This project concerns the development of electrical impedance tomography towards the production of complex impedance images. The prime intention was to investigate the feasibility of developing suitable instrumentation; but not clinical applications. It was aimed to develop techniques for the performance evaluation of data collection systems. To achieve this it was necessary to design and develop a multi· current source type impedance tomography system, to act as a platform for the current study and for future work. The system developed is capable of producing conductivity and permittivity images. It employs microprocessor based data collection electronics, providing portability between a range of possible host computers. The development of the system included a study of constant amplitude current source circuits leading to the design and employment of a novel circuit. In order to aid system testing, a surface mount technology resistor-mesh test object was produced. This has been adopted by the EEC Concerted Action on Impedance Tomography (CAIT) programme as the first standard test object. A computer model of the phantom was produced using the industry standard ASTEC3 circuit simulation package. This development allows the theoretical performance of any system topology, at any level of detail, to be established. The imaging system has been used to produce images from test objects, as well as forearm and lung images on humans. Whilst the conductivity images produced were good, the permittivity in-vivo images were noisy, despite good permittivity images from test objects. A study of the relative merits of multiple and single stimulus type systems was carried out as a result of the discrepancies in the in-vivo and test object images. This study involved a comparison of the author's system with that of Griffiths at the University Hospital of Wales. The results showed that the multi current source type system, whilst able to reduce stray capacitance, creates other more significant errors due to circuit matching; future development in semiconductor device technology may help to overcome this difficulty. It was identified that contact impedances together with the effective capacitance between the measurement electrode pairs in four-electrode systems reduces the measurability of changes in phase. A number of benchmarking indices were developed and implemented, both for system characterisation and for practical/theoretical design comparisons.

<p> Horses are powerful animals: a galloping horse&rsquo;s forefoot hits the ground with an average of about 2,000 pounds of force. This can result in many kinds of injuries. To work with and love a horse properly, the owner needs to understand more than just grooming and feeding. Owners must understand how the horse operates, particularly the structure and workings of the horse&rsquo;s legs, to comprehend how a broken leg impairs a horse. This understanding enables the owner to work well with a veterinarian in determining the best course of treatment for an injury. </p><p> A review of the current veterinary literature and public resources showed that illustrated information regarding types of limb fractures in horses, options for repair and post-operative outcomes, that can be easily understood by the lay person, do not exist. The lack of sufficiently illustrated resources covering this topic indicates a great need for this valuable information. </p><p> The objective of this thesis is to illustrate common types of fractures, to assist owners in understanding different types of fractures, repair options, and possible outcomes of any intervention. Three cases, each with a specific type of fracture, were analyzed to develop understanding of the damage, the impact on the horse and surgical options versus the need for euthanasia. The finished product of this research was two posters, one for repair and the other for euthanasia, designed to enhance the owner&rsquo;s comprehension of the injuries.</p><p>

<p> One pathway for a new device to gain access to the marketplace requires demonstration that it is equivalent to, or substantially better than, a legally marketed device. To evaluate the equivalence of a medical imaging device, we propose measuring the intra- or inter-reader agreement in a reader study, where the clinicians (readers) make diagnoses on the medical images (cases) using both the new and old imaging devices. Such an endpoint, as well as its variance estimate, enable us to make a statistical inference on the equivalence of two devices. A method for multiple-reader multiple-case agreement analysis was presented in Gallas et al. (2016) for fully-crossed study designs, where every reader reads every case. In practice, having every reader read every case may be impossible when readers have a limited amount of time to participate in the study. One alternative study design is the split-plot study design, where both the readers and the cases are partitioned into a fixed number of groups, and each group of readers reads its own group of cases. In this thesis, we adapt the multiple-reader multiple-case agreement analysis method in Gallas et al. (2016) to analyze split-plot study designs, and propose a new variance estimator based on splitting the analysis across the groups. In each split sub-study, we compute an estimate, and then combine these estimates to obtain the final estimate for the full study. Our numerical studies show that the "split-analysis" variance estimator provides more accurate estimation of the variance of concordance measurements than the full-study-based method for unbalanced split-plot study designs.</p><p>

