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Biomedical Engineering, IEEE Transactions on

Issue 5 • Date May 1991

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Displaying Results 1 - 14 of 14
  • Impedance cardiography using band and regional electrodes in supine, sitting, and during exercise

    Page(s): 393 - 400
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    The electrical impedance and its first derivative (dZ/dt) were measured at 100 kHz on ten normal males in supine and sitting positions and during upright bicycle exercise in order to compare the contribution of regional electrodes to the standard band electrode signal and to evaluate the possible use of spot electrodes for stroke volume (SV) measurements. Simultaneous measurements were made from band electrodes placed around the neck and lower thorax and from spot electrodes which recorded signals from the neck, upper thorax, and lower thorax. The results showed that approximately equal parts of the dZ/dt waveform came front the neck and upper thorax with the lower thorax contribution small but providing important features of the band signal. Changing from supine to sitting showed percentage decreases of 35% and 46% for the band and neck signals, respectively, with an increase of 19% for the upper thorax signal. The percentage increases in SV with upright exercise were 34%, 52%, and 24% for the band, neck, and upper thorax signals, respectively. View full abstract»

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  • In vitro measurement and characterization of current density profiles produced by nonrecessed, simple recessed, and radially varying recessed stimulating electrodes

    Page(s): 401 - 408
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    Potential fields induced by nonrecessed, simple recessed and radially varying recessed electrode designs were measured in vitro. Comparison of experimental results with theoretical analyses substantiated the experimental measurement technique and emphasized the importance of considering both nonuniform charge injection and surface electrochemistry when designing implantable stimulating electrodes. Radially varying recesses produced uniform charge injection at the electrode surface and at the aperture-tissue interface. In general, the radially varying recessed electrodes provided a combination of uniform charge injection and flexibility in design and fabrication that warrants their incorporation into all appropriate planar stimulating electrode designs. View full abstract»

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  • The potential distribution generated by surface electrodes in inhomogeneous volume conductors of arbitrary shape

    Page(s): 409 - 417
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    The use of the boundary-element technique in the computation of the potential distribution within isotropic inhomogeneous volume conductors of arbitrary shape set up by current injected through surface electrodes is presented. The derived algorithm is validated by comparing its solution to analytical solutions in the case of a concentric bipolar electrode configuration on a homogeneous, spherical volume conductor. This problem is essentially a mixed boundary value problem. It is shown that approximations that involve treating this problem as a Neumann problem, which have recently appeared in the literature, are valid for remote field points only. Applications to the modeling of the field of cardiac defibrillation electrodes are presented. View full abstract»

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  • Prediction of magnetically induced electric fields in biological tissue

    Page(s): 418 - 422
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    Noninvasive magnetic stimulation of neurons in the brain can be realized by high-intensity rapidly changing magnetic fields. Attention is focused on the calculation of the induced electric fields commensurate with rapidly changing magnetic fields in biological tissue. The problem is not a true eddy current problem in that the magnetic fields induced do not influence the source fields. Two techniques are introduced for numerically predicting the fields, each employing a different gauge for the potentials used to represent the electric field. The first method employs a current vector potential and is best suited to two-dimensional (2-D) models. The second represents the electric field as the sum of a vector plus the gradient of a scalar field; because the vector can be determined quickly using the Biot-Savart rule (which for circular coils degenerates to an efficient evaluation employing elliptic integrals), the numerical model is a scalar problem even in the most complicated three-dimensional geometry. These two models are solved for the case of a circular current carrying coil near a conducting body with sharp corners. View full abstract»

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  • Finite-difference time-domain calculations of absorbed power in the ankle for 10-100 MHz plane wave exposure

    Page(s): 423 - 428
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    The authors present finite-difference time-domain (FDTD) calculations of the short-circuit current and the specific energy absorption rate (SAR) in the ankle. Plane wave exposures from 10 to 100 MHz for an adult, a 10-year old, and 5-year old are considered. The calculations are performed in two parts. First, the coupling between a homogeneous whole body phantom and the applied field is calculated. The region around a lower leg is then expanded, the leg being described by a realistic fine-scale heterogeneous model. Tangential electric field components from the first part are used as boundary conditions on the reduced domain of the second part. Electric field values based on a maximum SAR of 20 W kg -1 are presented. View full abstract»

