Showing papers in "IEEE Transactions on Biomedical Engineering in 1983"
TL;DR: The driven-right-leg circuit is analyzed and it is shown that high loop gains can cause instability and equations that can be used to design circuits that minimize common mode voltage without instability are presented.
Abstract: The driven-right-leg circuit is often used with biopotential differential amplifiers to reduce common mode voltage. We analyze this circuit and show that high loop gains can cause instability. We present equations that can be used to design circuits that minimize common mode voltage without instability. We also show that it is important to consider the reduction of high-frequency interference from fluorescent lights when determining the bandwidth of the drivenright-leg circuit.
417 citations
TL;DR: An analytical expression is presented for the solid angle subtended by a plane triangle at some arbitrary point in space, and the time required for numerical computation is cut down to one third.
Abstract: An analytical expression is presented for the solid angle subtended by a plane triangle at some arbitrary point in space. Using this expression, the time required for numerical computation is cut down to one third.
308 citations
TL;DR: Results of a nerve model investigation indicated that the threshold difference between different diameter nerve fibers would be dependent on pulse width, the choice between monophasic and biphasic stimuli, and the delay between the primary cathodic and secondary anodic pulses.
Abstract: The effect of stimulus parameters on the recruitment characteristics of motor nerve was studied for regulated current monophasic and balanced charge biphasic stimuli. Results of a nerve model investigation indicated that the threshold difference between different diameter nerve fibers would be dependent on pulse width, the choice between monophasic and biphasic stimuli, and the delay between the primary cathodic and secondary anodic pulses. Threshold difference increased with decreasing pulse width, the greatest effects evident for pulses less than 100 ?s. Biphasic stimulation with no delay between pulses provided greater threshold separation than monophasic stimulation or biphasic stimulation with delay. Animal experiments, in which recruitment in a nerve trunk composed of mixed diameter nerve fibers was examined, showed a decrease in recruitment slope with a decrease in pulse width and with the use of a biphasic, zero delay pulse. These results were examined through muscle force measurements using both a metal loop electrode encircling the nerve trunk and a nerve cuff electrode, i. e., a loop electrode in an insulating tube.
298 citations
TL;DR: An analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatialcompounding, frequency compounding, and parallel processing.
Abstract: The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing.
260 citations
TL;DR: The transducer is probably the single most important component of any ultrasonic imaging system and the techniques for modeling the electromechanical impulse response are reviewed, with emphasis on the spatio-temporal impulse response technique.
Abstract: The transducer is probably the single most important component of any ultrasonic imaging system. A basic introduction to the problems and paradoxes of transducer design is given. After introducing the piezoelectric equations and discussing important transducer material such as lead zirconate titanate and polyvinylidene difluoride, the techniques for modeling the electromechanical impulse response are reviewed. Quarter-wave matching and short pulse techniques are discussed. The prediction of the ultrasound field of plane, spherical, and conical transducers is reviewed with emphasis on the spatio-temporal impulse response technique. Finally, the use of the above approaches is illustrated in a very practical fashion for three interesting transducer geometries: 1) a split aperture device with two focal lengths, 2) a five-element annular array, and 3) a 37.5 degree conical/annular array hybrid transducer.
232 citations
TL;DR: The filtered backprojection algorithm of X-ray tomography and the filtered backpropagation algorithm developed recently by the author for diffraction tomography are tested in computer simulations of ultrasonic tomography of two-dimensional objects for which the Rytov approximation is valid.
Abstract: The filtered backprojection algorithm of X-ray tomography and the filtered backpropagation algorithm developed recently by the author for diffraction tomography are tested in computer simulations of ultrasonic tomography of two-dimensional objects for which the Rytov approximation is valid It is found that the filtered backprojection algorithm gives unsatisfactory results even for wavelengths much smaller than the smallest scale over which the object varies The filtered back-propogation algorithm yields, in all cases studied, high-quality reconstructions which are simply low-pass filtered versions of the actual object profile It is shown that the filtered backpropagation algorithm can be approximated by a modified backprojection algorithm having essentially the same computation requirements as filtered backprojection, but yielding considerably higher quality object reconstructions
217 citations
TL;DR: Experimental results on-normal subjects are presented which demonstrate the advantages of using the spatial and time correlation of the signals, and this technique should be useful in generating control signals for prosthetic devices.
