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Biomedical Engineering, IEEE Transactions on

Issue 8 • Date Aug. 1995

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Displaying Results 1 - 13 of 13
  • Force-sensing microprobe for precise stimulation of mechanosensitive tissues

    Page(s): 745 - 750
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    Quantitative study of the transduction mechanisms in mechanically sensitive nerve terminals has been impeded by the lack of instrumentation with which to generate precisely controlled, physically localized mechanical stimuli. The authors have developed high-resolution force sensing mechanical microprobes for use in the characterization of such nerve terminals. This paper describes their design, fabrication, and testing. A microprobe is comprised of a 0.5- to 2-mm long silicon cantilever beam projecting from a larger supporting silicon substrate. Acting as the variable leg of a Wheatstone bridge circuit, a piezoresistive polysilicon element located at the base of the beam is used to measure the stimulation force applied at the tip. The microprobes exhibit a stable, linear relationship between the stimulation force and the resulting output voltage signal. Stimulation forces up to 3 mN have been generated with a measurement resolution of 10 μN. These microprobes have been used as the force sensing element of a closed loop feedback-controlled stimulation system capable of stimulating the mechanoreceptive nerve terminals of the rabbit corneal epithelium. View full abstract»

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  • A silicon micromachined device for use in blood cell deformability studies

    Page(s): 751 - 761
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    An application of silicon micromachining to the analysis of blood cell rheology is described. The system, based upon a micromachined flow cell, provides a specific measurement of each cell in a statistically significant population in terms of both flow velocity profile and an index of cell volume while the cells flow through an array of microchannels. The rationale, design, and fabrication of the silicon micromachined flow cell is discussed. Interrelated considerations determining the design of the associated fluidic, mechanical, imaging, and real-time image analysis subsystems are examined. Sample data comparing normal and iron deficiency anaemic blood are presented to illustrate the potential of this technique. View full abstract»

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  • Dynamic extraction of visual evoked potentials through spatial analysis and dipole localization

    Page(s): 762 - 768
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    The dynamic extraction of evoked potential is a problem of great interest in EEG signal processing. Here, a comprehensive method is presented which integrates spatial analysis and dipole localization to make full use of the spatial-temporal information contained in the multichannel stimulation records. A realistic double boundary head model is constructed through CT scans and a two-step method devised to overcome the ill-posed nature of the forward problem of EEG caused by the low conductivity of the skull. As a result, visual evoked potentials can be effectively extracted from only two consecutive records and the dynamic information of visual evoked potential thus procured. The efficiency of the presented method has been verified by means of computer simulation and a clinical experiment. View full abstract»

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  • Estimation of shape characteristics of surface muscle signal spectra from time domain data

    Page(s): 769 - 776
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    Myoelectric manifestations of muscle fatigue have been described by monitoring the first-order moment (mean frequency) of the power spectral density function during voluntary or electrically elicited sustained contractions. Higher order central moments provide additional information about the width, skewness, and kurtosis of the spectrum and its shape changes, thereby providing a description of slow nonstationarities more accurate than that allowed by the mean frequency alone. In 1986, B. Saltzberg introduced a method of representing the moments of the power spectral density function of band limited signals, without computing the Fourier transform, as weighted sums of samples of the autocorrelation function. If one allows for oversampling of the signal (and therefore of its autocorrelation function), more efficient weighted sums can be found which give Saltzberg's formula as a limiting case. The faster rate of decay of the weights implies a faster convergence of the estimates and the need to compute fewer samples of the autocorrelation function. The algorithm is particularly suitable for: 1) analysis of evoked potentials (M-waves), because it does not need zero padding to increase resolution and operates on any number of samples, and 2) on-line implementation by dedicated microprocessors performing simultaneous spectral moment analysis on a number of parallel channels. View full abstract»

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  • The application of cepstral coefficients and maximum likelihood method in EMG pattern recognition [movements classification]

