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Biomedical Engineering, IEEE Transactions on

Issue 11 • Date Nov. 1997

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Displaying Results 1 - 16 of 16
  • Early recognition of postural disorders in multiple sclerosis through movement analysis: a modeling study

    Publication Year: 1997 , Page(s): 1029 - 1038
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (211 KB)  

    In the present study, spontaneous postural behavior has been analyzed in freely standing multiple sclerosis (MS) patients, exhibiting no clinically assessable abnormalities of postural control. This population has been compared with two other groups, healthy people and hemiparetic patients. This latter group represents a situation where the central nervous system (CNS) lesion is precisely localized in one anatomical site and no signal-conduction disorders are present; i.e., it has an opposite anatomical character with respect to the MS at a preclinical stage. The hypothesis underlying the modeling study is the presence of a controller block working in a feedback posture control system. This controller block receives the body sway as input, and produces the corresponding ankle torque stabilizing the body, the latter being modeled as an inverted pendulum. The CNS damage, caused by MS, is supposed to be reflected in some detectable change in the structure of the controller of the posture control system. The identification of the controller has been performed by means of a parametric estimation procedure which employed as input sequences, data recorded by means of a movement-analysis (MA) system. Reported findings show a structural change of the model of the controller block in the posture control system. This result may suggest the presence of an MS-specific reorganization of the posture control system. Some speculation is finally made on the black-box approach in comparison with traditional posturography, to arrive at hypothesizing a progression path for postural disorders. View full abstract»

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  • A hybrid computational model for ultrasound phased-array heating in presence of strongly scattering obstacles

    Publication Year: 1997 , Page(s): 1039 - 1050
    Cited by:  Papers (23)  |  Patents (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (605 KB)  

    A computationally efficient hybrid ray-physical optics (HRPO) model is presented for the analysis and synthesis of multiple-focus ultrasound heating patterns through the human rib cage. In particular, a ray method is used to propagate the ultrasound fields from the source to the frontal plane of the rib cage. The physical-optics integration method is then employed to obtain the intensity pattern inside the rib cage. The solution of the matrix system is carried out by using the pseudo inverse technique to synthesize the desired heating pattern. The proposed technique guides the fields through the intercostal spacings between the solid ribs and, thus, minimal intensity levels are observed over the solid ribs. This simulation model allows for the design and optimization of large-aperture phased-array applicator systems for noninvasive ablative thermal surgery in the heart and liver through the rib cage. View full abstract»

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  • Electrical impedance tomography of complex conductivity distributions with noncircular boundary

    Publication Year: 1997 , Page(s): 1051 - 1060
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (547 KB)  

    Electrical impedance tomography (EIT) uses low-frequency current and voltage measurements made on the boundary of a body to compute the conductivity distribution within the body. Since the permittivity distribution inside the body also contributes significantly to the measured voltages, the present reconstruction algorithm images complex conductivity distributions. A finite element model (FEM) is used to solve the forward problem, using a 6017-node mesh for a piecewise-linear potential distribution. The finite element solution using this mesh is compared with the analytical solution for a homogeneous field and a maximum error of 0.05% is observed in the voltage distribution. The boundary element method (BEM) is also used to generate the voltage data for inhomogeneous conductivity distributions inside regions with noncircular boundaries. An iterative reconstruction algorithm is described for approximating both the conductivity and permittivity distributions from this data. The results for an off-centered inhomogeneity showed a 35% improvement in contrast from that seen with only one iteration, for both the conductivity and the permittivity values. It is also shown that a significant improvement in images results from accurately modeling a noncircular boundary. Both static and difference images are distorted by assuming a circular boundary and the amount of distortion increases significantly as the boundary shape becomes more elliptical. For a homogeneous field in an elliptical body with axis ratio of 0.73, an image reconstructed assuming the boundary to be circular has an artifact at the center of the image with an error of 20%. This error increased to 37% when the axis ratio was 0.64. A reconstruction algorithm which used a mesh with the same axis ratio as the elliptical boundary reduced the error in the conductivity values to within 0.5% of the actual values. View full abstract»

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  • Application of sonomicrometry and multidimensional scaling to cardiac catheter tracking

