Showing papers in "IEEE Transactions on Biomedical Engineering in 1981"
TL;DR: A theoretical analysis was performed to investigate the restrictions in estimating the three parameters, as well as their sensitivity to the conduction velocity, and the ratio parameter was found to be most sensitive to conduction Velocity, but was the least reliable of the three.
Abstract: Dunrng a sustained muscle contraction, the spectrum of the myoelectric signal is known to undergo compression as a function of time. Previous investigators have shown that the frequency compression is related to the decreasing conduction velocity of the muscle fibers. It is proposed that the frequency compression may be tracked by obtaining a continuous estimate of a characteristic frequency of the spectrum, such as the mean and median, or the ratio of low-frequency components to high-frequency components of the spectrum. A theoretical analysis was performed to investigate the restrictions in estimating the three parameters, as well as their sensitivity to the conduction velocity. The ratio parameter was found to be most sensitive to conduction velocity, but was the least reliable of the three. The median frequency was the least sensitive to noise. Therefore, from a theoretical point of view, the median frequency is the preferred parameter. A technique is described which determines an unbiased consistent estimate of the median frequency. The technique may be readily implemented in analog hardware.
559 citations
TL;DR: Under most practical conditions, the process of back projection and coherent summation over spherical surfaces in image space, without prior filtering, is shown to provide a close approximation to the exact inversion procedure.
Abstract: The problem of reconstructing the reflectivity of a three-dimensional medium with density and compressibility variations is examined. For the special case of continuous-wave (CW) insonification, exact inversion formulas have recently been reported for recovering an unknown scattering parameter from scattering measurements. In this work, exact solutions, or inversion formulas, are obtained for the general case of arbitrary broad-band insonification where the incident wave is assumed to be a spherically diverging broad-bandwidth pulse of arbitrary shape. Solutions are derived under the assumption that the scattering is sufficiently weak for the Born approximation to hold. Exact inversion formulas are obtained for three aperture geometries: a plane, cylindrical, or spherical recording surface enclosing the scattering region. Under most practical conditions, the process of back projection and coherent summation over spherical surfaces in image space, without prior filtering, is shown to provide a close approximation to the exact inversion procedure. Finally, in the case of the spherical geometry, the mathematical equivalence between the three-dimensional inverse Radon transform and the far-field approximation to the exact solution is demonstrated.
349 citations
TL;DR: It is shown that the position of the source in a head modeled by a sphere surrounded by two concentric shells of differing conductivities representing the skull and the scalp can be inferred from source localization calculations made on a homogeneous model.
Abstract: The problem of locating the position of the source of evoked potentials from measurements on the surface of the scalp has been examined. It is shown that the position of the source in a head modeled by a sphere surrounded by two concentric shells of differing conductivities representing the skull and the scalp can be inferred from source localization calculations made on a homogeneous model.
338 citations
TL;DR: An instrument is described which functions as a low light level ocular fundus camera and ophthalmoscope, and which is capable of making a wide range of quantitative measurements in the eye.
Abstract: An instrument is described which functions as a low light level ocular fundus camera and ophthalmoscope, and which is capable of making a wide range of quantitative measurements in the eye. Light levels for ophthalmoscopy (20 ?W/cm2 at the retina) are at least two orders of magnitude below those in current use. A focused laser bearn forms a flying spot, moved physically by scanning mirrors. This allows a 20 ?m or smaller resolution element, with only a 0.9 mm diameter area of the patient's pupil used for the entering beam. The remaining pupillary area forms the exit pupil?a critical inversion of the division of pupils necessary for systems using conventional imaging. It is this inversion which allows the low light level and the unique measurement capabilities. We discuss the constraints imposed by viewing the inside of a spheroid through a small hole in its wall, and our solutions?both optical and electronic?to these problems. We also describe electronic problems encountered in the video system, which arise from our special detection and display systems. Some specifics of the instrument's measurement capabilities are discussed.
