1. Articles in category: Student Theses

    1-24 of 260 1 2 3 4 ... 9 10 11 »
    1. Extending depth range of optical coherence tomography (Thesis)

      Extending depth range of optical coherence tomography (Thesis)

      Optical coherence tomography (OCT) is a noninvasive diagnostic imaging tool that has been established in various clinical fields. One of the most cited issue of OCT in clinical practices is the shortage of image depth range. This thesis proposes four novel techniques to significantly extend the depth range without compromising other imaging performances. The OCT depth range is fundamentally limited by two main factors, which are the axial field of view (FOV) and the system sensitivity. For standard OCT systems, the axial FOV can only be improved by decreasing the numerical aperture (NA) of the focusing optics, which unfortunately sacrifices ...

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    2. Exploring in vivo Optical Imaging Oximetry by Visible Light Optical Coherence Tomography (Thesis)

      Exploring in vivo Optical Imaging Oximetry by Visible Light Optical Coherence Tomography (Thesis)

      Biological functions rely on microvasculature to deliver oxygen and nutrients and carry away metabolic waste. Measuring microvascular oxygen saturation (sO2), the fraction of oxygensaturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood, can assess tissue oxygenation and provide insights into tissue metabolism, inflammation, and oxygen-related pathologies. Several major diseases, such as cancer, diabetes mellitus, cardiovascular diseases, hypertension, chronic kidney disease, and neurodegenerative diseases, are related to local microvascular sO2. Therefore, it is of crucial importance to demonstrate an accurate and reliable method to measure microvascular sO2 for early diagnosis, monitoring disease progression, and evaluating treatments of oxygen metabolism ...

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    3. Development of the human fovea after preterm birth measured using hand held spectral domain optical coherence tomography (HH SD-OCT) (Thesis)

      Development of the human fovea after preterm birth measured using hand held spectral domain optical coherence tomography (HH SD-OCT) (Thesis)

      Background: Much remains unknown about the influence of severity of prematurity and presence of retinopathy of prematurity (ROP) on the development of the fovea after preterm birth during the perinatal period from postmenstrual age (PMA) 30 to 44 weeks. Aims: Measures of foveal morphology, individual retinal layers and foveal oedema (CME), with and without ROP using HH-OCT, adjusting for gestational age (GA) and birthweight (BW). Methods: Prospective mixed cross-sectional and longitudinal study of infants (23 to 36 weeks GA). Foveal width, area, depth, central foveal thickness (CFT), individual retinal layers and CME severity were analysed. Infants with ROP were included ...

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    4. Optical Coherence Tomography for everyone (Thesis)

      Optical Coherence Tomography for everyone (Thesis)

      Optical Coherence Tomography (OCT) is a valuable tool which can non-invasively help not only clinicians, but also materials scientists and practitioners of various other fields. The relatively high costs of OCT instruments can be a deterrent to the application of OCT in academic settings. In work done at the Department of Physics, Sri Sathya Sai Institute of Higher Learning, Deemed to be University, located in a rural area of Anantapur district, Andhra Pradesh, India, we have attempted to make OCT more accessible by exploring options to lower costs. This book is an adaptation of a PhD thesis, which explores this ...

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    5. Progression in Glaucoma (Thesis)

      Progression in Glaucoma (Thesis)

      The treatment of glaucoma is focused on reducing the intraocular pressure to a level at which progression is impeded. A diagnosis of glaucoma is not considered certain until progression is confirmed, and thus detecting progression is a central aspect in both the diagnosing and the monitoring of glaucoma patients. Progression can be identified either through examination of either functional changes in the visual field or structural changes in the retinal nerve fibre layer in the optic disc or in the retina. Optic disc photography, and optical coherence tomography (OCT) that uses laser light, are two methods that are widely used ...

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    6. Measuring coronary artery flow rates using intravascular optical coherence tomography to improve the assessment of percutaneous coronary intervention (Thesis)

      Measuring coronary artery flow rates using intravascular optical coherence tomography to improve the assessment of percutaneous coronary intervention (Thesis)

      In this project, a blood flow quantification technique was developed based on a novel backscattering indicator-dilution approach for intravascular optical coherence tomography (IV-OCT). It achieved the goal of obtaining the flow velocity in a coronary artery of interest by analyzing the backscattering signal from blood after passage of a bolus of Ringer's lactate or another transparent injectate, in parallel to thermodilution coronary flow reserve (CFR). In contrast to thermodilution CFR, the structural OCT image can be used to determine the bolus volume and transit time, as well as used to account for motion and volume change between the two ...

