Center for Ultrasound Molecular Imaging and Therapeutics, University of Pittsburgh and University of Pittsburgh Medical Center, Pittsburgh, PA, USA.
Ultrasound Med Biol. 2012 Mar;38(3):511-23. doi: 10.1016/j.ultrasmedbio.2011.12.009. Epub 2012 Jan 21.
Strain developed under quasi-static deformation has been mostly used in ultrasound elasticity imaging (UEI) to determine the stiffness change of tissues. However, the strain measure in UEI is often less sensitive to a subtle change of stiffness. This is particularly true for Crohn's disease where we have applied strain imaging to the differentiation of acutely inflamed bowel from chronically fibrotic bowel. In this study, a new nonlinear elastic parameter of the soft tissues is proposed to overcome this limit. The purpose of this study is to evaluate the newly proposed method and demonstrate its feasibility in the UEI. A nonlinear characteristic of soft tissues over a relatively large dynamic range of strain was investigated. A simplified tissue model based on a finite element (FE) analysis was integrated with a laboratory developed ultrasound radio-frequency (RF) signal synthesis program. Two-dimensional speckle tracking was applied to this model to simulate the nonlinear behavior of the strain developed in a target inclusion over the applied average strain to the surrounding tissues. A nonlinear empirical equation was formulated and optimized to best match the developed strain-to-applied strain relation obtained from the FE simulation. The proposed nonlinear equation was applied to in vivo measurements and nonlinear parameters were further empirically optimized. For an animal model, acute and chronic inflammatory bowel disease was induced in Lewis rats with trinitrobenzene sulfonic acid (TNBS)-ethanol treatments. After UEI, histopathology and direct mechanical measurements were performed on the excised tissues. The extracted nonlinear parameter from the developed strain-to-applied strain relation differentiated the three different tissue types with 1.96 ± 0.12 for normal, 1.50 ± 0.09 for the acutely inflamed and 1.03 ± 0.08 for the chronically fibrotic tissue. T-tests determined that the nonlinear parameters between normal, acutely inflamed and fibrotic tissue types were statistically significantly different (normal/ fibrotic [p = 0.0000185], normal/acutely inflamed [p = 0.0013] and fibrotic/acutely inflamed [p = 0.0029]). This technique may provide a sensitive and robust tool to assess subtle stiffness changes in tissues such as in acutely inflamed bowel wall.
在超声弹性成像 (UEI) 中，通常使用准静态变形下产生的应变来确定组织的刚度变化。然而，UEI 中的应变测量对刚度的细微变化通常不太敏感。这在克罗恩病中尤其如此，我们已经将应变成像应用于区分急性炎症性肠和慢性纤维化性肠。在这项研究中，提出了一种新的软组织非线性弹性参数来克服这一限制。本研究旨在评估新提出的方法，并在 UEI 中验证其可行性。研究了软组织在较大应变动态范围内的非线性特性。基于有限元 (FE) 分析的简化组织模型与实验室开发的超声射频 (RF) 信号合成程序相结合。将二维散斑跟踪应用于该模型，以模拟目标内含物在施加于周围组织的平均应变下产生的应变的非线性行为。制定了一个非线性经验方程，并对其进行了优化，以最佳匹配从 FE 模拟中获得的开发应变与施加应变之间的关系。将提出的非线性方程应用于体内测量，并进一步经验优化非线性参数。对于动物模型，用三硝基苯磺酸 (TNBS)-乙醇处理诱导 Lewis 大鼠发生急性和慢性炎症性肠病。在 UEI 之后，对切除的组织进行组织病理学和直接力学测量。从开发的应变与施加应变关系中提取的非线性参数可以区分三种不同的组织类型，正常组织为 1.96±0.12，急性炎症组织为 1.50±0.09，慢性纤维化组织为 1.03±0.08。t 检验确定正常、急性炎症和纤维化组织类型之间的非线性参数存在统计学显著差异（正常/纤维化 [p=0.0000185]，正常/急性炎症 [p=0.0013] 和纤维化/急性炎症 [p=0.0029]）。该技术可能为评估组织的细微刚度变化提供一种敏感而稳健的工具，例如急性炎症性肠壁。
