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Biomedical Engineering, IEEE Transactions on

Issue 5 • Date May 1992

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Displaying Results 1 - 13 of 13
  • Calculation of the mutual induction between coplanar circular surface coils in magnetic resonance imaging

    Publication Year: 1992 , Page(s): 433 - 436
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB)  

    The induced current in a coil due to the presence of alternating currents in an adjacent coil is calculated for a case of two similar and coplanar, circular coils. By using an overlapping configuration, the mutual inductance is nullified, as is predicted theoretically and confirmed experimentally. View full abstract»

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  • Experimental tests of the cortical imaging technique-applications to the response to median nerve stimulation and the localization of epileptiform discharges

    Publication Year: 1992 , Page(s): 437 - 444
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    In a previous paper a method for simulating the electric potentials on the surface of the brain was introduced (see ibid., vol.38, p.294-9, 1991). This method consisted of the construction of a layer of radially oriented current dipoles in a conducting sphere that simulated the head so that the voltages generated by the layer would take the values measured on the surface of the medium (the scalp). The harmonic potential function for this layer was then evaluated in the interior of the medium in an attempt to approximate the potentials that would be generated by the actual neural sources but which could not be observed without recourse to invasive recording techniques. The method is tested here by applying it to the scalp-recorded potentials evoked by right median nerve stimulation, where direct cortical recordings are available for comparison, and to the scalp-recorded epileptiform discharges from two patients where the spike foci were well defined. The effects of varying the 'noise ratio', an input parameter in CIT which allows one to account for noise in scalp-recorded data, is discussed. View full abstract»

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  • Ultrasonic multifeature maps of liver based on an amplitude loss technique and a conventional B-scan

    Publication Year: 1992 , Page(s): 445 - 449
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (639 KB)  

    Recently, a novel ultrasonic amplitude loss technique for creating images of local tissue attenuation was presented. Based on this algorithm, global attenuation estimates were calculated and consistent variations of the estimated attenuation value were observed for different liver pathologies. With the exception of Hodgkin's and acute inflammatory liver disease, the detectability of the disease states was not increased by the global attenuation estimates. In an attempt to do so, pseudo-color maps, were used in this study. The conventional B-scan was presented as a gray-scale image and a color-code attribute was based on the local attenuation estimate. In the vicinity of strong reflectors, the author noted a typical artifact. Modification of the classical physical model, describing the ultrasonic-tissue interaction, was observed to reduce the artifacts in the attenuation estimates; however, the detectability of disease states was not increased. View full abstract»

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  • A unified approach to modeling the backscattered Doppler ultrasound from blood

    Publication Year: 1992 , Page(s): 450 - 461
    Cited by:  Papers (27)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1139 KB)  

    A unified approach to modeling the backscattered Doppler ultrasound signal from blood is presented. The approach consists of summing the contributions from elemental acoustic voxels, each containing many red blood cells (RBCs). For an insonified region that is large compared to a wavelength, it is shown that the Doppler signal is a Gaussian random process that arises from fluctuation scattering, which implies that the backscattered power is proportional to the variance of local RBC concentrations. As a result, some common misconceptions about the relationship between the backscattering coefficient and hematocrit can be readily resolved. The unified approach was also used to derive a Doppler signal simulation model which shows that, regardless of flow condition, the power in the Doppler frequency spectrum is governed by the exponential distribution. For finite beamwidth and paraxial flow, it is further shown that the digitized Doppler signal can be modeled by a moving average random process whose order is determined by the signal sampling rate as well as the flow velocity profile. View full abstract»

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  • The effects of hematocrit, shear rate, and turbulence on ultrasonic Doppler spectrum from blood

    Publication Year: 1992 , Page(s): 462 - 469
    Cited by:  Papers (32)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (674 KB)  