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    7. Investigation of Human Skin Tissues Using Optical Coherence Tomography (Thesis)

      Investigation of Human Skin Tissues Using Optical Coherence Tomography (Thesis)

      Over the decades various imaging technologies have been used for the investigation of skin tissues, but their poor sensitivity, specificity and accuracy limits their applications. In comparison to other imaging modalities, optical coherence tomography (OCT) is a preferred technique as it is a non-invasive imaging modality with a high resolution and is able to perform cellular level imaging as well as providing depth information. This imaging modality has been widely used to image tissues in the human body and thus manifests its potential for clinical applications. Further, OCT can be considered as the potential tool for the identification but the ...

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    8. Characterization of biofouling with 3D-printed spacers using 3D optical coherence tomography (Thesis)

      Characterization of biofouling with 3D-printed spacers using 3D optical coherence tomography (Thesis)

      Biofouling in membrane filtration is a common occurrence which impedes the efficiency of the separation process. By looking into the biofouling mechanisms via the observation of a filtration process, potential problems can be addressed and resolved. This study uses optical coherence tomography (OCT) to investigate the effects of using different 3D-printed spacers on the biofouling process. A compilation of OCT scans of a representative unit cell of each spacer was taken as a function of time to generate 3D-images showing the morphology of a foulant layer. Through the usage of various quantitative analysing methods (such as EIS, DOTM and etc ...

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    9. Optical Coherence Tomography–Guided Robotic System for Automated Retinal Microsurgery (Thesis)

      Optical Coherence Tomography–Guided Robotic System for Automated Retinal Microsurgery (Thesis)

      Retinal vein occlusion is one of the most common disease-related causes of vision loss. It occurs when a blood clot or other obstruction occludes a retinal vein inside the eye. While treatment options exist, there is no cure. One potential remedy is retinal vein cannulation, a surgical procedure where the occluded vein is cannulated and infused with an anticoagulant to dissolve the obstruction. However, due to the physiological limitations of human surgeons—including hand tremor and limited resolution of depth perception—retinal vein cannulation remains only a theoretical practice. This work presents a robotic system capable of performing automated retinal ...

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      Mentions: UCLA
    10. Automated Detection of Glaucoma from Fundus and Optical Coherence Tomography Images (Thesis)

      Automated Detection of Glaucoma from Fundus and Optical Coherence Tomography Images (Thesis)

      Medical image analysis can play a substantial role in diagnosis of different medical problems. Glaucoma is an asymptomatic neurological disease. Oculists mostly use fundoscopy or OpticalCoherence-Tomography (O-C-T) to diagnose glaucoma.Fundoscopy can be used to analyse the external stratum of posterior part of the eye whereas, O-C-T imaging technology has the ability to analyse the internalstratums of posterior part of the eye.In this thesis, a Hybrid Computer Aided Diagnosis (H-CAD) system has been proposed that integrates both fundus and O-C-T imaging technologies for reliable diagnosis. Fundus module has a novel combination of hybrid structural and textural features. The system ...

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    11. Findings from retinal optical coherence tomography in a large cohort, UK Biobank (Thesis)

      Findings	from retinal optical coherence tomography in a	large cohort,  UK Biobank (Thesis)

      Background: UK Biobank is a large prospective multi-center community-based study, which included macular optical coherence tomography (OCT) of 67,321 people. OCT is a mainstay of ophthalmic imaging and is a potential screening test for dementia. Aim of research: Cross-sectional analysis examined retinal layers, to determine the range of findings in normal individuals, as well as describe associations with demographic and physiologic variation. Longitudinal analysis assessed associations with not only current cognitive function, but future cognitive decline. Results: All layers showed progressive thinning with older age. As compared to white people, black ethnicity was associated with significantly thicker retinal pigment ...

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      Mentions: Fang Sarah Ko
    12. The Use of Optical Coherence Tomography as a Diagnostic Tool for Dental Caries (Thesis)

      The Use of Optical Coherence Tomography as a Diagnostic Tool for Dental Caries (Thesis)

      Dental caries is one of the most common human diseases, 60-90% of school children worldwide have dental cavities. Severity can vary, from early demineralisation, which preventive measures can improve, to cavitation, leading to fillings. Different diagnostic tools are available, such as clinical examination, radiographic investigation and Enhanced Visual examination/International Caries Detection and Assessment System (ICDAS). To date, there is no universal diagnostic tool that can be used to detect carious lesions at the very early stages. Optical Coherence Tomography (OCT) is a non-invasive and ionising radiation free technique that has been used in dentistry, but not to diagnose caries ...

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    13. Deep learning-based segmentation of retinal layers in intraoperative Optical Coherence Tomography (Thesis)

      Deep learning-based segmentation of retinal layers in intraoperative Optical Coherence Tomography (Thesis)

      This thesis studies the approaches for the segmentation of retinal layers in Optical Coherence Tomography (OCT) scans. It proposes an overview of the technology and the medical applications of these systems, with a focus on the advantages of intraoperative systems and, in particular, the added progress of having an automatic retinal layers' segmentation algorithm. It has been proved in these last years, that Deep Learning can deal efficiently computer vision tasks and there are examples in literature on using these recent methods to segment retinal layer on diagnostic OCT scans. In this thesis, it is presented a recap of the ...

