SignificanceArticular cartilage exhibits a zonal architecture, comprising three distinct zones: superficial, middle, and deep. Collagen fibers, being the main solid constituent of articular cartilage, exhibit unique angular and size distribution in articular cartilage zones. There is a gap in knowledge on how the unique properties of collagen fibers across articular cartilage zones affect the scattering properties of the tissue.AimThis study hypothesizes that the structural properties of articular cartilage zones affect its scattering parameters. We provide scattering coefficient and scattering anisotropy factor of articular cartilage zones in the spectral band of 400 to 1400 nm. We enumerate the differences and similarities of the scattering properties of articular cartilage zones and provide reasoning for these observations.ApproachWe utilized collimated transmittance and integrating sphere measurements to estimate the scattering coefficients of bovine articular cartilage zones and bulk tissue. We used the relationship between the scattering coefficients to estimate the scattering anisotropy factor. Polarized light microscopy was applied to estimate the depth-wise angular distribution of collagen fibers in bovine articular cartilage.ResultsWe report that the Rayleigh scatterers contribution to the scattering coefficients, the intensity of the light scattered by the Rayleigh and Mie scatterers, and the angular distribution of collagen fibers across tissue depth are the key parameters that affect the scattering properties of articular cartilage zones and bulk tissue. Our results indicate that in the short visible region, the superficial and middle zones of articular cartilage affect the scattering properties of the tissue, whereas in the far visible and near-infrared regions, the articular cartilage deep zone determines articular cartilage scattering properties.ConclusionThis study provides scattering properties of articular cartilage zones. Such findings support future research to utilize optical simulation to estimate the penetration depth, depth-origin, and pathlength of light in articular cartilage for optical diagnosis of the tissue.
Articular cartilage is a connective tissue that enables smooth movements between bones in articulating joints. Cartilage consists of extracellular matrix (ECM) and chondrocytes – the cells responsible for synthesis of the ECM. The ECM consists of type II collagen, proteoglycans, water, and some other minor components. Cartilage is prone to degenerative joint conditions, such as osteoarthritis, due to its weak repair capacity resulting from a lack of vascular, neural, and lymphatic networks. Osteoarthritis causes erosion of the cartilage matrix and therefore inhibits its function, resulting in joint pain, loss of mobility, and significant global socioeconomic burden. Currently, surgical treatment of cartilage pathologies is carried out during arthroscopy with variable outcomes. This variability occurs due to the subjective nature of arthroscopy, which relies on manual palpation and visual evaluation of the tissue surface. Diffuse optical spectroscopy in the near-infrared spectral region probes tissue structure and composition via a relationship with its optical properties (the absorption and reduced scattering coefficients). Due to its avascular nature, healthy cartilage is translucent. It thus has low absorption in the near-infrared region, providing the necessary conditions for light to traverse deep into the tissue. This research reports, for the first time, cartilage absorption and reduced scattering coefficients in the near-infrared spectral range and assess their capacity for characterizing the depth-wise profile of cartilage proteoglycan content. The results revealed that cartilage optical properties are strong predictors of its proteoglycan content. The best performance was observed with the prediction of the proteoglycan content by the absorption coefficient.
Combination of FTIR spectroscopy with fiber optics provides a powerful diagnostic tool for diagnosing of human diseases, including osteoarthritis. To detect cartilage degradation, an arthroscopic probe based on polycrystalline fibers was developed and evaluated on equine cartilage specimen. The hook shape allows reaching a significant portion of the articular surface; the flat tip ensures avoidance of tissue destruction. Efficient QCL-coupling and stable transmission of PIR fibers under bending allows the assembling of effective thin arthroscopy probes and customized multispectral systems for medical diagnostic applications. The presented work was performed within the MIRACLE project (Grant Agreement No 780598, Horizon 2020).
Optical spectroscopy offers unique opportunities for a label-free investigation of tissues at the molecular level to identify the variety of diseases. To transfer spectroscopic analysis from the scientific laboratories to clinical environment, fiber optic probes are required as optical bridges between the equipment and tissue.
We developed single and combined fiber optic probes for the following set of spectroscopy methods: Mid IR-absorption, Raman scattering, Diffuse NIR-reflection, and auto-fluorescence. We benchmarked these methods and selected the optimal one (or their combination), that differentiate between healthy and malignant tissue, based on optical spectra. We tested cancer-normal tissue pairs of human body such as colon, kidney, brain as well as cartilages with and without injuries. Equines cartilage samples with and without osteoarthritis were tested as well. Obtained spectral data were evaluated by multivariate discrimination analysis to enable clear separation of malignant and normal tissues. Data fusion was revealed a synergic effect resulted in increasing of sensitivity, specificity and accuracy (up to 98% for kidney cancer).
