共查询到20条相似文献,搜索用时 15 毫秒
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Artifact reduction in electrogastrogram based on empirical mode decomposition method 总被引:3,自引:0,他引:3
Severe contamination of the gastric signal in electrogastrogram (EGG) analysus by respiratory, motion, cardiac artifacts,
and possible myoelectrical activity from other organs, poses a major challenge to EGG interpretation and analysis. A generally
applicable method for removing a variety of artifacts from EGG recordings is proposed based on the empirical mode decomposition
(EMD) method. This decomposition technique is adaptive, and appears to be uniquely suitable for nonlinear, non-stationary
data analysis. The results show that this method, combined with instantaneous frequency analysis, effectively separate, identify
and remove contamination from a wide variety of artifactual sources in EGG recordings. 相似文献
4.
A method is proposed for modifying the time constant of an EEG amplifier after the recording. It is based on digital filtering and works for single sweeps, averaged potentials, and other neurophysiological data, e.g. spontaneous EEG. The validation is based on calibration signals and data from a study on event-related potentials. 相似文献
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This article describes a multistage signal processing scheme to enhance the quality of canine gastric signals recorded from
the abdominal surface. The scheme involves a cascade application oflinear prediction followed by a nonlinear processing known as α-TM filtering. The linear prediction is used to separate, in the minimum mean square error sense, the slow wave from other uncorrelated
interference signals. We make novel use of the order versus frequency response characteristics of linear predictors to achieve
this separation. The nonlinear filtering is used to suppress the residual wide band impulsive noise. Our studies have indicated
that such an optimized signal enhancement scheme produces a clean time domain signal, which is easy to interpret visually.
It not only preserves the periodicity of the slow wave, but also seems to track any irregularities in the periods. We believe
that this last feature, namely the potential to track nonstationarities in the signal, is the main contribution of our approach. 相似文献
6.
Adaptive cancellation of motion artifacts in the electrogastrogram (EGG) is presented in this paper. The EGG is a surface
measurement of gastric electrical activity. Like other noninvasive electrophysiological measurements, the EGG contains motion
artifacts. A number of papers have been published on the adaptive cancellation of motion artifacts or interferences in biomedical
signals. Adaptive filtering was performed in time domain in almost all of the previous publications. In this paper, however,
three different sorts of adaptive filters were investigated and their efficiencies in cancellation of motion artifacts were
compared with each other. These include time-domain, transform-domain, and frequency-domain adaptive filters. A series of
simulations were conducted to investigate the performance of these adaptive filters in cancellation of respiratory and motion
artifacts. The results show that the frequency-domain adaptive filter has superior performance over the time- and transform-domain
adaptive filters in the cancellation of stationary respiratory artifacts in the EGG. Although results focus on the EGG, this
paper provides useful information for adaptive filtering of other biomedical signals. 相似文献
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The thalamus is the principal relay station of sensory information to the neocortex. In return, the neocortex sends a massive feedback projection back to the thalamus. The thalamus also receives neuromodulatory inputs from the brain stem reticular formation, which is vigorously activated during arousal. We investigated the effects of two neuromodulators, acetylcholine and norepinephrine, on corticothalamic responses in vitro and in vivo. Results from rodent slices in vitro showed that acetylcholine and norepinephrine depress the efficacy of corticothalamic synapses while enhancing their frequency-dependent facilitation. This produces a stronger depression of low-frequency responses than of high-frequency responses. The effects of acetylcholine and norepinephrine were mimicked by muscarinic and alpha(2)-adrenergic receptor agonists and blocked by muscarinic and alpha-adrenergic antagonists, respectively. Stimulation of the brain stem reticular formation in vivo also strongly depressed corticothalamic responses. The suppression was very strong for low-frequency responses, which do not produce synaptic facilitation, but absent for high-frequency corticothalamic responses. As in vitro, application of muscarinic and alpha-adrenergic antagonists into the thalamus in vivo abolished the suppression of corticothalamic responses induced by stimulating the reticular formation. In conclusion, cholinergic and noradrenergic activation during arousal high-pass filters corticothalamic activity. Thus, during arousal only high-frequency inputs from the neocortex are allowed to reach the thalamus. Neuromodulators acting on corticothalamic synapses gate the flow of cortical activity to the thalamus as dictated by behavioral state. 相似文献
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M. A. Kentie E. J. van der Schee J. L. Grashuis A. J. P. M. Smout 《Medical & biological engineering & computing》1981,19(6):765-769
The modified adaptive filter method described in Part 1 was applied to 16 stretches of (cutaneous) electrogastrographic signal
of 17·07 min duration. A signal-to-noise ratio improvement of about 8 dB was achieved. The most characteristic feature of
