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Biomedical Engineering, IEEE Transactions on

Issue 3 • Date March 2000

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Displaying Results 1 - 18 of 18
  • A high-yield microassembly structure for three-dimensional microelectrode arrays

    Page(s): 281 - 289
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (389 KB)  

    This paper presents a practical microassembly process for three-dimensional (3-D) microelectrode arrays for recording and stimulation in the central nervous system (CNS). Orthogonal lead transfers between the micromachined two-dimensional probes and a cortical surface platform are formed by attaching gold beams on the probes to pads on the platform using wire-free ultrasonic bonding. The low-profile (150 μm) outrigger design of the probes allows the bonding of fully assembled high-density arrays. Micromachined assembly tools allow the formation of a full 3-D probe array within 30 min. Arrays having up to 8×16 shanks on 200-μm centers have been realized and used to record cortical single units successfully. Active 3-D probe arrays containing on-chip CMOS signal processing circuitry have also been created using the microassembly approach. In addition, a dynamic insertion technique has been explored to allow the implantation of high-density probe arrays into feline cortex at high-speed and with minimal traumatic injury. View full abstract»

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  • Long-term maintenance of patterns of hippocampal pyramidal cells on substrates of polyethylene glycol and microstamped polylysine

    Page(s): 290 - 300
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (306 KB)  

    For neurons to attach and remain in precise micropatterns for weeks in culture, background molecules that remain nonpermissive for extended culture durations need to be identified. Nonpermissive background molecules of either polyethylene glycol (PEG) or the amino acid serine (C 3H 7NO 3) were evaluated. The foreground regions were microstamped with 3-, 5-, or 10-μm lines of poly-D-lysine (PDL), which promotes neural attachment and growth. After 29 days in culture the foreground compliance, or the fraction of all live somata which rested on the desired PDL surface, averaged 86% for serine and 90% for PEG, with only a small decline. The background compliance, or the fraction of square areas in the pattern background which were free of neurite extension, declined from highs of 40% and 55% (midculture) to 5.5% and 12% (29 days) for serine and PEG, respectively. Images of the cultures suggest that PEG is significantly more effective as a nonpermissive substrate. The authors conclude that these materials, especially PEG, are adequate for the maintenance of long-term patterned cultures of neurons. They believe that this is the first report of high-quality long-term patterning of cultured neurons. View full abstract»

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  • Laser induced fluorescence attenuation spectroscopy: detection of hypoxia

    Page(s): 301 - 312
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    The development of a new laser-induced fluorescence (LIF) spectroscopy technique for the measurement of the attenuation spectrum of tissue is described. The technique, termed laser induced fluorescence attenuation spectroscopy (LIFAS), has been applied to study the effects of hypoxia on the in vivo optical properties of renal and myocardial tissue in the 350-600-nm band. Excimer laser (Xe-Cl) is used to excite a small volume of the tissue (rabbit model, N=20) and induce autofluorescence. The emitted LIF is monitored fiber optically at two locations that are unevenly displaced about the fluorescing volume. The optical attenuation of the tissue is calculated from the dual LIF measurements by assuming an exponential decay of the fluorescence with distance. The results indicate that hypoxia modulates the attenuation spectrum leading to characteristic changes in its shape. Primarily, the spectral profile becomes more concave between 455 nm and 505 nm and two spectral peaks at about 540 and 580 nm disappear leaving in their place a single peak at about 555 nm. The attenuation spectra of normoxic and hypoxic tissue are used to train partial least squares multivariate model for spectral classification. The model detected acute renal and myocardial hypoxia with an accuracy greater than 90% (range: 90%-96%) and 74% (range: 74%-90%), respectively. View full abstract»

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  • Effect of length on the fundamental resonance frequency of arterial models having radial dilatation

    Page(s): 313 - 318
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (121 KB)  

    The pressure wave moving along an elastic artery filled with blood was examined as a moving Windkessel having a natural oscillation angular frequency ν 0 and a damping coefficient b. The radial directional motion for an element of the wall segment and the adherent fluid was considered. This equation was solved with conditions at both ends of an artery of length L. An external impulse force was applied at one end and a static pressure P 0 at the other. Analytic solution allowed only certain oscillation modes of resonance frequencies f n, where f n 2=a+c nL -2 with a=ν 0 2/4π 2-b 2/16π 2, c n=(n+1/2) 2V 2/4, n=0, 1, 2, 3, ..., and V is the high frequency phase velocity. The relationship between f 0 and L was examined experimentally for tubes constructed of latex, rubber, or dissected aorta. The effect of raising the static pressure P 0 or increasing the tension in the tube was consistent with the prediction. The hypertension that accompanies an augmentation in arterial wall and the association between the heart rate and the mean blood pressure were discussed. View full abstract»

