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Biomedical Engineering, IEEE Transactions on

Issue 2 • Date Feb. 2003

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Displaying Results 1 - 18 of 18
  • Statistical performance analysis of signal variance-based dipole models for MEG/EEG source localization and detection

    Publication Year: 2003 , Page(s): 137 - 149
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (971 KB) |  | HTML iconHTML  

    A set of dipole fitting algorithms that incorporate different assumptions about the variability of the signal component into their mathematical models is presented and analyzed. Dipole fitting is performed by minimizing the squared error between the selected data model and available data. Dipole models based on moments that have 1) constant amplitude and orientation, 2) variable amplitude and fixed known orientation, 3) variable amplitude and fixed unknown orientation, and 4) variable amplitude and variable orientation are considered. The presence of a dipolar source is determined by comparing the fractional energy explained by the dipole model to a threshold. Source localization is accomplished by searching to find the location that explains the largest fractional signal energy using a dipole model. Expressions for the probability of a false positive decision and probability of correct detection are derived and used to evaluate the effect of variability in the dipole on performance and to address the effects of model mismatch and location errors. Simulated and measured data experiments are presented to illustrate the performance of both detection and localization methods. The results indicate that models which account for variance outperform the constant orientation and magnitude model even when the number of observations is relatively small and the signal of interest contains a very modest variance component. View full abstract»

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  • The effect of conductivity values on ST segment shift in subendocardial ischaemia

    Publication Year: 2003 , Page(s): 150 - 158
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (700 KB)  

    The aim of this study was to investigate the effect of different conductivity values on epicardial surface potential distributions on a slab of cardiac tissue. The study was motivated by the large variation in published bidomain conductivity parameters available in the literature. Simulations presented are based on a previously published bidomain model and solution technique which includes fiber rotation. Three sets of conductivity parameters are considered and an alternative set of nondimensional parameters relating the tissue conductivities to blood conductivity is introduced. These nondimensional parameters are then used to study the relative effect of blood conductivity on the epicardial potential distributions. Each set of conductivity parameters gives rise to a distinct set of epicardial potential distributions, both in terms of morphology and magnitude. Unfortunately, the differences between the potential distributions cannot be explained by simple combinations of the conductivity values or the resulting dimensionless parameters. View full abstract»

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  • A physiologic model of capillary-tissue exchange for dynamic contrast-enhanced imaging of tumor microcirculation

    Publication Year: 2003 , Page(s): 159 - 167
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    We present a multiple compartment, mammillary distributed-parameter model for capillary-tissue exchange, which can be implemented with dynamic contrast-enhanced imaging to study kinetic heterogeneity in tumors. The proposed n-compartment model consists of a vascular distributed-parameter compartment in direct exchange with a number (n-1) of interstitial compartments. It is applied to a prostate tumor case study to illustrate the possible co-existence of two kinetically distinct compartments in the tumor, and the estimation of useful physiological parameters (such as perfusion, mean transit time, fractional volumes, and transfer and rate constants) associated with tissue microcirculation. The present model exhibits the convenient property of a separable impulse residue response function in the time domain, which can be used to provide further insights and understanding on the physiological basis of tissue enhancement parameters commonly used for correlation studies with tumor histological diagnosis. View full abstract»

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  • Ischemic modulation of vulnerable period and the effects of pharmacological treatment of ischemia-induced arrhythmias: a simulation study

    Publication Year: 2003 , Page(s): 168 - 177
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (586 KB) |  | HTML iconHTML  

