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Biomedical Engineering, IEEE Transactions on

Issue 10 • Date Oct. 2001

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Displaying Results 1 - 19 of 19
  • Analysis of monophasic and biphasic electrical stimulation of nerve

    Publication Year: 2001 , Page(s): 1065 - 1070
    Cited by:  Papers (20)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (93 KB) |  | HTML iconHTML  

    In an earlier study, biphasic and monophasic electrical stimulation of the auditory nerve was performed in cats with a cochlear implant. Single-unit recordings demonstrated that spikes resulting from monophasic and biphasic stimuli have different thresholds and latencies. Monophasic thresholds are lower and latencies are shorter under cathodic stimulation. Results from stochastic simulations of a biophysical model of electrical stimulation are similar. A simple analysis of a linear, "integrate to threshold" membrane model accounts for the threshold and latency differences observed experimentally and computationally. Since biphasic stimuli are used extensively in functional electrical stimulation, this analysis greatly simplifies the biophysical interpretation of responses to clinically relevant stimuli by relating them to the responses obtained with monophasic stimuli. View full abstract»

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  • Analysis of galvanic skin responses with principal components and clustering techniques

    Publication Year: 2001 , Page(s): 1071 - 1079
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (181 KB) |  | HTML iconHTML  

    An advanced method for analyzing the patterning of successive galvanic skin responses (GSR) is presented. The proposed method is based on principal component analysis in which the vector containing the measured signal is presented as a weighted sum of orthogonal basis vectors. The method is tested using measurements from 20 healthy controls and 13 psychotic patients. For each subject, 11 surprising auditory stimuli were delivered to right ear at irregular intervals and evoked GSRs were recorded from the hand. For most of the healthy controls, there was a clear pattern in successive GSRs, whereas within psychotic patients the lack of time-locking of GSRs seemed to be characteristic. These between group differences can be revealed by the proposed method. With application to clustering a significant discrimination, with overall correct ratings of 82%, of healthy controls and psychotic patients is achieved. A significant fact is that all patients were ranked correctly giving the proposed method a sensitivity of 100%. View full abstract»

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  • Quantifying spatial localization of optical mapping using Monte Carlo simulations

    Publication Year: 2001 , Page(s): 1098 - 1107
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (165 KB)  

    Optical mapping techniques used to study spatial distributions of cardiac activity can be divided into two categories; (1) broad-field excitation method, in which hearts stained with voltage or calcium sensitive dyes are illuminated with broad-field excitation light and fluorescence is collected by image or photodiode arrays; (2) laser scanning method, in which illumination uses a scanning laser and fluorescence is collected with a photomultiplier tube. The spatial localization of the fluorescence signal for these two methods is unknown and may depend upon light absorption and scattering at both excitation and emission wavelengths. We measured the absorption coefficients (μ a), scattering coefficients (μ s), and scattering anisotropy coefficients (g) at representative excitation and emission wavelengths in rabbit heart tissue stained with di-4-ANEPPS or co-stained with both Rh237 and Oregon Green 488 BAPTA 1. Monte Carlo models were then used to simulate absorption and scattering of excitation light and fluorescence emission light for both broad-field and laser methods in three-dimensional tissue. Contributions of local emissions throughout the tissue to fluorescence collected from the tissue surface were determined for both methods. Our results show that spatial localization depends on the light absorption and scattering in tissue and on the optical mapping method that is used. A tissue region larger than the laser beam or collecting area of the array element contributes to the optical recordings. View full abstract»

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  • Inhomogeneity of action potential waveshape assists frequency entrainment of cardiac pacemaker cells

    Publication Year: 2001 , Page(s): 1108 - 1115
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (173 KB) |  | HTML iconHTML  

    In this paper, we have employed ionic models of sinoatrial node cells to investigate the synchronization of a pair of coupled cardiac pacemaker cells from central and peripheral regions of the sinoatrial node. The free-running cycle length of the cell models was perturbed using two independent techniques and the minimum coupling conductance required to achieve frequency entrainment was used to assess the relative ease with which various cell pairs achieve entrainment. The factors effecting entrainment were further investigated using single-cell models paced with an artificial biphasic coupling current. Our simulation results suggest that dissimilar cell types, those with largely different upstroke velocities entrain more easily, that is, they require less coupling conductance to achieve 1:1 frequency entrainment. We therefore propose that regional variation in action-potential waveshape within the sinoatrial node assists frequency synchronization in vivo. View full abstract»

