A Probabilistic Pose Estimation Algorithm for 3D Motion Capture Data

描述(由申请人提供)：康复研究面临的一个主要挑战是衡量损伤、功能限制和残疾之间的关系。生物力学分析是通过提供患者状态和治疗结果的定量客观测量来建立这些关系的关键工具。许多生物力学分析的核心是基于使用传感器(光学、电磁或惯性)记录的3D运动数据来估计多节段模型的姿势(位置和方向)。Visual3D是商业上可用于3D运动捕捉数据的最先进的临床生物力学分析软件，它包含从3D传感器数据估计姿势的解决方案，这些数据已在世界各地的实验室进行测试，并在日常临床评估中使用。研究人员已经开始依赖Visual3D的能力。C-Motion正在提议一项合作研究和开发工作，将新的姿势估计技术送到研究人员手中。第一阶段的算法和第二阶段的增强将包括在Visual3D中。Visual3D功能的核心是灵活的算法，用于识别从3D运动捕捉传感器到分段骨骼模型的3D姿势的映射。Visual3D姿势估计算法(和其他商业生物力学软件)的基本假设是传感器严格地随着它们所连接的身体部分移动。然而，可以接受的是，附着在皮肤上的传感器相对于底层骨骼移动，这种软组织伪影很难量化或建模，因为它通常是系统性的，但在个案的基础上有所不同。这种伪影对非侵入性临床运动分析的相关性是一个严重的挑战。目前的位姿估计算法并没有考虑软组织伪影的模型。数据中的不确定性(例如传感器噪声和伪影)不能直接使用当前的判别方法来解决，但可以通过在概率推理的一般框架中投射姿态估计问题来解决(Todorov，2007)。在该框架中，姿势和关于姿势的任何先验知识被以概率编码，并由生成模型来捕获“伪像和噪声”，该模型定义了给定姿势的数据的条件概率。在第一阶段，我们将实施和测试一个基于运动学的概率算法，用于根据托多罗夫博士的建议使用贝叶斯推理来计算对象的姿势(位置和方向)。研究结果将与我们的合作者Scott Tashman博士(匹兹堡大学生物动力学实验室)同时记录的一组双平面电影透视数据和3D运动捕捉数据进行比较，我们将把这些数据视为我们的骨骼运动的“黄金标准”。整个项目非常雄心勃勃，因此在第一阶段，我们正在尝试整体算法的一个重要子集，以证明这种方法的可行性，并提供证据，证明我们有能力处理更雄心勃勃的第二阶段项目。 公共卫生相关性：迫切需要改善康复研究和临床服务，以降低个人保健成本，提高生产力和生活质量。生物力学分析是了解损伤、功能限制和残疾之间关系的关键工具，它提供了对患者状态和治疗结果的定量、客观的测量。该项目旨在应用机器视觉领域开发的概率算法，使新一代生物力学技术商业化，这将使研究人员能够显著改善运动分析，并最终改善患者结果。

DESCRIPTION (provided by applicant): A major challenge facing rehabilitation research is to measure relationships between impairments, functional limitations, and disabilities. Biomechanical analyses are a key tool for establishing these relationships by providing quantitative objective measures of patient status and treatment outcomes. At the heart of many biomechanical analyses is estimation of the pose (position and orientation) of a multi-segment model based on recording of 3D motion data using sensors (optical, electro-magnetic, or inertial). Visual3D, the most advanced clinical biomechanics analysis software available commercially for 3D motion capture data, contains solutions for the estimation of pose from 3D sensor data that have been tested in laboratories throughout the world, and are used on a daily basis for clinical assessment. Researchers have come to rely on Visual3D's capabilities. C-Motion is proposing a collaborative research and development effort to get new pose estimation techniques into the hands of researchers. The algorithms from Phase I and the enhancements in Phase II will be included in Visual3D. At the core of Visual3D's functionality are flexible algorithms for identifying a mapping from 3D motion capture sensors to the 3D pose of a segmented skeletal model. The principle assumption of the Visual3D pose estimation algorithms (and other commercial biomechanics software) is that sensors move rigidly with the body segments to which they are attached. It is accepted, however, that sensors attached to the skin move relative to the underlying skeleton and that this Soft Tissue Artifact is challenging to quantify or model because it is often systematic but varies on a case by case basis. This artifact is a serious challenge to the relevance of non-invasive clinical motion analyses. The current pose estimation algorithms were not designed to incorporate models of soft tissue artifact. Uncertainty in data (e.g. sensor noise and artifact) cannot be addressed directly using current discriminative methods, but may be addressed by casting the Pose Estimation problem in the general framework of probabilistic inference (Todorov, 2007). In this framework, the pose and any prior knowledge about the pose are encoded probabilistically, and the "artifacts and noise" are captured by a generative model, which defines the conditional probability of the data given the pose. In Phase I we will implement and test a kinematics-based probabilistic algorithm for computing the pose (position and orientation) of a subject using Bayesian inference as proposed by Dr. Todorov. The results will be compared to a set of biplanar cinefluoroscopy data and 3D motion capture data recorded simultaneously by our collaborator Dr. Scott Tashman (Biodynamics Laboratory at the University of Pittsburgh), which we will treat as our "gold standard" for bone motion. The overall project is very ambitious, so in Phase I we are attempting an important subset of the overall algorithm to demonstrate feasibility of this approach, and to provide evidence that we are capable of tackling the even more ambitious Phase II project. PUBLIC HEALTH RELEVANCE: There is a tremendous need for improved rehabilitation research and clinical services to lower individual health care costs and improve productivity and quality of life. Biomechanical analysis is a key tool for understanding the relationships between impairments, functional limitations, and disabilities by providing quantitative, objective measures of patient status and treatment outcomes. This project is designed to apply probabilistic algorithms developed in the field of machine vision to make a new generation of biomechanical techniques available commercially, which will enable researchers to improve movement analysis dramatically and ultimately patient outcomes.