Showing papers in "IEEE Transactions on Biomedical Engineering in 1988"

A robot with improved absolute positioning accuracy for CT guided stereotactic brain surgery

Abstract: The use of a Unimation Puma 200 robot, properly interfaced with a computerized tomographic (CT) scanner and with a probe guide mounted at its end effector for CT-guided brain tumor biopsis is discussed. Once the target is identified on the CT picture, a simple command allows the robot to move to a position such that the end-effector probe guide points toward the target. This results in a procedure faster than one using a manually adjustable frame. Probably the most important advantage, as is shown, is the improved accuracy that can be achieved by proper calibration of the robot. >

Dielectric properties of breast carcinoma and the surrounding tissues

Abstract: Relative permittivity of infiltrating breast carcinoma and the surrounding tissue was measured. The experiments were performed at frequencies from 20 kHz to 100 MHz at 37 degrees C using an automatic network analyzer and an end-of-the-line capacitive sensor. Cole-Cole dielectric parameters were calculated by curve fitting using a computer program. Three main categories of tissues were considered: the central part of the tumor, the tumor surrounding tissue, and the peripheral tissue. Within each category, the large spread of the dielectric data for different specimens suggests structural and cellular inhomogeneities of the tumor tissue. However, certain consistency has been found in the dielectric relaxation time and the coefficient of the distribution of the relaxation time within each category. The results seem to indicate that RF impedance imaging can potentially be used as a diagnostic modality for the detection of human breast carcinoma. >

A spiral nerve cuff electrode for peripheral nerve stimulation

Abstract: A novel type of nerve cuff electrode consisting of conductive segments embedded within a self-curling sheath of biocompatible insulation has been developed. This spiral nerve cuff is biased to self-wrap around peripheral nerves and possesses a 'self-sizing' property, presenting an alternative to present commercially available, fixed-size nerve cuffs that are manually wrapped around nerves and sutured shut ('split-cylinder' cuffs). Spiral cuff design and manufacture are described. The authors hypothesize that unlike traditional cuffs, the spiral cuff potentially can be implanted safely when sized to fit peripheral nerves snugly. Theoretical pressure analyzes of traditional and spiral cuffs that support this hypothesis are presented. These analyses are designed to predict the minimum CNR (cuff diameter/nerve diameter ratio) at which there is no interference with intraneural blood flow. Results of a preliminary experiment in which snug spiral cuffs were implanted on feline peripheral nerve support the prediction that they may be safe. >

Performance of planar multisite microprobes in recording extracellular single-unit intracortical activity

Abstract: The microprobes consist of a thin-film electrode array supported by a silicon micromachined substrate and insulated using deposited dielectrics. Microprobes with multiple recording sites spaced from 30 mu m to 200 mu m apart are used to record spontaneous single-unit activity from rat cerebral cortex. Additionally, a theoretical model is used to establish a basis for interpreting the multisite single-unit data. The results suggest that the microprobes (1) couple tightly to the neural tissue with relatively little disturbance to the neural system, (2) facilitate the identification of single units in multiunit records through the use of spatially-separate recording sites, and (3) can be used to detect the cell position in tissue and observe events such as the propagation of electrical activity from the soma to the dendritic tree. >

A telemetry-instrumentation system for chronically implanted glucose and oxygen sensors

Abstract: An implantable potentiostat-telemetry system for in vivo operation of glucose and oxygen sensors is described. The device conveys signals from implanted chemical-specific sensors to a remote receiver via radio telemetry. Reference signals encoded in the analog FM transmission allow the receiver to automatically compensate for variability between simultaneously operated transmitters. The implant has several programmable operating modes that provide different signal gain and power consumption. All-CMOS circuitry is used, allowing operation for up to three months on a single lithium cell. Design, fabrication, and operation of the device are described. >

Skin impedance from 1 Hz to 1 MHz

Abstract: The impedance of skin coated with gel but otherwise unprepared was measured from 1 Hz to 1 MHz at ten sites on the thorax, leg, and forehead of ten subjects. For a 1-cm/sup 2/ area, the 1 Hz impedance varied from 10 k Omega to 1 M Omega , which suggests that the bipotential amplifier input impedance should be very high to avoid common-mode-to-differential-mode voltage conversion. The 1-MHz impedance was tightly clustered about 120 Omega . The 100-kHz impedance was about 220 Omega , which suggests that the variation in skin impedance can cause errors in two-electrode electrical impedance tomographs. >

Noninvasive pulse oximetry utilizing skin reflectance photoplethysmography

Abstract: The major concern in developing a sensor for reflectance pulse oximetry is the ability to measure large and stable photoplethysmograms from light which is backscattered from the skin. Utilizing a prototype optical reflectance sensor, locally heating the skin is shown to increase the pulsatile component of the reflected photoplethysmograms. Additional improvements to signal-to-noise ratio were achieved by increasing the active area of the photodetector and optimizing the separation distance between the light source and photodetector. The results from a series of in vivo studies to evaluate a prototype skin-reflectance pulse oximeter in humans are presented. >

