Durable phantoms with optical properties and layered structures like healthy and diseased tissues are highly desirable for reliable performance testing of novel high-resolution optical coherence tomography (HR-OCT) systems. In this context, we performed investigations on the establishment of durable 3D retina models from eyes dissected ex vivo from control mice and eyes from animals treated with N-methyl-D-aspartate (NMDA) which induces glaucoma-like tissue alterations. The comparison of data from resin-embedded tissue with native murine retina in gels demonstrates that by utilization of appropriate preparation protocols highly stable 3D samples with layered structures equivalent to native tissues can be fabricated which are suitable for reliable HR-OCT performance characterization.
For performance testing of high-resolution label-free optical coherence tomography (OCT) systems, durable test standards with optical properties similar to native biological tissues are highly desirable. Therefore, we explored the establishment of ex-vivo 3D samples from dissected mouse retina. To achieve high stability, dissected tissue parts were embedded in EPON resin. Results from comparative investigations with OCT on murine retina in agarose demonstrate that by utilization of appropriate EPON embedding protocols durable samples with adequate refractive index properties can be created in which even tiny structures near the OCT resolution limits can be detected.
In ophthalmologic imaging, the optical properties of the retina are essential parameters. The retina’s refractive index (RI) determines the light propagation inside the tissue towards the photoreceptors and its spatial distribution reflects biophysical tissue properties. In addition, information about the RI’s wavelength dependency is crucial for optical imaging, as it has to be considered, e.g., for dispersion compensation in high resolution optical coherence tomography (OCT). However, the spatial RI distribution in retinal tissue is difficult to access. We explored the capabilities of quantitative phase imaging (QPI) for RI characterization of murine retina utilizing digital holographic microscopy (DHM). Multispectral QPI was achieved by a Michelson interferometer-based DHM configuration that was combined with the light from a tunable supercontinuum laser light source.
The refractive index (RI) of the retina and its dispersion are essential parameters in ophthalmologic imaging. However, the spatial RI distribution in retinal tissue is difficult to access. We explored the capabilities of multispectral quantitative phase imaging (QPI) with digital holographic microscopy (DHM) for label-free refractive index characterization of dissected murine retina. The retrieved tissue refractive indices are in agreement with previously reported values for living cells and dissected tissues. Moreover, the detected spatial refractive index distributions correlate with results from complementary conducted OCT investigations. In summary, multispectral DHM is a promising tool for label-free characterization of optical retina properties.
Coherence induced noise and parasitic reflections in the experimental setup are main restrictions that limit the resolution and measurement accuracy in laser light-based digital holographic microscopy (DHM). We explored, if coherence properties of partial coherent light sources can be mimicked by utilizing spectrally tunable lasers. Moreover, the performance for label-free quantitative phase imaging of biological specimens is illustrated utilizing an experimental configuration including a commercial microscope and tunable super continuum laser sources with a wavelength range of up to 230 nm.
KEYWORDS: 3D modeling, Optical coherence tomography, Standards development, Performance modeling, Systems modeling, Animal model studies, Tissues, Eye models, In vitro testing, 3D imaging standards
Glaucoma is caused by a pathological rise in the intraocular pressure, which results in a progressive loss of vision by a damage to retinal cells and the optical nerve head. Early detection of pressure-induced damage is thus essential for the reduction of eye pressure and to prevent severe incapacity or blindness. Within the new European Project GALAHAD (Glaucoma Advanced, Label free High Resolution Automated OCT Diagnostics), we will develop a new low-cost and high-resolution OCT system for the early detection of glaucoma. The device is designed to improve diagnosis based on a new system of optical coherence tomography. Although OCT systems are at present available in ophthalmology centres, high-resolution devices are extremely expensive. The novelty of the new Galahad system is its super wideband light source to achieve high image resolution at a reasonable cost. Proof of concept experiments with cell and tissue Glaucoma test standards and animal models are planned for the test of the new optical components and new algorithms performance for the identification of Glaucoma associated cell and tissue structures. The intense training of the software systems with various samples should result in a increased sensitivity and specificity of the OCT software system.
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