    First identified in the 1930s (Ferris et al., 1936 and Wiggers and Wegria, 1939), the concept of vulnerability applies perfectly to biological oscillators. We can safely say that vulnerability is an inherent property of any excitable media. The duration of vulnerable period (VP) (the time interval during which single stimuli can initiate self-sustaining propagation) is sensitive to medium properties and stimulus parameters (stimulus field, timing behind the conditioning wave, and stimulus amplitude). Apart from medium properties and stimulus characteristics, heart vulnerability is affected by any intervention targeting the excitatory and recovery process. Therefore, we can expect that any pathological condition disturbing heart excitation or tissue recovery will most probably alter the duration of VP. In this paper, we shall explore the implications of ischemia and one of the arrhythmia counteracting methods widely used in clinical practice-antiarrhythmic drugs-in changing the boundaries of VP. The Cardiac Arrhythmia Suppression Trial (CAST) studies, as well as classification based on functional characteristics, revealed the arrhythmogenic potential of both Class I and Class III agents, but failed to identify the proarrhythmic mechanisms. This study presents results from a mathematical model (Cimponeriu et al., 2001) of the ventricle based on Luo-Rudy cellular formulation (Luo and Rudy, 1991) modified for studying the ischemic modulation of VP and the effects of pharmacological treatment of ischemia-induced arrhythmia. Simulations revealed the link between the cellular antiarrhythmic properties and the proarrhythmic effect at the multicellular level in the case of Na+ channel blockade. Na+ channel blockade delayed recovery of cellular excitability, but also introduced a nonuniform dispersion of refractoriness along the cardiac fiber that can serve as a substrate for initiating a new arrhythmia. Our initial analysis proved that fast unbinding rates are essential in reducing the proarrhythmic potential of Class I drugs. However, further investigations led us to believe that binding properties are equally important. An antiarrhythmic drug with high affinity for drug-channel complex formation elicits a higher level of blockade per time unit. Under thi- s light, we hypothesize that even the modern, fast unbinding drugs are not necessarily safe. View full abstract»

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  • Nonparametric 1-D temperature restoration in lossy media using Tikhonov regularization on sparse radiometry data

    Publication Year: 2003 , Page(s): 178 - 188
    Cited by:  Papers (9)  |  Patents (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    Microwave thermometry has the potential to characterize thermal gradients in lossy materials down to a few centimeters depth. The problem of retrieving temperature profiles from sets of brightness temperatures is studied using Galerkin expansion of one-dimensional (1-D) temperature profiles combined with Tikhonov regularization and predefined boundary conditions. From a priori knowledge of the temperature field shape, smooth Chebyshev polynomials are used as basis functions in the series expansion. The proposed estimator does not require iterative calculations that are normally performed using conventional numerical methods for signal parameter estimation and is, thus, very fast. Noise effects versus bandwidth limitations (smoothness of solutions) are studied in terms of four performance indexes defined in the text. In general, statistical spread of the temperature estimator increases with increasing number of Chebyshev polynomials. Systematic deviation from true values (bias) decreases as the number of Chebyshev polynomials increases. Results show that smooth temperature profiles can be reproduced using 6-7 Chebyshev polynomials. With additional constraints such as boundary conditions and maxima localization, a three-frequency-band radiometric scan is sufficient to produce acceptable results in regions with low thermal gradients. As the spatial variability of the 1-D temperature profile increases, more radiometric bands (5-6) are required to provide nonbiased estimates. View full abstract»

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  • Single-trial estimation of multichannel evoked-potential measurements

    Publication Year: 2003 , Page(s): 189 - 196
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    A method for single-trial estimation of multichannel evoked potentials is presented. The proposed method is based on the regularized least squares scheme. The spatial correlation between the channels is used as additional information in the estimation procedure. Amplitude estimates obtained with the proposed method are compared with estimates calculated without using the spatial information. The performance of the method is evaluated using simulated and real data of P300 responses measured using auditory stimuli. The multichannel approach is shown to give realistic and comparable information about the amplitude differences of the P300 peak between different channels. View full abstract»

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  • Application of an adaptive control grid interpolation technique to morphological vascular reconstruction

    Publication Year: 2003 , Page(s): 197 - 206
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1054 KB) |  | HTML iconHTML  

    The problem of interslice magnetic resonance (MR) image reconstruction arises in a broad range of medical applications. In such cases, there is a need to approximate information present in the original subject that is not reflected in contiguously acquired MR images because of hardware sampling limitations. In the context of vascular morphology reconstruction, this information is required in order for subsequent visualization and computational analysis of blood vessels to be most effective. Toward that end we have developed a method of vascular morphology reconstruction based on adaptive control grid interpolation (ACGI) to function as a precursor to visualization and computational analysis. ACGI has previously been implemented in addressing various problems including video coding and tracking. This paper focuses on the novel application of the technique to medical image processing. ACGI combines features of optical flow-based and block-based motion estimation algorithms to enhance insufficiently dense MR data sets accurately with a minimal degree of computational complexity. The resulting enhanced data sets describe vascular geometries. These reconstructions can then be used as visualization tools and in conjunction with computational fluid dynamics (CFD) simulations to offer the pressure and velocity information necessary to quantify power loss. The proposed ACGI methodology is envisioned ultimately to play a role in surgical planning aimed at producing optimal vascular configurations for successful surgical outcomes. View full abstract»

