Zebrafish has become a popular and highly effective animal model for human disease studies and biomedical discovery. Though multiple techniques have been developed for testing its resistance to environmental, toxicological and other stressors. For in vivo studies of the side effects of toxicants on particular organs, non-invasive imaging techniques are necessary. For example, optical tracking the variations of transmitted light intensity allows accurate blood vessel mapping of the whole animal while monitoring the polarization state of light allows muscles imaging. In this study, we propose to combine these two techniques into one using a Polarsens sensor with 4-directional on-chip polarizer. It provides singleshot acquisition of 4 multi-directional polarized images and calculating both temporal and polarization properties of light interacted with the specimen. Multiple experiments on zebrafish embryos demonstrate high efficiency of this approach for simultaneous hemodynamics and muscular structure analysis. We believe it might be highly effective for in vivo quantifying pathological reactions to various stressors in cardiovascular and skeletal muscle systems.
Identification of specific vascular patterns in skin formations is important for non-invasive differential diagnosis of benign and malignant tissues. Accurate blood vessel mapping and quantitative analysis of the vessels morphology may increase the diagnostic efficiency significantly in comparison to conventional dermatoscopy methods. In this paper, we propose videocapillaroscopy technique for non-invasive visualization of microvascular architecture right in the nevi area. It includes acquisition of skin lesion images by exoscope-based imaging system and their digital processing including non-uniformity correction, local and global stabilization, detection and quantification of vessels, comparison of the obtained vessel maps with the reference data. We have demonstrated the efficiency of microvascular network visualization in various melanocytic skin formations. Proposed technique may complement conventional dermatoscopy for diagnosing skin lesions and become especially effective in the early stages of diseases.
The industrial endoscopic remote visual inspection and endoscopic minimally invasive procedures in medicine provide the wide range of visualization and measurement techniques for hard-to-reach objects’ inner surfaces inspection. In common practice, the three-dimensional visualization, three-dimensional geometrical measurement and spectral imaging techniques are realized independently in different specialized endoscopic devices. Simultaneous implementation of these techniques in a single versatile endoscopic system may increase the efficiency of the inspection and diagnostic procedures. We propose a combined approach to multispectral stereoscopic endoscopic imaging. The prototype of an endoscopic probe able to carry out remote three-dimensional geometrical measurements as well as spectral visualization and measurements is demonstrated.
KEYWORDS: Calibration, Endoscopy, Modulation transfer functions, Imaging systems, Cameras, 3D metrology, Image quality, Stereoscopy, Prisms, RGB color model
We address the problem of non-contact geometrical measurements of hard-to-reach objects that is an important task in various industrial and medical applications. We have developed two small-size prism-based systems for simultaneous acquisition of stereoscopic images by a single sensor. For a correct mathematical description of these systems, we use a ray tracing camera model based on a vector form of Snell’s law. We demonstrate that using the chessboard calibration target allows simultaneous geometrical calibration and image quality assessment. We show that the appearance of chromatic aberrations in RGB images caused by the prism may be significantly reduced by applying separate rectification procedure to each color channel. Experiments confirm that the developed optical systems provide high image quality and the software provides high precision of three-dimensional (3D) geometrical measurements. Described systems may become the basis of small-diameter endoscopic probes for various applications.
Endoscopic imaging systems are widely used for non-invasive diagnostics of inner tissues for biomedical applications as well as for non-destructive testing of various hard-to-reach industrial objects. Conventional white light endoscopy often does not provide contrast visualization of the inspected objects and quantitative characterization of their differences. In these cases, spectral imaging techniques may be helpful to increase the effectiveness of endoscopic inspection. Acoustooptic (AO) filtration of light is a very promising technique for implementing spectral imaging capabilities. In this paper, we discuss the peculiarities and benefits of conjugating AO tunable filters (AOTF) with rigid borescopes, flexible fiberscopes and video endoscopes. We analyze and compare imaging and spectroscopy capabilities of two alternative technical implementations: AOTF-based tunable light sources and AOTF-based add-on imaging modules. The results of this analysis are confirmed by multiple experiments.
KEYWORDS: Calibration, Computer simulations, Cameras, 3D modeling, 3D metrology, 3D acquisition, 3D image processing, Ray tracing, 3D image reconstruction, Endoscopy
Stereoscopic video endoscopes are widely used for remote visual inspection and precise three-dimensional (3D) measurements in industrial and biomedical applications. The reconstruction of 3D points from the corresponding image points requires calibration procedure which accuracy affects the measurement uncertainty. We propose to perform an optimal choice of the calibration technique and the calibration target parameters using the computer simulation at the design stage. The effectiveness of this approach is demonstrated via the design of self-developed miniature prism-based stereoscopic system. We simulated acquisition of the calibration and measurement data using optical design software. The conventional calibration technique requiring many positions of the flat target with arbitrary displacements and rotations was compared with another one, which uses the translation stage to provide pure translation of the target. We analyzed the impact of the translation uncertainty, the number of positions, the number of targets and the uncertainty of image point coordinates on the uncertainty of calibration parameters and 3D measurements. We have shown that the second technique could provide the same calibration accuracy as the first one with less number of images. The results of computer simulation were confirmed experimentally using the prototype of the self-developed stereoscopic endoscope. The proposed approach may be used to optimize calibration techniques and reduce a cost of calibration equipment for various stereoscopic measurement systems.