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    14. Analysis of Retinal Vascular Density using Optical Coherence Tomography Angiography, to Differentiate Healthy, Glaucoma Suspect and Glaucomatous Eyes (Thesis)

      Analysis of Retinal Vascular Density using Optical Coherence Tomography Angiography, to Differentiate Healthy, Glaucoma Suspect and Glaucomatous Eyes (Thesis)

      OBJECTIVES: To study and compare vascular density in papillary retina using OCT Angiography in normals, Glaucoma suspects (Ocular hypertension), early POAG patients and its correlation with RNFL thickness and field changes. METHODS: All volunteers fulfilling eligibility criteria and willing to participate in the study, were recruited in three arms (Minimum sample size of 16 each) and underwent a full ophthalmic examination and investigations (Central corneal thickness, automated visual field testing (HFA 24-2 SITA, threshold test), optical coherence tomography (OCT) RNFL thickness (3.4 mm diameter circle around disc) and OCT angiography (3x3 mm scan) of optic disc, papillary and peri-papillary ...

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    15. Clinical feasibility of optical coherence elastography for tumour margin assessment in breast-conserving surgery (Thesis)

      Clinical feasibility of optical coherence elastography for tumour margin assessment in breast-conserving surgery  (Thesis)

      Currently, 20-30% of patients undergoing breast-conserving surgery require a second surgery due to tumour being found within the margin of the excised lump, determined days following surgery. The work presented in this thesis aims to develop a wide­field optical coherence elastography system suitable for intraoperative margin assessment to reduce additional procedures. Early feasibility studies are presented investigating the ability for three optical coherence elastography variants to visualise a range of tumour morphologies In human breast tissue. The thesis demonstrates the clinical feasibility of optical coherence elastography for tumour margin assessment and provides a strong foundation for future clinical translation.

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    16. Estimation of volumetric optical coherence tomography measurements from 2D color fundus photographs using machine learning

      Estimation of volumetric optical coherence tomography measurements from 2D color fundus photographs using machine learning

      The optic nerve head is the location in the rear of the eye where the nerves exit the eye towards the brain. Swelling of the optic nerve head (ONH) is most accurately quantitatively assessed via volumetric measures using 3D spectral-domain optical coherence tomography (SD-OCT). However, SD-OCT is not always available as its use is primarily limited to specialized eye clinics rather than in primary care or telemedical settings. Thus, there is still a need for severity assessment using more widely available 2D fundus photographs. In this work, we propose machine-learning methods to locally estimate the volumetric measurements (akin to those ...

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    17. Optical coherence tomography in people with epilepsy: symmetry and clinical correlations (Thesis)

      Optical coherence tomography in people with epilepsy: symmetry and clinical correlations (Thesis)

      Optical Coherence Tomography (OCT) provides detailed images by assessing the scattering properties of a tissue (1)⁠. OCT is precise and easily repeatable. It is quick to obtain and does not cause any significant discomfort to patients. For these reasons, it is a useful clinical tool to diagnose and monitor many conditions. Peripapillary retinal nerve fibre layer (pRNFL) thickness measured by OCT was recently confirmed as a biomarker of white matter (WM) integrity in various neurological conditions (2)⁠. In epilepsy, retinal thinning is found in people exposed to vigabatrin (3)⁠ but also in people not exposed to this antiepileptic drug (AED ...

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    18. Application of functional optical coherence tomography angiography in neurovascular research (Thesis)

      Application of functional optical coherence tomography angiography in neurovascular research (Thesis)

      Optical coherence tomography (OCT) is a revolutionary non-invasive imaging technique that can perform high-resolution, cross-sectional tomographic imaging of the internal microstructure in biological tissues by measuring backscattered or backreflected light. Its functional extension, OCT angiography (OCTA), analyzes the intrinsic scattering property of the heterogenous tissue bed to extract dynamic blood flow signals to the capillary level without a need of contrast agents. Aside from the commonly known application of OCTA in clinical ophthalmology for imaging the retinal blood flow in human subjects, the technique has recently emerged as a useful tool in pre-clinical neuroscience for imaging cerebral microcirculation and dynamics ...

