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The use of ultrasound has results with advantages for clinical applications. It is possible to made computerized simulations by different methods that save resources and time for many investigation groups. The Finite Element Method (FEM) has been employed in different software’s for solving real problems by the solution of differential equations. In the acoustic area, different solutions have been developed for therapeutic and clinical problems. This paper presents a simulation by the Finite Element Method of an emission system composed by two concave transducers with a work frequency of 1.7 MHz each. An analysis of acoustic propagation and thermal distribution in soft tissue of a rat brain was made. The results obtained were obtained for the best-case of work frequency for both transducers with an acoustic propagation and thermal distribution minimum in the tissue of the brain. This is a first approximation of our investigation group.

During the exposition of ultrasonic waves in a medium, like water, has been observed the presence of an effect called acoustic cavitation. Employing different numerical methods, like Finite Element Method, it could be created computational approximations of this phenomenon, for our case, to achieve a better understanding of its behavior with and without the presence of microbubbles. In our case, could help to understand the effects produced by the acoustic cavitation during the opening of the Blood-Brain Barrier. In this paper, it is presented an analysis of different frequencies for a planar ultrasonic transducer in a phantom with microbubbles (about 12 nm) immersed in water, able to produce a considerable effect that could be named acoustic cavitation. The results indicate that at low frequencies (200 kHz, 500 kHz) presents a different effect than higher frequencies which is represented in higher acoustic pressure in the microbubbles. For low frequencies, the acoustic pressure generated in the microbubbles inserted in the phantoms has better results with than the case of higher frequencies.

In order to find diagnosis methods making possible a preventive therapy of vascular diseases, it is necessary to investigate new non-invasive measurements of extremely-small changes in specific mechanical parameters, like dynamic strain, thickness and elastic moduli, into the tissues forming the walls of the blood vessels, mainly in the arteries. But, this challenging objective requires to dispose of very-high resolution external ultrasonic inspection methods, even ranging around 1 micron. Nevertheless, the state of the art in ultrasonic imaging offers resolution of 100-200 microns, and the most advanced processing algorithms to optimize axial resolutions, from A-Scans frames, only can attain several tens of microns. Recent previous proposals of the authors have shown solutions (using the SERHH method) in order to attain this difficult objective for the overall wall thickness and an averaged elasticity of the whole artery walls. In this paper the required ultrasonic parameters and the possible applicability of the SERHH method into each one of the intraparietal segments (distinct very narrow laminated internal layers) of the arteries walls, are preliminary analyzed.

This article presents a robust nonlinear control scheme applied for voltage regulation in a node of an electrical distribution network through power electronic converters. It is achieved utilizing a series of nested control loops that are based on sliding mode control. In the event of voltage variations in the common coupling point (PCC), the proposed control scheme drives the power converter to inject the necessary power to the grid node to perform voltage compensation. It is worth mentioning that this control scheme can be applied to control distributed generation systems that can provide auxiliary services to the electrical network in terms of voltage regulation. Simulation results demonstrate the effectiveness of the present control scheme.

In this paper, a two-stage state estimation algorithm is presented where operations are performed on a CPU-GPU platform. The state estimator used in this work consists of two stages: in a first stage, the conventional weighted least squares formulation is used and finally, in the second stage, the estimation process is carried out again with the PMU measurements and the vector of estimated states as a result of the first stage. The execution time of the two-stage state estimation algorithm is optimized through the use of parallel computing based on Graphics Processing Units (GPUs). From this approach, the parallel algorithm proposed in this work is 5.74 times faster than its sequential counterpart.

The application of ultrasound in medicine includes the detection of the functioning of the blood flow, in surgery and in the exploration with images of the interior of the human body. Acoustic cavitation has an important role in therapeutic and diagnostic applications in medicine. For specific cases, the acoustic cavitation has been presented as a booster of clinical applications in the opening of the Blood-Brain Barrier or the elimination of blood clots in blood vessels. In order to understand the behavior of this phenomenon, in this paper it is presented the elaboration of an agarose-gel phantom, the measurement of its properties and a proposal of experimental setup of transducers able to produce acoustic cavitation in the agarose-gel phantom with the processing of the signals detected employing spectrograms of frequencies. The results obtained showed the probability of appearance, the intensity, the duration and the frequencies in which the phenomenon of acoustic cavitation appear and show that when the power applied to the transducer increase, the parameters mentioned tend to increase as well being the highest power applied the level of power with the higher percentage in which the acoustic cavitation presents. Obtained results demonstrate that the appearance percentage of cavitation are less than 5% of the samples present the cavitation at low stimulating power, and near to 95% of the samples demonstrate the presence of the cavitation at maximum stimulation power applied.