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  • A new algorithm for linear and nonlinear ARMA model parameter estimation using affine geometry [and application to blood flow/pressure data]

    Publication Year: 2001 , Page(s): 1116 - 1124
    Cited by:  Papers (38)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (134 KB) |  | HTML iconHTML  

    A linear and nonlinear autoregressive (AR) moving average (MA) (ARMA) identification algorithm is developed for modeling time series data. The new algorithm is based on the concepts of affine geometry in which the salient feature of the algorithm is to remove the linearly dependent ARMA vectors from the pool of candidate ARMA vectors. For noiseless time series data with a priori incorrect model-order selection, computer simulations show that accurate linear and nonlinear ARMA model parameters can be obtained with the new algorithm. Many algorithms, including the fast orthogonal search (FOS) algorithm, are not able to obtain correct parameter estimates in every case, even with noiseless time series data, because their model-order search criteria are suboptimal. For data contaminated with noise, computer simulations show that the new algorithm performs better than the FOS algorithm for MA processes, and similarly to the FOS algorithm for ARMA processes. However, the computational time to obtain the parameter estimates with the new algorithm is faster than with FOS. Application of the new algorithm to experimentally obtained renal blood flow and pressure data show that the new algorithm is reliable in obtaining physiologically understandable transfer function relations between blood pressure and flow signals. View full abstract»

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  • Hepatic bipolar radio-frequency ablation between separated multiprong electrodes

    Publication Year: 2001 , Page(s): 1145 - 1152
    Cited by:  Papers (39)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB) |  | HTML iconHTML  

    RF ablation has become an important means of treatment of nonresectable primary and metastatic liver tumors. Major limitations are small lesion size, which make multiple applications necessary, and incomplete killing of tumor cells, resulting in high recurrence rates. We examined a new bipolar RF ablation method incorporating two probes with hooked electrodes (RITA model 30). We performed monopolar and bipolar in vivo experiments on three pigs. The electrodes were 2.5 cm apart and rotated 45° relative to each other. We used temperature-controlled mode at 95°C. Lesion volumes were 3.9±1.8 cm 3 (n=7) for the monopolar case and 12.2±3 cm 3 (n=10) for the bipolar case. We generated finite-element models (FEMs) of monopolar and bipolar configurations. We analyzed the distribution of temperature and electric field of the finite element model. The lesion volumes for the FEM are 7.95 cm 3 for the monopolar and 18.79 cm 3 for the bipolar case. The new bipolar method creates larger lesions and is less dependent on local inhomogeneities in liver tissue-such as blood perfusion-compared with monopolar RF ablation. A limitation of the new method is that the power dissipation of the two probes cannot be controlled independently in response to different conditions in the vicinity of each probe. This may result in nonuniform lesions and decreased lesion size. View full abstract»

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  • Balance prosthesis based on micromechanical sensors using vibrotactile feedback of tilt

    Publication Year: 2001 , Page(s): 1153 - 1161
    Cited by:  Papers (42)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (130 KB)  

    A prototype balance prosthesis has been made using miniature, high-performance inertial sensors to measure lateral head tilt and vibrotactile elements mounted on the body to display head tilt to the user. The device has been used to study the feasibility of providing artificial feedback of head tilt to reduce postural sway during quiet standing using six healthy subjects. Two vibrotactile display schemes were used: one in which the individual vibrating elements, called tactors, were placed on the shoulders (shoulder tactors); another in which columns of tactors were placed on the right and left sides of the trunk (side tactors). Root-mean-square head-tilt angle (Tilt) and center of pressure displacement (Sway) were measured for normal subjects standing in a semi-tandem Romberg position with eyes closed, under four conditions: no balance aids; shoulder tactors; side tactors; and light touch. Compared with no balance aids, the side tactors significantly reduced Tilt (35%) and Sway (33%). Shoulder tactors also significantly reduced Tilt (44%) and Sway (17%). Compared with tactors, light touch resulted in less Sway, but more Tilt. The results suggest that healthy normal subjects can reduce their lateral postural sway using head tilt information as provided by a vibrotactile display. Thus, further testing with balance-impaired subjects is now warranted. View full abstract»

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  • A 3-D differential coil design for localized magnetic stimulation

    Publication Year: 2001 , Page(s): 1162 - 1168
    Cited by:  Papers (16)  |  Patents (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (162 KB) |  | HTML iconHTML  

