Multi-Muscle Magnetic Resonance Elastography (MM-MRE): a new technique to measure non-invasively individual force of forearm muscles during fine motor tasks

冗余，这里的定义是使用多块肌肉来执行特定的任务，在神经肌肉系统中随处可见。冗余使人类能够执行熟练的任务，对环境变化做出反应，并适应结构破坏。对肌肉冗余的解决方案的分析，例如，前臂(肘部以下)的许多肌肉如何协调执行像旋转手腕这样的任务，可以揭示运动控制的基本过程，并为神经运动损伤的机制提供独特的见解。例如，神经肌肉冗余的解决方案在受“上运动神经元综合症”影响的个人中表现不同，这种综合症在40%的中风幸存者或大约200万美国公民中普遍存在。在这一人群中，手和手腕的功能受到最常见的影响。不幸的是，目前还没有能够测量和分析中枢神经系统如何管理和利用个体肌肉水平上的冗余来完成涉及手和手腕肌肉协调功能的精细运动任务的方法。为了满足这一需求，该项目将开发一种新的技术，使新的研究能够研究精细运动任务中的肌肉冗余。这项技术结合了先进的成像方法，可以测量肌肉力学，以及仪表化的手柄，可以测量手腕等长收缩时的手腕角度和扭矩。通过结合这些测量，研究人员将第一次能够非侵入性地测量前臂一整套肌肉的力量。一旦得到验证，这项技术将被用来评估中风患者在涉及主动运动功能的任务中的神经运动障碍，但这可以由具有各种损害水平的受试者执行。发展的技术是朝着定量理解神经肌肉控制的基本原理迈出的重要一步，并在评估神经运动损伤和恢复方面有重要应用。该项目还将为研究生和本科生提供关于需要结合基础和技术知识/技能的问题的培训，有助于发展一支随时准备应对学术界和工业界未来生物医学工程研究挑战的多学科劳动力队伍。计划的外展活动旨在让不同的K-12学生社区参与生物力学、成像和机器人交叉学科的主题。该项目专注于开发多肌肉磁共振弹性成像(MM-MRE)，将使新的调查能够研究精细运动任务中肌肉冗余的解决方案。MM-MRE结合了先进的磁共振弹性成像成像方法，允许整个前臂的空间分辨率为2 mm，体积采集时间低于10 S，以及MRE-BOT，这是一种新开发的磁共振兼容仪器手柄，可以在等长腕部收缩期间测量手腕角度和扭矩。通过将通过MRE获得的肌肉力学测量与通过MRE-bot在特定于对象的肌肉骨骼建模框架中获得的关节位置和扭矩测量相结合，研究人员将能够非侵入性地测量前臂一整套肌肉的活体力量。研究计划分为三个目标：第一个目标是开发和验证MM-MRE，这将涉及实施快速数据采集和分析计划，以提取等长收缩时涉及单个前臂肌肉的波速，并验证单个肌肉的波速测量和肌力计算。结果将是一种同时估计多个前臂肌肉力量的方法，具有足够的时间和空间分辨率，用于非侵入性和活体评估它们的个体收缩行为。第二个目标是使用MM-MRE来测试手腕等长任务中肌肉协调的模型。对健康个体进行的研究旨在确定成本函数，该成本函数的最小化将导致在等长任务中肌肉协调的“最佳”肌肉协调模式。MM-MRE测量独一无二地能够在不同的任务精度要求下测试当前已建立的成本函数(全局力量水平(GFL)和全局激活水平(GAL))的有效性，因为任务精度要求影响个体如何在存在神经肌肉错误的情况下协同激活他们的肌肉以稳定交互。第三个目标是确定MM-MRE是否可以在神经运动障碍中检测到前臂肌肉的异常肌肉共激活，从而作为一种评估工具，在慢性中风患者的飞行员队列中识别涉及手和腕肌肉的任务中的神经运动障碍。这项分析将基于偏瘫和非偏瘫手臂之间的比较，旨在验证所开发的技术足够灵敏，可以在临床人群中检测到预期的神经运动行为变化。总之，开发的技术代表了骨骼肌MRE的一种新方法和重大进步，将为研究神经肌肉控制和表征主动运动功能期间的病理性肌肉组织特性提供创新的测量方案。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Redundancy, defined here as having the use of multiple muscles to perform a particular task, is found everywhere in the neuromuscular system. Redundancy enables humans to perform skilled tasks, respond to environmental changes, and adapt to structural damage. The analysis of solutions to muscle redundancy, e.g., how the many muscles in the forearm (below the elbow) can co-ordinate to perform a task like rotating the wrist, could shed light on fundamental processes of motor control and provide unique insight of mechanisms of neuromotor impairment. For example, solutions to neuromuscular redundancy are expressed differently in individuals affected by the "upper motor neuron syndrome," prevalent in 40% of stroke survivors, or approximately two million United States citizens. In this population, function of the hand and wrist is most commonly affected. Unfortunately, there are no current methods capable of measuring and analyzing how the central nervous system manages and exploits redundancy at the individual muscle level for fine motor tasks involving coordinated function of muscles of the hand and wrist. To address this need, this project will develop a new technique that will enable new investigations to study muscle redundancy for fine motor tasks. The technique combines an advanced imaging method, which can measure muscle mechanics, with an instrumented handle, which can measure wrist angle and torque during isometric wrist contractions. By combining these measurements, the investigators will be able, for the first time, to noninvasively measure force in a complete set of muscles of the forearm. Once validated, the technique will be used to assess neuromotor impairment in stroke individuals during tasks involving active motor function, but that can be executed by subjects with a variety of impairment levels. The technique developed is an important step towards a quantitative understanding