published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

The Hotelling trace criterion (HTC) is a measure of class separability used in pattern recognition to find a set of linear features that optimally separate two classes of objects. In this dissertation we use the HTC not as a figure of merit for features, but as a figure of merit for characterizing imaging systems and designing filters for feature enhancement in nuclear medicine. If the HTC is to be used to optimize systems, then it must correlate with human observer performance. In our first study, a set of images, created by overlapping ellipses, was used to simulate images of livers. Two classes were created, livers with and without tumors, with noise and blur added to each image to simulate nine different imaging systems. Using the ROC parameter dₐ as our measure, we found that the HTC has a correlation of 0.988 with the ability of humans to separate these two classes of objects. A second study was performed to demonstrate the use of the HTC for system optimization in a realistic task. For this study we used a mathematical model of normal and diseased livers and of the imaging system to generate a realistic set of liver images from nuclear medicine. A method of adaptive, nonlinear filtering which enhances the features that separate two sets of images has also been developed. The method uses the HTC to find the optimal linear feature operator for the Fourier moduli of the images, and uses this operator as a filter so that the features that separate the two classes of objects are enhanced. We demonstrate the use of this filtering method to enhance texture features in simulated liver images from nuclear medicine, after using a training set of images to obtain the filter. We also demonstrate how this method of filtering can be used to reconstruct an object from a single photon-starved image of it, when the object contains a repetitive feature. When power spectrums for real liver scans from nuclear medicine are calculated, we find that the three classifications that a physician uses, normal, patchy, and focal, can be described by the fractal dimension of the texture in the liver. This fractal dimension can be calculated even for images that suffer from much noise and blur. Given a simulated image of a liver that has been blurred and imaged with only 5000 photons, a texture with the same fractal dimension as the liver can be reconstructed.

A Desordem do Espectro da Neuropatia Auditiva (DENA) é uma patologia que vem sendo foco de pesquisas e relatos de caso devido sua complexidade. A compreensão da fisiopatologia da DENA ainda não é precisa, o que proporciona desafios na prática médica, principalmente em relação à conduta mais adequada a ser adotada nestes casos. Neste contexto, a compreensão da anatomia do nervo vestibulococlear por meio do estudo de imagens, contribui para o diagnóstico das deficiências auditivas. Entretanto, apesar dos avanços tecnológicos e científicos nesta área, ainda existem inúmeros questionamentos quanto à localização da alteração em casos de DENA. Diante disso, o objetivo deste estudo foi descrever a correlação do quadro clínico audiológico e exame por imagem em indivíduos com diagnóstico de Desordem do Espectro da Neuropatia Auditiva dissociado de doenças pré-existentes por meio de uma revisão sistemática. A revisão sistemática foi realizada nas bases de dados LILACS, PubMed, Scopus e Web of Science. Foram identificados 1.966 artigos com a estratégia de busca, sendo 50 selecionados para leitura na integra e 20 textos analisados para a discussão. A ressonância magnética (RM) é um exame extremamente útil para diagnósticos de alterações do nervo coclear, possibilitando diagnóstico diferencial e auxilia na topografia da lesão. A avaliação da imagem no plano sagital permite avaliar o diâmetro do nervo coclear (NC) e suas características. O diâmetro do NC está relacionado com doenças durante a gestação e perinatal, contudo, na prática clínica a avaliação do diâmetro dos nervos é subjetiva. Não há padronização universal de análise e de uso quotidiano de mensurar o nervo coclear em pacientes submetidos a RM, quando em investigação etiológica para perdas auditivas sensorioneural. / Auditory Neuropathy Spectrum Disorder (ANSD) is a pathology that has been the focus of research and case reports, owing to its complexity. The understanding of ANSD pathophysiology is not yet precise, thus, presenting challenges in medical practice, especially regarding the most appropriate conduct to be adopted in these cases. In this context, the understanding of the anatomy of the vestibulocochlear nerve through the study of images contributes to the diagnosis of auditory deficiencies. However, despite the technological and scientific advances in this area, many questions about the location of the alteration, in cases of ANSD, still remain. Thus, this study aimed at describing, through a systematic review, the correlation of the clinical condition and the imaging examination in individuals diagnosed with Auditory Neuropathy Spectrum Disorder, dissociated from pre-existing diseases. The systematic review was carried out in the LILACS, PubMed, Scopus and Web of Science databases, identifying 1966 articles with the search strategy, 50 being selected for integral reading and 20 texts analyzed for discussion. Magnetic resonance imaging (MRI) is an extremely useful exam for the diagnosis of cochlear nerve alterations, allowing a differential diagnosis and aiding in the topography of the lesion. The evaluation of the image in the sagittal plane allows the assessment of cochlear nerve (CN) diameter and its characteristics. CN diameter is related to diseases during gestation and perinatal period, however, in clinical practice the evaluation of the diameter of the nerves is subjective. There is no analysis universal standardization of daily use to measure the cochlear nerve in patients submitted to MRI, in terms of etiological investigation for sensorineural hearing loss.