Abstract: A signal analysis technique is developed for discriminating a set of lower arm and wrist functions using surface EMG signals. Data wete obtained from four electrodes placed around the proximal forearm. The functions analyzed included wrist flexion/extension, wrist abduction/adduction, and forearm pronation/supination. Multivariate autoregression models were derived for each function; discrimination was performed using a multiple-model hypothesis detection technique. This approach extends the work of Graupe and Cline [1] by including spatial correlations and by using a more generalized detection philosophy, based on analysis of the time history of all limb function probabilities. These probabilities are the sufficient statistics for the problem if the EMG data are stationary Gauss-Markov processes. Experimental results on-normal subjects are presented which demonstrate the advantages of using the spatial and time correlation of the signals. This technique should be useful in generating control signals for prosthetic devices.
204 citations
TL;DR: A technique utilizing a combination of adaptive noise canceling and conventional signal processing is developed to enhance electrocardiographic monitoring in the operating room by reducing the noise interference that is created by an electrosurgical instrument.
Abstract: A technique utilizing a combination of adaptive noise canceling and conventional signal processing is developed to enhance electrocardiographic monitoring in the operating room by reducing the noise interference that is created by an electrosurgical instrument. Significant amounts of interference are eliminated by radio frequency shielding, passive and active low-pass filtering, and optical isolation. A digital adaptive canceler using the least mean-square algorithm of Widrow and Hoff is used to reduce the remainder of the interference, yielding an improvement in signal-to-noise ratio of approximately 110 dB. Clear electrocardiograms have been obtained with electrocautery equipment in operation.
202 citations
TL;DR: Several design approaches for two- and three-electrode amplifiers, both nonisolated and isolated, that reduce this interference are reviewed.
Abstract: We review how the nonideal properties of biopotential amplifiers can transform common mode voltage into interference. We then review several design approaches for two-and three-electrode amplifiers, both nonisolated and isolated, that reduce this interference. We consider the effects of static electricity on the various designs, and we show how to calculate the optimal values of the circuit components.
168 citations
TL;DR: An investigation to establish whether auditory evoked potentials (AEP's) are due to phase reordering of the background electroencephalogram or to an additive signal, found that all of the AEP's studied contained additive energy in at least one harmonic component.
Abstract: An investigation, carried out to establish whether auditory evoked potentials (AEP's) are due to phase reordering of the background electroencephalogram or to an additive signal, is described. New phase reordered and additive models of the AEP were introduced and used in conjunction with the techniques of angular statistics. It was established that all of the AEP's studied contained additive energy in at least one harmonic component.
156 citations
TL;DR: It is suggested that the olarizability observed at audio and radiowave frequencies is in part sssociated with the collagen phase, although other interfacial polarization effects can also be present.
Abstract: The dielectric permittivity and electrical conductivity of freshly excised and formalin fixed samples of rat femoral bone were determined over a frequency range of 10 Hz-100 MHz. Impedance measurements were performed in the frequency domain using a vector impedance meter and an impedance analyzer. The results of these measurements show that the conductivity of fixed and fresh bone is nearly independent of frequency below 100 kHz, with the conductivity of fresh bone being two to three times greater than that of the fixed sample. At higher frequencies, the conductivity increases as a power function of frequency. The permittivity of bone reaches very high values at low frequencies, but decreases rapidly with increasing frequencies and approaches a limiting value of about ten. This high-frequency limit is consistent with the water content of the tissue, and with the permittivity of the anhydrous matrix. It is suggested that the olarizability observed at audio and radiowave frequencies is in part sssociated with the collagen phase, although other interfacial polarization effects can also be present.