    Publication Year: 1997 , Page(s): 1061 - 1067
    Cited by:  Papers (10)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (134 KB)  

    This paper describes a technique for tracking the three-dimensional (3-D) position of a cardiac catheter using sonomicrometry and the mathematical method of multidimensional scaling (MDS). Sonomicrometry is used to measure the distances between ultrasonic transceivers. MDS is then used to calculate the 3-D coordinates of the ultrasonic transceiver locations, including the catheter tip, from the measured distances. Feasibility of catheter tracking was initially studied using simulated data from a geometric model in which the actual coordinates of all transceivers were known. The method was then shown to be feasible in vivo by tracking a catheter-mounted piezoelectric transducer using seven reference crystals sewn to the epicardial surface of a sheep heart. Simulation results indicate that a catheter can be tracked with a root-mean-square (rms) error of 1.51±0.05 mm and an average-distance error of e=1.06±0.27 mm using 12 reference points. In vivo results showed acceptable stress values (G<0.05) for 95% of the data samples with an average-distance error of e=0.52±0.66 mm. These simulation and experimental results show that sonomicrometry and MDS can be used to accurately localize the 3-D position and track the motion of a catheter tip within the heart. View full abstract»

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  • Parametric representation and screening of knee joint vibroarthrographic signals

    Publication Year: 1997 , Page(s): 1068 - 1074
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (131 KB)  

    The authors have been investigating analysis of knee joint vibration or vibroarthrographic (VAG) signals as a potential tool for noninvasive diagnosis and monitoring of cartilage pathology. In this paper, they present a comprehensive comparative study of different parametric representations of VAG signals. Dominant poles and cepstral coefficients were derived from autoregressive models of adaptively segmented VAG signals. Signal features and a few clinical features were used as feature vectors in pattern classification experiments based on logistic regression analysis and the leave-one-out method. The results using 51 normal and 39 abnormal signals indicated the superior performance of cepstral coefficients in VAG signal classification with an accuracy rate of 75.6%. With 51 normal and 20 abnormal signals limited to chondromalacia patella, cepstral coefficients again gave the highest accuracy rate of 85.9%. View full abstract»

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  • Spatio-temporal EEG source localization using simulated annealing

    Publication Year: 1997 , Page(s): 1075 - 1091
    Cited by:  Papers (16)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (431 KB)  

    The estimation of multiple dipole parameters in spatio-temporal source modeling (STSM) of electroencephalographic (EEG) data is a difficult nonlinear optimization problem due to multiple local minima in the cost function. A straightforward iterative optimization approach to such a problem is very susceptible to being trapped in a local minimum, thereby resulting in incorrect estimates of the dipole parameters. Here, the authors present and evaluate a more robust optimization approach based on the simulated annealing algorithm. The complexity of this approach for the STSM problem was reduced by separating the dipole parameters into linear (moment) and nonlinear (location) components. The effectiveness of the proposed method and its superiority over the traditional nonlinear simplex technique in escaping local minima were tested and demonstrated through computer simulations. The annealing algorithm and its implementation for multidipole estimation are also discussed. The authors found the simulated annealing approach to be 7-31% more effective than the simplex method at converging to the true global minimum for a number of different kinds of three-dipole problems simulated in this work. In addition, the computational cost of the proposed approach was only marginally higher than its simplex counterpart. The annealing method also yielded similar solutions irrespective of the initial guesses used. The proposed simulated annealing method is an attractive alternative to the simplex method that is currently more common in dipole estimation applications. View full abstract»

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  • Spectral decomposition in multichannel recordings based on multivariate parametric identification

    Publication Year: 1997 , Page(s): 1092 - 1101
    Cited by:  Papers (43)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (322 KB)  

