SEARCH · Search PubMed

Results for “Spectral estimation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources

PubMed1987

Treatment of some nonstationarities in the EEG.

In many situations, EEG recordings cannot be assumed to be second-order stationary. The definition of stationarity is reviewed and the implications of the nonstationarity of the EEG are investigated. Some methods to overcome the problem caused by the nonstationarity are discussed. They include measures of variability, condensed time series and segmentation. The discussion is restricted to FFT spectral estimators and broad-band parameters derived thereof.

Electroencephalography↗

PubMed1987

COMSTAT rule for vigilance classification based on spontaneous EEG activity.

For the classification of sleep stages, international standards based on visual EEG analysis have been established and are in common use, although we are well aware of their limitations. Several authors have suggested different procedures for classifying the stages of vigilance during the waking stages. No universally accepted paradigm, however, has yet been developed. The proposed vigilance classification procedures are based either on visual or automatic analysis procedures. Even though the EEG activity and patterns that reflect vigilance changes have been identified and described as indicators of the state of alertness, opinion is divided on how these should be combined in a vigilance classification rule. Automatic methods, on the other hand, have up to now used only part of the information available, the relationship of which to vigilance indicators has only been partially explored. The COMSTAT (Dept. of Computation and Statistics, AFB-Arzneimittelforschung, Berlin, FRG) rule combines visual and automatic analysis procedures. Different vigilance-dependent EEG patterns, such as the proportion of occipital background rhythm under resting conditions and its replacement by either faster or slower waves, the frequency range of the occipital rhythm and the anteriorization phenomena, have been used as information for a latent class analysis (LCA5) with 5 classes (stages of vigilance). There is a high correlation between the results of the LCA5 with visual classification rules made by experts. Using a robust discriminant analysis function which takes into account prior probabilities of the classes, and with a linear cost function for misclassification, an automatic rule with power spectrum variables was fitted to the results of the LCA5. Reclassification and split-half classification showed a high overlap between LCA5 and automatic classification. The result of this procedure is a new vigilance classification rule that is based on an objective mathematical rationale for the combination of different vigilance-indicative EEG activities and patterns but which can be applied to power-spectral estimators in an automatic EEG analysis procedure.

Aged↗

PubMed1989

Brain electrical imaging the dose-response effects of cigarette smoking.

Quantitative regional electroencephalographic (EEG) effects of cigarette smoking were examined within a repeated measures design which assessed, and topographically displayed, changes in power spectral estimates resulting from the smoking of low, medium and high tar/nicotine (T/N) yield cigarettes. Although intercigarette yield comparisons revealed no significant EEG differences between yields, comparison of the effects of smoking each yield with sham smoking indicated the presence of a qualitative dose-response effect whereby increasing T/N yields resulted in a progressive posterior-to-anterior spreading of significant relative power changes within both theta and alpha frequency bands. These exploratory findings are discussed in relation to smoking maintenance and working hypotheses are formulated for future testing.

Adult↗

PubMed2005

Robust detection of periodic time series measured from biological systems.

BACKGROUND: Periodic phenomena are widespread in biology. The problem of finding periodicity in biological time series can be viewed as a multiple hypothesis testing of the spectral content of a given time series. The exact noise characteristics are unknown in many bioinformatics applications. Furthermore, the observed time series can exhibit other non-idealities, such as outliers, short length and distortion from the original wave form. Hence, the computational methods should preferably be robust against such anomalies in the data. RESULTS: We propose a general-purpose robust testing procedure for finding periodic sequences in multiple time series data. The proposed method is based on a robust spectral estimator which is incorporated into the hypothesis testing framework using a so-called g-statistic together with correction for multiple testing. This results in a robust testing procedure which is insensitive to heavy contamination of outliers, missing-values, short time series, nonlinear distortions, and is completely insensitive to any monotone nonlinear distortions. The performance of the methods is evaluated by performing extensive simulations. In addition, we compare the proposed method with another recent statistical signal detection estimator that uses Fisher's test, based on the Gaussian noise assumption. The results demonstrate that the proposed robust method provides remarkably better robustness properties. Moreover, the performance of the proposed method is preferable also in the standard Gaussian case. We validate the performance of the proposed method on real data on which the method performs very favorably. CONCLUSION: As the time series measured from biological systems are usually short and prone to contain different kinds of non-idealities, we are very optimistic about the multitude of possible applications for our proposed robust statistical periodicity detection method.

