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Biomedical Engineering, IEEE Transactions on

Issue 8 • Date Aug. 1998

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Displaying Results 1 - 15 of 15
  • Ensembles of radial basis function networks for spectroscopic detection of cervical precancer

    Publication Year: 1998 , Page(s): 953 - 961
    Cited by:  Papers (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (151 KB)  

    The mortality related to cervical cancer can be substantially reduced through early detection and treatment. However, current detection techniques, such as Pap smear and colposcopy, fail to achieve a concurrently high sensitivity and specificity. In vivo fluorescence spectroscopy is a technique which quickly, noninvasively and quantitatively probes the biochemical and morphological changes that occur in precancerous tissue. A multivariate statistical algorithm was used to extract clinically useful information from tissue spectra acquired from 361 cervical sites from 95 patients at 337-, 380-, and 460-nm excitation wavelengths. The multivariate statistical analysis was also employed to reduce the number of fluorescence excitation-emission wavelength pairs required to discriminate healthy tissue samples from precancerous tissue samples. The use of connectionist methods such as multilayered perceptrons, radial basis function (RBF) networks, and ensembles of such networks was investigated. RBF ensemble algorithms based on fluorescence spectra potentially provide automated and near real-time implementation of precancer detection in the hands of nonexperts. The results are more reliable, direct, and accurate than those achieved by either human experts or multivariate statistical algorithms. View full abstract»

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  • Analysis-synthesis of the phonocardiogram based on the matching pursuit method

    Publication Year: 1998 , Page(s): 962 - 971
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    The matching pursuit method of Mallat and Zhang (1993) is applied to the analysis and synthesis of phonocardiograms (PCGs). The method is based on a classical Gabor wavelet or time-frequency atom which is the product of a sinusoid and a Gaussian window function, it decomposes a signal into a series of time-frequency atoms by an iterative process based on selecting the largest inner product of the signal (and the subsequent residues) with atoms from a redundant dictionary. The Gaussian window controls the envelope duration and time position of each atom; and the sinusoid represents the frequency. The method was applied to two sets of PCGs: one with very low-noise level and the other with 10% noise energy. Each database includes 11 PCGs representing the normal and the pathological conditions of the heart. The normalized root-mean-square error (NRMSE) was computed between the original and the reconstructed signals. The results show that the matching pursuit method is very suitable to the transient and complex properties of the PCGs, as it yielded excellent NRMSEs around 2.2% for the two sets of 11 PCGs tested. View full abstract»

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  • Time-frequency scaling transformation of the phonocardiogram based of the matching pursuit method

    Publication Year: 1998 , Page(s): 972 - 979
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    A time-frequency scaling transformation based on the matching pursuit (MP) method is developed for the phonocardiogram (PCG). The MP method decomposes a signal into a series of time-frequency atoms by using an iterative process. The modification of the time scale of the PCG can be performed without perceptible change in its spectral characteristics. It is also possible to modify the frequency scale without changing the temporal properties. The technique has been tested on 11 PCGs containing heart sounds and different murmurs. A scaling/inverse-scaling procedure was used for quantitative evaluation of the scaling performance. Both the spectrogram and a MP-based Wigner distribution were used for visual comparison in the time-frequency domain. The results showed that the technique is suitable and effective for the time-frequency scale transformation of both the transient property of the heart sounds and the more complex random property of the murmurs. It is also shown that the effectiveness of the method is strongly related to the optimization of the parameters used for the decomposition of the signals. View full abstract»

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  • An improved boundary element method for realistic volume-conductor modeling

    Publication Year: 1998 , Page(s): 980 - 997
    Cited by:  Papers (117)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (862 KB)  

    An improved boundary element method (BEM) with a virtual triangle refinement using the vertex normals, an optimized auto solid angle approximation, and a weighted isolated problem approach is presented. The performance of this new approach is compared to analytically solvable spherical shell models and highly refined reference BEM models for tangentially and radially oriented dipoles at different eccentricities. The lead fields of several electroencephalography (EEG) and magnetoencephalography (MEG) setups are analyzed by singular-value decompositions for realistically shaped volume-conductor models. Dipole mislocalizations due to simplified volume-conductor models are investigated for EEG and MEG examinations for points on a three dimensional (3-D) grid with 10-mm spacing inside the conductor and all principal dipole orientations. The applicability of the BEM in view of the computational effort is tested with a standard workstation. Finally, an application of the new method to epileptic spike data is studied and the results are compared to the spherical-shells approximation. View full abstract»

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  • Investigation of the Hammerstein hypothesis in the modeling of electrically stimulated muscle