TL;DR: Three fast and efficient "scan-along" algorithms for compressing digitized electrocardiographic data are described, based on the minimum perimeter polygonal approximation for digitized curves.
Abstract: Three fast and efficient "scan-along" algorithms for compressing digitized electrocardiographic data are described. These algorithms are "scan-along" in the sense that they produce the compressed data in real time as the electrocardiogram is generated. The algorithms are based on the minimum perimeter polygonal approximation for digitized curves. The approximation restricts the maximum error to be no greater than a specified value. Our algorithms achieve a compression ratio of ten on a database of 8000 5-beat abnormal electrocardiograms sampled at 250 Hz and a compression ratio of eleven on a database of 600 3-beat normal electrocardiograms (different from the preceding database) sampled at 500 Hz.
TL;DR: A technique which can determine the spatial position and orientation of a collection of real-time two-dimensional ultrasonic scanners with respect to a reference coordinate system appears to offer the potential for the accurate assessment of ventricular volume in man.
Abstract: Real-time two-dimensional ultrasonic scanners provide a series of cross-sectional images of the ventricle We have developed a technique which can determine the spatial position and orientation of a collection of such scans with respect to a reference coordinate system The scans need not be parallel, may intersect, and need not demonstrate a complete cross section The borders of interest are digitized to identify a set of points representing the surface of the ventricle These points are used to generate a 3-D reconstruction of the chamber and are processed to give an estimate of ventricular volume The technique has been validated using ten formalin-fixed hearts excised from dogs, sheep, and cows, with an actual volume range of 318-5706 cm3 Each ventricle was imaged five times by three observers for a total of 150 studies By the least squares linear regression analysis, calculated volume = 098 (actual volume) + 139 cm3, r = 099 The average error for all studies was 5 percent, while 88 percent of the individual calculated volume were within 10 percent of the actual volume The method appears to offer the potential for the accurate assessment of ventricular volume in man
TL;DR: An automated Holtes scanning system based on two microcomputers that detects QRS complexes and measures the QRS durations using computations of first and second derivatives, and can process Holter tapes at 60 times real time and produce printed summaries and 24 h trend plots.
Abstract: We have developed an automated Holtes scanning system based on two microcomputers. One is a preprocessor that detects QRS complexes and measures the QRS durations using computations of first and second derivatives. Thismicrocomputer interfaces to a secondmicro-computer that does arrhythmia analysis, logging, and reporting using R-R intervals and QRS durations. This system can process Holter tapes at 60 times real time and produce printed summaries and 24 h trend plots of several variables including heart rate and PVC count.
TL;DR: To investigate the potentialities of hyperthermia as a cancer therapy, computer simulations have been performed and numerical results pertaining to the temperature distribution in a model of the human pelvis are presented.
Abstract: To investigate the potentialities of hyperthermia as a cancer therapy, computer simulations have been performed. This simulation consists of two tuccessive steps. First, the heat generated in a distribution of biological tissue when irradiated by a source of electromagnetic radiation is computed. The mathematical tool for determining the disbution of generated heat is the domain-integral-equation technique. This technique enables us to determine in a body with arbitrary distribution of permittivity and conductivity the electromagnetic field due to prescribed sources. The integral equation is solved numerically by an iterative minimization of the integrated square error. From the computed distribution of generated heat, the temperature distribution follows by solving numerically the pertaining heat transfer problem. The relevant differential equation together with initial and boundary conditions is solved numerically using a finite-element technique in space and a finite-difference technique in time. Numerical results pertaining to the temperature distribution in a model of the human pelvis are presented.
TL;DR: This work discusses the low-pass filter characteristics of the two-point central difference algorithm and derives the optimal step size for two types of human eye movement data.
