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Biomedical subjects

W Sansen

Publications and source records attributed to W Sansen.

18 recordsLinked to original sources
PubMed1992

Electrical impedance tomography systems based on voltage drive.

At the ESAT-MICAS research facility in Leuven, several EIT systems have been designed and realised. The latest hardware set-up makes use of a PC to control the data collection and to reconstruct the images. A voltage drive strategy and no common-mode feedback are some of its specific characteristics. The function-generator produces signals with a frequency between 10 and 100 kHz, so multifrequency images can also be produced. Static images have already been obtained and (semi-)real time imaging is possible with our latest mark IV system. This system has 16 bit analogue-to-digital convertors and is capable of taking 50 x 10(3) samples/s.

Electric Conductivity↗
PubMed1990

Adaptive spectral analysis of cutaneous electrogastric signals using autoregressive moving average modelling.

The recording of the human gastric myoelectrical activity by means of cutaneous electrodes is called electrogastrography (EGG). It provides a noninvasive method of studying electrogastric behaviour. The normal frequency of the gastric signal is about 0.05 Hz. However, sudden changes of its frequency have been observed and are generally considered to be related to gastric motility disorders. Thus, spectral analysis, especially online spectral analysis, can serve as a valuable tool for practical purposes. The paper presents a new method of the adaptive spectral analysis of cutaneous electrogastric signals using autoregressive moving average (ARMA) modelling. It is based on an adaptive ARMA filter and provides both time and frequency information of the signal. Its performance is investigated in comparison with the conventional FFT-based periodogram method. Its properties in tracking time-varying instantaneous frequencies are shown. Its applications to the running spectral analysis of cutaneous electrogastric signals are presented. The proposed adaptive ARMA spectral analysis method is easy to implement and is efficient in computations. The results presented in the paper show that this new method provides a better performance and is very useful for the online monitoring of cutaneous electrogastric signals.

Electromyography↗
PubMed1990

Comparison of SVD methods to extract the foetal electrocardiogram from cutaneous electrode signals.

The paper presents and compares three methods making use of the singular value decomposition (SVD) of a matrix to extract the foetal electrocardiogram (FECG) from cutaneously recorded electrode signals. The first method constructs a set of orthogonal foetal signals (the so-called principal foetal signals) from the recordings, but needs electrode positions far from the foetal heart, in addition to the abdominal electrodes that pick up a mixture of maternal and foetal electrocardiogram. An online adaptive algorithm has been developed such that a real-time implementation becomes feasible. The second method is a new online approach to a technique presented by van Oosterom. Although this method has some important drawbacks and is suboptimal as far as foetal signal-to-noise ratio is concerned, it is still very useful when only a foetal trigger is required, as the signal obtained is not a complete FECG. Finally, a third method is proposed, based on the generalised SVD and interpreted with the new concept of oriented signal-to-signal ratio. An online version is also presented for this method and some results are shown.

Electrocardiography↗
PubMed1990

Multichannel adaptive enhancement of the electrogastrogram.

The electrogastric signal can be measured cutaneously on the abdomen. This is attractive because it is harmless to patients or volunteers. However, the poor quality of the cutaneous measurements necessitates signal enhancements. Hence, in this paper, an adaptive multichannel signal enhancing system is proposed. The mu-vector least mean square (LMS) algorithm is applied to adjust the weights of the adaptive filters in the system. The detailed description and the performance analysis of the system is given in the paper. Applying the proposed system, the respiratory artifact, the electrode-skin noise, some of motion artifacts, and the electrocardiography (ECG) can be efficiently reduced while the characteristics of the relevant gastric signal is less affected.

Adaptation, Physiological↗
PubMed1989

Observation of the propagation direction of human electrogastric activity from cutaneous recordings.

Electrogastric signals have been successfully measured both intraluminally and cutaneously. Although it has been claimed by several researchers that the propagation direction of the electrogastric activities cannot be observed from cutaneous recordings, it is the aim of the paper to show that it is feasible. The reason why the propagation direction has never been observed from cutaneous recordings is that the reported methods for the abdominal measurements are not adequate. In the paper it is pointed out that the stomach should be localised before the measurement and the electrodes should be attached along the longitudinal axis of the stomach.

Diabetes Mellitus↗
PubMed1989

Adaptive method for cancellation of respiratory artefact in electrogastric measurements.

Electrogastric measurements are useful for medical research and in clinical diagnosis. The measurements, however, contain very heavy respiratory artefact. Existing conventional frequency-domain filters cannot be used because of the possible overlap of the frequencies of the gastric signals and respiratory artefact. In the paper, the methods of measuring cutaneous and intraluminal gastric signals and reference respiratory signals are described. An adaptive cancellation technique is developed, which is simple and easy to implement for online processing. It is proved by experiments to be very efficient, i.e. the respiratory artefact can be completely cancelled, while the gastric signal component is not affected. Other possible applications in biomedical signal analysis are also discussed.