    A novel three-dimensional (3-D) differential coil has been designed for improving the localization of magnetic stimulation. This new coil design consists of a butterfly coil with two additional wing units and an extra bottom unit, both perpendicular to the plane of the butterfly coil. The wing units produce opposite fields to restrict the spread of induced fields while the bottom unit enhances the induced fields at the excitation site. The peak induced field generated by this new design is located at the center of the coil, providing an easy identification of the excitation site. The field localization of the new coil Is comparable with that of much smaller coils but with an inductance compatible to current magnetic stimulators. Numerical computations based on the principles of electromagnetic induction and using a human nerve model were performed to analyze the induced fields and the stimulation thresholds of new coil designs. The localization of the coil design was assessed by a half power region (HPB), within which the magnitude of the normalized induced field is greater than 1/√2. The HPR for a 3-D differential coil built is improved (decreased) by a factor of three compared with a standard butterfly coil. Induced fields by this new coil were measured and in agreement with theoretical calculations. View full abstract»

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  • Improving the homogeneity of the magnetic field in the magnetic search coil technique

    Publication Year: 2001 , Page(s): 1178 - 1185
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    The magnetic search coil technique is used to obtain accurate eye-movement measurements. For the data analysis it must be assumed that the magnetic field does not change over time (apart from the required modulation). To comply with this assumption either no translational movements of the eye coil(s) are allowed or the magnetic field has to be perfectly homogeneous. Both are normally not the case, i.e., measurement errors occur. These errors can he minimized by keeping the magnetic field as homogeneous as possible. Larger field coils are typically chosen to achieve this aim. However, sometimes the experimental setup imposes limitations on the size of the configuration. The authors present a method for improving the homogeneity of the magnetic field by adding supplementary field coils without changing the size of the configuration. View full abstract»

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  • Bayesian approach to segmentation of statistical parametric maps

    Publication Year: 2001 , Page(s): 1186 - 1194
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (254 KB) |  | HTML iconHTML  

    A contextual segmentation technique to detect brain activation from functional brain images is presented in the Bayesian framework. Unlike earlier similar approaches [Holmes and Ford (1993) and Descombes et al. (1998)], a Markov random field (MRF) is used to represent configurations of activated brain voxels, and likelihoods given by statistical parametric maps (SPM's) are directly used to find the maximum a posteriori (MAP) estimation of segmentation. The iterative segmentation algorithm, which is based on a simulated annealing scheme, is fully data-driven and capable of analyzing experiments involving multiple-input stimuli. Simulation results and comparisons with the simple thresholding and the statistical parametric mapping (SPM) approaches are presented with synthetic images, and functional MR images acquired in memory retrieval and event-related working memory tasks. The experiments show that an MRF Is a valid representation of the activation patterns obtained in functional brain images, and the present technique renders a superior segmentation scheme to the context-free approach and the SPM approach. View full abstract»

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  • A new 3-D display method for 12-lead ECG

    Publication Year: 2001 , Page(s): 1195 - 1202
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    A new three-dimensional (3-D) 12-lead electrocardiogram (EGG) display method is presented which employs a 3-D rectangular coordinate system to display the 12-lead cardiac electric signals in two 3-D graphs. The 3-D graph consists of a temporal axis representing the time domain of the cardiac signals, a spatial axis representing the lead positions, and an amplitude axis representing the voltages of the cardiac signals. The six horizontal plane leads and the other six frontal plane leads were displayed in two 3-D graphs, respectively. The voltages of the cardiac signals were represented in rainbow-like colors. Cubic interpolation was employed to insert interconnecting points between neighboring leads on each plane and to smooth the surface of the 3-D ECG graphs. The 3-D ECG graphs of a normal subject, a patient with myocardial infarction, and a patient with left bundle branch block were presented here. This new display method could not only be used as a complementary display method to the 12-lead EGG, but also provide physicians with an overall integral view about the spatial distribution of the cardiac signals. View full abstract»

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  • Multichannel ECG compression using multichannel adaptive vector quantization

