1,721,208 research outputs found
Finite element simulation of laser generated surface waves in layered skin model:effect of laser beam characteristics
No full textLaser ultrasonic technique has the potential as an access for quantifying skin property for diagnosis and accurate assessment for skin diseases. This paper presents a finite element (FE) modelling technique which studies the effect laser wavelength has on the generated surface acoustic waveforms in a multilayered skin model. By comparison, this paper discusses the suitability of using laser generated surface waveforms for the accurate non-destructive evaluation of skin layer mechanical and geometrical properties using surface wave phase velocity analysis.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ophthalmic Application of Optical Coherence Tomography Based Angiography for Choroidal Imaging
No full textThesis (Master's)--University of Washington, 2015We demonstrated in vivo choriocapillaris imaging in normal human subjects with a Cirrus HD 5000 spectral domain OCT prototype. With the tracking system installed in the prototype and the montage scanning protocol, wide field OCT angiograms of 9 mm * 11 mm were created. OCT angiography utilizes the intrinsic motion of red blood cells as contrast mechanism therefore requires no exogenous contrast agents as fluorescein angiography and indocyanine green angiography do. Four consecutive OCT scans were acquired at the same location for angiography generating, intensity based, phase based and complex signal based OCTA were all computed and compared. With the ability to resolve fine and detailed vascular lobules, complex signal based OMAG were selected for en face visualization. In consistency with histological studies, lobular vascular networks were observed and corresponding feeding arterioles were identified in OMAG images. Structural OCT en face image was also generated and at periphery regions, lobular structures can also be recognized with distinct brightness patterns. This study showcased the feasibility of using commercialized SD-OCT for in vivo choriocapillaris visualization and essentially opens the possibility for clinical imaging studies on choriocapillaris’ role in pathogenesis and early diagnosis of ocular disease
Development and Application of Multifunctional Optical Coherence Tomography
Get PDFThesis (Ph.D.)--University of Washington, 2014Microcirculation refers to the functions of capillaries and the neighboring lymphatic vessels. It plays a vital role in the pathophysiology of disorders in many clinical areas including cardiology, dermatology, neurology and ophthalmology, and so forth. It is crucial to develop imaging technologies that can provide both qualitative and quantitative information as to how microcirculation responds to certain injury and/or disease, and its treatment. Optical coherence tomography (OCT) is a non-invasive optical imaging technique for high-resolution cross-sectional imaging of specimens, with many applications in clinical medicine. Current state-of-the-art OCT systems operate in the Fourier domain, using either a broadband light source with a spectrometer, known as spectral domain OCT (SDOCT), or a rapidly tunable laser, known as swept source OCT (SSOCT). The current Fourier domain OCT systems have dramatically improvement in sensitivity, resolution and speed compared to time domain OCT. In addition to the improvement in the OCT system hardware, different methods for functional measurements of tissue beds have been developed and demonstrated. This includes but not limited to, i) Phase-resolved Doppler OCT for quantifying the blood flow, ii) OCT angiography for visualization of microvasculature, iii) Polarization sensitive OCT for measuring the intrinsic optical property/ birefringence of tissue, iv) spectroscopic OCT for measuring blood oxygenation, etc. Functional OCT can provide important clinical information that is not available in the typical intensity based structural OCT images. Among these functional OCT modalities, Doppler OCT and OCT angiography attract great interests as they show high capability for in vivo study of microvascular pathology. By analyzing the Doppler effect of a flowing particle on light frequency, Doppler OCT allows the quantification of the blood flow speed and blood flow rate. The most popular approach for Doppler OCT is achieved through analysis of the phase term in complex OCT signal which termed as Phase-resolved Doppler OCT. However, as limited by the phase noise and motion, Phase-resolved Doppler OCT can only be applied for relative large blood vessels, such as arterioles and venules. On the other hand, in order to visualize the microcirculation network, a number of strategies to enable better contrast of microvasculature components, which we termed OCT angiography, have been introduced during recent years. As a variation of Fourier domain OCT, optical microangiography (OMAG) is one of earliest proposed OCT angiography technique which is capable of generating 3D images of dynamic blood perfusion distribution within microcirculatory tissue beds. The OMAG algorithm works by separating the static and moving elements by high pass filtering on complex valued interferometric data after Fourier transform. Based on the conventional OMAG algorithm, we further developed ultra-high sensitive OMAG (UHS-OMAG) by switching the high-pass filtering from fast scan direction (adjacent A-lines within one B-frame) to slow scan direction (adjacent B-frames), which has a dramatically improved performance for capillary network imaging