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Biomedical Engineering, IEEE Transactions on

Issue 6 • Date June 2001

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Displaying Results 1 - 15 of 15
  • A novel robust index to assess beat-to-beat variability in heart rate time-series analysis

    Publication Year: 2001 , Page(s): 617 - 621
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (106 KB) |  | HTML iconHTML  

    A new index is proposed to estimate the variance of the differentiated heart rate (RR) time series from its truncated histogram. The index is more robust to artifacts than the standard deviation of the differentiated RR time series (rMSDD) and, unlike the pNN50, does not saturate for very high or very low heart rate variability. View full abstract»

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  • Accurate identification of periodic oscillations buried in white or colored noise using fast orthogonal search

    Publication Year: 2001 , Page(s): 622 - 629
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    The authors use a previously introduced fast orthogonal search algorithm to detect sinusoidal frequency components buried in either white or colored noise. They show that the method outperforms the correlogram, modified covariance autoregressive (MODCOVAR) and multiple-signal classification (MUSIC) methods. Fast orthogonal search method achieves accurate detection of sinusoids even with signal-to-noise ratios as low as -10 dB, and is superior at detecting sinusoids buried in 1/f noise. Since the utilized method accurately detects sinusoids even under colored noise, it can be used to extract a 1/f noise process observed in physiological signals such as heart rate and renal blood pressure and flow data. View full abstract»

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  • Electric field stimulation of cardiac myocytes during postnatal development

    Publication Year: 2001 , Page(s): 630 - 636
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (185 KB) |  | HTML iconHTML  

    Studies on cardiac cell response to electric field stimulation are important for understanding basic phenomena underlying cardiac defibrillation. In this work, the authors used a model of a prolate spheroidal cell in a uniform external field (Klee and Plonsey, 1976) to predict the threshold electric field (ET) for stimulation of isolated ventricular myocytes of rats at different ages. The model assumes that ET is primarily determined by cell shape and dimensions, which markedly change during postnatal development. Neonatal cells showed very high ET, which progressively decreased with maturation (experimental mean values were 29, 21, 13, and 5.9 and 6.3 V/cm for 3-6, 13-16, 20-21, 28-35, and 120-180 day-old rats, respectively, P<0.001; theoretical values were 24, 18, 11, 9, and 6 V/cm, respectively). Estimated maximum membrane depolarization at threshold (ΔV T≈35 mV, under the authors' experimental conditions) was reasonably constant during development, except for cells from 1-mo-old animals, in which ΔVT was lower than at other ages. It is concluded that the model reasonably correlates ET with cell geometry and size in most cases. The authors' results might be relevant for the development of efficient procedures for defibrillation of pediatric patients. View full abstract»

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  • Finite-element analysis of aortic valve-sparing: influence of graft shape and stiffness

    Publication Year: 2001 , Page(s): 647 - 659
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    Aortic valve incompetence due to aortic root dilation may be surgically corrected by resuspension of the native valve within a vascular graft. This study was designed to examine the effect of graft shape and material properties on aortic valve function, using a three-dimensional finite-element model of the human aortic valve and root. First, the normal root elements in the model were replaced with graft elements, in either a cylindrical or a "pseudosinus" shape. Next, the elements were assigned the material properties of either polyethylene terephthalate; expanded polytetrafluoroethylene, or polyurethane. Diastolic pressures were applied, and stresses, strains, and coaptation were recorded for the valve, root, and graft. Regarding shape, the cylindrical graft models increased the valve stresses by up to 173%, whereas the root-shaped graft model increased valve stresses by up to 40% as compared to normal. Regarding material properties, the polyurethane models demonstrated valve stress, strain, and coaptation values closest to normal, for either root shape. Graft shape had a greater effect on the simulated valve function than did the material property of the graft. Optimizing the shape and material design of the graft may result in improved longevity of the spared valve if a normal environment is restored. View full abstract»

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  • Localization of the site of origin of cardiac activation by means of a heart-model-based electrocardiographic imaging approach

