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Biomedical Engineering, IEEE Transactions on

Issue 10 • Date Oct. 1988

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Displaying Results 1 - 18 of 18
  • The inverse problem in electroneurography. I. Conceptual basis and mathematical formulation

    Page(s): 769 - 777
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    A mathematical technique for the analysis of the compound action potential (CAP) of a peripheral nerve is presented. The procedure deals with the estimation of the number of active fibers contributing to the CAP and the distribution of their conduction velocities. The CAP is described as a filtered Poisson process, the (time-varying) filter representing the single-fiber action potential waveshapes. The estimation procedure consists of two parts. The first part, related to the fast conducting fibers contributing to the CAP main complex, uses least-squares optimization techniques for the reconstruction of the CAP waveshape. The second part, applying to the small late components of the CAP due to slowly conducting fibres, explicitly uses the Poisson process formulism and is based on reconstructing the energy for variance in the CAP. View full abstract»

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  • The inverse problem in electroneurography. II. Computational aspects and evaluation using simulated data

    Page(s): 778 - 788
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    (For pt.1 see ibid., vol.35, no.10, p.769-77, 1988). Theoretical concepts of a technique for the estimation of fiber velocity distributions from compound nerve action potentials are illustrated using simulated compound action potential (CAP) data. After a concise summary of the estimation formalism, the numerical implementation of the procedure is given followed by the elaboration of a number of aspects of a practical nature. It is shown that reliable estimates of both fast and slow fiber distributions can be derived. The sensitivity of the procedure to various possible error sources is investigated. It is seen that many factors can be dealt with, properly including recording noise and incorrect determination of recording distance. Possible branching of the nerve can also be traced. A correct description of the amplitude and the waveshape of the single-fiber action potentials appears to be the most critical factor in a practical application. View full abstract»

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  • Temporal characterization of myoelectric spectral moments changes: analysis of common parameters

    Page(s): 789 - 797
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    To investigate the validity of common spectral shift parameterizations, two closely related studies were conducted. Simple linear and exponential regression models were applied to the time-series myoelectric mean power frequency and median power frequency data of two normal subjects as well as a single subject over multiple trials. Statistical analyses were applied to test the hypothesis that no significant differences in extracted features (measurands) exist between different epochs of spectral parameter data. Statistically significant differences were found to exist in both studies, implying that the trial duration can significantly influence the obtained measurement values, and that neither linear nor simple exponential regression models adequately characterize the time-dependent changes. It is concluded that parameterization techniques based on statistical curve-fitting strategies should be supplemented with physiologic models to gain insight into the functional nature of the time dependency. Results are discussed in this context. View full abstract»

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  • Noninvasive pulse oximetry utilizing skin reflectance photoplethysmography

    Page(s): 798 - 805
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    The major concern in developing a sensor for reflectance pulse oximetry is the ability to measure large and stable photoplethysmograms from light which is backscattered from the skin. Utilizing a prototype optical reflectance sensor, locally heating the skin is shown to increase the pulsatile component of the reflected photoplethysmograms. Additional improvements to signal-to-noise ratio were achieved by increasing the active area of the photodetector and optimizing the separation distance between the light source and photodetector. The results from a series of in vivo studies to evaluate a prototype skin-reflectance pulse oximeter in humans are presented. View full abstract»

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  • A totally automated system for the detection and classification of neural spikes

    Page(s): 806 - 816
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    A system for neural spike detection and classification is presented which does not require a priori assumptions about spike shape or timing. The system is divided into two parts: a learning subsystem and a real-time detection and classification subsystem. The learning subsystem, comprising of feature learning phase and a template learning phase, extracts templates for each separate spike class. The real-time detection and classification subsystems identifies spikes in the noisy neural trace and sorts them into classes, based on the templates and the statistics of the background noise. Comparisons are made among three different schemes for the real-time detection and classification subsystem. Performance of the system is illustrated by using it to classify spikes in segments of neural activity recorded from monkey motor cortex and from guinea pig and ferret auditory cortexes. View full abstract»

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  • Evaluation of digital unsharp masking and local contrast stretching as applied to chest radiographs

    Page(s): 817 - 827
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    The first six digital radiographs of the human chest generated by the Diode Array Digital Radiography scanner of the University of Pittsburg have been evaluated using a statistically designed experiment to study image-processing methods for displaying different anatomical landmarks. Linear and nonlinear unsharp masking and local contrast stretching were used. The experimental procedure, statistical analysis of the data obtained, and the results obtained are described and discussed. View full abstract»

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  • An electric current tomograph