<p> In volumetric image analysis and visualization, challenges have be induced by the increasing size of volume over recent years. Rendering and interacting with a volume with reduced size is preferable and highly needed. The primary concern in producing such downsized volumetric images is to preserve the important structures and those of the user's interest, such as boundaries between materials. Typical volume reduction approaches usually perform uniform subsampling without the awareness of user-specified parameters such as the opacity and color transfer functions. However, it is also handy for the algorithm to have "global'' encoding and control over the entire volume, meanwhile revealing some features of the data while it is being downsized. This thesis aims at providing a means of such type, extended from the famous seam carving operator that has been used widely in the task of image and video retargeting. </p><p> Our work applies and extends the seam carving algorithm for videos proposed by Rubinstein et al. to downsize three-dimensional volumetric images. This extended technique computes and removes from the volume two-dimensional seams, or what we name and define as sheets, to reduce the size of the volume with minimum loss of important details measured by gradient. We aim at learning through experimentation the visual quality of seam carved volumetric images, making improvements based on feedback and potentially paving ways towards applications. With the great flexibility of the graph cut formulation, we implement in our algorithm the existing backward and forward energy optimization, and add extensions including isosurface protection and the encoding of the opacity transfer function. </p><p> At the visual level, experimental results tell us when applied alone with fixed parameters, volumetric seam carving outperforms trivial approaches in preserving important structures only for part of the datasets, on which discussions are included at the best knowledge of the author.</p><p>

No description available.

No description available.

No description available.

Quantitative magnetic resonance imaging (MRI) measurements of the pediatric spinal cord is important for both diagnostic and treatment planning. In recent years several quantitative MRI (qMRI) techniques that have been developed and tested to measure functional and structural information of the spinal cord tissue and microstructure. Several of the existing structural and functional imaging biomarkers (i.e., diffusion tensor imaging (DTI)) have demonstrated potential for providing microstructural information about the spinal cord. However, due to the lack of a standard anatomical template of the pediatric spinal cord, quantification of the spinal cord tissue has been challenging. Therefore, one of the goals of this work is to develop and test tools for quantification as well as the creation of a standard structural template of the typically developing (TD) pediatric spinal cord. This will allow automated measurement of normative values of the spinal cord cross-sectional area (SCCSA) at various levels of the spinal cord. Furthermore, to examine the white matter (WM) microstructure of the pediatric cord we developed a processing pipeline for the atlas-based generation of TD pediatric spinal cord WM tracts. This will facilitate the measurements of normative diffusion values for various WM tracts.A group of 30 TD subjects (age range of 6-17 years old (12.38 ±2.81)), who had no evidence of spinal cord injury or pathology were recruited. We utilized a multiparametric MRI protocol, including high-resolution T2-w structural and diffusion-weighted MRI images to scan the subjects on a 3T MRI scanner. The diffusion data were acquired using a novel iFOV DTI sequence. For quantification, a post-processing pipeline was utilized to generate the structural pediatric template. Next, WM tracts were generated using an atlas-based approach, and diffusion metrics (FA, MD, RD and AD) were quantified in 34 tracts identified in the processing pipeline. Normative SCCSA and DTI diffusion indices were generated for the TD population. Lastly, we demonstrated that DTI indices (i.e. FA) can be a predictive measure of components of the clinical test for spinal cord injury, as well as an indicator of the white matter tracts integrity. Therefore, in the final step of this work, we expanded our quantitative analysis to look at the microstructural and macrostructural changes in 15 children with chronic spinal cord injury (SCI) (AIS A-D, mean age of 12.8 ± 3.1 years). This included measurements of SCCSA, diffusion metrics and T2* WM/GM ratio of various white matter tracts in the patient population. We also examined the relationships between all the metrics and the ISNCSCI clinical scores in SCI subjects. We then compared these measurements between the TD and SCI patients to evaluate the diagnostic utility of these techniques and biomarkers. Statistically significant difference was observed between the two populations in the studied metrics. The results show that the proposed techniques may have the potential to be used as surrogate biomarkers for the quantification of the injured spinal cord. Keywords: diffusion tensor imaging, typically developing, spinal cord injury, spinal cord cross-sectional area, fractional anisotropy, mean diffusivity, axial diffusivity, radial diffusivity / Bioengineering

No description available.

No description available.