the filter method appeared to be that wave-form and phase of the gastric component of the electrogastrographic signal are
preserved. It is concluded that the use of the modified adaptive filter forms a valuable tool in the study of the electrogastrographic
signal. 相似文献
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M. A. Kentie E. J. van der Schee J. L. Grashuis A. J. P. M. Smout 《Medical & biological engineering & computing》1981,19(6):759-764
The study of the relation between gastric myo-electrical activities recorded from serosal and cutaneous electrodes is hindered
by the poor quality of the cutaneous signal. This hindrance could be minimised by suitable filtering of the signal. Since
it is not yet clear which aspects of the cutaneous signal constitute valuable information, the filter process should not affect
phase, amplitude, frequency and waveform of the gastric component, while noise components should be suppressed strongly. The
system design of a modified adaptive filter that meets these requirements is described. The filter was implemented on a digital
Nova 2 minicomputer. the filter performance is described and tested. 相似文献
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The event-related optical signal (EROS) is a relatively new technology that provides noninvasive data about the time course of neural activity in circumscribed cortical areas. However, much still remains to be learned about the physiology and physics underlying the observed signals. We examined the instrumental and physiological noise observed in the intensity modulation and phase-delay measurements produced by a frequency domain oxymeter in response to steady-state auditory stimuli. We present here data on the effects of different filters on the between-subjects response consistency for amplitude and phase measurements. The results of these analyses may help explain some apparently discrepant results previously reported from different laboratories (Steinbrink et al., 2000), and illustrate differences between data from different types of measurements. 相似文献
13.
W. C. de Mello 《Pflügers Archiv : European journal of physiology》1977,371(1-2):135-139
Summary The passive electrical properties of the atrioventricular node and of the atrial muscle of the rabbit heart were determined. To polarize the cells, a small suction electrode was used. The space constant of the atrio-ventricular node was found to be small (430 ) compared to other cardiac fibers. The small value of in nodal cells is due to a high intracellular resistance (ra, 40.9 ± 9 M/cm) which is higher than in atrial muscle (9.6 ± 2.2 M/cm). The input resistance of cells of the N layer was found equals to 880 K while in the right atrium was 320 K. The time constant of nodal cells in the AN layer was 3.4 ms, in the N layer 9 ms and in the atrium 5 ms. Assuming a specific membrane capacity (C
m) of nodal and atrial fibers of 1 F/cm2,R
m was found equals to 9.000 cm2 in N layer, 3.400 cm2 in AN layer and 3.800 cm2 in the right atrium.Acetylcholine (5 g/ml) reduced the space constant of the atrio-ventricular node by 38% and the time constant of nodal cells by 33%.The delay of impulse conduction in the A-V node semms then related to a high intracellular resistance along the pathway of conduction.This work was supported by Grant # HL-10897 from the NHI, Bethesda, Maryland and in part by a Grant from the P. R. Heart Association 相似文献
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L. Lemaire Dr F. Franconi J. J. Lejeune P. Jallet P. Richomme 《Medical & biological engineering & computing》1999,37(2):244-246
In vivo detection and quantitation of metabolites is often limited by their low concentration. As far as magnetic resonance spectroscopy (MRS) is concerned, detection and quantitation can be significantly improved by reduction of the observed spectral width (SW). The reduction is limited to the spreading of resonances in the bandwidth unless high performance digital filters are used. Indeed, these filters avoid the folding of unwanted resonances such as water peak into the main frequency spectrum and therefore allow reduction of the spectral width to its optimal value. These filters are now available on most MRS systems but their use is not common even if, as we show in the particular case of proton MRS, a significant increase in signal-to-noise ratio (two-fold factor for SW reduction from 5000 Hz to 1351 Hz) can be achieved. This signal-to-noise improvement allows better quantitation accuracy. 相似文献
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The electro-encephalogram (EEG) is useful for clinical diagnosts and in biomedical research. EEG signals, however, especially
those recorded from frontal channels, often contain strong electro-oculogram (EOG) artifacts produced by eye movements. Existing
regression-based methods for removing EOG artifacts require various procedures for preprocessing and calibration that are
inconvenient and timeconsuming. The paper describes a method for removing ocular artifacts based on adaptive filtering. The
method uses separately recorded vertical EOG and horizontal EOG signals as two reference inputs. Each reference input is first
processed by a finite impulse response filter of length M (M=3 in this application) and then subtracted from the original
EEG. The method is implemented by a recursive leastsquares algorithm that includes a forgetting factor (λ=0.9999 in this application)
to track the non-stationary portion of the EOG signals. Results from experimental data demonstrate that the method is easy
to implement and stable, converges fast and is suitable for on-line removal of EOG artifacts. The first three coefficients
(up to M=3) were significantly larger than any remaining coefficients. 相似文献
16.
