University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 2014 Intervertebral Disc Structure and Mechanical Function Under Physiological Loading Quantified Non-invasively Utilizing MRI and Image Registration Jonathon H. Yoder University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Biomechanics Commons, Biomedical Commons, and the Radiology Commons Recommended Citation Yoder, Jonathon H., "Intervertebral Disc Structure and Mechanical Function Under Physiological Loading Quantified Non-invasively Utilizing MRI and Image Registration" (2014). Publicly Accessible Penn Dissertations. 1511. https://repository.upenn.edu/edissertations/1511 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/1511 For more information, please contact [email protected]. Intervertebral Disc Structure and Mechanical Function Under Physiological Loading Quantified Non-invasively Utilizing MRI and Image Registration Abstract The intervertebral discs (IVD) functions to permit motion, distribute load, and dissipate energy in the spine. It performs these functions through its heterogeneous structural organization and biochemical composition consisting of several tissue substructures: the central gelatinous nucleus pulposus (NP), the surrounding fiber einforr ced layered annulus fibrosus (AF), and the cartilaginous endplates (CEP) that are positioned between the NP and vertebral endplates. Each tissue contributes individually to overall disc mechanics and by interacting with adjacent tissues. Disruption of the disc's tissues through aging, degeneration, or tear will not only alter the affected tissue mechanical properties, but also the mechanical behavior of adjacent tissues and, ultimately, overall disc segment function. Thus, there is a need to measure disc tissue and segment mechanics in the intact disc so that interactions between substructures are not disrupted. Such measurements would be valuable to study mechanisms of disc function and degeneration, and develop and evaluate surgical procedures and therapeutic implants. The objectives of this study were to develop, validate, and apply methods to visualize and quantify IVD substructure geometry and track internal deformations for intact human discs under axial compression. The CEP and AF were visualized through MRI parameter mapping and image sequence optimization for ideal contrast. High-resolution images enabled geometric measurements. Axial compression was performed using a custom-built loading device that permitted long relaxation times outside of the MRI, 300 m isotropic resolution images were acquired, and image registration methods applied to measure 3D internal strain. In conclusion, new methods to visualize and quantify CEP thickness, annular tear detection and geometric quantification, and non-invasively measure 3D internal disc strains were established. No correlation was found between CEP thickness and disc level; however the periphery was significantly thicker compared to central locations. Clear distinction of adjacent AF lamellae enabled annular tear detection and detailed geometric quantification. Annular tears demonstrated "non-classic" geometry through interconnecting radial, circumferential, and perinuclear formations. Regional strain inhomogeneity was observed qualitatively and quantitatively. Variation in strain magnitudes might be explained by geometry in axial and circumferential strain while peak radial strain in the posterior AF may have important implications for disc herniation. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Mechanical Engineering & Applied Mechanics First Advisor Dawn M. Elliott Keywords annulus fibrosus, axial compression, image registration, internal strain, intervertebral disc, magnetic resonance imaging Subject Categories Biomechanics | Biomedical | Radiology This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/1511 INTERVERTEBRAL DISC STRUCTURE AND MECHANICAL FUNCTION UNDER PHYSIOLOGICAL LOADING QUANTIFIED NON-INVASIVELY UTILIZING MRI AND IMAGE REGISTRATION Jonathon Henry Yoder A DISSERTATION in Mechanical Engineering and Applied Mechanics Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2014 Supervisor of Dissertation ____________________ Dawn M. Elliott, Professor – Director of Biomedical Engineering University of Delaware Graduate Group Chairperson ____________________ Prashant Purohit, Chair and Associate Professor MEAM Dissertation Committee: Louis J Soslowsky, Fairhill Professor Orthopaedic Surgery and Professor Bioengineering James C Gee, Associate Professor Radiologic Science in Radiology Prashant Purohit, Chair and Associate Professor MEAM Beth A Winkelstein, Professor Bioengineering Edward J Vresilovic, Orthopaedic Surgery Penn State University ABSTRACT INTERVERTEBRAL DISC STRUCTURE AND MECHANICAL FUNCTION UNDER PHYSIOLOGICAL LOADING QUANTIFIED NON-INVASIVELY UTILIZING MRI AND IMAGE REGISTRATION Jonathon H Yoder Dawn M Elliott The intervertebral discs (IVD) functions to permit motion, distribute load, and dissipate energy in the spine. It performs these functions through its heterogeneous structural organization and biochemical composition consisting of several tissue substructures: the central gelatinous nucleus pulposus (NP), the surrounding fiber reinforced layered annulus fibrosus (AF), and the cartilaginous endplates (CEP) that are positioned between the NP and vertebral endplates. Each tissue contributes individually to overall disc mechanics and by interacting with adjacent tissues. Disruption of the disc’s tissues through aging, degeneration, or tear will not only alter the affected tissue mechanical properties, but also the mechanical behavior of adjacent tissues and, ultimately, overall disc segment function. Thus, there is a need to measure disc tissue and segment mechanics in the intact disc so that interactions between substructures are not disrupted. Such measurements would be valuable to study mechanisms of disc function and degeneration, and develop and evaluate surgical procedures and therapeutic implants. The objectives of this study were to develop, validate, and apply methods to visualize and ii quantify IVD substructure geometry and track internal deformations for intact human discs under axial compression. The CEP and AF were visualized through MRI parameter mapping and image sequence optimization for ideal contrast. High-resolution images enabled geometric measurements. Axial compression was performed using a custom-built loading device that permitted long relaxation times outside of the MRI, 300 m isotropic resolution images were acquired, and image registration methods applied to measure 3D internal strain. In conclusion, new methods to visualize and quantify CEP thickness, annular tear detection and geometric quantification, and non-invasively measure 3D internal disc strains were established. No correlation was found between CEP thickness and disc level; however the periphery was significantly thicker compared to central locations. Clear distinction of adjacent AF lamellae enabled annular tear detection and detailed geometric quantification. Annular tears demonstrated “non-classic” geometry through interconnecting radial, circumferential, and perinuclear formations. Regional strain inhomogeneity was observed qualitatively and quantitatively. Variation in strain magnitudes might be explained by geometry in axial and circumferential strain while peak radial strain in the posterior AF may have important implications for disc herniation. iii Table of Contents ABSTRACT ……………………………………………………………………………………………………. ii Table of Contents ..................................................................................................................... iv List of Tables ………………………………………………………………………………………………… vi List of Illustrations ............................................................................................................... viii CHAPTER 1 Introduction ........................................................................................................ 1 CHAPTER 2 Background ......................................................................................................... 5 2.1. Clinical Significance ....................................................................................................... 5 2.2. Intervertebral Disc Structure .................................................................................... 6 2.3. Disc Mechanical Function ............................................................................................ 7 2.4. Disc Degeneration .......................................................................................................... 9 2.5. Internal Deformations ............................................................................................... 14 2.6. Medical Image Analysis and Registration Applications ................................ 16 2.7. Advanced Normalization Tools Image Registration Parameters .............. 18 CHAPTER 3 Cartilaginous Endplate Geometry ............................................................. 20 3.1. Introduction .................................................................................................................. 20 3.2. Materials and Methods .............................................................................................