Xia Rongmin, Thittai Arun K
Ultrasonics Laboratory, Department of Diagnostic and Interventional Imaging, The University of Texas Medical School, Houston, TX, USA.
Ultrasonics Laboratory, Department of Diagnostic and Interventional Imaging, The University of Texas Medical School, Houston, TX, USA
Ultrason Imaging. 2015 Jan;37(1):70-82. doi: 10.1177/0161734614537044. Epub 2014 Jun 9.
Quasi-static ultrasound elastography was introduced in the early 1990s to provide a way to visualize the mechanical properties of target tissue. Most commonly, only the axial strain is imaged and referred to as an Axial Strain Elastogram (ASE) or elastogram for simplicity. It has been shown that one can image the axial-shear strain distributions as well in addition to ASE. The image of the axial-shear strain is referred to as an axial-shear strain elastogram (ASSE). It has also been shown that the presence or absence of non-zero axial-shear strain values inside the inclusion (referred to as fill-in) along with contrasting margin at its boundary may serve as a potential feature from ASSE that can aid in non-invasive breast lesion classification. However, during freehand elastography, deviations from uniaxial compression often occur typically appearing in several of the frames of a cine-loop obtained during compression. It was shown recently that accounting for such deviations would be important for reliable interpretation of the "fill-in" observed in ASSE. In this article, we describe a method to estimate the angle of iso-displacement contour at a given depth and use this as a measure to quantify the deviation from the desired uniaxial compression during freehand elastography. We validate the estimated angle obtained from the axial-displacement map against the designed values in simulation and tissue-mimicking phantom experiments. The potential of the angle estimate to detect unreliable ASSE frames among the freehand-acquired data cine-loop is demonstrated using example cases of in vivo breast lesion data. Based on the results, we conclude that the angle of the iso-displacement contour from the axial-displacement map can be used as a metric to qualify an ASSE frame as reliable to interpret or not. Importantly, this metric can be obtained in real time and thus can provide operator feedback to guide and improve in vivo freehand elastography data acquisition quality.
准静态超声弹性成像技术于20世纪90年代初被引入，旨在提供一种可视化目标组织力学特性的方法。最常见的情况是，仅对轴向应变进行成像，为简便起见，将其称为轴向应变弹性图（ASE）或弹性图。研究表明，除了ASE之外，还可以对轴向剪切应变分布进行成像。轴向剪切应变的图像被称为轴向剪切应变弹性图（ASSE）。研究还表明，内含物内部非零轴向剪切应变值的存在与否（称为填充）以及其边界处的对比边缘，可能作为ASSE的一个潜在特征，有助于无创性乳腺病变分类。然而，在徒手弹性成像过程中，通常会出现偏离单轴压缩的情况，这在压缩过程中获得的电影环的几个帧中经常出现。最近的研究表明，考虑这些偏差对于可靠解释ASSE中观察到的“填充”现象很重要。在本文中，我们描述了一种在给定深度估计等位移轮廓角度的方法，并将其用作量化徒手弹性成像过程中偏离所需单轴压缩的一种度量。我们在模拟和仿组织体模实验中，将从轴向位移图获得的估计角度与设计值进行了验证。通过体内乳腺病变数据的实例，展示了角度估计在检测徒手采集的数据电影环中不可靠的ASSE帧方面的潜力。基于这些结果，我们得出结论，轴向位移图中等位移轮廓的角度可以用作衡量ASSE帧是否可靠解释的指标。重要的是，这个指标可以实时获得，因此可以为操作者提供反馈，以指导和提高体内徒手弹性成像数据采集的质量。
