We recently reported on an Optical Coherence Microscopy technique, whose innovation intrinsically builds on a recently reported - 2 microm invariant lateral resolution by design throughout a 2 mm cubic full-field of view - liquid-lens-based dynamic focusing optical probe [Murali et al., Optics Letters 34, 145-147, 2009]. We shall report in this paper on the image acquisition enabled by this optical probe when combined with an automatic data fusion method developed and described here to produce an in-focus high resolution image throughout the imaging depth of the sample. An African frog tadpole (Xenopus laevis) was imaged with the novel probe and the Gabor-based fusion technique, demonstrating subcellular resolution in a 0.5 mm (lateral) x 0.5 mm (axial) without the need, for the first time, for x-y translation stages, depth scanning, high-cost adaptive optics, or manual intervention. In vivo images of human skin are also presented.
We report on the compact optical design of a high-resolution 3D scanning microscope with adaptive optics capability for refocusing with no moving parts designed for clinical research. The optical aberrations arising from refocusing are compensated for as part of the multiconfiguration optical design process. The lateral scanning is provided by a scanning mirror, and the depth scan is provided by an adaptive liquid lens embedded within the microscope as an integrated component of a custom optical design. The microscope achieves a performance of 250 lp/mm-a tenfold increase in performance over a liquid lens used as a stand-alone optical element. Results show that the optical design provides invariant modular transfer function over a 2 mm x 2 mm x 2 mm imaging volume, fully compensating (i.e., diffraction limited) for dynamic aberrations contributed by the scanning, the variation in the shape of the liquid lens, and the change in spherical aberration with depth in a slab of average index of refraction of skin. This design can find applications in biomedical imaging, white light interferometry for surface roughness measurements, and other 3D imaging systems.
The optical aberrations induced by imaging through skin can be predicted using formulas for Seidel aberrations of a plane-parallel plate. Knowledge of these aberrations helps to guide the choice of numerical aperture (NA) of the optics we can use in an implementation of Gabor domain optical coherence microscopy (GD-OCM), where the focus is the only aberration adjustment made through depth. On this basis, a custom-designed, liquid-lens enabled dynamic focusing optical coherence microscope operating at 0.2 NA is analyzed and validated experimentally. As part of the analysis, we show that the full width at half-maximum metric, as a characteristic descriptor for the point spread function, while commonly used, is not a useful metric for quantifying resolution in non-diffraction-limited systems. Modulation transfer function (MTF) measurements quantify that the liquid lens performance is as predicted by design, even when accounting for the effect of gravity. MTF measurements in a skinlike scattering medium also quantify the performance of the microscope in its potential applications. To guide the fusion of images across the various focus positions of the microscope, as required in GD-OCM, we present depth of focus measurements that can be used to determine the effective number of focusing zones required for a given goal resolution. Subcellular resolution in an onion sample, and high-definition in vivo imaging in human skin are demonstrated with the custom-designed and built microscope.
A primary limitation of optical coherence microscopy is the lack of sufficient lateral resolution over a usable imaging volume for diagnostic applications, even with high-numerical aperture imaging optics. In this paper, we first motivate the benefit of refocusing at multiple depths in a highly scattering biological sample using optical coherence microscopy, which experimentally shows invariant 2.5 mum axial and 6.5 mum lateral resolution throughout the sample. We then present the optical system design of a hand-held probe with the advanced capability to dynamically focus with no moving parts to a depth of 2 mm in skin-equivalent tissue at 3 mum resolution throughout an 8 cubic millimeter imaging volume. The built-in dynamic focusing ability is investigated with an addressable liquid crystal lens embedded in a custom-designed optics optimized for a Ti:Sa pulsed broadband laser source of bandwidth 100nm centered at 800nm. The design was developed not only to account for refocusing into the tissue but also to minimize and compensate for the varying on-axis and off-axis optical aberrations that would be introduced throughout a 2 mm thick and 2 mm wide skin imaging volume. The MTF contrast functions and distortion plots at three different skin depths are presented.
In this paper, we present the design of a 0.2 NA microscope objective operating across a 120nm broadband spectral range that requires only two doublets and an embedded liquid lens to achieve 3µm invariant lateral resolution throughout a large 8 cubic millimeter imaging sample. Achieving invariant lateral resolution comes with some sacrifice in imaging speed, yet in the approach proposed, high speed in vivo imaging is maintained up to a resolution of 3 µm for a 2x2 mm sample size. Thus, in anticipation to ultimately aim for a resolution of 0.5 to 1 µm, we are investigating the possibility to further gain in resolution using super-resolution methods so both hardware solutions and image processing methods together can provide the best trade-off in overall resolution and speed of imaging. As a starting point to investigate super-resolution methods, we evaluate in this paper three well-known super-resolution algorithms used to reconstruct a high resolution image from down-sampled low resolution images of an African frog tadpole acquired en face using our OCM set-up. To establish ground truth necessary for assessment of the methods, low resolution images were simulated from a high resolution OCM image. The specification and design performance of the custom designed microscope will be presented as well as our first results of super-resolution imaging. The performance of each algorithm was analyzed and all performances compared using two different metrics. Early results indicate that super-resolution may play a significant role in the optimization of high invariant resolution OCM systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.