1. Articles in category: Student Theses

    241-264 of 272 « 1 2 ... 8 9 10 11 12 »
    1. Miniature Optical Coherence Tomography Probe (Thesis)

      Miniature Optical Coherence Tomography Probe (Thesis)
      A piezo based optical scanner for high speed optical coherence tomography (OCT) has been developed. Design of the miniature probe has been optimized to take advantages of the high speed depth scanning that can be achieved with spectral domain OCT (SD-OCT) systems. Three prototype scanning probes were constructed and tested for OCT imaging. Movies and images of tissues are presented which were taken at frame rates ranging from 50~100fps. Data were acquired at 18000 A-lines per second at an effective integration time of 55us.
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    2. Low Coherence Interferometry and Optical Coherence Tomography in Paper Measurements (Thesis)

      Low Coherence Interferometry and Optical Coherence Tomography in Paper Measurements (Thesis)
      This thesis describes the application of Low Coherence Interferometry (LCI) and Optical Coherence Tomography (OCT) in paper measurements. The developed measurement system is a combination of a profilometer and a tomographic imaging device, which makes the construction versatile and applicable in several paper measurement applications. The developed system was first used to measure the surface structure of paper. Different grades of paper were selected to provide maximum variation in surface structure. The results show that the developed system is capable of measuring grades of paper from rough base paper to highly coated photo printing paper. To evaluate the developed system ...
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    3. Comparison of optical coherence tomography, the pulsed photoacoustic technique, and the time-of-flight technique in glucose measurements in vitro (Thesis)

      Comparison of optical coherence tomography, the pulsed photoacoustic technique, and the time-of-flight technique in glucose measurements in vitro (Thesis)
      The development of a non-invasive glucose monitoring technique is very important because it would tremendously diminish the need to puncture the skin when taking blood samples and help diabetic patients in controlling their blood glucose levels and in treating Diabetes Mellitus. The focus of this thesis is on measuring the effect of glucose on the light scattering properties of a tissue-simulating phantom and biological tissues in vitro. Optical coherence tomography (OCT), the pulsed photoacoustic (PA) technique, and the time-of-flight (TOF) technique are used in the measurements and their capabilities for detecting changes in the scattering properties are evaluated and compared ...
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    4. Analog Signal Processing for Optical Coherence Imaging Systems (Thesis)

      Analog Signal Processing for Optical Coherence Imaging Systems (Thesis)
      Optical coherence tomography (OCT) and optical coherence microscopy (OCM) are non-invasive optical coherence imaging techniques, which enable micron-scale resolution, depth resolved imaging capability. Both OCT and OCM are based on Michelson interferometer theory. They are widely used in ophthalmology, gastroenterology and dermatology, because of their high resolution, safety and low cost. OCT creates cross sectional images whereas OCM obtains en face images. In this dissertation, the design and development of three increasingly complicated analog signal processing (ASP) solutions for optical coherence imaging are presented. The first ASP solution was implemented for a time domain OCT system with a Rapid Scanning ...
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    5. Design and fabrication of an optical pressure micro sensor for skin mechanics studies (Thesis)

      Design and fabrication of an optical pressure micro sensor for skin mechanics studies (Thesis)
      The mechanics of skin is as central to touch as optics is to vision and acoustics is to hearing. With the advent of novel imaging technologies such as the Optical Coherence Tomography (OCT), we are now able to view structures within the skin to a resolution of a few microns in vivo and non-invasively. To fully understand the role of biomechanics of the skin in interpreting touch, we need to develop a quantitative understanding of how spatio temporal loads imposed on the surface of the skin are transmitted to mechanoreceptor locations within the skin. The following thesis presents a description ...
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    6. Optical frequency domain imaging of human retina and choroid (Thesis)

      Optical frequency domain imaging of human retina and choroid (Thesis)
      Optical coherence tomography (OCT) has emerged as a practical noninvasive technology for imaging the microstructure of the human eye in vivo. Using optical interferometry to spatially-resolve backreflections from within tissue, this high-resolution technique provides cross-sectional images of the anterior and posterior eye segments that had previously only been possible with histology. Current commercially-available OCT systems suffer limitations in speed and sensitivity, preventing them from effective screening of the retina and having a larger impact on the clinical environment. While other technological advances have addressed this problem, they are inadequate for imaging the choroid, which can be useful for evaluating choroidal ...
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    7. Optical Coherence Tomography For The Screening of Donor Corneas and Examination of the Retinal Nerve Fiber Directional Reflectance (Thesis)

