Developing and Validating Imaging Techniques for Accurate Quantification of Whole-Body Skeletal Muscle Architecture
Abstract
Muscle architecture, defined as “the number and orientation of the muscle fibers within a muscle”, has an important influence on a muscle’s ability to produce force and shorten or lengthen under load. Briefly, muscle fiber arrangements that result in more sarcomeres aligned in series to each other and parallel with the muscle’s mechanical line of action allow greater length excursions and contraction velocities, while muscle fiber arrangements that result in more sarcomeres aligned in parallel to each other and obliquely to the muscle’s mechanical line of action allow greater force production. In addition, the curved fiber geometry that is necessary for mechanical stability results in heterogeneous patterns of strain development and the formation of intramuscular fluid pressure gradients that may restrict perfusion. However, our tools to study the structure-function relationship of human skeletal muscle, including ultrasound (U/S) and diffusion-tensor magnetic resonance imaging (DTMRI), need further development. The overall goal of this dissertation research is to develop and validate imaging techniques for accurate quantification of whole-body muscle architecture. First, we developed a numerical simulation framework and systematically examined the effects of condition variables on the accuracy and precision of DTMRI-based muscle architecture estimates. Based on the simulation predictions, we made practical recommendations for the implementation of in vivo skeletal muscle DTMRI experiments. In the second part of our study, we implemented a fiducial-based co-registration framework which allowed the direct comparison between U/S- and DTMRI-reconstructed muscle fiber architectures in vivo. As previous studies showed that U/S had good agreement with direct anatomical inspection in muscle architecture measurements, our newly developed U/S-MR cross-modality registration framework demonstrated its potential to work as a validation tool for DTMRI-based in vivo muscle architecture measurements. In the third part of our study, we designed and implemented an in vivo experiment protocol for the characterization of human skeletal muscle. We focused on the muscle groups that act on the lower body, optimized the image acquisition and analysis protocols, and measured the architecture parameters of representative muscles. Overall, this work has produced an improved understanding of skeletal muscle architecture, and new tools for its validation and in vivo characterization.
Description
Keywords
skeletal muscle, muscle architecture, magnetic resonance imaging, 7T MRI, diffusion-tensor imaging, numerical simulation, ultrasound imaging, whole-body imaging, validation, cross-modality comparison, cross-modality image registration