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  • Hemodynamic mechanisms of penile erection

    Page(s): 319 - 326
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (166 KB)  

    A model of penile hemodynamics was developed to explain the process of erection that is not yet fully understood. Contradicting observations regarding blood flow and vessels occlusion during erection were examined. The model that was based on the physical structure and physiological function of the system was validated by comparing its predictions to clinical and experimental observations. Simulation of the process for both normal and pathological conditions indicates that pressure buildup in the corpus cavernosum during erection depends mainly on the interaction between the arterial inflow system and the venous draining system and that the venous draining vessels do not fully collapse and flow through the penis continues throughout the erection period. In pathological conditions, the model predicts that tumescence can be obtained without functional rigidity and demonstrates that small increases in vessel stiffness can result in such behavior. View full abstract»

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  • Spatial regularization of the electrocardiographic inverse problem and its application to endocardial mapping

    Page(s): 327 - 337
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (434 KB)  

    Numeric regularization methods for solving the inverse problem of electrocardiography in realistic volume conductor models have been mostly limited to uniform regularization in the spatial domain. A method of spatial regularization (SR) was developed and tested in canine, where each spatial spectral component of the volume conductor model was considered separately, and a SR operator was selected based on explicit a posteriori criterion at each time instant through the heartbeat. The inverse problem was solved in the left ventricle by reconstructing endocardial surface electrograms based on cavitary electrograms measured with the use of a noncontact, multielectrode probe. The results were validated based on electrograms measured in situ at the same endocardial locations using an integrated, multielectrode basket-catheter. A probe-endocardium three-dimensional model was determined from multiplane fluoroscopic images. The boundary element method was applied to solve the boundary value problem and derive the relationship between endocardial and probe potentials. Endocardial electrograms mere reconstructed during both normal and paced rhythms using SR as well as standard, uniform, zeroth-order Tikhonov (ZOT) regularization. Compared to endocardial electrograms measured by the basket, electrograms reconstructed using SR [relative error (RE)=0.32, correlation coefficient (CC)=0.97, activation error=3.3 ms] were superior to electrograms reconstructed using ZOT regularization (RE=0.59, CC=0.79, activation error=4.9 ms), Therefore, regularization based on spatial spectral components of the model improves the solution of the inverse problem of electrocardiography compared to uniform regularization. View full abstract»

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  • Pulse oximetry: an improved in vitro model that reduces blood flow-related artifacts

    Page(s): 338 - 343
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    Artifacts may occur in many in vitro models of pulse oximetry due to the optical effects of synchronously oriented and/or deformed erythrocytes. Although these artifacts are most likely negligible in living superficial tissues, they are demonstrated to have considerable influence on the calibration curve obtainable from the in vitro simulation of pulse oximetry in such models, especially at low oxygen saturations. Therefore, the authors have developed a modified in vitro model which reduces the effect of these artifacts. This is achieved by excluding data obtained during pressure transients and by raising the blood flow velocity. As a result, the model more closely approximates in vivo pulse oximetry, particularly under clinically important conditions of low blood oxygen saturation levels. View full abstract»

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  • Effects of mechanical stress/strain and estrogen on cancellous bone structure predicted by fuzzy decision

    Page(s): 344 - 351
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    A theoretical model was developed on the basis of fuzzy decision to predict cancellous bone structure following changes In mechanical stress/strain and estrogen. The model was validated experimentally by simulation of the normal structure of a rat distal femur, and further used to predict the structural alterations following ovarian hormone deficiency. The results show that net bone resorption after ovariectomy occurs in the metaphysis at locations where trabecula were subjected to the lowest mechanical stress/strain. These findings, consistent with experimental results, suggest that estrogen deficiency increase the mechanostat set point at which bone cells perceive mechanical stress/strain. Additionally, the results show that changes in bone architecture which are due to alterations in bone remodeling can be simulated by fuzzy decision without precise mathematical description, and multiple factors can also be readily incorporated into the model. View full abstract»

