基于波速法的离体牛软骨粘弹性测量研究

Cartilage viscoelasticity changes with cartilage degeneration. Hence, the ability to measure biomechanical quantities in articular cartilage could greatly enhance knowledge and understanding of cartilage health, damage, disease, and repair. However, the in-vivo, quantitative, and micro-invasive/noninvasive measurement of articular cartilage viscoelasticity is completely lacking. In previous studies, we confirmed the feasibility of viscoelasticity assessment in a bovine cartilage using the Lamb wave method (LWM), where a mechanical shaker and laser dopper detector were adopted to enhance the driving force and measurement sensitivity. In this study, we would go deep into the study to estimate the bovine cartilage viscoelasticity in vitro. The near and far field Lamb wave propagation in cartilage with complex surface shape would be studied to deeply understand the wave propagation. The fiber-based OCT method would be used to micro-invasive measure the motion with the high spatial resolution and short scanning time. The Finite-window 2-D FFT algorithms would be used to estimate the Lamb wave velocity and attenuation, and accordingly a model-free approach will be investigated to measure the material properties as a function of frequency. Finally, we would estimate the bovine cartilage viscoelasticity in vitro by micro-invasive method. This study will set up the new micro-invasive method for cartilage viscoelasticity detection.

关节软骨退变过程中伴随着软骨粘弹性特性的改变。因此，关节软骨的粘弹性测量研究，对发展新的诊疗方法及揭示骨关节发病机理具有重要意义。但目前的关节软骨粘弹性测量无法实现定量、微创或无创成像，也就无法真正用于临床。课题组前期基于兰姆波理论，利用机械振动和激光多普勒提高驱动力和测量分辨率，测量了离体牛关节软骨的粘弹性。本课题将在前期研究的基础上，更加深入的研究真实牛关节软骨中的波传播规律，并利用光学干涉成像（OCT）成像技术微创测量组织位移，通过有限窗口二维傅立叶算法计算波速和振幅衰减系数，建立与材料模型无关的软骨粘弹性计算算法，最终建立离体关节软骨粘弹性微创测量的新方法。本项目的完成将为关节软骨粘弹性微创测量提供理论基础和实验方法。

关节软骨退变过程中伴随着软骨粘弹性特性的改变。因此，关节软骨的粘弹性测量研究，对发展新的诊疗方法及揭示骨关节发病机理具有重要意义。但目前的关节软骨粘弹性测量无法实现定量、微创或无创成像，也就无法真正用于临床。本项目首先基于双层结构中的粘弹性兰姆波理论，实验测量了离体牛关节软骨的粘弹性。但软骨-骨结构中的兰姆波波速与软骨粘弹性有非常复杂的非线性关系，波速与软骨厚度、骨的特性相关，不利于软骨粘弹性反演。进一步研究发现，在靠近驱动源1-2个波长范围内，兰姆波还没有生成，高频下的波传播速度趋近于瑞利波波速（即近驱动源瑞利波理论），而瑞利波波速只与软骨粘弹性相关，与软骨厚度无关，与骨的弹性无关，显然有利于软骨粘弹性反演。但也发现，兰姆波法和瑞利波法，都需要驱动并测量5-10khz的波传播，现有的成像设备无法满足5-10khz波传播的测量。因此，一方面需要提高成像设备的测量速度；另一方面，需要研究其它粘弹性测量理论，降低对测量采样率的需求。对此，课题组通过数组模拟方法，初步研究了基于散射波理论的仿关节软骨弹性测量。该方法能够显著降低对采样率的需求，且对驱动和测量的位置未有限制。因此，基于散射波法的软骨粘弹性测量，有进一步研究的潜力。总体上，本项目实施过程中，建立了2种软骨粘弹性测量方法（即兰姆波法和近驱动源瑞利波法）并通过实验进行了验证，还初步验证了散射波法的可行性，为真正临床可用的软骨粘弹性测量打下了基础。