Images of the Twenty-First Century. Proceedings of the Annual International Engineering in Medicine and Biology Society
ABSTRACT Signal averaging in equal-shape and equal-width signal classes is discussed. The aim is ... more ABSTRACT Signal averaging in equal-shape and equal-width signal classes is discussed. The aim is to compare two similarity criteria associated with the same clustering algorithm; one derived from the distribution function method and the other derived from correlation. The superiority of the fist one is proven first by simulation and then in the estimation of the late potentials using QRS classification
Time-varying Evoked Potentials: Monitoring And Signal Processing
Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society Volume 13: 1991
ABSTRACT New monitoring instrumentation and signal processing methods are needed to record and an... more ABSTRACT New monitoring instrumentation and signal processing methods are needed to record and analyze time-varying evoked potentials (EP) in neurological critical care environments. A personal computer-based data-acquisition system is used to deliver repetitive stimulation and digitize the EP signals continuously over several hours. Traditional signal processing approaches are moving window averaging and exponentially weighted averaging. Recently we have proposed adaptive signal processing methods: adaptive ...
Noise effect on orthogonal transform compression of ECG signals
Proceedings of 18th Annual International Conference of the IEEE Engineering in Medicine and Biology Society
Abstract Modeling of signals using orthogonal transforms is a very appropriate technique for ECG ... more Abstract Modeling of signals using orthogonal transforms is a very appropriate technique for ECG data compression. An increase of coefficient number (n) increases both signal and noise power reconstruction. A method for selecting the optimum number of coefficients (n*) in noisy records is presented. Adaptive algorithms achieve better coefficient estimation when the input signal is corrupted with uncorrelated noise. In this work we analyze LMS algorithm that improves the estimation of classical inner product. A selection criteria of the μ ...
Improved alignment method in ECG signal averaging: application to late potentials detection
Proceedings. Computers in Cardiology 1988
The purpose of this study is to obtain the ventricular late activity from the surface ECG. The si... more The purpose of this study is to obtain the ventricular late activity from the surface ECG. The signal is measured by means of a two-channel electrocardiographic system: a low-gain amplifier for the reference ECG acquisition and a low-noise, high-gain amplifier for the late potential. The selected bipolar leads are a standard limb lead for reference and a special precordial lead for high amplification. A comparative analysis of three temporal alignment methods in the signal averaging has been performed: double level (DL), position of normalized integrals (NI) in coincidence, and matched filtering (MF). Results obtained by signal averaging from patients with documented ventricular tachycardia and volunteers without evidence of heart disease are presented. The influence of the bipolar precordial lead position and the selected bandwidth of the filters has also been evaluated. The MF and NI methods allow the estimation of higher magnitude and higher frequency components than the DL method. The MF method works better than the NI method for some ECG signal methodologies. The results show that there is not late activity over 300 Hz; the basis components are mainly in the narrow band of 100-150 Hz
Estimation Of Signal-to-noise Ratio In Signals Contaminated By White Noise
A method to estimate the SNR is very useful since it allows a knowledge of the signal contaminati... more A method to estimate the SNR is very useful since it allows a knowledge of the signal contamination. This estimation can be specially useful in signal averaging process of recurrent transient signals, because the error in the occurrence time estimation of each recurrence has been shown to be a function of the SNR. We propose a method to estimate the SNR in case of random noise. This method is based on a time delay estimate between two noisy transient signals. A simulation study, using a deterministic signal corrupted by additive white zero-mean gaussian noise, has shown that the proposed method is appropriate to estimate the SNR.
Digital low-pass filtering and differentiation (LPD) are useful in real-time processing of many b... more Digital low-pass filtering and differentiation (LPD) are useful in real-time processing of many biomedical signals. A general Manuscript
CORRESPONDENCE-Signal Processing Theory and Methods-Truncated Orthogonal Expansions of Recurrent Signals: Equivalence to a Linear Time-Variant Periodic Filter
This paper presents an algorithm for automatically locating the waveform boundaries (the onsets a... more This paper presents an algorithm for automatically locating the waveform boundaries (the onsets and ends of P, QRS and T waves) in multilead ECG signals (the 12 standard leads and the orthogonal XYZ leads). Given these locations, features of clinical importance (such as the RR interval, the PQ interval, the QRS duration, the ST segment, and the QT interval) may be measured readily. First, a multilead QRS detector locates each beat, using a di erentiated and low-pass ltered ECG signal as input. Next, the waveform boundaries are located in each lead. The leads in which the detected electrical activity is of longest duration are used for the nal determination of the waveform boundaries. The performance of our algorithm has been evaluated using the CSE multilead measurement database. In comparison with other algorithms tested by the CSE, our algorithm achieves better agreement with manual measurements of the T wave e n d and of interval values, while its measurements of other waveform boundaries are within the range of the algorithm and manual measurements obtained by the CSE.
In this correspondence, we show that orthogonal expansions of recurrent signals like electrocardi... more In this correspondence, we show that orthogonal expansions of recurrent signals like electrocardiograms (ECG's) with a reduced number of coefficients is equivalent to a linear time-variant periodic filter. Instantaneous impulse and frequency responses are analyzed for two classical ways of estimating the expansion coefficients: inner product and adaptive estimation with the LMS algorithm. The obtained description as a linear time-variant periodic filter is a useful tool in order to quantify the distortion produced by the effect of using a reduced number of coefficients in the expansion, and to give frequency criteria to select the appropriate number of functions. Moreover, the misadjustment of the LMS algorithm can be explained as a distortion of the instantaneous frequency response. Experimental results are illustrated with the Karhunen-Loeve transform of ECG signals, but this approach can also be applied to any orthogonal transform.
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