The diabetic foot is a disease that occurs as a result of diabetes mellitus (DM). This problem is caused after suffering by a long time from this pathology. The appearance of the diabetic foot can be prevented and combated through measurements and tracking of the physical characteristics of the tissues that compose the foot of the patient with DM disease. Some of those physical characteristics of the foot could modify the expected tissue thicknesses of the foot layers compared to those in healthy subjects. This article presents a multilayered numerical model of acoustic wave propagation in biological layered tissues with ideal thicknesses and geometry; the finite element method was used to study the behavior of echoes of ultrasound waves on each of the layers of the model. In this work, a non-invasive broadband ultrasonic pulse is applied on the layers of the tissues of a foot, to determine the already known thicknesses and evaluate the capabilities of this approach to detect possible thickness variations. With the detection of small differences, it will be eventually possible the early detection of patients with the possibility of suffering from diabetic foot disease. The results indicate that the average of the percentages of relative error observed in the determined thickness of each of the layers, using cross-correlation, does not exceed 5%, which allows the validation of our technique as a tool for detecting thickness variations.

In thermal ablation therapy, high intensity focused ultrasound is used to concentrate the acoustic beams in a specific region. This ultrasonic energy concentration causes a rapid temperature increase in a short time. In some clinical applications, a truncated cone coupled to the transducer contains a propagation medium to allow the delivery of the therapy; besides, its shape points in the target direction. This paper presents a parametric study of a conical applicator for a 4 MHz HIFU transducer with 100 mm focal length for the evaluation of its use in bone tumors. The conical applicator was varied in radius and thickness from 4 -7.5 mm and 1 to 2 mm, respectively, in order to achieve similar acoustic distribution to the HIFU transducer without cone. Three different materials compatible with 3D printing were studied: polylactic acid, acrylonitrile butadiene styrene and low density polyethylene. Simulations were realized in COMSOL Multiphysics® for Finite Element Method. A convergence study was realized for mesh values of $\lambda$ /6, $\lambda$/8 and $\lambda$ /10. The best results were achieved with a cone aperture radiuses larger than 5 mm and a cone tip thickness of 2 mm. The best mesh size was $\lambda$/8.

Diabetic foot represents one of the major causes of morbidity and mortality in people with Diabetes Mellitus. It is important to determine different parameters in the diabetic foot that can be used as indicators that help to prevent the development of this complication. In this work, we are presenting a system that allows the measurement of parameters that will be used for the early detection of diabetic foot composed of two main devices for measuring the electrical impedance and the temperature of the foot. These measurements were made in areas of the foot most prone to ulceration in people with diabetes. The two devices are connected to a concentrator and distributor of information system whose purpose is to obtain and store the data of other sub-systems for measuring other physical parameters, which permits to expand gradually the variables to analyze. Preliminary results indicate that there are significant differences in the measurements of electrical impedance in the interval of 5 to 22 kHz, when we compare diabetic people vs. non-diabetics. Another significant difference was found in the temperature measurement in the zone of the foot corresponding to the first metatarsal. These results could indicate that the temperature and the electrical impedance of the foot could be used as a tool for pre-diagnosis diabetic foot.

In order to get an estimator of the state of the arterial tissues in non-intrusive way, with the aim of preventing vascular accidents, some type of pulsed ultrasonic energy must be employed. But, the conventional pulse-echo ultrasonic imaging only provides a very limited spatial resolution (around hundreds of microns), so reducing the potential accuracy of these classical tools to know elastic properties in parietal tissues of the arteries with resolution enough. In this paper, a new spectral estimation of pulsed ultrasonic echoes and an experimental set-up for its laboratory emulation, both developed by the paper authors, are described. This estimation is based on analyzing with very-high resolution the spectral location of higher overtones in the repetitive pulse-echo signals, acquired from our experimental disposition mimicking the real arterial circulation. This new procedure achieves a radically better estimation (one / two magnitude orders) of the arterial elasticity, in comparison with previous ultrasonic methods. This proposal opens a new way to perform a non-invasive artery diagnosis, based on to accurately estimate its wall elasticity. This provides improvements in the effective resolution finally attainable, also for the real noisy echo-signal received from biomedical tissues. These finding have been corroborated in laboratory with ex-vivo arterial segments.