280 citations
TL;DR: Transmission ultrasound computer-assisted tomography has been developed for detection and diagnosis of cancer in the breast and estimates of sensitivity and specificity are approaching those of X-ray mammography techniques.
Abstract: Transmission ultrasound computer-assisted tomography has been developed for detection and diagnosis of cancer in the breast. Pulses of ultrasound (8 MHz ±3 MHz) are transmitted through the breast in a coronal plane from a plurality of directions. The received signal is processed for arrival time and for changes in amplitude. The measured values for arrival time and attenuation are used in a convolution-back projection reconstruction algorithm to obtain estimates of the two-dimensional distribution of acoustic speed and attenuation within the scanned planes of the breast. Over 1000 images in breasts of approximately 150 patients have been scanned of whom 30 had biopsy proven cancer. Some common characteristics of the reconstructed images which are associated with cancer are 1) increased speed relative to the embedding tissue associated with 2) decreased attenuation in central region of the lesion usually with 3) a ring of higher attenuation at the border of the lesion. Current estimates of sensitivity and specificity of this system for cancer are approaching those of X-ray mammography techniques.
269 citations
TL;DR: The merits of three alternative methods for estimating spectral features are compared to the fast Fourier transform (FFT), based on autoregressive (AR) modeling, and it is demonstrated that a fifth-order filter is sufficient to estimate EEG characteristics in 90 percent of the cases.
Abstract: The hypothesis that an electroencephalogram (EEG) can be analyzed by computer using a series of basic descriptive elements of short duration (1-5 s) has prompted the development of methods to extract the best possible features from very short (1 s) time intervals. In this paper, the merits of three alternative methods for estimating spectral features are compared to the fast Fourier transform (FFT). These procedures, based on autoregressive (AR) modeling are: 1) Kalman filtering, 2) the Burg algorithm, and 3) the Yule-Walker (YW) approach. The methods are reportedly able to provide high resolution spectal estimates from short EEG intervals, even in cases where intervals contain less than a ful period of a cyclic waveform. The first method is adaptive, the other two are not. Using Akaike's final prediction error (FPE) criterion, it was demonstrated that a fifth-order filter is sufficient to estimate EEG characteristics in 90 percent of the cases. However, visual inspection of the resulting spectra revealed that the order indicated by the FPE criterion is generally too low and better spectra can be obtained using a tenth-order AR model. The Yule-Walker method resulted in many unstable models and should not be used. Of two remaining methods, i.e., Burg and Kalman, the first provides spectra with peaks having a smaller bandwidth than the Kalman-flter method. Additional experiments with the Burg method revealed that, on the average, the same results were obtained using the FFT.
172 citations
TL;DR: In this paper, a back projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain.
Abstract: A back projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain. The filters used in transmission computed tomography (TCT)-comprised of a ramp multiplied by window functions?are modified so that the single-photon ECT filter is a function of the constant attenuation coefficient. The filters give good reconstruction results with sufficient angular and lateral sampling. With continuous samples the BKFIL algorithm has a point spread function that is the Hankel transform of the window function. The resolution and statistical properties of the filters are demonstrated by various simulations which assume an ideal detector response. Statistical formulas for the reconstructed image show that the square of the percent-root-mean-square (percent-rms) uncertainty of the reconstruction is inversely proportional to the total measured counts. The results indicate that constant attenuation can be compensated for by using an attenuation-dependent filter that reconstructs the transverse section reliably. Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.
158 citations
TL;DR: The spectral artifact problem in X-ray computed tomography (CI) is well known and many techniques have been suggested to correct for this problem, including linearization methods, iterative methods, and dual spectrum methods.
Abstract: The spectral artifact problem in X-ray computed tomography (CI) is well known. Many techniques have been suggested to correct for this problem, including linearization methods, iterative methods, and dual spectrum methods.
