A Noninvasive MRI-Based Method to Determine Three Dimensional Cartilage Deformations

关节软骨对人类关节的正常功能至关重要。 该组织具有独特的机械和摩擦学特性，通过提供几乎无摩擦和耐磨的关节表面允许日常活动（即运动）。 骨关节炎是最常见的风湿性疾病，并与不同程度的软骨退化。尽管正常软骨的独特功能和骨关节炎的流行，以前的研究没有量化的三维（3D）的机械变形的软骨使用非侵入性的实验方法。 缺乏关于软骨变形的全面信息严重限制了我们对正常软骨载荷-变形行为的理解，从而限制了我们完全描述、准确诊断和有效治疗软骨疾病的能力。 因此，本研究的目标是开发一种非侵入性地确定软骨三维变形的方法。为了实现这一目标，将测试以下三个假设：（1）可以设计非侵入性磁共振成像（MRI）脉冲序列，以50微米的高空间分辨率直接观察软骨变形，（2）应变相对误差小于5%的新的非侵入性方法可以测量变形;（3）骨关节炎软骨样品中的3D软骨变形与正常样品中的变形不同。为了检验第一个假设，将使用特定的MRI脉冲序列观察组织变形，该MRI脉冲序列在软骨上叠加网格图案，可以观察到该网格图案随着组织变形而移动。 为了检验第二个假设，将使用MRI兼容体模确定无创方法的准确性。将根据正常组织和骨关节炎组织样本的高分辨率MRI图像计算3D有限应变张量场，以检验第三个假设。这种新的非侵入性方法的发展受到许多基础科学和临床研究问题的推动。 一旦通过测试上述假设证明了该方法，它将允许对性别、年龄、退化、治疗、修复和愈合对软骨负荷变形的影响进行非侵入性调查。 这项研究是一项长期研究计划的基础，旨在增加我们对体内正常和异常3D软骨变形的理解。

Articular cartilage is critical to the normal function of human diarthrodial joints. The tissue has unique mechanical and tribological properties which allow for daily activities (i.e. locomotion) by providing a nearly frictionless and wear-resistant joint surface. Osteoarthritis is the most common rheumatic disease and is associated with various degrees of cartilage degradation. Despite the unique function of normal cartilage and the prevalence of osteoarthritis, previous studies have not quantified the three-dimensional (3D) mechanical deformation of cartilage using noninvasive experimental methods. The lack of such comprehensive information regarding cartilage deformations seriously limits our understanding of normal cartilage load-deformation behavior and hence our ability to completely describe, accurately diagnose, and effectively treat cartilage disorders. Thus the goal of this research is to develop a method to noninvasively determine the 3D deformation of cartilage.To meet this goal, three hypotheses will be tested as follows: (1) a noninvasive magnetic resonance imaging (MRI) pulse sequence can be designed to directly observe cartilage deformation at high spatial resolution of 50 microns, (2) deformation can be measured using the new noninvasive method with less than 5% relative error in strain, and (3) 3D cartilage deformation in osteoarthritic cartilage samples is altered from deformation in normal samples. To test the first hypothesis, tissue deformation will be observed using a specific MRI pulse sequence that superimposes a grid pattern on the cartilage which can be observed to move with the tissue as it deforms. To test the second hypothesis, the accuracy of the noninvasive method will be determined using a MRI-compatible phantom. The 3D finite strain tensor field will be computed from high-resolution MRI images from samples of normal and osteoarthritic tissues to test the third hypothesis. The development of the new noninvasive method is motivated by many basic science and clinical research questions. Once the method is proven by testing the above hypotheses, it will permit noninvasive investigation of the effects of gender, age, degeneration, treatment, repair and healing on cartilage load-deformation. This research represents the foundation of a long-term research program which aims to increase our understanding of normal and abnormal 3D cartilage deformations in vivo.