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PubMed2001

A wavelet-based continuous classification scheme for multifunction myoelectric control.

This work represents an ongoing investigation of dexterous and natural control of powered upper limbs using the myoelectric signal. When approached as a pattern recognition problem, the success of a myoelectric control scheme depends largely on the classification accuracy. A novel approach is described that demonstrates greater accuracy than in previous work. Fundamental to the success of this method is the use of a wavelet-based feature set, reduced in dimension by principal components analysis. Further, it is shown that four channels of myoelectric data greatly improve the classification accuracy, as compared to one or two channels. It is demonstrated that exceptionally accurate performance is possible using the steady-state myoelectric signal. Exploiting these successes, a robust online classifier is constructed, which produces class decisions on a continuous stream of data. Although in its preliminary stages of development, this scheme promises a more natural and efficient means of myoelectric control than one based on discrete, transient bursts of activity.

Algorithms↗
PubMed1998

A system for medical consultation and education using multimodal human/machine communication.

Recent developments in networking and computing have enabled collaborative biomedical engineering research by geographically separated participants. One of the most promising goals is to use these technologies to extend human intellectual capabilities in medical decision making. These emerging technologies are poised to drastically reduce healthcare cost by providing service at remote locations. This also increases diagnosis capacity since information is made available to experts at any location. In this paper, we propose a novel application of a recently developed interactive and distributed system in medical consultation and education. Our approach builds on the notion that interactive and distributive capabilities of the system are crucial for medical consultation and education. The presented application uses a multiuser, collaborative environment with multimodal human/machine communication in the dimensions of sight, sound, and touch. The experimental setup, consisting of two user stations, and the multimodal interfaces, including sight (eye-tracking), sound (automatic speech), and touch (microbeam pen), were tested and evaluated. The system uses a collaborative workspace as a common visualization space. Users communicate with the application through a fusion agent by eye-tracking, speech, and microbeam pen. The audio/video teleconferencing is also included to help the radiologists to communicate with each other simultaneously while they are working on the mammograms. The system used in this study has three software agents: a fusion agent, a conversational agent, and an analytic agent. The fusion agent interprets multimodal commands by integrating the multimodal inputs. The conversational agent answers the user's questions and detects human-related or semantic errors and notifies the user about the results of the image analysis. The analytic agent enhances the digitized images using the wavelet denoising algorithm if requested by the user. To show how well the system performs in practice, we used the system for medical consultation on mammograms. Results also show that the relevant information about the region of interest (ROI) of the mammograms chosen by the users is extracted automatically and used to enhance the mammograms.

Education, Distance↗
PubMed2004

Motor units are recruited in a task-dependent fashion during locomotion.

Muscle fibres have a range of contractile properties from fast to slow. Traditional understanding of muscle fibre recruitment suggests that the slower fibres within a mixed muscle are used for all contractions including those at rapid speeds. However, mechanical arguments predict that some locomotor tasks are best performed by solely the faster fibres. Motor recruitment patterns can be indicated by the spectral properties of the myoelectric signals. High- and low-frequency myoelectric spectra that have similar spectral power indicate the activity of faster and slower motor units, respectively. In this study, the myoelectric signals in humans were measured from nine muscles of the leg during walking and running at 1.5, 3 and 4.5 m s(-1). The myoelectric spectra for 20 points in each stride were calculated using wavelet techniques, and the spectral properties quantified using principal component analysis. Bursts of muscle activity were characterized by hysteresis in the myoelectric frequencies, with different frequencies occurring at different times, indicating time-varying shifts in the motor recruitment patterns. This hysteresis occurred at all locomotor speeds tested. It is likely that the different types of motor unit are recruited in a task-dependent fashion during locomotion.

Action Potentials↗
PubMed2005

Improvement to human-face recognition in a volume holographic correlator by use of speckle modulation.

