Design Guidelines for Feedforward Cancellation of the Occlusion-Effect in Hearing Aids.

The occlusion-effect is described as an unsatisfactory quality of the hearing-aid user's own voice that sounds hollow or boomy. Some fixed and adaptive feedback controllers have been suggested in order to reduce the occlusion-effect. More recently, a feedforward adaptive active-noise-control based strategy for unvented hearing aids was proposed. This paper presents a theoretical analysis of the convergence conditions for this canceller. This allows explicit analytical determination of its stability limits, providing an adequate setup of the algorithm parameters to achieve a priori performance requirements, such as convergence speed and sound quality. Design examples are presented, which validate the theoretical analysis and illustrate its practical application.

An image processing software applied to oral pathology.

This study presents the development and evaluation of an image processing software for computer-assisted cellular structure counting. The proposed software consists of a set of processing and analytical tools which allows its use in several applications of cell and cellular structure counting. A particular application in AgNOR quantitative analysis is presented. The knowledge obtained from experienced pathologists has been codified in a sequence of processing steps in order to allow automatic estimation of the mean number of AgNORs per cell in ameloblastomas. The performance of the presented software in such application was verified by comparing the data provided by visual analysis, by two observers previously calibrated and under supervision of two experienced specialists (Group 1) and by the computer program (Group 2). No statistical difference was observed (p<0.05) between the two groups. The use of the proposed method in AgNOR applications permitted attainment of accurate and precise data without the difficulties frequently found in the traditional visual analysis method (time, training and subjectivity). The developed software is an interesting tool as an aid in the study (estimation of the number of cells and cellular structures) of malignant and benign neoplasms.

Removing harmonic power line interference from biopotential signals in low cost acquisition systems.

This paper presents a new proposal of a very low cost and highly efficient interference canceller to be applied to biomedical signals. The power line reference is obtained from analog to digital conversion while higher harmonics are mathematically estimated by means of trigonometric relations. These signals are processed by an adaptive algorithm in order to suppress harmonic interference. Biomedical acquisition systems that incorporate a conventional adaptive canceller, whose reference signal is sampled from power line, can be easily modified to improve interference suppression without hardware modifications. Real application examples are supplied in order to demonstrate its usefulness in electroencephalographic, electrocardiographic and auditory evoked potential signals.

Eletronistagmografia computadorizada na investigaçäo dos distúrbios do equilíbrio / Computerized electronystagmography in the evaluation of equilibrium disorders

A eletronistagmografia (ENG) é uma importante etapa na investigaçäo completa dos distúrbios do equilíbrio corporal, popularizada a partir dos anos 60. Ao longo da última década diversos sistemas computadorizados de ENG foram introduzidos no mercado mundial, mas com custos elevados e portanto pouco freqüentes em nosso meio. Após dois anos de pesquisas, desenvolvemos um sistema próprio para aquisiçäo e processamento de dados par ENG, com dois canais. O sistema computadorizado e eletronistagmografia ("SCE UCPEL/CASTAGNO" versäo 2.2) é conectado a qualquer microcomputador padräo IBM-PC 386 ou superior, tendo custo comparável aos equipamentos convencionais de ENG, mas com significativas vantagens: 1) alta qualidade do tratamento digital do sinal elimina interferências (60Hz); 2) fácil operaçäo sem problemas mecânicos com papel ou tinta; 3) "ferramentas virtuais" no programa para medir velocidade angular da componente lente, amplitude e freqüência; 4) cálculos automáticos de preponderâncias nas provas optocinéticas, calóricas e rotatórias; 5) resultados gráficos na tela do computador; 6) armazenamento dos exames; 7) laudos padronizados de real utilidade ao médicos; 8) ENG de rápida execuçäo e interpretaçäo. Atualmente nosso grupo está desenvolvendo alguns complementos ao sistema, como processamento do terceiro canal (vectoniostagmografia computadorizada), análise automática do nistagmo, e controle do estímulo em barra de leds. Neste artigo também säo apresentados três casos ilustrativos da utilidade do sistema em pacientes normais, com Doença de Méniére, e neuromas do acústico