Browsing by Subject "polarimetry"
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Item Dual Wavelength Polarimetry for Glucose Sensing in the Anterior Chamber of the Eye(2012-02-14) Malik, Bilal HameedClinical guidelines dictate that frequent blood glucose monitoring in diabetic patients is critical towards proper management of the disease. Although, several different types of glucose monitors are now commercially available, most of these devices are invasive, thereby adversely affecting patient compliance. To this end, optical polarimetric glucose sensing through the eye has been proposed as a potential noninvasive means to aid in the control of diabetes. Arguably, the most critical and limiting factor towards successful application of such a technique is the time varying corneal birefringence due to eye motion artifact. In the first part of this research, we describe a birefringent ocular model along with a geometric ray tracing scheme to serve as a tool towards better understanding of the cornea?s birefringence properties. The simulations show that index-unmatched coupling of light is spatially limited to a smaller range when compared to index-matched situation. Polarimetric measurements on rabbits? eyes indicate relative agreement between the modeled and experimental values of corneal birefringence. In addition, the observed rotation in the plane of polarized light for multiple wavelengths demonstrates the potential for using a dual-wavelength polarimetric approach to overcome the noise due to time-varying corneal birefringence. These results will ultimately aid in the development of an appropriate eye coupling mechanism for in vivo polarimetric glucose measurements. The latter part of the dissertation focuses on design and development of a dual wavelength optical polarimeter. The described system utilizes real-time closed-loop feedback based on proportional-integral-derivative (PID) control, which effectively reduced the time taken by the system to stabilize while minimizing the effect of motion artifact, which appears as common noise source for both the wavelengths. Glucose measurements performed in both in vitro and ex vivo conditions demonstrate the sensitivity of the current system. Finally, in vivo results in rabbits indicate that dual-wavelength polarimetry has the potential to noninvasively probe glucose through the anterior chamber of the eye.Item Dual wavelength polarimetry for monitoring glucose in the presence of varying birefringence(Texas A&M University, 2006-04-12) Wan, QiujieIn a continuing effort to develop a noninvasive means of monitoring glucose levels using the aqueous humor of the eye, a dual wavelength system has been developed in order to show that varying birefringence, similar to what is seen with a moving cornea, can be compensated. In this paper a dual wavelength, closed-loop, system was designed and a model was developed to extract the glucose concentration information. The system and model were tested using various concentrations of glucose in a birefringent test cell subject to motion artifact. The results show that for a static, non-moving sample, glucose can be predicted to within 10 mg/dl for the entire physiologic range (0-600mg/dl) for either laser wavelength (523nm or 635nm). In the presence of moving birefringence, each individual wavelength produced standard errors on the order of a few thousand mg/dL. However, when the two wavelengths are combined into the developed model, this error is less than 20mg/dL. The approach shows that multiple wavelengths can be used to drastically reduce the error in the presence of a moving birefringent sample. This research also shows promising preliminary results that the error is less than 25mg/dl in presence of a motion induced cornea birefringence artifact in NZW rabbits?? eyes.Item Polarization-sensitive Mueller-matrix optical coherence tomography(Texas A&M University, 2004-09-30) Jiao, ShuliangMeasuring 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 of conventional PS-OCT, and can be calculated with a single incident polarization state although the one-way Jones matrix generally represents an elliptical retarder; otherwise, two incident polarization states are needed. We discovered the transpose symmetry in the roundtrip Jones matrix, which is critical for eliminating the arbitrary phase difference between the two measured Jones vectors corresponding to the two incident polarization states to yield the correct Jones matrix. We investigated the various contrast mechanisms provided by Mueller-matrix OCT. Our OCT system for the first time offers simultaneously comprehensive polarization contrast mechanisms including the amplitude of birefringence, the orientation of birefringence, and the diattenuation in addition to the polarization-independent intensity contrast, all of which can be extracted from the measured Jones or the equivalent Mueller matrix. The experimental results obtained from rat skin samples, show that Mueller OCT provides complementary structural and functional information on biological samples and reveal that polarization contrast is more sensitive to thermal degeneration of biological tissues than amplitude-based contrast. Finally, an optical-fiber-based multi-channel Mueller-matrix OCT was built and a new rigorous algorithm was developed to retrieve the calibrated polarization properties of a sample. For the first time to our knowledge, fiber-based polarization-sensitive OCT was dynamically calibrated to eliminate the polarization distortion caused by the single-mode optical fiber in the sample arm, thereby overcoming a key technical impediment to the application of optical fibers in this technology.Item The use of polarized light for biomedical applications(Texas A&M University, 2004-11-15) Baba, Justin ShekwogaPolarized light has the ability to increase the specificity of the investigation of biomedical samples and is finding greater utilization in the fields of medical diagnostics, sensing, and measurement. In particular, this dissertation focuses on the application of polarized light to address a major obstacle in the development of an optical based polarimetric non-invasive glucose detector that has the potential to improve the quality of life and prolong the life expectancy of the millions of people afflicted with the disease diabetes mellitus. By achieving the mapping of the relative variations in rabbit corneal birefringence, it is hoped that the understanding of the results contained herein will facilitate the development of techniques to eliminate the effects of changing corneal birefringence on polarimetric glucose measurement through the aqueous humor of the eye. This dissertation also focuses on the application of polarized light to address a major downside of cardiovascular biomechanics research, which is the utilization of toxic chemicals to prepare samples for histological examination. To this end, a polarization microscopy image processing technique is applied to non-stained cardiovascular samples as a means to eliminate, for certain cardiac samples, the necessity for staining using toxic chemicals. The results from this work have the potential to encourage more investigators to join the field of cardiac biomechanics, which studies the remodeling processes responsible for cardiovascular diseases such as myocardial infarct (heart attacks) and congestive heart failure. Cardiovascular disease is epidemic, particularly amongst the population group older than 65 years, and the number of people affected by this disease is expected to increase appreciably as the baby boomer generation transitions into this older, high risk population group. A better understanding of the responsible mechanisms for cardiac tissue remodeling will facilitate the development of better prevention and treatment regimens by improving the early detection and diagnosis of this disease.