    Publication Year: 2001 , Page(s): 1203 - 1207
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    Adaptive vector quantization (AVQ) is a recently proposed approach for electrocardiogram (ECG) compression. The adaptability of the approach can be used to control the quality of reconstructed signals. However, like most of other ECG compression methods, AVQ only deals with the single-channel ECG, and for the multichannel (MC) ECG, coding ECG signals on a channel by channel basis is not efficient, because the correlation across channels is not exploited. To exploit this correlation, an MC version of AVQ is proposed. In the proposed approach, the AVQ index from each channel is collected to form a new input vector. The vector is then vector quantized adaptively using one additional codebook called index codebook. Both the MIT/BIH database and a clinical Holter database are tested. The experimental results show that, for exactly the same quality of reconstructed signals, the MC-AVQ performs better than single-channel AVQ in terms of bit rate. A theoretical analysis supporting this result is also demonstrated in this paper. For the same and relatively good visual quality, the average compressed data rate/channel is reduced from 293.5 b/s using the single-channel AVQ to 238.2 b/s using the MC-AVQ in the MIT/BIH case. View full abstract»

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  • The effect of plunge electrodes during electrical stimulation of cardiac tissue

    Publication Year: 2001 , Page(s): 1207 - 1211
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (98 KB) |  | HTML iconHTML  

    The mechanism for far-field stimulation of cardiac tissue is not known, although many hypotheses have been suggested. This paper explores a new hypothesis: the insulated plunge electrodes used in experiments to map the extracellular potential may affect the transmembrane potential when an electric field is applied to cardiac tissue. The authors' calculation simulates a 10-mm-diameter sheet of passive tissue with a circular insulated plunge electrode in the middle of it, ranging in diameter from 0.05 to 2 mm. The authors calculate the transmembrane potential induced by a 500-V/m electric field. Their results shown that a transmembrane potential is induced around the electrode in alternating areas of depolarization and hyperpolarization. If the electric field is oriented parallel to the myocardial fibers, the maximum transmembrane potential is 89 mV. A layer of fluid around the electrode increases the transmembrane potential. It is concluded that plunge electrodes may introduce artifacts during experiments designed to study the response of the heart to strong electric shocks. View full abstract»

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  • A statistical technique for measuring synchronism between cortical regions in the EEG during rhythmic stimulation

    Publication Year: 2001 , Page(s): 1211 - 1215
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    The coherence function has been widely applied in quantifying the degree of synchronism between electroencephalogram (EEG) signals obtained from different brain regions. However, when applied to investigating synchronization resulting from rhythmic stimulation, misleading results can arise from the high correlation of background EEG activity. The authors, thus propose a modified measure, which emphasizes the synchronized stimulus responses and reduces the influence of the spontaneous EEG activity. Critical values for this estimator are derived and tested in Monte Carlo simulations. The effectiveness of the method is illustrated on data recorded from 12 young normal subjects during rhythmic photic stimulation. View full abstract»

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  • A multiresolution framework to MEG/EEG source imaging

    Publication Year: 2001 , Page(s): 1080 - 1087
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    A new method based on a multiresolution approach for solving the ill-posed problem of brain electrical activity reconstruction from EEG/MEG signals is proposed in a distributed source model. At each step of the algorithm, a regularized solution to the inverse problem is used to constrain the source space on the cortical surface to be scanned at higher spatial resolution. We present the iterative procedure together with an extension of the ST-maximum a posteriori method that integrates spatial and temporal a priori information in an estimator of the brain electrical activity. Results from EEG in a phantom head experiment with a real human skull and from real MEG data on a healthy human subject are presented. The performances of the multiresolution method combined with a nonquadratic estimator are compared with commonly used dipolar methods, and to minimum-norm method with and without multiresolution. In all cases, the proposed approach proved to be more efficient both in terms of computational load and result quality, for the identification of sparse focal patterns of cortical current density, than the fixed scale imaging approach View full abstract»

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  • Development of a time-cycled volume-controlled pressure-limited respirator and lung mechanics system for total liquid ventilation

    Publication Year: 2001 , Page(s): 1134 - 1144
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    Total liquid ventilation can support gas exchange in animal models of lung injury. Clinical application awaits further technical improvements and performance verification. Our aim was to develop a liquid ventilator, able to deliver accurate tidal volumes, and a computerized system for measuring lung mechanics. The computer-assisted, piston-driven respirator controlled ventilatory parameters that were displayed and modified on a real-time basis. Pressure and temperature transducers along with a lineal displacement controller provided the necessary signals to calculate lung mechanics, Ten newborn lambs (<6 days old) with respiratory failure induced by lung lavage, were monitored using the system. Electromechanical, hydraulic, and data acquisition/analysis components of the ventilator were developed and tested in animals with respiratory failure. All pulmonary signals were collected synchronized in time, displayed in real-time, and archived on digital media. The total mean error (due to transducers, analog-to-digital conversion, amplifiers, etc.) was less than 5% compared with calibrated signals. Components (tubing, pistons, etc.) in contact with exchange fluids were developed so that they could be readily switched, a feature that will be important In clinical settings. Improvements in gas exchange and lung mechanics were observed during liquid ventilation, without impairment of cardiovascular profiles. The total liquid ventilator maintained accurate control of tidal volumes and the sequencing of inspiration/expiration. The computerized system demonstrated its ability to monitor in vivo lung mechanics, providing valuable data for early decision making View full abstract»

