Abstract 4_21

Friday, April 21 3pm McKinly 337 refreshments and skateboarding prior
John Novotny, PhD (host ME)
Title: Dynamic Imaging of Muscle Function and an Application to the
Rotator Cuff
Abstract: Our understanding of muscle function is limited by the
methods that are available for its study. These include predominantly
strength testing, electromyography, electrical stimulation and
mathematical modeling. The results of these studies are conceptualized
through models of sacromere behavior at small scales of size and scaled
up to muscles as linear elements. In this presentation, we describe
our methods to dynamically image muscle in vivo using cine phasecontrast magnetic resonance imaging (CPC-MRI). This allows us to study
muscle as a two-dimensional continuous material and quantify its
mechanics during contraction. We have developed techniques that allow
us to interpolate the CPC-MRI velocity data to sub-pixel resolutions
and to calculate displacements and Lagrangian finite strain for regions
of interest within muscle. Studies of the biceps brachii and the
supraspinatus muscles during cyclic motions of the forearm and humerus
were performed in normal populations. For the biceps brachii,
identification of maximum and minimum principal strains and maximum inplane shear strain describe regions of muscle elongation near the
aponeurosis, isostrain lines across muscle fibers and functional lines
of action through the muscle length. In the supraspinatus, we have
focused our techniques on investigating muscle function near the
muculotendinous junction. We have found functional differences in the
supraspinatus muscle that relate to clinical findings of muscle atrophy
after rotator cuff tears and perhaps hint to a level of internal muscle
coordination that, if lost, may initiate or propagate tears.