Elisabeth Costa Monteiro

Improvement of a technique for localization of steel needles in humans using a SQUID magnetometer

A technique was previously developed, based on magnetic field measurements, to localize hypodermic and sewing needles lost in the human body, with the purpose of surgical extraction. The measurements are performed using a SQUID magnetometer, which detects the magnetic field associated with the remanent magnetization of the needle. The technique allowed easy surgical localization of the needles with good precision in all six clinical cases studied so far. The procedure greatly decreases the surgery time for foreign body extraction, and also reduces the generally high odds of failure. This paper presents an improvement of the original algorithm, which is now independent of any constant magnetic field component, thus overcoming the main experimental difficulty usually found, namely that a SQUID system does not measure absolute fields.

Modelagem da sensibilidade de amostras GMI por redes neurais

Over the past few years, several studies have been developed in order to quantitatively model the GMI effect (Giant Magnetoimpedance). However, these models adopt simplifications that significantly affect its theoretical-experimental performance and its generalization capability, and models that incorporate parameters that generate asymmetry - AGMI (asymmetric GMI) - such as the DC level of the excitation current of the GMI samples are still rare. This work aims to develop a new model, sufficiently general, which also incorporates the asymmetry induced by the DC level of the excitation current, capable of guiding the experimental procedures of characterization of the GMI samples. Thus, this paper proposes, presents and discusses the use of a computational model based on feedforward Multilayer Perceptron Neural Networks to model the impedance magnitude sensitivity and impedance phase sensitivity, of the GMI effect, as functions of the magnetic field, for Co70Fe5Si15B10 ferromagnetic amorphous alloys. The proposed model allows obtaining these sensitivities based on some of the main parameters that affect it: length of the samples, DC level and frequency of the excitation current and the external magnetic field.

Incerteza de Medição do Manômetro Usado em Esfigmomanômetros

There is a growing interest on the measurement uncertainty determination for the conformity evaluation and quality assurance, mainly in the enviroment, safety and health sectors. In these areas the measurement result is considered critical since they deal directly with human beings. For the blood pressure measurement, according to studies accomplished in Australia, England and Brazil, a great concern is observed with the reliability of the results obtained by aneroid sphygmomanometers. In these studies, errors of up to 4,4 kPa (33 mmHg) were detected in the appraised sphygmomanometers, against the maximum value of 0,5 kPa (4 mmHg) standardized by OIML recommendation (R-16-1:2002). These errors result in a reduction of the sensitivity of hypertension diagnosis, with normal blood pressure patients being classified as hypertensive and vice versa. According to R-16, the evaluation of the reliability of these sphygmomanometers for medical diagnosis is obtained through the error measurement, and the uncertainty measurement is not required.

Safe exposure distances for transcranial magnetic stimulation based on computer simulations

The results of a computer simulation examining the compliance of a given transcranial magnetic stimulation device to the 2010 International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines are presented. The objective was to update the safe distance estimates with the most current safety guidelines, as well as comparing these to values reported in previous publications. The 3D data generated was compared against results available in the literature, regarding the MCB-70 coil by Medtronic. Regarding occupational exposure, safe distances of 1.46 m and 0.96 m are derived from the simulation according to the 2003 and 2010 ICNIRP guidelines, respectively. These values are then compared to safe distances previously reported in other studies.

Application of genetic algorithms to the solution of the biomagnetic inverse problem, using data acquired by a 16-Channel SQUID system

This paper proposes a new technique based on the employment of genetic algorithms to solve the inverse biomagnetic problem. The biomagnetic measurements analyzed in this paper were performed on isolated rabbit hearts and acquired by a 16-Channel SQUID system. The developed method focused on defining the single equivalent current dipole that best fits the experimental data. The genetic algorithm is used to determine the position, angle and magnitude of the current dipole, attempting to minimize the error between the experimental magnetic field map and the one obtained by using the estimated current dipole.