Search

Thesis (Ph. D.)--University of Rochester. The Institute of Optics, 2019., Optical coherence tomography (OCT) has opened a new horizon for biomedical imaging, especially in ophthalmology. Its capability of non-destructive and three-dimensional visualization of a sample has let OCT hold a special place among many other biomedical imaging techniques. OCT technology and industry have been rapidly growing and evolving to meet a wide variety of demands among researchers, clinicians, or practitioners. A high numerical aperture (NA) microscope objective in optical coherence microscopy (OCM) granted high transverse resolution for OCT. A dynamic focusing capability by a liquid lens technology together with the Gabor-transform-based algorithm to fuse multiple cross-sectional images of OCM at different depths effectively extended the depth of OCM imaging into the millimeter range, which was named Gabor domain optical coherence microscopy (GD-OCM). In this dissertation, the principles of OCT, spectral-domain OCT (SD-OCT), OCM, and GD-OCM are summarized on the foundation of Fourier optics and coherence optics in chapter 1. In chapter 2, the development of the dispersion compensator for Fourier domain OCT (FD-OCT) as well as GD-OCM is covered. In chapter 3, the pathway of the quantitative assessment of human corneal endothelium with the GD-OCM technology is reported. As a hardware-wise solution to improve the imaging speed and the sensitivity of SD-OCT, a linear-in-K spectrometer using the freeform optic is reported in chapter 4. In chapter 5, Fluo GD-OCM (the combination of GD-OCM with laser scanning confocal fluorescence microscopy (LSCFM)) is introduced in the perspectives of the system architecture, data acquisition and image processing, and the imaging performance. The dual imaging system is experimentally demonstrated by imaging the cerebral pericytes, the retinal ganglion cells, and the retinal astrocytes of the mouse.

In optical coherence microscopy (OCM) with a given numerical aperture (NA) of the objectives the transverse resolution can be increased by increasing the numerical aperture of illumination (NAi). However, this may also lead to attenuation of the signal with defocus preventing the effective numerically focused 3D imaging of the required sample volume. This paper presents an approach to structuring the illumination aperture, which allows combining the advantages of increased transverse resolution (peculiar to high NAi) with small attenuation of the signal with defocus (peculiar to low NAi) for high-resolution numerically focused 3D imaging in OCM.

Excisional biopsy is the current gold standard for disease diagnosis; however, it requires a relatively long processing time and it may also suffer from unacceptable false negative rates due to sampling errors. Optical coherence tomography (OCT) is a promising imaging technique that provide real-time, high resolution and three-dimensional (3D) images of tissue morphology. Optical coherence microscopy (OCM) is an extension of OCT, combining both the coherence gating and the confocal gating techniques. OCM imaging achieves cellular resolution with deeper imaging depth compared to confocal microscopy. An integrated OCT/OCM imaging system can provide co-registered multiscale imaging of tissue morphology. 3D-OCT provides architectural information with a large field of view and can be used to find regions of interest; while OCM provides high magnification to enable cellular imaging. The integrated OCT/OCM system has an axial resolution of <4um and transverse resolutions of 14um and <2um for OCT and OCM, respectively. In this study, a wide range of human pathologic specimens, including colon (58), thyroid (43), breast (34), and kidney (19), were imaged with OCT and OCM within 2 to 6 hours after excision. The images were compared with H & E histology to identify characteristic features useful for disease diagnosis. The feasibility of visualizing human pathology using integrated OCT/OCM was demonstrated in the pathology laboratory settings.

The salivary pellicle plays an important role in oral physiology, yet noninvasive in situ characterization and mapping of this layer remains elusive. The goal of this study is to develop an optical approach for the real-time, noninvasive mapping and characterization of salivary pellicles using optical coherence tomography (OCT) and optical coherence microscopy (OCM). The long-term goals are to improve diagnostic capabilities in the oral cavity, gain a better understanding of physiological and pathological processes related to the oral hard tissues, and monitor treatment responses. A salivary pellicle is incubated on small enamel cubes using human whole saliva. OCT and OCM imaging occurs at 0, 10, 30, 60 min, and 24 h. For some imaging, spherical gold nanoparticles (15 nm) are added to determine whether this would increase the optical signal from the pellicle. Multiphoton microscopy (MPM) provides the baseline information. In the saliva-incubated samples, a surface signal from the developing pellicle is visible in OCT images. Pellicle "islands" form, which increase in complexity over time until they merge to form a continuous layer over the enamel surface. Noninvasive, in situ time-based pellicle formation on the enamel surface is visualized and characterized using optical imaging.

