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Biomedical Engineering, IEEE Transactions on

Issue 9 • Date Sept. 1993

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Displaying Results 1 - 18 of 18
  • A stochastic network model of the interaction between cardiac rhythm and artificial pacemaker

    Publication Year: 1993 , Page(s): 845 - 858
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1225 KB)  

    In order to study heart-pacemaker interaction (HPI), a computer model of the cardiac conduction system has been developed which includes the effects of artificial pacemaker function and failure. The stochastic network model of cardiac conduction consists of five vertices, each representing a functional electrophysiologic element. Electrophysiologic multidimensional conditional probability functions determine the depolarization status of each vertex. The atrioventricular (AV) node is emulated using a mathematical model which includes the influence of past cycle lengths on AV nodal conduction time. Twenty-three classes of arrhythmias may be simulated and, for pacing simulation, one of 12 antibradycardia pacing modes may be chosen. Random effects of pacemaker malfunction including oversensing, undersensing, or failure-to-capture may be simulated through the use of probability distribution functions. This model should prove useful in the development of pacemaker algorithms, determining patient-specific pacemaker therapy, and predicting causes for apparent pacemaker malfunction. The model has been used in the development of an expert system to analyze paced ECGs for pacemaker function and malfunction. View full abstract»

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  • Sampling theory for neuromagnetic detector arrays

    Publication Year: 1993 , Page(s): 859 - 869
    Cited by:  Papers (7)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (933 KB)  

    The sampling theorem for wave-number-limited multivariable functions is applied to the problem of neuromagnetic field mapping. The wave-number spectrum and other relevant properties of these fields are estimated. A theory is derived for reconstructing neuromagnetic fields from measurements using sensor arrays which sample either the field component B z perpendicular to the planar grid of measurement points, or the two components partial B z/partial x and partial B z/partial y of its gradient in the xy plane. The maximum sensor spacing consistent with a unique reconstruction is determined for both cases. It is shown that, when two orthogonal components of the gradient are measured at every site of the measurement grid, the density of these sensor-pair units can be reduced, without risk of aliasing, to half of what is necessary for single-channel sensors in an array sampling B z alone. Thus the planar and axial gradiometer arrays are equivalent in the sampling sense provided that the number of independent measurements per unit area is equal. View full abstract»

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  • Nonlinear analysis of the hippocampal subfields of CA1 and the dentate gyrus

    Publication Year: 1993 , Page(s): 870 - 876
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The authors discuss the use of nonlinear bispectral analysis in examining the hippocampal EEG collected at subfields of CA1 and the dentate gyrus during the vigilance state of rapid-eye-movement (REM) sleep. The cross-bispectrum and its unique capabilities of detecting and quantifying quadratic nonlinear interactions occurring between these two hippocampal subfields are explained and demonstrated with simulation examples and EEG data. It was found that quadratic nonlinear interactions exist between CA1 and the dentate gyrus in the 6-8 frequency band which dominates the theta ( theta ) rhythm observed in the hippocampal EEG during REM sleep. As a result, energy components around the frequency band of the second-order harmonics of theta rhythm are not totally spontaneous, but generated largely due to quadratic nonlinear interactions. View full abstract»

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  • ECG compression using long-term prediction

    Publication Year: 1993 , Page(s): 877 - 885
    Cited by:  Papers (58)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (646 KB)  

    A new algorithm for ECG signal compression is introduced. The compression system is based on the subautoregression (SAR) model, known also as the long-term prediction (LTP) model. The periodicity of the ECG signal is employed in order to further reduce redundancy, thus yielding high compression ratios. The suggested algorithm was evaluated using an in-house database. Very low bit rates on the order of 70 b/s are achieved with a relatively low reconstruction error (percent RMS difference-PRD) of less than 10%. The algorithm was compared, using the same database, with the conventional linear prediction (short-term prediction-STP) method, and was found superior at any bit rate. The suggested algorithm can be considered a generalization of the recently published average beat subtraction method. View full abstract»

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  • A feedback control system for real-time formant estimation. I. Static and dynamic analysis for sinusoidal input signals

