Size constraint to limit interference in DRL-free single-ended biopotential measurements

Purpose: In this work, it is shown that small, battery-powered wireless devices are so robust against electromagnetic interference that single-ended amplifiers can become a viable alternative for biopotential measurements, even without a Driven Right Leg (DRL) circuit. Methods: A power line interference analysis is presented for this case showing that this simple circuitry solution is feasible, and presenting the constraints under which it is so: small-size devices with dimensions less than 40 mm × 20 mm. Results: A functional prototype of a two-electrode wireless acquisition system was implemented using a single-ended amplifier. This allowed validating the power-line interference model with experimental results, including the acquisition of electromyographic (EMG) signals. The prototype, built with a size fulfilling the proposed guidelines, presented power-line interference voltages below 1.2 µVPP when working in an office environment. Conclusion: It can be concluded that a single-ended biopotential amplifier can be used if a sufficiently large isolation impedance is achieved with small-size wireless devices. This approach allows measurements with only two electrodes, a very simple front-end design, and a reduced number of components.Fil: Catacora, Valentin Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales. Universidad Nacional de La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales; ArgentinaFil: Guerrero, Federico Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales. Universidad Nacional de La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales; ArgentinaFil: Spinelli, Enrique Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales. Universidad Nacional de La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales; Argentin

Real-Time Artifacts Reduction during TMS-EEG Co-Registration: A Comprehensive Review on Technologies and Procedures

Transcranial magnetic stimulation (TMS) excites neurons in the cortex, and neural activity can be simultaneously recorded using electroencephalography (EEG). However, TMS-evoked EEG potentials (TEPs) do not only reflect transcranial neural stimulation as they can be contaminated by artifacts. Over the last two decades, significant developments in EEG amplifiers, TMS-compatible technology, customized hardware and open source software have enabled researchers to develop approaches which can substantially reduce TMS-induced artifacts. In TMS-EEG experiments, various physiological and external occurrences have been identified and attempts have been made to minimize or remove them using online techniques. Despite these advances, technological issues and methodological constraints prevent straightforward recordings of early TEPs components. To the best of our knowledge, there is no review on both TMS-EEG artifacts and EEG technologies in the literature to-date. Our survey aims to provide an overview of research studies in this field over the last 40 years. We review TMS-EEG artifacts, their sources and their waveforms and present the state-of-the-art in EEG technologies and front-end characteristics. We also propose a synchronization toolbox for TMS-EEG laboratories. We then review subject preparation frameworks and online artifacts reduction maneuvers for improving data acquisition and conclude by outlining open challenges and future research directions in the field

Procesamiento de señales aplicado a dispositivos de ayuda para personas con discapacidades motoras

Las afecciones motrices más graves, que involucran la parálisis o pérdida de los miembros, pueden imposibilitar a quien las padece para la realización de tareas de índole doméstico, necesitando ayuda externa para concretárlas. El avance tecnológico ha abierto una carrera incesante en el desarrollo de dispositivos que permiten aumentar el grado de autonomía del discapacitado, aún en personas con afecciones neurológicas y motrices severas, a las que se les suma la pérdida de la capacidad del habla. En la presente tesis se estudian los dispositivos de ayuda que son controlados por los usuarios a partir de señales biopotenciales que los mismos pueden modular a voluntad. La medición de biopotenciales requiere de técnicas analógicas para reducir el impacto del ruido y la interferencia electromagnética en la calidad de las señales, dado los bajos niveles de tensión y las altas impedancias que presentan los biopotenciales. Una vez medidas las señales de interés se aplican técnicas digitales para detectar las órdenes voluntarias del usuario codificadas de distintas maneras en dichas señales biológicas. En la primera parte de esta tesis se analizan problemáticas de la instrumentación de biopotenciales aplicada a dispositivos de ayuda, como las condiciones de acoplamiento de interferencia en entornos domésticos y distintas técnicas para la reducción de la tensión de modo común. También se evalúa la posibilidad de adquirir los biopotenciales en forma aislada mediante electrodos capacitivos. En la segunda parte de la tesis se plantea como caso particular de aplicación, un dispositivo de ayuda de tipo switch controlado por señales de EMG. Se realizó un análisis de distintas técnicas de procesamiento de la señal de EMG para la detección de contracciones y se proponen nuevos métodos de procesamiento que mejoran la robustez de la detección ante cambios en los niveles de ruido y de señal. Finalmente los temas tratados a lo largo de la tesis se integran en la implementación de un prototipo de dispositivo de ayuda de tipo switch controlado por señales de EMG, robusto ante distintas condiciones de uso y que prácticamente no requiere calibración ni ajustes para operar sobre distintos músculos y usuarios.Facultad de Ingenierí

Brain computer interfaces: an engineering view. Design, implementation and test of a SSVEP-based BCI.

