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Biomedical Engineering, IEEE Transactions on

Issue 9 • Date Sept. 1991

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Displaying Results 1 - 14 of 14
  • Frequency analysis of the electrocardiogram with maximum entropy method for identification of patients with sustained ventricular tachycardia

    Publication Year: 1991 , Page(s): 821 - 826
    Cited by:  Papers (14)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (571 KB)  

    The authors developed frequency analysis using the maximum entropy method (MEM) based on an autoregressive (AR) model. Orthogonal electrocardiograms were recorded from the body surface of patients with and without VT (ventricular tachycardia), and healthy persons after low noise, high-gain amplification. Multiple 40 ms segments (time intervals 2 ms, AR-parameters tapered) were analyzed (spectrotemporal mapping). Low-frequency components were eliminated by building different spectra with optimal high order and fixed low order. The MEM-spectra revealed high frequency components (40-200 Hz) in the terminal phase of the QRS-complex and in the ST-section in 26/38 patients with VT, but only in 2/20 without VT and in 1/20 healthy persons (p<0.05). Unlike FFT, MEM allowed localization of late potentials by the analysis of short data segments. View full abstract»

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  • Optimal a posteriori time domain filter for average evoked potentials

    Publication Year: 1991 , Page(s): 827 - 833
    Cited by:  Papers (4)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (603 KB)  

    For evoked potentials measured with scalp electrodes, the common procedure to determine the signal is to average N repetitive measurements, allowing signal detection to be improved. An algorithm that estimates the signal autocorrelation from N measurements is proposed. The estimator is consistent and unbiased, and its variance tends to zero as O(N). Two filters that are applied to the average response are introduced. Both depend on the estimation of the signal and the noise autocorrelations. One is based on the assumption that the average response is a stationary process. For the second, coefficients are obtained by minimizing the mean squared error (MSE) of an optimal filter of a nonstationary process applied on a single sweep. When a small number of sweeps are averaged the stationary assumption is adequate, and the MSE of the stationary optimal filter is two to five times less than the MSE of the average response. When a large number of measurements are considered the error in estimating the autocorrelations decreases. In this case applying the optimal filter for a nonstationary process leads to a significant improvement in the signal estimation. View full abstract»

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  • Nonlinear system identification by m-pulse sequences: application to brainstem auditory evoked responses

    Publication Year: 1991 , Page(s): 834 - 845
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (882 KB)  

    A method is introduced for characterizing the nonlinear behavior of the auditory system. The method uses an m-pulse sequence as the stimulus and uses a general nonlinear framework for the auditory system. Like E.E. Sutter's (1987) binary m-sequence approach, the m-pulse sequence approach is computationally efficient since calculation of the first-order input-output cross-correlation function is all that is necessary for obtaining the nonlinear characteristics of the system. The nonlinear system characteristics are reflected in pulse kernels in contrast to binary kernels associated with the binary m-sequence approach. By assuming the system under study is a third-order nonlinear system, binary and pulse kernels are shown to be related to Volterra kernels. The results suggest that the m-pulse sequence can be used to study the system nonlinear effects of varying the stimulus repetition rate more effectively then conventional methods. Preliminary physiological data obtained by applying m-pulse sequences to the brainstem auditory evoked responses (BAER) clearly illustrate the feasibility of obtaining replicable evoked response using this method. View full abstract»

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  • Information contained in sensory nerve recordings made with intrafascicular electrodes

    Publication Year: 1991 , Page(s): 846 - 850
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    Multiunit recordings were made in anesthetized cats with chronically implanted intrafascicular electrodes over a period of six months. Neural signals recorded with these electrodes consisted of activity in sensory fibers innervating a variety of cutaneous mechanoreceptors. Mechanical stimuli were used to selectively activate individual nerve fibers, and the receptive field and receptor type were identified for each unit. Over a period of six months, there was a net shift in the recorded population, but the electrodes contained to provide a representative sample of the activity in the fascicle as a whole. The total number of units from which activity could be recorded remained roughly constant with time, and individual units persisted in the recordings for up to six months. These results indicate that intrafascicular electrodes could be used to sample information carried by individual somatosensory fibers on a long term basis. View full abstract»

