JoséP.P. Domingues

A time-of-flight spectroscopy system based on digital signal processing techniques☆

Abstract A modular VME system, based on digital signal processors (DSPs) capable of building several independent histograms of the MCS (multichannel scaler) type with dwell times down to a minimum of 2.3 μs, is described. Depending on the actual dwell time one or more MCS spectra can be taken care of by one single digital signal processor.

Slit-lamp Based Ocular Fluorometry Scanning

The aim of this work is to develop and present new slit-lamp based instrumentation and methods to measure anterior segment ocular fluorescence with clinical significance, mainly in diabetic patients. With those measurements we have been able to quantify both endogenous and exogenous fluorescence (after systemic tracer administration, in the last case) and to detect alterations in Blood-Ocular Barriers (BOB) permeability.

Data acquisition and laser scanning synchronism in SS-OCT — An experimental apparatus

Optical Coherence Tomography (OCT) is a high-resolution, non-invasive and contactless imaging technique based on optical interferometry. After the Time Domain (TD) and the Spatially Encoded Frequency Domain (SEFD), the Swept-Source (SS) OCT, also known as Time Encoded Frequency Domain (TEFD) OCT, is the latest technology available. It is based on a fast wavelength-sweeping of a narrow laser line over the bandwidth of the source. SWEEP TRIGGER and K-CLOCK signals are provided by the laser source and establish the time base for the overall system. Data acquisition and the two-dimensional scanning of the object of interest must be accurately synchronized after those signals. The proposed solution for the overall scanning/acquisition/sweeping synchronism is an integrated and dedicated FPGA-based control system that is being developed and will generate the automatic, programmable and flexible operation that will replace the present, manually adjustable, system. This way, complete reproducibility of experimental conditions will be obtained, along with the possibility of optimizing the galvanometer /mirrors control. This system is being built around a Xilinx XC6SLX45 FPGA and will be integrated in the already developed control software of the OCT system.

Corneal metabolic imaging by FAD autofluorescence lifetime

The final goal of this work is to develop an corneal microscope based on fluorescence lifetime imaging microscopy (FLIM) of the metabolic co-factor FAD. In several corneal pathologies metabolic alterations occur prior to the pathologic expression therefore the assessment of corneal cells metabolic state could be a great advantage. Here, we aim to demonstrate the feasibility of using FAD autofluorescence lifetime to assess corneal cells metabolic state. We found an increase in protein-bound FAD fluorescence lifetime and a decrease in this component relative contribution 48h and 72h after animal sacrifice. These results are in agreement with the expected decrease in cell metabolism which has also been confirmed by MTT assay. Although the results are promising, the number of animals per conditions must be increased and further in-vivo studies are required to fully characterize FAD fluorescence lifetime in corneal tissues.

Development of an Optical Coherence Tomograph (OCT) for small animal retinal imaging

Optical Coherence Tomography (OCT) is a medical imaging technique mostly used in ophthalmology that has been developed since early 1990s. Based on optical interferometry it is capable of producing high-resolution cross-sectional images of non-homogeneous tissues such as the ocular retina. Our goal is to develop a high speed OCT for retinal imaging in small animals. This will be a fundamental tool for research on retinal physiology and for developing new instrumentation and methods for OCT-based morphological and functional retinal imaging. The overall system is assembled from separated modular blocks to allow performance improvement and easy upgrading. Here, we present the first results obtained with this system.

Corneal Cells Metabolic Imaging using FAD Fluorescence Lifetime

We tested the feasibility of a new method for imaging in vivo corneal cells metabolism. Fluorescence lifetime images of rat corneal epithelial layer were measured. The lifetime values correspond to the metabolic co-factor FAD.

Apparatus for Quantitative Slit-Lamp Ocular Fluorometry

Ocular Fluorometry has long been used to measure the presence and concentration of tracers in ocular tissues and fluids and, more and more, quantification of natural occurring fluorescence. Early detection of abnormalities in Diabetic Retinopathy has been a major field of application of this non-invasive technique.

