1,721,170 research outputs found
A Review on Guided Optical Feedback in Super-Luminescence Diodes for Metrological Purposes
No full textLow-coherence interferometry (LCI) is a widely used measurement technique. Typical applications of LCI range from optical low-coherence reflectometry (OLCR) to optical coherence tomography (OCT). The main advantages offered by LCI over coherent-interferometry (CI) are its usual greater capacity to spatially locating the region of the sample from where the interferometric signal came from (the volume under test VUT), and the greater robustness to stray-light. When the LCI technique is combined with the self-mixing (SM or optical-feedback, OF) technique, it is possible to obtain additional benefits in terms of compactness, and signal to noise ratio (SNR) of the interferometric signal. Optical layouts based on guided lightwaves generally allow to further improve the robustness and performances of the system. In this review, we focus on metrological applications of guided LCI-SM and, in particular, on the use of LCI-SM to measure positions and absolute distances, flow rates, fluid velocity profiles, and thicknesses
Determination of the concentrations of interferents in blood serum by use of a novel solid-state colorimeter
No full textThe quality of the clinical-chemistry analysis of blood serum is greatly affected by interfering substances contained in the sample. At present, skilled laboratory personnel select specimens which can be processed by the analyser. Selection is performed by visual inspection of the serum colour. To reduce laboratory labour costs and risk of infections, we developed an inexpensive, simple and compact solid-state colorimeter to determine concentrations of interferents. This sensor can be integrated into modern clinical-chemistry analysers. The determination of concentrations of interferents is based on the measurement of the extinction coefficients of the serum sample at four different wavelengths. In this paper, this instrument and its performance are presented
A Preliminary Prototype of Smart Healthcare Modular System for Cardiovascular Diseases Remote Monitoring
No full textIn vivo dynamic light scattering changes of the vitreous in diabetes mellitus
No full textPurpose. Dynamic light scattering (DLS) is a well known non-invasive diagnostic tool used in the anter or segment. In this study in vivo DLS measurements of the human vitreous have been performed to detect changes during the course of diabetes mellitus both with and without diabetic retinopathy. Material and Methods. 50 diabetes mellitus patients with ocular complications varying form no diabetic retinopathy through to severe diabetic retnopathy were examined using DLS techniques. Measurements were performed at different topographical locations of the vitreous, the retrovitreal space and the retina. The results were compared to measurements of 50 normal subjects. Results. The autocorrelation function obtained from the DLS signal in the normal vitreous exhibits two peaks which correspond to the contribution from macromolecules These peaks were found to alter, either in applitude or location, during the course of diabetic retinopathy. The degree and form of these alterations was correlated to the severity of the ocular complicatons in the structures investigated. DLS measurements in the cornea exhibited similar effects to those made in the vitreous. Conclusions. DLS is capable of detecting the changes of the vitreous associated with diabetes mellitus. Moreover, due to the close correlation of the DLS results with the severity of viteo-retinal changes, DLS may serve as an important tool for the early diagnosis and monitoring of ocular complications due to diabetes mellitus
Imaging the human iris: a hyperspectral approach
No full textPurpose: Hyperspectral (HS) imaging is a promising optical technique that allows the detection of both spatial and
spectral information in a single data acquisition. Here we investigate the capability of a prototype HS instrument to
measure the iris spectral reflectance in vivo. Moreover, we evaluate the intra- and inter-session repeatability of
quantitative HS measurements of the human iris.
Methods: Eight healthy volunteers (all males, average age 27 ± 2 years) participated in the study. Irises colors were
classified using the grading system of Franssen et al [Grading of Iris Color with an Extended Photographic Reference
Set, J Optom 2008; 1:36-40]. Each HS acquisition (duration: 4125 ms) consists of 22 images (HS cube) captured
between 480 – 900 nm, in 20nm intervals. Each acquisition was repeated 6 times. The instrument was calibrated
using a NIST white reflectance standard, to ensure quantitative and repeatable measurements. Reflectance was
analyzed across the 22 spectral bands in an annular region of interest concentric to the pupil. Repeatability was
assessed from images captured in 3 sessions, at the same exposure time, with realignment of the iris and refocusing
between each session.
Results: Inter-subject variability was highest at short wavelengths (Fig. 1) and reflectance exhibited opposite trends in
the visible and near infrared. This might be the result of melanin scattering. The influence of water absorption is
detected above 850 nm. Repeatability was highest for lighter irises and for wavelengths from 520 to 900 nm. In that
range, the coefficient of repeatability (95% of confidence interval) for measurements between sessions was ±10% and
±5% for dark and light irises, respectively. The within-session repeatability was ±7.5% and ±4%, respectively.
Conclusions: Automated in vivo HS imaging of the human iris appears to be reliable and reproducible. This technique
could potentially be exploited for monitoring iris pigmentation changes with time induced by prostaglandin analogues.
In addition, the iris spectral reflectance could be correlated with the development of certain ocular pathologies
Optical feedback into a superluminescent diode cavity for absolute distance measurements
No full textThe development of accurate absolute distance interferometers is a long-term research goal. The key impact of this paper is the development of an absolute distance interferometer based on the optical feedback into a superluminescent diode cavity. The proposed approach employs a two arms interferometer feeds by a superluminescent diode. Thanks to the optical feedback, we obtained huge interference fringes even with diffusive targets. The proposed signal processing exploits a zero-crossing approach to determine the absolute target position. Preliminary results show a ratio between measurement uncertainty and range of about 50 ppm
Health Status Remote Monitoring System: ECG Peaks Detection by Successive Thresholding Algorithm Employing Envelope Function
No full textToday, there is a growing need for improved remote health monitoring solutions. For example, according to the World Health Organization (WHO), more than 32Unfortunately, most existing systems have neither continuous data transmission, as they store and transmit data once (or a few times) per day, nor real-time capabilities, a very important and not obvious specification for a remote health monitoring system that triggers immediate actions to address unpredictable patient needs. In addition, the algorithms for the elaboration of vital parameters, especially those analyzing the ECG (electrocardiographic) signal, mainly apply a single peak detection method, resulting in many discarded peaks that could be useful instead. To these regards, this paper aims to propose an elaboration algorithm for the ECG signal where peaks detection (related to P-waves, T-waves and QRS complex) is obtained by the application of an envelope function and successive thresholding, which is sufficiently fast and simple to implement in a low-resource wearable device. A further aim is to provide continuous data acquisition and wireless transmission from the portable part to the system, with very low packet loss and real-time characteristics, using low-cost off-the-shelf devices
Spectral Repeatability of a Hyperspectral System for Human Iris Imaging
No full textThe present study was conducted to evaluate the measuring performance of a prototype hyperspectral imaging system. This instrument was developed to measure the human iris spectral reflectance in vivo. Several previous works highlighted how changes in the iris pigmentation and morphology may provide an indication of the development and progression of certain eye pathologies. The use of hyperspectral imaging could aid physicians in the early detection of such diseases, by exploiting both the spatial and spectral features that this optical technique is able to collect. We evaluated the measurements repeatability from images acquired across 22 spectral bands in the visible and near-infrared range (480-900 nm), from 8 healthy volunteers. Moreover, we assessed the intra-and inter-session repeatability of the quantitative hyperspectral measurements. Repeatability was lower for darker irises and for wavelengths from 520 to 900nm. In particular, the coefficient of repeatability (95% of confidence interval) for measurements between sessions was ±10% and ±5% for dark and light irises, respectively. The within session repeatability was ±7.5% and ±4%, respectively. The obtained repeatability coefficients confirm the reliability and reproducibility of the hyperspectral data collected by our system
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