    Publication Year: 2001 , Page(s): 660 - 669
    Cited by:  Papers (43)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    The authors have developed a new approach to solve the inverse problem of electrocardiography in terms of heart model parameters. The inverse solution of the electrocardiogram (ECG) inverse problem is defined, in the present study, as the parameters of the heart model, which are closely related to the physiological and pathophysiological status of the heart, and is estimated by using an optimization system of heart model parameters, instead of solving the matrix equation relating the body surface ECGs and equivalent cardiac sources. An artificial neural network based preliminary diagnosis system has been developed to limit the searching space of the optimization algorithm and to initialize the model parameters in the computer heart model. The optimal heart model parameters were obtained by minimizing the objective functions, as functions of the observed and model-generated body surface ECGs. The authors have tested the feasibility of the newly developed technique in localizing the site of origin of cardiac activation using a pace mapping protocol. The present computer simulation results show that, the present approach for localization of the site of origin of ventricular activation achieved an averaged localization error of about 3 mm [for 5-μV Gaussian white noise (GWN)] and 4 mm (for 10-μV GWN), with standard deviation of the localization errors of being about 1.5 mm. The present simulation study suggests that this newly developed approach provides a robust inverse solution, circumventing the difficulties of the ECG inverse problem, and may become an important alternative to other ECG inverse solutions. View full abstract»

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  • Estimating the posterior probability of LTP failure by sequential Bayesian analysis of an imperfect Bernoulli trial model

    Publication Year: 2001 , Page(s): 670 - 683
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (307 KB) |  | HTML iconHTML  

    A tetanically stimulated (TS) neuron is said to have failed to fire if its voltage-clamped excitatory postsynaptic current (EPSC) measurement is devoid of a long-term potentiation (LTP) response. This paper provides a method for evaluating the posterior probability of "failure" for TS neurons. A sequential Bayes algorithm is employed on an imperfect Bernoulli trial model to refine the posterior with each EPSC data record processed. The method is applied to both real and simulated LTP data and is shown to be consistent with the theoretical Beta-distributed posterior and the reported in vitro voltage-damped EPSC failure rates. View full abstract»

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  • Improved coil design for functional magnetic stimulation of expiratory muscles

    Publication Year: 2001 , Page(s): 684 - 694
    Cited by:  Papers (7)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    The authors' studies have demonstrated effective stimulation of the expiratory muscles in patients with spinal cord injury (SCI) using functional magnetic stimulation (FMS). The observed contraction of the expiratory muscles and functional improvement of the pulmonary functions make functional magnetic stimulation an appropriate tool for expiratory muscle training. To fully capitalize on the benefits of FMS for expiratory muscle training, this study aimed to optimize the magnetic coils (MCs). The primary goal of this study was to investigate how two parameters of the MC size and winding structure, would affect expiratory muscle training. By varying these parameters, the authors' approach was to conceptualize and evaluate the induced electric field and nerve activation function distributions of six coils, round 9.2, 13.7, and 20 cm, and spiral 9.2-, 13.7-, and 20-cm coils in the computer modeling phase. Round 9.2 cm, spiral 13.7 cm, and spiral 20-cm coils were also evaluated in experimental studies for induced electrical field and in clinical studies of expiratory muscles. Both the computer models and experimental measurements indicated that the spiral 20-cm coil can not only stimulate more expiratory spinal nerves but can also stimulate them more evenly. In addition, coils with larger diameters had better penetration than those with smaller diameters. The clinical results showed that the spiral 20-cm coil produced higher expiratory pressure, flow and volume in five able-bodied subjects, and it was the coil of choice among the subjects when asked their preferences. In the authors' attempt to optimize MC design for FMS of expiratory muscle training, they followed the designing guidelines set out in their previous study and arrived at a more effective tool. View full abstract»

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  • A low-cost fiber-optic instrument to colorimetrically detect patients with Barrett's esophagus for early detection of esophageal adenocarcinoma