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  • Recursive parameter identification of constrained systems: an application to electrically stimulated muscle

    Page(s): 429 - 442
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    A method of incorporating constraints on model parameters is developed. This method is applicable to most recursive parameter-identification algorithms. It enforces linear equality constraints on identified parameters. The use of this method for the real-time identification of autoregressive-moving-average time series models, subject to parameter constraints, is described. These constraints may be time varying. The use of this algorithm is demonstrated in the identification of electrically stimulated quadriceps muscles in paraplegic human subjects, using percutaneous intramuscular electrodes. The nonlinear steady-state force versus pulsewidth recruitment characteristic of the electrode-muscle system is identified simultaneously with the input-output muscle response dynamics, using a Hammerstein-type model. Knowledge of the recruitment curve's shape is translated into constraints on the identified parameters. This information improves the experimental predictive quality of the identified model. View full abstract»

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  • A method for evaluating the selectivity of electrodes implanted for nerve simulation

    Page(s): 443 - 449
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    The authors describe a method based on the compound action potential (CAP) that provides a precise measurement of the selectivity of an electrode array and yet is relatively simple to use. The method uses the refractory interaction of the CAPs elicited by a stimulus pulse pair, along with high-resolution recording of those potentials, to achieve measurements of the selectivity of stimulation down to the scale of a few axon diameters. The feasibility of this technique is demonstrated in sciatic nerves of frogs (Rana Catesbiana) acutely implanted with a sapphire electrode array. The high-resolution recording of the compound action potential provides a method for evaluating dense neurostimulation electrode arrays. The refractory interaction of these CAP responses provides a simple method for studying current spread and electrode interaction down to a spatial resolution of about 25 mu m, depending upon the particular nerve used. View full abstract»

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  • Air cooling for an interstitial microwave hyperthermia antenna: theory and experiment

    Page(s): 450 - 460
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    Microwave antennas are inserted through brachytherapy catheters implanted in a tumor to deliver interstitial hyperthermia cancer therapy. Theoretical calculations show that a cooling rate on the order of 0.1 W/cm length of catheter will significantly improve the radial uniformity of the temperature distribution of single antennas or arrays. Experiments and theoretical calculations show that air passing through the annulus between the antenna and the catheter at 10 L/min or less will produce such a cooling rate in a 2.2-mm OD catheter that has both ends accessible. To maintain uniformity of cooling rate along the catheter, it is better to control the cooling rate by preheating the air entering the catheter to 30-40 degrees C than it is to control the flow rate of room-temperature air. Ohmic heating of the antenna feedline does not confound the air cooling action significantly. View full abstract»

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  • A blind mobility aid modeled after echolocation of bats

    Page(s): 461 - 465
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    A new model of a mobility and for the blind was designed using a microprocessor and ultrasonic devices. This mobility and was evaluated based on psychophysical experiments. In this model, a downswept frequency-modulated (FM) ultrasound signal is emitted from a transmitting array with broad directional characteristics in order to detect obstacles. The ultrasound reflections from the obstacles are picked up by a two-channel receiver. The frequency of the emitted ultrasound is swept from 70 to 40 kHz within 1 ms, so it has almost the same characteristics as the ultrasound a bat produces for echolocation. The frequency of the reflected ultrasound wave is downconverted by about 50:1 by using a microcomputer with analog-to-digital and digital-to-analog converters. These audible waves are then presented binaurally through earphones. In this method obstacles may be perceived as localized sound images corresponding to the direction and the size of the obstacles. From the results of psychophysical experiments, it was found that downswept FM ultrasound was superior to other ultrasonic schemes for the recognition of small obstacles. With it a blind person can recognize a 1-mm-diameter wire. It was also proved that the blind could discriminate between several obstacles at the same time without any virtual images. This mobility aid is very effective at detecting small obstacles placed in front of the head. View full abstract»

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  • Magnetic search coil system for linear detection of three-dimensional angular movements

    Page(s): 466 - 475
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (882 KB)  

    The design of a two-dimensional magnetic field search coil system based on the extension of the phase detection principle for measuring the angular position and displacements of a search coil in three-dimensional space is described. The extended phase detection principle was implemented in a two-axis angular detector, which generates a spatially rotating magnetic field. The system was developed to record horizontal and vertical eye and head movements of small, unrestrained laboratory animals. It is also applicable for measuring 3-D eye and head movements in primates and man. The output is linear over 355 degrees in the horizontal plane and over +or-60 degrees in the vertical direction. The procedure of recording 3-D eye and head movements is discussed. View full abstract»

