Photoacoustic Microscopy (PAM) is a noninvasive imaging method with high acoustic resolution and high optical contrast. It can image deeper tissues than optical microscopy methods, such as multi-photon fluorescence microscopy and optical coherence tomography (OCT). Current scanning mechanism in photoacoustic microscopy is mainly based on positional stage, mirror galvanometer and microelectromechanical system (MEMS). My thesis proposes a novel scanning mechanism using Lead zirconate titanate (PZT), which is one type of piezoelectric ceramics. In my study, the PZT raster scanner is fabricated by mounting a multi-mode optical fiber onto the PZT, which is controlled by a functional generator. When a resonant frequency signal is applied to the PZT, the fiber tip will be vibrated, resulting in a raster scanning light beam in one-dimension. Two-dimensional scanning can be realized by combining another orthogonally mounted PZT. Compared with scanning systems such as the linear stage, mirror galvanometer and MEMS, the PZT scanning system has a faster scanning speed, while preserving satisfactory resolution and a sufficient field-of-view (FOV). In addition, the low cost and compatible configuration of the scanner make it promising for the PAM system to be used in clinical application.

Functional optical imaging techniques have become increasingly important due to their high resolution and non-invasive nature, and have been used to address many unmet needs in the biomedical imaging field. In the area of ophthalmology, mechanical properties have been shown to be an early indicator of retinal disease, but current imaging modalities are unable to provide high resolution in-vivo imaging to capture the minute changes in the elasticity of thin tissue layers at the back of the eye. For respiratory diseases, the ciliary cell function inside the airway have been discovered to play an important role in respiratory health and the onset of disease. Similarly, current techniques are not equipped to image and characterize the cellular level changes in in-vivo tissues. Phase-resolved Doppler (PRD) imaging is a technology developed by our F-OCT lab, primarily for visualizing blood flow and angiography. Recently, it has been determined that the PRD technique is able to provide high phase sensitivity, which can be used to obtain the tissue displacement as well as particle motions. Using this principle, we developed two types of imaging systems: confocal acoustic radiation force optical coherence elastography (ARF-OCE) and spectrally-encoded interferometric microscopy (SEIM). Using the confocal ARF-OCE system, we present the first spatially mapped elasticity imaging in a live animal retina, and obtained a better understanding of the elasticity of different retinal layers. With the SEIM system, we introduced a novel method of spatially tracking ciliary activity in real-time of in vitro tracheal and oviduct tissues. We demonstrate that the SEIM system can image and quantify ciliary beating frequency and ciliary beating pattern with high speed and large field of view. While both these technologies use the PRD technique, the optical system has been optimized for the respective applications. The results in this dissertation serve as a stepping stone to the optimization and ultimately, the clinical translation of the PRD technique to diagnostic imaging. The developed technology has great potential for clinical diagnosis and management of a number of ocular disease, such as age related macular degeneration, glaucoma, presbyopia and myopia, as well as airway diseases such as asthma.

Optical coherence tomography (OCT) is a non-invasive imaging technique that uses coherence light to acquire information from light scattering material. Based on its high-resolution, cross-sectional and three-dimensional volumetric image property, it becomes a major optical imaging modality in biomedical optics and medicine. Optical coherence electrography (OCE) is an extension of OCT, it gives out optical elastic imaging based on tissue’s biomechanical properties, which provides more information compared to traditional OCT. Another functional extension of OCT is known as polarization sensitive optical coherence tomography (PSOCT). Different from intensity based OCT, PSOCT provides additional contrast information on tissues based polarization state of light. During my master period, I mainly focused on the applications on the OCT, including 1) OCT in early diagnosis on androgenic alopecia; 2) real-time viscosity-based monitoring of blood coagulation by optical coherence electrography; 3) polarization sensitive optic coherence tomography in spun fiber.

Mechanical elasticity often serves as a major indicator for pathological changes in ocular as well as intravascular diseases. For example, age-related macular degeneration is an ocular disease that occurs in the posterior eye, where central vision gets damaged due to drusen formation and neovascularization. The mechanical elasticity of the tissue is often altered during the onset of disease before structural changes are detectable with existing technologies. It is necessary to detect these changes early and provide timely treatment due to either the irreversible nature of the disease progression or the fatal consequences associated with late diagnosis. This thesis focuses on the development of an acoustic radiation force optical coherence elastography (ARF-OCE) system to map the mechanical elasticity of tissues, and the translation of this laboratory technology to in vivo animal studies. This technique uses ultrasonic excitation to apply a force onto the tissue and optical coherence elastography to detect the spatial and frequency responses of the tissue, which combines to quantify the elasticity and provide an elasticity map. The resonance frequency method is validated and used to measure the bulk modulus of the tissue while a Voigt spring model calculates the individual layer elasticity. We first test the feasibility of the system using tissue-mimicking phantoms. Then we perform tissue imaging on the ex vivo anterior and posterior eye, where we are able to provide quantified elasticity maps of the rabbit cornea and porcine retina The system is then translated to in vivo imaging, for which quantified elasticity mapping of the rabbit retinal layers can be obtained. In addition, we have also fabricated an ARF-OCE catheter with a diameter of 3.5 mm, which was validated using phantom studies, and intravascular imaging was performed on a human cadaver artery. This study is a major stepping stone to the translation of the ARF-OCE technology in measuring the mechanical properties of tissues in clinical settings. Future studies using this technology include monitoring the retinal elasticity during and after electrode stimulation treatment and also intravascular elasticity imaging to diagnose atherosclerosis.