This research uses Brillouin Microscopy and Optical Coherence Tomography (OCT) to improve our understanding of presbyopia, an age-related condition that affects near vision. Lens thickness change during accommodation and depth-dependent Brillouin shift profile were measured in vivo in 6 subjects in the age range from 21 to 54 years. We observed an age-dependent increase in lens thickness, decrease in lens thickness change and an increase in the central plateau in the Brillouin shift, consistent with previous research. We also found that the increase in the width of the plateau is associated with a decrease in the accommodative response.
KEYWORDS: In vivo imaging, Elastography, Mechanics, Visual process modeling, Microscopy, Eye, Data modeling, Visualization, Visual system, Therapeutics
Presbyopia is a loss of the dynamic accommodation response of our vision and affects everybody as they age. Despite many static corrections available, we still do not address the underlying biomechanical cause of lens stiffness. Novel lens softening therapies are limited by no ability to assess biomechanics in vivo. To address this, we developed a multimodal OCE/Brillouin system that maps spatial-varying modulus of a lens. The lens mechanical signature was measured, and a forward model was used to demonstrate the structure-function relationship of lens stiffness on clinical accommodation. This technique has the potential for patient-specific presbyopia models and therapeutic planning.
Optical coherence elastography (OCE), the elastography extension of optical coherence tomography (OCT), has been proposed to quantify the biomechanical properties of ocular tissues (e.g., cornea and sclera) for early detection of different diseases, such as keratoconus and cataract. In wave-based OCE, various tissue stimulation methods have been demonstrated to induce waves in ocular tissues. Acoustic radiation force (ARF) is commonly used as a non-contact excitation source with tightly controlled stimulation parameters for various tissues, including the cornea and crystalline lens. However, ARF’s reliance on tightly focusing acoustic pressure within the tissue raises concerns about potential tissue damage. The aim of this study was to assess the safety of ARF-OCE on freshly enucleated ex vivo porcine eyes and investigate the ability of safe acoustic pressures to produce detectable displacements for OCE. In this study, the maximum value for ophthalmic acoustic pressure set by the Food and Drug Administration (FDA) was set as the 100% threshold in our assessment, and it was determined using a needle hydrophone. OCT and confocal microscopy were used to assess the integrity of the porcine crystalline lens before and after ARF-based OCE experiments. The maximum ARF intensity allowed by the FDA produced detectable wave propagation on the crystalline lens without damaging the lens.
Presbyopia is a loss of the dynamic accommodation response of our vision and affects everybody as they age. Despite many static treatment options, we still do not address the biomechanical cause of lens stiffness. Novel therapies are limited by no ability to monitor in vivo biomechanics. To address this unmet need, we developed a combination OCE/Brillouin system capable of measuring co-located Brillouin spectra and elastography information to derive depth-dependent elastic moduli. The system specifications were quantified for evaluating a human lens and testing performed in vivo. This technique has the potential for patient-specific predictive models of presbyopia.
Tumor volume measured from computed tomography images is considered a biomarker for disease progression or treatment response. The estimation of the tumor volume depends on the imaging system parameters selected, as well as lesion characteristics. In this study, we examined how different image reconstruction methods affect the measurement of lesions in an anthropomorphic liver phantom with a non-uniform background. Iterative statistics-based and model-based reconstructions, as well as filtered back-projection, were evaluated and compared in this study. Statistics-based and filtered back-projection yielded similar estimation performance, while model-based yielded higher precision but lower accuracy in the case of small lesions. Iterative reconstructions exhibited higher signal-to-noise ratio but slightly lower contrast of the lesion relative to the background. A better understanding of lesion volumetry performance as a function of acquisition parameters and lesion characteristics can lead to its incorporation as a routine sizing tool.
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