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Biomedical Engineering, IEEE Transactions on

Issue 1 • Date Jan. 1995

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Displaying Results 1 - 14 of 14
  • Image-based display of activation patterns derived from scattered electrodes

    Publication Year: 1995 , Page(s): 111 - 115
    Cited by:  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (931 KB)  

    Presentation of electrophysiologic data, such as activation patterns, can take many forms, the most common of which are hand or machine-drawn isochronal maps. The authors present an image-based method which provides accurate matching between electrophysiologic data and the anatomic sites from which the data were derived. This method is linear, simple, and straightforward to implement, and presents results in a format which is easy to understand and interpret. View full abstract»

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  • Two-channel enhancement of a multifunction control system

    Publication Year: 1995 , Page(s): 109 - 111
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    The enhancement of an existing myoelectric control system has been investigated. The original one-channel system used an artificial neural network to classify myoelectric patterns. This research shows that a two-channel control system can improve the classification accuracy of the pattern classifier significantly, thus improving the reliability of the prosthesis. View full abstract»

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  • Magnetic backprojection imaging of the vascular lumen

    Publication Year: 1995 , Page(s): 102 - 108
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (691 KB)  

    Current injected into a phantom model generated a magnetic field which was distorted above a simulated atherosclerotic lesion. The output of a Hall effect magnetic sensor was used in a backprojection to reconstruct the centroid of the simulated blood flow and thus localize the modeled atherosclerotic plaque region. View full abstract»

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  • Evaluation of a long-range adaptive predictive controller for computerized drug delivery systems

    Publication Year: 1995 , Page(s): 79 - 86
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (806 KB)  

    A closed-loop adaptive control system, based on the generalized predictive control law with a terminal matching condition, has been developed for computerized drug delivery. The control law is a minimization of the squares of prediction errors over a small future prediction horizon plus weighted square of the prediction error at steady-state. A control relevant, long-range identification algorithm is used for on-line parameter estimation. Since the control and identification are mutually compatible, the system truly satisfies the approximate dual control criterion. The system has been applied to the control of mean arterial pressure (MAP) by automatic infusion of sodium nitroprusside in the presence of physical and physiological constraints. Experimental evaluation on six mongrel dogs, in an ethics-approved manner, included setpoint tracking and regulation of MAP in the presence of unpredictable disturbances. The system was found to he capable of inducing hypotension in an average of 2.44±0.31 min (mean±standard error of mean) after probing without any overshoots in mean arterial pressure. The nitroprusside infusion was also free of any ringing. When the subjects were not disturbed, 96.2% of mean arterial pressure remained within 5 mm Hg of the target pressure. A series of disturbances introduced in the presence and absence of closed-loop control affirms the robustness and effectiveness of this control system. View full abstract»

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  • Transformation of multichannel magnetocardiographic signals to standard grid form

    Publication Year: 1995 , Page(s): 72 - 78
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (642 KB)  

    Multichannel magnetocardiographic (MCG) recordings with fixed sensor arrays are not directly comparable with single-channel measurements carried out at standard grid locations. In addition, comparison of data obtained with different types of magnetometers is difficult. The authors present a method for transforming multichannel measurements to the standard-grid format. The minimum-norm estimate (MNE) of the source current distribution in the body is calculated, and the desired field components in standard grid points are then computed from the MNE. The authors measured three subjects with both a 24-channel and a single-channel instrument. The signals extrapolated from the multichannel measurements corresponded quite well to the single-channel data registered at the standard grid locations, especially in those grid points that were covered by the 24-channel device. The signal-amplitude-weighted correlations between the extrapolated and directly measured signals were 0.73-0.87. In simulations with ideal measurement geometry but with a realistic amount of random noise in the signals, the authors obtained a 0.99 correlation. It was also found that the method is relatively tolerant to errors in the location and orientation of the multichannel magnetometer. For example, a simulated 20-mm displacement in the location of the sensor array caused only a 3% decrease in the correlation, and when it was rotated and tilted by 10°, the correlation decreased by 5%. The basic advantage of the authors' extrapolation method is its physiologic nature: the method is based on the mathematical modeling of the source current distribution, rather than on direct constraints applied to the magnetic field. View full abstract»

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  • A method for localizing EEG sources in realistic head models

    Publication Year: 1995 , Page(s): 68 - 71
    Cited by:  Papers (21)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB)  

