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Proceedings of the IEEE

Issue 9 • Date Sep 1988

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Displaying Results 1 - 22 of 22
  • Applications of VLSI circuits to medical imaging

    Page(s): 1106 - 1114
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    The application of advanced VLSI circuits to medical imaging is explored. The relationship of both general-purpose signal processing chips and custom devices to medical imaging is discussed using examples of fabricated chips. In addition, advanced-aided design tools for silicon compilation are presented. Particular attention is given to the application of VLSI circuits to 3-D image display with ultrasound systems. It is concluded that devices built with these tools represents a possible alternative to custom devices and general-purpose signal processors for the next generation of medical imaging systems View full abstract»

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  • Lithotripter systems

    Page(s): 1236 - 1246
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    Lithotripsy in its various forms has revolutionalized the treatment of kidney and ureter stones. In extracorporeal lithotrips, pulsed acoustic shock waves are generated outside the body and focused via a coupling medium to the concrement. The location of the focus is controlled by fluoroscopy of ultrasound imaging. Starting from simplified models, two methods for generating shock wave pulses are described: (a) point-like supersonic emitters; and (b) two-dimensional emitters of finite amplitude waves. The principles and performance of a spark-gap emitter with a focusing ellipsoid, an electromagnetic acoustic source with a focusing lens, and a spherical concave piezoceramic source are described and discussed. Commercial lithotripter systems and their components for coupling, imaging, patient handling, and triggering are described and their performance is discussed View full abstract»

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  • An efficient multiplexing technique for packet-switched voice/data networks

    Page(s): 1254 - 1256
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    The authors propose a multiplexing frame structure that makes it possible to transmit voice messages synchronously without loss or clipping of contents. This scheme has discrete delay characteristics, and provides a simple play-out method for reproduction of voice signal. The authors investigate its performance by obtaining the cumulative distribution of delay of voice packets and the mean waiting time of data packets. It is concluded that this synchronous frame structure can easily be applied to enhance services with various transmission rates, such as flow control of message streams, node congestion control, and service-class or throughput-class negotiation of channels without significant degradation of trunk utilization View full abstract»

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  • Electrical stimulation of excitable cells-a model approach

    Page(s): 1122 - 1129
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    The authors provide an introduction to the study of the quantitative response of excitable cells to stimulating currents through the use of mathematical models. Considered is the behavior of a spherical cell in a uniform field and a circular fiber in a point source field, where, for simplicity, only steady-state solutions are included. In each case a characteristic length is associated with the cell and governs the nature of its response. Some work is presented on the response of a fiber bundle to a point-source stimulus. Here, too, a characteristic length is found to be important. In this case, the steady-state behavior of a particular fiber depends on the location of that fiber within the bundle. It is concluded that these results should be useful in the initial design of electrodes for functional electrical simulation View full abstract»

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  • Multidimensional ultrasonic imaging for cardiology

    Page(s): 1063 - 1073
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    Previous extensions of two-dimensional ultrasonic imaging to three dimensions used lattice diagrams which give measurement information, but no anatomic detail. The authors conducted three sets of experiments to test the hypothesis that complete acoustic backscatter data should be retained to produce useful information about heart structure and function. First, in vitro compound B-scans were taken under ideal conditions; second, in vitro rotating conventional sector scans were taken to test clinically applicable methods; and third, clinical in vivo rotating conventional sector scans were taken of a human volunteer. It is concluded that the resulting images show details of cardiac anatomy and have great clinical promise. Interactive analysis and surface and volume displays give context and perspective information which should improve diagnostic accuracy, communication with noncardiologists and yield more precise measurements of anatomical structure and function View full abstract»

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  • Applied neural control in the 1990s

    Page(s): 1115 - 1121
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    The authors describe some of the current neural prostheses and examine technological developments needed for future generations of neural prosthetic implants. Current developments include the peroneal nerve stimulator, upper and lower extremity functional neuromuscular stimulation and the auditory prosthesis. Three issues connected with future developments include stimulating and recording electrodes, the interconnection system, encapsulation, the command unit, force, touch, and position sensors, and signal conditioning View full abstract»

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  • Implantable defibrillator with high-output pacing function after defibrillation

    Page(s): 1187 - 1193
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    An experimental implantable defibrillator with a temporary pacing function was developed. The pacing function was activated after defibrillation to work as a high-output ventricular-demand pacemaker. The developed system was tested in animal experiments involving anesthesized and mechanically ventilated mongrel dogs. In the animal experiments, fibrillation was electrically induced, and the automatic defibrillation and pacing function were confirmed. After defibrillation, it was possible to continue the fixed-rate pacing for more than three minutes View full abstract»

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  • Linear-predictive data extrapolation narrow-band spectral estimation