    Publication Year: 2001 , Page(s): 695 - 705
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    In Barrett's esophagus, the precursor to esophageal adenocarcinoma, the squamocolumnar junction (SCJ) between the normal esophagus and the stomach like mucosa is proximally displaced. Currently it can be detected only by an expensive upper GI endoscopic procedure. The authors have developed a minimally invasive and easy to operate colorimetric instrument for the low-cost detection of Barrett's esophagus. The instrument is based on a flexible, narrow diameter, fiber-optic probe that performs a colorimetric scan of the esophageal lumen. The instrument was clinically evaluated in 50 subjects. The instrument could identify both symmetric and asymmetric SCJ's. The SCJ locations determined by the colorimetric instrument correlated strongly (R 2=0.89) with those determined by endoscopy. The instrument identified the SCJ locations accurately (Mean of difference ±SEM: 0.97±1.72 cm) and reproducibly (mean of absolute difference ±SEM: 1.33±1.40 cm). The instrument has a 90% sensitivity of identifying patients with Barrett's esophagus, based on the clinical algorithm that if the SCJ is located at a distance less than 37 cm from the teeth, then the subject has Barrett's esophagus, otherwise the subject does not have Barrett's esophagus. In conclusion, the colorimetric instrument has the potential of being a cost-effective way of determining patients likely to have Barrett's esophagus in the population. View full abstract»

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  • Computer-assisted quantification of axo-somatic boutons at the cell membrane of motoneurons

    Publication Year: 2001 , Page(s): 706 - 717
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB)  

    This paper presents a system for computer-assisted quantification of axe-somatic boutons at motoneuron cell-surface membranes. Different immunohistochemical stains can be used to prepare tissue of the spinal cord. Based on micrographs displaying single neurons, a finite element balloon model has been applied to determine the exact location of the cell membrane. A synaptic profile is extracted next to the cell membrane and normalized with reference to the intracellular brightness. Furthermore, a manually selected reference cell is used to normalize settings of the microscope as well as variations in histochemical processing for each stain. Thereafter, staining, homogeneity, and allocation of boutons are determined automatically from the synaptic profiles. The system is evaluated by applying the coefficient of variation (C v) to repeated measurements of a quantity. Based on 1856 motoneuronal images acquired from four animals with three stains, 93% of the images are analyzed correctly. The others were rejected, based on process protocols. Using only rabbit anti-synaptophysin as primary antibody, the correctness increases above 96%, C v values are below 3%, 5%, and 6% for all measures with respect to stochastic optimization, cell positioning, and a large range of microscope settings, respectively. A sample size of about 100 is required to validate a significant reduction of staining in motoneurons below a hemi-section (Wilcoxon rank-sum test, α=0.05, β=0.9). The authors' system yields statistically robust results from light micrographs. In future, it is hoped that this system will substitute for the expensive and time-consuming analysis of spinal cord injury at the ultra-structural level, such as by manual interpretation of nonoverlapping electron micrographs. View full abstract»

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  • Automatic identification of human helminth eggs on microscopic fecal specimens using digital image processing and an artificial neural network

    Publication Year: 2001 , Page(s): 718 - 730
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (286 KB) |  | HTML iconHTML  

    In order to automate routine fecal examination for parasitic diseases, the authors propose in this study a computer processing algorithm using digital image processing techniques and an artificial neural network (ANN) classifier The morphometric characteristics of eggs of human parasites in fecal specimens were extracted from microscopic images through digital image processing. An ANN then identified the parasite species based on those characteristics. The authors selected four morphometric features based on three morphological characteristics representing shape, shell smoothness, and size. A total of 82 microscopic images containing seven common human helminth eggs were used. The first stage (ANN-1) of the proposed ANN classification system isolated eggs from confusing artifacts. The second stage (ANN-2) classified eggs by species. The performance of ANN was evaluated by the tenfold cross-validation method to obviate the dependency on the selection of training samples. Cross-validation results showed 86.1% average correct classification ratio for ANN-1 and 90.3% for ANN-2 with small variances of 46.0 and 39.0, respectively. The algorithm developed will be an essential part of a completely automated fecal examination system. View full abstract»