We show that a speckle-modulation technique can improve the parallelism and the recognition accuracy of volume holographic correlators. The object patterns are modulated by a speckle pattern generated by a diffuser. These modulated patterns are stored as Fourier holograms by use of angular-fractal multiplexing. With the speckle modulation the sidelobes are completely suppressed, the cross talk is negligible, and the correlation peak becomes a bright sharp spot. Thus higher recognition accuracy is achieved. The angular separation between adjacent patterns in the multiplexing could be much smaller, resulting in larger capacity and higher parallelism of the correlator. Also, this technique can be combined with other methods such as wavelet filtering to achieve a large invariant tolerance range. Theoretical analysis, numerical evaluation, and experimental results are presented to confirm that sidelobes and cross talk are sharply suppressed by the speckle modulation.

Journal Article↗
PubMed2005

Extracting mode components in laser intensity distribution by independent component analysis.

With increasingly sophisticated laser applications in industry and science, a reliable method to characterize the intensity distribution of the laser beam has become a more and more important task. However, traditional optic and electronic methods can offer only a laser beam intensity profile but, cannot separate the main mode components in the laser beam intensity distribution. Recently, independent component analysis has been a surging and developing method in which the goal is to find a linear representation of a non-Gaussian data set. Such a linear representation seems to be able to capture the essential structure of a laser beam profile. After assembling image data of a laser spot, we propose a new analytical approach to extract laser beam mode components based on the independent component analysis technique. For noise reduction and laser spot area location, wavelet thresholding, Canny edge detection, and the Hough transform are also used in this method before extracting mode components. Finally, the experimental results show that our approach can separate the principal mode components in a real laser beam efficiently.

Journal Article↗
PubMed2006

The influence of recombination on human genetic diversity.

In humans, the rate of recombination, as measured on the megabase scale, is positively associated with the level of genetic variation, as measured at the genic scale. Despite considerable debate, it is not clear whether these factors are causally linked or, if they are, whether this is driven by the repeated action of adaptive evolution or molecular processes such as double-strand break formation and mismatch repair. We introduce three innovations to the analysis of recombination and diversity: fine-scale genetic maps estimated from genotype experiments that identify recombination hotspots at the kilobase scale, analysis of an entire human chromosome, and the use of wavelet techniques to identify correlations acting at different scales. We show that recombination influences genetic diversity only at the level of recombination hotspots. Hotspots are also associated with local increases in GC content and the relative frequency of GC-increasing mutations but have no effect on substitution rates. Broad-scale association between recombination and diversity is explained through covariance of both factors with base composition. To our knowledge, these results are the first evidence of a direct and local influence of recombination hotspots on genetic variation and the fate of individual mutations. However, that hotspots have no influence on substitution rates suggests that they are too ephemeral on an evolutionary time scale to have a strong influence on broader scale patterns of base composition and long-term molecular evolution.

Animals↗
PubMed1998

Analysis of wave reflections in the arterial system using wave intensity: a novel method for predicting the timing and amplitude of reflected waves.

The timing and amplitude of reflected arterial waves in the ascending aorta were studied by analysis of the aortic pressure waveform and were compared with those derived using wave intensity analysis. Wave intensity analysis considers aortic pressure changes to be the result of forward and backward wavelets carrying energy. Wave intensity (dI = dPdU) is calculated from changes in pressure (dP) and flow velocity (dU), and its sign indicates the direction of travel of propagating wavelets (positive for forward-traveling waves and vice versa). We measured aortic pressure and flow velocity in 14 patients, mean age 60+/-9 years, with three-vessel coronary artery disease at the time of surgical revascularization. The travel time of the reflected wave derived from analysis of the aortic pressure waveform (tp) was measured from the foot of the aortic pressure waveform to the inflection point of the aortic pressure (derived objectively from the zero of second derivative of aortic pressure). From wave intensity analysis, the travel time of the reflected wave was measured to the onset of the wave intensity of the backward-traveling wave dI_ (t(i)), and to the onset of the separated backward pressure wave (t(b)). All patients showed an aortic pressure waveform characterized by an inflection point on the rising limb of the aortic pressure, followed by a secondary rise in pressure, representing the return of reflected waves. Wave intensity analysis consistently showed a negative peak in mid systole, the timing of its onset corresponding closely to the inflection point of the aortic pressure. The travel time of the reflected wave derived from the analysis of the aortic pressure waveform (t(p)) was 121+/-21ms and showed close agreement with ti (118+/-28 ms) and t(b) (115+/-29ms), with mean differences of 4 and 6ms, and 95% confidence intervals of difference (-2 to 7 ms) and (1 to 12ms), respectively. The augmentation index, a measure of the secondary increase in aortic pressure due to reflected waves, was significantly correlated with the magnitude of dI_ (r = 0.63, P < 0.001). Wave intensity is a quantity that indicates the rate of energy flux due to wave travel and since its value is positive for forward-traveling waves and negative for backward-traveling waves, its calculation allows the timing of reflected waves to be accurately predicted. Furthermore, the magnitude of wave intensity in backward-traveling waves (dI_) is related to the augmentation index and may provide a measure of the amplitude of the reflected wave. This analysis of the arterial system is done in the time domain and therefore can be easily applied to assess temporal changes in arterial characteristics.