Corneal Quantitative Fluorometry – A Slit-Lamp Based Platform

Ocular Fluorometry has long been used (since early eighties) to measure non-invasively the presence and concentration of tracers in ocular tissues and fluids. The most common tracer has been sodium fluorescein, after systemic administration, but tissue native fluorescence has also been clinically valuable. Our goal is the development of a cooled CCD-camera based instrument configured as an accessory to a slit-lamp - a common instrument in ophthalmic observation of anterior eye - capable of measuring fluorescence in the eye from cornea to anterior vitreous with enough sensitivity and spatial resolution. Sensitivity of 0.1 ng/ml fluorescein equivalent concentration and 100 μm axial spatial resolution have been achieved with in vitro tests. This represent a crucial step forward in slitlamp based quantitative measurements as several new clinical issues can be addressed: Cornea auto-fluorescence and its relation with Diabetic Retinopathy and corneal function evaluation are two of them. With those figures of sensitivity and spatial resolution one can use narrower excitation bands in different wavelengths to address different fluorophores and also reduce slit widths and optimize angular positioning in order to reach inner locations in the eye with enough axial resolution. Accurate corneal in vivo fluorescence quantification evaluating its relation with age and pathologies like diabetes is our first step. Some results have already been achieved and are presented. These developments will also make it possible to improve quantification of Blood-Aqueous Barrier (BAB) leakage into anterior chamber and to assess anterior vitreous fluorescence resulting from Blood-Retinal Barrier (BRB) breakdown. Both are closely related with Diabetes progression.

The improvement of solid state light sensors' performance using temperature control in ocular fluorometry applications

Ocular fluorometry is a non-invasive diagnostic technique that has been used widely in research to measure the amount of fluorescein leakage from the blood into the ocular tissues and fluids after intravenous injection. This information has been demonstrated to be valuable in a number of clinically relevant situations. This paper mainly deals with demonstrating how the use of modern sensors associated with effective temperature control can configure a low-cost solution to an ocular fluorometry instrument and still upgrade the performance previously obtained with bench-top units only. A new ocular fluorometer is briefly described and special attention is dedicated to the temperature cooling and control system that has been developed and to the quantification of its effects on the detector signal-to-noise ratio (SNR), lowest level of detection (LLOD) and error of measurement (EOM) within the context of ocular fluorometry requirements. Experimental evidence is given that shows not only the improvements in LLOD with moderate cooling (more then 35% for a decrease in temperature in the range), but also the attenuation of the EOM by temperature stabilization ( uncertainty in the range induces a EOM), the current LLOD being lower then , as we will see.

Optical characterization of a new photodiode array ocular fluorometer

Ocular fluorometry has been considered an important technique in ophthalmology diagnosis and research. It consists in the application of a fluorometric method for determination of some important physiologic parameters in the eye in a non-invasive way. The need for new instrumentation for ocular fluorometry has been reported in the literature -- there is an ocular fluorometer commercially available, the Fluorotron Master, FM, but lack of axial resolution and high cost call for new instruments based on modern solid state sensors. Also the field of application of this technique is broadening due to availability of new tracers and exploitation of native fluorescence of ocular tissues and fluids (for which the FM is not fitted). In this paper we present the optics of a new instrument (ocular fluorometer) and report most of the tests to completely characterize the optical parameters of this fluorescence imaging system. Optical amplification, image spatial energy distribution over the detector -- a linear array of photodiodes, quantification and correction of slit- lamp angle, excitation and emission filter characteristics are some of the parameters that must be evaluated for a reliable interpretation of results. With a complete fluorometer characterization both in terms of performance parameters related mainly with the detector (linearity, sensitivity, reproducibility) in vitro and in vivo and in terms of optical system regarding the properties of the image obtained and possible aberrations correction by software we can perform reliable clinical evaluations of normal or abnormal situations in order to give the physician valid data he can store and recall for future reference.