N. A. Shaw 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1987,65(3):686-690
Summary The effects of low pass filtering on the brainstem auditory evoked potential (BAEP) were studied in the adult male rat. The bandpass of the recording system was progressively widened while the cut-off frequency of the high pass filter remained constant at 3.2 Hz. When the high frequency cut-off was 320 Hz or less, the principal waveform recorded in response to a click stimulus was a slow positive-negative complex. As the high frequency setting was raised from 800 Hz to 3.2 kHz, the slow components of the brainstem were replaced by four fast BAEP waves (I, II, III and IV). As the bandpass widened there was an increase in amplitude and a decrease in the absolute latency of all four fast waves in the order of 0.1 ms although the wave I–IV interpeak latency remained unaffected. The results confirm that the high frequency components of the BAEP are underlain by a slow positivity of uncertain origin followed by a slow negativity which probably arises within the inferior colliculus.This study was supported by the Medical Research Council of New Zealand 相似文献
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L. Lemaire F. Franconi J. J. Lejeune P. Jallet P. Richomme 《Medical & biological engineering & computing》1999,37(1):244-246
In vivo detection and quantitation of metabolites is often limited by their low concentration. As far as magnetic resonance
spectroscopy (MRS) is concerned, detection and quantitation can be significantly improved by reduction of the observed spectral
width (SW). The reduction is limited to the spreading of resonances in the bandwidth unless high performance digital filters
are used. Indeed, these filters avoid the folding of unwanted resonances such as water peak into the main frequency spectrum
and therefore allow reduction of the spectral width to its optimal value. These filters are now available on most MRS systems
but their use is not common even if, as we show in the particular case of proton MRS, a significant increase in signal-to-noise
ratio (two-fold factor for SW reduction from 5000 Hz to 1351 Hz) can be achieved. This signal-to-noise improvement allows
better quantitation accuracy. 相似文献
18.
Robert Franklin 《Computers in biology and medicine》1982,12(2):175-178
A program is presented for the Texas Instruments SR-52 calculator which calculates moving averages of time series data. In addition to providing averages the programs also keeps track of which data item in a sequence to enter next. 相似文献
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Kotas M 《Computers in biology and medicine》2008,38(1):127-137
The paper proposes a modification of the nonlinear state-space projections (NSSP) method. Our approach, when applied to ECG signal processing, considerably improves the method's performance. One of the crucial operations in NSSP is the search for neighborhoods of the state-space trajectory points. The modification proposed is based on imposing a few restrictions on the time location of the neighborhood points. Dynamic time warping, a technique which allows for nonlinear alignment of time series or sequences of vectors, is applied as a straightforward solution to the task of neighborhoods determination with the restrictions imposed. The influence of nonlinear alignment on the distributions of the determined neighborhoods is presented, and the resulting method of ECG enhancement is investigated. 相似文献
20.
ECG signal conditioning by morphological filtering 总被引:9,自引:0,他引:9
Clinically obtained electrocardiographic (ECG) signals are often contaminated with different types of noise and baseline drifting commonly occurs. In order to facilitate automated ECG analysis, signal conditioning is undoubtedly a necessity. In this paper, a modified morphological filtering (MMF) technique is used for signal conditioning in order to accomplish baseline correction and noise suppression with minimum signal distortion. Compared with existing methods for ECG signal conditioning, MMF performs well in terms of the filtering characteristics, low signal distortion ratio, low computational burden as well as good noise suppression ratio and baseline correction ratio. 相似文献