Characterization of Soft Fibrous Materials by MRI of Ultrasound-Induced Shear Waves

这项研究将开发一种新的实验技术，以非侵入性和非破坏性的方式测量柔软纤维材料的复杂特性。肌肉、肌腱和脑组织都是这种材料的例子，它们遍布人体和自然界。人工纤维增强的柔软生物材料越来越多地用于工程应用。了解这些材料的机械性能至关重要，例如它们的刚度以及储存和耗散能量的能力。在该项目中，磁共振成像和高强度聚焦超声的新型组合将用于全面测量人体内或受控环境中软纤维材料的机械性能。对社会的好处包括提高诊断损伤和纤维化疾病的能力，设计和评估人工组织，以及对创伤性脑损伤进行精确的计算机模拟。在劳动力发展方面，来自工程和成像的研究人员将共同努力，构建，测试和演示新技术。研究生将开发一套复杂的研究技能，跨越这两个学科。本项目将通过暑期研究项目、暑期和周末工作坊，为不同背景的本科生和初高中生提供工程和成像交叉领域的培训和研究经验。开发谐波超声诱导运动的MR成像，并将其应用于精确测量软组织和纤维生物材料的复杂、各向异性和非线性行为。首先，参数的线性，各向异性（横观各向同性和正交各向异性），粘弹性模型的纤维软生物材料将估计从慢（纯横向）和快（准横向）剪切波。剪切波具有相对于材料对称轴的不同传播和偏振方向，将由聚焦超声诱导，并通过MRI在人工对齐的生物材料、肌肉和白色脑组织中成像。剪切模量和拉伸模量将通过将定向过滤的平面波的速度拟合到解析表达式和模拟结果来估计。第二，纤维，软材料的非线性行为的特点。将探讨两种类型的非线性。(i)在小应变区的非线性，所产生的强材料的非线性，将通过量化的高次谐波分量的波动来测量。 (ii)非线性，大应变行为的特点是成像慢，快剪切波叠加在大变形。这种新方法有望在这些日益重要的材料中以前所未有的分辨率提供各向异性和非线性的全面表征。

This research will develop a new experimental technique to measure the complex properties of soft, fibrous materials, non-invasively and non-destructively. Muscle, tendons, and brain tissue are examples of such materials, which are found throughout the human body and in nature. Artificial fiber-reinforced, soft biomaterials are increasingly being used in engineering applications. It is critical to know the mechanical properties of such materials, such as their stiffness and ability to store and dissipate energy. In this project, a novel combination of magnetic resonance imaging and high-intensity focused ultrasound will be used to comprehensively measure the mechanical properties of soft fibrous materials, either inside the human body, or in a controlled environment. Benefits to society include the improved ability to diagnose injury and fibrotic disease, to design and evaluate artificial tissues, and to perform accurate computer simulations of traumatic brain injury. In terms of workforce development, researchers from engineering and imaging will work together to build, test, and demonstrate the new technology. Graduate students will develop a set of sophisticated research skills that span these two disciplines. Leveraging a summer research program, as well as summer and weekend workshops, this project will provide training and research experience at the intersection of engineering and imaging to undergraduate students and middle/high school students from diverse backgrounds.MR imaging of harmonic ultrasound-induced motion will be developed and applied to accurately measure the complex, anisotropic, nonlinear behavior of soft tissue and fibrous biomaterials. First, parameters of linear, anisotropic (transversely isotropic and orthotropic), viscoelastic models of fibrous soft biomaterials will be estimated from slow (pure transverse) and fast (quasi-transverse) shear waves. Shear waves, with varying propagation and polarization directions relative to material symmetry axes, will be induced by focused ultrasound and imaged by MRI in artificially aligned biomaterials, in muscle, and in white matter brain tissue. Shear moduli and tensile moduli will be estimated by fitting speeds of directionally-filtered plane waves to analytical expressions and simulated results. Second, the nonlinear behavior of fibrous, soft materials will be characterized. Two types of nonlinearity will be explored. (i) Nonlinearity in the small-strain regime, arising from strong material nonlinearity, will be measured by quantifying the higher harmonic components of wave motion. (ii) Nonlinear, large-strain behavior will be characterized by imaging slow and fast shear waves superimposed on large deformations. This novel approach is expected to provide comprehensive characterization of anisotropy and nonlinearity, with unprecedented resolution, throughout these increasingly-important materials.