This thesis presents the realization of a compact, yet flexible BCI platform, which, when compared to most commercially-available solution, can offer an optimal trade-off between the following requirements: (i) minimal, easy experimental setup; (ii) flexibility, allowing simultaneous studies on other bio-potentials; (iii) cost effectiveness (e.g. < 1000 €); (iv) robust design, suitable for operation outside lab environments. The thesis encompasses all the project phases, from hardware design and realization, up to software and signal processing. The work started from the development of the hardware acquisition unit. It resulted in a compact, battery-operated module, whose medium-to-large scale production costs are in the range of 300 €. The module features 16 input channels and can be used to acquire different bio-potentials, including EEG, EMG, ECG. Module performance is very good (RTI noise < 1.3 uVpp), and was favourably compared against a commercial device (g.tec USBamp). The device was integrated into an ad-hoc developed Matlab-based platform, which handles the hardware control, as well as the data streaming, logging and processing. Via a specifically developed plug-in, incoming data can also be streamed to a TOBI-interface compatible system. As a demonstrator, the BCI was developed for AAL (Ambient Assisted Living) system-control purposes, having in mind the following requirements: (i) online, self-paced BCI operation (i.e., the BCI monitors the EEG in real-time and must discern between intentional control periods, and non-intentional, rest ones, interpreting the user’s intent only in the first case); (ii) calibration-free approach (“ready-to-use”, “Plug&Play”); (iii) subject-independence (general approach). The choice of the BCI operating paradigm fell on Steady State visual Evoked Potential (SSVEP). Two offline SSVEP classification algorithms were proposed and compared against reference literature, highlighting good performance, especially in terms of lower computational complexity. A method for improving classification accuracy was presented, suitable for use in online, self-paced scenarios (since it can be used to discriminate between intentional control periods and non-intentional ones). Results show a very good performance, in particular in terms of false positives immunity (0.26 min^-1), significantly improving over the state of the art. The whole BCI setup was tested both in lab condition, as well as in relatively harsher ones (in terms of environmental noise and non-idealities), such as in the context of the Handimatica 2014 exhibition. In both cases, a demonstrator allowing control of home appliances through BCI was developed

Instrumentación para neuroprótesis vestibles

La tesis pretende contribuir al conocimiento en adquisición de biopotenciales mediante técnicas no invasivas con aplicación a neuroprótesis (NPs). Las NPs son dispositivos que, interactuando con el cuerpo humano, permiten recuperar o reemplazar capacidades perdidas o disminuidas incrementando drásticamente la comodidad e independencia de las personas. Por lo tanto es de interés que las NPs se utilicen de forma muy sencilla y sin asistencia profesional, en correspondencia con el paradigma de los sistemas ``vestibles''. El objetivo general de la tesis es desarrollar etapas de instrumentación que permitan adquirir biopotenciales útiles a las NPs en forma robusta en las condiciones de medida impuestas por los sistemas vestibles. Por lo tanto, se desarrollan sistemas de adquisición de señal mixta en el estado del arte como plataformas para validar los modelos y circuitos de acondicionamiento propuestos, y se diseñan, implementan y verifican experimentalmente circuitos de acondicionamiento analógico que permiten enfrentar este desafío. En primer lugar, se desarrolla un circuito de realimentación de modo común con ganancia aumentada como estrategia general para la robustez frente a interferencia electromagnética. En segundo lugar se proponen electrodos activos para la medición de señales de electromiograma, desarrollando herramientas de análisis e implementando amplificadores para electrodos de múltiples contactos. Finalmente, los electrodos secos son el factor clave del registro de biopotenciales en sistemas vestibles. Por lo tanto, se desarrolla un electrodo activo con impedancia de entrada aumentada utilizando bootstrap de fuente y conservando una topología de baja complejidad.This thesis contributes to the topic of non-invasive biopotential acquisition techniques applied to Neuroprostheses (NPs). NPs are technological devices that, through interaction with the body, allow to recover or replace lost or diminished capabilities, thus dramatically increasing the comfort and independence of a person. It is desirable for NPs to be able to be used in a simple manner without professional assistance, in correspondence with the paradigm of wearable devices. The general objective of the thesis is to develop instrumentation circuits which allow to acquire the biopotential signals that NPs need robustly, even under the measurement conditions imposed by wearable systems. Therefore, state of the art mixed-signal acquisition systems are developed as a platform upon which models and conditioning circuits can be validated, and a set of analog conditioning circuits are designed, implemented, and experimentally tested. First, a common mode feedback circuit with increased gain is developed as a general strategy for increased robustness against electromagnetic interference. Next, active electrodes for electromyography signal measurement are proposed. An analysis tool as well as an implementation alternative for multiple-input electrodes are proposed. Finally, dry-contact electrodes are a key factor in wearable biopotential measurements. Hence, an active electrode with increased input impedance is developed using power supply bootstrapping and a low complexity topology.Facultad de Ingenierí