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PubMed2003

[Application of AOTF in spectral analysis. 4. Enhancing spectral resolution of AOTF atomic emission spectrometer with FSD].

Using Fourier self-deconvolution (FSD) to enhance spectral resolution of AOTF atomic emission spectrometer is described. Choosing the appropriate deconvolution parameters: full width at half maximum (FWHM) and breaking point, the FWHM of the simulated overlapping peaks could be decreased by a factor of 3.5, and the peak height by a factor of 5, but retaining the peak position. Practical samples of La and Ca-Al mixture were scanned by AOTF-ICP-AES respectively, the overlapping spectra of La 407.735 nm and La 408.672 nm as well as Ca 393.366 nm and Al 394.401 nm were well resolved into their respective lines after FSD; as to sample of Eu-Sr mixture and Sc-Sr mixture, after FSD treatment, the overlapping spectra of Eu 420.505 nm and Sr 421.552 nm as well as Sc 424.693 nm and Sr 421.552 nm at various concentration of Eu and Sc respectively were also well resolved into their respective lines. The slopes of their corresponding calibration curves were increased by a factor of 2 to 3.

Acoustics↗
PubMed2003

Spectral analysis: principle and clinical applications.

This review article describes the principle and clinical applications of spectral analysis. Spectral analysis provides a spectrum of the kinetic components which are involved in the regional uptake and partitioning of tracer from the blood to the tissue. This technique allows the tissue impulse response function to be derived with minimal modeling assumptions. Spectral analysis makes no a priori assumptions regarding the number of compartments or components required to describe the time course of tracer in the tissue. Spectral analysis can be applied to various dynamic data acquired by planar scintigraphy, single photon emission computed tomography (SPECT) or positron emission tomography (PET) as an alternative approach to compartment analysis. This analysis appears to be clinically useful, because it not only facilitates the interpretation of dynamic scintigraphic, SPECT or PET data, but also simplifies comparisons between regions and between subjects.

Algorithms↗
PubMed1991

Modern spectral analysis techniques for blood flow velocity and spectral measurements with pulsed Doppler ultrasound.

Four spectral analysis techniques were applied to pulsed Doppler ultrasonic quadrature signals to compare the relative merits of each technique for estimation of flow velocity and Doppler spectra. The four techniques were 1) the fast Fourier transform method, 2) the maximum likelihood method, 3) the Burg autoregressive algorithm, and 4) the modified covariance approach to autoregressive modeling. Both simulated signals and signals obtained from an in vitro flow system were studied. Optimal parameter values (e.g., model orders) were determined for each method, and the effects of signal-to-noise ratio and signal bandwidth were investigated. The modern spectral analysis techniques were shown to be superior to Fourier techniques in most circumstances, provided the model order was chosen appropriately. Robustness considerations tended to recommend the maximum likelihood method for both velocity and spectral estimation. Despite the restrictions of steady laminar flow, the results provide important basic information concerning the applicability of modern spectral analysis techniques to Doppler ultrasonic evaluation of arterial disease.

Algorithms↗
PubMed1999

Hepatic extraction fraction of hepatobiliary radiopharmaceuticals measured using spectral analysis.

Measuring the hepatic extraction fraction (HEF) of a hepatobiliary radiopharmaceutical helps to differentiate hepatocyte from biliary tract diseases, and it is generally performed using deconvolution analysis. In this study, we measured HEF using spectral analysis. With spectral analysis, HEF was calculated from (the sum of the spectral data obtained by spectral analysis--the highest frequency component of the spectrum) divided by (the sum of the spectral data) x 100 (%). We applied this method to dynamic liver scintigraphic data obtained from six healthy volunteers and from 46 patients with various liver diseases, using 99Tcm-N-pyridoxyl-5-methyltryptophan (PMT). We also measured HEF using deconvolution analysis, in which the modified Fourier transform technique was employed. The HEF values obtained by spectral analysis correlated closely with those obtained by deconvolution analysis (r = 0.925), suggesting our method is valid. The HEF values obtained by spectral analysis decreased as the severity of liver disease progressed. The values were 100.0 +/- 0.0%, 94.7 +/- 13.6%, 76.2 +/- 27.4%, 45.7 +/- 15.6%, 82.7 +/- 24.2% and 95.2 +/- 11.8% (mean +/- S.D.) for the normal controls (n = 6), mild liver cirrhosis (n = 16), moderate liver cirrhosis (n = 11), severe liver cirrhosis (n = 5), acute hepatitis (n = 8) and chronic hepatitis groups (n = 6), respectively. The HEF was obtained more simply and rapidly by spectral analysis than by deconvolution analysis. The results suggest that our method using spectral analysis can be used as an alternative to the conventional procedure using deconvolution analysis for measuring HEF.