    Publication Year: 1993 , Page(s): 886 - 891
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (473 KB)  

    A scheme suitable for the real-time estimation of formant frequencies is presented. Formant tracking is based on a feedback technique which uses both the amplitude and phase characteristics of two stagger-tuned bandpass filters to give an improved dynamic behavior. The implementation of the system requires a small number of components, and is practical for low-power applications. An analysis of the static and dynamic behavior is given for sinusoidal input signals. The transient response is independent of the amplitude level of the input signal. The system is designed for second formant detection in a cochlear prosthesis system. View full abstract»

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  • A feedback control system for real-time formant estimation. II. Analysis of a hysteresis effect and F2 estimation

    Publication Year: 1993 , Page(s): 892 - 898
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (523 KB)  

    For pt.I see ibid., vol.40, no.9, pp.886-91 (1993). The feedback control system behavior is analyzed for an input signal composed of two sinusoids. If the frequency difference between the two input spectral lines is sufficiently great and the amplitude ratio is within certain limits, a hysteresis effect occurs. Then the system shows a tendency to select one of the two input spectral lines. The existence of the second line has only little influence on the accuracy of the detection of the selected line. From the analysis, conclusions of the system behavior regarding formant estimation can be drawn. A design example for second formant detection is simulated and compared with the results obtained by simulation of a zero-crossing system for F2 estimation and linear predictive coding (LPC) analysis. View full abstract»

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  • The response of a spherical heart to a uniform electric field: a bidomain analysis of cardiac stimulation

    Publication Year: 1993 , Page(s): 899 - 908
    Cited by:  Papers (30)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (769 KB)  

    A mathematical model describing electrical stimulation of the heart is developed, in which a uniform electric field is applied to a spherical shell of cardiac tissue. The electrical properties of the tissue are characterized using the bidomain model. Analytical expressions for the induced transmembrane potential are derived for the cases of equal anisotropy ratios in the intracellular and interstitial (extracellular) spaces, and no transverse coupling between fibers. Numerical calculations of the transmembrane potential are also performed using realistic electrical conductivities. The model illustrates several mechanisms for polarization of the cell membrane, which can be divided into two categories, depending on if they polarize fibers at the heart surface only or if they polarize fibers both at the surface and within the bulk of the tissue. The latter mechanisms can be classified further according to whether they originate from continuous or discrete properties of cardiac tissue. View full abstract»

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  • Frequency domain dipole localization: extensions of the method and applications to auditory and visual evoked potentials

    Publication Year: 1993 , Page(s): 909 - 918
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    A statistical frequency domain approach to localizing equivalent dipole generators of human brain evoked potentials is described. The frequency domain representation allows considerable data reduction, constrains the magnitude function of the dipoles to be smooth, and accounts for the statistical properties of the background EEG. A general model in which dipole orientation can vary over time, and which includes multiple dipole generators is considered. The varying orientation model has the practical advantage of being more nearly linear and more flexible than a fixed orientation model, which facilitates convergence of the iterative fitting algorithm. A measure of goodness-of-fit that compares the likelihood of the dipole model with the likelihoods of saturated and null models is suggested. The results of fitting the model report recorded auditory and visual evoked potentials are reported. A single dipole with fixed orientation seems to be an adequate model of the auditory midlatency response, while two dipoles with varying orientation are needed to fit the later P200 component. Analysis of the visual P100 response to unilateral stimulation localized a generator in the contralateral occipital cortex, as expected from anatomical considerations. View full abstract»

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  • Relationship between dipole parameter estimation errors and measurement conditions in magnetoencephalography

    Publication Year: 1993 , Page(s): 919 - 924
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (477 KB)  