Focused ultrasound has been used in clinic for the treatment of different diseases, but predominantly in oncology. The main characteristic of this technique is the production of a strongly focused acoustic field composed by a near-field and far-field zones, separated by a well-defined focus. Usually, due to the complexity of the vibration of real transducers, this acoustic field is assumed to be produced by a uniform vibrating curved radiator, with a characteristic but unreal acoustic field. If the radiation of the transducer is not uniform, the acoustic field changes importantly. In this paper, we are proposing a technique to characterize the shape of the focused transducers and to measure the radiation distribution very close to the transducer radiating curved surface. The technique uses the electric continuity to detect the position of the transducer surface at each point using a 3D automated positioner (6.4 μm of step resolution). The position is saved, and another measurement is carried out using a hydrophone to measure the pressure at each same point, and obtain the radiating profile. The technique has shown to be appropriate for determining the transducer's shape, with a resolution limited by the positioning system. The pressure radiating profile shown a ring-type behaviors as expected.

The diabetic foot is a disease that occurs as a result of diabetes mellitus (DM). This problem is caused after suffering by a long time this pathology. The appearance of the diabetic foot can be prevented and combated through measurements and tracking of the physical characteristics of the tissues that compose the foot of the patient with DM disease. The measurement of blood flow in some areas of the foot correlates with the health status of the tissues in this foot of the diabetic patient. Through regular measurements, it is possible to follow up and to describe the effectiveness of the applied preventive therapeutics. In this work, a virtual platform is presented to be used in a Web site, specialized in diabetic foot. The purpose is to offer support for: data logging related to patient medical history, medical diagnostic observations, therapeutic prescriptions, particular observations of the treating medical specialist and follow-up in the evolution of ulcers or changes in the areas most prone to ulceration in patients with diabetes mellitus. The platform is designed for easy handling, allowing an efficient communication from a general server with a number of computers connected through the medical network. This article shows the first results of applying our virtual platform proposal for diabetic foot tracking. It is expected that, from its employment by medical specialists and their subsequent observations, extensions and adjustments in its programming should be made in the future.

Robust control algorithms may improve the efficiency of wave power conversion systems since they present intrinsic nonlinear dynamics and the system uncertainties. Sometimes, the generators that can operate al variable speed (e.g. double feed induction generator) are used at wave power generation plants, since they may improve the system efficiency to generate power when compared to fixed speed generators. The main reason is that this generators with variable speed may adapt the speed of the turbine in order to maintain the optimun flow coefficient value which improving its efficiency. This paper proposes a sliding mode controller for wave power plants based on a double feed induction generator. Also, the presented robust control scheme introduces an adaptive sliding gain that avoids calculating the upper bound for the uncertainties of the system, facilitating its application. The stability of the proposed control scheme is analyzed by means of the Lyapunov stability theory. Finally, the proposed control scheme is validated through some simulation examples.

This study was made in order to prove the feasibility of two of the most promising thermal therapies to treat bone tumors. Microwave (MW) and ultrasound (US) ablation were analyzed. For MW ablation, a single slot antenna was designed. The best characteristics of the antenna, to generate an electromagnetic field and its absorption by the bone, were obtained by a parametric modeling. Length and location of the slot and work frequency were analysed. On the other hand, for US ablation, the acoustic propagation of a 4 MHz spherical transducer was done. Then, two models were proposed: in water and in a 2 layer media (water and bone). Four antennas with the best characteristics to heat up bone were chosen (best cases scenarios). The optimal length position was 6.9 mm (slot length 1 mm & 2 mm) and 4.9 (slot length: 3 mm & 4 mm). These antennas work properly from 2.45 GHz– 2.60 GHz. The SWR was around 1.22±0.07 (m±sd). Finally, these antennas show a covered area of 10.23±0.05 cm2 (m±sd) of bone tissue. Acoustic and thermal distributions depict that US can enter 5 mm in the bone. This results show that both techniques are suitable to treat bone tumors.

The first results in the design of a pulsed Doppler ultrasound system are presented, which aims to detect alterations of diabetic foot cataloged as “high risk”, associated with the processes that lead to occlusion of blood vessels. Therefore, measurement of blood flow gives the level of damage in the affected area and the state of the blood vessels, constituting a noninvasive diagnostic test. The system was designed from the classical conceptions of Pulsed Doppler systems and it incorporates advanced digital design techniques, based on hybrid hardware-software implementations (FPGA) on reconfigurable platforms. Analog system architecture is shown and finally, its most outstanding features and the expected results of the design are exposed.

