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Biomedical Engineering, IEEE Transactions on

Issue 5 • Date May 1999

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Displaying Results 1 - 15 of 15
  • A computer-aided approach to the structural analysis and modification of a large circulatory system model

    Page(s): 485 - 493
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    The purpose of this study is to show an approach to making an intelligent support system for understanding and modifying a large circulatory system model using techniques of system analysis. Structural analysis makes it possible to visualize hierarchies of Coleman's (1981) circulatory model Human. Two techniques are successively applied for structural analysis, model reduction and graph analysis by interpretative structural modeling (ISM). First, the analysis for model reduction removes input-output relations with an input-output gain less than a given threshold, and second, the ISM technique applied to the reduced model of Human provides hierarchical directed graphs. The proposed approach: (1) enables visualization of a hierarchy graph of cause and effect relations of the large circulatory model, (2) suggests control and diagnostic information to the model by tracing back a path in the hierarchy, and (3) allows the user to modify the circulatory model. The efficiency and performance of the proposed approach demonstrates technical indications of success in analyzing and justifying experimental evidences with the online help of the system. View full abstract»

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  • Study of the cause of the temperature rise at the muscle-bone interface during ultrasound hyperthermia

    Page(s): 494 - 504
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    Undesirable temperature rise at the muscle-bone interface has been one of the major problems during ultrasound hyperthermia treatment. In this study, the authors examined by both computer calculation and phantom experiment the cause of this problem. Ultrasound penetrates a bone in two different waveforms, longitudinal and transversal. The transmission coefficient of these two waves vary greatly with the incident angle. From both theoretical and experimental results, the incident angle dependency of the interface heat was confirmed. When the incident angle is less than the critical angle of the longitudinal wave, the main cause of the temperature elevation is the absorption of the longitudinal wave in the bone. When the incident angle is larger than the critical angle of the longitudinal wave, the transversal wave becomes the major cause of the heat generation. At the incident angles larger than the critical angle of the transversal wave, no temperature rise is produced by the absorption of the ultrasound at the bone; the incident longitudinal wave, strengthened by the reflected wave, is absorbed in the muscle just in front of the bone. The heat generated in the muscle is transported to the interface so that the temperature of the interface and bone increases slightly. View full abstract»

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  • A computational model of electrical stimulation of the retinal ganglion cell

    Page(s): 505 - 514
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    Localized retinal electrical stimulation in blind volunteers results in discrete round visual percepts corresponding to the location of the stimulating electrode. The success of such an approach to provide useful vision depends on elucidating the neuronal target of surface electrical stimulation. To determine if electrodes preferentially stimulate ganglion cells directly below them or passing fibers from distant ganglion cells, the authors developed a compartmental model for electric field stimulation of the retinal ganglion cell (RGC). In this model a RGC is stimulated by extracellular electrical fields with active. Channels and realistic cell morphology derived directly from a neuronal tracing. Three membrane models were applied: a linear passive model, a Hodgkin-Huxley model with passive dendrites (HH), and a model composed of all active compartments (FCM) with five nonlinear ion channels. Idealized monopolar point and disk stimulating electrodes were positioned above the cell, For the HH and FCM models, the position of lowest cathodal threshold to propagate an action potential was over the soma. Brief (100 μs) cathodic stimuli were 20% (HH with disk electrode) to 73% (FCM with point-source) more effective over the soma than over the axon. In the passive model, the axon is preferentially stimulated versus the soma. Although it may be possible to electrically stimulate RGC's near their cell body at lower thresholds than at their axon, these differences are relatively small. Alternative explanations should be sought to explain the focal perceptions observed in previously reported patient trials. View full abstract»

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  • MEG spatio-temporal analysis using a covariance matrix calculated from nonaveraged multiple-epoch data

    Page(s): 515 - 521
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    The authors propose a magnetoencephalographic (MEG) spatio-temporal analysis in which the measurement-covariance matrix is calculated using nonaveraged multiple epoch data. The proposed analysis has two advantages. First, a very narrow time window can be used for the source estimation. Second, accurate localization is possible even when the source activation has a time jitter. Experiments using auditory evoked MEG data clearly demonstrate these advantages. View full abstract»

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  • Combined MEG and EEG source imaging by minimization of mutual information

    Page(s): 522 - 534
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    Though very frequently assumed, the necessity to operate a joint processing of simultaneous magnetoencephalography (MEG) and electroencephalography (EEG) recordings for functional brain imaging has never been clearly demonstrated. However, the very last generation of MEG instruments allows the simultaneous recording of brain magnetic fields and electrical potentials on the scalp. But the general fear regarding the fusion between MEG and EEG data is that the drawbacks from one modality will systematically spoil the performances of the other one without any consequent improvement. This is the case for instance for the estimation of deeper or radial sources with MEG. In this paper, the authors propose a method for a cooperative processing of MEG and EEG in a distributed source model. First, the evaluation of the respective performances of each modality for the estimation of every dipole in the source pattern is made using a conditional entropy criterion. Then, the algorithm operates a preprocessing of the MEG and EEG gain matrices which minimizes the mutual information between these two transfer functions, by a selective weighting of the MEG and EEG lead fields. This new combined EEG/MEG modality brings major improvements to the localization of active sources, together with reduced sensitivity to perturbations on data. View full abstract»

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  • Correlation dimension estimation: can this nonlinear description contribute to the characterization of blood pressure control in rats?

    Page(s): 535 - 547
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    The application of correlation dimension estimation to the study of cardiovascular control, via the blood pressure (BP) time series was investigated. The authors chose to calculate the Grassberger-Procaccia (GP) correlation dimension. In order to obtain a reliable estimate of the correlation dimension, they studied impact of various parameters such as the appropriate sampling rate, the time delays, the embedding dimension, the minimal trace length required, and the number of points needed as reference points. The authors developed a recipe for the reliable treatment of the continuous BP signal in rats, their animal model, and discussed the possible pitfalls which demand special attention. Next, they applied the surrogate data method to a BP time series, looking for the existence of nonlinear components, in order to test whether the nonlinear modeling is necessary for accurately describing the system. The authors found that, indeed, the correlation dimension does reveal information which cannot be unveiled by the commonly used power spectral technique, thus, making the nonlinear modeling an important approach, providing additional insight into the cardiovascular control system. View full abstract»

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  • Detecting ventricular tachycardia and fibrillation by complexity measure

    Page(s): 548 - 555
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    Sinus rhythm (SR), ventricular tachycardia (VT) and ventricular fibrillation (VF) belong to different nonlinear physiological processes with different complexity. In this study, the authors present a novel, and computationally fast method to detect VT and VF, which utilizes a complexity measure suggested by Lempel and Ziv (1976). For a specific window length (i.e., the length of data segment to be analyzed), the method first generates a 0-1 string by comparing the raw electrocardiogram (ECG) data to a selected suitable threshold. The complexity measure can be obtained from the 0-1 string only using two simple operations, comparison and accumulation. When the window length is 7 s, the detection accuracy for each of SR, VT, and VF is 100% for a test set of 204 body surface records (34 SR, 85 monomorphic VT, and 85 VF). Compared with other conventional time- and frequency-domain methods, such as rate and irregularity, VF-filter leakage, and sequential hypothesis testing, the new algorithm is simple, computationally efficient, and well suited for real-time implementation in automatic external defibrillators (AED's). View full abstract»

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  • ECG data compression using cut and align beats approach and 2-D transforms

    Page(s): 556 - 564
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    A new electrocardiogram (ECG) data compression method is presented which employs a two dimensional (2-D) transform. This 2-D transform method utilizes the fact that ECG signals generally show two types of redundancies-between adjacent heartbeats and between adjacent samples. A heartbeat data sequence is cut and beat-aligned to form a 2-D data array. Any 2-D compression method can then be applied. Transform coding using the 2-D discrete cosine transform (DCT) [2-D DCT] is employed here as an example. Using selections from the MIT-BIH arrhythmia and Medtronic databases, results are presented that illustrate substantial improvement in compression ratio over one-dimensional methods for comparable percent root-mean-square difference (PRD). View full abstract»

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  • Bone image segmentation

    Page(s): 565 - 573
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1183 KB)  

    Characteristics of microscopic structures in bone cross sections carry essential clues in age determination in forensic science and in the study of age-related bone developments and bone diseases. Analysis of bone cross sections represents a major area of research in bone biology. However, traditional approaches in bone biology have relied primarily on manual processes with very limited number of bone samples. As a consequence, it is difficult to reach reliable and consistent conclusions. In this paper the authors present an image processing system that uses microstructural and relational knowledge present in the bone cross section for bone image segmentation. This system automates the bone image analysis process and is able to produce reliable results based on quantitative measurements from a large number of bone images. As a result, using large databases of bone images to study the correlation between bone structural features and age-related bone developments becomes feasible. View full abstract»

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  • Three-dimensional filtering approach to brain potential mapping

    Page(s): 574 - 583
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    The spatial distribution of electroencephalogram (EEG) features on the scalp surface, both in time or frequency, is of great importance in clinical applications and medical research. Traditionally, mathematical methods based on interpolation algorithms have been widely applied to obtain the EEG mappings. This paper presents an innovative approach to reconstructing the brain potential mappings from multichannel EEGs. The three-dimensional (3-D) filtering approach, differing from the numerical interpolating methods, considers the spatial distribution of brain potentials as a 3-D signal, which is processed and interpolated according to its spatial frequency characteristics. The performance of the 3-D filtering method evaluated on simulated brain potentials is shown to be comparable to the four-nearest-neighbors method. Moreover, the 3-D filtering method is superior to the spherical splines method in efficiency. Two main advantages of this method are: the prospect of developing realtime, animated EEG mappings utilizing powerful digital signal processors and its capability of processing and interpolating the brain potentials on the realistic irregular scalp surface. View full abstract»

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  • Characterization of cell deformation and migration using a parametric estimation of image motion

    Page(s): 584 - 600
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    This paper deals with the spatio-temporal analysis of two-dimensional deformation and motion of cells from time series of digitized video images. A parametric motion approach based on an affine model has been proposed for the quantitative characterization of cellular movements in different experimental areas of cellular biology including spontaneous cell deformation, cell mitosis, individual cell migration and collective migration of cell populations as cell monolayer. The accuracy and robustness of the affine model parameter estimation, which is based on a multiresolution algorithm, has been established from synthesized image sequences. A major interest of the authors' approach is to follow with time the evolution of a few number of parameters characteristic of cellular motion and deformation. From the time-varying eigenvalues of the affine model square matrix, a precise quantification of the cell pseudopodial activity, as well as of cell division has been performed. For migrating cells, the motion quantification confirms that cell body deformation has a leading role in controlling nucleus displacement, the nucleus itself undergoing a larger rotational motion. At the cell population level, image motion analysis of in vitro wound healing experiments quantifies the heterogeneous cell populations dynamics. View full abstract»

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  • Time-frequency matching of warped depth-EEG seizure observations

    Page(s): 601 - 605
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    A methodology of comparing depth-EEG seizure recordings is presented. The approach is based on an extension of Wagner and Fischer's (1974) algorithm to N×2-dimensional sets, allowing a confrontation of nonequal duration observations characterized by their time-frequency distributions. It proceeds by time and frequency warping on the first observation to match the second, under cost constraints. Preliminary results show that relevant signatures can be extracted from recordings. View full abstract»

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  • Transformer miniaturization for transcutaneous current/voltage pulse applications

    Page(s): 606 - 608
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    A general procedure for the design of a miniaturized step up transformer to be used in the context of surface electrode based current/voltage pulse generation is presented. It has been shown that the optimum secondary current pulse width is 4.5 τ, where τ is the time constant associated with the pulse forming network associated with the transformer/electrode interaction. This criteria has been shown to produce the highest peak to average current ratio for the secondary current pulse. The design procedure allows for the calculation of the optimum turns ratio, primary turns, and secondary turns for a given electrode load/tissue and magnetic core parameters. Two design examples for transformer optimization are presented. View full abstract»

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  • Preamplifier with a second-order high-pass filtering characteristic

    Page(s): 609 - 612
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    A new preamplifier for suppressing low-frequency interference is presented. The proposed preamplifier, with its front end being implemented by an instrumentation amplifier, enjoys the following advantages: differential high-pass filtering, high input impedance, high common-mode rejection ratio and low passive sensitivity. This circuit can be realized with commercial operational amplifiers with enough phase margin, or fabricated in a chip for practical measurement of physiological signals. View full abstract»

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  • Effect of a bath on the epicardial transmembrane potential during internal defibrillation shocks

    Page(s): 612 - 614
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (101 KB)  

    Using a three dimensional model of cardiac tissue, the authors consider a rectangular slab of tissue. They examine the effect of a defibrillating shock from an intracavitary electrode upon the epicardial transmembrane potential (Vm) for two cases: one in which the epicardium is bounded by air and another in which it is bounded by a conductive bath. The authors find that the inclusion of the bath changes the polarity of the steady-state Vm in the epicardial region that is closest to the shock electrode. In addition, the magnitude of Vm is increased dramatically if the bath is present; the degree of hyperpolarization increases twenty fivefold, while the degree of depolarization increases elevenfold. The remaining bulk of the cardiac tissue is relatively unaffected by the inclusion of the bath. View full abstract»

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Aims & Scope

IEEE Transactions on Biomedical Engineering contains basic and applied papers dealing with biomedical engineering. Papers range from engineering development in methods and techniques with biomedical applications to experimental and clinical investigations with engineering contributions.

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Meet Our Editors

Editor-in-Chief
Bin He
Department of Biomedical Engineering