1,720,977 research outputs found
Integrated instrument for dynamic light scattering and natural fluorescence measurements
No full textOver the past two decades, great efforts have been made in ophthalmology to use optical techniques based on dynamic light scattering and tissue natural fluorescence for early (at molecular level) diagnosis of ocular pathologies. In our previous studies, the relationship between the corneal AF and DLS decay widths of ocular tissues were established by performing measurements on diabetes mellitus patients. In those studies, corneal AF mean intensities were significantly correlated with DLS decay width measurements for each diabetic retinopathy grade in the vitreous and in the cornea. This suggested that the quality of the diagnosis could be significantly improved by properly combining these two powerful techniques into a single instrument. Our approach is based on modifying a commercial scanning ocular fluorometer (Fluorotron Master, Ocumetrics Inc., CA, USA) to include both techniques in the same scanning unit. This configuration provides both DLS and AF real time measurements from the same ocular volume: they can be located in each section of the optical axis of the eye from the cornea to the retina. In this paper, the optical setup of the new system is described and preliminary in-vitro and in-vivo measurements are presented
A NOVEL TISSUE OXYMETER COMBINING THE MULTIDISTANCE APPROACH WITH AN ACCURATE SPECTRAL ANALYSIS
No full textIn this paper a novel optical tissue oxymeter thatintegrates the multidistance approach and the evaluation of thedifferential pathlength qloiting the absorption features of waferis presented This system tukes advantage from the peculiarities ofthese techniques to extract the scatterirrg and the absorptioncoeficient reducing errors introduced by the heterogeneousstructure of the tissue and improving the signal-to-noise ratio
Design and performance of a wide-bandwidth and sensitive instrument for near-infrared spectroscopic measurements on human tissue
No full textThe article describes an instrument designed to perform in vivo near-infrared spectroscopic measurements on human tissues. The system integrates five continuous-wave laser diode sources emitting in the near-infrared spectral region and a low-noise detection system based on an avalanche photodiode. The optical probe is based on a compact, reliable, and low-cost fiber based system with four quantitative measuring points. The excellent sensitivity of the instrument allows one to perform quantitative assessments of the hemoglobin concentration exploiting precise absorption measurements close to the absorption peak of the water: 975 nm. Moreover, a good signal to noise ratio is obtained also at a high acquisition rate, allowing us to follow rapid changes in oxidative metabolism. The system bandwidth is selectable within the range 2.3-27 Hz, i.e., 20 channels (five chromatic and four spatial channels) can be acquired 27 times for each measuring second, whereas the system amplification can be set to measure optical density ranging from 3.5 to 8.5. A prototype version of the instrument has been realized and characterized
Dynamic light scattering and natural fluorescence measurements in healthy and pathological ocular tissues
No full textDynamic light scattering (DLS) and autofluoresence (AF) are two promising optical diagnostic techniques for use in ophthalmology. In this paper the DLS and AF are integrated in one instrument and applied to study healthy and pathological ocular tissues to detect changes at the molecular level. Measurements performed on 17 patients (age range 20-80 years) are presented. Out of these, 7 patients were healthy normals, 10 had glaucoma and the two oldest patients had both glaucoma and cataracts
Dynamic light scattering and natural fluorescence measurements of the corneal tissue
No full textDynamic light scattering (DLS) and autofluorescence (AF) are non-invasive diagnostic techniques that can monitor changes at the molecular level in ocular tissues. In the present study, we demonstrate as simultaneous measurements of autofluorescence and dynamic light scattering on the corneal tissues can be performed using a novel specifically designed instrument. The integrated instrument takes advantage of the singular techniques by improving the measurement quality and the reliability of the diagnosis. Preliminary tests on volunteers show promise in relation to possible use in the clinical practice
Microcontroller-based front-end electronics for simultaneous measurements of dynamic light scattering and natural fluorescence
No full textA digital control unit for use with a new integrated instrument for dynamic light scattering and natural fluorescence measurements is presented. This unit, based on a microcontroller (Microchip PIC16F877), process signals from an optical head and controls instrument functions. The microcontroller internal counters are used to perform real- time photon counting measurement by processing the TTL signals obtained from the photodetectors. The new system provides reliable and simultaneous DLS and AF measurements from the same ocular volume located from the cornea to the retina
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Particle sizing of aqueous humor components by dynamic light scattering in pigmentary glaucoma
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