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    19. Precision Microfabrication of Optical Probes for Intravascular Diagnostics (Thesis)

      Precision Microfabrication of Optical Probes for Intravascular Diagnostics (Thesis)

      This thesis details a collection of design, optimisation, fabrication and characterisation work to form fiber-optic probes and optical phantom devices for intravascular diagnostics in minimally invasive surgery (MIS). Optically generated ultrasound is an emerging technique to create broadband high frequency ultrasound via the photoacoustic effect. In the first segment of this thesis, the development of a novel miniature fiber-optic ultrasound transmitter is detailed. A morphologically controlled coating was formed at the endface of a multimode optical fiber by controlled electrospinning of a carbon-nanotube composite. Efficient optical ultrasound generation was realised, with signal amplitude, bandwidth and device form factor suited to ...

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    20. Techniques in Optical Coherence and Resonance for Sensing (Thesis)

      Techniques in Optical Coherence and Resonance for Sensing (Thesis)

      Optical sensors are ubiquitous for their precision and non-contact acquisition, and have enjoyed widespread use in applications such as biosensing, environmental monitoring, and security. Despite their sensitivity, many of these sensors rely on costly laboratory instrumentation, and are not adaptable to the ever-growing volume of consumer detectors and optics that are readily available, making their application limited to benchtop analytics. This work leverages plasmonic resonances and optical coherence phenomena to make modifications upon traditional sensing formats that improve their sensitivity when deployed in off-the-shelf optical systems. In particular, we demonstrate that label-free plasmonic sensors can be combined with electrochemical impedance ...

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    21. Improving optical coherence tomography theories and techniques for advanced performance and reduced cost (Thesis)

      Improving optical coherence tomography theories and techniques for advanced performance and reduced cost (Thesis)

      Optical coherence tomography (OCT) has been developed as a high-resolution three-dimensional imaging technique for clinical diagnosis. This thesis proposes several theoretical discoveries and technical improvements to the current OCT systems aiming to drastically reduce system costs while achieving the state-of-the-art performance. Polarization-sensitive OCT (PS-OCT) is a functional extension of conventional OCT which offers the depth-resolved birefringence imaging capability. To resolve local retardation in tissue samples, the current PS-OCT system employs two multiplexed polarization states to illuminate the sample under investigation and detects the backscattered light with two detection channels. We observed that the polarization state of light after round-trip propagation ...

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    22. Optical Coherence Photoacoustic Microscopy (OC-PAM) for Multimodal Imaging (Thesis)

      Optical Coherence Photoacoustic Microscopy (OC-PAM) for Multimodal Imaging (Thesis)

      Optical coherence tomography (OCT) and Photoacoustic microscopy (PAM) are two noninvasive, high-resolution, three-dimensional, biomedical imaging modalities based on different contrast mechanisms. OCT detects the light backscattered from a biological sample either in the time or spectral domain using an interferometer to form an image. PAM is sensitive to optical absorption by detecting the light-induced acoustic waves to form an image. Due to their complementary contrast mechanisms, OCT and PAM are suitable for being combined to achieve multimodal imaging. In this dissertation, an optical coherence photoacoustic microscopy (OC-PAM) system was developed for in vivo multimodal retinal imaging with a pulsed broadband ...

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    23. Parapapillary Atrophy : prevalence and distribution of alpha, beta and gamma parapapillary atrophy identified by the means of spectral domain optical coherence tomography (SD-OCT) (Thesis)

      Parapapillary Atrophy : prevalence and distribution of alpha, beta and gamma parapapillary atrophy identified by the means of spectral domain optical coherence tomography (SD-OCT) (Thesis)

      Purpose: The purpose of this study was to estimate the prevalence and distribution of alpha, beta and gamma parapapillary atrophy in diabetic adults over the age of 40 years, as identified by the means of spectral domain optical coherence tomography (SD-OCT). Methods: All subjects underwent anamnesis, subjective binocular refraction and imaging with SD-OCT in both eyes. The obtained OCT sections provided 24 degree sections for assessment of the parapapillary retina, which were analysed for the presence of alpha, beta and gamma parapapillary atrophy. Results: 135 eyes of 70 subjects, with mean age of 61.33 years (range: 43-81, SD: 9 ...

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    24. DEEP LEARNING OPTIMIZATION FOR OPTICAL COHERENCE TOMOGRAPHY MEDICAL IMAGE ANALYSIS (Thesis)

      DEEP LEARNING OPTIMIZATION FOR OPTICAL COHERENCE TOMOGRAPHY MEDICAL IMAGE ANALYSIS (Thesis)

      Optical Coherence Tomography (OCT) is an interferometric imaging modality that can visualize biological microstructure via cross-sectional images. OCT can construct 3D image data and produce a concise summary of the scanned objects. Because of the non-invasiveness and swift diagnostic procedure, OCT becomes a high potential technology for the real-time surgery guidance. Machine learning algorithms have been widely applied and investigated for automatic medical image analysis. This research proposes two deep learning models for OCT human tissue image classification. Based on the inception module structure, a deep dilated depthwise separable convolution neural network (DDSCN) model is proposed to combine the strength ...

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