Cortical spreading depression (CSD) is a slowly propagating wave of depolarization of neurons and glia and has a less characterized vascular component. CSD is a commonly used phenomenon to test new methods of live brain imaging. Application of a blood pulsations imaging (BPI) technique to study of CSD induced with high-potassium solution in rat cortex allowed us to visualize for the first time the novel vascular component of a CSD wave. In our study, this wave component propagated in the limited part of the cortex along the bow-shaped trajectory in sharp contrast with concentric development of CSD measured by concurrently applied optical intrinsic signal (OIS) imaging technique. It was associated with a significant increase of the blood pulsations amplitude (BPA), started with a delay of 20 to 90 s comparing to signal measured with OIS, and propagated 40% faster than OIS signal. These findings suggest that the BPA and slower change of the cerebral blood volume are not directly related to each other even though both characterize the same vascular system. Our study indicates that the BPI technique could be used for characterization of the new pulsatile vascular component of CSDs in animal models of migraine, stroke, and brain trauma.
We present novel experimental method for estimation of the light penetration depth (LPD) in turbid media based on the
analysis of the cross-correlation function of speckle patterns. Under certain illumination conditions, the amplitude of the
correlation function is strongly dependent on the penetration depth. Presented theoretical model based on the Bragg
diffraction from the thick holograms allows LPD estimation if only one parameter of the material, namely refractive
index, of the material is known. However, qualitative LPD comparison is possible without knowledge of the material
properties. Feasibility of the method was checked experimentally. Experimental results were additionally verified by
alternative experimental method.
In this paper we propose novel method possessing high fidelity and versatility for surface defect detection based on the
spatially filtered dynamic speckles. It is shown that resolution of proposed method depends on the geometrical
parameters of the optical system. The feasibility of the novel method for surface defect detection is demonstrated by
experimental results which are in good agreement with theoretical estimations.
We present a study of parameters that affect the accuracy of a reflectance spectrum recovery from the compressed data obtained in a multispectral imaging (MSI) system consisting of a computer-controlled set of light-emitting diodes (LEDs) synchronously switched with a digital monochrome camera. The system allows recovery of a two-dimensional distribution of reflection spectra in a wide spectral range (400 to 700 nm) just from a few captured frames. It is shown that the MSI system designed and assembled by students in a University laboratory is capable of measuring of absolute values of smooth reflectance spectra with an error smaller than 3%. Further, the increasing of the system accuracy could be achieved by providing higher spatial uniformity and higher overlapping of object illumination by all the LEDs.
We present novel optical system capable for fast acquisition of two-dimensional distribution of reflection spectra with
high spatial resolution. It is based on a subspace vector model of surface reflections. The system consists of a computer
controlled set of light-emitting diodes (LED) and a monochrome CCD camera. Spatial distribution of reflection spectra
is acquired in the compressed form. These compressed data can be directly used for accurate classification or recognition
of different parts of the surface under study. We demonstrated experimentally that 2D distribution of spectral reflectance
from the object surface can be captured within 140ms. Such a fast instrument of multispectral imaging could be
extremely useful particularly for researchers who study living biological objects.
In this paper, we report theoretical description and first experimental observation of recently predicted phenomenon called optical orientation of local centers with permanent dipole moment. An electrical current arising at periodical modulation of the polarization of incident light was observed in a crystal of Bi12SiO20 grown in the argon atmosphere. Modulation frequency-dependence of the current amplitude allows us to attribute this current to the predicted effect. This deduction was additionally supported by our experimental data of light-induced dichroism and photoconductivity of the sample. Using a model of donor-acceptor pairs as dipolar centers we were able to explain features of optical orientation of dipolar centers in the crystal.
We present a novel approach that enables online, real-time and non-contact measurements of thickness of protective coatings. The proposed technique based on spatial filtering of dynamic speckles generated by rapidly deflected laser beam. An advantageous feature of the technique is that it is capable for very fast measurement of coating thickness with accuracy of one micrometer while their roughness is 20 μm or higher. Such a high performance is achieved due to proper consideration of statistical properties of spatially filtered dynamic speckles. In this paper we report experimental study of correlation properties of photodiode responses in different configurations of optical setup. The results are in good agreement with theoretical estimations. Performance of a laboratory prototype of the proposed sensor is demonstrated in application to profile measurements of a tube coated by protective layers of different thickness.
An adaptive fiber-optical interferometer, which is based on dynamic reflection hologram recorded in the photorefractive
crystal of cubic symmetry without applying any electrical field, is developed. Adaptive properties of dynamic hologram
enable the solution of an interferometer's working point uncontrollable drift problem caused by external factors.
Theoretical analysis has allowed us to find the optimal set of parameters for both interacting waves and crystal to reach
the maximal sensitivity of the measuring system. Use of semiconductor crystal CdTe with fast recording time of a
dynamic hologram makes it possible to achieve high cutoff frequencies at reasonably low light intensities. As a result
the measuring system is characterized by low energy consumption and ability of stable operation of long duration in
industrial environment.