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  • Computer-assisted transurethral laser resection of the prostate (CALRP): theoretical and experimental motion plan

    Publication Year: 2001 , Page(s): 1125 - 1133
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    Computer-Assisted transurethral laser resection of the prostate (CALRP) is a treatment modality that was designed and developed based on an integrated system of computer, robotics and laser technology in association with a minimally invasive surgery known as laser transurethral resection of the prostate (LRP), CALRP possesses complementary capabilities that could remedy many of the problems faced by surgeons in conventional LRP by delivering a treatment with repeatability and reliability. The work deals primarily in determining the feasibility study of the computer-assisted lasing motion plan (planned motion sequence controlled by a program) for LRP. A theoretical motion plan that analyzes numerically the lasing motion of the fiber was designed by calculating the profile removal rate and in vitro experiments conducted on human cadaveric prostate to verify and validate the designed motion plan. The novel motion plan, which was executed experimentally using the LaserTrode lightguide, accomplished the objective of resecting the enlarged prostate with the aid of computer and robotics technology View full abstract»

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  • Artificial neural networks for discriminating pathologic from normal peripheral vascular tissue

    Publication Year: 2001 , Page(s): 1088 - 1097
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    The identification of the state of human peripheral vascular tissue by using artificial neural networks is discussed in this paper. Two different laser emission lines (He-Cd, Ar+) are used to excite the chromophores of tissue samples. The fluorescence spectrum obtained, is passed through a nonlinear filter based on a high-order (HO) neural network neural network (NN) [HONN] whose weights are updated by stable learning laws, to perform feature extraction. The values of the feature vector reveal information regarding the tissue state. Then a classical multilayer perceptron is employed to serve as a classifier of the feature vector, giving 100% successful results fur the specific data set considered. Our method achieves not only the discrimination between normal and pathologic human tissue, but also the successful discrimination between the different types of pathologic tissue (fibrous, calcified). Furthermore, the small time needed to acquire and analyze the fluorescence spectra together with the high rates of success, proves our method very attractive for real-time applications View full abstract»

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  • Parametric dependence of SAR on permittivity values in a man model

    Publication Year: 2001 , Page(s): 1169 - 1177
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    The development and widespread use of advanced three-dimensional digital anatomical models to calculate specific absorption rate (SAR) values in biological material has resulted in the need to understand how model parameters (e.g., permittivity value) affect the predicted whole-body and localized SAR values. The application of the man dosimetry model requires that permittivity values (dielectric value and conductivity) be allocated to the various tissues at all the frequencies to which the model will be exposed. In the 3-mm-resolution man model, the permittivity values for all 39 tissue-types were altered simultaneously for each orientation and applied frequency. In addition, permittivity values for muscle, fat, skin, and bone marrow were manipulated independently. The finite-difference time-domain code was used to predict localized and whole-body normalized SAR values. The model was processed in the far-field conditions at the resonant frequency (70 MHz) and above (200, 400, 918, and 2060 MHz) for E orientation. In addition, other orientations (K, H) of the model to the incident fields were used where no substantial resonant frequency exists. Variability in permittivity values did not substantially influence whole-body SAR values, while localized SAR values for individual tissues were substantially affected by these changes. Changes in permittivity had greatest effect on localized SAR values when they were low compare to the whole-body SAR value or when errors involved tissues that represent a substantial proportion of the body mass (i.e., muscle). Furthermore, the authors establish the partial derivative of whole-body and localized SAR values with respect to the dielectric value and conductivity for muscle independently. It was shown that uncertainties in dielectric value or conductivity do not substantially influence normalized whole-body SAR. Detailed investigation on localized SAR ratios showed that conductivity presents a more substantial factor in absorption of energy in tissues than dielectric value for almost all applied exposure conditions 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.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Bin He
Department of Biomedical Engineering