| As the single most important contributor to cardiovascular disease-related deaths, atherosclerosis serves as a significant topic for scientific research, particularly in terms of diagnosis and prevention. Of particular interest is the atheromatous plaque -- an accumulation of harmful fatty materials embedded within the intimal layer of the arterial wall. However, due to the asymptomatic nature of atherosclerotic disease, detection and characterization of atherosclerosis at its earliest developmental stages remain difficult endeavors. Although several arterial imaging techniques have been developed to visualize and characterize various features of the disease, these methods either suffer from limitations in resolution or provide an inaccurate assessment of physiological conditions. These limitations therefore necessitate a high-resolution, label-free imaging technique for atherosclerotic disease detection.;Nonlinear optical microscopy has emerged as a viable label-free means for imaging thick biological tissue, at submicron resolution and with highly specific chemical identification. Based on the nonlinear optical response of certain materials to light, nonlinear optical microscopy employs the use of long-wavelength photons in the nearinfrared region of the electromagnetic spectrum to provide contrast and optical sectioning capabilities in highly scattering tissue. Recent studies have applied nonlinear microscopic techniques to the study of atherosclerosis, particularly with regards to characterizing structural features of the arterial wall and the protective plaque cap, as well as identifying cells and lipids within the plaque core.;This dissertation investigates the use of three nonlinear optical processes -- two-photon excited fluorescence, second harmonic generation, and coherent anti-Stokes Raman scattering -- to identify and characterize structural and compositional features of the atherosclerotic plaque. In this work, a multimodal imaging platform capturing all three nonlinear signals is implemented to study cellular and structural changes in animal models of disease. Specifically, changes in the accumulation of lipids, macrophage cells, and structural collagen based on dietary conditions are analyzed in an atherosclerotic mouse model. Lipid morphology, composition, and crystal formation are also characterized. Finally, collagen structure and reorganization in an injury-based, rabbit model of disease is investigated. These findings reveal several important features of the atherosclerotic plaque and further establish nonlinear optical microscopy as a powerful tool for biological tissue imaging. |
