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Adaptive spatial filtering of multichannel surface electromyogram signals
Umeå University, Faculty of Medicine, Department of Radiation Sciences.
SLU, Centre of Biostochastics.
Umeå University, Faculty of Medicine, Department of Radiation Sciences.
2004 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 42, no 6, 825-831 p.Article in journal (Refereed) Published
Abstract [en]

Spatial filtering of surface electromyography (EMG) signals can be used to enhance single motor unit action potentials (MUAPs). Traditional spatial filters for surface EMG do not take into consideration that some electrodes could have poor skin contact. In contrast to the traditional a priori defined filters, this study introduces an adaptive spatial filtering method that adapts to the signal characteristics. The adaptive filter, the maximum kurtosis filter (MKF), was obtained by using the linear combination of surrounding channels that maximises kurtosis. The MKF and conventional filters were applied to simulated EMG signals and to real EMG signals recorded with an electrode grid to evaluate their performance in detecting single motor units. The MKF was compared with conventional spatial filtering methods. Simulated signals, with different levels of spatially correlated noise, were used for comparison. The influence of one electrode with poor skin contact was also investigated. The MKF was found to be considerably better at enhancing a single MUAP than conventional methods for all levels of spatial correlation of the noise. For a spatial correlation of 0.97 of the noise, the improvement in the signal-to-noise ratio, where a MUAP could be detected, was at least 6dB. With a simulated poor skin contact for one electrode, the improvement over the other methods was at least 19 dB.

Place, publisher, year, edition, pages
2004. Vol. 42, no 6, 825-831 p.
Keyword [en]
Electromyography, EMG, multichannel, spatial filter, kurtosis
National Category
Medical Engineering
Research subject
Signal Processing
URN: urn:nbn:se:umu:diva-14746PubMedID: 15587475OAI: diva2:154418
Available from: 2006-11-10 Created: 2006-11-10 Last updated: 2013-01-03
In thesis
1. Adaptive signal processing of surface electromyogram signals
Open this publication in new window or tab >>Adaptive signal processing of surface electromyogram signals
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electromyography is the study of muscle function through the electrical signals from the muscles. In surface electromyography the electrical signal is detected on the skin. The signal arises from ion exchanges across the muscle fibres’ membranes. The ion exchange in a motor unit, which is the smallest unit of excitation, produces a waveform that is called an action potential (AP). When a sustained contraction is performed the motor units involved in the contraction will repeatedly produce APs, which result in AP trains. A surface electromyogram (EMG) signal consists of the superposition of many AP trains generated by a large number of active motor units. The aim of this dissertation was to introduce and evaluate new methods for analysis of surface EMG signals.

An important aspect is to consider where to place the electrodes during the recording so that the electrodes are not located over the zone where the neuromuscular junctions are located. A method that could estimate the location of this zone was presented in one study.

The mean frequency of the EMG signal is often used to estimate muscle fatigue. For signals with low signal-to-noise ratio it is important to limit the integration intervals in the mean frequency calculations. Therefore, a method that improved the maximum frequency estimation was introduced and evaluated in comparison with existing methods.

The main methodological work in this dissertation was concentrated on finding single motor unit AP trains from EMG signals recorded with several channels. In two studies single motor unit AP trains were enhanced by using filters that maximised the kurtosis of the output. The first of these studies used a spatial filter, and in the second study the technique was expanded to include filtration in time. The introduction of time filtration resulted in improved performance, and when the method was evaluated in comparison with other methods that use spatial and/or temporal filtration, it gave the best performance among them. In the last study of this dissertation this technique was used to compare AP firing rates and conduction velocities in fibromyalgia patients as compared with a control group of healthy subjects.

In conclusion, this dissertation has resulted in new methods that improve the analysis of EMG signals, and as a consequence the methods can simplify physiological research projects.

Place, publisher, year, edition, pages
Umeå: Strålningsvetenskaper, 2006. 52 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1009
Signalbehandling, electromyography, signal processing, Signalbehandling
Research subject
Biomedical Radiation Science
urn:nbn:se:umu:diva-743 (URN)91-7264-033-2 (ISBN)
Public defence
2006-04-28, 244, 7, Norrlands universitetssjukhus, Umeå, 13:00 (English)
Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2010-01-18Bibliographically approved

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