Havre R F, Waage J R, Gilja O H, Ødegaard S, Nesje L B
Institute of Medicine, University of Bergen.
Department of Surgery, Haukeland University Hospital.
Ultraschall Med. 2012 Dec;33(6):559-568. doi: 10.1055/s-0031-1273247. Epub 2011 Jun 10.
Real-time elastography (RTE) is an ultrasound-based method for the visualization of relative strain distribution in soft tissues. Strain ratio is a semi-quantitative measurement of strain differences between two user-defined areas in an elastogram. The aim of this study was to evaluate the impact of the size and location of a reference area when measuring the strain ratio of focal lesions in a tissue-mimicking phantom and in normal liver tissue. We also investigated whether the strain ratio was affected by changing the scanner parameter: elasticity dynamic range (E-dyn).
Two investigators individually collected data by scanning 4 spherical inclusions with different elasticity in a phantom in which the elastic modulus was known in both the lesions and the background. Subsequently, a liver scan was performed in-vivo using the same scanning protocol. Five different setups with changes in reference area position or size were tested. All eight levels of the scanner setting Edyn were recorded for each setup and the strain ratio was measured in 3 different representative elastograms for each recording situation.
The four inclusions had significantly different mean strain ratio levels (p < 0.01) when compared to the surrounding material. Changing the position of the reference area to a deeper position influenced the strain ratio measurements significantly for all phantom lesions and in the liver. Changing the size of the reference area, while keeping the center depth unchanged, did not influence the mean strain ratio levels significantly. The strain ratio was independent of the E-dyn parameter setting. The intraand interobserver reliability was high when measuring the strain ratio with a free-hand technique.
Strain ratio provides reproducible measurements of inclusions representing different elastic contrasts using a free-hand technique in vitro. Changes in the distance of the reference areas to the ultrasound probe, representing the stress source, seem to have a significant impact on strain ratio measurements.
实时弹性成像（RTE）是一种基于超声的用于可视化软组织相对应变分布的方法。应变比是弹性图中两个用户定义区域之间应变差异的半定量测量。本研究的目的是评估在组织模拟体模和正常肝组织中测量局灶性病变的应变比时，参考区域的大小和位置的影响。我们还研究了应变比是否受扫描参数——弹性动态范围（E-dyn）变化的影响。
两名研究人员分别通过扫描体模中4个具有不同弹性的球形内含物来收集数据，该体模中病变和背景的弹性模量均已知。随后，使用相同的扫描方案进行肝脏活体扫描。测试了5种不同的设置，其中参考区域的位置或大小发生了变化。记录每种设置下扫描仪设置E-dyn的所有8个级别，并在每种记录情况下的3个不同代表性弹性图中测量应变比。
与周围材料相比，这4个内含物的平均应变比水平有显著差异（p<0.01）。将参考区域的位置改变到更深的位置，对所有体模病变和肝脏中的应变比测量都有显著影响。在保持中心深度不变的情况下改变参考区域的大小，对平均应变比水平没有显著影响。应变比与E-dyn参数设置无关。使用徒手技术测量应变比时，观察者内和观察者间的可靠性很高。
应变比在体外使用徒手技术可对代表不同弹性对比的内含物进行可重复测量。参考区域到超声探头（代表应力源）的距离变化似乎对应变比测量有显著影响。