University of Macau / Faculty of Health Sciences

by Chung-fai Kwok. / Thesis (M.Sc.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 65). / Contents --- p.i / Table of Figures --- p.iii / Abstract --- p.v / Acknowledgment --- p.vii / Introduction --- p.viii / Chapter 1. --- Overview : Medical image network system --- p.1 / Chapter 1.1 --- MAGNET --- p.1 / Chapter 1.2 --- Medical image --- p.2 / Chapter 2. --- System configuration --- p.4 / Chapter 2.1 --- Hardware setting --- p.4 / Chapter 2.2 --- Software functions design --- p.5 / Chapter 3. --- Color handling --- p.7 / Chapter 3.1 --- Color --- p.7 / Chapter 3.2 --- Colormap and color display --- p.9 / Chapter 3.3 --- Static and dynamic color mapping --- p.10 / Chapter 4. --- Color image processing --- p.11 / Chapter 4.1 --- Color image quantization --- p.11 / Chapter 4.1.1 --- Pre-quantization --- p.13 / Chapter 4.1.2 --- Median cut Algorithm --- p.15 / Chapter 4.1.3 --- Remapping colors --- p.16 / Chapter 4.1.4 --- Hashing --- p.17 / Chapter 4.1.5 --- Distortion Measures --- p.21 / Chapter 4.1.6 --- Experiment results and Discussion --- p.22 / Chapter 4.2 --- Intensity mapping --- p.30 / Chapter 4.2.1 --- Graylevel image contrast enhancement and reduction --- p.30 / Chapter 4.2.2 --- Graylevel image brightness increment and reduction --- p.36 / Chapter 4.2.3 --- Contrast enhancement and reduction on color components --- p.40 / Chapter 4.2.4 --- Brightness increment and reduction on color components --- p.41 / Chapter 4.3 --- Pseudocoloring --- p.45 / Chapter 5. --- Color image analysis --- p.47 / Chapter 5.1 --- Region Measures --- p.47 / Chapter 5.1.1 --- Region measures function design --- p.47 / Chapter 5.1.2 --- Region growing mechanism --- p.48 / Chapter 5.1.3 --- Region smoothing --- p.49 / Chapter 5.2 --- Distance measures --- p.53 / Chapter 5.3 --- Statistical analysis --- p.53 / Chapter 6. --- Summary and future work --- p.57 / Appendix : User interfaces and functions --- p.58 / Bibliography --- p.65

by Tin Pong. / Thesis (M.Sc.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaf 73). / Abstract --- p.2 / Acknowledgement --- p.4 / Table of Contents --- p.5 / Chapter I. --- Introduction --- p.8 / Chapter II. --- Segmentation Tools --- p.11 / Chapter 2.1. --- Segmentation of Object --- p.11 / Chapter 2.1.1. --- Segmentation algorithm --- p.11 / Chapter 2.1.2. --- Region growing algorithm --- p.16 / Chapter 2.2. --- Noise Reduction --- p.19 / Chapter 2.2.1. --- Median filtering --- p.19 / Chapter 2.2.2 --- Mean filtering --- p.20 / Chapter 2.3. --- Other functions --- p.21 / Chapter 2.3.1. --- Contrast enhancement and reduction --- p.21 / Chapter 2.3.2. --- Brightness increment and reduction --- p.22 / Chapter III. --- 3D Visualization Tools --- p.23 / Chapter 3.1. --- Interpolation --- p.23 / Chapter 3.1.1. --- Estimate distance between slices --- p.23 / Chapter 3.1.2. --- Trilinear Interpolation --- p.24 / Chapter 3.2. --- Projection --- p.26 / Chapter 3.2.1. --- Parallel projection --- p.26 / Chapter 3.2.2. --- Z-Buffers --- p.27 / Chapter 3.3. --- Rotation of 3D image --- p.29 / Chapter 3.4. --- Shading --- p.30 / Chapter IV. --- Description of the software developed --- p.32 / Chapter 4.1. --- Programming environment --- p.32 / Chapter 4.2. --- Software developed --- p.32 / Chapter 4.3. --- 2D object segmentation panel --- p.35 / Chapter 4.4. --- 3D object segmentation panel --- p.45 / Chapter V. --- Results and analysis --- p.56 / Chapter 5.1. --- Results of segmentation of object --- p.56 / Chapter 5.2. --- Results of 3D visualization tools --- p.64 / Chapter VI. --- Future Development --- p.70 / Chapter VII. --- Conclusion --- p.72 / References --- p.73