For getting reliable measurements of the arteries state, by a non-invasive via, to prevent dangerous vascular events (heart attacks, atheromas, cerebral strokes, etc.), ultrasonic tools must be used. Nevertheless, the conventional echographic equipment gives a poor spatial resolution (several hundreds of micron), clearly insufficient to study the arterial elastic properties. In this paper, the possibility of performing a spectral study of ultrasonic echoes coming from arterial walls, is analyzed, with the aim of seeing viability of achieving a much better estimation of the arterial elasticity, respecting to previous ultrasonic tools proposed with this aim. A comparison will be made between preliminary results obtained with our new proposal and with the better classical procedure for elastic measurements: the cross-correlation based techniques. Results suggest that our hypothesis can constitute a promising via to attain a non-invasive diagnostic of the arterial state with high resolution, by the measurement of its Young's elastic modulus.

This paper presents the characterization of an infrared (IR) Longwave camera kit (Lepton-Flir), based on a bolometer array; for the telemetry measuring of temperature in the human skin. It is important to adapt the device to the measured material since the radiometry depends on the emissivity of the material in question. The characterization took place with the comparison with a thermocouple placed on each skin phantom, and one placed inside a box with controlled room temperature. The thermocouples were calibrated with a thermometer pattern with a resolution of 0.1°C. The obtained equation describes a linear behavior in a window of 17°C to 40°C, and allows to know the approximate temperature in each bolometer. This work is an antecedent to the construction of a prototype for the early detection of the diabetic foot complication.

This paper analyzes the behavior of the Incremental Conductance (IC) maximum power point tracking algorithm used in photovoltaic modules. Three variants of the algorithm are compared under both simulations and real world tests with a DSP 1104 card control. The results obtained show that the variant whose simulated behavior is the best, actually is the worst in real world experiments, indicating that it is mandatory to test this kind of algorithms in real facilities. In this case, the facilities are placed in the laboratories of the Faculty of Engineering of Vitoria-Gasteiz (UPV/EHU, Spain), and the photovoltaic modules are on its roof.

A new Extremum Seeking Control (ESC) scheme is proposed in this paper for multimodal function with two dimension (2D), named as ESC 2D — scheme. This ESC 2D-scheme is a Single Input — Double Outputs (DISO) control system that combine two ESC 1D-schemes of asymptotic perturbed type. Each ESC 1D-scheme has two control loop. The scanning loop generates the signal that sweep the searching space in order to locate the desired peak on the multimodal pattern. The tuning parameter (k 2 ) will define the space of searching. The locating loop generates the gradient signal that will find accurately this peak. The tuning parameter (k 1 ) will define the searching speed under the constraint of stability of the ESC loop. The performance obtained for the ESC 2D scheme proposed is evaluated on multimodal benchmark patterns.

In future new medical applications, like non-invasive ultrasonic thermometry into tissues, to assure an efficient broadband driving in rather high-voltage conditions is an important aspect to make an acquisition of echo-waveforms with the required high signal-to-noise ratios (SNR) and short-time durations. A way to attain these aims is to employ a high-energy pulsed driving, by using electrical spikes for excitation of the arrays and transducers. These special driving systems contain non-linear components like semiconductor and high-voltage switching devices; and the classical linear analysis tools are non applicable to analyze them. Some analyses have been previously performed, but only for studying simple influences of damping resistances with a few values in driving capacitors under un-tuning conditions or well with a fix inductive tuning. In this paper, the effect of the selected pulsed driving energy on the classical figure of merit [Spectrum Peak Amplitude × Bandwidth Product (SpaBwP)], is analyzed, for different typical values in reactive tuning. Firstly, some effects, experimentally observed by the designers of these systems, are confirmed by our calculation results. Nevertheless, some behaviors related to the time domain responses and some non linear component, included in the commercial and of-new-design high-voltage driving systems for these applications, are not well described by the mentioned classical figure of merit, so that some criteria are proposed for create a new merit figure more adapted to this problematic.

Some new researches for non-invasive diagnostic applications, by detecting local thermal gradients on internal tissues, seeking a very-early detection of some types of cancer are a promising investigation way with high medical interest.