    Page(s): 777 - 785
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    A new technique for classifying patterns of movement via electromyographic (EMG) signals is presented. Two methods (conventional autoregressive (AR) coefficients and cepstral coefficients) for extracting features from EMG signals and three classification algorithms (Euclidean Distance Measure (EDM), Weighted Distance Measure (WDM), and Maximum Likelihood Method (MLM)) for discriminating signals representative of broad classes of movements are described and compared. These three classifiers are derived from Bayes classifier with some assumptions, the relationship among them is discussed. The conventional MLM is modified to avoid heavy matrix inversion. Six able-bodied subjects with two pairs of surface electrodes located on bilateral sternocleidomastoid and upper trapezius muscles were studied in the experiment. The EMG signals of 20 repetitions of 10 motions were analyzed for each subject. Experimental results showed that mean recognition rate of the cepstral coefficients was at least 5% superior to that of the AR coefficients. The improvement achieved by the cepstral method was statistically significant for all the three classifiers. Reasons for the superiority of cepstral features were investigated from the feature space and frequency domain, respectively. The cepstral coefficients owned better cluster separability in feature space and they emphasized the more informative part in the frequency domain. The discrimination rate of the MLM was the highest among three classifiers. Incorporation of the cepstral features with the MLM could reduce the misclassification rate by 10.6% when compared with the combination of AR coefficients and EDM. Proper choice of five of ten motions could further raise the recognition rate to more than 95%. View full abstract»

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  • Fuzzy classification of patient state with application to electrodiagnosis of peripheral polyneuropathy

    Page(s): 786 - 792
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    A methodology which accounts for uncertainty or imprecision in experimental observations and both norm and pathology definitions is developed on the basis of a distance measure between fuzzy numbers. These fuzzy numbers may represent, respectively, the measurements, norm, and pathology. The distance measure, called normalized fuzzy pathology index (NFPI), evaluates the difference of distance between observed experimental values for a given patient and norm on the one hand, and pathology on the other hand. The NFPI characterizes patient state as a continuous index; however, to conform to medical usage, categories of values are defined. Each of these categories corresponds to a linguistic variable. The case study used to illustrate the methodology is the electrodiagnosis of peripheral polyneuropathy in diabetic patients. Here, four initial linguistic categories are defined by a physician, namely: normal state, borderline state, clear-cut, and severe pathology. The NFPI is calculated in three cases that provide a sensitivity analysis on measurement fuzziness and distance function weighting. The model is calibrated using 203 cases and validated using 291 different cases. The results correspond very closely to the physician's diagnosis. The loss of information in discretizing the continuous state of patients is discussed. Transferring this fuzzy approach to other cases where the concept of distance is relevant offers no difficulty. View full abstract»

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  • Functional design features and initial performance characteristics of a magnetic-implant guidance system for stereotactic neurosurgery

    Page(s): 793 - 801
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    A helmet with a roughly cubic array of six superconducting coils is used to apply force on a small permanent magnet pellet in brain or in brain phantom material. This apparatus, called the Magnetic Stereotaxis System, will be used to deliver drugs and other therapies directly into deep brain tissues, under control of a computer and fluoroscopic imaging system. This paper considers only the force application aspects of the instrument. The primary design features of the helmet and power supply controls are presented, along with field plot data and single-axis motion results. The field plot data show that agreement with the finite-element iron-free field calculations is sufficiently high (>1%) for the instrument. These preliminary motion data indicate accuracy better than 2 mm for the impulsive pellet motion, even though the visual position observations had significantly greater error than the completed imaging system will have. The companion paper will take up analysis of the control aspects of the motion, and the authors' recent solutions to difficulties found in the experimental work described here. View full abstract»

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  • Characteristics of an improved magnetic-implant guidance system

    Page(s): 802 - 808
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    The previous companion paper (see ibid., vol. 42, no. 8, p.793, 1995) described the motivation, design, and early experiments of a Magnetic Stereotaxis System. The part of the system considered in these papers is a helmet with a roughly cubic array of six superconducting coils used to apply force on small permanent magnet pellets in brain and in brain phantom material. This apparatus will be used to deliver drugs and other therapies directly into deep brain tissues, under control of a computer and fluoroscopic imaging system. Here, the authors analyze the general stability problems of controlling the currents in the coils for impulsive stepwise motion of the pellet, subject to quench avoidance in the superconducting coils, and in the face of Earnshaw's theorem governing stability in static magnetic fields. The authors also describe solutions that have been found to the primary difficulties limiting controlled pellet motion in the studies presented in the companion paper. View full abstract»

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  • Reducing muscle fatigue in FES applications by stimulating with N-let pulse trains