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  • Influence of tissue inhomogeneities on noninvasive muscle fiber conduction velocity measurements-investigated by physical and numerical modeling

    Publication Year: 1991 , Page(s): 851 - 860
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (860 KB)  

    The hypothesis that the observed fluctuations in propagation velocity are caused by electrically inhomogeneous tissue, regions of different electrical conductivity which are located between the excited muscle fibers and the recording electrodes and which cause a deformation of the extracellular electric current field, was examined. The investigation was performed by means of a physical model as well as by finite element model calculations. In both models single, simple shaped (cylindrical) inhomogeneity regions with a conductivity of 0.1 to 10 times that of the surrounding medium and diameters ranging between 1.6 and 2.7 mm were placed between excitation sources and recording site. The results indicate that the observed conduction velocity fluctuations of up to some 10% can be attributed to inhomogeneity effects of the tissue conductivity. View full abstract»

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  • Computer-aided design of two dimensional electric-type hyperthermia applicators using the finite-difference time-domain method

    Publication Year: 1991 , Page(s): 861 - 870
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (887 KB)  

    The fundamental limitations of 2-D electric-field-type applicators with heterogeneous tissue distributions are studied using the finite-different time-domain (FDTD) techinque configured as a hyperthermia applicator design tool. This design tool allows the designer to investigate ideas much more rapidly than could be done experimentally. The technique is described and the fundamental limitations of E-field applicators, including an unsuspected capacitive-coupling mode found in some electric dipole configurations is explained. The results of a numerical study of E applicators are summarized, and the utility of the FDTD technique as an applicator design tool is demonstrated. View full abstract»

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  • Eccentric spheres models of the head

    Publication Year: 1991 , Page(s): 871 - 878
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    Equations are derived for electric potentials (electroencephalograms) and magnetic fields (magnetoencephalograms) produced by dipolar sources in three eccentric spheres models of the head. In these models, the thickness of the layer representing the skull varies around the model, the thickness of the scalp layer varies, and the electrical conductivity of an eccentric spherical bubble in the brain region varies. Using these equations, it was found that variations in these features of the models have at most only small effects on the general spatial patterns of the electric potentials and the radial component of the magnetic fields. However, some significant effects on the amplitudes were found. The effects of the variations in the skull and scalp layer thicknesses on the field amplitudes were found to be significantly smaller than on the potential amplitudes. The effects on the field amplitudes of the variations in the bubble conductivity were found to be only somewhat smaller than on the potential amplitudes. The effects of variations in these features of the models on source localization accuracy were significantly smaller for inverse solutions using fields than for solutions using potentials. View full abstract»

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  • A model for the cortico-cortical neural interaction in multisensory-evoked potentials

    Publication Year: 1991 , Page(s): 879 - 890
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (767 KB)  

    The authors address the methodological problem of enhancing selective responses from the central nervous system when two (or more) different sensorial stimuli are simultaneously presented to the subject. In particular, contemporaneous visual and somato-sensory stimulation is considered and a model of signal and noise interaction is developed for the processing of the evoked responses. An ARXX (autoregressive with two exogenous inputs) parametric model is introduced and a least squares algorithm is used to determine the selective response of the two neural systems from the overall evoked response. Such an analysis may be also carried out on a sweep-by-sweep basis. Applications of this method are (1) modeling of multisensory potentials; (2) description of facilitation or defacilitation phenomena in multitasking experiments; and (3) analysis of cortico-cortical neural interactions. View full abstract»

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  • A control method for a nonlinear multivariable system: application to interstitial laser hyperthermia

    Publication Year: 1991 , Page(s): 891 - 898
    Cited by:  Papers (3)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (657 KB)  

    An original adaptive control method is presented for controlling a nonlinear multivariable system. The method, a modified quasi-linear approach, involves dividing the source excitation into a series of pulsing rounds and is implemented as a control algorithm on a computer. The theory underlying the method is developed with reference to an application involving temperature control in interstitial laser hyperthermia. The method is both successful and necessary to achieve optimally uniform elevated temperatures in a ground beef phantom. Apart from variable and parameter definitions, the method is otherwise general and might be useful for controlling a nonlinear system in which no prior exact characterization of the system is possible. Simulations were conducted to assess the effectiveness of the method in systems for which the unit excitation response changes by factors ranging from zero to three over the total period of excitation. In each case the method has proven stable. View full abstract»

