<p>Spectral&#8208;domain optical&#8208;coherence tomography (SDOCT) has recently emerged as a powerful new tool for noninvasive human retinal imaging. I have developed a low&#8208;cost, high resolution real&#8208;time Spectral Domain Optical Coherence Tomography (SDOCT) system optimized for rapid 3D imaging of the human retina in vivo. Then functional retinal OCT imaging such as polarization sensitive OCT (PSOCT) and Doppler OCT were also developed based on phase technique. Unique phase unwrapping method in retina is described to extract the total reflectivity, accumulative retardance and fast axis orientation of the retinal nerve fiber layer (RNFL). The polarization scrambling layer of the retinal pigment epithelium was segmented by employing single camera sequential scan bsed PSOCT. As an extension, synthetic wavelength method will be also introduced for phase unwrapping in cell imaging. Finally I present an algorithm for 3D refraction correction based on a vector representation which accounts for refraction of CT light in the cornea. Following 3D refraction correction of volumetric corneal datasets, we can estimate the corneal optical power, thickness and the individual wavefront aberrations of the epithelial and the refraction&#8208;corrected endothelial surfaces by using Zernike spectrum analysis.</p> / Dissertation

Atherosclerosis and specifically rupture of vulnerable plaques account for 23% of all deaths worldwide, far surpassing both infectious diseases and cancer. Plaque-based macrophages, often associated with lipid deposits, contribute to atherogenesis from initiation through progression, plaque rupture and ultimately, thrombosis. Therefore, the macrophage is an important early cellular marker related to vulnerability of atherosclerotic plaques. The objective of my research is to assess the ability of multiple optical imaging modalities to detect, and further characterize the distribution of macrophages (having taken up plasmonic gold nanoparticles as a contrast agent) and lipid deposits in atherosclerotic plaques. Tissue phantoms and macrophage cell cultures were used to investigate the capability of nanorose as an imaging contrast agent to target macrophages. Ex vivo aorta segments from a rabbit model of atherosclerosis after intravenous nanorose injection were imaged by optical coherence tomography (OCT), photothermal imaging (PTW) and two-photon luminescence microscopy (TPLM), respectively. OCT images depicted detailed surface structure of atherosclerotic plaques. PTW images identified nanorose-loaded macrophages (confirmed by co-registration of a TPLM image and corresponding RAM-11 stain on a histological section) associated with lipid deposits at multiple depths. TPLM images showed three-dimensional distribution of nanorose-loaded macrophages with a high spatial resolution. Imaging results suggest that superficial nanorose-loaded macrophages are distributed at shoulders on the upstream side of atherosclerotic plaques at the edges of lipid deposits. Combination of OCT with PTW or TPLM can simultaneously reveal plaque structure and composition, permitting assessment of plaque vulnerability during cardiovascular interventions. / text

No description available.

Sensory adaptation to blur improves visual acuity under defocused conditions. This phenomenon has been successfully demonstrated using subjective measures of acuity and is known as blur adaptation. This study investigates aspects of the mechanism of blur adaptation in human vision using subjective and objective methods. Parafoveal visual acuity measured under defocused conditions demonstrates that blur adaptation is not limited to the fovea. The presence of the adaptive mechanism in the parafovea also suggests that the neural compensation that takes places under defocused conditions acts across a spatial range and is not limited to specific frequency bands. An evaluation of the contrast sensitivity function under defocus provides further evidence. Electrophysiological methods measure the effect of blur adaptation at the retina and at the visual cortex to provide objective evidence for the presence of the blur adaptation mechanism. Finally enhanced-depth imaging optical coherence tomography examines whether a period of prolonged defocus triggers any short-term changes in choroidal thickness in a similar manner to that reported in animal emmetropisation.