134 citations
TL;DR: In two-dimensional image reconstruction from line integrals using maximum likelihood, Bayesian, or minimum variance algorithms, the x-y plane on which the object estimate is defined is decomposed into nonoverlapping regions, or "pixels".
Abstract: In two-dimensional image reconstruction from line integrals using maximum likelihood, Bayesian, or minimum variance algorithms, the x-y plane on which the object estimate is defined is decomposed into nonoverlapping regions, or "pixels." This decomposition of an otherwise continuous structure results in significant errors, or model noise, which can exceed the effects of the fundamental measurement noise.
128 citations
TL;DR: A technique for nerve stimulation has been developed to elicit a single unidirectionally propagated action potential through a quasitrapezoidal stimulus current wave delivered through an asymmetric tripolar electrode.
Abstract: A technique for nerve stimulation has been developed to elicit a single unidirectionally propagated action potential. A quasitrapezoidal stimulus current wave delivered through an asymmetric tripolar electrode effectively blocks propagation in one direction from the stimulus site.
127 citations
TL;DR: A previously reported stimulation technique which elicits a unidirectionally propagated nerve action potential has been evaluated with repetition rates from 10 to 100 Hiz.
Abstract: A previously reported stimulation technique which elicits a unidirectionally propagated nerve action potential has been evaluated with repetition rates from 10 to 100 Hiz. Block of propagation in one direction from the stimulus site was sustained up to 50 Hz with monophasic stimulation and 30 Hz with biphasic stimulation. The use of long stimulating pulses produces pronounced degradation of the block at high frequencies.
TL;DR: A portable device that measures energy expenditure per unit time of a human subject and may prove to be useful in providing an objective measurement of the level of physical activity of human subjects is developed and tested.
Abstract: We have developed and tested a portable device that measures energy expenditure per unit time of a human subject. A modified ceramic phonocartridge senses the acceleration of the body. After amplification and rectification a Curtis 120 CP3 elapsed time meter integrates the output. This may prove to be useful in providing an objective measurement of the level of physical activity of human subjects and can be used in studying habitual and leisure time activities in a large population setting. It is worn on the waist, weighs 400 g, measures 14 X 8 X 4 cm, costs $ 30 plus 5 h assembly time, and runs 10 days on two 9 V transistor batteries.
TL;DR: It is shown how this estimate can be used to alter the measured projections in such a way that the image of the heart region can be significantly improved.
Abstract: Using a stroboscopic procedure based on electrocardiographic gating, "stationary" images of the beating heart can be obtained from X-ray computed tomography body scanners. However, due to the limited amount of time over which the heart motion is periodic, only a small number of projections (X-ray views) per phase of the heart cycle can be measured. It is suggested here how to obtain satisfactory image quality when only a limited number of projections per phase are available. The procedure involves recognizing that the material surrounding the heart is stationary, and so can be estimated using a large number of projections. It is shown how this estimate can be used to alter the measured projections in such a way that the image of the heart region can be significantly improved.
TL;DR: In this paper, an exact interpolation formula was proposed for reconstructing computerized tomographic (CT) imagery by direct Fourier methods, which is shown to yield superior results compared with other interpolation methods.
Abstract: In this paper an exact interpolation formula forms the basis for reconstructing computerized tomographic (CT) imagery by direct Fourier methods. Practical variations of exact interpolation are compared with other interpolation methods (i.e., nearest neighbor, etc.) and are shown to yield superior imagery. Images produced by the direct Fourier approach using near-exact interpolation are shown to be equal in quality with those produced by filtered convolution backprojection (FCBP). Moreover, the direct Fourier approach computes an image in O(N2 log N) time versus O(N3) for the FCBP method.
TL;DR: This paper presents a method for evaluating the properties of features that describe the shape of a QRS complex by examining the distances in the feature space for a class of nearly similar complexes.