Abstract: There are many algorithms for calculating derivatives. The two-point central difference algorithm is the simplest. Besides simplicity, the two most important characteristics of this algorithm are accuracy and frequency response. The frequency content of the data prescribes a lower limit on the sampling rate. The smoothness and accuracy of the data determine the optimal step size. We discuss the low-pass filter characteristics of this algorithm and derive the optimal step size for two types of human eye movement data. To calculate the velocity of fast (saccadic) eye movements, the algorithm should have a cutoff frequency of 74 Hz. For typical slow (smooth pursuit) eye movements, a step size of 25 or 50 ms is optimal.
TL;DR: It is expected that these adaptive controllers, based upon a minimum variance control law, will significantly improve the performance of drug infusion systems in clinical applications.
Abstract: Stochastic adaptive controllers have been developed for automatic control of blood pressure during infusions of cardiostimulatory or vasoactive drugs. An adaptive algorithm based upon a minimum variance control law is presented. A more advanced algorithm obtained by augmenting the performance measure to include the rate of charge of the control signal is also presented. An autoregressive-moving-average (ARMA) model, representing the dynamics of the system, and a recursive least-squares parameter estimation technique are used for both algorithms. A series of experiments was performed in dogs, utilizing an electronically activated drug infuser. Stable control was achieved, even when the circulatory state of the animal underwent major changes, using either algorithm. On the basis of theoretical considerations and experimental results, we expect that these adaptive controllers will significantly improve the performance of drug infusion systems in clinical applications.
TL;DR: Initial results indicate that an above normal percentage of high-frequency energy is closely associated with narrowed coronary arteries.
Abstract: A noninvasive approach to detecting coronary artery disease analyzes thoracic sounds to isolate acoustical correlates of stenosed coronary arteries. The analysis includes time windowing, frequency (power spectra) windowing, and averaging of thoracic sounds from normal and diseased patients. Initial results indicate that an above normal percentage of high-frequency (180-300 Hz) energy is closely associated with narrowed coronary arteries.
TL;DR: An initial report on the design and performance of a device which combines the heating and coagulating effects of a microwave field with the surgical scalpel intended to control hemorrhage in the surgical treatment of highly vascular organs such as the spleen and liver.
Abstract: We present an initial report on the design and performance of a device which combines the heating and coagulating effects of a microwave field with the surgical scalpel. The device is intended to control hemorrhage in the surgical treatment of highly vascular organs such as the spleen and liver. Preliminary experiments in splenic surgery using dogs have indicated the utility of this technique.
TL;DR: The ventricular gradient G is shown to be related to the area under the cellular action potential and an expression is developed which relates the secondary T wave to the QRS complex and the shape of the action potential.
Abstract: The ventricular gradient G is shown to be related to the area ?under the cellular action potential. For ac-coupled amplifiers, ? is calculated by taking the resting potential for each cell to be zero. The contribution to G for a small volume of the heart is then proportional to the gradient of ?weighted by the transfer impedance or lead field Z. An expression is developed which relates the secondary T wave to the QRS complex and the shape of the action potential. This expression is evidently equivalent to a procedure originally proposed by Abildskov et al. [6].
TL;DR: It is the site of insulin infusion, which appears to play an essential role in terms of the ability to normalize the metabolic state of a diabetic subject, in this evaluation of portal versus peripheral routes for insulin delivery in diabetes with three representative closed-loop glucose control algorithms.
Abstract: In this paper we present an evaluation of portal versus peripheral routes for insulin delivery in diabetes with three representative closed-loop glucose control algorithms. A novel noninvasive approach is used which is based on a model of the blood glucose regulation system which simulates a Type I diabetic subject. The two routes and three algorithms are compared in controlling the simulated patient for 24 h, challenged with two dynamic glucose perturbations. The evaluation is performed by comparing both plasma accessible variables (e.g., glucose and insulin) and metabolic fluxes (e.g., glucose production and uptake, peripheral glucose utilization). Similar performances are achieved by the three algorithms both with peripheral and with portal infusions, especially in the postabsorptive steady state. An almost complete metabolic normalization is obtained with the portal route. With the peripheral route, normality is not restored; in particular, hyperinsulinemia and enhanced insulin-dependent glucose utilization are produced. From these simulation results, it is the site of insulin infusion, which appears to play an essential role in terms of the ability to normalize the metabolic state of a diabetic subject.