We propose novel technique for z-distance measurement to an optically rough surface using dynamic speckles. The technique is based on the continuous frequency measurements of the power modulation of the spatially filtered scattered light. The dynamic speckle pattern is created when the laser beam scans the surface under study. We use an acousto-optical deflector to perform scanning the surface. Acousto-optical deflector provides the surface scanning at very high speed up to 500 m/s. Therefore, by using spatial filtering technique of dynamic speckle, the distance to the object surface can be measured within extremely small time window, less than 100 ns. The proposed technique can be very useful for monitoring the surface profile and/or vibrations of the fast moving or fast rotating surfaces in various industrial applications.
An adaptive fiber-optical measuring system for vibrations monitoring, which is based on dynamic reflection hologram recorded in the photorefractive crystal of cubic symmetry without applying any electrical field is developed. Adaptive properties of dynamic hologram enable the solution of a interferometer's working point uncontrollable drift problem caused by external factors. Use of semiconductor crystal CdTe with fast recording time of a dynamic hologram makes it possible to achieve high cutoff frequencies at reasonably low light intensities. As a result the measuring system is characterized by low energy consumption and ability of stable operation of long duration in real environment. Theoretical analysis has allowed us to find the optimal set of parameters for both interacting waves and crystal to reach the maximal sensitivity of the measuring system.
We present novel technique for fast non-contact and continuous profile measurements of rough surfaces by use of dynamic speckles. The dynamic speckle pattern is generated when the laser beam scans the surface under study. The most impressive feature of the proposed technique is its ability to work at extremely high scanning speed of hundreds meters per second. The technique is based on the continuous frequency measurements of the light-power modulation after spatial filtering of the scattered light. The complete optical-electronic system was designed and fabricated for fast measurement of the speckles velocity, its recalculation into the distance, and further data acquisition into computer. The measured surface profile is displayed in a PC monitor in real time. The response time of the measuring system is below 1 μs. Important parameters of the system such as accuracy, range of measurements, and spatial resolution are analyzed. Limits of the spatial filtering technique used for continuous tracking of the speckle-pattern velocity are shown. Possible ways of further improvement of the measurements accuracy are demonstrated. Owing to its extremely fast operation, the proposed technique could be applied for online control of the 3D-shape of complex objects (e.g., electronic circuits) during their assembling.
In this work we present the novel technique for z-distance measurement to an optically rough surface using dynamic speckles. The technique is based on the continuous frequency measurements of the power modulation of the spatially filtered scattered light. The dynamic speckle pattern is created when the laser beam scans the surface under study. The complete optical-electronic system was designed and fabricated for fast measurement of the speckles velocity, its recalculation into the distance, and further data acquisition into computer. The measured surface profile is displayed in a PC monitor in real time. Main advantage of the proposed technique is high scanning speed providing an extremely short response time below 1 μs. Important parameters of the system such as accuracy, range of measurements, and spatial resolution are analyzed. Limits of the spatial filtering technique used for continuous tracking of the speckle-pattern velocity are shown. Possible ways of further improvement of the measurements accuracy are demonstrated. Due to its extremely fast operation the proposed technique could find applications in such areas as online quality control of materials (paper thickness, rolled metal roughness, etc.) moving on production lines with high velocities (up to 20 m/s) or online control of the 3D-shape of complex objects (e.g., electronic circuits) during their assembling.
We propose novel technique for z-distance measurement to an optically rough surface using dynamic speckles. The
technique is based on the continuous frequency measurements of the power modulation of the spatially filtered scattered
light. The dynamic speckle pattern is created when the laser beam scans the surface under study. We use an acoustooptical
deflector to perform scanning the surface. Acousto-optical deflector provides the surface scanning at very high
speed of 200 m/s. The complete optical-electronic system was designed and fabricated for measuring acquisition of two
instant coordinates of the surface into a computer. The response time of the z-distance sensor in our first experiments is
16 microseconds. However, it is shown that the response of the sensor may be as fast as 100 nanoseconds. First measurements of the
surface profile using fast scanning of the laser beam were experimentally demonstrated. The proposed technique can be
very useful for monitoring the surface profile and/or vibrations of the fast moving or fast rotating surfaces in various
industrial applications.
The polarization self-modulation effect has been applied for the effective measurement of the characteristic response time of nominally pure Bi12SiO20 at wavelengths of 810 nm and 980 nm. Owing to the oxygen deficiency in the crystal lattice, the studied BSO crystals have shown the unusual photorefractive sensitivity and the remarkable operation speed in near infrared spectral region. The response time of 130 ms has been measured at the wavelength of 810 nm and the response time of 540 ms at 8 equals 980 nm with the incident intensities of 110 mW/cm2 and 200 mW/cm2, respectively. To our knowledge this is the first experimental evidence of subsecond response in the infrared for the non- semiconductor photorefractive material.
In a photorefractive Bi12SiO20 crystal with high applied electric AC field of square-wave shape a fast two- wave coupling response (less than 1 second) and a slow hologram readout decay (minutes) was found for a wavelength of 633 nm. This can be explained by electron-hole transport with two trap-levels. An intensity dependence of the slower complementary grating was found. Illuminating with the readout wave without applied electric field leads to a very slow grating decay (many hours).
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