Multi-modal Image Registration

In different areas, particularly medical image analysis, there is a vital need to access and analyse dynamic three dimensional (3D) images of the anatomical structures of the human body. This can enable specialists to track events as well as clinically conduct and evaluate surgical and radio therapeutical procedures. For example, measuring the 3D kinematics of knee joints in a dynamic manner is essential for understanding their normal functions and diagnosing any pathology, such as ligament injury and osteoarthritis. For evaluations of subsequent treatments, such as surgery and rehabilitation, and designs of joint replacements, having knowledge of the movements of knee joints is necessary. Image registration is increasingly being applied to medical image analysis. Whereas in mono-modal registration, the images to be registered are acquired by the same sensor, in multi-modal image registration, they can be taken from different devices or imaging protocols which makes this registration process much more challenging. The invasive or non-invasive nature of the registration method used, the computational time it requires as well as its accuracy and robustness against a large range of initial displacements are the most important features used for its evaluation. As currently available approaches have limited capabilities to register images with large initial displacements and are either not sufficiently accurate or very computationally expensive, the objective of this research is to propose new registration methods, that provide dynamic 3D images, to address these issues. In the first part of this study, I conducted research on registering an individuals’ natural knee bones that can provide 3D information of knee joint kinematics which can be very helpful for improving the accuracy of diagnosis and enabling targeted treatments. A fast, accurate and robust hybrid rigid body registration method based on two different multi-modal similarity measures, the edge position difference (EPD) and sum-of-conditional variance (SCV), is proposed. It uses a gradient descent optimisation technique to register multi-modal images and determine the best transformation parameters. It helps to achieve a trade-off among different challenges, including time complexity, accuracy and robustness against a large range of initial displacements. To evaluate it, several experiments were performed on two different databases: one collected from the knee bones of four patients and the other from three knee cadavers installed on a mechanical positioning system, with the results showing that this method is accurate, fast and robust against large initial displacement. Then, I conducted research on registering implanted human knee joints and proposed a non-invasive, robust 3D-to-2D registration method which can be used for 3D evaluations of the status of knee implants after joint replacement surgeries. In this method, 3D models of the implants for an individual with the relevant post-operative fluoroscopy frames are able to be used in the registration process. As a result, it is possible to perform 3D analysis at any time after a surgery by simply taking single-plane radiographs. This approach uses the EPD multi-modal similarity measure together with a steepest descent optimisation method. It applies coarse-to-fine registration steps to determine the transformation parameters that lead to the best alignment between the model used and X-ray images to be registered. The experimental results showed that not only does the proposed registration method have a high success rate but that it is also much faster than the most relevant competitive approach. Although the experiments were designed for a 3D analysis of total knee arthroplasty (TKA) components, this proposed method can be applied to other joints such as the ankle or hip. In the final part of my research, I developed a multi-frame 2D fluoroscopy to 3D model registration method for measuring the kinematics of post-operative knee joints. It uses a coarse-to-fine approach and applies the normalised EPD (NEPD) and SCV similarity measures together with a gradient descent optimisation method and an interpolation estimation one. In order to measure the kinematics of post- operative knee joints, after a TKA surgery, a 3D knee implant model can be registered with a number of single-plane fluoroscopy frames of the patient’s knee. Generally, when this number is quite high, the computational cost for registering the frames and a 3D model is expensive. Therefore, in order to speed up the registration process, a cubic spline interpolation prediction method is applied to initialise and estimate the 3D positions of the 3D model in each fluoroscopy frame instead of applying a registration algorithm on all the frames, one after the other. The estimated 3D positions are then tuned using a registration improvement step. The experimental results demonstrated that the proposed registration method is much faster than the best existing one and achieves almost the same accuracy. It also provides smooth registration results which can lead to more natural 3D modelling of joint movements

Low Back Pain Pathogenesis and Treatment

Low back pain is a common disorder which affects the lumbar spine, and is associated with substantial morbidity for about 80% of the general population at some stages during their lives. Although low back pain usually is a self-limiting disorder that improves spontaneously over time, the etiology of low back pain is generally unknown and the diagnostic label, "non-specific low back pain", is frequently given. This book contains reviews and original articles with emphasis on pathogenesis and treatment of low back pain except for the rehabilitative aspect. Consisting of three sections, the first section of the book has a focus on pathogenesis of low back pain, while the second and third sections are on the treatment including conservative and surgical procedure, respectively