TL;DR: Pulse spectral graphs (PSG) were obtained from pulses taken on the wrist by using electronics and computers and find that the ER for healthy persons is above 100 at all three-finger positions on both wrists, but those for sick persons are below 100 at some specific positions of pulse-taking.
Abstract: Pulse spectral graphs (PSG) were obtained from pulses taken on the wrist by using electronics and computers. Energy ratio (ER) is defined as the ratio of the energy of PSG below 10 Hz to that above 10 Hz. We find that the ER for healthy persons is above 100 at all three-finger positions on both wrists, but those for sick persons are below 100 at some specific positions of pulse-taking. The specific positions giving low ER values are related to the troubled organs, as would be expected from Chinese medicine. Potential application of this novel method in the health field is indicated.
TL;DR: The calculation of absolute ultrasonic attenuation as a function of frequency by processing backscattered signals obtained from a clinical imaging instrument is described to illustrate the requirements for incorporating quantitative attenuation measurements with clinical imaging.
Abstract: This paper describes the calculation of absolute ultrasonic attenuation as a function of frequency by processing backscattered signals obtained from a clinical imaging instrument The signal processing steps are developed from a mathematical model of scattering in an attenuating medium with random inhomogeneities Attenuation data are derived from the imaging system by recording amplitude-compressed ultrasonic echo waveforms along with transducer position information and time-varying gain values The input-output characteristics of the receiver are employed to remove the effects of compression and gain Attenuation values are calculated for selected regions within scans of two tissue phantoms and a normal breast The values agree with other independent measurements and illustrate the requirements for incorporating quantitative attenuation measurements with clinical imaging
TL;DR: It is found that only 4 equivalent cardiac dipoles or only 15 independent epicardial potentials can be estimated from body surface potentials when they are measured with an accuracy as high as 99 percent.
Abstract: The inverse problem in electrocardiography is ill-conditioned, and small noise included in the measured potentials causes large errors in the solution. Since the inverse problem is mostly described as a linear problem, the entire problem has often been treated in terms of a transfer matrix. The degree of linear independence among the vectors in the transfer matrix, which is directly related to the stability of the solution, is well represented by the singular values of the transfer matrix. By means of the singular value decomposition of the transfer matrix, the stability of solution to the inverse problem has been discussed when the potential data contain noise or the transfer matrix includes some error. We have derived expressions of maximum possible error magnification and a root-mean-square error magnification and, in terms of these parameters, found that only 4 equivalent cardiac dipoles or only 15 independent epicardial potentials can be estimated from body surface potentials when they are measured with an accuracy as high as 99 percent.
TL;DR: The design of time-invariant and time-varying minimum mean square error filters for processing event related brain potentials and a model for taking into account the randomness associated with the signal as well as that of the noise are described.
Abstract: The design of time-invariant and time-varying minimum mean square error filters for processing event related brain potentials is considered. A model for taking into account the randomness associated with the signal as well as that of the noise is described. Results using simulated data show the perfonnance of the time-varying filter to be greatly superior to that of the time-invariant filter. Results of processing measured visual evoked potentials are presented.
TL;DR: A simple quantitative electrophysiologic model is presented which successfully accounts for the salient statistical features of the RR interval sequence and may be utilized to characterize a sequence of RR intervals recorded from a given individual in terms of the numerical magnitudes of the model's four parameters.
