I. Bazán

Analyzing wall thickness of artery phantoms in a noninvasive way

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.

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.

Simulation and experimental verification of the acoustic field produced by an annular piezoelectric array

In the field of ultrasound transducers to generate frozen rings waves generated a tendency for use in biomedical applications. This paper proposes simulate through Finite Element Method (FEM) simulation of a transducer with 10 rings to find patterns of acoustic field and get a model attached to the real transducer designed by Castellanos et al [3]. This work focuses on obtained results of acoustic field as close as possible to those real measurements, with all this process entails: geometry, the definition of materials piezoelectric, the FEM equations governing the physics of problem and the resolution of the mesh. Whereby are obtained results showing patterns similar to those obtained in the real acoustic field measurements, in order to propose to extend this work to find the combination of this transducer modeling using the FEM.

Ultrasonic measuring of the change in spacing between membranes in a human thorax phantom, focused to detect pleural effusions

The objective of this paper is to develop ultrasound signal processing techniques suitable to measure changes in distance between two membranes in a basic human thorax phantom. The two proposed techniques are based on correlation and phase analysis, getting an accuracy of 94.93% and 92.60% respectively regarding to the measurements obtained with the vernier caliper.

Proposal of a mechanism for an electrical elbow prosthesis

This work focuses on the description of the system of mechanism for a electrical prosthesis. Considering system performance and system of transmission, both will allow to make the movements of the electrical prosthesis. The electrical prosthesis was designed to replace the function of the elbow joint of an upper limb. In the system of transmission is based on rotary motion since it is similar to the movements of the elbow joint which is flexion and extension, to carry out these movements were determined using the gears; of which were calculated to produce them, it is described in this work. On the other hand, the system performance was chosen by using the electrical actuators for high efficiency, high availability and variety of sizes. To be able to define our system of mechanism of a electrical prosthesis, it should be considered several criteria listed in this work, and finally the torque output was calculated to know how much weight can load the prosthesis designed.

Multi-echo signals simulation based on a mathematical model adjusted to hepatic tissue echographic behavior

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).

Computational evaluation of the thermal resolution on ultrasonic thermometry using an improved spectral analysis of echo-signal patterns modeled ad-hoc

This work provides a quantitative specific evaluation of the spectral analysis performance when applied to ultrasonic multiecho-signals, in order to extract information from them, for non-invasive temperature estimation purposes, inside a biological tissue. This specific evaluation was oriented to assess the thermal resolution provided by the application of resolution improvements in this tool. Simulated signals, based on a numerical model of an ultrasonic echo-trace acquired from biological media, were used to perform tests considering several parameters under a controlled situation. One of the most important parameters to be controlled, in calculations for this simulated approach, was the minimum temperature rise considered for evaluation: 0.05°C. Results about harmonics behavior in the here obtained High-Resolution Power Spectral Densities (HR-PSD) are shown and compared with the theoretically expected shift calculations. Commitments between ultrasonic parameters, biological tissues characteristics and signal processing requirements, are discussed for a real experiment, and some conclusions about results are presented.

Valuation of responses in spectral techniques for thermal estimation into biological media, from ultrasonic echo-signals contaminated with increasing noise levels

The objective of this work is to define the preliminary bases needed for achieving an evaluation of responses of the spectral analysis technique for non invasive temperature estimation, when applied to multi-echo ultrasonic signals contaminated with increasing noise levels. Power Spectral Density (PSD) of an ultrasonic signal is calculated in order to obtain accurate information about signal frequency components. The frequency of interest in non invasive thermal estimation is the one associated to the average distance among internal scatterers, which defines a fundamental resonance mode. This fundamental frequency is also associated with the speed of the ultrasound in the propagation media and with its variations versus the temperature. The final objective of this on-going study is to determine potential disturbances on that fundamental resonance frequency, and mainly on its harmonics related to the indirect detection of temperature increments or decrements, for the realistic case of be working with ultrasonic echo-signals contaminated with different noise levels.

Non-invasive estimation of a non-linear temperature gradient using spectral analysis of multi-echo ultrasonic signals

An spectral analysis technique, that establishes a linear relation between the temperature changes in a body and the frequency displacement in the overtone peaks being displayed in the power spectral density (PSD) of ultrasonic echo-signal, has been improved and applied by the paper authors to estimate temperature gradients induced inside a biological phantom by means of ultrasonic therapeutic radiation. In order to evaluate the technique results under controlled conditions, multi-pulse ideal waveforms are properly simulated, considering a non-linear temperature gradient as the thermal distribution induced on this simulated body. The results obtained by means of a very accurate spectral analysis are contrasted, at different depths, with the established increasing-decreasing temperature gradient. The adequacy of the technique to effectively estimate such a realistic temperature spatial distribution, inside a body, is evaluated regarding to selected frequency peaks behavior in comparison with thermal distribution along the central axis of the simulated body, under ultrasonic radiation.

A 3D pseudospectral solver for nonlinear wave propagation in inhomogeneous attenuating media

The present paper describes an approach to solve a forward problem of nonlinear wave propagation in inhomogeneous and linear attenuating media. The implementation was written in Matlab code, but the equations and algorithm described can be implemented in other programming languages. The object of this work is to create an algorithm of nonlinear wave solver that is useful for ultrasound research and the instruction of nonlinear and ultrasound acoustics, by simulations. In other cases, the model can be quickly and easily modified to address a range of simulation tasks or including improvements with GPUs or Cluster PCs. Validation of acoustics field absorption is showed and compared with Finite Element simulations.