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  • Line patterns in the mosaic electrical properties of human skin-a cross-correlation study

    Publication Year: 2001 , Page(s): 731 - 734
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (82 KB) |  | HTML iconHTML  

    A vehicle with 16 electrodes for the two-dimensional electrical admittance mapping of human skin is presented. Measurements on 20 test subjects have been carried out and analyzed for the possible detection of line patterns in the electrical properties of the skin, claimed to coincide with the so-called acupuncture meridian lines of ancient Chinese medicine. No such lines were found. View full abstract»

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  • An ultralight biotelemetry backpack for recording EMG signals in moths

    Publication Year: 2001 , Page(s): 734 - 737
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (337 KB) |  | HTML iconHTML  

    A two-channel FM biopotential recording system fabricated on a foldable, lightweight, polyimide substrate is presented. Each channel consists of a biopotential amplifier followed by a Colpitts oscillator with operating frequency tunable in the 88-108 MHz commercial FM band. The overall system measures 10 mm×10 mm×3 mm, weighs 0.74 g, uses two 1.5-V batteries, dissipates about 2 mW, and has a transmission range of 2 m. Using this system, electromyogram signals have been recorded from the dorsal ventral muscle and the dorsal longitudinal muscle of a giant sphinx moth (Manduca sexta). View full abstract»

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  • Estimated generalized least squares electromagnetic source analysis based on a parametric noise covariance model [EEG/MEG]

    Publication Year: 2001 , Page(s): 737 - 741
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (122 KB) |  | HTML iconHTML  

    Estimated generalized least squares (EGLS) electromagnetic source analysis is used to downweight noisy and correlated data. Standard EGLS requires many trials to accurately estimate the noise covariances and, thus, the source parameters. Alternatively, the noise covariances can be modeled parametrically. Only the parameters of the model describing the noise covariances need to be estimated and, therefore, less trials are required. This method is referred to as parametric EGLS (PEGLS). In this paper, PEGLS is developed and its performance is tested in a simulation study and in a pseudoempirical study. View full abstract»

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  • Correction to "Regional head tissue conductivity estimation for improved EEG analysis"

    Publication Year: 2001
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (23 KB) |  | HTML iconHTML  

    Two equations in the Appendix of the title paper (see T.C. Ferree et al., ibid., vol. 47, p. 1584-92, 2000) included typographical errors. They should be replaced by the corrected equations given here. The errors were merely typographical. The authors have verified that the equations used to generate the numerical results in the original paper were implemented correctly. Consequently, the conclusions of the original paper are still equally valid. These corrections affect only readers wishing to reproduce the authors' results. The authors sincerely thank A. Liston for pointing out the errors. They apologize for any inconvenience. View full abstract»

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  • A novel approach for precise simulation of the EMG signal detected by surface electrodes

    Publication Year: 2001 , Page(s): 637 - 646
    Cited by:  Papers (68)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    The authors propose a new electromyogram generation and detection model. The volume conductor is described as a nonhomogeneous (layered) and anisotropic medium constituted by muscle, fat and skin tissues. The surface potential detected in space domain is obtained from the application of a two-dimensional spatial filter to the input current density source. The effects of electrode configuration, electrode size and inclination of the fibers with respect to the detection system are included in the transfer function of the filter. Computation of the signal in space domain is performed by applying the Radon transform; this permits to draw considerations about spectral dips and clear misunderstandings in previous theoretical derivations. The effects of generation and extinction of the action potentials at the fiber end plate and at the tendons are included by modeling the source current, without any approximation of its shape, as a function of space and time and by using again the Radon transform. The approach, based on the separation of the temporal and spatial properties of the muscle fiber action potential and of the volume conductor, includes the capacitive tissue properties 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