Deformable Multisurface Segmentation of the Spine for Orthopedic Surgery Planning and Simulation

Purpose: We describe a shape-aware multisurface simplex deformable model for the segmentation of healthy as well as pathological lumbar spine in medical image data. Approach: This model provides an accurate and robust segmentation scheme for the identification of intervertebral disc pathologies to enable the minimally supervised planning and patient-specific simulation of spine surgery, in a manner that combines multisurface and shape statistics-based variants of the deformable simplex model. Statistical shape variation within the dataset has been captured by application of principal component analysis and incorporated during the segmentation process to refine results. In the case where shape statistics hinder detection of the pathological region, user assistance is allowed to disable the prior shape influence during deformation. Results: Results demonstrate validation against user-assisted expert segmentation, showing excellent boundary agreement and prevention of spatial overlap between neighboring surfaces. This section also plots the characteristics of the statistical shape model, such as compactness, generalizability and specificity, as a function of the number of modes used to represent the family of shapes. Final results demonstrate a proof-of-concept deformation application based on the open-source surgery simulation Simulation Open Framework Architecture toolkit. Conclusions: To summarize, we present a deformable multisurface model that embeds a shape statistics force, with applications to surgery planning and simulation

Multi-Surface Simplex Spine Segmentation for Spine Surgery Simulation and Planning

This research proposes to develop a knowledge-based multi-surface simplex deformable model for segmentation of healthy as well as pathological lumbar spine data. It aims to provide a more accurate and robust segmentation scheme for identification of intervertebral disc pathologies to assist with spine surgery planning. A robust technique that combines multi-surface and shape statistics-aware variants of the deformable simplex model is presented. Statistical shape variation within the dataset has been captured by application of principal component analysis and incorporated during the segmentation process to refine results. In the case where shape statistics hinder detection of the pathological region, user-assistance is allowed to disable the prior shape influence during deformation. Results have been validated against user-assisted expert segmentation

Development of ultrasound to measure deformation of functional spinal units in cervical spine

Neck pain is a pervasive problem in the general population, especially in those working in vibrating environments, e.g. military troops and truck drivers. Previous studies showed neck pain was strongly associated with the degeneration of intervertebral disc, which is commonly caused by repetitive loading in the work place. Currently, there is no existing method to measure the in-vivo displacement and loading condition of cervical spine on the site. Therefore, there is little knowledge about the alternation of cervical spine functionality and biomechanics in dynamic environments. In this thesis, a portable ultrasound system was explored as a tool to measure the vertebral motion and functional spinal unit deformation. It is hypothesized that the time sequences of ultrasound imaging signals can be used to characterize the deformation of cervical spine functional spinal units in response to applied displacements and loading. Specifically, a multi-frame tracking algorithm is developed to measure the dynamic movement of vertebrae, which is validated in ex-vivo models. The planar kinematics of the functional spinal units is derived from a dual ultrasound system, which applies two ultrasound systems to image C-spine anteriorly and posteriorly. The kinematics is reconstructed from the results of the multi-frame movement tracking algorithm and a method to co-register ultrasound vertebrae images to MRI scan. Using the dual ultrasound, it is shown that the dynamic deformation of functional spinal unit is affected by the biomechanics properties of intervertebral disc ex-vivo and different applied loading in activities in-vivo. It is concluded that ultrasound is capable of measuring functional spinal units motion, which allows rapid in-vivo evaluation of C-spine in dynamic environments where X-Ray, CT or MRI cannot be used.2020-02-20T00:00:00

Nanofibrous Disc-Like Angle Ply Structure for Total Disc Replacement in a Small Animal Model