      Optical Coherence Tomography For The Screening of Donor Corneas and Examination of the Retinal Nerve Fiber Directional Reflectance (Thesis)
      Optical coherence tomography (OCT) is a high resolution, non-invasive imaging technology that employs light to create detailed images of the body. In medicine, OCT is most widely used in ophthalmology to create high resolution images of the cornea and the retina. The group index of cornea, rather than phase refractive index, is required for thickness calculations with optical coherence tomography (OCT). Recent advances with high speed OCT at 1.3 m make index measurement at this wavelength of great interest. Group indices of 3 human eye bank corneas were measured in vitro using optical low-coherence reflectometry. Measurements were made in ...
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    8. Anatomical optical coherence tomography in the human upper airway (Thesis)

      Anatomical optical coherence tomography in the human upper airway (Thesis)
      This thesis describes the development, clinical validation and initial application of a technique for taking measurements of the shape and dimensions of the human upper airway, called anatomical optical coherence tomography (aOCT). The technique uses a transparent catheter containing a rotating optical probe which is introduced transnasally and positioned in the airway and oesophagus. Optical coherence tomography is used to take calibrated cross-sectional images of the airway lumen as the probe rotates. The probe can also be advanced or withdrawn within the catheter during scanning to build up three-dimensional information. The catheter remains stationary so that the subject is not ...
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    9. Fiber lasers and all-fiber optic devices for applications in sensing and medical imaging (Thesis)

      Fiber lasers and all-fiber optic devices for applications in sensing and medical imaging (Thesis)
      The field of fiber lasers and fiber optic devices has experienced a sustained rapid growth despite witnessing the infamous 'telecom bubble burst'. All-fiber optic devices have inherent advantages of relatively low cost, compact design, light weight, low maintenance, and increased vibration tolerances. In this research, a novel fiber laser and several fiber optic devices for applications in sensing and medical imaging have been proposed, demonstrated, and analyzed. Differential absorption lidars (DIALs) are used to monitor trace gases and require two synchronized narrow linewidth laser sources of nearly the same wavelength. Sophisticated airborne lidar systems may benefit from the fiber laser ...
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    10. Tactile sensing of shape: biomechanics of contact investigated using imaging and modeling (Thesis)

      Tactile sensing of shape: biomechanics of contact investigated using imaging and modeling (Thesis)
      The overall goal of this research effort is to improve the understanding of the biomechanics of skin as it pertains to human tactile sense. During touch, mechanoreceptors beneath the skin surface are mechanically loaded due to physical contact of the skin with an object and respond with a series of neural impulses. This neural population response is decoded by the central nervous system to result in tactile perception of properties such as the shape, surface texture and softness of the object. The particular approach taken in this research is to develop a realistic model of the human fingertip based on ...
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    11. Estimation of nonlinear mechanical properties of atherosclerotic plaques (Thesis)

      Estimation of nonlinear mechanical properties of atherosclerotic plaques (Thesis)
      A numerical method has been developed to estimate the mechanical properties of atherosclerotic plaques by combining genetic algorithm with finite element methods. Plaque images derived from optical coherence tomography were employed to construct finite element models which were subsequently used in conjunction with a genetic algorithm to determine the parameters in a nonlinear constitutive model. A new multi-frame scheme is introduced to better perform the estimation on a nonlinear mechanical model and reduce the effects of noise. Results show while it is feasible to estimate the nonlinear mechanical properties of plaque, the accuracy can depend on various factors, especially the ...
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    12. Enhanced visualization of retinal pathologies with ultrahigh resolution optical coherence tomography (Thesis)

      Enhanced visualization of retinal pathologies with ultrahigh resolution optical coherence tomography (Thesis)
      Current clinical practice calls for the development of techniques to diagnose diseases in its early stages, when treatment is most effective and significant irreversible damage can either be prevented or delayed. Optical coherence tomography (OCT) is an emerging medical diagnostic technology being investigated for applications in a number of medical fields including ophthalmology, cardiology, and gastroenterology. OCT is analogous to ultrasound except that it uses light waves rather than sound waves. OCT can achieve a much higher resolution than ultrasound in measuring the underlying tissue microstructures. Another advantage of OCT is that it can achieve imaging in a non-contact and ...
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    13. Ultrahigh resolution optical coherence tomography for the detection of early stage neoplastic pathologies (Thesis)