Algorithms↗

PubMed2006

Iterative image reconstruction using prior knowledge.

A method is proposed to reconstruct signals from incomplete data. The method, which can be interpreted both as a discrete implementation of the so-called prior discrete Fourier transform (PDFT) spectral estimation technique and as a variant of the algebraic reconstruction technique, allows one to incorporate prior information about the reconstructed signal to improve the resolution of the signal estimated. The context of diffraction tomography and image reconstruction from samples of the far-field scattering amplitude are used to explore the performance of the method. On the basis of numerical computations, the optimum choice of parameters is determined empirically by comparing image reconstructions of the noniterative PDFT algorithm and the proposed iterative scheme.

Algorithms↗

PubMed2006

Description of Wiener bounds of multicomponent composites by barycentric coordinates.

Wiener bounds for effective complex permittivity of multicomponent composites are treated by use of barycentric coordinates, a convex hull, and conformal mapping in a complex plane. Depending on the complexity of the multiphase system, the bounds provide singly or multiply connected regions that can be used in estimating the limits of the effective permittivity of the composite. The present modeling is important, e.g., in estimating spectral properties of nanocomposites in engineering and nanomedicine and in terahertz-based security imaging.

Journal Article↗

PubMed1991

[Automatic classification of the greatly amplified ECG in relation to time and frequency].

The non-invasive recording of cardiac micro-potentials from the surface of the body, in particular of the so-called ventricular late potentials from the highly amplified ECG, makes it possible to identify those patients at high risk from severe arrhythmics or sudden death. By using more extensive automatic parameter extraction methods, we were able to increase the detection rate of pathological ECGs. We were also able to show that the calculation of the power density spectrum, in particular on the basis of maximum entropy spectral estimation, in combination with the variance extraction method of eliminating the influence of residual noise, is capable of providing separate additional valuable information.

Arrhythmias, Cardiac↗

PubMed1995

Monitoring accumulative fatigue of finger by autoregressive modeling of physiological tremor.

In this study, block data structured autoregressive (AR) method is used to evaluate fatigue, based on physiological tremor during and after loading a weight mass on the index finger. The temporal changes in the prediction coefficients and the reflection coefficients are determined. AR spectral estimation with the ninth-order is obtained and presented in graphical form. The results indicate that the first prediction coefficient a1 can be used to characterize the state of fatigue of finger muscle and the other prediction coefficients do not show any tendency for the finger load. The coefficient a1 can be applied to monitor the accumulative fatigue induced by the weight loading for a duration of time.

Adult↗

PubMed1975

Electroencephalographic correlates of verbally induced stress in man.

This article is a review of some of the sparse investigation of EEG concomitants of verbally induced stress. The difficulties encountered in good experimental design in this formidable area, which may account for the paucity of work, are discussed. A recent experiment in which spectral analysis of EEG played a prominent role, with spectral estimators selected as correlated with stressful questions, is presented in some detail. Autonomic measurements provided the stress indicators. The value of animal experiments for psychiatry in the investigation of stress is briefly examined.

Alpha Rhythm↗

PubMed1987

Pain related cerebral potentials: late and ultralate components.

Brief CO2 laser radiant heat pulses activate both A delta- and C-fibres. In the evoked potential (EP) late and ultralate components can be seen as correlates of first and second pain. Usually the ultralate EP appears to be suppressed. It could be uncovered by a preferential A-fibre block, and in two neurological patients with tabes dorsalis and with a polyneuropathy involving myelinated fibre loss. Due to a strong latency jittering the shape of the ultralate component is distorted in the conventional average. Latency corrected averaging, adaptive filters or parametric spectral estimators are needed to analyze these EP components. As a result the filtered ultralate waveforms look very similar to the late EP components. Clinical application of CO2 laser EPs promises to nonivasively assess A delta- and C-fibre function.