and analysis. Apart from the microvascular study with current available functional OCT for, visualization of the lymphatic system (lymph nodes and lymphatic vessels) plays a significant role in assessing patients with various malignancies and lymphedema. However, there is a lack of label-free and noninvasive method for lymphangiography. Hence, a cutting edge research to investigate the capability of OCT as a tool for non-invasive and label-free lymphangiography would be highly desired. The objective of my thesis is to develop a multiple-functional SDOCT system to image the microcirculation and quantify the several important parameters of microcirculation within microcirculatory tissue beds, and further apply it for pre-clinical research applications. The multifunctional OCT system provides modalities including structural OCT, OCT angiography, Doppler OCT and Optical lymphangiography, for multi-parametric study of tissue microstructure, blood vessel morphology, blood flow and lymphatic vessel all together. The thesis mainly focus on two parts: first, development of multi-functional OCT/optical microangiography (OMAG) system and methods for volumetric imaging of microvasculature and quantitative measurement of blood flow, and its application for pathological research in ophthalmology on rodent eye models; second, development of ultra-high resolution OCT system and algorithm for simultaneous label free imaging of blood and lymphatic vessel, and its application in wound healing study on mouse ear flap model. Objectives of my research are achieved through the following specific aims: Aim 1: Improve the sensitivity of OMAG for microvasculature imaging; perform volumetric and quantitative imaging of vasculature with combined OMAG and Phase-resolved Doppler OCT for in vivo study of vascular physiology. Aim 2: Develop high speed high resolution OCT system and method for rodent eye imaging. Apply the combined OMAG and Phase-resolved Doppler OCT approach to investigate the impact of elevated intraocular pressure on retinal, choroidal and optic nerve head blood flow in rat eye model, which aids to the better understanding of the mechanism and development of glaucoma. Aim 3: Apply the developed OCT system and ultra-high sensitive OMAG algorithm for noninvasive imaging of retinal morphology and microvasculature in obese mice, which may play an important role in early diagnosis of Diabetic retinopathy. Aim 4: Developing an ultra-high resolution SDOCT system using broadband Supercontinuum light source to achieve ultra-high resolution microvasculature imaging of biological tissue. Aim 5: Develop methods for simultaneous label free optical imaging of blood and lymphatic vessel and demonstrate its capability by monitoring the blood and lymph response to wound healing on mouse ear pinna model
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Ophthalmic Application of Optical Coherence Tomography Based Angiography for Choroidal Imaging
Get PDFThesis (Master's)--University of Washington, 2015We demonstrated in vivo choriocapillaris imaging in normal human subjects with a Cirrus HD 5000 spectral domain OCT prototype. With the tracking system installed in the prototype and the montage scanning protocol, wide field OCT angiograms of 9 mm * 11 mm were created. OCT angiography utilizes the intrinsic motion of red blood cells as contrast mechanism therefore requires no exogenous contrast agents as fluorescein angiography and indocyanine green angiography do. Four consecutive OCT scans were acquired at the same location for angiography generating, intensity based, phase based and complex signal based OCTA were all computed and compared. With the ability to resolve fine and detailed vascular lobules, complex signal based OMAG were selected for en face visualization. In consistency with histological studies, lobular vascular networks were observed and corresponding feeding arterioles were identified in OMAG images. Structural OCT en face image was also generated and at periphery regions, lobular structures can also be recognized with distinct brightness patterns. This study showcased the feasibility of using commercialized SD-OCT for in vivo choriocapillaris visualization and essentially opens the possibility for clinical imaging studies on choriocapillaris’ role in pathogenesis and early diagnosis of ocular disease
Development of Functional Optical Coherence Tomography for Structural and Microangiography Assessment of Heart and Skin
No full textThesis (Ph.D.)--University of Washington, 2025This thesis explores the potential of developing functional Optical Coherence Tomography (OCT) for structural and microangiographic applications in heart and skin tissues. As a noninvasive imaging technique, OCT has revolutionized fields such as ophthalmology, cardiology, and dermatology by providing high-resolution visualization of biological structures and microvasculature. However, its capacity to capture physiological characterization, both qualitatively and quantitatively, remains limited. This research aims to bridge that gap by advancing functional OCT techniques to provide novel insights into tissue and vascular behavior in complex vascularized areas like coronary microcirculation and skin. Chapter 1 introduces OCT principles and their clinical significance for noninvasive imaging. Chapter 2 focuses on advanced OCT techniques for assessing microvascular networks and tissue composition. Methods such as Optical Microangiography (OMAG) and OCT velocimetry demonstrate OCT's capability to visualize capillary morphology and blood flow