Abstract: We review the principal statistical properties of the RR interval sequence during atrial fibrillation. A simple quantitative electrophysiologic model is presented which successfully accounts for these statistical features. In this model the atrioventricular junction (AVJ) is treated as a single cell equivalent characterized by a refractory period and spontaneous rate of phase 4 depolarization. The atria are presumed to bombard the AVJ with impulses that arrive randomly in time; each impulse induces a partial depolarization of the AVJ equivalent cell. We show that other models for the ventricular response during atrial fibrillation (e. g., concealed conduction models) do not adequately account for the salient statistical features of the RR interval sequence. The present model may be utilized to characterize a sequence of RR intervals recorded from a given individual in terms of the numerical magnitudes of the model's four parameters: the mean rate at which atrial impulses bombard the AVJ, the relative amplitude of the impulses, the relative rate of spontaneous phase 4 depolarization of the AVJ equivalent cell, and the refractory period of the AVJ equivalent cell. Such a characterization may be useful in studying mechanisms of drug action and interaction, as well as potentially offering a quantitative means for optimizing pharmacologic manangement of chronic atrial fibrillation.
TL;DR: A video-based technique for measuring the torsional movement of the eye (counterroll) by processing video images of the eyeball by using cross correlation between sequences that are obtained by circular sampling of the digitized image of the iris is presented.
Abstract: A video-based technique for measuring the torsional movement of the eye (counterroll) by processing video images of the eyeball is presented. Spectral estimates show that most of the variance of the iris image is in the angular direction. It will be demonstrated that cross correlation between sequences that are obtained by circular sampling of the digitized image of the iris is sufficient to extract the counterroll information. Computation time for angular correlation is thus significantly reduced and real-time hardware implementation becomes feasible. As the result of a preprocessing step, we obtain the information about the horizontal and vertical movement of the eye and also the diameter of the pupil. To improve the measurement resolution, a fast second degree local least square interpolation of the cross-correlation function is used. Possible sources of error and the limitations of the algorithm will be studied. The results of the computer simulations made using the algorithm serve to experimentally confirm the error estimates. Application of the algorithm to photographically obtained image data from human subjects demonstrates its practicality on normal eyes. The system design for a device for measuring 3D movement of the eye will be discussed.
TL;DR: A model of the dependence of electrical conductivity on blood composition and indicator concentration is developed here, based in part on a review of earlier work on variation with hematocrit and on recognition of the profound effect on conductivity of even transient alterations of blood temperature by the indicator itself.
Abstract: Recent developments in indicator-dilution measurement of pulmonary edema have generated new interest in the use of electrical-conductivity sensing for measurement of indicator concentrations in blood. This approach has always suffered from the lack of an appropriate and validated model of the dependence of electrical conductivity on blood composition and indicator concentration. Such a model is developed here, based in part on a review of earlier work on variation with hematocrit and on recognition of the profound effect on conductivity of even transient alterations of blood temperature by the indicator itself. Shifts of water into and out of erythrocytes, in response to osmotic pressures, are properly included. The model predicts approximately linear changes in blood conductivity'over a large range of indicator concentrations (e. g., independent nonlinearity of 2.6 percent for 3 percent saline over a 0-30 percent concentration in blood). Changes in resistivity can be nonlinear, particularly with hypertonic indicators (e. g., independent nonlinearity of 7.9 percent for 3 percent saline over a 0-15 percent concentration in blood). Overlooking the thermal and osmotic effects can lead to significant errors in signal interpretation; consequent errors in flow rate determinations can be greater than 10 percent. Model predictions are verified in vitro with various indicators and canine blood using a miniature tetrapolar conductivity cell of our own design. The multicomponent nature of most conductivity indicators and the associated implications are discussed.
TL;DR: A microcomputer-based filter that removes line induced electrical interference from biopotential signals by learning one period of the noise waveform and subtracting it from the signal is developed.
Abstract: We have developed a microcomputer-based filter that removes line induced electrical interference from biopotential signals by learning one period of the noise waveform and subtracting it from the signal. Since it uses a noise template, the filter can remove noise waveforms containing several harmonics of the 60 Hz line frequency.