    A method of spectral decomposition in multichannel recordings is proposed, which represents the results of multivariate (MV) parametric identification in terms of classification and quantification of different oscillating mechanisms. For this purpose, a class of MV dynamic adjustment (MDA) models in which a MV autoregressive (MAR) network of causal interactions is fed by uncorrelated autoregressive (AR) processes is defined. Poles relevant to the MAR network closed-loop interactions (cl-poles) and poles relevant to each AR input are disentangled and accordingly classified. The autospectrum of each channel can be divided into partial spectra each relevant to an input. Each partial spectrum is affected by the cl-poles and by the poles of the corresponding input; consequently, it is decomposed into the relevant components by means of the residual method. Therefore, different oscillating mechanisms, even at similar frequencies, are classified by different poles and quantified by the corresponding components. The structure of MDA models is quite flexible and can be adapted to various sets of available signals and a priori hypotheses about the existing interactions; a graphical layout is proposed that emphasizes the oscillation sources and the corresponding closed-loop interactions. Application examples relevant to cardiovascular variability are briefly illustrated. View full abstract»

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  • Estimation of conduction velocity distribution by regularized-least-squares method

    Publication Year: 1997 , Page(s): 1102 - 1106
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    A novel technique for estimating the distribution of the conduction velocity of peripheral nerve fibers is described in this paper. In order to overcome the sensitivity of present methods to noisy data, a regularized-least-squares (RLS) method with a smoothing constraint and a self-adaption of regularization parameter was adopted. The simulation results demonstrated that the improved technique maybe applied in clinical diagnosis because it yielded reliable and almost undistorted results even when the simulated data are severely contaminated by noise. View full abstract»

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  • Automated feedback control of body temperature for small animal studies with MR microscopy

    Publication Year: 1997 , Page(s): 1107 - 1113
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    A temperature control system consisting of a thermistor, signal processor, and computer algorithm was developed for magnetic resonance (MR) microscopy of small live animals. With control of body temperature within ±0.2°C of the set point, heart rate is stabilized and, in turn, repetition time (TR) during cardiac-gated studies is less variable. Thus, image quality and resolution are improved. View full abstract»

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  • Real-time frequency domain temperature and oxygen sensor with a single optical fiber

    Publication Year: 1997 , Page(s): 1114 - 1121
    Cited by:  Papers (14)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (211 KB)  

    The combined excited-state phosphorescence lifetimes of an alexandrite crystal and platinum tetraphenylporphyrin Pt(TPP) in a single-fiber sensor are used to monitor temperature and oxygen concentration in the physiological range from 15-45°C and 0-50% O 2 with precision of 0.24°C and 0.15% O 2 and accuracy of 0.28°C and 0.2% O 2. A 500-μm cubic alexandrite crystal bound to the distal end of a 750-μm-diameter optical fiber core and the Pt(TPP) coated circumferentially with a length of 1 cm from the end of the same fiber are excited with pulsed super-bright blue LED light. This apparatus uses a 125-kHz sampler for data acquisition and frequency domain methods for signal processing. The instrument amplifies both the dc and ac components of the photomultiplier output and band limits the signal to 20 kHz. The fundamental frequency of the excitation is set to 488.3 Hz and the highest harmonic used is the 35th. This bandlimited signal is sampled and averaged over a few hundred cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic are then computed. At least four log-spaced harmonic phases or modulations are averaged before decoding the two lifetimes of temperature and oxygen phosphorescent sensors. A component of zero lifetime is introduced to account for the excitation backscatter leakage through optical interference filters seen by the photodetector. Linear and second-order empirical polynomials are employed to compute the temperatures and oxygen concentrations from the inverse lifetimes. In the situation of constant oxygen concentration, the lifetime of Pt(TPP) changes with temperature but can be compensated using the measured temperature lifetime. The system drift is 0.24°C for the temperature measurement and 0.59% for the oxygen concentration measurement over 30 - - h of continuous operation. The instrumentation and methods allow for 6-s update times and 90-s full-response times. View full abstract»

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  • Nanoliter volume, high-resolution NMR microspectroscopy using a 60-/spl mu/m planar microcoil