Aorta, Thoracic↗
PubMedDate not supplied

Representations of ECG--late potentials in the time frequency plane.

It is shown that time frequency signal analysis could be a useful technique in detecting late potentials (LP). In particular, the spectrogram, the Wigner distribution and the wavelet transform have been applied to ECG signals from patients with sustained ventricular tachycardia. Comparisons of the three algorithms reveals that much better time localization is achieved by the wavelet transform. Moreover, it is concluded that a separation between healthy subjects and patients could be obtained based upon time frequency analysis.

Action Potentials↗
PubMed1994

The human suprathreshold photopic oscillatory potentials: method of analysis and clinical application.

The oscillatory potentials (OPs) of the electroretinogram (ERG) identify the high frequency wavelets which are seen riding on the top of the ascending limb of the b-wave. Despite the refinement in ERG recording techniques, which now allow for a more selective amplification of the OPs, their clinical utility still remains somewhat limited. Furthermore, while it has long been recognized that the different OPs which builds a given response are generated by distinct retinal events, amplitudes of clinically recorded oscillatory potentials are still reported using the artificial variable 'sum of OPs (SOPs)' which represent the sum amplitude of all the OPs identified in a given response; a method which is prone to compromise the diagnostic possibilities of the oscillatory potential response. The purpose of this report is to present a method of analysis of the OP response which is based on the relative amplitude of each OP. For the sake of clarity this report will focus on the analysis of the suprathreshold photopic OP response evoked the flash for 8.9 cd-m-2-sec in energy delivered against a rod desensitizing background of 30 cd-m-2 in luminance. The amplitude of each of the three major OPs (ie: OP2, OP3 and OP4) that normally compose this response was reported in relative units (ie: OP chi/SOPs) a method shown to minimize intersubject variability and at the same time allow for each OP to be evaluated individually. With the above method I have reviewed 289 clinical OP responses collected during a 7 year interval and identified more than 10 different categories of responses of which 6 were shown to demonstrate specific anomalies for one or two OPs. The selectivity and reproducibility of my observation were confirmed on follow-up testings as well as in pedigree studies. Use of this method of OP analysis should significantly increase the clinical utility of the oscillatory potentials and also facilitate comparisons between clinical laboratories.

Adolescent↗
PubMed2000

Time normalization of voice signals using functional data analysis.

The harmonics-to-noise ratio (HNR) has been used to quantify the waveform irregularity of voice signals [Yumoto et al., J. Acoust. Soc. Am. 71, 1544-1550 (1982)]. This measure assumes that the signal consists of two components: a harmonic component, which is the common pattern that repeats from cycle-to-cycle, and an additive noise component, which produces the cycle-to-cycle irregularity. It has been shown [J. Qi, J. Acoust. Soc. Am. 92, 2569-2576 (1992)] that a valid computation of the HNR requires a nonlinear time normalization of the cycle wavelets to remove phase differences between them. This paper shows the application of functional data analysis to perform an optimal nonlinear normalization and compute the HNR of voice signals. Results obtained for the same signals using zero-padding, linear normalization, and dynamic programming algorithms are presented for comparison. Functional data analysis offers certain advantages over other approaches: it preserves meaningful features of signal shape, produces differentiable results, and allows flexibility in selecting the optimization criteria for the wavelet alignment. An extension of the technique for the time normalization of simultaneous voice signals (such as acoustic, EGG, and airflow signals) is also shown. The general purpose of this article is to illustrate the potential of functional data analysis as a powerful analytical tool for studying aspects of the voice production process.

