whole region of the inclusion, the estimated modulus contrast (obtained using the analytical expression present in the literature) can be computed to within a systematic error of 10% of the actual modulus contrast. Additional estimation errors are expected to accrue in experimental and in vivo conditions.     

Feasibility and reliability of strain and strain rate measurement in neonates by optimizing the analysis parameters settings

The optimal combination of region-of-interest (ROI) size and strain length (SL) allowing two-segment strain and strain rate analyses in term neonates was investigated. The impact of different ROI sizes and SLs on the strain and strain rate beat-to-beat variation (BBV) was assessed in 80 good-quality tissue velocity images. Both BBVs decreased with increased ROI length and with increased SL (p < 0.05). There were no significant differences in the BBVs for ROI width 2, 3 and 4 mm (p > 0.05). Among the combinations eligible for two segment analysis, the lowest BBVs were found using SL 10 mm, ROI length 1 mm and ROI width 3 mm. Using this combination, the mean difference between the single-cycle value and two-cycle compound value for peak systolic strain rate was 6.2%, peak systolic strain was 2.9% and end systolic strain was 3.2% of the two-cycle compound mean values. Hence, strain and strain rate measurement in tissue velocity images in neonates is feasible and reliable.     

IN VITRO EVALUATION OF THE PRECISION OF WORKING CASTS FOR IMPLANT-SUPPORTED RESTORATION WITH MULTIPLE ABUTMENTS

Objective:

The purpose of this study was to compare the accuracy of two working cast fabrication techniques using strain- gauge analysis.

Methods:

Two working cast fabrication methods were evaluated. Based on a master model, 20 working casts were fabricated by means of an indirect impression technique using polyether after splinting the square transfer copings with acrylic resin. Specimens were assigned to 2 groups (n=10): Group A (GA): type IV dental stone was poured around the abutment analogs in the conventional way; Group B (GB), the dental stone was poured in two stages. Spacers were used over the abutment analogs (rubber tubes) and type IV dental stone was poured around the abutment analogs in the conventional way. After the stone had hardened completely, the spacers were removed and more stone was inserted in the spaces created. Six strain-gauges (Excel Ltd.), positioned in a cast bar, which was dimensionally accurate (perfect fit) to the master model, recorded the microstrains generated by each specimen. Data were analyzed statistically by the variance analysis (ANOVA) and Tukey''s test (α= 5%).

Results:

The microstrain values (με) were (mean±SD): GA: 263.7±109.07με, and GB: 193.73±78.83με.

Conclusion:

There was no statistical difference between the two methods studied.     

室壁应力与应变的关系评价高血压病左室收缩功能

目的　探索用室壁应力 (stress)与应变 (strain)的关系评价高血压病左室收缩功能的临床价值。方法　研究对象为 5 5例高血压病患者和 3 0例健康人。应用超声心动图计算左室射血分数 (EF)、心指数 (CI)、重量指数 (LVMI)和相对室壁厚度 (RWT) ,并联合袖带肱动脉血压值计算左心室收缩期室壁经线峰值应力 (Pσm)。根据LVMI和RWT将高血压病分为左室正常构型和左室重构两组。在数字化超声工作站中应用定量组织速度成像 (QTVI)获取左室前壁心肌 2个节段长轴应变曲线和峰值收缩应变值 (PSS)。结果　①以EF ,CI表示的心脏收缩功能 ,在高血压病左室正常构型组值中无明显变化 ;而在高血压病左室重构组中下降 ,差异具有极显著意义 (P <0 .0 1)。②Pσm在高血压病两组中较对照组均有增高 (P <0 .0 5～ 0 .0 1) ,两组间比较差异具有极显著意义 (P <0 .0 1)。③高血压病两组左室前壁基底段 (Bas)和中段 (Mid)的 pSS值均显著下降 (P <0 .0 1) ,两组间比较差异具有极显著意义 (P <0 .0 1)。④直线相关分析结果显示高血压病两组Pσm与PSSBas和PSSMid均呈显著负相关。根据正常构型组Pσm与PSSBas直线回归方程计算 ,在相同Pσm水平 ,左室重构组PSSBas的实测值显著低于预测值及实测值与预测值的比值较正常构型组显著下降 ,差     