    Publication Year: 1998 , Page(s): 998 - 1009
    Cited by:  Papers (38)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    To restore functional use of paralyzed muscles by automatically controlled stimulation, an accurate quantitative model of the stimulated muscles is desirable. The most commonly used model for isometric muscle has had a Hammerstein structure, in which a linear dynamic block is preceded by a static nonlinear function. To investigate the accuracy of the Hammerstein model, the responses to a pseudo-random binary sequence (PRES) excitation of normal human plantarflexors, stimulated with surface electrodes, were used to identify a Hammerstein model but also four local models which describe the responses to small signals at different mean levels of activation. Comparison of the local models with the linearized Hammerstein model showed that the Hammerstein model concealed a fivefold variation in the speed of response. Also, the small-signal gain of the Hammerstein model was in error by factors up to three. We conclude that, despite the past widespread use of the Hammerstein model, it is not an accurate representation of isometric muscle. On the other hand, local models, which are more accurate predictors, can be identified from the responses to short PRES sequences. The utility of local models for controller design is discussed. View full abstract»

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  • A simple model of force generation by skeletal muscle during dynamic isometric contractions

    Publication Year: 1998 , Page(s): 1010 - 1016
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (134 KB)  

    The force that an isometric skeletal muscle will produce in response to time-varying stimulation ("dynamic isometric" force) is important both for understanding muscle function and for designing neuroprostheses. The paper reports a model for predicting the force produced by an isometric skeletal muscle at rest length in response to a wide range of stimulation patterns. The model consists of two linear, first-order systems separated by a static nonlinearity. The rate constant of the second first-order system varies with force level. The model was validated using three cat soleus and three cat plantaris muscles. The following whole-nerve stimulation trains were used: single pulses (twitches), 2-4 pulses, constant rates, triangularly modulated interpulse intervals, and randomly modulated interpulse intervals. The model reproduced most responses accurately. The model shows that a force-dependent rate constant is essential for model validity, and could be used in the control of neuroprostheses. View full abstract»

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  • State transitions in physiologic systems: a complexity model for loss of consciousness

    Publication Year: 1998 , Page(s): 1017 - 1023
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (139 KB)  

    Complex physiologic systems in which the emergent global (observable) behavior results from the interplay among local processes cannot be studied effectively by conventional mathematical models. In contrast to traditional computational methods which provide linear or nonlinear input-output data mapping without regard to the internal workings of the system, complexity theory offers scientifically and computationally tractable models which take into account microscopic mechanisms and interactions responsible for the overall input-output behavior. This article offers a brief introduction to some of the tenets of complexity theory and outlines the process involved in the development and testing of a model that duplicates the global dynamics of the induction of loss of consciousness (LOG) in humans due to cerebral ischemia. Under the broad definition of complexity, we view the brain of humans as a complex system. Successful development of a model for this complex system requires careful combination of basic knowledge of the physiological system both at the local (microscopic) and global (macroscopic) levels with experimental data and the appropriate mathematical tools. It represents an attempt to develop a model that can both replicate human data and provide insights about possible underlying mechanisms. View full abstract»

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  • Long-term biocompatibility of a miniature stimulator implanted in feline hind limb muscles

    Publication Year: 1998 , Page(s): 1024 - 1035
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (243 KB)  

    Chronic foreign-body responses and muscular changes were examined following the implantation of active miniature stimulators into the hind limb muscles of cats for periods of up to three months. The radio-frequency (RF)-powered stimulators were injected into muscles through a 12-gauge hypodermic needle. The tissue responses around the active stimulators were compared histologically to those provoked by passive devices, broken glass, silicone tubing, polyester suture material coated with polybutylate, and two of the internal components of the stimulator (ferrite, integrated circuit chip). Active and passive stimulators produced similar, benign foreign-body reactions that resulted in an essentially identical fibrous capsule over time. The responses were similar to those produced by the internal components and the suture material, and were more modest than those produced by the broken glass. The capsule did not appear to interfere with the functionality of active devices because thresholds measured during the post-implantation survival period did not change significantly over time. Unexpectedly, the severity of the reaction differed significantly amongst the various target muscles. Medial gastrocnemius exhibited the most severe response, whereas tibialis anterior had the least reaction. View full abstract»

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  • Effects of regional stimulation using a miniature stimulator implanted in feline posterior biceps femoris

    Publication Year: 1998 , Page(s): 1036 - 1043
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (135 KB)  

    The effects of placement of a miniature implantable stimulator on motor unit recruitment were examined in the posterior head of cat biceps femoris. The implantable stimulator (13-mm long×2-mm diameter) was injected either proximally near the main nerve branch, or distally near the muscle insertion, through a 12-gauge hypodermic needle. Glycogen-depletion methods were used to map the distribution of fibers activated by electrical stimulation. Muscle fibers were found to be depleted at most or all proximodistal levels of the muscle, but the density of depleted fibers varied transversely according to the stimulus strength and proximity of the device to the nerve-entry site. Thus, muscle cross sections often had a "patchy" appearance produced because different proportions of depleted fibers intermingled with undepleted fibers in different parts of the cross section. In other preparations, the force of muscle contraction was measured when stimuli of varying strengths were delivered by the stimulator positioned at the same proximal or distal sites within the muscle. Devices placed close to the nerve-entry site produced the greatest forces. Those placed more distally produced less force. As stimulus current and/or pulse width increased, muscle force increased, often in steps, until a maximum was reached, which was usually limited by the compliance voltage of the device to less than the force produced by whole nerve stimulation. View full abstract»