Two applications of second harmonic generation (SHG), a nonlinear optical technique, are studied. First, Fresnel factors are used with a bond model to describe SHG from vicinal silicon at five incidence angles: 7.5°, 22°, 30°, 45°, and 52°. Second, a prototype apparatus for applying SHG to enhance imaging capabilities of optical coherence tomography, a microscopy technique used in many biological fields, is briefly described. / text

Confocal microendoscopy provides real-time high resolution cellular level images via a minimally invasive procedure. Results from an ongoing clinical study to detect ovarian cancer with a novel confocal fluorescent microendoscope are presented. As an imaging modality, confocal fluorescence microendoscopy typically requires exogenous fluorophores, has a relatively limited penetration depth (100μm), and often employs specialized aperture configurations to achieve real-time imaging in vivo. Two primary research directions designed to overcome these limitations and improve diagnostic capability are presented. Ideal confocal imaging performance is obtained with a scanning point illumination and confocal aperture, but this approach is often unsuitable for real-time, in vivo biomedical imaging. By scanning a slit aperture in one direction, image acquisition speeds are greatly increased, but at the cost of a reduction in image quality. The design, implementation, and experimental verification of a custom multi-point-scanning modification to a slit-scanning multi-spectral confocal microendoscope is presented. This new design improves the axial resolution while maintaining real-time imaging rates. In addition, the multi-point aperture geometry greatly reduces the effects of tissue scatter on imaging performance. Optical coherence tomography (OCT) has seen wide acceptance and FDA approval as a technique for ophthalmic retinal imaging, and has been adapted for endoscopic use. As a minimally invasive imaging technique, it provides morphological characteristics of tissues at a cellular level without requiring the use of exogenous fluorophores. OCT is capable of imaging deeper into biological tissue (~1-2 mm) than confocal fluorescence microscopy. A theoretical analysis of the use of a fiber-bundle in spectral-domain OCT systems is presented. The fiber-bundle enables a flexible endoscopic design and provides fast, parallelized acquisition of the optical coherence tomography data. However, the multi-mode characteristic of the fibers in the fiber-bundle affects the depth sensitivity of the imaging system. A description of light interference in a multi-mode fiber is presented along with numerical simulations and experimental studies to illustrate the theoretical analysis.

Optical coherence tomography (OCT) is a technology that enables 2D cross-sectional images of tissue microstructure. This interferometric technique provides resolutions of approximately 10-20 um with a penetration depth of 1-2 mm in highly scattering tissues. With the use of fiber optics, OCT systems have been developed for intravascular imaging with a demonstrated improvement in both resolution and dynamic range compared to commercial intravascular ultrasound systems. OCT studies of normal, atherosclerotic, and stented arteries indicate the ability of OCT to visualize arterial structures. These results suggest OCT may be a valuable tool for studying luminal structures in tissue engineered constructs.In the present study, new endoscopic OCT systems and analysis techniques were developed to visualize the growth and response of the cellular lining within a tissue engineered blood vessel mimic (BVM). The BVM consists of two primary components. A biocompatible polymeric scaffold is used to form the tubular structure. Human microvessel cells from adipose tissue are sodded on to the inner surface of the scaffold. These constructs are then developed and imaged within a sterile bioreactor.Three specific aims were defined for the present study. First, an OCT longitudinal scanning endoscope was developed. With this endoscope, a study of 16 BVMs was performed comparing images from OCT and corresponding histological sections. The study demonstrated that endoscopic imaging did not visually damage the mimic cellular lining. OCT images showed excellent correlation with corresponding histologicalsections. Second, a concentric three element endoscope was developed to provide radial cross-sections of the BVM. OCT images using this endoscope monitored lining development on three types of polymeric scaffolds. In the third specific aim, automated algorithms were developed to assess the percent cellular coverage of a stent using volumetric OCT images.The results of the present study suggest that OCT endoscopic systems may be a valuable tool for assessing and optimizing the development of tissue engineered constructs. Conversely, the BVMs modeled the arterial response to deployed stents allowing the development of automated OCT analysis software. These results suggest that blood vessel mimics may be used to advance OCT technology and techniques.