    A computationally practical method for performing moving dipole calculations to localize EEG sources in realistic, boundary element (integral equation) type of head models is presented. This method makes use of a rapid method of solving the forward problem of calculating the EEG's produced by a dipole in a realistic head model. This rapid forward calculation method allows the use of standard Simplex search techniques to solve the inverse problem of localizing electrical sources in the brain from EEG's measured on the scalp. View full abstract»

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  • Principal-component localization of the sources of the background EEG

    Publication Year: 1995 , Page(s): 59 - 67
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1021 KB)  

    A method, based on principal components for localizing the sources of the background EEG, is presented which overcomes the previous limitations of this approach. The spatiotemporal source model of the EEG is assumed to apply, and the method involves attempting to fit the spatial aspects of this general model with an optimal rotation of a subset of the principal components of a particular EEG. The method is shown to be equivalent to the subspace scanning method, a special case of the MUSIC algorithm, which enables multiple sources to be localized individually rather than all at once. The novel aspect of the new method is that it offers a way of selecting the relevant principal components for the localization problem. The relevant principal components are chosen by decomposing the EEG using spatial patterns common with a control EEG. These spatial patterns have the property that they account for maximally different proportions of the combined variances in the two EEG's. An example is given using a particular EEG from a neurologic patient. Components containing spike and sharp wave potentials are extracted, with respect to a standard EEG derived from 15 normal volunteers. Spike and sharp wave potentials are identified visually using the common spatial patterns decomposition and an EEG reconstructed from these components. Four dipole sources are fitted to the principal components of the reconstructed EEG and these source account for over 88% of the temporal variance present in that EEG. View full abstract»

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  • Evaluation of boundary element methods for the EEG forward problem: effect of linear interpolation

    Publication Year: 1995 , Page(s): 52 - 58
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (731 KB)  

    The authors implement the approach for solving the boundary integral equation for the electroencephalography (EEG) forward problem proposed by de Munck (1992), in which the electric potential varies linearly across each plane triangle of the mesh. Previous solutions have assumed the potential is constant across an element. The authors calculate the electric potential and systematically investigate the effect of different mesh choices and dipole locations by using a three concentric sphere head model for which there is an analytic solution. Implementing the linear interpolation approximation results in errors that are approximately half those of the same mesh when the potential is assumed to be constant, and provides a reliable method for solving the problem. View full abstract»

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  • Nonlinear changes in brain's response in the event of injury as detected by adaptive coherence estimation of evoked potentials

    Publication Year: 1995 , Page(s): 42 - 51
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (962 KB)  

    Injury-related changes in evoked potentials are studied with the aid of the coherence function, which effectively measures the degree of linear association between a pair of signals recorded during normal and abnormal states of the brain. The performance of an adaptive algorithm for estimating coherence function is studied, and the effects of additive noise on the estimated coherence function is discussed. Further, a linearity index is formulated and, through analysis and simulations, the index is shown to respond in a predictable manner to increasing nonlinearity while maintaining the robustness to the observation noise. Somatosensory evoked potentials are shown to be sensitive to injury resulting from acute cerebral hypoxia. The authors analyze the somatosensory evoked potentials recorded from anesthetized cats during inhalation of 8-9% oxygen gas mixtures and during recovery with 100% oxygen. Analyses of the experimental data show a very sharp drop in the magnitude coherence estimates during hypoxic injury and a corresponding rapid decline in the linearity index at the very early stages of the hypoxic injury. Thus, injury may lead to nonlinearities in the electrical response of the brain, and such measurements analyzed by the adaptive coherence estimation method may be used for diagnostic purposes. View full abstract»

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  • Phase and group-delay characteristics of signal-averaged electrocardiograms from patients with ventricular tachycardia

    Publication Year: 1995 , Page(s): 29 - 41
    Cited by:  Papers (1)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1323 KB)  

    Fourier analysis of the signal-averaged ECG (SAECG) has previously revealed significant differences in magnitude spectra that differentiate patients with ventricular tachycardia (VT) from those without VT. To determine additional distinguishing features in the frequency domain, the authors analyzed phase spectra of SAECG's of sinus beats from 57 patients with VT, 65 without VT, and 20 normal controls. Unwrapped phase spectra from SAECG's of the entire cardiac cycle were calculated with respect to three fiducial points: onset of the P and Q waves, and the negative of the slope of the phase (group delay for frequencies in the band, which accounted for 97.5% of the energy in the vector magnitude of the Frank SAECG leads. Phase spectra of SAECG's from patients with VT differed from the non-VT patients at frequencies ≥21 Hz (p=0.000039) for the P-wave fiducial, at frequencies ≥60 Hz (p=0.00085) for the Q-wave fiducial, and at frequencies ≥62 Hz (p=0.0035) for the 97.5% energy fiducial. Group delays in SAECG's from patients with and without VT differed from 10 to 26 Hz (p=0.000016) for the P-wave fiducial, and from 14 to 24 Hz (p=0.00000070) for the Q-wave fiducial. Group delays with respect to the Q-wave fiducial in the VT patients in the 14-24 Hz band were, on average, 9 ms and 5 ms longer than those of the non-VT's and normals, respectively. Thus, phase spectra of SAECG's contain previously undetected features that together with magnitude may be helpful in improving methods for stratifying the risk of VT. View full abstract»