This paper describes the application of parallel processing techniques based on graphic processing units (GPUs) to the fast steady state solution of electric power systems. A Newton technique based on a Numerical Differentiation (ND) procedure is used. Conventionally, this technique requires of a significant computational effort, measured in terms of computation time. Parallel processing technology based on GPUs is applied in this investigation to considerably reduce the computational time required to reach the steady state solution of the reported case studies. It is shown that the proposed parallel processing scheme is an effective and efficient alternative to obtain the steady state solution, in particular for larger-scale power grids.

In this paper, the application of a parallel processing technique in order to obtain a more efficient version of an analytical method for estimation of voltage sags in electric power systems is presented. The algorithm was written in C programming language and performed using the GNU/Linux operating system The parallelization of the analytical method is made by using multi-thread programming (POSIX threads). POSTX is a standard for UNIX-like operating systems which specifies an application programming interface for multithreaded programming. The implemented parallelized analytical method was applied to the evaluation of voltage sags of the 30-bus and 118-bus IEEE test systems, in order to show its proper operation.

Modern power systems analysis becomes more challenging due to their increasing complexity, greater interConnectivity of elements and sub-systems and the use of alternative generation systems, among others. In order to efficiently conduct these analyses, it is necessary the use of modern computational and numerical techniques, such as parallel processing and fast periodic steady state solution techniques. The Numerical Differentiation (ND) method has been successfully applied to meet the last issue. This paper introduces a modification to the ND method using GPUs, which allows a significant reduction on the computation time required to reach the steady state solution in nonlinear power systems.

Several studies, including the most recent report of the Program for International Students Assessment, accompanied by the annual measurements by the Colombian Institute for Education Evaluation ICFES (for its acronym in Spanish: Instituto Colombiano para la Evaluacion de la Educacion) agree an obvious deficiency of students tested, both in the apprehension of different knowledge areas, as well as their skills and competences to solve problems on daily situations. Given this weakness and taken into account the relevance of incorporating Information Technology and Communications (ICT) in the teaching process, we develop a software that supported on the Kinect™ sensor, captures images from certain physics lab experiments. This application also extracts information from the real-time experiment to generate an interface in Augmented Reality (AR) that visualizes some specific physical parameters.

In this paper, the parallelization of the Fault Positions Method for the stochastic assessment of voltage sags is presented. Using the GNU/Linux operating system, an algorithm was written in C programming language which exploits multi-thread programming by including functions defined by the POSIX threads header and library, in order to perform parallel calculations. A comparative analysis of the parallelized Fault Positions Method with respect to the traditional method is presented by analyzing a small 5-bus test system and the IEEE 118-bus test system. Results of case studies demonstrate the proper operation of the parallelized Fault Positions Method and the reduction in required computational time.

This paper deals with the implementation of parallel processing SPWM multilevel techniques through programmable gate arrays (Field Programmable Gate Arrays, FPGAs). It is shown that switching losses in power converters significantly decreases with an increased number of levels in the SPWM signal, thus providing an efficient energy transfer. The multilevel SPWM control response of 3, 9 and 21 levels in VHDL through the FPGA Xilinx Spartan family is illustrated.

Modern advances in computer technology will definitely have a great impact on the methodologies used in the expansion and operational planning of power systems. Parallel and distributed systems are the new tendencies in technologies that present a great potential for application in these areas. Graphics processing units (GPUs) have recently become popular in several fields of science due to their capability of performing massively large computational tasks. The use of a GPU for efficiently obtaining the periodic steady state solution in the time domain of large-scale electric power systems with nonlinear components is presented in this paper. Two programming models of the numerical differentiation process are proposed and implemented on a single GPU. The computation time of the simulation performed by co-processing GPU-CPU has been compared with the simulation time required when using a conventional CPU. Several test cases have been analyzed to demonstrate the acceleration of the GPU-CPU simulation and the speed-up achieved.

Global responses (efficiency, spatial resolution and dynamic range) of piezoelectric equipment for ultrasonic NDE also depend on the related high-voltage driving-receiving electronics. But, usually, this is only considered by using simplified approaches. In fact, reactive, non-ideal and non-linear aspects of the front-end electronics, in practical NDE commercial units, notably modify the evaluation results. Here, accurate modelling, that includes realistic inductive and also non-linear aspects of piezoelectric & electronic stages, is applied to predict ultrasonic responses in practical units. A fan of electrical behaviours in NDE pulsers are found, using parametric analyses of some effects due to the damping impedances and the energy-discharge capacitors, under distinct inductive tuning situations. This is based on a global pulse-echo modelling with: a quadratic approach for the mechanical losses in the piezoceramics, and non-ideal frequency-dependent effects of reactive nature in the spike generators. Non linear influences on ultrasonic responses, from piezoelectric losses and realistic driving, are accurately taken into account, showing that these details should be included for a real modelling of future NDE ultrasonic designs.