Advanced optical imaging techniques are emerging as useful ways to screen tissues for the presence of cancer. Plasmon resonant nanoparticles have unique optical properties that make them ideal for use as optical contrast agents. The capacity of these particles to serve a multifunctional role dependent on their composition and the intensity of incident light enables them to serve as diagnostic tools and to provide the therapeutic capability of photo-thermal energy conversion or the controlled release of an encapsulated agent. Likewise, the ability to degrade into components of a clearable size may enable the clinical translation of these types of particles.These properties were demonstrated by means of experiments in the support of three specific aims. The first specific aim was to determine whether the unique and tunable optical properties of nanorods lend them to generate signal in advanced optical imaging techniques, and that nanorods can facilitate photo-thermal conversion. The second specific aim was to show that liposomes can serve as a scaffold for the support of an array of gold nanodots to generate a structure that exhibit tunable plasmon resonant characteristics and a resultant ability to generate signal in optical imaging techniques while having the capability to degrade into inert particles of a size that can be readily cleared from the body via the kidney. The final specific aim was to determine whether the gold-coated liposomes of the second specific aim can serve as system for light-based delivery of an encapsulated agent in addition to its role as an optical contrast agent and its biodegradation capacity.Plasmon resonant nanorods and plasmon resonant gold-coated liposomes were generated by reducing free gold from solution onto surfactant coated seed particles and phospholipid liposomes, respectively. Both structures demonstrated the ability to generate signal in optical coherence tomography and in multi-photon confocal microscopy images. Nanorods in high intensity light demonstrate a capacity to mediate photo-thermal energy conversion. While, in similar conditions, gold-coated liposomes are shown to release their contents. Gold-coated liposomes are also shown to degrade to bioinert components of a size reasonable for rapid renal clearance using either surfactant or enzyme.

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 Optical Delay line (RSOD)-based optical signal modulation and logarithmic amplifier (Log amp) based demodulation. This OCT system can acquire up to 1600 A-scans per second. The measured dynamic range is 106dB at 200A-scan per second. This OCT signal processing electronics includes an off-the-shelf filter box with a Log amp circuit implemented on a PCB board.The second ASP solution was developed for an OCM system with synchronized modulation and demodulation and compensation for interferometer phase drift. This OCM acquired micron-scale resolution, high dynamic range images at acquisition speeds up to 45,000 pixels/second. This OCM ASP solution is fully custom designed on a perforated circuit board.The third ASP solution was implemented on a single 2.2 mm x 2.2 mm complementary metal oxide semiconductor (CMOS) chip. This design is expandable to a multiple channel OCT system. A single on-chip CMOS photodetector and ASP channel was used for coherent demodulation in a time domain OCT system. Cross-sectional images were acquired with a dynamic range of 76dB (limited by photodetector responsivity). When incorporated with a bump-bonded InGaAs photodiode with higher responsivity, the expected dynamic range is close to 100dB.

This thesis presents the first work, to our knowledge, to evaluate the potential of Optical Coherence Tomography (OCT) as an intravascular imaging modality to characterize and guide interventions on chronic total occlusions (CTOs) in arteries. An ex vivo imaging study using OCT is presented that characterizes various pathologies associated with peripheral CTOs and illustrates the ability to differentiate between the vessel wall and the occluded lumen. We also found that, while OCT could image approximately 1mm through tissue, it was effective for imaging deeper through clarified microchannels seen within the occluded lumen. While others had reported observing such microchannels within the lumen before, little was known about the global architecture of these channels. This motivated a study of the global morphology of microchannels in occlusions using micro computed tomography (microCT). In this microCT study, we found that microchannels within the occluded lumen of the artery appeared to be continuous over several millimeters. However, these channels also exited the artery frequently, suggesting the need for some form of imaging guidance. As a potential intravascular imaging set-up, a forward-viewing OCT catheter was built. This catheter uses a novel scanning mechanism that combines high voltage and a dissipative polymer to achieve fast compact actuation. Doppler OCT results are presented using this catheter to image flow in the forward direction. Doppler OCT imaging of microchannels in vivo is also shown in a surgically exposed occluded artery in situ.