Identification of human postural dynamics

Abstract: Human postural dynamics was investigated for six healthy subjects using a force platform recording body sway induced by vibrators attached to the calf muscles The model of body mechanics adopted was that of an inverted pendulum, the dynamics of postural control being assumed to be reflected in the stabilizing forces exerted on the platform by the feet as a result of complex muscular activity subject to state feedback of body sway and position The approach to signal processing has been that of parametric identification of a transfer function representing the stabilized inverted pendulum Posture control was quantified in three variables: swiftness, stiffness, and damping It is shown that the identification fulfils ordinary statistical validation criteria, and it is conjectured that the state feedback parameters identified are suitable for use in assessing ability to maintain posture >

Cardiovascular variability signals: towards the identification of a closed-loop model of the neural control mechanisms

Abstract: The authors consider parametric methods for processing cardiovascular signals and try to provide a global, although indirect evaluation of some neural regulatory activities. In particular, the variability signals of the heart rate (under the form of interval tachogram) and arterial blood pressure (systogram) together with respiratory movement signal (respirogram) are considered as inputs to a closed-loop model which describes a few aspects of the physiological interactions among the signals themselves. The identifiability of the transfer function of the model is demonstrated from the joint process black-box description of the signals. A direct identification procedure is proposed dividing the system into two dynamic adjustment models. A few suggestions are deduced on how and where the respirogram enters the model and on the genesis of the 10-s rhythm, parameters relevant to the Starling effect, Windkessel model, and the gain of baroreceptor mechanisms. The approach presented is intended also to provide a general frame for closed-loop identification in different pathophysiological conditions. >

Mathematical dipoles are adequate to describe realistic generators of human brain activity

Abstract: It is investigated whether a mathematical dipole description is adequate for the localization of brain activity on the basis of visually evoked potentials (VEPs). Extended sources (dipole disks and dipole annuli) are stimulated and fitted with a mathematical dipole. It is found that the deviation between the positions of the disks and annuli and the equivalent dipole is very small. Also, the differences in the direction and amplitude may be neglected. The position of the extended source with respect to the electrode grid does not much influence these conclusions. >

An articulated neurosurgical navigation system using MRI and CT images

Abstract: Neurosurgical operations sometimes involve difficulties in finding out the real positions of small-size neoplasms shown on tomographical images. The articulated navigation system, with the aid of a computer, gives ongoing positional correspondence between the position in the patient's brain and the one in the tomographic images to assist neurosurgery. >

Charge injection limits of activated iridium oxide electrodes with 0.2 ms pulses in bicarbonate buffered saline (neurological stimulation application)

Abstract: The maximum charge injection without electrode solution decomposition for activated iridium wire electrodes in bicarbonate buffered saline was 2.1 and 1.0 mC/cm/sup 2/ geometric for anodic-first and cathodic-first, respectively, 0.2-ms balanced-charge biphasic current pulses. Electrodes biased at +0.8 V vs. SCE (saturated calomel electrode) accepted charge up to 3.5 mC/cm/sup 2/ geometric with monophasic cathodal pulses. >

The depolarization sequence of the human heart surface computed from measured body surface potentials

Abstract: A method for computing the activation sequence at the ventricular surface from body surface potentials, has been adapted to handle measured data. By using measured anatomical data together with a 64-channel ECG (electrocardiogram) recording of the same subject for three subjects, it is shown that the model is able to determine activation sequences on the heart surface which closely resemble similar data obtained through invasive measurement as reported in literature. >

RF powering of millimeter- and submillimeter-sized neural prosthetic implants

Abstract: The size of the transducers for neural stimulation has shrunk steadily with application of thin-film techniques to electrode design. The feasibility is examined of designing millimeter- and submillimeter-sized power sources based on RF coupling that could be integrated into these implants to provide power without a tethering power cable. The coupling between a transmitter coil and receiver coil when the coil diameters are markedly different is analyzed, and for these circumstances, a simple Thevenin equivalent model is developed to describe the power transmission between the transmitter and receiver. The equivalent circuit developed gives insight into the way that coil diameters, frequency, and turns affect coupling between large and small coils. Several examples demonstrate that milliwatt range power sources can be implemented with millimeter- and submillimeter-diameter receivers. >

A 3-D impedance method to calculate power deposition in biological bodies subjected to time varying magnetic fields

Abstract: A previously described two-dimensional impedance method (ibid., vol.31, p.644-51, 1984) for modeling the response of biological bodies exposed to time-varying electromagnetic fields has been extended to three dimensions. This method is useful at those frequencies where the quasistatic approximation is valid and calculates the fields, current densities, and power depositions in the bodies. Solutions using this method for homogeneous spheres in plane waves are presented and compared to the analytic solutions for the same configuration. Solutions for a man exposed to a uniform radio-frequency magnetic field at 30 MHz, are presented, as well as for a man exposed to either circularly or linearly polarized magnetic fields at 63 MHz, uniform within a portion of his body and linearly decreasing outside of that portion, which approximates the exposure in some nuclear-magnetic-resonance imaging devices. >