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  • Improved nerve cuff electrode recordings with subthreshold anodic currents

    Publication Year: 1998 , Page(s): 1044 - 1050
    Cited by:  Papers (4)  |  Patents (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (137 KB)  

    A method has been developed for improving the signal amplitudes of the recordings obtained with nerve cuff electrodes. The amplitude of the electroneurogram (ENG) has been shown to increase with increasing distance between the contacts when cuff electrodes are used to record peripheral nerve activity. The effect is directly related to the propagation speed of the action potentials. Computer simulations have shown that the propagation velocity of action potentials in a length of a nerve axon can be decreased by subthreshold extracellular anodic currents. Slowing the action potentials is analogous to increasing the cuff length in that both result in longer intercontact delays, thus, larger signal outputs. This phenomenon is used to increase the amplitudes of whole nerve recordings obtained with a short cuff electrode. Computer simulations predicting the slowing effect of anodic currents as well as the experimental verification of this effect are presented. The increase in the amplitude of compound action potentials (CAPs) is demonstrated experimentally in an in vitro preparation. This method can be used to improve the signal-to-noise ratios when recording from short nerve segments where the cuff length is limited. View full abstract»

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  • Identification of human joint mechanical properties from single trial data

    Publication Year: 1998 , Page(s): 1051 - 1060
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (259 KB)  

    A method is presented for estimating the time-varying compliance parameters of the elbow joint from a single movement. The method separates by frequency the perturbed from the voluntary response, then determines the parameters by exponentially weighted least squares. The tracking performance of the method is established by simulation and by a calibrated mechanical joint. Experimental results are presented on time-varying posture and slow movement. View full abstract»

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  • A method for matching high-temperature superconductor resonators used for NMR signal pickup at 400 MHz

    Publication Year: 1998 , Page(s): 1061 - 1066
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    This paper describes a method for matching high-temperature superconducting nuclear magnetic resonance (NMR) signal pickup coils to field-effect transistor (FET) preamplifiers using amplifier-specific noise figure and gain parameters to obtain a matching compromise that improves gain flatness for a given permissible noise figure. A technique for obtaining these parameters is also described in an appendix. View full abstract»

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  • Finite-difference time-domain analysis of a complete transverse electromagnetic cell loaded with liquid biological media in culture dishes

    Publication Year: 1998 , Page(s): 1067 - 1076
    Cited by:  Papers (19)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (217 KB)  

    Transverse electromagnetic (TEM) cells can be used for exposing biological culture specimens to electromagnetic fields and observing possible anomalous effects. The uniformity of field exposure is critical to quantifying the biological response versus the electromagnetic dose. Standing waves and other electromagnetic field nonuniformities can cause nonuniform exposure. This paper reports the results of high-resolution three-dimensional finite-difference time-domain (FDTD) simulations of a complete TEM cell designed for operation at 837 MHz. Several different cases were studied in which the number of culture dishes, the depth of the culture liquid, and the orientation of the culture dishes were varied. Further, the effect of the culture-dish glass bottom thickness and the meniscus of the liquid medium were examined. The FDTD results show that there is a significant nonuniform field and specific absorption rate (SAR) distribution within the culture medium for each case examined. Hence, biological dose-response experiments using the TEM cell should account for the possibility of strong localized SAR peaking in the culture media to provide useful data in setting exposure standards for wireless communications. View full abstract»

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  • Application of adaptive signal processing for determining the limits of P and T waves in an ECG

    Publication Year: 1998 , Page(s): 1077 - 1080
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (86 KB)  

    A new algorithm for the determination of the limits of P and T waves is proposed, and its foundations are mathematically analyzed. The algorithm performs an adaptive filtering so that the searched point corresponds to a minimum. Crucial properties of its performance are discussed, i.e., immunity to base line drifts and full adaptation to any cardiological criteria. A series of tests are made involving real registers with different morphologies for P and T-waves. View full abstract»

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  • Predicting quadriceps muscle activity during gait with an automatic rule determination method

    Publication Year: 1998 , Page(s): 1081 - 1085
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (117 KB)  

    It has been suggested that control using a skill-based expert system can be applicable to gait restoration. Rule-based systems have several advantages for this application: they generate a fast response (they are not computationally intensive) and they are easy to comprehend and implement. A major problem with using such systems is the inability of users to determine its rules. In this study, an automatic method for obtaining the production rules from a set of examples is described. The rule base was automatically induced from a model which used external sensor signals as inputs and electromyogram (EMG) patterns as outputs. The method is based on the minimization of entropy. A production rule estimated the muscle activity pattern using the sensor information. The algorithm was tested using data recorded from six able-bodied individuals during ground level walking, with and without ankle-foot orthoses. The data showed that gait variability will increase in able-bodied subjects when the motion of ankle joints is restricted, thus, providing a good test for generalization. The experimental results illustrate performance of the production rule that estimates quadriceps muscle group activity pattern for ground level walking in able-bodied subjects. View full abstract»

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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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Department of Biomedical Engineering