Aged↗
PubMed1993

Effect of antihypertensive treatment on daytime and nighttime power spectral analysis of heart rate.

Power spectral analysis of heart rate may provide useful information about cardiac neural activity. The aim of this study was to evaluate cardiac sympathetic and parasympathetic activity, as assessed by power spectral analysis of heart rate, in hypertensive patients before and after antihypertensive treatment. In 14 hypertensive patients and in 7 normotensive subjects 24 h Holter electrocardiogram monitoring was performed under basal conditions and after 6 months of treatment with nifedipine (n = 7) or enalapril (n = 7). Sequences of 512 RR intervals were taken for the evaluation of power spectral analysis (autoregressive method); absolute and normalized power spectral density of the peak at 0.10 Hz (low frequency peak: LF) and at 0.25 Hz (high frequency peak: HF), as well as their ratio (index of sympatovagal interaction: SVI) were calculated. Under basal conditions SVI was significantly decreased from daytime to nighttime in normotensives, while no change was observed in hypertensive patients. In all hypertensive patients a reduction of SVI during nighttime in respect to basal values was observed after treatment. SVI during nighttime was significantly reduced with both nifedipine and enalapril, while SVI during daytime was slightly increased during nifedipine treatment, and significantly reduced during enalapril treatment. Systolic and diastolic arterial pressure as well as left ventricular mass index were significantly reduced with both treatments. In conclusion, long term treatment with nifedipine or enalapril seems to be able to restore an impaired daytime to nighttime SVI modulation in hypertensive patients, even considering the potential limitations of power spectral analysis of heart rate.

Adult↗
PubMed2002

[Spectral analysis in nanometer material science].

Spectral analysis is an important means in studies of nanometer scale systems, and is essential for deep understanding the structure and properties of nanometer materials. This paper reviews the recent progresses made in studies of nanometer materials using spectral analysis methods such as UV-Visible spectroscopy, FTIR spectroscopy, Raman spectroscopy, Mössbauer spectroscopy, positron annihilation and photoacoustic spectroscopy. The principle, characteristics and applications of most frequently employed spectral methods are introduced briefly and illustrated with typical examples. Future perspectives of spectral analysis in nanometer field are discussed. New directions of establishing spectral analysis methods at nanometer scale resolution and developing new spectroscopy technology in nanometer material studies are also emphasized.

Nanotechnology↗
PubMed1989

EEG spectral analysis in delirium.

Spectral analysis of EEG was conducted for 51 elderly delirious patients meeting the Diagnostic and Statistical Manual of Mental Disorders III (DSM-III) criteria and for 19 controls. As a whole group, and also when subdivided according to the type of delirium, severity of cognitive decline or the type of central nervous system disease, delirious patients showed significant reductions of alpha percentage, increased theta and delta activity and slowing of the peak and mean frequencies and these changes were also obvious in individual recordings. The alpha percentage and various ratio parameters correlated significantly with Mini Mental State score, and delta percentage and mean frequency with the lengths of delirium and hospitalisation. The results indicate an association between spectral EEG changes and severity of cognitive deterioration in delirium.

Aged↗
PubMed2003

Assessing autonomic disturbances of hypertension in the general practitioner's office: a transtelephonic approach to spectral analysis of heart rate variability.