    Page(s): 1249 - 1251
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    It is demonstrated that T.J. Ulrych et al.'s (J. Geophys., Res., vol.78, p.4959-64, 1973) hybrid Fourier-Burg method of narrowband spectral estimation has significant advantages which may have been overlooked. Apart from improved resolution in comparison to the conventional Fourier approach, it also exhibits reduced sensitivity to model order compared to the Burg maximum-entropy-method algorithm. Additionally, the hybrid method has a frequency-estimation variance which is less than that of the Burg technique, approaching that of the conventional (unwindowed) Fourier method for low signal/noise ratio. Finally, it can provide for enhanced tonal detection in some instances View full abstract»

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  • Speech processors for cochlear prostheses

    Page(s): 1143 - 1154
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    The authors review considerations in the design of speech processors for cochlear prostheses. To illustrate issues of processor design, two fundamentally different processing strategies are described in terms of the information that they can convey and in terms of how they might perform under various conditions on nerve survival. A summary is presented of clinical tests comparing these strategies in eight implant patients. Key findings from the comparison studies are that (a) one processor (the interleaved pulse processor) is clearly superior for patients with psychophysical signs of poor nerve survival, (b) another processor (the compressed analog processor) may be superior for patients with signs of good survival, and (c) different processing strategies can produce widely different outcomes for individual patients. Future directions in the future development of speech processors for cochlear prostheses are outlined View full abstract»

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  • Neural aspects of vision and related technological advances

    Page(s): 1130 - 1142
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    The author examines the physiological aspects of the visual systems of animals and humans and several models that explain or try to explain physiological or psychophysical data. Particular attention is given to the decomposition of patterns by the human brain. Both digital and analog implementations are discussed and some projections to future applications are also mentioned. The development of a neuronal computer vision system is considered View full abstract»

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  • On the use of pitch power spectrum in the evaluation of vocal tremor

    Page(s): 1166 - 1175
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    A point process model of the speech excitation wave for sustained vowels has been formulated, where the pitch is modulated by a physiological disturbance (vocal tremor). It has been demonstrated that the power spectrum of an impulse train, representing the glottal pulses, is composed of a periodic replication of the spectrum of the modulating signal, accompanied by an impulse train at the carrier frequency. Hence, the power spectrum of the vocal tremor can be estimated from the pitch. A trend location algorithm has been developed to locate and remove local trends from the signal prior to the evaluation of the pitch power spectrum. Thus, spectral representation of the speech excitation enables estimation of vocal tremor View full abstract»

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  • Recent advances in magnetic resonance

    Page(s): 1095 - 1105
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    The author describes some advances in magnetic resonance imaging which have been made in approximately the last two years. These are in general areas of improved speed of image acquisitions, improved spatial resolution, selective imaging of blood vessels, and reduction of image artifact View full abstract»

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  • Millimeter-wave propagation through a terrestrial atmosphere

    Page(s): 1251 - 1254
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    At millimeter-wave frequencies, the terrestrial atmosphere is absorptive, dispersive, and inhomogeneous. Because it is inhomogeneous, rays are bent by refraction, and because it is dispersive, the amount of bending depends on the frequency. Thus the path length between two terminals depends on frequency, which means that there is an additional frequency distortion to be accounted for. The author derives an `effective reactivity' to do such an accounting. He shows that the correction involved is rather small View full abstract»

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  • Control aspects of intraaortic balloon pumping: an overview

    Page(s): 1210 - 1217
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    Temporary or permanent, internal or external, in-series or bypass cardiac assist devices are examined with emphasis on intraaortic balloon pumping. Physiological and clinical consequences of the medical assistance are discussed. Major advantages of the devices are to provide adequate perfusion and, secondarily, to unload the heart and to reduce oxygen consumption of the failing myocardium. Major problems with the cardiac assist devices are related to synchronization with the natural heart, or proper timing, and to the determination of suitable control variables. Optimization algorithms based on the selected performance criteria and computer-based automatic controls are instituted to overcome some of these shortcomings. Finally schemes of automatic control of implantable assist devices are discussed View full abstract»

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  • Biomedical sensors in interventional systems: present problems and future strategies

    Page(s): 1218 - 1225
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    The authors consider important problems in biomedical sensor development, including physical configuration, packaging connection to the remaining system, power supply, simultaneous sensing of multiple variables, signal processing, and costs. In addition to using conventional sensing technologies, biomedical sensors have recently incorporated microelectronic, signal processing, and optical techniques. Traditional sensing approaches have been used in ways, and novel technologies have been developed for biomedical sensors View full abstract»

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  • Measurement of defibrillation shock potential distributions and activation sequences of the heart in three dimensions

    Page(s): 1176 - 1186
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1060 KB)  