组织多普勒技术定量评价心肌梗死患者左室壁的收缩后收缩

目的：讨论急性与陈旧性心肌梗死（MI）患者左心室收缩后收缩（PSS）出现的比例和峰值，以及与左心室节段功能的关系。方法：入选（MI）患者42例，其中急性（MI）、陈旧性（MI）和正常对照组各14例（A，B，C组）。运用GEvivid 7彩色超声仪采集惠者心尖3个切面的超声图像，并用Q-analyse分析软件测量左心室12节段的收缩期峰值速度（Sm），收缩后收缩峰值速度（PSS），舒张早期、晚期峰值速度（Em，Am），收缩期峰值位移（Ds）和收缩期峰值应变力（εs），用双平面Simposon法测量患者的EF值。结果：（1）MI后，PSS节段占总节段数的比例较正常增加，且A组比B组的增加更明显（P〈0．01）；PSS峰值较正常升高，且A组比B组升高更显著（P〈0．01）。（2）A、B两组的Sm，Em，Am，Ds和如均明显低于C组（P〈0．01），但A、B两组间除了Em外（P〈0．01），其余参数无显著差异（P〉0．05）。（3）C组左心室基底段的平均PSS与EE值正相关（P〈20．05），而A、B两组平均PSS与EF值呈现负相关趋势。结论：组织多普勒技术评价（MI）患者左心室PSS的比例和峰值，可以反映心肌的缺血、存活和节段功能的细微变化，是一种无创、快捷、定量的客观指标。     

加标记的心脏磁共振成像研究进展

加标记的心脏磁共振影像(tagged MRI)是20世纪80年代末期出现的一种医学成像技术.标记线的引入,为使用非介入方式研究心肌运动提供了新的方法.如何有效地获取和使用tagged MRI提供的信息成为当前医学影像领域的一个研究热点.作者结合近年来在tagged MRI所做的研究工作,从信息处理角度,对tag线跟踪、心脏MRI分割方法、左心室的形状恢复与运动重建、心肌形变应变研究和验证方法等进行了论述,并就该领域今后的研究方向提出了建议.     

Comparison of Longitudinal and Apical Foetal Speckle Tracking Echocardiography Using Tissue Motion Annular Displacement and Segmental Longitudinal Strain

The aim of our prospective pilot study with exploratory analysis was to compare longitudinal and apical foetal speckle tracking echocardiography (STE) using tissue motion annular displacement (TMAD) and segmental longitudinal strain (SLS). We compared two different STE quantification tools in a longitudinal and apical four-chamber view in 57 normal foetuses between 20 and 40 wk of gestation. Myocardial mechanical dyssynchrony and strain were assessed using offline quantification software (QLab Version 10.3, Philips Medical Systems, Andover, MA, USA). We compared the dyssynchrony measurements with TMAD and SLS in longitudinal and apical four-chamber views. Furthermore, we examined the segmental strain values of both ventricles with SLS and compared the differences between longitudinal and apical measurements. Dyssynchrony measurements with TMAD and SLS and strain measurements with SLS were feasible in all cases. In the apical view, the dyssynchrony measurements with TMAD were systematically greater than those achieved with SLS (p < 0.001). For the longitudinal view, no differences were observed between tools (p?=?0.153). The application of SLS provided similar results for dyssynchrony in both views (intra-class correlation coefficient [ICC]?=?0.281, p?=?0.623), but the strain measurements in the left and right ventricles differed significantly between views (ICC?=?–0.082, p?=?0.011, and ICC?=?–0.061, p?=?0.024, respectively). For TMAD, we found large differences in the dyssynchrony values between longitudinal and apical assessment (ICC?=?–0.060, p?=?0.03). Furthermore, TMAD exhibited reduced accuracy in the system's automatic tracking algorithm, limiting the data quality. The dyssynchrony assessment is affected less by the foetal position in SLS than in TMAD. The strain readings in SLS varied depending on the view in which they were assessed. The application of TMAD cannot be recommended for foetal STE.     

应变率成像定量评价冠状动脉支架置入术前后左室局部心肌张功能变化

目的 采用应变率成像技术定量评估冠状动脉支架置入术前后左室局部心肌舒张功能的变化.方法 应用应变率成像技术对56例健康体检者和60例冠心病患者冠状动脉支架置入术前后心尖四腔、两腔、左室长轴切面相应节段局部心肌舒张功能进行定量分析.结果 冠心病患者术前缺血节段心肌应变率曲线中舒张期E、A峰值均小于健康体检者相应心肌节段,术后经治疗的缺血节段心肌舒张期E、A峰值较术前明显增加,差异均有统计学意义（P＜0.05）.结论 冠状动脉支架置入术可改善心肌缺血,应变率成像技术能定量评价冠状动脉支架置入术前后左室局部心肌舒张功能的变化.