by Young Lee Kei, Ricky. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 205-207). / Abstract also in Chinese. / Acknowledgements --- p.i / Statement of Originality --- p.ii / Abstract --- p.iii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Anatomy of liver --- p.1 / Chapter 1.2 --- Anatomical Implications --- p.16 / Chapter Chapter 2 --- Background / Chapter 2.1 --- Common focal hepatic lesions --- p.21 / Chapter 2.2 --- Imaging techniques --- p.28 / Chapter 2.3 --- Characterization by sonography --- p.34 / Chapter 2.4 --- Color Power Angiography --- p.38 / Chapter Chapter 3 --- Hypothesis & Aims / Chapter 3.1 --- Hypothesis --- p.44 / Chapter 3.2 --- Aims & Objectives --- p.45 / Chapter Chapter 4 --- Material and Methods / Chapter 4.1 --- Materials --- p.47 / Chapter 4.2 --- Mode of confirmation --- p.52 / Chapter 4.3 --- Final number of subjects recruited --- p.54 / Chapter 4.4 --- Method for obtaining CD and CPA image --- p.58 / Chapter 4.5 --- Method for image analysis --- p.61 / Chapter 4.6 --- Statistical analysis --- p.68 / Chapter Chapter 5 --- Results / Chapter 5.1 --- Qualitative CD and CPA images assessment --- p.70 / Chapter 5.2 --- Interobserver qualitative analysis --- p.78 / Chapter 5.3 --- Spectral analysis --- p.84 / Chapter 5.4 --- Semi-quantitative signal parameters --- p.87 / Chapter 5.5 --- Dominance of quantified signals --- p.91 / Chapter 5.6 --- Distribution of signals in various lesions (graphical presentation) --- p.97 / Chapter 5.7 --- Penetrating vessel --- p.103 / Chapter 5.8 --- Relationship between size of lesion and quantified signal parameters --- p.104 / Chapter Chapter 6 --- Discussion / Chapter 6.1 --- Study Review --- p.109 / Chapter 6.2 --- Methods of quantitation --- p.110 / Chapter 6.3 --- Value of quantitation --- p.111 / Chapter 6.4 --- Instrumentation --- p.112 / Chapter 6.5 --- Subjects --- p.114 / Chapter 6.6 --- Image analysis --- p.115 / Chapter 6.7 --- Results --- p.117 / Chapter 6.8 --- Relationship between size and amount of signals --- p.131 / Chapter 6.9 --- Differentiation of focal hepatic lesions --- p.132 / Chapter 6.10 --- Origin of CPA signals in small hyperechoic lesions --- p.144 / Chapter 6.11 --- Limitations of CPA in focal hepatic lesion imaging --- p.146 / Chapter 6.12 --- Comparison with similar studies --- p.151 / Chapter 6.13 --- Validation of quantitation results --- p.158 / Chapter Chapter 7 --- Conclusions --- p.159 / References --- p.162 / Legends --- p.176 / Tables --- p.186 / Glossary of abbreviations --- p.193 / Selected publications relevant to thesis --- p.197 / Appendix --- p.198 / Bibliography --- p.205

