Time-Domain Low-Coherence Interferometry (TD-LCI) is a well-known optical method to perform absolute distance measurements. As an alternative to conventional TD-LCI, the Self-Mixing Super Luminescent Diode (SM-SLD) technique represents a unique approach for simplicity and compactness. The presence of optical feedback in the source cavity allows obtaining huge interference fringes, even with diffusive targets and without using high-sensitivity and low-noise detectors. In this work, we present the performances of a custom-made SM-SLD interferometer for absolute distance measurements compared with a reference incremental interferometer. Thanks to the simplified acquisition method and the resulting improved signal-to-noise ratio, the system exhibits excellent metrological performances.
The three classes of photoreceptors cones, rods, and intrinsically photosensitive retinal ganglion cells (ipRGCs) contribute to the pupillary light reflex (PLR). The Silent Substitution technique has been proposed to analyze the contribution of individual photoreceptor to PLR. Through the usage of properly selected pairs of light stimuli, this approach allows stimulating a single class of photoreceptors while keeping the activation of all the others constant. In this way, it is possible to understand the single photoreceptors class effect on both image-forming and non-image-forming functions of the human eyes. In this work, a simple approach to perform the Silent Substitution technique is presented and tested. The instrumentation has been designed with four primaries RGBY fiber-coupled LEDs and a double lens system to achieve a Maxwellian-View like optical system. Preliminary tests were conducted on three volunteers in which the PLRs induced by melanopic and chloropic stimulation were measured. The preliminary results confirm the expectations, the light-adapted pupil diameter is principally regulated by the activation level of the melanopsin-expressing ipRGCs photoreceptors, while conedriven induced pupil responses to peak in color contrast are transitory, reverting to the light-adapted baseline pupil diameter more rapidly in respect to melanopsin counterpart.
The possibility to monitor blood-pH has long been acknowledged to provide significant information for the diagnosis, management and treatment of a variety of diseases and it would be of considerable support for the administration of several treatments such as, for example, extracorporeal (blood) circulation (ECC). During ECC, the patient’s blood flows outside the body in disposable bloodlines and devices for treatments such as blood purification or circulation/ventilation/oxygenation support. Although blood-pH can be measured since the early twentieth century by using ion-selective electrodes (ISEs) and, more recently, also by using point-of-care testing (POCT) instruments, nowadays no measurement method has fully succeeded in providing a cost-effective, reliable and accurate estimate of the blood-pH to be routinely used for its real-time monitoring. In a recent paper, we have proposed and demonstrated a measuring instrument for the in-line and real-time monitoring of blood-pH during ECC. Such a measuring system consists of a low-cost fluorescent disposable sensor that can be integrated into the bloodline and, of a non-disposable reading system that interrogates the sensor without contacting the patient’s blood. In this paper, we investigated the robustness of such a measuring system to variations of blood parameters such as blood flow and hematocrit. The obtained results demonstrate that, although during the tests the pH, flow, and hematocrit values were significantly varied — pH from ≈ 6.8 pH, to ≈ 7.4 pH; hematocrit from 32%, to 40%; flow from 250 ml/min, to 400 ml/min, — the measuring system continued to guarantee a measurement error inferior to ±0.04 pH, thus complying with the metrological requirements for in-line and real-time monitoring of blood-pH during ECC
Pupillary light re ex involves many sensory and motor functions of the eye. For this reason, it represents an important emergency diagnostic tool and provides information to assess brain stem function. The pupil system can be considered in terms of input-output black-box behavior: light stimuli can be easily applied to the eyes, and the pupil size can be measured effortlessly and non-invasively. In this paper, a model for short-light- ash-induced transient pupillary light re ex is presented and preliminary experiments designed to test the model features are described. Results confirm that the developed pupillary light re ex model is suitable to describe the pupil oculomotor system exposed to short-light- ashes.
Primary Angle Closure Glaucoma occurs more frequently in people with a narrower limbal anterior chamber depth (LACD) condition. Nowadays, clinical gold standard as an assessment technique, i.e. gonioscopy, is invasive and complex, whereas Van Herick (VH) technique is non-invasive, but subjective. The instrument, we propose, can automatically performs the VH procedure using a blue laser line, a piezo-actuator, and an image recognition algorithm embedded on a Raspberry Pi board. Preliminary measurements have been carried out on volunteers, and the results proved the feasibility of our approach. The final instrument unveils a high potential for early-stage diagnosis and screening applications.
In veterinary practice antibiotics are used and abused all over the world both to treat diseases and prevent infections and, to increase feed efficiency thus promoting growth in food producing animals. With more than 30 years history, β−lactam antibiotics are nowadays one of the most important group of antibiotics in veterinary medicine. In this paper we investigate the possibility to realize a measurement method suitable for field testing and we propose a competitive biosensor based on a relatively low-cost chromogenic cephalosporin (CENTA) for the quantitative analysis of β−lactams concentration in milk. In particular, the reported preliminary study has been focused on cloxacillin and the reported results indicates that the method is potentially able to detect cloxacillin at a concentration of about one order of magnitude lower than the maximal residue limits (MRL) set by the European Commission.
In this paper we present a fiber-based low-coherence self-mixing interferometer exploiting a single-arm approach to measure the flow in a pipe. The main advantages of the proposed system are the flexibility offered by fiber-connected optical head, a greater ease of alignment, the rejection of “common-mode” vibrations, and greater stability. Thanks to the use of a low-coherence source, the proposed system investigates the velocity of the scattering particles owing only in a fixed and well defined region located close to the duct wall itself. The reported experimental results demonstrate that in laminar flow regime the developed system is able to determine the flow and it is quite robust to variation in the scatterers concentration. Increasing the scatterers concentration of about 24 times, the sensitivity S has reduced of less than 30%.