of basic principles of neuromuscular control and has important applications in assessing neuromotor impairment and recovery. The project will also provide training to graduate and undergraduate students in problems that require a combination of fundamental and technological knowledge/skills, contributing to the development of a multidisciplinary workforce ready to tackle the future challenges of biomedical engineering research in both academia and industry. The planned outreach activities are targeted to engage a diverse community of K-12 students in topics at the intersection between biomechanics, imaging, and robotics.This project focuses on developing multi-muscle magnetic resonance elastography (MM-MRE) that will enable new investigations to study solutions to muscle redundancy for fine motor tasks. MM-MRE combines advanced magnetic resonance elastography imaging methods, which allow 2 mm spatial resolution and volume acquisition time below 10 s for the entire forearm, with the MRE-bot, a newly developed MRI compatible instrumented handle to measure wrist angle and torque during isometric wrist contractions. By combining measurements of muscle mechanics obtained via MRE with joint position and torque measurements obtained via the MRE-bot in a subject-specific musculoskeletal modeling framework, investigators will be able to non-invasively measure in vivo force in a complete set of muscles of the forearm. The Research Plan is organized under three objectives: The FIRST Objective is to develop and validate MM-MRE, which will involve implementing a rapid data acquisition and analyses scheme to extract the wave speed involving individual forearm muscles during isometric contractions and validating wave speed measurements and calculation of muscle force from individual muscles. The outcome will be a methodology for estimating force in multiple forearm muscles simultaneously, with sufficient temporal and spatial resolution for evaluating their individual contractile behavior non-invasively and in vivo. The SECOND Objective is to use MM-MRE to test models of muscle coordination in isometric tasks of the hand/wrist. Studies, conducted with healthy individuals, are designed to determine the cost function whose minimization would lead to the "optimal" muscle coordination pattern for muscle coordination during the isometric tasks. MM-MRE measurements uniquely enable testing of the validity of currently established cost functions, global force level (GFL) and global activation level (GAL), under different task accuracy requirements, as task accuracy requirements have an effect on how individuals co-activate their muscles to stabilize interaction in presence of neuromuscular error. The THIRD Objective is to establish if MM-MRE can detect abnormal muscle coactivation of forearm muscles in neuromotor impairment and thus be used as an assessment tool to identify neuromotor impairment in tasks involving hand and wrist muscles in a pilot cohort of individuals with chronic stroke. The analysis will be based on comparisons between the paretic and non-paretic arm and will be aimed at validating the developed technique as being sensitive enough to detect expected changes in neuromotor behavior in a clinical population. In summary, the technique developed represents a novel approach and significant advancement for skeletal muscle MRE that will enable an innovative measurement scheme for the study of neuromuscular control and for characterizing pathologic muscle tissue properties during active motor function.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.