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

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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.