    Page(s): 828 - 833
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    A description is given of an instrument designed to acquire data for the construction of images of internal body structures based on measurements of electrical impedance made from a set of electrodes applied around the periphery of the body. The instrument applies currents at 15 kHz in any desired pattern to 32 electrodes and measures the resulting voltage at each electrode. The construction of a test phantom is also described and the results of initial studies showing the distinguishability of targets of differing sizes and conductivities placed in the phantom are reported. The system is able to distinguish the presence of 9-mm-diameter insulators or conductors placed in the center of a 30-cm-diameter circular tank of salt water. This system is capable of implementing an adaptive process of produce the best currents to distinguish the unknown conductivity from a homogeneous conductivity. View full abstract»

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  • Three-dimensional Doppler velocimetry of flow jets

    Page(s): 834 - 841
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    A closed-form solution is derived of the Doppler equation for the magnitude and angle to the three-dimensional velocity vector. The resultant solution is more general than previous formulations and, since it is based on multiple conventional transmit-receive Doppler probes, it can be readily applied by adapting existing Doppler units. Turntable experiments demonstrated that the three-dimensional angle-independent theory correctly predicted velocity within average 32% over a 26. degrees -range of Doppler angles. Experiments with a flow phantom showed general agreement with the angle-independent theory in the more demanding setting of an actual flow stream. Experiments utilizing a jet stream which modeled the clinically important conditions that exist in stenotic vessels, valvular abnormalities, and septal defects within 1.4-3.8% of the actual velocity, over an 18 degrees range of Doppler angles. View full abstract»

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  • Multispectral imaging of burn wounds: a new clinical instrument for evaluating burn depth

    Page(s): 842 - 850
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    A real-time video imaging system called the imaging burn depth indicator (IBDI) is described; IBDI can discriminate areas of burn wounds expected to heal in three weeks or less from the day of injury from those areas not expected to heal in that time period. The analysis can be performed on or about the third day postburn on debrided burn wounds. The relative diffuse reflectivity of the burn-wound is measured in the red, green, and near-infrared wavelength bands and an algorithm established previously is used to translate this optical data into burn healing probabilities. Over 100 burn wound sites were studied. Burn sites were evaluated on day three postburn by the IBDI and by the attending physician. Overall, the IBDI was found to be more accurate in predicting burn healing than were the attending physicians. View full abstract»

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  • SAR distributions for 915 MHz interstitial microwave antennas used in hyperthermia for cancer therapy

    Page(s): 851 - 857
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    Theoretical and experimental specific absorption rate (SAR) distributions are presented for single insulated antennas operating at 915 MHz in muscle phantom; the SAR is deduced from measured temperature rise. Results show that dipoles with lengths much shorter than their resonant length have a characteristically large reactive input impedance component and a substantially smaller absolute SAR magnitude than resonant dipoles. All cases investigated demonstrate that the maximum SAR occurs near the junction, regardless of insertion depth. Experimental results show that an antenna with the tip section equal to a quarter-wavelength and the insertion depth equal to a half-wavelength achieves a substantial increase in the longitudinal power distribution compared to other antenna designs that were evaluated. View full abstract»

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  • Identification of human postural dynamics

    Page(s): 858 - 869
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    Human postural dynamics was investigated for six healthy subjects using a force platform recording body sway induced by vibrators attached to the calf muscles. The model of body mechanics adopted was that of an inverted pendulum, the dynamics of postural control being assumed to be reflected in the stabilizing forces exerted on the platform by the feet as a result of complex muscular activity subject to state feedback of body sway and position. The approach to signal processing has been that of parametric identification of a transfer function representing the stabilized inverted pendulum. Posture control was quantified in three variables: swiftness, stiffness, and damping. It is shown that the identification fulfils ordinary statistical validation criteria, and it is conjectured that the state feedback parameters identified are suitable for use in assessing ability to maintain posture. View full abstract»

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  • In vitro life tests of Faradaic neural stimulation electrodes at high current densities

    Page(s): 870 - 874
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    Membrane-coated Ag/AgCl, uncoated iridium, and membrane-coated iridium electrodes were pulsed with typical neural stimulation waveforms in vitro in 0.13-M NaCl. Life tests were made at various current densities for periods of time up to 2000 h. Iridium electrodes performed successfully at higher current densities that smooth platinum, but membrane-coated Ag/AgCl was no better than platinum. Shape change appears to limit the life of both iridium and Ag/AgCl electrodes at high current densities and charge densities. View full abstract»

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  • A real-time multiprocessor system for acquisition of multichannel neural data

    Page(s): 875 - 877
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    A neural workstation is described which is composed of a host computer and two peripheral action potential detection processors, each of which uses a TMS32010 digital signal processors to attain real-time action potential detection and classification. The host is freed to perform online analysis and display of the event data. The system's use is demonstrated with cockroach ventral nerve cord recordings. View full abstract»