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  • Detection of ECG characteristic points using wavelet transforms

    Publication Year: 1995 , Page(s): 21 - 28
    Cited by:  Papers (333)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (735 KB)  

    An algorithm based on wavelet transforms (WT's) has been developed for detecting ECG characteristic points. With the multiscale feature of WT's, the QRS complex can be distinguished from high P or T waves, noise, baseline drift, and artifacts. The relation between the characteristic points of ECG signal and those of modulus maximum pairs of its WT's is illustrated. By using this method, the detection rate of QRS complexes is above 99.8% for the MIT/BIH database and the P and T waves can also be detected, even with serious base line drift and noise. View full abstract»

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  • Performance of filters for noise reduction in maxillary alveolar bone imaging

    Publication Year: 1995 , Page(s): 13 - 20
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (842 KB)  

    Film-grain noise degrades image detail, hinders detection of subtle radiographic bone changes, and could thwart attempts to use dental radiographs of alveolar bone to detect osteoporosis. The purpose of this investigation was to quantify and compare the performance of various 1- and 2-D spatial and frequency domain filters in suppressing this noise. Estimates of noise-free bone profiles (scan lines) from each of five maxillary interdental areas were made by superimposing and averaging 16 identically exposed and digitized radiographs. The average mean absolute error and mean-squared error between the 80 initially noisy images and their respective noise-free profiles were calculated to provide an estimate of initial noise. Filter performance was measured as the change in these values after filtering the noisy images. Frequency domain analysis revealed that bone signal power spectra dominated at frequencies less than 23 cycles/mm and that some form of low-pass filtering would be applicable. The 2-D Butterworth lowpass filter provided the best performance, removing 57% of the film-grain noise when measured by mean absolute error, and over 80% when measured by mean-squared error. Surprisingly, the Lee, L p mean, geometric mean, binomial, median, and simple neighborhood averaging filters offered comparable levels of performance. View full abstract»

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  • Live cell image segmentation

    Publication Year: 1995 , Page(s): 1 - 12
    Cited by:  Papers (39)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1211 KB)  

    A major requirement of an automated, real-time, computer vision-based cell tracking system is an efficient method for segmenting cell images. The usual segmentation algorithms proposed in the literature exhibit weak performance on live unstained cell images, which can be characterized as being of low contrast, intensity-variant, and unevenly illuminated. The authors propose a two-stage segmentation strategy which involves: 1) extracting an approximate region containing the cell and part of the background near the cell, and 2) segmenting the cell from the background within this region. The approach effectively reduces the influence of peripheral background intensities and texture on the extraction of a cell region. The experimental results show that this approach for segmenting cell images is both fast and robust. View full abstract»

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  • An optimal control model for analyzing human postural balance

    Publication Year: 1995 , Page(s): 87 - 101
    Cited by:  Papers (63)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1564 KB)  

    The question posed in this study is whether optimal control and state estimation can explain selection of control strategies used by humans, in response to small perturbations to stable upright balance. To answer this question, a human sensorimotor control model, compatible with previous work by others, was assembled. This model incorporates linearized equations and full-state feedback with provision for state estimation. A form of gain-scheduling is employed to account for nonlinearities caused by control and biomechanical constraints. By decoupling the mechanics and transforming the controls into the space of experimentally observed strategies, the model is made amenable to the study of a number of possible control objectives. The objectives studied include cost functions on the state deviations, so as to control the center of mass, provide a stable platform for the head, or maintain upright stance, along with a cost function on control effort. Also studied was the effect of time delay on the stability of controls produced using various control strategies. An objective function weighting excursion of the center of mass and deviations from the upright stable position, while taking advantage of fast modes of the system, as dictated by inertial parameters and musculoskeletal geometry, produces a control that reasonably matches experimental data. Given estimates of sensor performance, the model is also suited for prediction of uncertainty in the response. 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