Uff Christopher, Garcia Leo, Fromageau Jeremie, Chakraborty Aabir, Dorward Neil, Bamber Jeffrey
Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Joint Department of Physics, Sutton, Surrey, United Kingdom.
Southampton General Hospital, Department of Neurosurgery, Southampton, United Kingdom.
J Med Imaging (Bellingham). 2018 Apr;5(2):021211. doi: 10.1117/1.JMI.5.2.021211. Epub 2018 Feb 5.
Elastography measures tissue strain, which can be interpreted under certain simplifying assumptions to be representative of the underlying stiffness distribution. This is useful in cancer diagnosis where tumors tend to have a different stiffness to healthy tissue and has also shown potential to provide indication of the degree of bonding at tumor-tissue boundaries, which is clinically useful because of its dependence on tumor pathology. We consider the changes in axial strain for the case of a symmetrical model undergoing uniaxial compression, studied by characterizing changes in tumor contrast transfer efficiency (CTE), inclusion to background strain contrast and strain contrast generated by slip motion, as a function of Young's modulus contrast and applied strain. We present results from a finite element simulation and an evaluation of these results using tissue-mimicking phantoms. The simulation results show that a discontinuity in displacement data at the tumor boundary, caused by the surrounding tissue slipping past the tumor, creates a halo of "pseudostrain" across the tumor boundary. Mobile tumors also appear stiffer on elastograms than adhered tumors, to the extent that tumors that have the same Young's modulus as the background may in fact be visible as low-strain regions, or those that are softer than the background may appear to be stiffer than the background. Tumor mobility also causes characteristic strain heterogeneity within the tumor, which exhibits low strain close to the slippery boundary and increasing strain toward the center of the tumor. These results were reproduced in phantom experiments. In addition, phantom experiments demonstrated that when fluid lubrication is present at the boundary, these effects become applied strain-dependent as well as modulus-dependent, in a systematic and characteristic manner. The knowledge generated by this study is expected to aid interpretation of clinical strain elastograms by helping to avoid misinterpretation as well as provide additional diagnostic criteria stated in the paper and stimulate further research into the application of elastography to tumor mobility assessment.
弹性成像测量组织应变，在某些简化假设下，该应变可被解释为代表潜在的硬度分布。这在癌症诊断中很有用，因为肿瘤的硬度往往与健康组织不同，并且还显示出有潜力提供肿瘤 - 组织边界处粘连程度的指示，由于其对肿瘤病理学的依赖性，这在临床上很有用。对于一个经历单轴压缩的对称模型，我们通过表征肿瘤对比度转移效率（CTE）、内含物与背景应变对比度以及由滑动运动产生的应变对比度的变化，作为杨氏模量对比度和施加应变的函数，来研究轴向应变的变化。我们展示了有限元模拟的结果以及使用组织模拟体模对这些结果的评估。模拟结果表明，由于周围组织滑过肿瘤，肿瘤边界处位移数据的不连续性会在肿瘤边界上产生一个“伪应变”晕圈。在弹性图上，可移动肿瘤也比粘连肿瘤显得更硬，以至于与背景具有相同杨氏模量的肿瘤实际上可能表现为低应变区域，或者比背景软的肿瘤可能看起来比背景更硬。肿瘤的移动性还会在肿瘤内部引起特征性的应变不均匀性，在靠近滑动边界处表现为低应变，向肿瘤中心应变增加。这些结果在体模实验中得到了重现。此外，体模实验表明，当边界处存在流体润滑时，这些效应不仅取决于模量，还系统且有特征地取决于施加的应变。预计本研究产生的知识将有助于临床应变弹性图的解读，避免误判，同时提供本文所述的额外诊断标准，并激发对弹性成像在肿瘤移动性评估中的应用的进一步研究。