Data Interpretation, Statistical↗
PubMed2004

Quantitative assessment of pain-related thermal dysfunction through clinical digital infrared thermal imaging.

BACKGROUND: The skin temperature distribution of a healthy human body exhibits a contralateral symmetry. Some nociceptive and most neuropathic pain pathologies are associated with an alteration of the thermal distribution of the human body. Since the dissipation of heat through the skin occurs for the most part in the form of infrared radiation, infrared thermography is the method of choice to study the physiology of thermoregulation and the thermal dysfunction associated with pain. Assessing thermograms is a complex and subjective task that can be greatly facilitated by computerised techniques. METHODS: This paper presents techniques for automated computerised assessment of thermal images of pain, in order to facilitate the physician's decision making. First, the thermal images are pre-processed to reduce the noise introduced during the initial acquisition and to extract the irrelevant background. Then, potential regions of interest are identified using fixed dermatomal subdivisions of the body, isothermal analysis and segmentation techniques. Finally, we assess the degree of asymmetry between contralateral regions of interest using statistical computations and distance measures between comparable regions. RESULTS: The wavelet domain-based Poisson noise removal techniques compared favourably against Wiener and other wavelet-based denoising methods, when qualitative criteria were used. It was shown to improve slightly the subsequent analysis. The automated background removal technique based on thresholding and morphological operations was successful for both noisy and denoised images with a correct removal rate of 85% of the images in the database. The automation of the regions of interest (ROIs) delimitation process was achieved successfully for images with a good contralateral symmetry. Isothermal division complemented well the fixed ROIs division based on dermatomes, giving a more accurate map of potentially abnormal regions. The measure of distance between histograms of comparable ROIs allowed us to increase the sensitivity and specificity rate for the classification of 24 images of pain patients when compared to common statistical comparisons. CONCLUSIONS: We developed a complete set of automated techniques for the computerised assessment of thermal images to assess pain-related thermal dysfunction.

Female↗
PubMed2006

Quantitative adsorption and local structures of gallium(III) at the water-alpha-FeOOH interface.

The adsorption of Ga(III) at the water-alpha-FeOOH (goethite) interface has been investigated by means of quantitative adsorption experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy, and surface complexation modeling. Under the conditions studied, pH range 3-11 and surface coverages of 0.9-3.2 micromol/m2, Ga(III) was found to adsorb strongly to alpha-FeOOH, and the surface species were more resistant toward hydrolysis and formation of soluble Ga(OH)4- than either solid gallium hydroxides or soluble polynuclear complexes. The EXAFS measurements revealed the presence of octahedral Ga(III) complexes at the water-alpha-FeOOH interface, with practically no structural variations as a function of pH or total gallium concentration. Analysis of the first coordination shell required an anharmonic model indicating a distorted geometry of the GaO6 octahedra, with mean Ga-O distances at 1.96-1.98 angstroms. A method based on the continuous Cauchy wavelet transforms (CCWT) was used to identify backscattering atoms in the higher coordination shells. This analysis indicated predominately Fe backscattering, and the quantitative data fitting resulted in three Ga-Fe paths at 3.05, 3.2, and 3.55 angstroms, which correspond to two edge-sharing and one corner-sharing linkage, respectively. The collective results from EXAFS spectroscopy showed that Ga(III) adsorbs to Fe equivalent sites at the surface alpha-FeOOH as an extension of the rows of Fe octahedra in the bulk structure. This interpretation was further corroborated by a Ga-Fe-Fe multiple scattering path at 6.13 angstroms. The quantitative adsorption and proton data were modeled using a surface complexation formalism based on a 1 pK(a) constant capacitance model. In agreement with the EXAFS results, the model obtained included one predominating surface complex with the stoichiometry [triple bond]FeOGa(OH)2(-0.5) and the stability constant log beta(intr.) = -2.55 +/- 0.04 ([triple bond]FeOH(-0.5) + Ga3+ + 2H2O <--> [triple bond]FeOGa(OH)2(-0.5) + 3H+).