Action Potentials↗

PubMed2001

Confocal image characterization of human papillomavirus DNA sequences revealed with Eu in HeLa cell nuclei stained with Hoechst 33342.

OBJECTIVE: To visualize and localize specific viral DNA sequences revealed with Eu by fluorescence in situ hybridization, confocal laser scanning microscopy (CLSM) and factor analysis of biomedical image sequences (FAMIS). STUDY DESIGN: Human papillomavirus DNA (HPV-DNA) was identified in HeLa cells with biotinylated DNA probes recognizing HPV-DNA types 16/18. DNA-DNA hybrids were revealed by a three-step immunohistochemical amplification procedure involving an antibiotin mouse monoclonal antibody, a biotinylated goat antimouse polyclonal antibody and streptavidin-Eu. Cell nuclei were counterstained with Hoechst 33342. Image sequences were obtained using a CLSM that made possible ultraviolet excitation. The location of fluorescent signals inside cellular preparations was determined by FAMIS and selection of filters at emission. Image sequences were summarized into a reduced number of images, or factor images, and curves, or factors. Factors estimate spectral or temporal patterns and depth emission profiles. Factor images correspond to spatial distributions of the different factors. RESULTS: We distinguished between Eu corresponding to HPV-DNA hybridization signals and nuclear staining by taking into account differences in their spectral and temporal patterns and (using their decay rates). CONCLUSION: FAMIS, together with CLSM and Eu, made possible the detection and characterization of viral papillomavirus DNA sequences in HeLa cells.

Base Sequence↗

PubMed1997

[Time-variant AR spectral method for non-stationary heart rate variability signal under gravitational stress].

In order to study the nonstationary heart rate variability (HRV) signals under gravitational stress, a time-variant autoregressive spectral estimation method has been implemented, which made it possible to study dynamically the process of cardiac autonomic regulation during various gravitational stresses. The HRV signals obtained from 8 subjects during seated-LBNP testing before and after a six-month aerobic training were analyzed by the implemented algorithm. The obtained time-variant spectra might clearly reveal the time course of changes of decrease in HFn and increase in LF/HF, reflecting the time course of cardiac vagal withdrawal and indices with time during seated-LBNP were increased in most of the subjects. In brief, our work shows that the method of time-variant AR spectrum analysis for non-stationary HRV signals makes it possible to elucidate the dynamics of cardiac autonomic regulatory activity under gravitational stress and to detect the subtle changes in HRV after aerobic training.

Arrhythmias, Cardiac↗

PubMed2001

[A study on quantitative assessment of osteoporosis based on texture analysis].

A quantitative assessment on osteoporosis by using texture analysis has been developed on the basis of coherence mapping, two-dimensional power spectral estimation with modulated transfer function correction and fractal features analysis on trabecular pattern of bone X-ray images. Three objective features of trabecular pattern are selected to form a feature set that can be used in automatic classification for two grades of bone: normal bone and the bone with a medium degree of osteoporosis. This set of features is extracted from each of 16 sample bone X-ray images. With the use of Euclidean norm in the feature space, a center of cluster of each grade of bone is defined as the prototype. For each bone X-ray image, the distance from its features to the two prototypes in feature space is computed to provide an objective judgement on the degree of osteoporosis. The machine classification of 10 bone X-ray images based on the developed prototype is given, and the result indicates that the proposed method is potentially applicable to the objective diagnosis of osteoporosis.

Femur↗

PubMed2001

Frequency domain analysis of endocardial signals.