      Ultrahigh resolution optical coherence tomography for the detection of early stage neoplastic pathologies (Thesis)
      Identification of changes associated with early stage disease remains a critical objective of clinical detection and treatment. Effective screening and detection is important for improving outcome because advanced disease, such as metastatic cancer, can be difficult to impossible to cure. Many existing diagnostic modalities, including x-ray imaging, magnetic resonance imaging, ultrasound, and endoscopy do not have sufficient resolution to detect changes in architectural morphology associated with early neoplasia and other pathologies. Diagnostic modalities capable of identifying pre-malignant tissue at an early stage could therefore significantly improve treatment outcome. Optical coherence tomography (OCT) is an emerging biomedical imaging technique that can ...
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    14. Optical coherence tomography for retinal imaging (Thesis)

      Optical coherence tomography for retinal imaging (Thesis)
      In this thesis, two new imaging modalities are proposed for the early detection of glaucoma. Both modalities are based on optical coherence tomography, a technology that uses low-coherence light to create two-dimensional images of the retina. Depth scans are made as reflections are detected as a function of path length difference by rapidly changing the reference arm length of an interferometer. The sensitive coherence window that is created rejects light returning from other depths.
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    15. Semiconductor Light Source for Optical Coherence Tomography (Thesis)

      Semiconductor Light Source for Optical Coherence Tomography (Thesis)
      Optical coherence tomography (OCT) is an emerging medical imaging technology based on the coherent interference of light. Current use of OCT in clinical settings is limited by the lack of a suitable light source. This thesis describes the design of a new type of source for OCT, based on the GaInNAs semiconductor materials system. A semiconductor heterostructure consisting of several di erent quantum wells is discussed as a device for generating broadband (>100 nm) light in the near infrared (900-1500 nm). The use of temperature to control spectral shape and intensity is examined. Other aspects of device design are investigated ...
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    16. Optical measurement of neural action potentials using low coherence heterodyne interferometry (Thesis)

      Optical measurement of neural action potentials using low coherence heterodyne interferometry (Thesis)
      We present a novel non-invasive optical method for detection of neural action potentials using low coherence interferometry. The dual beam heterodyne interferometer (DBHI) is a modified Michelson with a low coherence source and an optical referencing method capable of detecting sub-nanometer optical path changes. In this interferometer, acousto-optical modulators were used to produce an interfering heterodyne signal between the sample and a nearby surface. To cancel the noise, a differential phase measurement was made between this heterodyne signal and a stable reference heterodyne. DBHI has a stability of 30 picometers over 100ms. We have used this interferometer to measure the ...
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    17. Tissue spectroscopic characterization based on fluorescence, second harmonic generation, and reflected light (Thesis)

      Tissue spectroscopic characterization based on fluorescence, second harmonic generation, and reflected light (Thesis)
      The diagnosis of many diseases often requires a histological analysis of tissues. Histology analysis compares the microscopic structure of a tissue specimen with an image database containing known physiological and pathological tissue structures. Three new microscopy technologies are developed to complement histology based on novel contrast mechanisms to better visualize and understand tissue structure and function: two-photon spectral resolved imaging, tri-modal imaging, and interferometric second harmonic imaging. First, two-photon spectral resolved microscopy utilizes the 3D localization ability of two-photon excitation to extract spectroscopic information from a femtoliter volume in tissue. The method is capable of the identification of biochemical species ...
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    18. Elastography of coronary vessels using optical coherence tomography (Thesis)

      Elastography of coronary vessels using optical coherence tomography (Thesis)
      Atherosclerosis is an inflammatory disease characterized by an accumulation of lipid and fibrous tissue in the arterial wall. Postmortem studies have characterized rupture-prone atherosclerotic plaques by the presence of a large lipid=rich core covered by a thin fibrous cap. Studies employing finite element analysis (FEA) based on ex vivo plaque geometry have found that most plaques rupture at sites of high circumferential stress, thus diagnosis of plaque vulnerability may be enhanced by probing the mechanical behavior of individual plaques. Elastrography is a method of strain imaging in which an image sequence of the artery undergoing deformation is acquired, pixel ...
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    19. Minimally invasive diagnostic imaging using high resolution Optical Coherence Tomography (Thesis)