Adsorption↗
PubMed2004

[Frequency-domain analysis methods for single ion channel currents].

The frequency domain of single channel currents is analyzed by the power distribution function (PDF) constructed by the discrete wavelet transform (DWT) and power spectral density (PSD). The result shows that the power distribution function based on DWT is an effective frequency-domain analysis method for single channel currents.

Fourier Analysis↗
PubMed2004

Classification of cereal flours by chemometric analysis of MIR spectra.

Different kinds of cereal flours submitted to various technological treatments were classified on the basis of their mid-infrared spectra by pattern recognition techniques. Classification in the wavelet domain was achieved by using the wavelet packet transform for efficient pattern recognition (WPTER) algorithm, which allowed singling out the most discriminant spectral regions. Principal component analysis (PCA) on the selected features showed an effective clustering of the analyzed flours. Satisfactory classification models were obtained both on training and test samples. Furthermore, mixtures of varying composition of the studied flours were distributed in the PCA space according to their composition.

Algorithms↗
PubMed2005

Imaging system of wavelet optics described by the Gaussian linear frequency-modulated complex wavelet.

The image formation and the point-spread function of an optical system are analyzed by use of the wavelet basis function. The image described by a wavelet is no longer an indivisible whole image. It is, rather, a complex image consisting of many wavelet subimages, which come from the changes of different parameters (scale) a and c, and parameters b and d show the positions of wavelet subimages under different scales. A Gaussian frequency-modulated complex-valued wavelet function is introduced to express the point-spread function of an optical system and used to describe the image formation. The analysis, in allusion to the situation of illumination with a monochromatic plain light wave, shows that using the theory of wavelet optics to describe the image formation of an optical system is feasible.

Journal Article↗
PubMed1996

Wavelets, adapted waveforms and de-noising.

This is a short summary of a talk given at the Frontier Science in EEG Symposium, Continuous Waveform Analysis, held on 9 October 1993 in New Orleans. We describe some new libraries of waveforms well-adapted to various numerical analysis and signal processing tasks. The main point is that by expanding a signal in a library of waveforms which are well-localized in both time and frequency, one can achieve both understanding of structure and efficiency in computation. We briefly cover the properties of the new "wavelet packet" and "localized trigonometric" libraries. The main focus will be applications of such libraries to the analysis of complicated transient signals: a feature extraction and data compression algorithm for speech signals which uses best-adapted time and frequency decompositions, and an adapted waveform analysis algorithm for removing fish noises from hydrophone recordings. These signals share many of the same properties as EEG traces, but with distinct features that are easier to characterize and detect.

Electricity↗
PubMed2002

A quality-on-demand algorithm for wavelet-based compression of electrocardiogram signals.

For the compression of medical signals such as electrocardiogram (ECG), excellent reconstruction quality of a highly compressed signal can be obtained by using a wavelet-based approach. The most widely used objective quality criterion for the compressed ECG is called the percent of root-mean-square difference (PRD). In this paper, given a user-specified PRD, an algorithm is proposed to meet the PRD demand by searching for an appropriate bit rate in an automatic, smooth, and fast manner for the wavelet-based compression. The bit rate searching is modeled as a root-finding problem for a one-dimensional function, where an unknown rate-distortion curve represents the function and the desired rate is the root to be sought. A solution derived from root-finding methods in numerical analysis is proposed. The proposed solution is incorporated in a well-known wavelet-based coding strategy called set partitioning in hierarchical trees. ECG signals taken from the MIT/BIH database are tested, and excellent results in terms of convergence speed, quality variation, and coding performance are obtained.

Algorithms↗