    In this study, a model in a computer simulation uses a single current dipole in a spherical homogeneous medium. Dipole parameters are estimated using a moving dipole procedure. Signal-to-noise ratio (SNR) is defined as the square-root of the ratio of the average signal power to the average noise power over all measurement points. At SNR>20, accurate estimation can be carried out independently of dipole depth and coil size. At SNR<20, dipole depth influences estimation error. When the dipole is located near the center of the sphere, the measurement region should include both extrema of the magnetic field to minimize estimation error. However, when the dipole is not so deep, the position of the measurement region does not influence estimation error. When SNR<4, estimation error increases as coil size increases. Coil size minimizing estimation error is determined by the ratio of environmental magnetic field noise to electrical noise. For a constant size of measurement region, increasing the number of measurement points decreases estimation error to a certain level. This error level depends on SNR. View full abstract»

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  • SAR distributions in interstitial microwave antenna arrays with a single dipole displacement

    Publication Year: 1993 , Page(s): 925 - 932
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (613 KB)  

    The use of interstitial microwave antenna array hyperthermia (IMAAH) as a treatment for cancer, in conjunction with radiation therapy and chemotherapy, has been investigated widely. The heating pattern produced by a coherently phased 915 MHz asymmetric antenna array displays the maximum power deposition in the array center. The authors report on the effect of variable insertion depth between antennas of an array on the heating patterns produced. The study of this heating behavior demonstrates a similar effect to that of the variably phased arrays, showing a shift of the heating peak towards the periphery of the tumor, offering a more simple method for the clinical treatment of such tumors. View full abstract»

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  • Finite element computations of specific absorption rates in anatomically conforming full-body models for hyperthermia treatment analysis

    Publication Year: 1993 , Page(s): 933 - 945
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1193 KB)  

    The formulations used center on Helmholtz weak forms which have been shown to be numerically robust and to afford additional sparsity in the resulting system of algebraic equations. Practical solution of these equations depends critically on the realization of an effective sparse matrix solver. Experience with several conjugate gradient-type methods is reported. The findings show that convergence rate (and even convergence in some cases) degrades significantly with increasing matrix rank and decreasing electrical loss for mesh spacings which adequately resolve the physical wavelengths of the electromagnetic wave propagation. However, with proper choice of algorithm and preconditioning, reliable convergence has been achieved for matrix ranks exceeding 2*10 5 on domains having sizeable volumes of electrically lossless regions. An automatic grid generation scheme for constructing meshes which consist of variable element sizes that conform to a predefined set of boundaries is discussed. View full abstract»

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  • Analysis and optimization of waveguide multiapplicator hyperthermia systems

    Publication Year: 1993 , Page(s): 946 - 952
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (562 KB)  

    A method is proposed for determining the excitation coefficients of an antenna array operating in a large rectangular waveguide and used as a hyperthermia system. The excitation coefficients of the array elements are optimized for attaining an improved specific absorption rate (SAR) distribution around a deep-seated tumor. The method is applied to a two-dimensional problem of a piecewise homogeneous post in a waveguide representing a section of the human torso. The array is operating below the cutoff frequency of the dominant mode of the waveguide. Numerical simulations have been performed to check the effectiveness of this approach. The results show that by using the proposed optimization method, SAR distributions can be improved. View full abstract»

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  • Cyclic variation of the power of ultrasonic Doppler signals backscattered by polystyrene microspheres and porcine erythrocyte suspensions

    Publication Year: 1993 , Page(s): 953 - 962
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (933 KB)  

    Factors affecting the power of the ultrasonic Doppler signal within the flow cycle have been evaluated experimentally using a pulsatile flow loop model. Polystyrene microspheres and porcine red cells suspended in saline solution for hematocrits between 2 and 40% were used as scattering fluid in the flow model. Experiments were performed at mean flow velocities of 11, 64, and 76 cm/s. In laminar flow experiments performed at a mean velocity of 11 cm/s, no variation of the Doppler power was found for both polystyrene microspheres and red cell suspensions (40% hematocrit). When turbulence was induced in the flow model, the power increasing during systole, a maximum was observed early after peak systole, and a decrease was obtained in diastole during deceleration of flow. View full abstract»

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  • Development of a piezopolymer pressure sensor for a portable fetal heart rate monitor

    Publication Year: 1993 , Page(s): 963 - 969
    Cited by:  Papers (20)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (677 KB)  