    Previous studies of ultrasonic scattering properties of blood using a pulse-echo experimental arrangement show that ultrasonic backscatter from blood is influenced by a number of factors, including hematocrit, shear rate, and the nature of flow. Since the Doppler frequency spectrum from a Doppler flowmeter is derived from echoes backscattered by red blood cells in the flowing blood, it is also undoubtedly a function of these parameters. The effects of these parameters on Doppler spectrum from blood have been investigated using a pulsed Doppler flowmeter. The results agree well with those obtained in previous studies. One important conclusion of this study is that the assumption that the Doppler spectral power density at a frequency in the Doppler spectrum is linearly proportional to the number of red cells flowing at that velocity used in many theoretical models developed to explain the Doppler phenomenon may be erroneous. An alternative is proposed. It is shown that conclusions derived from these theoretical models would remain valid by making this assumption. View full abstract»

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  • Body conformable 915 MHz microstrip array applicators for large surface area hyperthermia

    Publication Year: 1992 , Page(s): 470 - 483
    Cited by:  Papers (18)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1318 KB)  

    The optimal treatment with hyperthermia of superficially located tumors which involve large surface areas requires applicators which can physically conform to body contours, and locally alter their power deposition patterns to adjust for nonuniform temperature caused by tissue inhomogeneities and blood flow variations. A series of 915-MHz microstrip array applicators satisfying these criteria have been developed and clinically tested. Clinical and engineering design tradeoff's for practical devices are discussed. Measurements taken in tissue equivalent phantoms and a summary of clinical experiences with these microstrip arrays are presented. View full abstract»

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  • Abnormal cardiovascular responses induced by localized high power microwave exposure

    Publication Year: 1992 , Page(s): 484 - 492
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (899 KB)  

    A hypothesis of microwave-induced circulatory under perfusion was tested in ketamine-anesthetized rats. Fifty-eight ventral head and neck exposures in a waveguide consisted of sham-exposure and exposure to continuous-wave (CW) and pulsed 1.25-GHz microwaves for 5 min. Respiration rate and mean arterial pressure were not altered. Changes in heart rate and pulse pressure were observed in rats exposed to higher power (16-Hz pulses and 6.4-W CW) but not to the lower average power microwave (0.5-Hz pulses and 2 W CW). Depression of pulse pressure, an indication of a decrease in stroke volume, and increased (tachycardia) or decreased (bradycardia) heart rate were noted in presence of whole-body hyperthermia. The cardiac output of those animals exposed to higher average power microwaves was considered to be below normal, as hypothesized. Decreased cardiac output and normal mean arterial pressure resulted in an increase in the total peripheral resistance which was contrary to the anticipated thermal response of animals. View full abstract»

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  • Estimation of electronic parameters of neurons using an inverse Fourier transform technique

    Publication Year: 1992 , Page(s): 493 - 501
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    The authors estimate the passive electronic parameters of hippocampal granule cells. A shunt cable model, where the somatic and dendritic time constants can be different, is used to describe the potential changes in the soma and along the dendritic tree. Parameter values are estimated by nonlinear least-squares fitting of the model output to the voltage response of the stimulated cell to current pulses. The solutions are obtained in a two-step process. First, the sensitivity functions are derived from the Laplace transform solution of the theoretical model. Second, the time-domain solutions are obtained numerically by an inverse FFT. A sensitivity analysis indicates that accurate estimates require the use of a short current pulse injected at the soma and the sampling of the voltage response close to the end of that pulse. This parameter estimation procedure has been tested on hippocampal granule cells. It yields accurate estimations of neural parameters and will be a useful tool for measuring passive properties of neurons. View full abstract»

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  • Time-frequency representation of electrocorticograms in temporal lobe epilepsy

    Publication Year: 1992 , Page(s): 502 - 509
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Three time-frequency distributions are evaluated in terms of their efficacy in representing nonstationary electrocorticograms (ECOGs) in human temporal lobe epilepsy. The results of a new method, the exponential distribution, are compared with those of the spectrogram and the Wigner distribution. It is shown that the exponential distribution represents a considerable improvement over the spectrogram in terms of resolution and markedly reduces cross-terms present in the Wigner distribution. Exponential distribution representations of ECOGs from different stages of an epileptic record are developed as contour maps. These high-resolution representations offer a lucid display of temporal-spectral features of the rapidly varying signals that constitute ECOGs recorded in temporal lobe epilepsy. View full abstract»