Abstract: Automated classification of ECG patterns is facilitated by careful selection of waveform features This paper presents a method for evaluating the properties of features that describe the shape of a QRS complex By examining the distances in the feature space for a class of nearly similar complexes, shape transitions which are poorly described by the feature under investigation can be readily identified To obtain a continuous range of waveforms, which is required by the method, a mathematical model is used to simulate the QRS complexes
TL;DR: Algorithms based on interpolating techniques introduced the least amount of error when 16 bit data were used while algorithms based on least-squares data fit methods performed best on the less accurate 8 bit data.
Abstract: Five commonly used algorithms for digital differentiation are evaluated to determine how they perform in the presence of 8, 12, and 16 bit quantization noise. The algorithms are compared on the basis of rms error between a model derivative of the left ventricular pressure waveform and the approximate results of each algorithm. Algorithms based on interpolating techniques introduced the least amount of error when 16 bit data were used while algorithms based on least-squares data fit methods performed best on the less accurate 8 bit data. Some of the band-limiting characteristics of the algorithms are also discussed.
TL;DR: A multichannel microelectrode that has 24 recording sites, spaced at 85 ¿m intervals along the edge of its tip, that can be arranged as a 1 ×24 linear array along one edge or as a 2 ×12 array along both edges.
Abstract: We have developed a multichannel microelectrode that has 24 recording sites, spaced at 85 ?m intervals along the edge of its tip. The sites are arranged in one of two ways: either as a 1 ×24 linear array along one edge or as a 2 ×12 array along both edges. In the first, the sites span 2 mm while in the second, the sites span 1 mm ×135 ?m.
TL;DR: The theoretical background of this method is given, as well as the required operational conditions and electrode positions, leading to an FECG reading guaranteed free of maternal electrocardiogram (MECG).
Abstract: After a review of the different techniques in use up to now for the detection of an interference-free abdominal fetal electrocardiogram (FECG), with the limitations of these techniques indicated, a new technique is described which does not suffer from these limitations. This technique is based on an optimization procedure applied to the multiplication coefficients of six independent abdominal signals which are added together. The theoretical background of this method is given, as well as the required operational conditions and electrode positions, leading to an FECG reading guaranteed free of maternal electrocardiogram (MECG).
TL;DR: The relationship between the instantaneous frequency and the mean frequency of ultrasonic Doppler signals in blood velocity measurements and the effect of hard limiting of the signal on the estimator performance is discussed.
Abstract: The relationship between the instantaneous frequency and the mean frequency of ultrasonic Doppler signals in blood velocity measurements is discussed. The probability distribution density for the instantaneous frequency is calculated. The time interval histogram (TIH), which has been used to characterize the Doppler signal, is found to be an approximation of this probability density. The probability density will also describe the output of phase-lock loop analysis of the Doppler signal. The variance of mean frequency estimators is calculated, and the implication of this for practical estimators is discussed. The effect of hard limiting of the signal on the estimator performance is also discussed.
TL;DR: The forced oscillation technique used to determine the impedance of the respiratory system has been modified by measuring, instead of pressure and airflow at the mouth of the subject, the transfer function over a rigid tube.
Abstract: The forced oscillation technique used to determine the impedance of the respiratory system has been modified by measuring, instead of pressure and airflow at the mouth of the subject, the transfer function over a rigid tube. An exact description of the aerodynamic characteristics of a cylindrical conduit is needed in this method. Therefore, a line model was developed, describing the tube as a pneumatic transmission line and taking into account the axial pressure losses, the gas compressibility, and the thermal conductivity of the tube wall. The quality of this model was verified by measuring velocity profiles at the end of an open tube at various frequencies. The agreement with the predictions of the model was satisfactory.
TL;DR: Four iterative parameter estimation algorithms were used to obtain estimates in three parallel compartment models of the respiratory system and the combination of a two-stage simplex algorithm with a five element model provided the most stable parameter estimates and the second best fit to the data.