    The authors note that knowledge of the extracellular potential gradient field of the defibrillation shock and the cardiac-tissue response to the shock should lead to better understanding of the mechanism of defibrillation and stimulate improvement of defibrillation techniques. By measuring the potential distribution of the defibrillation shock throughout the heart and the location of the recording electrodes, the potential gradient field may be calculated. By recording local electrograms throughout the heart immediately before and after the shock, the tissue response to the shock can be evaluated View full abstract»

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  • High resolution intravascular imaging via ultrasonic catheters: proof of concept

    Page(s): 1074 - 1078
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    The potential image quality and resolution of medical ultrasonic imaging catheters (UIC) for use in minimally invasive determinations of vascular disease was examined with the aid of a prototype, small-aperture, high-resolution imaging system. The value of high-resolution ultrasonic imaging derives from the potential ability to quantitate intimal roughening, `see' beyond the intimal lining of the vessel, and compute tissue attenuation to help identify tissue histology. High-resolution images of an in vitro human arterial samples were obtained using the prototype UIC. Excellent correlations between the ultrasonic images, high-resolution, magnetic resonance images, and pathology specimens are demonstrated. It is concluded that high-quality images for small, clinically useful UICs are definitely feasible using current technology View full abstract»

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  • Fast sequential least squares design of FIR filters with linear phase

    Page(s): 1247 - 1248
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    The authors propose a fast adaptive least-squares algorithm for linear-phase finite-impulse-response (FIR) filters. The algorithm requires 10m multiplications per data point where m is the filter order. This reduced computation stems from the fast adaptive forward-backward least-squares method. Both linear-phase cases i.e. with constant phase delay and with constant group delay, are examined. Simulation results demonstrate that the proposed algorithm is superior to the least-mean-squares gradient algorithm and the averaging scheme used for the modified fast Kalman algorithm View full abstract»

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  • Control of functional neuromuscular stimulation systems for standing and locomotion in paraplegics

    Page(s): 1155 - 1165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1388 KB)  

    The authors adopt a control-systems perspective in reviewing past applications of functional neuromuscular stimulation for providing lower extremity motor function in paralyzed individuals. Specifically, their approach emphasizes direct computer-controlled electrical stimulation of paralyzed muscle rather than triggering reflexes. In experimental settings it provides paralyzed individuals with the ability to do functional tasks while standing, to walk short distances on varying surfaces, to negotiate obstacles, and to climb and descend stairs View full abstract»

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  • Tomographic radiopharmaceutical imaging

    Page(s): 1079 - 1094
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    Tomographic radiopharmaceutical imaging, or emission computed tomography (ECT), provides in vivo three-dimensional maps of a pharmaceutical labeled with a gamma-ray-emitting radionuclide. ECT has developed in two complimentary directions based on the type of radionuclide that is used. Positron emission computed tomography (PET) detects the two coincident 511-keV annihilation photos from position emitters such as 11C, 13N, 15O, and 18F. Single-photon-emission computed tomography (SPECT) involves detection of gamma rays emitted singly, and sequentially, by the radionuclide tracer. The author presents examples of PET and SPECT imaging devices and reviews a widely used reconstruction algorithm. Current research areas that are under active investigation are also described View full abstract»

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  • Cerebrospinal fluid control system

    Page(s): 1226 - 1235
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    An implantable, therapeutic system for hydrocephalus, with an noninvasively adjustable flow valve and a telemetered intracranial pressure (ICP) and cerebrospinal fluid (CSF) flow is presented. The system contains an implant unit, a patient unit, and a physician's console. This system provides an improved shunt system for the better treatment of hydrocephalus, accommodates changing patient needs without revision, helps to wean patients from shunt dependency, and collects information the physiological behavior of CSF generation and absorption. The nearly constant-flow microvalve can adjust its flow rate by external command through a transceiver link. The patients unit as well as the physician's console have a communications head that can communicate with the implant unit. It will receive online data and send in commands to adjust the valve position to alter CSF flow. The system has been designed and is currently being prototyped View full abstract»

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  • Development of an automatic implanted drug infusion system for the management of cardiac arrhythmias

    Page(s): 1204 - 1209
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    Conventional management of cardiac arrythmias relies on oral drug therapy which minimizes recurrence of the arrhythmia, but risks unpleasant side effects and even long-term toxicity. The authors propose acute management instead, from an implanted drug pump which automatically senses the onset of arrhythmia, delivers a pharmacokinetically-based infusion to terminate the episode, and discontinues drug delivery until the next occurrence. A bedside system consisting of a personal computer and conventional intravenous pump has been developed and tested in five dogs and 24 patients during a catheter electrophysiologic study. After detection of the arrhythmia plasma levels of the antiarrhythmia drug rose immediately to the therapeutic range and were subsequently well-controlled for 30 to 60 minutes. In all five dogs and in seven of the eight patients in whom atrial fibrillation was induced during the study, conversion to normal rhythm occurred within fifteen minutes View full abstract»

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