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  • Design and validation of the transparent oxygen sensor array

    Page(s): 476 - 482
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (685 KB)  

    A new oxygen monitoring system has been developed that consists of an array of transparent independently connected oxygen sensors mounted on a glass plate. This system is intended for continuous monitoring of oxygen at multiple locations on the surface of exteriorized tissues, while simultaneously visualizing microvascular activity. The sensor array is fabricated by techniques similar to those employed for semiconductors, which facilitate customization of sensor size and pattern to best monitor oxygen in a given physiologic preparation. Methods are described for characterizing the performance of the sensor array in vitro, including studies on the oxygen sensitivity stability of the signal, and detection of oxygen gradients. An example of in vivo application of the sensor array is also presented. View full abstract»

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  • Reconstruction of sequential cardiac in-plane displacement patterns on the chest wall by laser speckle interferometry

    Page(s): 483 - 489
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    Time-average speckle interferometry has been applied to obtain displacement patterns on the chest wall produced by cardiac action, in the absence of breathing, during various phases of the cardiac cycle. This has been achieved by an electronic shutter, controlled by the electrocardiogram of the subject. The recorded holographic plates processed under identical conditions are scanned by the pointwise method to obtain the absolute displacements at various locations corresponding to the activities of the various cardiac chambers and valves. These data are transformed to a 40*30 matrix by an interpolation method and, from this, three-dimensional displacement plots are reconstructed by an IBM PC/AT computer. These patterns show the displacements over the entire cardiac area corresponding to the activities of various regions during the cardiac cycle. The apex and aortic valve areas show the maximum displacements during the systolic phase. During the diastolic phase the activities over the low-pressure atrial regions are also observed. The results obtained outline the functional details of the normal heart and the activities over various areas are in agreement with those obtained by other noncontact techniques. View full abstract»

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  • A fast and simple algorithm for the calculation of convective heat transfer by large vessels in three-dimensional inhomogeneous tissues

    Page(s): 490 - 501
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    Three-dimensional anatomical data of tissues and vessel structures are decomposed into elementary cubic nodes by a special digitizing routine with vessels represented by connected strings of vessel nodes. Vessel cross sections may be irregularly shaped and/or tapered. Conductive and convective heat transfer was calculated through use of the heat balance technique on each cubic node, resulting in an explicit finite-difference computational scheme. Employing a three-time-level scheme, the Fourier stability criterion is circumvented allowing arbitrary time steps to be defined in the algorithm. Time steps as large as 100 times the Fourier restricted one still result in stable and convergent calculations of the stationary temperature distribution. Vessels with different flows and diameters are incorporated by performing a vessel-specific second discretization step in time. Using the new algorithm as a mathematical tool the thermal equilibration lengths of vessel segments have been established under a broad range of geometrical and flow conditions. Validation followed from comparing transient and stationary temperature distributions derived by the proposed algorithm to those from an accurate cylindrical numerical model. Predicted values for the thermal equilibration lengths are compared to an analytical expression and phantom experiments. View full abstract»

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  • A pseudomatched filter model applied to the transient system of human vision

    Page(s): 502 - 510
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    A pseudomatched filter configuration is presented as a model for the transient system of human visual perception. This model resembles the models proposed by W. Reichardt (1971) and C. Rashbass (1970), but the pseudomatched filter model is linear. The choice of the model is based on the shape of the psychophysically measured impulse response and on physiological and functional arguments. The parameters of the model are estimated for different data sets. The model was fitted to experimentally determined impulse responses of the transient channel of the visual system. In most cases the model's parameters were found, so a reasonable fit was obtained. It was found that under the same conditions (background level and field diameter) the estimated model was essentially the same for different subjects. Comparison of the results from the fits at different background levels showed that from the three parameters in the model only the angular frequency changed by more than the estimated standard deviation. It is shown that the model is in agreement with other psychophysical data. This is shown by predicting the threshold-versus-duration curve and the sensitivity to sinusoidal stimuli. The model's threshold-versus-duration curves agree well with the experimental data. 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