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Biomedical Engineering, IEEE Transactions on

Issue 7 • Date July 1992

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Displaying Results 1 - 12 of 12
  • Magnetic source images determined by a lead-field analysis: the unique minimum-norm least-squares estimation

    Page(s): 665 - 675
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1045 KB)  

    The minimum norm least-squares approach based on lead field theory provides a unique inverse solution for a magnetic source image that is the best estimate in the least-squares sense. This has been applied to determine the source current distribution when the primary current is confined to a surface or set of surfaces. In model simulations of cortical activity of the human brain, the magnetic field pattern across the scalp is interpreted with prior knowledge of anatomy to yield a unique magnetic source image across a portion of cerebral cortex, without resort to an explicit source model. View full abstract»

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  • Assessing the effect of uncertainty in intracavitary electrode position on endocardial potential estimates

    Page(s): 676 - 681
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (521 KB)  

    The aim of the simulation study is to determine the effect of uncertainty in intracavitary probe electrode position on the accuracy of estimated endocardial potentials. Intracavitary probe position uncertainty is simulated by randomly moving an idealized probe surface about the center of an idealized left ventricular endocardial surface. These random deviations represent possible probe locations that are incorporated as correlated noise. An optimum inverse transfer coefficient matrix, relating intracavitary potentials to endocardial potentials, is computed and subsequently used to calculate the best linear estimate of the true endocardial potentials. These simulation results imply that position uncertainty of a multielectrode, intracavitary probe can be a major source of error in estimating endocardial potentials from intracavitary potentials. View full abstract»

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  • A minimum profile uniform current density electrode

    Page(s): 682 - 692
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    An electrode that produces an injected charge density that is uniform over the surface of the electrode and thus permits maximum utilization of the surface is described. Charge density is the time integral of current density, and the alteration of the current density is obtained by adding curvature to the electrode and recessing it within a cylindrical insulating well. A novel numerical method is used to determine the recession and curvature. The benefit of this technique is that it permits a reduction in the electrode size while maintaining the maximum safe injected charge level of a disk-type electrode. A minimum profile uniform current density electrode and the algorithms used in its design are presented. Finally, a flat electrode that is recessed by as little as 1/10 of its diameter is shown to have an injected current density on the electrode surface that is superior to that of a flat surface mounted electrode. View full abstract»

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  • Neural stimulation with magnetic fields: analysis of induced electric fields

    Page(s): 693 - 700
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    Spatial distribution of the derivative of the electric field induced in a planar semi-infinite tissue model by various current-carrying coils and their utility in neural stimulation are evaluated. Analytical expressions are obtained for the electric field and its spatial derivatives produced by an infinitely short current element. Fields and their derivatives for an arbitrarily shaped coil are then obtained by numerical summation of contributions from all the elements forming the coil. The simplicity of the solution and a very short computation time make this method particularly attractive for gaining a physical insight into the spatial behavior of the stimulating parameter and for the optimization of coils. Such analysis is useful as the first step before undertaking a more complex numerical analysis of a model more closely representing the tissue geometry and heterogeneity. View full abstract»

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  • Maximal dynamic range electrotactile stimulation waveforms

    Page(s): 701 - 715
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1302 KB)  

    A new method to measure the dynamic range of electrotactile (electrocutaneous) stimulation uses both steepest ascent (gradient) and one-variable-at-a-time methods to determine the waveform variables that maximize the subjective magnitude (intensity) of the electrotactile percept at the maximal current without discomfort for balanced-biphasic pulse bursts presented at a 15-Hz rate. The magnitude at the maximal current without discomfort is maximized by the following waveform (range tested in parenthesis): number of pulses/burst=6 (1-20), pulse repetition rate within a burst=350 Hz (200-1500), and phase width=150 mu s (40-350). The interphase interval (separation between positive and negative phases in a biphasic pulse) does not affect dynamic range from 0-500 mu s. The number of pulses/burst has a large effect on the perceived dynamic range when this is measured using a subjective-magnitude-based algorithm, whereas it has little effect on the traditional dynamic range measure, i.e., (maximal current without discomfort)/(sensation threshold current). View full abstract»

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  • A movement pattern generator model using artificial neural networks

    Page(s): 716 - 722
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (671 KB)  

    The authors have developed a movement pattern generator, using an artificial neural network (ANN) for generating periodic movement trajectories. This model is based on the concept of 'central pattern generators'. Jordan's (1986) sequential network, which is capable of learning sequences of patterns, was modified and used to generate several bipedal trajectories (or gaits), coded in task space, at different frequencies. The network model successfully learned all of the trajectories presented to it. The model has many attractive properties, such as limit cycle behavior, generalization of trajectories and frequencies, phase maintenance, and fault tolerance. The movement pattern generator model is potentially applicable for improved understanding of animal locomotion and for use in legged robots and rehabilitation medicine. View full abstract»