OBJECTIVES: Spectral analysis of heart rate variability (HRV) provides potentially useful information on autonomic disturbances of human hypertension. However, its practical use outside the clinical laboratory is largely unexplored. The aim of this study was to test the feasibility of assessing HRV from the general practitioner's (GP's) office, using a novel transtelephonic approach. DESIGN: Parallel study on two similar groups: 150 subjects (100 hypertensives and 50 normotensives) studied in our hospital clinic and compared with 150 subjects studied in an out-of-hospital practice (100 hypertensive subjects from GPs' surgeries and 50 normotensive subjects participating in a multinational company's health maintenance programme). METHODS: Spectral analysis of RR interval variability was used to assess autonomic regulation of the sino-atrial (SA) node, both at rest and during standing. For the out-of-hospital practice, strings of continuous electrocardiograms (ECGs), recorded with a microminiature instrument, were fed, off line, through standard telephone lines to our laboratory for subsequent spectral analysis. RESULTS: RR spectral profiles obtained from healthy controls or hypertensive patients examined in their GPs' surgeries were similar to those obtained in a hospital clinic, both at rest and when standing up. CONCLUSIONS: The present study shows the feasibility of using a transtelephonic approach to perform spectral analysis of heart rate variability from physicians' surgeries. This method could favour a more widespread use of autonomic assessment in the clinical management of hypertension.

Adult↗
PubMed1970

Epileptic focus location: spectral analysis method.

A spectral analysis technique for locating the site of an epileptic focus in the cat brain with the use of multielectrode data, obtained during a generalized seizure, is described. The data, indicating widespread appearance of epileptic activity, does not lend itself to conclusive analysis by conventional means. Three channels of data are examined at a time. One channel is said to drive the other channels if the first channel explains or accounts for the linear relation between the other two over a frequency interval corresponding to the interval of greatest energy concentration. The method of analysis involves computation of the coherence and partial coherence between data from all electrode pairs.

Animals↗
PubMed2000

Acoustic and airflow spectral analysis of voice tremor.

Acoustic spectral analysis has been used to describe voice tremor with some success, but no feature distinguishing pathological from normal tremor has been clearly identified. To assist in monitoring voice tremor associated with neurological diseases, objective and quantifiable measures that can distinguish between normal and pathological tremor are desired. This study explored the plausibility of using airflow and acoustic signals to quantify the frequency and amplitude of voice tremor and potentially to distinguish pathological from normal tremor. Subjects were 10 individuals with pathological tremor, most of them individuals with Parkinson's disease, and 10 gender and age-matched individuals with no voice disorder. Simultaneous acoustic and airflow signals were recorded during sustained vowel phonation. The acoustic intensity contours and the airflow signals were submitted to spectral analysis. A peak prominence ratio, defined as the ratio of the spectral peak energy to the overall signal energy, was calculated for each spectral peak below 30 Hz. For each subject, the 6 spectral peaks with the highest peak prominence ratios were selected. Frequency values of the 6 selected acoustic or airflow spectral peaks failed to distinguish tremor group from control group. Peak prominence ratios of the 6 selected acoustic spectral peaks were significantly higher for tremor group than for control group. Although spectral analysis of airflow signals was not useful in differentiating tremor group from control group, acoustic intensity contours and airflow time waveforms were highly and positively correlated in more tremor subjects (90%) than control subjects (40%). This finding suggests that the relationship between acoustic intensity contours and airflow time waveforms may reflect the presence and the source of voice tremor.

Adult↗
PubMed1998

Parametric image reconstruction using spectral analysis of PET projection data.