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  • A novel spectral microscope system: application in quantitative pathology

    Publication Year: 2003 , Page(s): 207 - 217
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (835 KB) |  | HTML iconHTML  

    A novel spectral microscope system is presented together with a method for the quantitative assessment of the uptake by histologic samples of stains used in pathology to label tissue features of diagnostic importance. The critical component of the microscope is a variable interference filter-based monochromator. The system is capable of performing real-time spectral imaging in a plurality of spectral bands and micro-spectroscopy in any image pixel, in the spectral range 400-1000 nm. The wavelength-tuning step is 2.4-2.6 nm, while the full-width at half maximum in each step is about 1.5% of the operating central wavelength. The developed system integrates algorithms and calibration procedures for the calculation of the stain-uptake by the tissue. The acquired spectra from both stained tissue and calibration stain solutions enable the calculation of the concentration maps of the stains, even if the latter are multiple and overlap spatially and spectrally. The system was used for the quantitative mapping of the expression of estrogen and progesterone receptors in breast cancer cells. In this particular case, model validation shows that although two stains are employed, capturing of their transmittance at more than ten wavelengths is required in order to obtain an acceptable accuracy. These findings highlight the need for the development and implementation of spectral microscopy in pathology and its potential to introduce novel more reliable diagnostic criteria. View full abstract»

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  • Noncontact radio-frequency ablation for obtaining deeper lesions

    Publication Year: 2003 , Page(s): 218 - 223
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    Radio-frequency (RF) cardiac catheter ablation has been very successful for treating some cardiac arrhythmias, however, the success rate for ventricular tachycardias is still not satisfactory. Some existing methods for developing deeper lesions include active cooling of the electrode and modifying the electrode shape. We propose a method of noncontact ablation, to solve this problem. We apply 120 W of power through an 8-mm electrode for a 120-s duration, with distances from 0 to 3 mm between electrode and myocardium, to create lesions in myocardium. We apply flow rates of 1, 3, and 5 L/min to determine their effect. Results show that with an optimal distance from 0.5 to 1.5 mm between electrode and myocardium, we increase lesion depth from 7.5 mm for contact ablation to 9.5 mm for noncontact ablation. For different flow rates, the optimal distance various. The effect of flow rate is not obvious. Higher flow rate does not lead to a deeper lesion. View full abstract»

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  • Human exposure assessment in the near field of GSM base-station antennas using a hybrid finite element/method of moments technique

    Publication Year: 2003 , Page(s): 224 - 233
    Cited by:  Papers (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1236 KB) |  | HTML iconHTML  

    A hybrid finite-element method (FEM)/method of moments (MoM) technique is employed for specific absorption rate (SAR) calculations in a human phantom in the near field of a typical group special mobile (GSM) base-station antenna. The MoM is used to model the metallic surfaces and wires of the base-station antenna, and the FEM is used to model the heterogeneous human phantom. The advantages of each of these frequency domain techniques are, thus, exploited, leading to a highly efficient and robust numerical method for addressing this type of bioelectromagnetic problem. The basic mathematical formulation of the hybrid technique is presented. This is followed by a discussion of important implementation details-in particular, the linear algebra routines for sparse, complex FEM matrices combined with dense MoM matrices. The implementation is validated by comparing results to MoM (surface equivalence principle implementation) and finite-difference time-domain (FDTD) solutions of human exposure problems. A comparison of the computational efficiency of the different techniques is presented. The FEM/MoM implementation is then used for whole-body and critical-organ SAR calculations in a phantom at different positions in the near field of a base-station antenna. This problem cannot, in general, be solved using the MoM or FDTD due to computational limitations. This paper shows that the specific hybrid FEM/MoM implementation is an efficient numerical tool for accurate assessment of human exposure in the near field of base-station antennas. View full abstract»

