This thesis discusses certain aspects of the noninvasive imaging technique known as optical coherence tomography (OCT). Topics include three-dimensional image rendering as well as application of the Fast Fourier Transform to reconstruct the axial scan as a function of depth. Implementations use LabVIEW system design software and a Xilinx Spartan-6 field-programmable gate array (FPGA). The inherent parallel-processing capability of an FPGA opens the possibility of designing a "super-sensor" which entails simultaneous capturing of image and sensor data, giving medical practitioners more data for potentially improved diagnosis. FPGA-based processing would benefit many methods of characterizing biological samples; OCT and photonic crystal microarray biosensors are discussed. / text

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Not available / text

Optical coherence tomography (OCT) has been shown to be a versatile three-dimensional imaging tool in diagnostic medicine, combining micrometre-scale resolutions with fast acquisition times. This imaging modality uses the interference between light backscattered from a sample and light that has traversed a known reference path delay to determine the scattering profile over penetration depths of up to several millimetres in tissue. A novel OCT system is presented that uses nonlinear optics to process the backscattered light in the optical domain prior to standard Fourier-domain OCT acquisition and processing. The nonlinear optical effects experienced between short light pulses are strongly intensity-dependent, occurring only significantly when the pulses are temporally and spatially overlapped. These conditions allow for the creation of a user-controlled time gate that restricts the light backscattered from the sample to a narrow (~100 micrometres) depth field of view prior to detection. When strong and weak scattering interfaces exist across the sample depth range, the signal-to-noise ratio of the weaker scattering sites can be limited by the finite detector dynamic range in Fourier-domain OCT systems. By aligning the time gate temporal delay to the backscatter from the weak interfaces of interest, a user can completely remove the strong backscattered light and enhance imaging contrast. The nonlinear effect used in the current time-gated OCT design is sum-frequency generation, which provides an additional advantage of imaging at near infrared (1280 nm) wavelengths, used for long penetration depths in tissue, while detection is performed in the visible (504 nm) with silicon-based camera technology. With the reduced depth field of view, the number of sampling points required per depth scan is also proportionately reduced, permitting faster acquisition rates for the time-gated region of interest. A complete description of the time-gated OCT system design is presented, along with proof-of-concept images demonstrating contrast enhancement and operation in a highly scattering biological medium. Based on its successful initial performance, future development of this system is expected for its eventual use in many OCT imaging applications. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-01-15 20:05:41.665 / This work was funded by the Natural Sciences and Engineering Research Council and the Cancer Imaging Network of Ontario, supported by Cancer Care Ontario

Optical Coherence Tomography (OCT) is a sub-surface imaging modality with growing number of applications. An accurate and practical OCT simulator could be an important tool to understand the physics underlying OCT and to design OCT systems with improved performance. All available OCT simulators are restricted to imaging planar multilayered media or non-planar multilayered media. In this work I developed a novel Monte Carlo based simulator of OCT imaging for turbid media with arbitrary spatial distributions. This simulator allows computation of both Class I diffusive reflectance, due to ballistic and quasi-ballistic scattered photons, and Class II diffusive reflectance due to multiple scattered photons. A tetrahedron-based mesh is used to model any arbitrary-shaped medium to be simulated. I have also implemented a known importance sampling method to significantly reduce computational time of simulations by up to two orders of magnitude. The simulator is verified by comparing its results to results from previously validated OCT simulators for multilayered media. I present sample simulation results for OCT imaging of non-layered media which would not have been possible with earlier simulators.