Spectral analysis is a general modelling approach that enables calculation of parametric images from reconstructed tracer kinetic data independent of an assumed compartmental structure. We investigated the validity of applying spectral analysis directly to projection data motivated by the advantages that: (i) the number of reconstructions is reduced by an order of magnitude and (ii) iterative reconstruction becomes practical which may improve signal-to-noise ratio (SNR). A dynamic software phantom with typical 2-[11C]thymidine kinetics was used to compare projection-based and image-based methods and to assess bias-variance trade-offs using iterative expectation maximization (EM) reconstruction. We found that the two approaches are not exactly equivalent due to properties of the non-negative least-squares algorithm. However, the differences are small (< 5%) and mainly affect parameters related to early and late time points on the impulse response function (K1 and, to a lesser extent, VD). The optimal number of EM iteration was 15-30 with up to a two-fold improvement in SNR over filtered back projection. We conclude that projection-based spectral analysis with EM reconstruction yields accurate parametric images with high SNR and has potential application to a wide range of positron emission tomography ligands.

Algorithms↗
PubMed2000

Acoustic X-wave reflection and transmission at a planar interface: spectral analysis

The spectral structure of a three-dimensional X-wave pulse incident on a planar surface of discontinuity is examined. Introducing a novel superposition of azimuthally dependent pulsed plane waves, it is shown for oblique incidence that the reflected pulse has a localized wave structure. On the other hand, the transmitted field maintains its localization up to a certain distance from the interface, beyond which it starts disintegrating. An estimate of the localization range of the transmitted pulse is established; also, the parameters affecting the localization range are identified. The reflected and transmitted fields are deduced for X-waves incident from either a slower medium or a faster one. For the former case the evanescent fields in the second medium are calculated and their explicit time dependence is deduced for a normally incident X-wave. Furthermore, at near-critical incidence the transmitted pulse exhibits significant pulse compression and focusing.

Journal Article↗
PubMed2000

Comparison between using spectral analysis of electrogoniometer data and observational analysis to quantify repetitive motion and ergonomic changes in cyclical industrial work.

Spectral analysis of continuously measured joint angles using an electrogoniometer was considered as a potentially efficient method for quantifying exposure to physical stress in repetitive manual work. The method was previously demonstrated in the laboratory but has not yet been tested extensively in the field. Spectral analysis was compared against observational analysis, consisting of time-and-motion study and posture classification. Six industrial jobs were selected: (1) press operation, (2) large parts hanging, (3) product packaging, (4) small parts hanging, (5) parts counting and sorting and (6) construction vehicle operation. The posture angle data were synchronized with activities on the video using an interactive multimedia video data acquisition system. Motion for every joint was analyzed using both spectral analysis and observational analysis. Joint angles for the wrist, elbow and shoulder were directly measured using electrogoniometers. Visual posture classification involved determining joint angles from a frozen videotape image sampled three times per s. Repetitiveness was quantified for observational analysis using time study to measure the frequency that specific motions repeat, while spectral analysis measured repetitiveness as the frequency where spectral peaks occurred. Spectral analysis agreed closely with observational analysis. Correlation between the repetition frequencies obtained using time study and spectral analysis was 0.97, with no statistically significant difference observed. Average sustained posture was quantified as the mean, and posture deviation as the RMS angle of joint motion. No statistically significant differences between data obtained using posture classification or spectral analysis were observed for either posture deviation or sustained posture. Since posture classification was very limited in resolution and often contained measurement errors caused by poor joint visibility, the correlation between the postural classification and spectral analysis was 0.77 for sustained posture and 0.53 for posture deviation. When considering only large motions that exceeded the posture classification angle precision, the correlation between postural classification and spectral analysis was 0.81 for sustained posture and 0.81 for posture deviation. Spectral analysis of electrogoniometer data were, therefore, an efficient method for analyzing repetitive manual work that obtained equivalent results, and was more precise than observational analysis.

Electrophysiology↗
PubMed1986

EEG and spectral analysis in acute hyperventilation.