Abstract: Four iterative parameter estimation algorithms were used to obtain estimates in three parallel compartment models of the respiratory system. The stability of the parameter estimates and the agreement between the forced random noise impedance data and the model's response were evaluated for each algorithm-model combination. The combination of a two-stage simplex algorithm with a five element model provided the most stable parameter estimates and the second best fit to the data.
TL;DR: A theoretical model of neural interaction at the macroscopic level of brain hierarchy is developed in order to predict cortical current density and the resulting spatial-temporal properties of scalp EEG.
Abstract: A relationship between cortical current density and resulting scalp potential is first obtained by means of arguments about volume conduction through brain, skull, and scalp. Next, a theoretical model of neural interaction at the macroscopic level of brain hierarchy is developed in order to predict cortical current density and the resulting spatial-temporal properties of scalp EEG. EEG frequencies in the 6 to 24 cycle/s range are predicted when a threshold parameter is small. When the threshold parameter approaches a critical value, there is an abrupt decrease in EEG frequency and increase in amplitude in a manner suggestive of the transition from the awake to sleeping state.
TL;DR: Bacterial growth was best detected with stainless steel electrodes at low frequency and including the imaginary component of impedance, which is consistent with characteristics of diffusion and electron exchange at the electrode.
Abstract: The growth of bacteria in culture was found to produce impedance changes between two metal electrodes which result from changes both in conductivity and electrode impedance. Predominant changes were found in the imaginary impedance component at low frequency. Linear ac impedance characteristics were found in the relation between real and imaginary impedance components before and during bacterial growth. This linear relation is consistent with characteristics of diffusion and electron exchange (oxidation-reduction) at the electrode. The measurement of impedance in this system was limited below 100 Hz by nonlinearity in the voltage-current relation. Bacterial growth was best detected with stainless steel electrodes at low frequency (100 Hz) and including the imaginary component of impedance.
TL;DR: Interestingly, some recently "optimized" versions provide only a near normalization of glycemia in patients with insulin-dependent diabetes, a degree ofglycemic control which is not significantly different from intensified conventional insulin therapy.
Abstract: Over the past 15 years, several algorithms have been proposed and used for closed-loop blood glucose regulation. Their intent is to artificially replace the normal responses of the pancreatic beta cell absent in insulin-dependent diabetes. All of these algorithms calculate insulin infusion rates on the basis of minute-by-minute measurements of whole blood glucose concentration and its calculated rate of rise or fall. In addition, various techniques are employed to compensate for measurement delay time and the presence of noise in the measured signals. The goal of these feedback systems is to normalize blood glucose in diabetes mellitus. Interestingly, some recently "optimized" versions provide only a near normalization of glycemia in patients with insulin-dependent diabetes, a degree ofglycemic control which is not significantly different from intensified conventional insulin therapy.
TL;DR: Two algorithms used in the clinical analysis of nystagmus are described, which uses a new set of fast phase detection conditions which allow for automatic processing of reversals in nyStagmus direction and for wide variability for clinical data.
Abstract: Two algorithms used in the clinical analysis of nystagmus are described. Their development was necessitated by the greater complexity of the nystagmus waveforms in response to system identification types of vestibular and optokinetic stimuli as compued to the less complex response to a step input. Practical considerations for clinical application also influenced their development. The first algorithm converts nystagmus data into a regulary sampled estimate of slow phase velocity (SPV), an important feature of the signal. It uses a new set of fast phase detection conditions which allow for automatic processing of reversals in nystagmus direction and for wide variability for clinical data. The second algorithm detects noise induced spikes in this SPV estimate using an adaptive criterion based upon a measure of the overall "noisiness" of the data compared to the stimulus.
TL;DR: Bismuth germanate has emerged as the scintillation material of choice for high resolution scanners, as its detection efficiency with small crystals is higher than that of NaI.
