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Biomedical Engineering, IEEE Transactions on

Issue 2 • Date Feb. 2000

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Displaying Results 1 - 16 of 16
  • Coil design for real and sham transcranial magnetic stimulation

    Page(s): 145 - 148
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (61 KB)  

    Transcranial magnetic stimulation (TMS) can be used to excite the human cortex noninvasively. TMS also activates scalp muscles and sensory receptors; additionally, the loud sound from the stimulating coil activates auditory pathways. These side effects complicate the interpretation of the results of TMS studies. For control experiments, the authors have designed a coil that can produce both real and sham stimulation without moving the coil. The sham TMS is similar to the real TMS, except for the different relative direction of the currents in the two loops of the figure of eight coil. While the real TMS elicited activation of hand muscles, sham TMS had no such effect; however, the auditory-evoked potentials were similar. View full abstract»

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  • Applications of SPICE for modeling miniaturized biomedical sensor systems

    Page(s): 149 - 154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (173 KB)  

    This paper proposes a model for a miniaturized signal conditioning system for biopotential and ion-selective electrode arrays. The system consists of three main components: sensors, interconnections, and signal conditioning chip. The model for this system is based on SPICE. Transmission-line based equivalent circuits are used to represent the sensors, lumped resistance-capacitance circuits describe the interconnections, and a model for the signal conditioning chip is extracted from its layout. In conclusion, a system for measurements of biopotentials and ionic activities can be miniaturized and optimized for cardiovascular applications based on the development of an integrated SPICE system model of its electrochemical, interconnection, and electronic components. View full abstract»

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  • A micropower dry-electrode ECG preamplifier

    Page(s): 155 - 162
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (131 KB)  

    This paper describes the development of a very low-power preamplifier intended for use in pasteless-electrode recording of the human electrocardiogram. The expected input signal range is 100 μV-10 mV from a lead-II electrode configuration. The amplifier provides a gain of 43 dB in a 3-dB bandwidth of 0.05 Hz-2 kHz with a defined high input impedance of 75 MΩ. It uses a driven common electrode to enhance rejection of common-mode interfering signals, including low-frequency motion artifact, achieving a common-mode rejection ratio (CMRR) of better than 80 dB over its entire bandwidth. The gain and phase characteristics meet the recommendations of the American Heart Association, ensuring low distortion of the output ECG signal and making it suitable for clinical monitoring. The amplifier has a power consumption of 30 μW operating from a 3.3-V battery and is intended for use in small, lightweight, portable electrocardiographic equipment and heart-rate monitoring instrumentation. View full abstract»

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  • Effects of sample geometry and electrode configuration on measured electrical resistivity of skeletal muscle

    Page(s): 163 - 169
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    Over the past 40 years, researchers from a variety of scientific backgrounds have been using Rush's equations to analyze results of their electrophysiological studies. A lack of understanding of the constraints and the domain in which these equations are valid, often results in situations in which it is challenging to evaluate and compare results obtained by different investigators. Here, the authors reanalyzed the conditions for which Rush's equations were derived, and using mathematical modeling, computer simulation and in vitro measurements, they delineated areas of their appropriate application. The authors' studies showed that both sample geometry and test electrode configuration affect the measured tissue electrical resistivities: (1) The sample can be considered semi-infinite only if its dimensions are >50 inter-electrode separation distances (IESD), and thickness >2.5 IESD, (2) smaller sample sizes increase the transversally measured resistivity, (3) semi-infinite samples thinner than 2.5 IESD, and samples tested with needle electrodes demonstrate reduced anisotropy, and (4) when surface-spot electrodes are longitudinally aligned, as the IESD/tissue thickness ratio decreases, the measured resistivity increases. The authors' conclusion is that in most experimental situations, it is necessary to use modeling techniques to decouple the electrode configuration/sample geometry influence from the measured tissue resistivity. View full abstract»

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  • A viscoelastic model of phagosome motion within cells based on cytomagnetometric measurements

    Page(s): 170 - 182
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    Cytomagnetometry is a noninvasive method to investigate intracellular movements of organelles such as phagosomes by introducing magnetic particles into cells by phagocytosis, magnetizing them and measuring the field from the cells. To analyze the results of the cell-field measurement, the authors introduce a model for intracellular phagosome motion and investigate their behavior in terms of the cell field. The model includes an elastic body and two viscosity components which are ascribed to the filamentous structures surrounding the phagosomes. The magnetic relaxation phenomenon is assumed to derive from the rotationary Brownian motion as in the authors' previous model. Although the model is simple, its behavior is not trivial because it contains a nonlinear term and the Brownian motion term. This model is the simplest one possible having a viscoelastic body and its behavior hence should be investigated thoroughly. View full abstract»