      Minimally invasive diagnostic imaging using high resolution Optical Coherence Tomography (Thesis)
      Advances in medical imaging have given researchers unprecedented capabilities to visualize, characterize and understand biological systems. Optical Coherence Tomography (OCT) is a high speed, high resolution imaging technique that utilizes low coherence interferometry to perform cross-sectional tomographic imaging of tissue in real time and in vivo. The design, development, and implementation of ultrahigh resolution OCT systems in both laboratory and clinical experiments has been pursued in this work. Biomedical imaging studies in the areas of arthroscopy, cardiology, and endoscopy have been investigated with ultrahigh resolution capability achieved through the use of broadband femtosecond oscillators such as Ti:Sapphire and Cr ...
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    20. Digital signal processing techniques for optical coherence tomography: OCT and OCT image enhancement (Thesis)

      Digital signal processing techniques for optical coherence tomography: OCT and OCT image enhancement (Thesis)
      Digital signal processing (DSP) techniques were developed to improve the flexibility, functionality, and image quality of ultrahigh resolution optical coherence tomography (OCT) systems. To reduce the dependence of OCT research systems on fixed analog electronics and to improve overall system flexibility, a digital demodulation scheme implemented entirely in software was developed. This improvement allowed rapid reconfiguration of the OCT imaging speed and source center wavelength without having to construct new analog filters and demodulators. This demodulation scheme produced a highly accurate envelope and was immune to local variations in carrier frequency. To provide an alternative contrast modality to conventional intensity-based ...
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    21. Polarization-sensitive Mueller-matrix optical coherence tomography (Thesis)

      Polarization-sensitive Mueller-matrix optical coherence tomography (Thesis)
      Measuring the Mueller matrix with optical coherence tomography (OCT) makes it possible to acquire the complete polarization properties of scattering media with three-dimensional spatial resolution. We first proved that the measured degree-of-polarization (DOP) of the backscattered light by OCT remains unity-a conclusion that validated the use of Jones calculus in OCT. A multi-channel Mueller-matrix OCT system was then built to measure the Jones-matrix, which can be transformed into a Mueller matrix, images of scattering biological tissues accurately with single depth scan. We showed that when diattenuation is negligible, the round-trip Jones matrix represents a linear retarder, which is the foundation ...
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    22. Low-coherence interferometric imaging: solution of the one-dimensional inverse scattering problem (Thesis)

      Low-coherence interferometric imaging: solution of the one-dimensional inverse scattering problem (Thesis)
      Optical coherence tomography (OCT) is a non-invasive imaging technique based on the use of light sources exhibiting a low degree of coherence. Low coherence interferometric microscopes have been successful in producing internal images of thin pieces of biological tissue; typically samples of the order of 1 milimeter in depth have been imaged, with a resolution of the order of 10 to 20 microns in some portions of the sample. In this thesis, I deal with the imaging problem of determining the internal structure of a body from backscattered laser light and low-coherence interferometry. In detail, I formulate and solve an ...
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    23. Optical coherence tomography: technology enhancements and novel applications (Thesis)

      Optical coherence tomography: technology enhancements and novel applications (Thesis)
      In the last fifteen years, a great deal of effort has been put forth, worldwide, for investigating and enhancing various aspects of optical coherence tomography (OCT). This thesis begins with a description of the technique of OCT, and an analysis of its underlying theory. The design and construction of an OCT system is described, with particular emphasis on a novel delay scanning method, and novel signal processing. Application of OCT to non-destructive characterisation of seeds, examination of skin lesions, measurement of fluid flow, and refractive index determination, are then demonstrated. Two technological enhancements to OCT are presented in this thesis ...
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    24. Optical Coherence Tomography (Thesis)

      Optical Coherence Tomography (Thesis)
      Beam splitting interferometry yields high visibility interference fringes when the path length difference (PLD)of the two beams is an integer multiple of the wavelength of light used, with the maximum PLD over which fringes are observed being the coherence length of the source. Low coherence interferometry enables high axial resolution scans to be taken, as the coherence length of the source (a super-luminescent diode) is relatively small (10 - 20 um). This project aims to use Optical Coherence Tomography (OCT) in the form of beam splitting interferometry with a low coherence light source, to produce detailed axial scans of objects ...
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