Noncontact photoplethysmography (PPG) has been studied as a method to provide low-cost, noninvasive, two-dimensional blood oxygenation measurements and medical imaging for a variety of near-surface pathologies. To evaluate this technology in a laboratory setting, dynamic tissue phantoms were developed with tunable parameters that mimic physiologic properties of the skin, including blood vessel volume change, pulse wave frequency, and tissue scattering and absorption. Tissue phantoms were generated using an elastic tubing to represent a blood vessel where the luminal volume could be modulated with a pulsatile fluid flow. The blood was mimicked with a scattering and absorbing motility standard, and the tissue with a gelatin–lipid emulsion hydrogel. A noncontact PPG imaging system was then evaluated using the phantoms. Noncontact PPG imaging accurately identified pulse frequency, and PPG signals from these phantoms suggest that the phantoms can be used to evaluate noncontact PPG imaging systems. Such information may be valuable to the development of future PPG imaging systems.
Fresnel lenses have been found by some optical systems designers to be useful in combination with a main lens to provide quality telecentric images. Aspheric Fresnel lenses are an ideal choice for this application because they achieve a high degree of telecentricity across the entire field of view and introduce very little distortion. In a telecentric system consisting of an aspheric Fresnel lens and an off the shelf non-telecentric main lens, the design parameters are few. Aberration theory, constraints on the visibility of the grooves, and physical constraints can effectively be used to quickly determine if a solution exists for a given application and identify the solution space if it does.
A miniature objective designed for digital detection of Mycobacterium tuberculosis (MTB) was evaluated for diagnostic accuracy. The objective was designed for array microscopy, but fabricated and evaluated at this stage of development as a single objective. The counts and diagnoses of patient samples were directly compared for digital detection and standard microscopy. The results were found to be correlated and highly concordant. The evaluation of this lens by direct comparison to standard fluorescence sputum smear microscopy presented unique challenges and led to some new insights in the role played by the system parameters of the microscope. The design parameters and how they were developed are reviewed in light of these results. New system parameters are proposed with the goal of easing the challenges of evaluating the miniature objective and maintaining the optical performance that produced the agreeable results presented without over-optimizing. A new design is presented that meets and exceeds these criteria.
Four-axis single point diamond machining is a diamond machining technique recently introduced as a higher speed
alternative to 3-axis micro-milling for the fabrication of arrays of spherical miniature lenses. For some applications of
lens arrays, aspheric lenses are preferred over spherical lenses. In this study, an array of aspheric lens surfaces that were
designed for an array microscope for digital pathology were fabricated, and the surface quality was found to have the
same surface accuracy as previous experiments with 4-axis SPDM with an “open loop” tool path correction process. The
open loop process demonstrated here will lead to additional time savings when fabricating an array microscope
compared to the more common closed loop compensation processes. This study also shows that the 4-axis SPDM is
capable of producing arbitrary surfaces with high surface quality, enabling technologies such as array microscopy.
Two lens arrays of 20 lenses (4×5) are fabricated in polystyrene (Rexolite 1422) using a 3-D, three-axis micromilling process. The lenses of one array are concave (Rcurv = -2 mm) and the lenses of the other array are convex (Rcurv = 2 mm). A method for correcting a 3-D micromilling program for a single lens is described and evaluated. The lens separation is 4 mm and Ødiam = 2.6 mm for all lenses. Based on a measurement of key optical parameters (radius error, wavefront error, and surface roughness), micromilled lenses are shown to be of high optical quality compared with the form error and surface roughness obtained with plastic injection molded lenses.
The long-term purpose of this project is to build inexpensive endomicroscope systems from optical plastics that operate
over a wide spectral range. We report on a design of a plastic achromatic doublet using PMMA and optical grade
polystyrene, as well as a design of an achromatized endomicroscope system using the same materials. The fabrication of
such optical elements and systems is feasible using methods such as diamond turning or diamond milling. Finally, a
multispectral Shack-Hartmann test bed has been created that can measure the chromatic focal shift of a lens over a broad
spectral band (from 400 nm to 1,000 nm) and detect shifts in focal length down to 90 nanometers.
The multispectral Shack-Hartmann test bed has been used to characterize the chromatic focal shift of a glass singlet lens
and a glass achromat triplet lens. The lenses were tested from 500 nm to 700 nm in 5 nm and 10 nm steps, respectively.
In both cases, we found close agreement between test results obtained from a ZEMAX model of the test bed and those
obtained by experiment.
Six microlens arrays are fabricated in a single step process using diamond milling techniques, plunging and micromilling.
Four of the lenses are cut using plunging, two each in poly(methyl methacrylate) and polystyrene (Rexolite
1422), and the other two are cut in polystyrene using 3D micro-milling. Half of the lenses are concave and the other half
are convex. These are high power lenses having steep sag at the edges and radii between 2.0 - 2.1 mm for each array.
The clear aperture diameters of the lenses are about 3.2 mm for plunged lenses and 2.6 mm for micro-milled lenses. The
lenses are spaced 4 mm apart in a square grid. Setup and method of these techniques is described and the lens arrays are
characterized based on radius (power) error, wavefront error, roughness, and grid position error. Micro-milled lenses are
shown to be of high optical quality compared with standards for injection molded plastic lenses.
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