    Publication Year: 1997 , Page(s): 1122 - 1127
    Cited by:  Papers (25)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    Previous studies demonstrated the feasibility of using 100-μm inner diameter planar spiral inductors (microcoils) as detectors in 1H nuclear magnetic resonance (NMR) microspectroscopy. However, high-resolution NMR applications were not possible due to poor spectral resolution and low signal-to-noise ratio (SNR). These limitations in performance have now been largely overcome by using a nonconductive liquid fluorocarbon (FC-43) to minimize the effects of susceptibility mismatch between materials, and by carefully optimizing the microcoil geometry for maximum SNR. In this study, liquid samples were loaded into a fused silica capillary (75-μm inner diameter, 147-μm outer diameter). The capillary was positioned 50 μm above a 3.5-turn microcoil so that approximately 1 nL of the sample was present in the sensitive region of the microcoil. The microcoil was fabricated on a gallium arsenide substrate with an inner diameter of 60 μm, an outer diameter of 200 μm, trace width of 10 μm, trace spacing of 10 μm, and trace height of 3 μm. At 5.9 T (250 MHz) in 1H-NMR microspectroscopy experiments using a spectral width of 1 kHz, 4096 sampled data points, and a recovery delay of 1 s, a SNR of 25 (per acquisition) and a spectral linewidth of less than 2 Hz were obtained from a sample of water. These results demonstrate that planar microcoils can be used for high-resolution NMR microspectroscopy. Such coils may also be suitable for localized NMR studies at the cellular level and as detectors in capillary electrophoresis or microbore liquid chromatography. View full abstract»

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  • Electrothermal branding for embryo labeling

    Publication Year: 1997 , Page(s): 1128 - 1138
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A novel embryo labeling technique based on electrothermal branding is developed. Two types of micro branding irons are fabricated and tested. One utilizes 25 μm tungsten wire as the heating element. The other utilizes surface micromachining techniques to fabricate polysilicon branding irons. The thermal behavior of the branding irons and the heat distributions in the embryos are analytically modeled. Micron-scale labels on unfertilized bovine embryos are achieved. View full abstract»

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  • Factors affecting the accuracy of the boundary element method in the forward problem. I. Calculating surface potentials

    Publication Year: 1997 , Page(s): 1139 - 1155
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    A comprehensive review of factors affecting the accuracy of the boundary element method (BEM) for calculating surface potentials is presented. A relative-error statistic is developed which is only sensitive to calculation errors that could affect the inverse solution for source position, and insensitive to errors that only affect the solution for source strength. The factors considered in this paper are numerical approximations intrinsic to the BEM, such as constant-potential versus linear-potential basis functions and sharp-edged versus smooth-surfaced volumes; aspects of the volume conductor including the volume shape, density of surface elements, and element shape; source position and orientation; and effects of "refinements" in the numerical methods. The effects of these factors are considered in both smooth-shaped (spheres and spheroids) and sharp-edged (cubes) volume conductors. This represents the first attempt to assess the effects of many of these factors pertaining to the numerical methods commonly used in fields such as electrocardiography (ECG) and electroencephalography (EEG). Strategies for obtaining the most accurate solutions are presented. View full abstract»

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  • Analog circuit for real-time computation of respiratory mechanical impedance in sleep studies

    Publication Year: 1997 , Page(s): 1156 - 1159
    Cited by:  Papers (5)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB)  

    The aim of this work was to develop a low-cost circuit for real-time analog computation of the respiratory mechanical impedance in sleep studies. The practical performance of the circuit was tested in six patients with obstructive sleep apnea. The impedance signal provided by the analog circuit was compared with the impedance calculated simultaneously with a conventional computerized system. The authors concluded that the low-cost analog circuit developed could be a useful tool for facilitating the real-time assessment of airway obstruction in routine sleep studies. View full abstract»

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  • Microelectrode arrays for electrophysiological monitoring of hippocampal organotypic slice cultures

    Publication Year: 1997 , Page(s): 1159 - 1163
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (135 KB)  

    A three-dimensional platinum (Pt) microelectrode array embedded on a micromachined silicon (Si) substrate (porosity of 13%, via hole diameter of 40 μm) has been developed. Electrodes are 35-μm wide and 20-μm high, spaced 200 μm apart and arranged in an elliptic geometry. Integrated within a microperfusion chamber, the devices were used for stimulation and recording experiments of hippocampal slice cultures over a period of several days. View full abstract»

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  • Correction to "A Bioelectric Inverse Imaging Technique Based On Surface Laplacians"

    Publication Year: 1997 , Page(s): 1163
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (21 KB)  

    First Page of the Article
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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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Bin He
Department of Biomedical Engineering