Electricity↗
PubMed1989

Description of a real-time system to extract the fetal electrocardiogram.

An overview is given of the FEMME-project (Fetal Electrocardiogram Measuring Method and Equipment). The project started in 1981 and is, at the moment, close to producing a prototype personal computer-based system. This records simultaneously a number of cutaneous potential signals and derives from this set one or more maternal electrocardiogram-free fetal heart signals, by combining linearly the recorded signals. An on-line adaptive algorithm based on the Singular Value Decomposition (SVD) has been designed to compute the coefficients in these linear combinations. This algorithm will be implemented on a DSP board that can be plugged into the real-time recording system. The system will be very useful in studies of the fetal electrocardiogram during pregnancy, but also in all other studies such as fetal heart rate variability, fetal movements, etc., where a precise trigger of the electrical signal from the fetal heart is required.

Computer Systems↗
PubMed1986

An adaptive on-line method for the extraction of the complete fetal electrocardiogram from cutaneous multilead recordings.

The detection of a fetal electrocardiogram (FECG) is described to be a so-called inverse problem. A geometric interpretation of such a problem is presented. It can be solved by determining the weights to be used in one or more weighted sums of measurement signals. A novel method is presented to determine these weights. Theoretical and experimental evidence is given that this method has the following attractive properties. Application of the method results in one or more FECG signals, free of maternal ECG (MECG) which are at the same time maximal with respect to noise. It is shown that one FECG signal does not always suffice to describe the observed electrical heart activity in a set of cutaneous electrodes, equivalently to the adult ECG (see figure 7). It is explained and experimentally verified that the application of three thoracic signals is useful to guarantee the suppression of the MECG. The positions of the abdominal electrodes then determine the obtained FECG to noise ratio, and will have no influence on the degree of MECG suppression (see figure 6). It is expected that a total of about eight measurement signals are sufficient in most cases. The method is simple to apply by medical personnel, and after a transient of about 1 s the signals with the mentioned properties are obtained (see figure 5). Further on, the weights are allowed to change in order to adapt automatically to sudden changes in the measurement signal properties (see figure 6). These may occur e. g. due to fetal movement. Application of the method requires no human interpretation or decision in order to obtain the claimed properties.

Electrocardiography↗
PubMed1985

The UIA-KUL cochlear implant. Goals and status praesens.

The authors describe the characteristics and specific advantages of their 8 channel bipolar intrascalar stimulator, its main asset being flexibility. They emphasize the need for caution in the use of cochlear implants in children.

Adult↗
PubMed1980

Distortion products f1 + fh and 2f1 + fh in the inner ear.

The ear introduces spectral components which are not present in the stimulating sound. These components are commonly attributed to nonlinearities in the inner ear. In this paper it is shown that the sum product of f1 + fh and cubic sum product 2f1 + fh, perceptively measured, do behave as predicte d by the conventional distortion theory of a power series nonlinearity and that they are most likely masked by the d.c. component generated by the same nonlinearity. We present a model in an attempt to explain the data.

Ear, Inner↗
PubMed1976

Experimental study on the electrical impedance of bone and the effect of direct current on the healing of fractures.

An experimental study of the electrical impedance of cortical bone and medullary cavity and on the effect of a D.C. or a periodically interrupted D.C. on the healing of fractures in rabbits, suggests that the bone behaves as a capacitance of about 20 muF in parallel with a high D.C. resistance. Also a 10 muA periodically interrupted D.C. current stimulates osteogenesis.

Animals↗
PubMedDate not supplied

The Internal Human Conditioning System: a multipurpose programmable biomedical system.

A proposed general-purpose implantable biomedical system is described. This Internal Human Conditioning System (IHCS) is capable of measuring biomedical data of various kinds on a number of independent input channels. The number and specifications of these channels are software selectable by means of a low-power microprocessor. The system is also equipped with different programmable stimulation devices. These stimulators can deliver a programmable waveform in order to stimulate a specific muscle or to carry out an impedance measurement. The on-board eight bit microprocessor is used for communication with the outside world, by means of a serial link. The processor used is the 68HC11 from Motorola. By extensive use of the processor's 'sleep' mode and by switching off all unnecessary electronics, the amount of power consumed is drastically reduced. At present, a two-channel input chip and a programmable stimulator chip have been developed so that a complete system can be produced. For the sake of illustration, some realized and possible future applications are discussed.

Biomedical Engineering↗