Encompassing with fields on engineering and medical image quality, this dissertation proposes a novel framework for diagnostic performance evaluation based on objective image-quality assessment, an important step in the development of new imaging devices, acquisitions, or image-processing techniques being used for clinicians and researchers. The objective of this dissertation is to develop computational modeling tools that allow comprehensive evaluation of task-based assessment including clinical interpretation of images regardless of image dimensionality. Because of advances in the development of medical imaging devices, several techniques have improved image quality where the format domain of the outcome images becomes multidimensional (e.g., 3D+time or 4D). To evaluate the performance of new imaging devices or to optimize various design parameters and algorithms, the quality measurement should be performed using an appropriate image-quality figure-of-merit (FOM). Classical FOM such as bias and variance, or mean-square error, have been broadly used in the past. Unfortunately, they do not reflect the fact that the average performance of the principal agent in medical decision-making is frequently a human observer, nor are they aware of the specific diagnostic task. The standard goal for image quality assessment is a task-based approach in which one evaluates human observer performance of a specified diagnostic task (e.g. detection of the presence of lesions). However, having a human observer performs the tasks is costly and time-consuming. To facilitate practical task-based assessment of image quality, a numerical observer is required as a surrogate for human observers. Previously, numerical observers for the detection task have been studied both in research and industry; however, little research effort has been devoted toward development of one utilized for multidimensional imaging studies (e.g., 4D). Limiting the numerical observer tools that accommodate all information embedded in a series of images, the performance assessment of a particular new technique that generates multidimensional data is complex and limited. Consequently, key questions remain unanswered about how much the image quality improved using these new multidimensional images on a specific clinical task. To address this gap, this dissertation proposes a new numerical-observer methodology to assess the improvement achieved from newly developed imaging technologies. This numerical observer approach can be generalized to exploit pertinent statistical information in multidimensional images and accurately predict the performance of a human observer over the complexity of the image domains. Part I of this dissertation aims to develop a numerical observer that accommodates multidimensional images to process correlated signal components and appropriately incorporate them into an absolute FOM. Part II of this dissertation aims to apply the model developed in Part I to selected clinical applications with multidimensional images including: 1) respiratory-gated positron emission tomography (PET) in lung cancer (3D+t), 2) kinetic parametric PET in head-and-neck cancer (3D+k), and 3) spectral computed tomography (CT) in atherosclerotic plaque (3D+e). The author compares the task-based performance of the proposed approach to that of conventional methods, evaluated based on a broadly-used signal-known-exactly /background-known-exactly paradigm, which is in the context of the specified properties of a target object (e.g., a lesion) on highly realistic and clinical backgrounds. A realistic target object is generated with specific properties and applied to a set of images to create pathological scenarios for the performance evaluation, e.g., lesions in the lungs or plaques in the artery. The regions of interest (ROIs) of the target objects are formed over an ensemble of data measurements under identical conditions and evaluated for the inclusion of useful information from different complex domains (i.e., 3D+t, 3D+k, 3D+e). This work provides an image-quality assessment metric with no dimensional limitation that could help substantially improve assessment of performance achieved from new developments in imaging that make use of high dimensional data.

Peripheral arterial disease (PAD) affects approximately 200 million individuals worldwide. It is characterized by a reduction in blood flow to the lower extremities due to atherosclerosis. This can result in leg pain, tissue loss, and ultimately amputation. Revascularization procedures aim to restore blood flow, but up to 50% of patients require another intervention within a year. Revascularization monitoring and early detection of failure are crucial in preventing limb loss and adverse cardiovascular events. However, current evaluation methods do not directly measure perfusion and are limited in a significant segment of PAD patients, such as those with diabetes and renal insufficiency. Diffuse optical imaging (DOI) techniques are promising tools to overcome these limitations. Employing near-infrared light, they are non-invasive, non-ionizing, contrast-free, and cost-effective methods that are sensitive to hemodynamic parameters such as changes in oxy-, deoxy-, and total hemoglobin concentration, making DOI ideal for revascularization monitoring. In this dissertation, I investigate and develop DOI systems for the purpose of monitoring lower extremity revascularization procedures in PAD patients. We utilize a contact-based diffuse optical spectroscopy (DOS) system to monitor localized foot perfusion in an ongoing clinical study of 100 patients undergoing lower extremity angiography. I demonstrate the utility of DOS measurements to provide valuable insights into revascularization related hemodynamic remodeling and to predict revascularization success. Furthermore, I also develop a clinic friendly contact-free diffuse optical tomography (DOT) system that is better-suited for PAD patients with ulcers. I show that this system can provide spatial maps of perfusion within the foot. Collectively, this work establishes diffuse optical imaging as a valuable imaging modality for the evaluation of lower extremity perfusion.