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  • Sensor for measuring surface fluid conductivity in vivo

    Page(s): 877 - 881
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    Thin-film microelectronic technology was used to fabricate a miniature, flexible sensor that can be placed directly onto the surface of the airway to measure the electrical conductance of the fluids present. Gold was deposited on glass, oxidized silicon, and polyimide substrates. The parallel gold electrodes were etched into an interdigitated configuration that increased the effective sensing area without increasing the sensor size. A temperature-sensitive resistor was added to make calculations possible to account for the effect of temperature on fluid conductivity. Fluid conductivity was measured and from this information osmolarity was calculated. Physiologic evaluation of the device and corroboration of the calculations was obtained by placing the sensor in the airway of mongrel dogs and simultaneously collecting surface fluids for atomic absorption spectroscopy and freezing-point-depression analysis. Osmolarity calculations made from the sensor data were consistently about 25% lower than clinical laboratory osmolarity analysis. In vitro tests of the sensor included calibration in multiple dilute salt solutions, temperature sensitivity assessment, and evaluation of the effects of solution concentration on electrical conductance. View full abstract»

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  • Telemetry of human electrocardiograms in aerial and aquatic environments

    Page(s): 881 - 884
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    A technique for human electroencephalogram (ECG) telemetry that is equally useful on land and in water (i.e. amphibious ECG telemetry) with a single transmitter was developed. For the ECG on land, an electromagnetic wave of 79 MHz FM VHF was used, while for the ECG under water, a 77-kHz FM current was used. The VHF was received by an aerial of an FM radio and the current by two underwater antennas along course-marker ropes. When a subject jumped from a diving platform into the water, continuous recording of ECG signals was possible with only a short time disturbance of the signals due to change in posture of the subject before jumping. This indicates rapid switching from electromagnetic to conductive transmission. The ECGs on land and during surface or underwater swimming showed a clear difference in the QRS complex and T wave. View full abstract»

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  • Fast Hartley transforms for spectral analysis of ultrasound Doppler signals

    Page(s): 885 - 888
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    Spectral analysis of Doppler ultrasound is known to yield valuable information to assess the state of circulation in the peripheral blood vessels. In the past, the raw Doppler data have been directly input into a dedicated spectrum analyzer or transformed on a microcomputer using the fast Fourier transform (FFT) technique. In the present study, the first Hartley technique is used to transform on a microcomputer to the digitized Doppler data obtained from a normal common carotid artery is presented and the resulting spectra are compared to those obtained by using the Cooley-Tukey FFT algorithm. The Hartley transform has the advantages of being a purely real-numbered transform; therefore, for real Doppler data, it is not only more conceptually straightforward, but also requires less computer memory, is simpler to calculate, and is better suited to large-scale integration implementation. The raw Doppler data were input into a digital oscilloscope from the analog Doppler unit, digitized in real time with 12-b resolution, and displayed on the computer monitor. These data were then stored in a file, on floppy or hard disk, using software provided with the digitizing oscilloscope, and then transformed to the spectral domain using either transform technique. In this application, the transforms were performed using a compiled BASIC language. View full abstract»

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  • Instrumentation for quantitative assessment of intestinal viability

    Page(s): 888 - 892
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    The development of an instrumentation system to quantify the survivability of ischemic intestine is reported. The device is a second-generation effort intended to provide the surgeon with an instrument to give immediate information on the amount of ischemic bowel which will not survive and must be surgically resected. The instrument delivers a precisely-controlled electrical stimulus to a small segment of bowel measures the resulting evoked contractile response. This device, which is termed the electronic contractility meter, was evaluated in a series of preliminary experiments. The instrument consist of two main components: a measurement probe which attaches to the intestine and a signal processing/display module. The probe provides an electrode interface for the electrical stimulus as well as the transducer for the measurement of contractile response. The probe can be detached and gas-sterilized for reuse. The signal processing/display module produces a precisely-controlled electrical stimulus, detects and processes the probe contractility signals, and displays the results. View full abstract»

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  • A magneto-acoustic method for the noninvasive measurement of bioelectric currents

    Page(s): 892 - 894
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    A method for the noninvasive measurement of low-level ionically conducted electric currents flowing in electrolytes and tissue is investigated. Experiments show that the application of oscillating magnetic fields to current-carrying media will cause focal Lorentz forces which generate detectable vibrations. These vibrations can be sensitively and noninvasively detected by surface contact detectors and can be used to determine the magnitude of internal current flows. Microampere-level currents introduced in hamsters to simulate natural bioelectric currents have been sensitively detected by this approach. 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