    Page(s): 809 - 817
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    Applications of electrical stimulation for restoration of functional movements such as standing, gait, and grasp have always been hindered by the rapid fatigue of stimulated muscle. This paper describes an experimental investigation of stimulation with N-lets (a set of N closely spaced stimulation pulses) as a means of producing contractions with improved fatigue characteristics. Experiments were conducted on 27 able-bodied and four SCI human subjects using surface stimulation of the quadriceps muscle to produce isometric knee joint torque. Based upon evidence from the literature on muscle fatigue, parameters of the N-let trains for N=1-6 were optimized to produce the most force per pulse. The results demonstrated that: 1) nonlinear summation of the twitch response occurs in human subjects with N-let surface stimulation; 2) for most subjects, doublet stimulation (N=2) with a pulse interval of about 5 ms produced the maximum torque-time integral per pulse of the resulting twitch; and 3) on average, optimal N-let stimulation resulted in a 36% increase in isometric torque tracking when compared to traditional singlet stimulation. The results have immediate implications for alleviating the problem of premature fatigue during functional electrical stimulation. View full abstract»

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  • Multipoint temperature control during hyperthermia treatments: theory and simulation

    Page(s): 818 - 827
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    A real-time multipoint feedback temperature control system has been designed and implemented with an ultrasound phased-array applicator for hyperthermia. The control parameters are the total power available from the supply and the dwell times at a sequence of preselected heating patterns. Thermocouple measurements are assumed for temperature feedback. The spatial operator linking available heating patterns to temperature measurements is measured at the outset of the treatment and can be remeasured on line an adaptive implementation. A significant advantage of this approach is that the controller does not require a priori knowledge of either the placement of the thermocouples or the power distribution of the ultrasound heating patterns. Furthermore, the control loop uses a proportional integral (PI) gain in conjunction with a singular value decomposition (SVD) of the spatial transfer operator. This approach is advantageous for robust implementation and is shown to properly balance the power applied to the individual patterns. The controller also deals with saturation in the inputs without integrator windup and, therefore, without temperature overshoot. Here, the authors present the theoretical formulation and representative simulation results of the proposed controller. The control algorithm has been verified experimentally, both in vitro and in vivo. A subsequent paper describing these results and the practical implementation of the controller will follow. View full abstract»

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  • Noninvasive estimation of tissue temperature response to heating fields using diagnostic ultrasound

    Page(s): 828 - 839
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    A noninvasive technique for monitoring tissue temperature changes due to heating fields using diagnostic ultrasound is described. The approach is based on the discrete scattering model used in the tissue characterization literature and the observation that most biological tissues are semi-regular scattering lattices. It has been demonstrated by many researchers and verified by the authors that the spectrum of the backscattered radio frequency (RF) signal collected with a diagnostic ultrasound transducer from a semi-regular tissue sample exhibits harmonically related resonances at frequencies determined by the average spacing between scatterers along a segment of the A-line. It is shown theoretically and demonstrated experimentally (for phantom, in vitro, and in vivo media) that these resonances change with changes in the tissue temperature within the processing window. In fact, changes in the resonances (Δf) are linearly proportional to changes in the temperature (ΔT), with the proportionality constant being determined by changes in the speed of sound with temperature and the linear coefficient of thermal expansion of the tissue. Autoregressive (AR) model-based methods aid in the estimation of Δf. It should be emphasized that this new technique is not a time of flight velocimetric one, so it represents a departure from previously used ultrasonic methods for tissue temperature estimation. View full abstract»

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  • A simple method to incorporate the effects of an RF shield into RF resonator analysis for MRI applications

    Page(s): 840 - 843
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    A simple but effective method is proposed to incorporate the effects of a radiofrequency (RF) shield into the analysis of RF resonators for magnetic resonance imaging (MRI) applications. It Is shown that the method can predict the resonant frequencies of RF resonators within 5% of the measured values. View full abstract»

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  • Modeling of micturition characteristics based on prostatic stiffness modulation induced using hormones and adrenergic antagonists

    Page(s): 843 - 848
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    The authors present a biosensor intended to evaluate prostatic stiffness. The stiffness of the prostate was modulated using hormonal induction and adrenergic stimulation. The results show that the sensor can be sufficiently accurate to discriminate between soft prostates used as controls and those stiffened with hormones. The modulation produced by an adrenergic agent on prostatic stiffness was detected using this system. An electrical model was constructed embodying the parameters of prostatic stiffness, micturition frequency, and volume, demonstrating that prostatic stiffness correlates with micturition frequency. 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