without contrast agents, while quantitatively characterizing hemodynamic properties and microvascular health. Additionally, OCT structural imaging techniques, such as calibrated optical attenuation coefficient (OAC), are presented to differentiate tissue compositions in distinct skin layers based on scattering properties. Chapter 3 applies OCT Angiography (OCTA) to assess microvascular damage in infarcted hearts, uncovering structural and functional changes post-myocardial infarction (MI), such as capillary loss, vessel enlargement, and altered blood flow, offering insights into coronary network remodeling. Chapter 4 investigates OCTA's ability to detect depth-resolved blood flow signals and pulse patterns across different skin layers, showcasing potential applications in non-invasive cardiovascular monitoring. Chapter 5 explores OCT's dermatological applications, including monitoring skin aging, UV-induced changes, and light-tissue interactive behaviors. It highlights OCT's ability to detect subclinical changes—such as vessel dilation, epidermal thickening, and structural organization differences—before clinically visible signs appear, supporting early intervention
Development and Application of High-speed and Wide-field Functional Swept Source Optical Coherence Tomography
No full textThesis (Ph.D.)--University of Washington, 2025Recent advances in optical coherence tomography (OCT) have significantly broadened their utility in biomedical imaging, particularly for the diagnosis and monitoring of vascular-related and microstructural diseases. However, clinical OCT systems remain constrained by limited imaging speed, shallow ranging distance, narrow field of view (FoV), and the lack of robust functional imaging capabilities. These limitations hinder broader in vivo clinical applications of OCT. In this study, we develop a high-speed, long-range, wide-field swept-source OCT (SS-OCT) system based on a 600 kHz micro-mlectro-mechanical system vertical-cavity durface-emitting laser (MEMS-VCSEL) laser, designed to deliver high-fidelity morphological and functional imaging. To overcome the depth limitation inherent in conventional k-clock acquisition, we develop a multi-channel delay sampling technique that splits the analog OCT signal into N-channel time-delayed electrical paths. This method increases the effective k-space sampling density without altering k-clock triggering, thereby doubling the imaging depth without compromising acquisition speed or resolution. To further enhance imaging performance, we introduce the concept of electrical dispersion, which arises from the nonlinear phase response of electronic components operating under high-speed k-clock triggering. A global k-space compensation algorithm is proposed to mitigate this distortion, and a vector field-based distortion correction technique is implemented to restore spatial fidelity in wide-field scans. Together, these methods enable high-quality structural and optical coherence tomography angiography (OCTA) imaging across a lateral FoV of 42 à 42 mm² and an extended axial range of 36 mm. To address challenges in imaging samples with complex surface topography, such as the oral cavity, we propose an adaptive contour tracking and scanning strategy. This approach integrates an electrically tunable lens and motorized optical delay line with real-time surface profiling to maintain focus and SNR across curved surfaces. Experimental validation confirms improved image consistency and flow visualization across large and irregularly contoured regions. Finally, we incorporate a novel fiber-based polarization-sensitive OCT (PS-OCT) system based on the platform. To address the instability of the input state of polarization in single-input fiber configurations, we introduce a real-time Stokes vector feedback mechanism that dynamically stabilizes incident circular polarization at the sample surface. This innovation enables reliable birefringence imaging under wide-field and handheld conditions. Together, these system-level advancements result in an OCT platform capable of high-speed, long-range, wide-field, and functionally enhanced imaging. The proposed system demonstrates significant potential for clinical applications in oral health assessment and other settings requiring comprehensive, real-time evaluation of tissue structure, microvasculature, and optical anisotropy
Studying Cerebral Blood Flow in Mouse Cortex with Optical Microangiography
Get PDFThesis (Master's)--University of Washington, 2020Optical coherence tomography (OCT) is a non-contact three-dimensional (3D) imaging modality which enables fast in vivo volumetric visualization of internal structures of biological tissues with high resolution. In this thesis, first, the application of OCT advanced extension - optical microangiography (OMAG) - was used to reveal the temporal profile of hemodynamic response to neural activation and the variation of depth-resolved blood flow changes in mouse cerebral cortex. The results showed that the largest hemodynamic response occurred in cortical layer IV. Second, OMAG and Doppler OMAG (DOMAG) techniques were applied to quantitatively evaluate the anesthesia effect on cerebral vessel morphology and blood flow in mouse model. According to the results, isoflurane and ketamine-xylazine caused vasodilation both in large and capillary vessels, which led to increased CBF. Overall, this thesis demonstrated that OMAG is an effective tool for studying depth-resolved microvasculature and blood flow in animal cortex
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