A deep knowledge of the piezoelectric probe parameters is mandatory for optimizing the responses in typical ultrasonic transceivers used for Non-Destructive Evaluation and Medical Imaging. But, usually, practical construction details are not known for the users of commercial probes. A prediction of these data is necessary during the simulation tasks intended to improve the final performances of these broadband transceivers. Here, a Genetic Algorithmic (GA) based option is aimed to make “a posteriori” estimations of five internal parameters, in broadband piezoelectric probes acoustically matched to radiation media, under realistic spike excitation. An original GA procedure is described for “inverse” prediction of internal data, using a matrix model for the matched ultrasonic probes. Up to five probe characteristics could be found with this approach. Agreement in the probe input admittance |Yin| curve was used as an index of good estimation. In spite of noisy transfer function measurements and distortions in experiments, good results were obtained in the parameters estimations, and in the experimental vs estimated comparisons. This proves that our GA procedure is a valuable tool to discover hidden design data in matched ultrasonic probes.

The classical therapeutic applications based on ultrasound is one of the most widely and frequently used technique to treat people with pain, musculoskeletal injuries, and soft-tissue lesions. Despite the research already made on ultrasonic therapy devices, it is well known that an explanation of the real behavior of the radiation patterns in commercial physiotherapy applicators hardly has been investigated. Thus, it is of interest to make new extensive evaluations of these aspects to facilitate proposals of thermal treatments over delimitated areas with enough precision and patient safety. This work presents a comparative experimental evaluation of the acoustic patterns produced by two ultrasonic therapy applicators, of the same series and model in a commercial company. Some anomalous unexpected radiations observed in the near zones of both devices have been analyzed, showing unhomogeneities of very distinct magnitude in each one; their possible origins are analyzed. An authors' modeling of the complex radiation in such therapeutic applicators is improved to numerically simulate these radiated CW fields. Numerical results approach in part experimental radiated patterns, which would explain a possible origin of the spurious radiations and their influence on the effectively measured ultrasonic fields.

Segments of vessels from the own patient, as saphenous vein or mammary or radial arteries, are used to make coronary bypasses. The most effective technique, employed to evaluate the quality of these vessel, prior to their implantation into the periphery of the heart is the so called ultrasonic transit time flowemeter (TTFM). Some improvements in that technology still must be made to extract its full potential in order to achieve reliably measurements of very small blood flows in narrow lumen arteries and veins. In this paper, we present a software program, specifically developed to facilitate the surgical work of the surgeons, providing additional facilities for a quantitative dynamic visualization of flows in the implants during the surgical process. The flow-meter equipment integrates a TTFM analog-digital system, PC-compatible and with FPGA control, developed in a multilateral project funded by CYTED. The system is portable, low cost, robust, and easy to be used.

An advanced procedure for Parametric Spectral Analysis (PSA), developed by the authors [1], was applied to three groups of ultrasonic echo-signals acquired from liver tissue of Wistar rats. Each group consisted on multiecho signals acquired from 5 specimens. The first group of signals was acquired from liver of 5 healthy rats, selected as a control group; the second and third groups were acquired from liver of rats with experimental hepatitis induced by carbon tetrachloride (CCl4) at 5 and 24 hours before liver extraction respectively. The fundamental frequencies associated with the initial regular structures [2, 3] of the tissue were obtained and changes on the Power Spectral Densities were estimated from the three different groups. A displacement of the fundamental frequency estimation was encountered between control and other two groups with induced hepatitis, related probably with inflammation or tissue damage.

