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Biomedical Engineering, IEEE Transactions on

Issue 7 • Date July 1993

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Displaying Results 1 - 13 of 13
  • A test for teratological effects of power frequency magnetic fields on chick embryos

    Page(s): 605 - 610
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    An analysis of thirteen studies of the teratological effects of pulsed magnetic fields on chick embryos from ten independent laboratories permits no clear conclusions. It is noted that comparatively little has been done to follow up on the reports by J. Juutilainen et al. (Rad. Environ. Biophys., vol.25, p.65-7, 1986) on the effects of extremely-low-frequency, sinusoidal magnetic fields on the malformation rate in chick embryos. An attempt to follow up on their results using similar but not identical exposures of 10- mu T, 50-Hz magnetic fields, which produced negative results, is reported. View full abstract»

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  • Multiple multipole method for simulating EM problems involving biological studies

    Page(s): 611 - 620
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    The three-dimensional implementation of the multiple multipole (MMP) method, based on the generalized multipole technique (GMT), is presented. Its performance in simulating electromagnetic problems involving biological bodies is analyzed. In particular, the step-by-step simulation technique and the built-in procedures to validate the solution on a numerical basis are discussed and demonstrated by two examples. A comparison is made with other numerical techniques often applied in this field. The advantages of the MMP method are shown to be in its validation capability, in its efficiency for smoothly shaped bodies and in the achievable accuracy, in particular near boundaries. The method is especially suited to handle high-gradient fields in the vicinity of biological bodies. View full abstract»

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  • Boundary element analysis of the directional sensitivity of the concentric EMG electrode

    Page(s): 621 - 631
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    Employing the boundary element method, the authors improve earlier models of the concentric electromyography (EMG) electrode by including an accurate geometric representation of the electrode, as well as the mutual electrical influence between the electrode surfaces. A three-dimensional sensitivity function is defined from which information about the preferential direction of sensitivity, blind spots, phase changes, rate of attenuation, and range of pick-up radius can be derived. The study focuses on the intrinsic features linked to the geometry of the electrode. The results show that the cannula perturbs the potential distribution significantly. The preferential directions of sensitivity are determined by the amount of geometric offset between the individual sensitivity functions of the core and the cannula. The sensitivity function also reveals a complicated pattern of phase changes in the pick-up range. Rotation of the electrode about its axis was found to alter the duration, the peak-to-peak amplitude, and the risetime of waveforms recorded from a moving dipole. View full abstract»

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  • Excitation of dorsal root fibers in spinal cord stimulation: a theoretical study

    Page(s): 632 - 639
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    In epidural spinal cord stimulation it is likely not only that dorsal column fibers are activated, but also that dorsal root fibers will be involved as well. In this investigation a volume conductor model of the spinal cord was used and dorsal root fibers were modeled by an electrical network including fiber excitation. The effects of varying some geometric fiber characteristics, as well as the influence of the dorsal cerebrospinal fluid layer and the electrode configuration on the threshold stimulus for their excitation, were assessed. The threshold values were compared with those of dorsal column fibers. The results of this modeling study predict that, besides the well known influence of fiber diameter, the curvature of the dorsal root fibers and the angle between these fibers and the spinal cord axis are a major influence on their threshold values. Because of these effects, threshold stimuli of dorsal root fibers were relatively low as compared to dorsal column fibers. Excitation of the dorsal root fibers occurred near the entry point of the fibers. View full abstract»

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  • Selective control of muscle activation with a multipolar nerve cuff electrode

    Page(s): 640 - 653
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    Acute experiments were performed on adult cats to study selective activation of medial gastrocnemius, soleus, tibialis anterior, and extensor digitorium longus with a cuff electrode. A spiral nerve cuff containing twelve dot electrodes was implanted around the sciatic nerve, and evoked muscle twitch forces were recorded in six experiments. Spatially isolated dot electrodes in four geometries (monopolar, longitudinal tripolar, tripolar with four common anodes, and two parallel tripoles) were combined with transverse field steering current(s) from an anode(s) located 180 degrees around from the cathode(s) to activate different regions of the nerve trunk. A selectivity index was used to construct recruitment curves for a muscle with the optimal degree of selectivity. Physiological responses were correlated with the anatomical structure of the sciatic nerve by identifying the nerve fascicles innervating the four muscles, and by determining the relative positions of the electrodes and the nerve fascicles. The results indicated that the use of transverse field steering current improved selectivity. The relative performance of the various electrode arrangements is discussed. View full abstract»

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  • Axon termination conditions for electrical stimulation

    Page(s): 654 - 663
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    The cable model for electrical stimulation near the terminal of a passive fiber is derived for excitation by an arbitrary, time-varying, applied extracellular field. Unless the termination impedance is comparable to that of the mammalian node of Ranvier, the end-conditions require the longitudinal intracellular current at the fiber terminal to be negligibly small. This requirement substantially alters the membrane potential profile from that obtained with a fiber of infinite length. Stimulation near the end of a fiber may result in lower thresholds and may reverse the anodal/cathodal threshold ratio obtained with stimulation in the mid-portion of the fiber. Chronaxie for stimulation near the terminal may be much smaller than at a distance from the terminal and the strength-duration curve may be nonmonotonic. These differences may have significant implications for any application of electrical stimulation where fiber terminations may play a role in the excitatory process. View full abstract»

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  • A musculotendon model of the fatigue profiles of paralyzed quadriceps muscle under FES