The salivary pellicle plays an important role in oral physiology, yet noninvasive in situ characterization and mapping of this layer remains elusive. The goal of this study is to develop an optical approach for the real-time, noninvasive mapping and characterization of salivary pellicles using optical coherence tomography (OCT) and optical coherence microscopy (OCM). The long-term goals are to improve diagnostic capabilities in the oral cavity, gain a better understanding of physiological and pathological processes related to the oral hard tissues, and monitor treatment responses. A salivary pellicle is incubated on small enamel cubes using human whole saliva. OCT and OCM imaging occurs at 0, 10, 30, 60 min, and 24 h. For some imaging, spherical gold nanoparticles (15 nm) are added to determine whether this would increase the optical signal from the pellicle. Multiphoton microscopy (MPM) provides the baseline information. In the saliva-incubated samples, a surface signal from the developing pellicle is visible in OCT images. Pellicle "islands" form, which increase in complexity over time until they merge to form a continuous layer over the enamel surface. Noninvasive, in situ time-based pellicle formation on the enamel surface is visualized and characterized using optical imaging.

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.

In the United States, over 27,000 new cases and approximately 7,000 deaths attributable to oral cancer are expected in 2003. In some areas of the world this malignancy is much more common; oral cancer is the most common cancer among men and the third most common cancer in women in India. Prognosis for patients with oral cancer remains low with 5-year survival rates hovering in the 50th percentile. High resolution, in vivo optical imaging may offer a clinically useful adjunct to standard histopathologic diagnosis. The work in this dissertation centered on optical imaging in the oral cavity to determine whether confocal microscopy and optical coherence microscopy could detect and diagnose oral neoplasia. A survey of features of normal epithelium and SSCs using a reflectance confocal microscope resolved nuclear density and morphology differences between neoplastic and non-neoplastic oral cavity specimens and features of noncancerous and cancerous oral tissue such as inflammation, fibrosis, muscle fibers, and salivary glands. A detailed study of the differences between normal, preneoplastic, and neoplastic oral cavity tissue using images from a reflectance confocal microscope found that descriptive statistics characterizing nuclear morphology allowed slight differentiation between normal and dysplastic epithelium. Reviews of confocal images by trained pathologists and untrained engineers emphasized the need for situational awareness of the region of the epithelium occupied by the image plane. An optical coherence microscope with subcellular resolution and an estimated penetration depth (based on SNR) of 690-1,227 microns was built to support imaging deeply within oral mucosa. This increased penetration depth supported a study of epithelial scattering coefficients from reflected nuclear intensities that was successful in non-hyperkeratotic layers and showed differentiation between scattering properties of normal and dysplastic epithelium and SCCs.

Optical coherence microscopy (0CM) is a new optical imaging technology that can provide detailed images of tissue architecture and cellular morphology of living tissue. The technique combines the sub-cellular resolution of high numerical aperture (NA) confocal microscopy with the increased sensitivity and penetration depth of optical coherence tomography (OCT) to acquire detail similar to that available in histologic tissue evaluation, except that images can be achieved non-invasively and without the need for fixation and histochemical staining. 0CM images have been acquired from biological structures with a resolution of 2 microns with a 200-500 micron field of view at a penetration depth of 600 microns in plant specimens and in vitro human colon tissue. Thus, 0CM provides the potential to image epithelial tissue with the subcellular resolution needed to assess the pathologic state of tissue. The goal of this study was to characterize the features of normal and neoplastic oral mucosa using 0CM and to compare these to the image features available with confocal microscopy. The authors report the results of a pilot study using both a confocal microscopy and an 0CM system to image pairs of clinically normal and abnormal biopsies obtained from 12 patients. The findings show that, like confocal microscopy, 0CM can image oral mucosa with a resolution comparable to histology without the need for tissue fixation, sectioning, or staining. In addition to subcellular resolution, the 0CM demonstrated consistently deeper penetration depths than achieved by the confocal arm of the system. Analysis of epithelial scattering coefficients clearly discerns a difference between the hyperkeratotic layers and the non-keratinized epithelium below and an increase in scattering associated with premalignancy. (2 tables, 7 figures, 41 refs.), Prepared in collaboration with the Departments of Head and Neck Surgery and Pathology at the University of Texas M.D. Anderson Cancer Center, Houston, TX.