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  • Magnetostatic image current and its application to an analytic identification of a current dipole inside a conducting sphere

    Page(s): 183 - 191
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    The image solution for the static magnetic field outside a conducting sphere with an internal current dipole is considered. The image current, which is a linear distribution of magnetic dipoles on the line segment between the dipole point and the center of the sphere, is derived by using the fact that the induced current does not have any contribution to the radial component of the magnetic field outside the sphere. The image is then used to obtain some explicit formulas for identifying the location and tangential moment of the primary current dipole. This explicit identification method is also tested with a real model for a patient's brain. View full abstract»

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  • A model of EMG generation

    Page(s): 192 - 201
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    Simulation models are unavoidable in experimental research when the point is to develop new processing algorithms to be applied on real signals in order to extract specific parameter values. Such algorithms have generally to be optimized by comparing true parameter values to those deduced from the algorithm. Only a simulation model can allow the user to access and control the actual process parameter values. This constraint is especially true when dealing with biomedical signals like surface electromyogram (SEMG). This work is an attempt to produce an efficient SEMG simulation model as a help for assessing algorithms related to SEMG features description. It takes into account the most important parameters which could influence these characteristics. This model includes all transformations from intracellular potential to surface recordings as well as a fast implementation of the extracellular potential computation. In addition, this model allows multiple graphically-programmable electrode-set configurations and SEMG simulation in both voluntary and elicited contractions. View full abstract»

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  • Experimental and numerical determination of SAR distributions within culture flasks in a dielectric loaded radial transmission line

    Page(s): 202 - 208
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    The effect of dielectric loading on the cell layer specific absorption rate (SAR) within a T-75 culture flask being irradiated within a transverse electromagnetic (TEM) cell was studied both experimentally and numerically. Direct thermal measurements of a T-75 containing 40 mL of culture medium and resting upon a 3-mm-thick slab of alumina ceramic (ε r=9.6) revealed that, compared to the same flask resting upon a foam slab (ε r1.0) of the same thickness, the average SAR at the cell layer was increased roughly fourfold. This fourfold increase is significant experimentally because it allows biologists to perform experiments over a larger range of SAR values needed to determine possible dose-response curves without the costs and difficulties of a fourfold increase in amplifier power. Finite-difference time-domain (FDTD) simulations of the SAR distribution were in good quantitative agreement with the experimental measurements. It is concluded that FDTD modeling can be a cost effective and scientifically acceptable means of obviating the thermal measurement of SAR. View full abstract»

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  • Quality driven gold washing adaptive vector quantization and its application to ECG data compression

    Page(s): 209 - 218
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    The gold washing (GW) adaptive vector quantization (AVQ) (GW-AVQ) is a relatively new scheme for data compression. The adaptive nature of the algorithm provides the robustness for wide variety of the signals. However, the performance of GW-AVQ highly dependent on a preset parameter called distortion threshold (dth) which must be determined by experience or trial-and-error. The authors propose an algorithm that allows them to assign an initial dth arbitrarily and then automatically progress toward a desired dth according to a specified quality criterion, such as the percent of root mean square difference (PRD) for electrocardiogram (ECG) signals. A theoretical foundation of the algorithm is also presented. This algorithm is particularly useful when multiple GW-AVQ codebooks and, thus, multiple dth's are required in a subband coding framework. Four sets of ECG data with entirely different characteristics are selected from the MIT/BIH database to verify the proposed algorithm. Both the direct GW-AVQ and a wavelet-based GW-AVQ are tested. The results show that a user specified PRD can always be reached regardless of the ECG waveforms, the initial selection of dth or whether a wavelet transform is used in conjunction with the GW-AVQ. An average result of 6% in PRD and 410 bits/s in compressed data rate is obtained with excellent visual quality. View full abstract»

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  • Vibration arthrometry in the patients with failed total knee replacement

    Page(s): 219 - 227
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB)  