Purpose To examine soft contact lens fitting characteristics using anterior segment imaging techniques and comfort. The specific aims of each chapter are as follows: Chapter 2: To calibrate the new ZEISS VisanteTM anterior segment optical coherence tomographer (OCT) using references with known physical thickness and refractive index equal to the human cornea and to compare the Visante measures to those from a previous generation OCT (Zeiss-Humphrey OCT II). Chapter 3: The first purpose of this study was to measure the repeatability of the Visante TM OCT in a normal sample. The second was to compare corneal thickness measured with the Visante TM OCT to the Zeiss-Humphrey OCT II (model II, Carl Zeiss Meditec, Jena Germany) adapted for anterior segment imaging and to the Orbscan II TM (Bausch and Lomb, Rochester New York). Chapter 4: Conjunctival displacement observed with the edges of the contact lens, when imaged may be real or may be an artefact of all OCT imagers. A continuous surface appears displaced when the refractive index of the leading medium changes at the edge of a contact lens. To examine this effect, edges of the contact lenses were imaged on a continuous surface using the UHR-OCT. Contact lens edges on the human conjunctival tissue were also imaged to see if the lens indentation on the conjunctival tissue is real or an artefact at the edge of the lens. Chapter 5: The main purpose of this study was to determine if we can predict end of the day discomfort and dryness using clinical predictive variables. The second purpose of the study was to determine if there was any relationship between lens fitting characteristics and clinical complications and especially to the superior cornea and conjunctiva with a dispensing clinical trial. Methods Chapter 2: Twenty two semi-rigid lenses of specified thicknesses were manufactured using a material with refractive index of 1.376. Central thickness of these lenses was measured using VisanteTM OCT and Zeiss-Humphrey OCT II (Zeiss, Germany). Two data sets consisting of nominal measures (with a standard pachymeter of the lenses and one obtained using a digital micrometer) were used as references. Regression equations between the physical and optical (OCT) measures were derived to calibrate the devices. Chapter 3: Fifteen healthy participants were recruited. At the Day 1 visit the epithelial and total corneal thickness, across the central 10mm of the horizontal meridian were measured using the OCT II and the Visante TM OCT. Only total corneal thickness across the central 10mm of the horizontal meridian was measured using the Orbscan II. The order of these measurements was randomized. These measurements were repeated on Day 2. Each individual measurement was repeated three times and averaged to give a single result. Chapter 4: (2-D) Images of the edges of marketed silicone hydrogel and hydrogel lenses with refractive indices (n) ranging from 1.41-1.51 were taken placing them concave side down on a continuous surface. Five images for each lens were taken using a UHR-OCT system, operating at 1060 nm with ~3.2um (axial) and 10μm (lateral) resolution at the rate of 75,000 A-scans/s. The displacement of the glass slide beneath the lens edge was measured using Image J. Chapter 5: Thirty participants (neophytes) were included in the study and the four lenses (Acuvue Advance 8.3, Acuvue Advance 8.7, Pure Vision 8.3, and Pure Vision 8.6) were randomly assigned for each eye. The lenses were worn for a period of two weeks on a daily wear basis for 8 to 10hrs per day. Lens performance was monitored over the 2week period. Assessment of subjective comfort was made using visual analogue scales. Total corneal and epithelium thickness was measured using the Visante OCT, the lens edge profiles of the contact lenses were observed using the ultra-high resolution OCT and the conjunctival epithelial thinning was measured using the RTVue OCT. Conjunctival blood velocity was measured at the baseline and 2 week visit using a high magnification camera. Results Chapter 2: Before calibration, repeated measures ANOVA showed that there were significant differences between the mean lens thicknesses from each of the measurement methods (p<0.05), where Visante measurements were significantly different from the other three (OCT II, MG and OP) methods (p<0.05). Visante thickness was significantly higher than the microgauge measures (453±37.6 µm compared to 445.1±38.2 µm) and the OCT II was significantly lower (424.5±36.1 µm both, p<0.05). After calibration using the regression equations between the physical and optical measurements, there were no differences between OCT II and Visante OCT (p<0.05). Chapter 3: Mean central corneal and epithelial thickness using the Visante™ OCT after calibration at the apex of the cornea was 536± 27 µm (range, 563-509 µm) and 55± 2.3 µm (range, 57.3-52.7 µm), respectively. The mean corneal and epithelial thickness using OCT II at the apex was 520±25µm and 56±4.9 µm, respectively. The mean of total corneal thickness measured with the Orbscan II was 609±29µm. Visante OCT was the most repeatable for test-retest at the apex, nasal and temporal quadrants of the cornea compared to OCT II and Orbscan II. COR’s of Visante OCT ranged from ±7.71µm to ±8.98µm for total corneal thickness and ± 8.72 µm to ± 9.92 µm for epithelial thickness. CCC’s with Visante OCT were high for total corneal thickness for test-retest differences ranging from 0.97 to 0.99, CCC’s for epithelial thickness showed moderate concordance for both the instruments. Chapter 4: Results showed that artefactual displacement of the contact lens edge was observed when the lenses were imaged on the glass reference sphere, custom made rigid contact lenses (1.376) and on the conjunctival tissue. The displacement measured on the conjunctival tissue ranged from 7.0±0.86 µm for the Air Optix Night and Day to 17.4±0.22 µm for the Acuvue Advance contact lenses. The range of displacement with the soft lens edges imaged on the rigid contact lens was from 5.51±0.03 µm to 9.72±0.12 µm. Chapter 5: The lenses with the steepest sag (Acuvue Advance 8.3, Pure Vision 8.3) resulted not only with the tightest fit, but with compromise to the superior conjunctiva. This was especially seen with the Acuvue Advance lenses. The steeper lenses caused more total corneal swelling, superior epithelial thinning, mechanical compression of conjunctiva, conjunctival staining, bulbar hyperemia, conjunctival indentation and reduced blood flow at the lens edge. Not many associations were observed between baseline clinical and 2 weeks sensory variables. However, significant associations were observed when comparing the baseline clinical variables to end of the day sensory variables. Baseline clinical variables compared to 2 week clinical variables also showed significant correlations. Conclusions Chapter 2: Using reference lenses with refractive index of the cornea (1.376) allows rapid and simple calibration and cross calibration of instruments for measuring the corneal thickness. The Visante and OCT II do not produce measurements that are equal to physical references with refractive index equal to the human cornea. Chapter 3: There is good repeatability of corneal and epithelial thickness using each OCT for test-retest differences compared to the between instruments repeatability. Measurements of epithelial thickness are less repeatable compared to the total corneal thickness for the instruments used in the study. Chapter 4: When contact lenses are imaged in-situ using UHR-OCT the conjunctival tissue appeared displaced. This experiment indicates that this displacement is an artefact of all OCT imagers since a continuous surface (glass slide) was optically displaced indicating that the displacement that is observed is a function of the refractive index change and also the thickness of the contact lens edges. Chapter 5: Discomfort is a complex issue to resolve since it appears to be related to ocular factors such as the corneal and conjunctival topography and sagittal depth; to lens factors that is 1) how the sag depth of the lenses relate to the corneal/conjunctival shape and depth and therefore how well it moves on the eye. 2) Also with the lens material; whether they are high or low modulus, low or high water content, dehydration properties, wetting agents used and its resistance to deposits, lens edge profile and thickness and its interaction with the upper eyelid.

Thesis (M.S.)--Michigan State University. Electrical Engineering, 2008. / Title from PDF t.p. (viewed on July 27, 2009) Includes bibliographical references (p. 127-131). Also issued in print.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

The thesis deals with speckle suppression in images acquired by optical coherence tomograph. It is divided into four parts. The first part describes basic information about the medical imaging method. It also deals with principle of measurement. The second section discusses the formation of image speckle and selected methods to reduce them. Next part is practical and consists of data acquisition, determination of the evaluation methodology and the implementation of speckle reduction methods. The last part is focused on testing and reviews of algorithms and discussion about their results.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18499号 / 医博第3919号 / 新制||医||1005(附属図書館) / 31385 / 京都大学大学院医学研究科医学専攻 / (主査)教授 伊藤 壽一, 教授 河野 憲二, 教授 富樫 かおり / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM