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Biomedical Engineering, IEEE Transactions on

Issue 4 • Date April 2004

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Displaying Results 1 - 19 of 19
  • Table of contents

    Page(s): c1 - c4
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  • IEEE Transactions on Biomedical Engineering publication information

    Page(s): c2
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  • Prediction of paroxysmal atrial fibrillation by analysis of atrial premature complexes

    Page(s): 561 - 569
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    Currently, no reliable method exists to predict the onset of paroxysmal atrial fibrillation (PAF). We propose a predictor that includes an analysis of the R-R time series. The predictor uses three criteria: the number of premature atrial complexes (PAC) not followed by a regular R-R interval, runs of atrial bigeminy and trigeminy, and the length of any short run of paroxysmal atrial tachycardia. An increase in activity detected by any of these three criteria is an indication of an imminent episode of PAF. Using the Physionet database of the Computers in Cardiology 2001 Challenge, the predictor achieved a sensitivity of 89% and a specificity of 91%. View full abstract»

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  • A wavelet-based ECG delineator: evaluation on standard databases

    Page(s): 570 - 581
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (623 KB) |  | HTML iconHTML  

    In this paper, we developed and evaluated a robust single-lead electrocardiogram (ECG) delineation system based on the wavelet transform (WT). In a first step, QRS complexes are detected. Then, each QRS is delineated by detecting and identifying the peaks of the individual waves, as well as the complex onset and end. Finally, the determination of P and T wave peaks, onsets and ends is performed. We evaluated the algorithm on several manually annotated databases, such as MIT-BIH Arrhythmia, QT, European ST-T and CSE databases, developed for validation purposes. The QRS detector obtained a sensitivity of Se=99.66% and a positive predictivity of P+=99.56% over the first lead of the validation databases (more than 980,000 beats), while for the well-known MIT-BIH Arrhythmia Database, Se and P+ over 99.8% were attained. As for the delineation of the ECG waves, the mean and standard deviation of the differences between the automatic and manual annotations were computed. The mean error obtained with the WT approach was found not to exceed one sampling interval, while the standard deviations were around the accepted tolerances between expert physicians, outperforming the results of other well known algorithms, especially in determining the end of T wave. View full abstract»

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  • Support vector machine-based expert system for reliable heartbeat recognition

    Page(s): 582 - 589
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    This paper presents a new solution to the expert system for reliable heartbeat recognition. The recognition system uses the support vector machine (SVM) working in the classification mode. Two different preprocessing methods for generation of features are applied. One method involves the higher order statistics (HOS) while the second the Hermite characterization of QRS complex of the registered electrocardiogram (ECG) waveform. Combining the SVM network with these preprocessing methods yields two neural classifiers, which have been combined into one final expert system. The combination of classifiers utilizes the least mean square method to optimize the weights of the weighted voting integrating scheme. The results of the performed numerical experiments for the recognition of 13 heart rhythm types on the basis of ECG waveforms confirmed the reliability and advantage of the proposed approach. View full abstract»

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  • Predicting the threshold of pulse-train electrical stimuli using a stochastic auditory nerve model: the effects of stimulus noise

    Page(s): 590 - 603
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB) |  | HTML iconHTML  

    The incorporation of low levels of noise into an electrical stimulus has been shown to improve auditory thresholds in some human subjects (Zeng et al., 2000). In this paper, thresholds for noise-modulated pulse-train stimuli are predicted utilizing a stochastic neural-behavioral model of ensemble fiber responses to bi-phasic stimuli. The neural refractory effect is described using a Markov model for a noise-free pulse-train stimulus and a closed-form solution for the steady-state neural response is provided. For noise-modulated pulse-train stimuli, a recursive method using the conditional probability is utilized to track the neural responses to each successive pulse. A neural spike count rule has been presented for both threshold and intensity discrimination under the assumption that auditory perception occurs via integration over a relatively long time period (Bruce et al., 1999). An alternative approach originates from the hypothesis of the multilook model (Viemeister and Wakefield, 1991), which argues that auditory perception is based on several shorter time integrations and may suggest an NofM model for prediction of pulse-train threshold. This motivates analyzing the neural response to each individual pulse within a pulse train, which is considered to be the brief look. A logarithmic rule is hypothesized for pulse-train threshold. Predictions from the multilook model are shown to match trends in psychophysical data for noise-free stimuli that are not always matched by the long-time integration rule. Theoretical predictions indicate that threshold decreases as noise variance increases. Theoretical models of the neural response to pulse-train stimuli not only reduce calculational overhead but also facilitate utilization of signal detection theory and are easily extended to multichannel psychophysical tasks. View full abstract»

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  • A mathematical model of neonatal tidal liquid ventilation integrating airway mechanics and gas transfer phenomena

    Page(s): 604 - 611
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (457 KB) |  | HTML iconHTML  

    Tidal liquid ventilation (TLV) was proposed as an alternative to conventional mechanical ventilation in the case of surfactant-deficiency diseases, particularly for very premature subjects. Although many experimental studies have been conducted up to now, the effects of variations in ventilatory settings, such as frequency and tidal volume, on blood arterialization and lung mechanics have not been studied quantitatively. We developed a mathematical model simulating the breathing processes occurring during neonatal TLV treatments. The model integrates the description of O2 and CO2 transport, from the trachea to pulmonary capillary blood and vice versa, with the description of fluid mechanics within the airways and the saccules (the alveoli precursors). Gas transfer is described with a mono-dimensional model, accounting for convective and diffusive transport through the airways, coupled with a 3-compartment model, simulating gas diffusion between saccules, plasma and red blood cells, and chemical reactions dependent on the concentrations of gases and related chemical species. Mechanic loads on airways are calculated by means of a lumped-parameters approach. The model calculates mechanical stress and gas exchange as a function of the ventilatory settings. The integration of these results sheds light on possible ventilation strategies to allow for optimal management of blood arterialization and lung mechanical load. View full abstract»

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  • Numerical study on an equivalent source model for inhomogeneous magnetic field dosimetry in the low-frequency range

    Page(s): 612 - 616
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (410 KB) |  | HTML iconHTML  

    A new equivalent numerical source model is proposed for efficient dosimetric investigations in the low-frequency range. This approach allows the reproduction of complicated inhomogeneous magnetic field distributions around electronic appliances with full generality (i.e., supports three-dimensional vector fields). This paper investigates the accuracy of the equivalent source model using the geometry-based numerical reference model of a current loop to simulate the magnetic field distribution of a real electronic appliance. Good agreement between the equivalent source model and the reference is obtained with regard to the magnetic field distribution and the induced electric current density in a homogeneous human body model, respectively. View full abstract»

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  • Fetal brain MRI: segmentation and biometric analysis of the posterior fossa

    Page(s): 617 - 626
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    This paper presents a novel approach to fetal magnetic resonance image segmentation and biometric analysis of the posterior fossa's midline structures. We developed a semi-automatic segmentation method (based on a region growing technique) and tested the algorithm on images of 104 normal fetuses. Using the segmented regions of interest (posterior fossa, vermis, and brainstem), we computed four relative area ratios. Statistical and clinical analysis of our results showed that the relative development of these structures appears to be independent of pregnancy term. In an additional study of 23 pathological cases, one of the four measurements was always significantly different from the corresponding value observed in normal cases. View full abstract»

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  • In vivo inflammatory and wound healing effects of gold electrode voltammetry for MEMS micro-reservoir drug delivery device

    Page(s): 627 - 635
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (479 KB) |  | HTML iconHTML  

    The in vivo biocompatibility and biofouling of gold electrodes for a microelectromechanical systems drug delivery device were investigated in a rodent model. The role of the applied voltage and gold electrolysis products in modulating the inflammatory response (biocompatibility), and the temporal adhesion of cellular populations onto macroscopic gold film electrodes (biofouling) were analyzed in reference to two controls, devices to which voltage was not applied (uncorroded) or voltage was applied to inert platinum electrodes (electrical controls). Voltammetry was applied to the gold surfaces once (day 4, 7, 14, 21, 28, 35, 42, or 49), while voltage of identical magnitude was applied to the electrical controls. An inflammatory response characterized by a rapid decrease of leukocyte concentration to control levels was observed 48 h following voltage application with no significant cell concentration difference (p>0.05) between the corroded devices and electrical controls. The histological evaluation of the direct implant fibrous capsule showed comparable thickness of voltage applied and control specimens. The gold corrosion peak current showed no significant difference (p>0.05) among peak values at all time points. It was concluded that gold electrode corrosion was biocompatible and its electrochemical performance was not hindered by fibrous capsule formation. View full abstract»

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  • Robot-assisted adaptive training: custom force fields for teaching movement patterns

    Page(s): 636 - 646
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB) |  | HTML iconHTML  

    Based on recent studies of neuro-adaptive control, we tested a new iterative algorithm to generate custom training forces to "trick" subjects into altering their target-directed reaching movements to a prechosen movement as an after-effect of adaptation. The prechosen movement goal, a sinusoidal-shaped path from start to end point, was never explicitly conveyed to the subject. We hypothesized that the adaptation would cause an alteration in the feedforward command that would result in the prechosen movement. Our results showed that when forces were suddenly removed after a training period of 330 movements, trajectories were significantly shifted toward the prechosen movement. However, de-adaptation occurred (i.e., the after-effect "washed out") in the 50-75 movements that followed the removal of the training forces. A second experiment suppressed vision of hand location and found a detectable reduction in the washout of after-effects, suggesting that visual feedback of error critically influences learning. A final experiment demonstrated that after-effects were also present in the neighborhood of training-44% of original directional shift was seen in adjacent, unpracticed movement directions to targets that were 60° different from the targets used for training. These results demonstrate the potential for these methods for teaching motor skills and for neuro-rehabilitation of brain-injured patients. This is a form of "implicit learning," because unlike explicit training methods, subjects learn movements with minimal instructions, no knowledge of, and little attention to the trajectory. View full abstract»

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  • Ceramic-based multisite electrode arrays for chronic single-neuron recording

    Page(s): 647 - 656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB) |  | HTML iconHTML  

    A method is described for the manufacture of a microelectrode array for chronic, multichannel, single neuron recording. The ceramic-based, multisite electrode array has four recording sites patterned onto a ceramic shaft the size of a single typical microwire electrode. The sites and connecting wires are applied to the ceramic substrate using a reverse photolithographic procedure. Recording sites (22×80 μm) are separated by 200 μm along the shaft. A layer of alumina insulation is applied over the whole array (exclusive of recording sites) by ion-beam assisted deposition. These arrays were capable of recording single neuron activity from each of their recording sites for at least three weeks during chronic implantation in the somatosensory cortex of rats, and several sites had recordings that lasted for more than 8 weeks. The vertical arrangement of the recording sites on these electrodes is ideal for simultaneously recording across the different layers of brain areas such as the cerebral cortex and hippocampus in chronic preparations. View full abstract»

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  • Optic nerve signals in a neuromorphic chip I: Outer and inner retina models

    Page(s): 657 - 666
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    We present a novel model for the mammalian retina and analyze its behavior. Our outer retina model performs bandpass spatiotemporal filtering. It is comprised of two reciprocally connected resistive grids that model the cone and horizontal cell syncytia. We show analytically that its sensitivity is proportional to the space-constant-ratio of the two grids while its half-max response is set by the local average intensity. Thus, this outer retina model realizes luminance adaptation. Our inner retina model performs high-pass temporal filtering. It features slow negative feedback whose strength is modulated by a locally computed measure of temporal contrast, modeling two kinds of amacrine cells, one narrow-field, the other wide-field. We show analytically that, when the input is spectrally pure, the corner-frequency tracks the input frequency. But when the input is broadband, the corner frequency is proportional to contrast. Thus, this inner retina model realizes temporal frequency adaptation as well as contrast gain control. We present CMOS circuit designs for our retina model in this paper as well. Experimental measurements from the fabricated chip, and validation of our analytical results, are presented in the companion paper [Zaghloul and Boahen (2004)]. View full abstract»

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  • Optic nerve signals in a neuromorphic chip II: testing and results

    Page(s): 667 - 675
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    Seeking to match the brain's computational efficiency , we draw inspiration from its neural circuits. To model the four main output (ganglion) cell types found in the retina, we morphed outer and inner retina circuits into a 96×60-photoreceptor, 3.5×3.3 mm2, 0.35 μm-CMOS chip. Our retinomorphic chip produces spike trains for 3600 ganglion cells (GCs), and consumes 62.7 mW at 45 spikes/s/GC. This chip, which is the first silicon retina to successfully model inner retina circuitry, approaches the spatial density of the retina. We present experimental measurements showing that the chip's subthreshold current-mode circuits realize luminance adaptation, bandpass spatiotemporal filtering, temporal adaptation and contrast gain control. The four different GC outputs produced by our chip encode light onset or offset in a sustained or transient fashion, producing a quadrature-like representation. The retinomorphic chip's circuit design is described in a companion paper [Zaghloul and Boahen (2004)]. View full abstract»

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  • Improving calibration of 3-D video oculography systems

    Page(s): 676 - 679
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    Eye movement recordings with video-based techniques have become very popular, as long as they are restricted to the horizontal and vertical movements of the eye. Reliable measurement of the torsional component of eye movements, which is especially important in the diagnosis and investigation of pathologies, has remained a coveted goal. One of the main reasons is unresolved technical difficulties in the analysis of video-based images of the eye. Based on simulations, we present solutions to two of the primary problems: a robust and reliable calibration of horizontal and vertical eye movement recordings, and the extraction of suitable iris patterns for the determination of the torsional eye position component. View full abstract»

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  • Ellipsoidal refinement of the regularized inverse: performance in an anatomically realistic EEG model

    Page(s): 679 - 683
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    Functional brain imaging and source localization based on the scalp's potential field requires a solution to the inverse electrostatic problem. This is an underdetermined problem with many solutions. Minimum norm and regularization methods involving the norm are often used, but generally give solutions in which current is widely distributed. One method for reducing the spatial distribution of a solution is to apply it iteratively within the bounds of a shrinking ellipsoid. This paper compares the performance of this approach with an exhaustive search at various noise levels using a numeric simulation of the electroencephalogram in a realistic conductor model. The results show that inverting a single dipolar source with a location accuracy comparable to an exhaustive search requires in the range of 5 to 10 dB higher signal-to-noise ratio. View full abstract»

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  • New for 2004!

    Page(s): 684
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  • 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society

    Page(s): 685 - 688
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  • IEEE Transactions on Biomedical Engineering information for authors

    Page(s): c3
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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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Editor-in-Chief
Bin He
Department of Biomedical Engineering