Low back pain affects 85% of the population and carries a socioeconomic price tag of $100 billion USD per year. Lumbar intervertebral disc disease is strongly implicated as a causative factor in back pain, as degeneration, which is ubiquitous in the population, leads to loss of normal spine function. For these reasons, our lab has developed disc-like angle ply structures (DAPS) for total disc replacement. These cell-seeded replacements are designed to match the natural hierarchical structure and function of the native disc and correct spinal kinematics after end-stage disc disease. In this dissertation, I describe the development of a rat caudal spine (tail) model of total disc replacement as a platform to evaluate DAPS in vivo; an external fixation system that immobilized caudal vertebrae at the site of implantation was required for DAPS retention and a radiopaque scaffold was developed to confirm intervertebral DAPS positioning. A detailed analysis of the DAPS in vitro growth trajectory was performed to select the optimum pre-culture duration before implantation. Cell-seeded DAPS were subsequently implanted in the rat tail and evaluated by histological, mechanical, and MRI analyses. DAPS successfully restored the mechanical properties of the native motion segment in compression, providing the first evidence of the efficacy of engineered disc replacements. Adaptations of the implant to the in vivo environment were identified; there was a reduction in glycosaminoglycan after implantation, structural modifications to the NP material, and no evidence of vertebral integration. In tackling the first of these issues, a pre-culture strategy that primed DAPS for the in vivo environment was developed; using a rat subcutaneous model, implant phenotype was best conserved post-implantation using a pre-culture strategy with a transient high dose of TGF-b3. Future work will address maintenance of NP structure, vertebral integration and scaling up to human sizes. In my work, the most promising finding was that DAPS replicated compressive motion segment mechanical properties after implantation supporting the idea that engineered biological disc replacement is a possibility for clinical treatment of advanced disc disease

Percutaneous Curettage and Continuous Irrigation for MRSA Lumbar Spondylodiscitis: A Report of Three Cases

There has been a recent increase in pyogenic spondylitis caused by methicillin-resistant Staphylococcus aureus (MRSA) associated with an increasing number of compromised patients. As long as serious paralysis is absent, we recommend percutaneous curettage and continuous irrigation as an effective treatment for MRSA lumbar spondylodiscitis. Under local anesthesia, the affected lumbar discs were curetted using percutaneous nucleotomy, and tubes were placed for continuous irrigation. The period of continuous irrigation was generally 2 weeks. Infection was controlled after one procedure in two cases and after two procedures in one case. Postoperative radiography and magnetic resonance imaging (MRI) showed callus formation, normalized signal intensity in vertebral bodies, and regression of abscesses. Open surgery under general anesthesia has been considered risky in patients with poor performance status or old age. The present method, which is an application of needle biopsy, can be performed under local anesthesia and is minimally invasive

Active appearance pyramids for object parametrisation and fitting

Object class representation is one of the key problems in various medical image analysis tasks. We propose a part-based parametric appearance model we refer to as an Active Appearance Pyramid (AAP). The parts are delineated by multi-scale Local Feature Pyramids (LFPs) for superior spatial specificity and distinctiveness. An AAP models the variability within a population with local translations of multi-scale parts and linear appearance variations of the assembly of the parts. It can fit and represent new instances by adjusting the shape and appearance parameters. The fitting process uses a two-step iterative strategy: local landmark searching followed by shape regularisation. We present a simultaneous local feature searching and appearance fitting algorithm based on the weighted Lucas and Kanade method. A shape regulariser is derived to calculate the maximum likelihood shape with respect to the prior and multiple landmark candidates from multi-scale LFPs, with a compact closed-form solution. We apply the 2D AAP on the modelling of variability in patients with lumbar spinal stenosis (LSS) and validate its performance on 200 studies consisting of routine axial and sagittal MRI scans. Intervertebral sagittal and parasagittal cross-sections are typically used for the diagnosis of LSS, we therefore build three AAPs on L3/4, L4/5 and L5/S1 axial cross-sections and three on parasagittal slices. Experiments show significant improvement in convergence range, robustness to local minima and segmentation precision compared with Constrained Local Models (CLMs), Active Shape Models (ASMs) and Active Appearance Models (AAMs), as well as superior performance in appearance reconstruction compared with AAMs. We also validate the performance on 3D CT volumes of hip joints from 38 studies. Compared to AAMs, AAPs achieve a higher segmentation and reconstruction precision. Moreover, AAPs have a significant improvement in efficiency, consuming about half the memory and less than 10% of the training time and 15% of the testing time