    This is a preliminary research on the vibration arthrometry of artificial knee joint in vitro. Analyzing the vibration signals measured from the accelerometer on patella, there are 2 speed protocols in knee kinematics: 1) 20/s, the signal is called "physiological patellofemoral crepitus (PPC", and 2) 67°/s, the signal is called "vibration signal in rapid knee motion" The study has collected 14 patients who had revision total knee arthroplasty due to prosthetic wear or malalignment represent the failed total knee replacement (FTKR), and 12 patients who had just undergone the primary total knee arthroplasty in the past 2 to 6 months and have currently no knee pain represent the normal total knee replacement (NTKR). FTKR is clinically divided into 3 categories: metal wear, polyethylene wear of the patellar component, and no wear but with prosthesis malalignment. In PPC, the value of root mean square (rms) is used as a parameter; in vibration signals in rapid knee motion, autoregressive modeling is used for adaptive segmentation and extracting the dominant pole of each signal segment to calculate the spectral power ratios in f<100 Hz and f>500 Hz. It was found that in the case of metal wear, the rms value of PPC signal is far greater than a knee joint with polyethylene wear and without wear, i.e., PPC signal appears only in metal wear. As for vibration signals in rapid knee motion, prominent time-domain vibration signals could be found in the FTKR patients with either polyethylene or metal wear of the patellar component. The authors also found that for normal knee joint, the spectral power ratio of dominant poles has nearly 80% distribution in f<100 Hz, is between 50% and 70% for knee with polyethylene wear and below 30% for metal wear, whereas in f>500 Hz, spectral power ratio of dominant poles has over 30% distribution in metal wear but only nonsignificant distribution in polyethylene wear, no wear, and normal knee. The results show that vibration signals in r- - apid knee motion can be used for effectively detecting polyethylene wear of the patellar component in the early stage, while PPC signals can only be used to detect prosthetic metal wear in the late stage. View full abstract»

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  • Time-frequency analysis of myoelectric signals during dynamic contractions: a comparative study

    Page(s): 228 - 238
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (263 KB)  

    Introduces nonstationary signal analysis methods to analyze the myoelectric (ME) signals during dynamic contractions by estimating the time-dependent spectral moments. The time-frequency analysis methods including the short-time Fourier transform, the Wigner-Ville distribution, the Choi-Williams distribution, and the continuous wavelet transform were compared for estimation accuracy and precision on synthesized and real ME signals. It is found that the estimates provided by the continuous wavelet transform have better accuracy and precision than those obtained with the other time-frequency analysis methods on simulated data sets. In addition, ME signals from four subjects during three different tests (maximum static voluntary contraction, ramp contraction, and repeated isokinetic contractions) were also examined. View full abstract»

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  • Nonlinear adaptive noise compensation in electrogastrograms recorded from healthy dogs

    Page(s): 239 - 248
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (166 KB)  

    Adaptive noise compensation is a popular method for improving signal-to-noise ratio in a variety of biomedical applications with its major disadvantage being the requirement for a reference channel containing noise strongly correlated to the noise in the primary channel. In many biomedical applications the utilization of a channel containing such noise without any representation of the information signal is difficult if not impossible. In this study the authors investigated the possibility of applying adaptive compensation in nonideal noise environments containing substantial presence of information signal in the reference channel. The signal in the reference channel was subjected to nonlinear manipulations for reducing the signal-to-noise ratio, thus diminishing the representation of information signal. The methodology was tested on canine electrogastrographic (EGG) signals of 4 unconscious dogs which underwent laparotomy and implantation of 6 pairs internal stainless steel electrodes in addition to the 8-channel abdominal EGG. Fourteen-channel (6 internal and 8 cutaneous) were obtained from each dog for 1/2 h. The signals were digitized and processed by computer. All internal signals showed regular and coupled gastric electrical activity with frequency of repetition in the normogastric range [3-9 cycles-per-minute (cpm)]. A single pair of primary and reference channels was selected from each cutaneous recording and exponential manipulators in the reference channels were introduced. The manipulators were tuned to maximize the percent distribution of spectral components in the canine normogastric range of each frequency spectrum calculated from the signal at the output of the adaptive compensator. Significant increment in the percent distributions in the normogastric range (p<0.01) was noted after tuning the exponential manipulator, and in many frequency spectra the recovery of the genuine dominant frequency peak of gastric electrical activity as determined by the i- - nternal recordings was noted. This study indicated that low percent distributions registered by some EGG channels are related to external nonlinear factors, the impart of which can be partially compensated. View full abstract»