Stereoscopic imagers are widely used tools for precise three-dimensional (3D) characterization of various objects in industrial and biomedical applications. Narrow-band spectral imaging significantly increases capabilities of these devices, i.e. allows to analyze spatial distribution of spectral properties as well as to achieve higher image contrast, lower optical aberrations and, therefore, to improve geometrical measurements accuracy. Using spectral stereoscopic images for 3D measurements requires a proper choice of a number, positions and width of spectral bands used for calibration and interpolation of the calculated parameters. The experimental determination of these parameters does not guarantee the optimal choice and may be difficult to implement and time-consuming for a large number of spectral bands. In this paper, we demonstrate that the optical design software can be effective for the computer simulation of calibration, comparison of mathematical models and assigning spectral calibration parameters. We show the possibility to optimize the parameters of multi-spectral geometrical calibration to ensure the required measurement accuracy provided by the stereoscopic system on the stage of its optical design before manufacturing via the design of self-developed prism-based imager. Computer simulation allowed us to compare two camera models and various spectral options (conventional white-light as well as arbitrary number, positions and width of spectral channels) applied to calibration procedure. The results of computer simulation are confirmed by multiple experiments. Proposed approach may be used for estimation of 3D measurements errors caused by image noise, tolerances of optical components, temperature variations and other factors.
Nowadays, stereoscopic devices are widely used for precise three-dimensional (3-D) measurements of hard-to-reach elements in industrial and biomedical applications. The most common approach for their implementation is the utilization of prism-based optical systems, which allows simultaneous acquisition of two images from different viewpoints on a single sensor. Normally, they are equipped with a wideband (WB) white-light source, but contrast visualization of the inspected object and, therefore, accurate quantitative characterization of its parameters, often requires narrow-band (NB) spectral imaging. We show that the standard geometrical calibration may lead to significant measurement errors when obtained using WB illumination and applied to NB images. As the criterion to evaluate the calibration error, we have chosen the difference between reference and measured lengths of the 1 mm segment along transverse x, y, and longitudinal z axes. If WB calibration data are applied to NB images, the measurement bias increases from the middle of the working spectral range to its edges and can reach significant values: up to 0.1 mm along x axis and 0.15 mm along z axis in 10 to 25 mm distance range. To overcome this, we propose the calibration and image processing procedures based on a proper choice of a few spectral bands for calibration and interpolation of the calculated calibration parameters. Results of multiple experiments using stereo video endoscope confirmed that the proposed technique allows a decrease in the measurement bias by three times in comparison to conventional WB calibration for all wavelengths of the visible range, which essentially improves the measurement accuracy. The impact of WB calibration on random errors of measurements and the quality of image rectification was also analyzed and shown to be insignificant.
We have developed a prototype of a miniature prism-based optical system for simultaneous acquisition of two stereoscopic images on a single image sensor. The scheme and optical characteristics of the system are presented. We show that after a proper geometrical calibration and image processing it is possible to calculate three-dimensional (3-D) shape of the inspected objects. The devices based on this system may be effectively used for 3-D machine vision applications and remote visual inspection.
Spectrally tunable illumination is widely used for colorimetry, spectroscopy, spectral-domain optical coherence tomography and other applications. Most of the swept light sources suffer either from a limited number of spectral channels or from a spatial noise and speckles. In this paper, we discuss an approach based on acousto-optic filtration of wide-band illumination. We show experimentally that acousto-optical tunable filter (AOTF) provides a unique collection of features: arbitrary spectral tuning, multi-bandpass mode and acoustic frequency modulation. It allows assigning a number, positions and width of the spectral channels. Results of multiple experiments show that the proposed technique may become the basis of the swept light sources.
Nowadays, the stereoscopic endoscopy is a widely used tool for precise three-dimensional (3D) measurements of hard-to-reach elements in industrial and biomedical applications. The most common approach for its implementation is the utilization of prism-based optical tips which allow to acquire two images from different viewpoints on a single sensor. Stereo video endoscopes are typically equipped with a wideband white light source, but contrast visualization of the inspected object and, therefore, accurate quantitative characterization of its parameters often requires narrow band spectral imaging. We show that the standard geometrical calibration may lead to significant measurement errors when obtained using white illumination and applied to narrow band images. In order to overcome this, we propose the new calibration procedure based on a proper choice of a few spectral bands for calibration and interpolation of the calculated parameters. Results of multiple experiments show that the proposed technique fosters the measurement accuracy increase.
Endoscopic instrumentation is widely used for diagnostics and surgery. The imaging systems, which provide the hyperspectral information of the tissues accessible by endoscopes, are particularly interesting and promising for in vivo photoluminescence diagnostics and therapy of tumour and inflammatory diseases. To add the spectral imaging feature to standard video endoscopes, we propose to implement acousto-optical (AO) filtration of wide-band illumination of incandescent-lamp-based light sources. To collect maximum light and direct it to the fiber-optic light guide inside the endoscopic probe, we have developed and tested the optical system for coupling the light source, the acousto-optical tunable filter (AOTF) and the light guide. The system is compact and compatible with the standard endoscopic components.
We report on the calculation method for the development of fiber-coupled acousto-optical (AO) spectral filtration modules compatible with conventional inexpensive wide-band light sources (incandescent lamps). The formulas for main parameters of the optical systems of such modules are given. Two possible schemes (collimating and telecentric confocal) of AO filtration are discussed and compared. Their optical throughput and aberration parameters are analyzed. The proposed approach may be useful for the tunable light filtration in various applications (microscopy, endoscopy, interferometry, etc.).
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