J. M. de la Rosa

Possible application of spectral analysis techniques on ultrasonic echo-traces improved for studying changes in blood vessel walls

Parametric algorithms previously developed by authors for spectral evaluation of biological multi-echo waveforms are adapted and improved here in order to achieve a more elevated frequency resolution. These results permit to undertake viability studies around the possible application of a new auto-regressive spectral technique to estimate physical properties like wall thickness changes in blood vessels, with accuracy enough. These difficult and sophisticated measurements in vessels have an increasing interest as tools to estimate basic parameters for calculating elastic properties in the vessel walls. Laboratory thickness data obtained for a latex phantom (mimicking vessel properties) are shown, giving a promising expectative for this improved estimation technique in blood vessels characterization, a diagnostic tool nowadays of growing attention by the researches. In fact, the results suggest clear improvement in spatial resolution, over the classic cross-correlation and non-parametric techniques, to estimate delays between pulsed signals. But, still further efforts and rigorous analyses of ultrasonic echo-signals acquired from well-controlled sanguineous tissues phantoms are needed in order to optimize the potential resolution of this new thickness measurement procedure and also to evaluate its possible clinic limitations.

Electro-optical, DSO-supported fast position detector

A fast, solid-state, two-dimensional position detector based on photodiodes as a means of image conversion is described. The detector uses conventional optics to project an image onto a matrix of photodiodes; the resulting electric pulses are encoded both in amplitude and time duration and merged into a one-channel signal which can be stored in a fast digital storage oscilloscope (DSO). The stored oscillograms can then be analyzed to reconstruct the trajectory of the moving target. The maximum tracking speed of the device is of the order of tens of nanoseconds. An application in which the device tracks the propagation of a fast electrical discharge is also described.

A longitudinal coil for measuring fast pulsed currents flowing along sheets

In this paper the theory, design and performance of an auto-integrating longitudinal coil used to measure fast pulsed currents flowing along sheets is presented. The sensitivity is given as a function of the sheet width, the coil-sheet distance and the coil load impedance. The coil has been used in N2 laser investigations where current measurements are very difficult to achieve.

Optimization of irradiation patterns using light emitting diodes

Since light emitting diodes have undergone a huge development in the last decades, they are achieving a widespread use in almost every activity substituting older light sources. The properties of the light emitting diodes such as their size, efficiency, wavelength of the emitted radiation, among others, have turn these devices into an increasingly applied solution for different applications. Some applications require a proper design of the illumination patterns. Here, it is presented a design solution for the radiation pattern of the light emitting diode using as the approximation the cone equation. Also, a method to design specific irradiance distributions using a certain number of diodes is discussed.

An irradiation system for photodynamic therapy with a fiber-optic sensor for measuring tissue oxygen

Photodynamic Therapy is a well known treatment based on the interaction of light of specific wavelength with a photosensitizing drug. In the presence of oxygen molecules, the illumination of the photosensitizer can activate the production of reactive oxygen species, which leads to the death of target cells within the treated tissue. In order to obtain the best therapy response, the tissue oxygen concentration should be measured to adjust the therapy parameters before and during the treatment. In this work, an irradiation system for 5−Aminolevulinic Acid Photodynamic Therapy is presented. It allows the application of visible light radiation of 630 nm using as a light source a high-brightness light emitting diode with an optical-power automatic control considering a light depth-distribution model. A module to measure the tissue oxygen saturation has been implemented into the system. It is based on two light emitting diodes of 660 nm and 940 nm as light sources, a photodiode as a detector and a new handheld fiber optic reflectance pulse oximetry sensor for estimating the blood oxygen saturation within the tissue. The pulse oximetry sensor was modeled through multilayered Monte Carlo simulations to study the behavior of the sensor with changes in skin thickness and melanin content.

Optical spectroscopy for differentiation of liver tissue under distinct stages of fibrosis: an ex vivo study

Liver fibrosis is the decisive step towards the development of cirrhosis; its early detection affects crucially the diagnosis of liver disease, its prognosis and therapeutic decision making. Nowadays, several techniques are employed to this task. However, they have the limitation in estimating different stages of the pathology. In this paper we present a preliminary study to evaluate if optical spectroscopy can be employed as an auxiliary tool of diagnosis of biopsies of human liver tissue to differentiate the fibrosis stages. Ex vivo fluorescence and diffuse reflectance spectra were acquired from biopsies using a portable fiber-optic system. Empirical discrimination algorithms based on fluorescence intensity ratio at 500 nm and 680 nm as well as diffuse reflectance intensity at 650 nm were developed. Sensitivity and specificity of around 80% and 85% were respectively achieved. The obtained results show that combined use of fluorescence and diffuse reflectance spectroscopy could represent a novel and useful tool in the early evaluation of liver fibrosis.

Irradiation system for interstitial photodynamic therapy

Interstitial Photodynamic Therapy (IPDT) is a promising form of treatment of deep-seated and bulky malignant tumors, based on the lethal cell response to the photochemical reactions when drug is light activated in presence of oxygen. In order to accomplish an effective internal illumination, laser sources are preferably used because of two important reasons: the monochromatic light can be confined to the narrow absorption band of the drug and the laser beam is easily focused into optical fibers. In this work the development of a diode-laser-light-source is presented. The system is tuned by temperature to get a better match in the 5-ALA absorption band. This system also comprises a trifurcated fiber system to accomplish interstitial illumination.

A diffuse reflectance spectroscopy system to study biological tissues

Diffuse reflectance spectroscopy (DRS) is a technique that allows the study of the structural and biochemical condition of tissues in a noninvasive-nonionizing way. DRS has been widely used in biomedical applications, mainly as an alternative to biopsy. Generally, the technique consists in the irradiation of a specific zone of a tissue with a reference spectrum. Then, the reemitted by the tissue light is detected. The changes suffered by the backscattered spectrum (after light-tissue interaction) with respect to the incident one carry information about the tissue properties. This work presents a novel system designed and developed to use DRS in biomedical applications. The system uses a LED as a light source and a specially designed optical fiber probe as a mean to deliver the light to the tissue surface, and to collect the reemitted photons from the studied sample. This probe was designed to accomplish two different tasks: to increase the sensitivity of the diagnosis; and to study the radial dependence of the backscattered light. The measuring probe was built in a way that allows taking readings when the exerted pressure on the tissue reaches certain predetermined values.

Time-resolved laser-induced fluorescence system

Fluorescence methods are being used increasingly in the measurement of species concentrations in gases, liquids and solids. Laser induced fluorescence is spontaneous emission from atoms or molecules that have been excited by laser radiation. Here we present a time resolved fluorescence instrument that consists of a 5 μJ Nitrogen laser (337.1 nm), a sample holder, a quartz optical fiber, a spectrometer, a PMT and a PC that allows the measurement of visible fluorescence spectra (350-750 nm). Time response of the system is approximately 5 ns. The instrument has been used in the measurement of colored bond paper, antifreeze, diesel, cochineal pigment and malignant tissues. The data acquisition was achieved through computer control of a digital oscilloscope (using General Purpose Interface Bus GPIB) and the spectrometer via serial (RS232). The instrument software provides a graphic interface that lets make some data acquisition tasks like finding fluorescence spectra, and fluorescence lifetimes. The software was developed using the Lab-View 6i graphic programming package and can be easily managed in order to add more functions to it.