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  • Recognition of multiunit neural signals

    Page(s): 723 - 729
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (567 KB)  

    An essential step in studying nerve cell interaction during information processing is the extracellular microelectrode recording of the electrical activity of groups of adjacent cells. The recording usually contains the superposition of the spike trains produced by a number of neurons in the vicinity of the electrode. It is therefore necessary to correctly classify the signals generated by these different neurons. This problem is considered, and a new classification scheme is developed which does not require human supervision. A learning stage is first applied on the beginning portion of the recording to estimate the typical spike shapes of the different neurons. As for the classification stage, a method is developed which specifically considers the case when spikes overlap temporally. The method minimizes the probability of error, taking into account the statistical properties of the discharges of the neurons. The method is tested on a real recording as well as on synthetic data. View full abstract»

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  • Time-frequency transforms: a new approach to first heart sound frequency dynamics

    Page(s): 730 - 740
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    The binomial joint time-frequency transform is used to test the hypothesis that first heart sound frequency rises during the isovolumic contraction period. Cardiac vibrations were recorded from eight open-chest dogs using an ultralight accelerometer cemented directly to the epicardium of the anterior left ventricle. Three characteristic time-frequency spectral patterns were evident in the animals investigated: (1) a frequency component that rose from approximately 40-140 Hz in a 30-50-ms interval immediately following the ECG R-wave, (2) a slowly varying or static frequency of 60-100 Hz beginning midway through the isovolumic contraction period, and (3) broadband peaks occurring at the time of the Ia and Ib high frequency components. The binomial transform provided much better resolution than the spectrograph or spectrogram. By revealing the onset and dynamics of first heart sound frequencies, time-frequency transforms may allow mechanical assessment of individual cardiac structures. View full abstract»

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  • Analysis of ECG from pole-zero models

    Page(s): 741 - 751
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    A complete solution for the delineation of the ECG signal into its component waves is proposed from a system theoretic point of view. The discrete cosine transform (DCT) of a bell-shaped biphasic function is approximated mathematically by a system function with two poles and two zeros, i.e., of order View full abstract»

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  • Noninvasive optical polarimetric glucose sensing using a true phase measurement technique

    Page(s): 752 - 756
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    The development and testing of a noninvasive true phase optical polarimetry sensing system to monitor in vivo glucose concentrations is described. To demonstrate the applicability of this optical sensor for glucose movement, the authors calibrate the system and then test it in vitro using both a glass test cell filled with glucose solution in the physiologic range, with a path length of 0.9 cm to approximate the 1-cm path length present in the anterior chamber of the eye, and then on an excised human eye. The technique used helium neon laser light which was coupled through a rotating linear polarizer along with two stationary linear polarizers and two detectors to produce reference and signal outputs whose amplitudes varied sinusoidally with a frequency of twice the angular velocity of the rotating polarizer, and whose phase was proportional to the rotation of the linear polarization vector passing through the glucose solution. View full abstract»

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  • Measuring lung resistivity using electrical impedance tomography

    Page(s): 756 - 760
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (570 KB)  

    The use of electrical impedance tomography (EIT) imaging techniques in the measurement of lung resistivity for detection and monitoring of apnea and edema is proposed. In EIT, currents are injected into a subject using multiple electrodes, and boundary voltages are measured to reconstruct a cross-sectional image of internal resistivity distribution. It is found that a simplified, therefore fast, version of the impedance imaging method can be used for detection and monitoring of apnea and edema. The feasibility of this method has been shown through computer simulations and human experiments. The authors speculate that the EIT imaging technique will be more reliable than the current impedance apnea monitoring method, since they are monitoring the change of internal lung resistivity. However, more study is required to verify that this method performs better in the presence of motion artifact than the conventional two-electrode impedance apnea monitoring method. View full abstract»

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  • Minimal repetition evoked potentials by modified adaptive line enhancement

    Page(s): 760 - 764
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    A method called modified adaptive line enhancement (MALE) for obtaining evoked potentials with minimum stimulus repetitions is described. The theory of MALE is developed and the assumptions made are tested and shown to be adequate in the case of brainstem auditory evoked potential. The signal distortion is characterized, and methods to alleviate the problem are developed. Using the weighted exact least squares lattice algorithm, the MALE method is implemented and applied to real data. It is shown that brainstem auditory evoked potentials can be obtained with less than 40 repetitions using the MALE method, compared to the 2000 required if the conventional ensemble averaging method is used. 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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Editor-in-Chief
Bin He
Department of Biomedical Engineering