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  • The trans-cardiac conductance method for on-line measurement of left ventricular volume: assessment of parallel conductance offset volume

    Publication Year: 2003 , Page(s): 234 - 240
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    The trans-cardiac conductance (TCC) method provides on-line left ventricular (LV) volume signals by determining the electrical conductance of blood in the LV by means of central venous and epithoracic electrodes. Conductive structures outside the LV blood pool cause a "parallel conductance" offset term (Vp) that can be determined by bolus injections of hypertonic saline in the pulmonary artery (Vpsaline), which cause a transient increase in blood conductivity. This study in anesthetized sheep evaluates the accuracy of the saline calibration method and the variabilities of Vp between animals, between hemodynamic conditions and during the cardiac cycle. The conventional intra-cardiac conductance catheter method was used to obtain independent estimates of Vp by the zero-volume method (Vpzerovolume). Mean baseline Vpsaline and Vpzerovolume were 104 ± 6 ml and 106 ± 6 ml, respectively. Bland-Altman analysis showed a small nonsignificant bias (-2.5 ml) and narrow limits of agreement (4.6 ml). Vp was not significantly different between hemodynamic conditions (baseline, dobutamine, volume load, propranolol), but had a substantial interanimal variability (IAV) (38%). Average variations during the cardiac cycle were <10% of mean Vp. We conclude that the saline method can be applied to determine Vp for TCC. IAV is substantial, so that Vp must be determined in each animal, but within-animal variability is relatively small. View full abstract»

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  • A system for MEA-based multisite stimulation

    Publication Year: 2003 , Page(s): 241 - 248
    Cited by:  Papers (65)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (861 KB) |  | HTML iconHTML  

    The capability for multisite stimulation is one of the biggest potential advantages of microelectrode arrays (MEAs). There remain, however, several technical problems which have hindered the development of a practical stimulation system. An important design goal is to allow programmable multisite stimulation, which produces minimal interference with simultaneous extracellular and patch or whole cell clamp recording. Here, we describe a multisite stimulation and recording system with novel interface circuit modules, in which preamplifiers and transistor transistor logic-driven solid-state switching devices are integrated. This integration permits PC-controlled remote switching of each substrate electrode. This allows not only flexible selection of stimulation sites, but also rapid switching of the selected sites between stimulation and recording, within 1.2 ms. This allowed almost continuous monitoring of extracellular signals at all the substrate-embedded electrodes, including those used for stimulation. In addition, the vibration-free solid-state switching made it possible to record whole-cell synaptic currents in one neuron, evoked from multiple sites in the network. We have used this system to visualize spatial propagation patterns of evoked responses in cultured networks of cortical neurons. This MEA-based stimulation system is a useful tool for studying neuronal signal processing in biological neuronal networks, as well as the process of synaptic integration within single neurons. View full abstract»

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  • Principal component analysis as a method to facilitate fast detection of transient-evoked otoacoustic emissions

    Publication Year: 2003 , Page(s): 249 - 252
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (326 KB) |  | HTML iconHTML  

    Transient-evoked otoacoustic emissions (TEOAE) are acoustic signals coming from the inner ear (outer hair cells of the cochlea) after acoustic stimulation by clicks. They can be used to investigate the status of the peripheral hearing system. Some of their potential applications (e.g., their use as a tool in newborn hearing screening programs) are deeply related to the duration of each recording session. This duration can be strongly reduced by applying a principal component analysis approach to a set of TEOAE recorded from the same ear at different stimulus levels averaging only a few sweeps (a maximum of 100 versus the classical 260). The PCA approach is shown to be able to enhance the signal-to-noise ratio and, in turn, to allow a correct detection of the responses. Results of the application of this approach in comparison with responses recorded from the same subjects with the classical technique are shown. View full abstract»

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  • Doppler ultrasound imaging of magnetically vibrated brachytherapy seeds

    Publication Year: 2003 , Page(s): 252 - 254
    Cited by:  Papers (15)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    Vibration induced by an alternating magnetic field is proposed as a method for the identification of modified brachytherapy seeds with Doppler ultrasound. In vitro experiments with agar and liver-tissue phantoms using a clinical scanner and simple apparatus demonstrate that the technique is feasible. View full abstract»