The spectral analysis techniques has been widely used to extract information about certain signals and the process in which those are generated. Ultrasonic (US) signal acquired from biological tissues are a particular case of that. Spectral analysis has been used to extract information from US signal related to biological tissue condition, mainly related with the internal scattering structure distribution and regularity. High-resolution spectral analysis techniques are applied to determine pathological characteristics that could indicate the presence of disease in the tissue. Some small changes in harmonics location could be drastically affected by the presence of noise in the analyzed signal. In this work, an evaluation of two parametric HR spectral analysis techniques is performed, first applied to signals acquired from a biological tissue phantom in a temperature range from 21°C to 45°C. A second evaluation was performed, considering simulated US signals, which were added with three different levels of SNR, and then they were analyzed with two parametric methods, which present variations in the error estimated for different noise level conditions. But the general behavior is a smaller error when noise decreases.

Research looking for the achieving of an accurate measurement of thickness changes in thin biological walls (e.g. of blood vessels), is a promising work line in the medical area, because it would provide the bases to analyze the possibility of attaining early diagnoses of some diseases such as hypertension or atherosclerosis. But, to obtain a non-invasive estimation of these parameters on internal tissues, currently presents many difficulties that must be overcome. The use of high-frequency ultrasonic systems appears to offer a possible solution. In fact, the application of conventional ultrasonic imaging has shown this, but the spatial resolution related to this commercial option is not sufficient for a thickness evaluation with sufficient clinical significance, which would require accuracies of few microns. In this paper, some preliminary results of applying a new broadband ultrasonic procedure, recently developed by the authors for thickness measurement purposes, are analyzed for sub-millimeter layers made of materials similar (phantoms) to that of the biological tissues to be encountered into the artery walls. Two optional algorithms for estimating the power spectral density of the multi-pulse signals are assessed with some experimental echoes. Their potential resolutions and capabilities to provide accuracies around a micron are comparatively analyzed, for walls thickness estimation.

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.

Nowadays new methods of echographic signal processing have emerged to support the medical diagnosis. In the first stage of development, these methods should be assessed with a considerable number of realistic echo-signals. In this paper, a mathematical model of hepatic tissue is proposed. This will be used to generate echo-graphic signals adjusted to realistic acquired waveforms. The model is based on a set of characteristics computed from echographic signals produced by the inspection of the healthy liver tissue. These characteristics were a) average power, b) signal to noise ratio (SNR) and c) inter-arrival time standard deviation. In order to emulate the realistic signals, the model was fitted accordingly throughout different values of the three parameters. A comparative analysis between real and simulated signals is presented. Conclusions about obtained results are given, including the parameters values (SNR equal to 6 dB, Average Power equal to 4.08e-4 W and an inter-arrival time standard deviation equal to 1.43e-6 s) of the simulated signals that presented the higher correlation coefficient (0.3003).

The properties of different bio-compatible silicone rubbers (BSRs) are studied with the purpose to determine the best material to fabricate the coupling pad between the piezomaterials and the vessels in an ultrasonic transit time probe to measure the blood flow in coronary vessels. The objective is to reduce the energy loss due to reflection at the interfaces and due to attenuation in the coupling material. In addition, we also seek to eliminate unwanted shear waves. Different BSRs samples are fabricated and studied using two different ultrasonic techniques: air-coupled and water immersion. In addition, the possibility to introduce some material modifications is also discussed. I. INTRODUCTION The ischemic cardiopathy is one of the main causes of death, being the coronary revascularization an effective therapeutic approach to reduce the morbidity and improve the life quality of the patients. The finality of this solution is to ensure that the blood flows toward the heart muscle (myocardium), which in a healthy human being takes place primarily through the coronary artery. But in many persons, a series of problems such elevated levels of cholesterol, reduce the aperture of the aorta and the coronary vessels and bring about changes in their elasticity, so limiting the blood flow, which finally leads to heart attacks.

This paper presents a fine-grained parallel processing technique applied to the transient and steady state analysis of electric power systems containing linear, nonlinear and time varying elements. This approach is based on the application of the parallel processing platform named OpenMP. This work presents five test cases that show the advantage of using the proposed technique compared with traditional sequential techniques.

In this paper, a quantitative and predictive evaluation is presented, to assess the responses observed in a procedure intended for measuring internal thermal properties, from biological tissues, in a rigorously non-invasive way. A set of multi-echo ultrasonic traces is generated, trying to simulate resulting signal traces from a typical inspection of biological tissues. Distinct conditions to generate them are considered for evaluating specific parameters on the response of a parametric power spectral density (PSD) estimation. It is applied to those traces, as a non-invasive procedure to measure properties that, in a real clinic case, could be related, well to tissue temperature changes, or well with other clinical parameters indicative of possible infectious diseases. Discussion about analysis results provides some conclusion under different adverse situation.