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  • Bispectrum analysis of focal ischemic cerebral EEG signal using third-order recursion method

    Page(s): 352 - 359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (195 KB)  

    In this paper, a model for Sprague-Dawley (SD) rat focal ischemic cerebral injury is presented. Based on this experimental model, the electroencephalogram (EEG) from the ischemic region and from a normal region are collected during the first 30 min of ischemia. The EEG bispectrum analysis is carefully investigated by using the third-order recursion method. The authors found that some characteristics of the bispectrum are very sensitive to focal ischemic cerebral injury. The maximum magnitude and the weighted center of EEG bispectrum (WCOB) change according to the extent and the place of the injury region. The bispectrum analysis results have been verified by the heat shock protein (HSP) test. The study indicates that the EEG bispectrum analysis may be useful to distinguish the ischemic region from the normal one and to estimate the ischemic extent. View full abstract»

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  • Wavelet-based noise removal for biomechanical signals: a comparative study

    Page(s): 360 - 368
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    The purpose of this paper is to present wavelet-based noise removal (WBNR) techniques to remove noise from biomechanical acceleration signals obtained from numerical differentiation of displacement data. Manual and semiautomatic methods were used to determine thresholds for both orthogonal and biorthogonal filters. This study also compares the performance of WBNR approaches with four automatic conventional noise removal techniques used in biomechanics. The conclusion of this work is that WBNR techniques are very effective in removing noise from differentiated signals with sharp transients while leaving these transients intact. For biomechanical signals with certain characteristics, WBNR techniques perform better than conventional methods, as indicated by quantitative merit measures. View full abstract»

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  • Detection of characteristic waves of sleep EEG by neural network analysis

    Page(s): 369 - 379
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    In psychiatry, the sleep stage is one of the most important forms of evidence for diagnosing mental disease. However, doctors require much labor and skill for diagnosis, so a quantitative and objective method is required for more accurate diagnosis since it depends on the doctor's experience. For this reason, an automatic diagnosis system must be developed. In this paper, the authors propose a new type of neural network (NN) model referred to as a sleep electroencephalogram (EEG) recognition neural network (SRNN) which enables one to detect several kinds of important characteristic waves in sleep EEG which are necessary for diagnosing sleep stages. Experimental results indicate that the proposed NN model was much more capable than other conventional methods for detecting characteristic waves. View full abstract»

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  • Noninvasive estimation of motor unit conduction velocity distribution using linear electrode arrays

    Page(s): 380 - 388
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB)  

    Determining the conduction velocity of motor unit action potentials is one of the most important problems in surface electromyography. The estimate of one average conduction velocity value depends on a variety of uncontrollable factors. More meaningful information is obtained from the estimation of the distribution of the different delays in the myoelectric signals. A solution to the problem is the separation and characterization of the individual components propagating at different velocities. A technique, based on surface electrode array recording, is proposed to estimate motor unit conduction velocity distribution. The method consists in the identification of the single action potentials in the time scale domain (with the continuous wavelet transform) and in the estimation of their conduction velocities based on the beamforming algorithm. The performances of the technique have been evaluated using simulated and real myoelectric signals. The results demonstrate that the technique Is accurate and reliable. The method may be useful for the diagnosis of neuromuscular disorders, for the monitoring of muscle fatigue and for noninvasive investigation of individual motor units. View full abstract»

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  • Nonlinear adaptive filtering of stimulus artifact

    Page(s): 389 - 395
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    Noninvasive measurements of somatosensory evoked potentials have both clinical and research applications. The electrical artifact which results from the stimulus is an interference which can distort the evoked signal, and introduce errors in response onset timing estimation. Given that this interference is synchronous with the evoked signal, it cannot be reduced by the conventional technique of ensemble averaging. The technique of adaptive noise cancelling has potential in this regard however, and has been used effectively in other similar problems. An adaptive noise cancelling filter which uses a neural network as the adaptive element is investigated in this application. The filter is implemented and performance determined in the cancelling of artifact for in vivo measurements on the median nerve. A technique of segmented neural network training is proposed in which the network is trained on that segment of the record time window which does not contain the evoked signal. The neural network is found to generalize well from this training to include the segment of the window containing the evoked signal. Both quantitative and qualitative measures show that significant stimulus artifact reduction is achieved. View full abstract»

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  • Variability in EMF permittivity values: implications for SAR calculations