    Page(s): 664 - 674
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    A musculotendon model of the quadriceps muscle of the activated leg of a paraplegic patient incorporating fatigue was developed. The right quadriceps of a paraplegic patient who was engaged in a functional electrical stimulation (FES) training program was used for the measurements. The muscle studied was considered trained, both relating to strength and fatigue resistance. Extended stimulation was applied with an adjustable electrical stimulator, providing monophasic rectangular pulse trains with a frequency of 20 Hz, pulse width of 0.2 ms, and an intensity of up to 220 mA. The intensity used corresponded to the intensity required for the tested patient to stand up. This intensity was selected to deliberately encourage fatigue, and the result was a gradual and steady decay of the muscle force due to fatigue. The model was able to predict the decaying force during continuous electrical stimulation, as well as to indicate the muscle parameters which yield the best fit between the model prediction and the previously obtained experimental force profiles. View full abstract»

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  • Automated tuning of a closed-loop hand grasp neuroprosthesis

    Page(s): 675 - 685
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    An automated tuning algorithm was developed to reduce the time and skill required to tune a closed-loop hand grasp neuroprosthesis. The time reduction results from simultaneous tuning of four gain parameters controlling the dynamic response of the system, and from automation of the calculation and decision processes. The method is therefore an automated parallel tuning method, replacing a manual sequential method in which only one parameter at a time was tuned. RMS error between the step input and the grasp output is minimized, with absence of oscillation as a constraint. The difference between the system's RMS ramp tracking errors for the two tuning methods was less than 1% of the ramp size regardless of the initial values of the parameters, implying that the tuning methods were equivalent. However, the parallel tuning method was faster and required fewer trials than the sequential method. The capability of the closed-loop system to regulate grasp output in the presence of disturbances was shown to be better than the capability without feedback. View full abstract»

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  • Generation of two-dimensional spatial and temporal properties through spatiotemporal convergence between one-dimensional neurons

    Page(s): 686 - 692
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    Primary otolith afferents are characterized by diverse temporal and spatial response properties. The temporal properties of these neurons vary from tonic to phasic response characteristics during stimulation with linear acceleration. This study examines the response properties of target neurons that arise from spatiotemporal convergence (STC) between purely tonic and phasic-tonic afferents. The transfer function of the phasic-tonic afferent is described by either fractional leaky differentiator or integrator terms. Target neurons would generally exhibit two-dimensional spatial sensitivity and are characterized by two perpendicular response vectors. It is shown that target neurons have different temporal properties during stimulation along different spatial directions. Specifically, they could exhibit tonic temporal response dynamics during stimulation along the second response vector. The phasic dynamics along one response vector are described by a complete ideal differentiator for frequencies below the corner frequency of the leaky operator terms. View full abstract»

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  • A moment-based three-dimensional edge operator

    Page(s): 693 - 703
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    A three-dimensional edge operator for detecting anatomical structures in medical imaging is presented. It uses the spatial moments of the gray-level surface, and operates in three dimensions with any window size. It allows the location and the contrast surface, as well as the surface orientation, to be estimated. The computation of the discrete version is reported. Bias and errors due to the spatial sampling and noise are analyzed at both a theoretical and experimental level. The moment-based operator is compared with other well-known edge operators using simple shaped primitives for which the analytical solution is known. The 3-D rendering of real data is then provided by merging the operator in a ray-tracing framework. View full abstract»

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  • Mechanics of the occlusive arm cuff and its application as a volume sensor

    Page(s): 704 - 708
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    The occlusive arm cuff is examined using a mathematical mechanics model and experimental measurements. Cuff stretch was modeled by a nonlinear pressure-volume function. Air compression was represented by Boyle's law. An apparatus was developed to measure pressure due to the air volume pumped into the cuff for fixed arm volume. Data were obtained for two different cuff designs, and reveal a nonlinear cuff pressure-volume relationship that could be represented accurately by the mathematical model. Calibration constants are provided for the two types of occlusive cuff. The cuff pressure was found to consist of a balance between that produced by stretch of the elastic cuff bladder and that of the compression of the air contained within the bladder. The use of the gas law alone was found to be inadequate to represent the cuff mechanics. It is found that when applying the cuff to measure change in arm volume, such as during plethysmography or oscillometry, it cannot be assumed that the cuff sensitivity is constant. View full abstract»

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  • A system for the exposure of small laboratory animals to a 25-mT 60-Hz alternating or traveling magnetic field

    Page(s): 708 - 711
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    A versatile exposure system which can be used to investigate the effects of a 60-Hz alternating magnetic field or traveling magnetic field on small laboratory animals is described. Special attention was given to the design of the electric circuit to simplify the supply requirements and to keep the overall current to a minimum. A magnetic field having a flux density up to 30 mT (300 G) can be generated, and a traveling magnetic field is obtained by reconnecting the coils to a three-phase supply. The total magnetic field due to the currents in the three coils used in the exposure system is analyzed. A computer program was written to evaluate the magnetic field in the region where the animals are located. The difference observed between measured and computed values is attributed to the representation of the multiturn, multilayer coils by equivalent single-turn coils. View full abstract»

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  • High permittivity patch radiator for single and multi-element hyperthermia applicators

    Page(s): 711 - 715
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    A compact, low-profile patch radiator which is the base element for efficient, small-size applicators suitable for superficial hyperthermia is described. The design criteria and the technological processes involved are presented. The electromagnetic characteristics of the patch element are outlined, and possible application of the radiator are discussed. 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