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  • Two multichannel integrated circuits for neural recording and signal processing

    Publication Year: 2003 , Page(s): 255 - 258
    Cited by:  Papers (30)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (251 KB) |  | HTML iconHTML  

    We have developed, manufactured, and tested two analog CMOS integrated circuit "neurochips" for recording from arrays of densely packed neural electrodes. Device A is a 16-channel buffer consisting of parallel noninverting amplifiers with a gain of 2 V/V. Device B is a 16-channel two-stage analog signal processor with differential amplification and high-pass filtering. It features selectable gains of 250 and 500 V/V as well as reference channel selection. The resulting amplifiers on Device A had a mean gain of 1.99 V/V with an equivalent input noise of 10 μVrms. Those on Device B had mean gains of 53.4 and 47.4 dB with a high-pass filter pole at 211 Hz and an equivalent input noise of 4.4 μVrms. Both devices were tested in vivo with electrode arrays implanted in the somatosensory cortex. View full abstract»

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  • Real-time signal processing for fetal heart rate monitoring

    Publication Year: 2003 , Page(s): 258 - 261
    Cited by:  Papers (30)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (317 KB) |  | HTML iconHTML  

    An algorithm based on digital filtering, adaptive thresholding, statistical properties in the time domain, and differencing of local maxima and minima has been developed for the simultaneous measurement of the fetal and maternal heart rates from the maternal abdominal electrocardiogram during pregnancy and labor for ambulatory monitoring. A microcontroller-based system has been used to implement the algorithm in real-time. A Doppler ultrasound fetal monitor was used for statistical comparison on five volunteers with low risk pregnancies, between 35 and 40 weeks of gestation. Results showed an average percent root mean square difference of 5.32% and linear correlation coefficient from 0.84 to 0.93. The fetal heart rate curves remained inside a ±5-beats-per-minute limit relative to the reference ultrasound method for 84.1% of the time. View full abstract»

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  • Fatigue analysis of the surface EMG signal in isometric constant force contractions using the averaged instantaneous frequency

    Publication Year: 2003 , Page(s): 262 - 265
    Cited by:  Papers (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (245 KB) |  | HTML iconHTML  

    The averaged instantaneous frequency (AIF) is proposed as an alternative method for the frequency analysis of surface electromyography (EMG) in the study of muscle fatigue during sustained, isometric muscle contractions. Results from performance analysis using experimental EMG signals demonstrate the low variability of the proposed frequency variable. Indeed, the AIF measure is shown to perform significantly better than the widely used mean and median frequency variables, in terms of robustness to the length of the analysis window. View full abstract»

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  • Biological constraints simplify the recognition of hand shapes

    Publication Year: 2003 , Page(s): 265 - 269
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (597 KB) |  | HTML iconHTML  

    This study sought to identify constraints that might lead to a concise system of recognizing fingerspelling hand shapes. Previous studies of grasping suggested that hand shape is controlled using combinations of a small number of neuromuscular synergies, but fingerspelling shapes appear to be more highly individuated and, therefore, might require a larger number of degrees of freedom. Static hand postures of the American Sign Language manual alphabet were recorded by measuring 17 joint angles. Principal components (PCs) analysis was compared to the use of subsets of individual variables (i.e., joint angles) for reduction in degrees of freedom. The first four PCs were similar across subjects. Classification using weightings from these four components was 86.6% accurate, while classification using four individual variables was 88.5% accurate (thumb abduction, as well as flexion at the index and middle finger proximal interphalangeal joints and the ring finger metacarpalphalangeal joint). When chosen for each subject, particular four-variable subsets yielded correct rates above 95%. This superior performance of variable subsets over PC weighting vectors suggests that the reduction in degrees of freedom is due to biomechanical and neuromuscular constraints rather than synergistic control. Thus, in future application to dynamic fingerspelling, reasonable recognition accuracy might be achieved with a significant reduction in both computational and measured degrees of freedom. 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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Meet Our Editors

Editor-in-Chief
Bin He
Department of Biomedical Engineering