    Page(s): 396 - 401
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    Digital anatomical models of man and animals are available for use in numerical calculations to predict electromagnetic field (EMF)-induced specific absorption rate (SAR) values. To use these models, permittivity values are assigned to the various tissues for the EMF frequencies of interest. There is, as yet, no consensus on what are the best permittivity data. This study analyzed the variability In published permittivity data and investigated the effects of permittivity values that are proportional on SAR calculations. Whole-sphere averaged and localized SAR values along the diameter of a 4-cm sphere are calculated for EMF exposures in the radio frequency range of 1 MHz to 1 GHz. When the dimensions of a sphere are small compared to the wavelength (i.e., wavelength inside the material is greater than ten times the dimensions of the object), the whole-sphere averaged SAR is inversely proportional to the permittivity of the material composing the sphere. However, the localized SAR values generally do not have the same relation and, as a matter of fact, vary greatly depending on the location within the sphere. These results indicate that care must be taken In choosing the permittivity values used in calculating SAR values and some estimate of the dependence of the calculated SAR values on variability in permittivity should be determined. View full abstract»

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  • A box coil for the stimulation of biological tissue and cells in vitro and in vivo by pulsed magnetic fields

    Page(s): 402 - 408
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    An alternative coil system to the Helmholtz coil-pair is described for the stimulation of biological tissue and cells: a relatively large box coil made of copper or aluminum sheet stock. The design is based on the principal determinant of the induced electric field, namely, the magnetic vector potential (A), in the equation, E=-∂A/∂t-∇V. The second term in the equation is needed when boundaries of the conducting medium are in close proximity to the region of interest, such as in a culture dish. An electric surface charge builds up on the boundaries to generate an electric field which cancels -∂A/∂t at the surface. The effectiveness of the new coil is demonstrated in a study of the outgrowth enhancement of axons from rat embryonic dorsal root ganglia. View full abstract»

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  • Noninvasive feature-based detection of delayed gastric emptying in humans using neural networks

    Page(s): 409 - 412
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    Radioscintigraphy is currently the gold standard for gastric emptying test which involves radiation exposure and is considerably expensive. The authors present a feature-based detection approach using neural networks for the noninvasive diagnosis of delayed gastric emptying from the cutaneous electrogastrogram (EGG). Simultaneous recordings of the EGG and scintigraphic gastric emptying test were made in 152 patients with symptoms suggestive of delayed gastric emptying. Spectral analyses were performed to derive EGG parameters which were used as the input of the neural network. The result of scintigraphic gastric emptying was used as the gold standard for the training and testing of the neural network. A correct classification of 85% (a specificity of 89% and a sensitivity of 82%) was achieved using the proposed method. View full abstract»

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  • Multivariate dynamic analysis of cerebral blood flow regulation in humans

    Page(s): 419 - 423
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    The contributions of beat-to-beat changes in mean arterial blood pressure (MABP) and breath-by-breath fluctuations in end-tidal CO 2 (EtCO 2) as determinants of the spontaneous variability of cerebral blood flow velocity (CBFV) were studied in 16 normal subjects at rest. The two input variables (MABP and EtCO 2) had significant cross-correlations with CBFV but not between them. Transfer functions were estimated as the multivariate least mean square finite impulse response causal filters. MABP showed a very significant effect in explaining CBFV variability (p<10 -11, Fisher's aggregated-p test) and the model mean square error was significantly reduced (p<0.001) by also including the contribution EtCO 2. The estimated mean CBFV step response to MABP displayed the characteristic return to baseline caused by the cerebral autoregulatory response. The corresponding response to EtCO 2 showed a gradual rise taking approximately 10 s to reach a plateau of 2.5%/mmHg. This study demonstrated that spontaneous fluctuations in EtCO 2 can help to explain the CBFV variability at rest if appropriate signal processing techniques are employed to address the limited power and bandwidth of the breath-by-breath EtCO 2 signal. View full abstract»

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  • A new video-synchronized multichannel biomedical data acquisition system

    Page(s): 412 - 419
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (163 KB)  

    This data acquisition system records video frames onto a video tape, and simultaneously acquires biomedical data along with video time codes onto a computer hard disk to achieve a 30-min video-synchronized data recording with a summed data rate of 2.16 Mbit/s. A time-code-bridge file created during acquisition matches each video frame-start with the corresponding index number of the acquired data. The mean synchronization accuracy of the system is 0.22 ms. 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