Imaging of thoracolumbar spine traumas

Spine trauma is an ominous event with a high morbidity, frequent mortality, and significant psychological, social, and financial consequences for patients, their relatives and society. On average three out of four spinal fractures involve the thoracolumbar spine and up to one-third are complicated by spinal cord injury. Spinal cord injuries (SCI) are a significant cause of disability in US and in all western countries. Knowledge of the main principles of biomechanics is essential in understanding the patho-morphology of spinal injuries, and the evolution of the various classification systems. Classification systems should be able to create a common language between specialists in order to improve patients' prognosis, guide treatment and compare treatment outcomes. Imaging has always been crucial in the evaluation of the injury type and accompanied the development of different classification systems. Thoracolumbar spine (TLS) trauma has a wide spectrum ranging from minor isolated fractures to highly unstable fracture-dislocations. Early classification systems were based on the analysis of the pattern of bony injuries on radiographs and CT. Traditionally, conventional radiographs are performed to confirm the clinical suspicion and to depict the level and type of bone injury. However, because of their inherent limitations, radiographs are often more helpful in proving the existence of a suspected bony spinal injury rather than excluding it. Multidetector computed tomography (MDCT) is superior in evaluating bone anatomy and, especially in polytrauma patients, it is the first line imaging modality. Morphological bone damage may be accurately shown and classified on CT. the most recent classifications also incorporate the integrity of soft tissues structures, which is considered equally relevant to spinal stability. Injuries to ligaments and discs can only be suspected on radiographs and conventional CT, although dual-energy CT is offering new insights on collagen mapping of damaged discs. Magnetic resonance imaging (MRI) may directly assess disc and ligamentous injuries, but also subtle osseous injuries, playing a complementary role in defining the whole spinal damage and an eventual instability. MRI is the only valid modality to assess the spinal cord (SC) and is indicated whenever a neurologic injury is suspected. Advanced MRI techniques, such as diffusion weighted imaging (DWI) and tractography, may provide further information regarding the integrity of the white matter which may improve outcome prognostication. Despite challenges in terms of costs, availability, accessibility and specificity, MRI and advanced MRI techniques are increasingly being used in spinal injuries. We present a review on TLS traumas discussing on the development of different classification system used in their evaluation, the role of imaging for their detection and the correlation to the patients' outcomes and treatment options

The safety and efficacy of mesenchymal stem cells for prevention or regeneration of intervertebral disc degeneration: a systematic review

General Posters: abstract no. GP86INTRODUCTION: Mesenchymal stem cells (MSCs) have been used to halt the progression or regenerate the disc with hopes to prevent or treat discogenic back pain. However, the safety and efficacy of the use of MSCs for such treatment in animal and human models at short and long term assessment (i.e. greater than 48 weeks) have not been systematically addressed. This study addressed a systematic review of comparative controlled studies addressing the use of MSCs to that of no treatment/saline for the treatment of disc degeneration. METHODS: Online databases were extensively searched. Controlled trials in animal models and humans were eligible for inclusion. Trial design, MSC characteristics, injection method, disc assessment, outcome intervals, and complication events were assessed. Validity of each study was assessed addressing trial design. Two individuals independently addressed the aforementioned. RESULTS: Twenty-two animal studies were included. No human comparative controlled trials were reported. All three types of MSCs (i.e. derived from bone marrow, synovial and adipose tissue) showed successful inhibition of disc degeneration progression. From three included studies, bone marrow derived MSC showed superior quality of disc repair when compared to other treatments, including TGF-β1, NP bilaminar co-culture and axial distraction regimen. However, osteophyte development was reported in two studies as potential complication of MSC transplantation. CONCLUSIONS: Based on animal models, the current evidence suggests that in the short-term MSC transplantation is safe and effective in halting disc degeneration; however, additional and larger studies are needed to assess the long-term regenerative effects and potential complications. Inconsistency in methodological design and outcome parameters prevent any robust conclusions. In addition, randomized controlled trials in humans are needed to assess the safety and efficacy of such therapy.published_or_final_versio

Cube-Cut: Vertebral Body Segmentation in MRI-Data through Cubic-Shaped Divergences

In this article, we present a graph-based method using a cubic template for volumetric segmentation of vertebrae in magnetic resonance imaging (MRI) acquisitions. The user can define the degree of deviation from a regular cube via a smoothness value Delta. The Cube-Cut algorithm generates a directed graph with two terminal nodes (s-t-network), where the nodes of the graph correspond to a cubic-shaped subset of the image's voxels. The weightings of the graph's terminal edges, which connect every node with a virtual source s or a virtual sink t, represent the affinity of a voxel to the vertebra (source) and to the background (sink). Furthermore, a set of infinite weighted and non-terminal edges implements the smoothness term. After graph construction, a minimal s-t-cut is calculated within polynomial computation time, which splits the nodes into two disjoint units. Subsequently, the segmentation result is determined out of the source-set. A quantitative evaluation of a C++ implementation of the algorithm resulted in an average Dice Similarity Coefficient (DSC) of 81.33% and a running time of less than a minute.Comment: 23 figures, 2 tables, 43 references, PLoS ONE 9(4): e9338