Development, in vitro and in vivo evaluation of a new artificial disc prothesis (Kineflex/Centurion disc) and the relevant insertion instrumentation for the human lumbar spine

Ph.D., Faculty of Health Sciences, University of the Witwatersrand, 2008.Lumbar disc replacement is a rapidly expanding surgical treatment modality for longstanding back and leg pain due to intervertebral disc degeneration. Compared to fusion surgery, it has the advantage of preserving segmental mobility, but convincing evidence of superiority over fusion surgery is missing. As part of this research project, I participated in the development of a new intervertebral disc prosthesis, with several international patents attached to the design of the prosthesis, the instrumentation and the insertion technique. The Kineflex (Centurion) lumbar disc is a mechanical, un-constrained, re-centering disc prosthesis developed in South Africa. After the development and manufacturing of the disc, prototype test racks were custom-made at the premises of the manufacturer and the disc was extensively tested for mechanical wear and fatigue. The first implantation took place in October 2002. I prospectively captured all cases performed by our centre, with documentation including demographic data, co-morbidities, clinical history, symptoms and signs. The completed consent forms were filed. The outcome was monitored, pre-operatively and in follow-up, with complete radiological documentation of all radiographs on JPEG files. Clinical outcome results were documented using two different internationally validated questionnaires as well as our own questionnaire, which expands further on work and demographic details, previous operative and conservative treatment, and satisfaction with the treatment outcome. The aim of the this project was to develop a disc prosthesis that is suitable and safe for human implantation into the lumbar spine disc space, even in severely advanced disc degeneration and to verify this in the outcome studies presented in this thesis. Existing indications and contra-indications for artificial disc replacement were critically evaluated regarding their validity for this particular implant. Results: Chapter 3 elaborates on the extensive pre-clinical mechanical wear and fatigue testing protocol to which the Centurion (Kineflex) lumbar disc prosthesis was subjected. The results of this testing protocol, together with our early clinical outcome results, formed the basis for the awarding of the European quality recognition (CE-Mark). In these extensive in vitro studies, we were able to show the durability of the Kineflex disc prosthesis in the long term. This, together with our initial clinical outcome results, formed the basis for the acceptance into a “prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the KINEFLEX Lumbar Artificial Disc versus the CHARITÉ™ Artificial Disc”. Chapter 4 is compiled from an invited submission to a new book on motion preservation surgery in the human spine, edited by leading spine surgeons in the field (James J. Yue, Rudolf Bertagnoli, Paul McAfee, and Howard An) and published by Elsevier Publishers: Chapter 42: Kineflex. In this chapter, an overview is given of the ideas behind the Kineflex disc development, as well as of the insertion instrumentation used for disc implantation. It further reports on early clinical outcome results of the first patients implanted with the device in our centre (the first 40 implantations worldwide were all performed by me). Chapter 5, our first peer reviewed international publication, reports on clinical and radiological 2-year outcome results of our first 100 patients. With the Kineflex implant, we could demonstrate equally good radiological placement accuracy in patients with severe and less severe disc degeneration of the index level, rendering the implant suitable even in severe degeneration of a spinal motion segment. Chapter 6 and Chapter 7 of this thesis consist of two further peer-reviewed publications. They both report on so-called “off-label” patient sub-groups in our disc replacement series. In Chapter 6 we present the second published series on a larger group of patients presenting with adjacent segment disease after previous lumbar fusion surgery as well as the first publication, which investigated the radiological changes in alignment parameters secondary to the disc replacement surgery in this patient group. Chapter 7 consists of the first published series on patients with “degenerative spondylolisthesis” treated with disc replacement surgery. A detailed description of the operative reduction technique is provided, which is unique to the Kineflex disc and its insertion instrumentation. In this pilot study, two-year results on a limited patient group are presented. This thesis concludes with the overall discussion in Chapter 8. It outlines the current knowledge on artificial disc replacement and places my results into perspective with recent discoveries published in the literature. It finishes with my assessment of what future research should concentrate on