Frequency domain analysis, applied to atrial endocardial electrograms during atrial fibrillation, has been used to develop automated arrhythmia detection schemes for implantable devices and to investigate electrophysiologic mechanisms. Such analysis may be used to quantify both temporal and spatial organization during atrial fibrillation. Specifically, autopower spectra and coherence spectra reveal electrogram characteristics that are powerful in discriminating atrial fibrillation from sinus rhythm and regular atrial tachycardias. Furthermore, changes in spectral characteristics with drug administration reveal nonstationarities in spatial organization and in underlying electrophysiologic mechanism. The usefulness of frequency domain analysis in the study of atrial fibrillation is influenced by electrode configuration, the method of spectral estimation and other clinical variables.

Atrial Fibrillation↗

PubMed2002

[Research on HRV signals for heroin addicts].

In this paper, the method of power spectral estimation is used to analyze the heart rate variability (HRV) signals for 15 heroin addicts and 15 healthy persons. The analysis result shows that there is a significant difference of the locations of the high-frequency peaks between the power spectra of heroin addicts' HRV signals. It means that the locations for heroin addicts lie in 0.437 +/- 0.064 Hz and the locations for healthy persons lie in 0.325 +/- 0.052 Hz.

Adolescent↗

PubMedDate not supplied

A profile of the female cycle length.

"This study suggests some points of view about the menstrual cycle length. In the first part aggregate indicators of cycle characteristics are computed for various types of data aggregations.... In the second part, the period analysis and the consequent estimated spectral density functions are applied to the basal body temperature series." Data are for 1,798 women in London, England. (SUMMARY IN ITA)

Biology↗

PubMed2002

[Personal long-term reproducibility of the TEOAE time-frequency distributions].

The TEOAE signal is relatively short and content changes in time. Due to the fact that signal is very short (20 ms) a special approach must be applied for the analysis of this nonstationarity. Usually the spectral estimation in TEOAE is based on procedures directly employing the fast Fourier transform (FFT). Because TEOAE signal is non stationary the classical Fourier analysis is not adequate for this signal. The aim of our study was the personal comparison of the TEOAE spectograms by using Wigner-Ville distribution (WVD) before and after one year period. Material consisted of 152 men (304 ears) in the age between 18-19 year with good quality OAE. After one year period the comparison of WVD spectrograms showed the highest similarity in the 274 ears (90%), less in the 24 (8%) and in 6 (2%) similarity was not noticed. Personal similarity of the spectrum TEOAE and differences between individual people's ears despite a long time, give a proof about individual architecture of outer hearing cell and maybe useful in the biometrics as a ear-print.

Adult↗

PubMed1992

[Maximum entropy method and Fourier transform for wave analysis of pattern visual evoked potentials].

To estimate spectral analysis of pattern visual evoked potentials (P-VEPs) the maximum entropy method (MEM) and fast Fourier transform (FFT) were investigated. P-VEPs were recorded in 16 normal eyes using the reversal pattern of 2 c/d vertical sine wave gratings. Six temporal frequencies (2, 3, 4, 6, 8, 12 Hz) were used. MEM power spectrum with the parameter (dimension of autoregression model) which was decided final prediction error (FPE) method did not necessarily always give satisfactory results. The MEM power spectrum of transient VEP changed in manner different from that of steady state VEP as the dimension of autoregression model varied. In steady state VEP the peak of the MEM spectrum was positioned accurately at dimension 50 but in transient VEP the peak positioned accurately at a larger dimension. Both in MEM and FFT the curves of the square root of the power vs temporal frequency resembled each other and had temporal tuning with a maximum at 6 Hz. At lower temporal frequencies (2, 3 Hz) the correlation coefficient increased gradually as the harmonic component became higher (2 nd less than 4 th less than 6 h). MEM powers in the second harmonic component were highly correlated with FFT power in temporal frequency above 4Hz. These results showed that the MEM power spectrum had higher resolution than FFT and had different properties especially at lower temporal frequencies. MEM with optimum parameters should be very useful for wave analysis of P-VEPs.

Evoked Potentials, Visual↗