Acute hypocapnia decreases CBF, increases hemoglobin affinity for oxygen and causes cerebral tissue hypoxia. This tissue hypoxia is reversed with inhalation of 100% O2 in dogs. EEG slowing produced by hyperventilation is considered a manifestation of cerebral hypoxia due to decreased CBF and is thought to be reversed with hyperoxia. This study evaluated the effects of 3 gas mixtures (16% O2, 21% O2, 100% O2) on posterior frequencies of the resting and hyperventilatory EEG in normal subjects aged 23-37. Hypocapnia was maintained to an end-tidal pCO2 of 21 mm Hg for 3 min. Respiratory measures, heart rate, saO2, minute ventilation and side effects were recorded. EEG was analyzed by visual inspection and by spectral analysis. Spectral analysis evaluated total amplitude, percentile frequencies, and peak frequencies. There were significant changes from eucapnia to hypocapnia for the group in all physiologic parameters, total amplitude by spectral analysis, and posterior frequencies by visual analysis. There were no significant differences among the gases. We conclude that the EEG changes of hyperventilation are independent of the concentration of inspired oxygen over the range studied in our subjects. Symptoms of hyperventilation are likewise independent of the inspired oxygen concentration for the range studied.

Acute Disease↗
PubMed1985

Assessment of prosthetic mitral valve pressure gradients by means of ultrasound Doppler technique and on-line spectral analysis.

The blood speed through prosthetic mitral valves was determined using ultrasound Doppler techniques combined with on-line spectral analysis. Spectral analysis was particularly suitable for maximum velocity estimation due to its superior ability in discriminating between Doppler signals and white background noise. From a simplified Bernoulli equation the corresponding transprosthetic pressure drop was calculated and estimates were compared against pressure gradients obtained by conventional intracardiac catheterization. A close relationship between the ultrasonic- and the manometric transprosthetic pressure gradients was found, but the ultrasonic method tended to systematically underestimate the pressure gradients slightly.

Blood Flow Velocity↗
PubMed1993

Spectral analysis of 24 h blood pressure recordings.

Spectral analysis of blood pressure and heart rate signals allows overall blood pressure and heart rate variabilities to be split into their different frequency components. When used to analyze 24 h discontinuous blood pressure recordings, the low sampling frequency that characterizes these devices allows only the slow fluctuations in day and night blood pressure to be adequately described by the spectral approach. Conversely, spectral analysis of continuous blood pressure recordings provides information both on fast and slow changes in blood pressure and heart rate. Because blood pressure and heart rate powers are characterized by a 1/f distribution over the 24 h, slow fluctuations in blood pressure and heart rate contribute most importantly to 24 h variance, while faster components provide only a minor contribution. However, spectral analysis of the latter has raised considerable interest due to the possible association of these components with cardiovascular regulatory mechanisms. It is now possible to perform 24 h dynamic spectral analysis of blood pressure and heart rate on continuous blood pressure recordings obtained noninvasively by a finger pressure device.

Blood Pressure↗
PubMed1993

An application of phase spectral analysis to amplitude-modulation following response.

A phase spectral analysis developed by Fridman (1982) was applied to the detection of amplitude-modulated frequency following response (AMFR) and its clinical usefulness was evaluated. A 1000 Hz sinusoidally amplitude-modulated tone with a modulation frequency of 40 Hz and a modulation depth of 90% was delivered to the right ear of 10 normal-hearing subjects. According to Fridman's technique, an ensemble of sweeps was divided into 10 groups and group averages were obtained. Then phase variances were calculated using fast Fourier transform for the group averages. In order to determine the optimal conditions of analysis for constructing an automatic detection program using phase spectral analysis, frequency spacing, number of sampling points and number of sweeps averaged per group were investigated. The sensitivity of phase spectral analysis for automatic detection of AMFR was also evaluated. The results suggested that the optimal number of sampling points and frequency spacing are 512 points and 4.9 Hz (observation window 204.8 ms), respectively. Concerning the average number of sweeps, the synchrony measure of the frequency component corresponding to the modulation frequency increased as the number of sweeps increased. Furthermore, it was demonstrated that threshold determination by phase spectral analysis is more sensitive than detection of the threshold by visual analysis of waveform configuration.

Adult↗