    A piezopolymer pressure sensor has been developed for service in a portable fetal heart rate monitor, which will permit an expectant mother to perform the fetal nonstress test, a standard predelivery test, in her home. Several sensors are mounted in an array on a belt worn by the mother. The sensor design conforms to the distinctive features of the fetal heart tone, namely, the acoustic signature, frequency spectrum, signal amplitude, and localization. The components of a sensor serve to fulfill five functions: signal detection, acceleration cancellation, acoustical isolation, electrical shielding, and electrical isolation of the mother. A theoretical analysis of the sensor response yields a numerical value for the sensor sensitivity, which is compared to experiment in an in vitro sensor calibration. Finally, an in vivo test on patients within the last six weeks of term reveals that nonstress test recordings from the acoustic monitor compare well with those obtained from conventional ultrasound. View full abstract»

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  • A parametric modeling of ionic channel current fluctuations using third-order statistics and its application to estimation of the kinetic parameters of single ionic channels

    Publication Year: 1993 , Page(s): 970 - 980
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (700 KB)  

    The case where third-order cumulants of stationary ionic-channel current fluctuations (SICFs) are nonzero, and where SICFs are corrupted by an unobservable additive colored Gaussian noise that is independent of SICFs is considered. First, a virtual synthesizer that yields an output whose third-order cumulants are equivalent to those of SICFs on a specific slice is constructed. The synthesizer output is expressed by the sum of N s-1 first-order differential equation systems, where N s denotes the number of states of single ionic channels. Next, discretizing the synthesizer output, a discrete autoregressive (AR(N s-1)) process driven by the sum of N s-1 moving average (MA(N s-2)) processes is derived. Then the AR coefficients are explicitly related to the kinetic parameters of single ionic channels, implying that the kinetic parameters can be estimated by identifying the autoregressive moving-average coefficients using the third-order cumulants. In order to assess the validity of the proposed modeling and the accuracy of parameter estimates, Monte Carlo simulation is carried out in which the closed-open and closed-open-blocked schemes are treated as specific examples. View full abstract»

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  • On-line estimation of myoelectric signal spectral parameters and nonstationarities detection

    Publication Year: 1993 , Page(s): 981 - 985
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    A method for detecting nonstationarities of random time series with an approximately Gaussian distribution of amplitudes is presented. This method is suitable for real time implementation. Some results obtained by applying them to a time series of spectral parameters of surface myoelectric signals are reported. The computerized system used to implement the detector of nonstationarity is described. This system realizes on-line estimation and display of spectral parameters, as well as detection of their nonstationarities, featuring a sampling frequency up to 20 k samples/s. A user friendly interface, fully menu driven, allows the user to select different options during the system's operation by means of hot keys. The accuracy of the system was tested by comparing its estimates with those of an off-line system, previously characterized. The estimates of spectral parameters obtained by means of the two systems were always consistent. The on-line stationarity detector was able to recognize rates of variation of the spectral parameters as small as 1% during contractions lasting 10-15 s. This sensitivity makes it suitable for clinical application. View full abstract»

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  • Statistical discriminant analysis of arrhythmias using intracardial electrograms

    Publication Year: 1993 , Page(s): 985 - 989
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (355 KB)  

    The problem of classifying ventricular arrhythmias from intracardial electrograms is considered. Standard statistical discrimination procedures are applied using a simple parametric model for the shape of the pulse near its peak. This approach makes simultaneous use of the model parameters, has well known statistical properties, and involves computations that can be carried out efficiently. Preliminary analyses of real data sets, using both linear and quadratic discrimination functions, yield promising results. View full abstract»

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  • An example of thermometry in volume by microwave radiometry

    Publication Year: 1993 , Page(s): 990 - 992
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB)  

    A method of determination of the size D depth z and temperature T0+ Delta T of a cylindrical thermal structure embedded in an homogeneous lossy material, in the present case, water, is presented. A microwave radiometric image at 3 GHz points out the location of the thermal structure; its threshold provides the diameter D of the structure. The depth z derives from the ratio of the maximal radiometric intensities at 1.5 and 3 GHz. The combination of D, z and of the radiometric intensities gives Delta T. View full abstract»

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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