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  • A spectral-discrimination method for tear-film lipid-layer thickness estimation from fringe pattern images

    Page(s): 249 - 258
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB)  

    Examination of the tear-film lipid layer is often helpful in the prognosis of prospective contact lens patients and contact lens related problems, and in the analysis of symptomatic noncontact lens-wearing patients. In particular, the thickness of the lipid layer is considered to be an informative cue in studying the tear-film stability and uncovering of certain disorders. The authors propose a method for the accurate estimation of the lipid-layer thickness, exploiting the intensity and color information in Fizeau fringe images. The technique is based on a quantitative measure for discriminating among the spectra associated with different thicknesses. The authors propose an optical system for imaging the interference patterns, develop a mathematical model based on the physics of the fringe formation and sensing, and describe the calibration of the optical system using this model. The thickness extraction is readily carried out utilizing a lookup table. The proposed method would enable objective evaluation of the lipid layer characteristics, and provide a means for examining the dynamic changes in its thickness and spatial distribution during inter-blink periods. View full abstract»

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  • Determination of intracranial tumor volumes in a rodent brain using magnetic resonance imaging, Evans Blue, and histology: a comparative study

    Page(s): 259 - 265
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (113 KB)  

    The measurement of tumor volumes is a practical and objective method of assessing the efficacy of a therapeutic agent. However, the relative accuracy of different methods of assessing tumor volume has been unclear. Using T 1-weighted, gadolinium-enhanced magnetic resonance imaging (T 1-MRI), Evans Blue infusion and histology the authors measured intracranial tumor volumes in a rodent brain tumor model (RT2) at days 10, 16 and 18 after implantation of cells in the caudate putamen. There is a good correlation between tumor volumes comparing T 1-MRI and Evans Blue (r 2=0.99), T 1-MRI and histology (r 2=0.98) and histology and Evans Blue (r 2=0.93). Each of these methods is reliable in estimating tumor volumes in laboratory animals. There was significant uptake of gadolinium and Evans Blue in the tumor suggesting a wide disruption of the blood-brain barrier. View full abstract»

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  • In vivo quantification of a homogeneous brain deformation model for updating preoperative images during surgery

    Page(s): 266 - 273
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB)  

    Clinicians using image-guidance for neurosurgical procedures have recently recognized that intraoperative deformation from surgical loading can compromise the accuracy of patient registration in the operating room. While whole brain intraoperative imaging is conceptually appealing it presents significant practical limitations. Alternatively, a promising approach may be to combine incomplete intraoperatively acquired data with a computational model of brain deformation to update high resolution preoperative images during surgery. The success of such an approach is critically dependent on identifying a valid model of brain deformation physics. Towards this end, the authors evaluate a three-dimensional finite element consolidation theory model for predicting brain deformation in vivo through a series of controlled repeat-experiments. This database is used to construct an interstitial pressure boundary condition calibration curve which is prospectively tested in a fourth validation experiment. The computational model is found to recover 75%-85% of brain motion occurring under loads comparable to clinical conditions. Additionally, the updating of preoperative images using the model calculations is presented and demonstrates that model-updated image-guided neurosurgery may be a viable option for addressing registration errors related to intraoperative tissue motion. View full abstract»

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  • Three-dimensional blind deconvolution of SPECT images

    Page(s): 274 - 280
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (231 KB)  

    Thanks to its ability to yield functionally rather than anatomically-based information, the three-dimensional (3-D) SPECT imagery technique has become a great help in the diagnostics of cerebrovascular diseases. Nevertheless, due to the imaging process, the 3-D single photon emission computed tomography (SPECT) images are very blurred and, consequently, their interpretation by the clinician is often difficult and subjective. In order to improve the resolution of these 3-D images and then to facilitate their interpretation, the authors propose herein to extend a recent image blind deconvolution technique (called the nonnegativity support constraint-recursive inverse filtering deconvolution method) in order to improve both the spatial and the interslice resolution of SPECT volumes. This technique requires a preliminary step in order to find the support of the object to be restored. Here, the authors propose to solve this problem with an unsupervised 3-D Markovian segmentation technique. This method has been successfully tested on numerous real and simulated brain SPECT volumes, yielding very promising restoration results. 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