The developed measuring system is based on a low-coherence source and a self-mixing (or internal) detection. The proposed optical layout exploits the reflection from the internal wall of the duct as reference arm, thus reducing system complexity, cost, size and increasing its robustness to movements of the measurand. Moreover, the usage of a low-coherence source allows reducing the problems related to the poor definition of the volume under test (sensing region or measurement volume) typical of “coherent” self-mixing systems. Although preliminary analysis have been performed by simply investigating the frequencies relative to the maximum in the Doppler spectrum, the obtained results demonstrates that by increasing scatterers concentration of +300%, the system sensitivity increases of about only +20%.
Diffuse correlation spectroscopy (DCS) measurements in vivo recorded from rabbits’ ocular fundus are presented. Despite the complexity of these ocular tissues, we provide a clear and simple demonstration of the DCS abilities to analyze variations in physiological quantities of clinical interest. Indeed, the reported experimental activities demonstrate that DCS can reveal both choroidal-flow and temperature variations and detect nano- and micro-aggregates in ocular fundus circulation. Such abilities can be of great interest both in fundamental research and practical clinical applications. The proposed measuring system can be useful in: (a) monitoring choroidal blood flow variations, (b) determining the end-point for photo-dynamic therapy and transpupillary thermo therapy and, (c) managing the dye injection and determining an end-point for dye-enhanced photothrombosis. Moreover, it could allow both diagnoses when the presence of nano- and micro-aggregates is related to specific diseases and verifying the effects of nanoparticle injection in nanomedicine. Even though the reported results demonstrate the applicability of DCS to investigate ocular fundus, a detailed and accurate investigation of the limits of detection is beyond the scope of this article.
A laser Doppler module easily integrated into a commercial ophthalmic microscope is proposed.
Such setup adds flow measurement capability to standard visual inspection of the fundus.
The proposed instrument may provide important clinical information such as the detection
of vessel occlusion provided by surgical treatments (i.e. photocoagulation).
The measuring system is based on a self-mixing laser diode Doppler flowmeter (SM-DF). Reduced
costs, easy implementation and small size represent the main features of SM-DF. Moreover, this
technique offers the advantage to have the excitation and measurement beams spatially overlapped,
thus both overcoming the alignment difficulty of traditional laser Doppler flowmeter
and, well fitting with to limited optical aperture of the pupil.
Thanks to an on-board DSP-microcontroller, the optoelectronic module directly estimates the
blood flow; USB connection and an ad-hoc developed user-friendly software interface allow displaying
the result on a personal computer.
Preliminary test demonstrates the applicability of the proposed measuring system.
An ophthalmic instrument for innovative analyses of the eye microcirculation is presented.
The developed system employs a laser source to performs the DWS (diffusing-wave-spectroscopy)
analysis of the light intensity back diffused by the ocular fundus structures, thus allowing a noninvasive
detection of changes and modulations of both optical and dynamical properties of blood
flow.
The reported preliminary experimental results recorded in-vivo on rabbits' ocular fundus, demonstrate
the ability of the system to detect nano- micro-aggregates carried by the blood flow in the
ocular fundus.
The paper is focused on the description of a measurement procedure and image analysis technique
able to easily estimate the exitance diffused by light-transmitting posts. The exitance
has been measured by making use of a digital colour camera (DP20, Olympus) coupled to the
optics of a microscope (SZX12, Olympus). Posts have been illuminated by using: a blue LED
source (LS-450 Blue LED, Ocean Optics) with emission peak close to camphorquinone activator
peak, an optical fibre and an ad-hoc realized post holder. The obtained results demonstrate
that different translucent posts give rise to different exitance profiles, thus allowing to reach
different polymerization depths along the post, providing different polymerization performances
and, requiring different source powers and exposure times. Even though, other factors such us
mechanical performances, biocompatibility and aesthetics have to be consider once choosing the
more suitable post, the reported measurement procedure and data may help both in choosing
the proper post and defining the optimum light-source power and exposure time.
To measure blood flow rate in ex-vivo circulation, we propose an optical Doppler flowmeter
based on the self-mixing effect within a laser diode (SM-LD). Advantages in adopting SM-LD
techniques derive from reduced costs, ease of implementation and limited size. Moreover, the
provided contactless sensing allows sensor reuse, hence further cost reduction. Preliminary measurements performed on bovine blood are reported, thus demonstrating the applicability of the proposed measurement method.
A Doppler velocimeter exploiting a self-mixing laser diode is proposed. The system has been design to evaluate the
retinal blood flow velocity. The central frequency of the Doppler band obtained from the self-mixing laser diode
measurement is related to the blood flow velocity in the vessel under test. The measurement can be done under the light-intensity
feedback ratio below -100 dB without using highly sensitive electronics since the laser acts as a high-efficiency
mixer oscillator and a shot-noise-limited quantum detector.
The advantages in adopting such technique consist in its low cost, easiness of implementation and small size. Moreover,
the self-mixing laser diode method offers the advantage to have the excitation and measurement beams spatially
overlapped overcoming the alignment difficulty due to limited optical accessibility imposed by the finite aperture of the
pupil.
As a consequence of pigmentation inhomogeneities and/or different vascularizations of the retinal tissue, retinal laser
thermo-treatments are often over- or under-exposed. Our study is focused on the determination of suitable parameters to
identify a convenient end-point of the laser treatment. The proposed method is based on the analysis of the temporal
fluctuations of the scattered light intensity from the spot area. Motion of molecules and thus frequency of the scattered
light fluctuations changes during the laser exposure due to variations of temperature, blood flow and optical parameters,
i.e. absorption and scattering coefficient.
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