Abstract: The surge of interest in medical research with positron-emitting nuclides has been accompanied by improvements in the design of positron emission tomographs (scanners). Bismuth germanate has emerged as the scintillation material of choice for high resolution scanners, as its detection efficiency with small crystals is higher than that of NaI. Other detector materials, such as CsF, may be useful when timing accuracy is of great importance, as in high count rate studies or time-of-flight measurements. Circular detector arrays are now generally preferred because they provide the best sensitivity and uniformity of coverage. Multiple rings are used to increase the axial coverage. Other design parameters, such as detector and collimator dimensions, are surveyed and their effect on scanner performance is discussed.
TL;DR: The permittivities of bovine muscle, artery, kidney, and liver are measured in vitro using a coaxial-line reflection technique and an automatic network analyzer, and compare well with those published for similar animal tissues.
Abstract: The permittivities of bovine muscle, artery, kidney, and liver are measured at 37°C in vitro at 2.0, 3.0, and 4.0 GHz, using a coaxial-line reflection technique and an automatic network analyzer. Uncertainties, evaluated by measurements on organic alcohols whose permittivities are well known, are consistently less than ±10 percent in both ??and ??. The data compare well with those published for similar animal tissues.
TL;DR: A simulation study that evaluated alternative techniques for estimating the spectrum of the ABR signal and of the background EEG found that narrow-band filtering suggests that the midfrequency component is primarily associated with Jewett wave V, while the high- frequencies are primarilyassociated with the early Jewett waves.
Abstract: Human auditory brainstem responses (ABR's) are sensory evoked potentials that can be recorded within a few milliseconds following a transient acoustic stimulus. This paper describes results of a simulation study that evaluated alternative techniques for estimating the spectrum of the ABR signal and of the background EEG. The effects of residual noise in the average signal, the number of responses in the average, and the use of smoothing windows were considered. Spectra of human ABR's were also obtained. The spectral energy decreases with frequency to 2 kHz and seems to flatten above 2 kHz. The ABR signal spectrum is limited to below approximately 1.5 kHz. There are three main components: a low-frequency component around 100 Hz, a midfrequency component around 500 Hz, and a high-frequency component at 1000 Hz. Narrow-band filtering suggests that the midfrequency component is primarily associated with Jewett wave V, while the high-frequency component is primarily associated with the early Jewett waves. These two components are probably the most important for determining the latencies of waves. The low-frequency component appears to correspond to a slow wave on which the Jewett waves are superimposed.
TL;DR: A numerical procedure to simulate several physiological and geometrical changes occurring during development of edema and to study their effects on the sensitivity of the microwave detection method is presented, using a model based on a two-dimensional cross section of a thorax.
Abstract: A numerical procedure to simulate several physiological and geometrical changes occurring during development of edema and to study their effects on the sensitivity of the microwave detection method is presented. The method of solution utilizes a model which consists of a two-dimensional cross section of a thorax. The model is based on an X-ray CAT scan taken with the microwave applicators in place. The electromagnetic boundary value problem is then solved numerically using the method of moments. Numerical results are presented to show the effects of several parameters, such as the uneven water distribution in the lung, the field distribution in the aperture of the microwave transmitter, and the location of the receiver on the sensitivity of the microwave detection method. Based on these results, several suggestions are made to help optimize the sensitivity of the microwave method of measuring changes in lung water content.
TL;DR: A new type of X-ray Compton scatter imaging technique which has potential application to medical diagnostic radiography and uses the information to generate an interior view of an object from a frontal backprojection imaging perspective.
Abstract: This paper describes a new type of X-ray Compton scatter imaging technique which has potential application to medical diagnostic radiography. This system detects the Compton interacted radiation which is scattered back toward the X-ray source and uses the information to generate an interior view of an object from a frontal backprojection imaging perspective. X-ray scatter radiographs can provide a three-dimensional imaging ability that is different from computerized axial tomography and may provide additional medical diagnostic information which is difficult or expensive to derive from conventional techniques.