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  • Goniometric motion controller for the superconducting coil in a magnetic stereotaxis system

    Publication Year: 1991 , Page(s): 899 - 905
    Cited by:  Papers (9)  |  Patents (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1069 KB)  

    For the purpose of positioning the 80 kg, 2 T superconducting coil/cryostat used in the development version of a magnetic stereotaxis system, a four degree-of-freedom goniometer has been designed, built, and tested. Computer-controlled, stepping motor actuators enable movement of the coil via either joystick, keyboard, or translator-module keypad commands. An integral arrangement of counterweights and counterbalances minimizes the overall weight and size of the goniometer while maintaining static and dynamic stability during operation. As much of the structure as possible has been made of nonmagnetic materials (mostly aluminium) to minimize distortion of the superconducting coil's field. The design principles for the goniometer, the essential features of its construction, and its performance characteristics and limitations are discussed, along with a strategy for performing precision magnetic stereotaxis procedures with an arrangement of static superconducting coils. View full abstract»

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  • A quantitative analysis of pendular motion of the lower leg in spastic human subjects

    Publication Year: 1991 , Page(s): 906 - 918
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1098 KB)  

    Gravity-induced oscillations of the lower leg in normal and spastic subjects were examined with a view towards evaluating a clinical test of spasticity called the pendulum test. For passive limb motion (in which no reflex excitation occurred), a second-order linear model did not provide an adequate description of the motion for either spastic or normal legs. System equations including nonlinear mechanical properties simulating asymmetries in the swing and amplitude dependent variations in stiffness and damping provided a more accurate description. For spastic limb motion (in which reflex excitation did occur) accurate simulation required components accounting for abnormal reflex activation, coinciding with the time course of EMG activation. These included increased stiffness and damping with their gains related to reflex EMG magnitude, and changes in the rest length of the stiffness. Comparison of numerical with experimental data showed that the nonlinear model simulated the motion accurately, with the variance accounted for usually exceeding 90%. View full abstract»

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  • A low-cost fiber-optic strain gage system for biological applications

    Publication Year: 1991 , Page(s): 919 - 924
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    A novel low-cost strain measurement system has been developed for the mechanical testing of biological soft tissues. The technique creates four spots of light on a tissue sample surface by piercing the tissue sample with two pairs of small light-conducting optical fibers (one pair for each axis of a biaxial stretch), terminated by high intensity infrared emitters. A large-area photodiode, located below the tissue sample, detects the light emitted from the two pairs of light-spots. Analog and digital circuitry analyze the current signal from the photodiode to determine the position of a light-spot in real time. Each infrared emitter is sequentially cycled 'on' at a rate of 3 kHz and the resulting photodiode current signal, after being converted to a voltage signal, is held by an integrated circuit sample and hold amplifier. Analog differencing of pairs of light-spot voltage signals provides a final output proportional to the separation between coaxial light-spots. View full abstract»

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  • A water-cooled EM applicator radiating in a phantom equivalent tissue-experiments and numerical analysis

    Publication Year: 1991 , Page(s): 924 - 928
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    A prototype of a water-cooled electromagnetic applicator for intracavitary hyperthermia has been tested. The temperature distributions produced in a polyacrylamide dissipative medium have been shown using liquid crystals. It is shown that a complete electromagnetic and heat transfer model can predict the experimental temperatures. View full abstract»

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  • Laser Doppler velocimetry stabilized in one dimension

    Publication Year: 1991 , Page(s): 928 - 930
    Cited by:  Papers (1)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    Routine use of LDV for measurement of retinal hemodynamics has proven difficult. One reason is the susceptibility of the measurement to eye movement. Valid data are often distributed among data obtained while the beam is decentered or completely off the vessel. One remedy is to develop complex rejection criteria in an effort to circumvent the problem. The authors discuss a more direct solution, the stabilization of the incident laser beam on the target retinal vessel. A valid measurement of V max corresponds to measuring the fastest component of flow; even slight decentering of the beam can bias the measurement of V max to smaller values. Stabilization of the beam on the vessel center provides a more reliable measure of V max. 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