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  • Unidirectional block in cardiac fibers: effects of discontinuities in coupling resistance and spatial changes in resting membrane potential in a computer simulation study

    Publication Year: 1992 , Page(s): 510 - 522
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (874 KB)  

    The mechanisms for conduction and unidirectional block (UDB) in cardiac tissue under spatial changes in cell-to-cell coupling resistivity (R i) and resting potential (V rest) were studied. The effects of discontinuities in R i as would result from collagenous or fibrotic tissue on propagation characteristics, in the border zone between normal and ischemic tissue, were studied. It was found that conduction block is more likely to occur when an abrupt decrease in R i is encountered as compared to an abrupt increase in R i. Discontinuities in R i were found to cause changes in propagation characteristics, changing regions of bidirectional block to UDB or bidirectional propagation. Spatial changes in V rest were also studied. It is found that when V rest alone was altered, block was not likely to occur, while discontinuities in R i superimposed with V rest gradients increased the likelihood of block. It is also found that R i discontinuities located in the border zone between normal and ischemic tissue can create exit block or propagation of a parasystolic focus. View full abstract»

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  • Correlation between low-frequency electric conductivity and permittivity in the diaphysis of bovine femoral bone

    Publication Year: 1992 , Page(s): 523 - 526
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (374 KB)  

    The relationship between the low-frequency electric properties in the axial, tangential, and radial directions along the diaphysis of a femoral bovine bone is presented. It is shown that below 1 MHz the relative permittivity of the diaphysis exhibits a significant positive correlation with respect to the low-frequency conductivity, as measured in any direction, and therefore it could be related to the amount of fluid contained in the channels that provide low-frequency electrical connectivity in the measurement direction. There is no significant correlation between permittivity, in either of the three measurement directions, and the total fluid volumetric fraction in the bone. View full abstract»

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  • Estimation of epicardial strain using the motions of coronary bifurcations in biplane cineangiography

    Publication Year: 1992 , Page(s): 526 - 531
    Cited by:  Papers (11)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (678 KB)  

    A quantitative method for estimating epicardial deformation from the motion of the superficial coronary arteries is described. A structural model of the time-varying surface is constructed using tensor product basis functions which are bicubic Hermite in the spatial domain and sinusoidal in the temporal domain. The locii of the superficial coronary arteries are reconstructed interactively at diastasis and the bifurcations are tracked semiautomatically throughout as cardiac cycle. An initial surface is fitted to the vessels at diastasis and is subsequently deformed under the influence of the bifurcations. The Lagrange-Green strain tensor is used to obtain a complete description of surface strain over the entire region spanned by the model. The calculated deformation field varies smoothly over space and time and is not constrained by assumptions of isotropy or piecewise homogeneity. Results for a single cycle of a human heart are presented. View full abstract»

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  • Development of a medical fiber-optic pH sensor based on optical absorption

    Publication Year: 1992 , Page(s): 531 - 537
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    A new fiber-optic pH sensor system has been developed. The sensor uses an absorptive indicator compound with a long wavelength absorption peak near 625 nm; change in absorption over the pH range 6.8 to 7.8 is reasonably linear. The sensor is interrogated by a pulsed, red LED. The return light signal is split into short- and long-wavelength components with a dichroic mirror; the respective signals are detected by photodiodes, and their photocurrents are used to form a radiometric output signal. In laboratory tests, the sensor system provided resolution of 0.01 pH, accuracy of +or-0.01 pH, and response time of 30-40 s. Following gamma sterilization, laboratory sensor testing with heparinized human blood yielded excellent agreement with a clinical blood gas analyzer. Excellent sensor performance and low cost, solid-state instrumentation are hallmarks of this sensor-system design. 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