An electric current tomograph

Abstract: A description is given of an instrument designed to acquire data for the construction of images of internal body structures based on measurements of electrical impedance made from a set of electrodes applied around the periphery of the body. The instrument applies currents at 15 kHz in any desired pattern to 32 electrodes and measures the resulting voltage at each electrode. The construction of a test phantom is also described and the results of initial studies showing the distinguishability of targets of differing sizes and conductivities placed in the phantom are reported. The system is able to distinguish the presence of 9-mm-diameter insulators or conductors placed in the center of a 30-cm-diameter circular tank of salt water. This system is capable of implementing an adaptive process of produce the best currents to distinguish the unknown conductivity from a homogeneous conductivity. >

Multispectral imaging of burn wounds: a new clinical instrument for evaluating burn depth

Abstract: A real-time video imaging system called the imaging burn depth indicator (IBDI) is described; IBDI can discriminate areas of burn wounds expected to heal in three weeks or less from the day of injury from those areas not expected to heal in that time period The analysis can be performed on or about the third day postburn on debrided burn wounds The relative diffuse reflectivity of the burn-wound is measured in the red, green, and near-infrared wavelength bands and an algorithm established previously is used to translate this optical data into burn healing probabilities Over 100 burn wound sites were studied Burn sites were evaluated on day three postburn by the IBDI and by the attending physician Overall, the IBDI was found to be more accurate in predicting burn healing than were the attending physicians >

A parametric method of identification of single-trial event-related potentials in the brain

Abstract: A parametric method of identification of event-related (or evoked) potentials on a single-trial basis through an ARX (autoregressive with exogenous input) algorithm is discussed. The basic estimation of the information contained in the single trial is taken from an average carried out on a sufficient number of trials, while the noise sources, EEG and EOG, are characterized as exogenous inputs in the model. The simulations as well as the experimental results confirm the capability of the model of drastically improving the S/N (signal-to-noise) ratio in each single trial and satisfactorily identifying the contributions of signal and noise to the overall recording. A particularly efficient reduction of ocular artifacts is also achieved. >

Topographic components model for event-related potentials and some biophysical considerations

Abstract: Models for decomposing averaged event-related potentials in component functions are discussed. Biophysical considerations motivate a sample model, which is shown to lead to unique identifiable components, thereby overcoming a major drawback of the customary approach by principal components analysis. >

Use of the finite-difference time-domain method for calculating EM absorption in man models

Abstract: The finite-difference time-domain method is used to calculate the specific absorption rate (SAR) within the human body. SAR distributions are calculated using incident frequencies of 100 MHz and 350 MHz for three different cases: (1) a homogeneous man model in free space; (2) an inhomogeneous man model in free space; and (3) an inhomogeneous man model standing on a ground plane. These various cases are used to evaluate the advantage of inhomogeneous models over homogeneous models, and grounded models versus free space models. Comparison is made between the results obtained here and those obtained using the method of moments. >

Noninvasive measurement of cardiac output using partial CO/sub 2/ rebreathing

Abstract: A noninvasive algorithm for estimating cardiac output is discussed The technique is based on a differential form of the CO/sub 2/ Fick equation applied during normal ventilation and a 30-s period of partial rebreathing using additional deadspace Using the Fick equation in a differential form eliminates the need to estimate mixed venous pCO/sub 2/, also the sensitivity of the cardiac output estimate to changes in the alveolar deadspace fraction is greatly reduced The procedure is fully automated, requires minimal staff supervision, and provides cardiac output estimates every 3 1/2-min Estimates of cardiac output when compared to thermodilution yielded a correlation coefficient of 092 with a linear regression slope of 092 (n=451) Temporary increases in alveolar deadspace did not significantly alter this relationship Cardiac output estimates obtained during period of increased pulmonary shunt due to oleic acid infusion yielded a correlation coefficient of 090 with a linear regression slope of 092 when compared to direct thermodilution measurements >

Segmentation of echocardiographic images using mathematical morphology

Abstract: A semiautomatic technique for isolating the ventricular endocardial border in echocardiograms from a commercially available two-dimensional phased array ultrasound system is presented. This method processes echo images using mathematical morphology to reduce the effects of range and azimuth variation inherent in echo. After morphological filtering, the endocardial border is extracted with traditional segmentation methods. Further processing of the resulting border using binary morphology produces a region of interest suitable for derivation of motion parameters of the endocardium. The area and the shape of semiautomatically-derived regions correlate well (r>0.93) with those defined by expert observers in a study of induced ischemia in seven canines. >

A video system for measuring motion in contracting heart cells

Abstract: The design and characteristics of a video-based device that can noninvasively measure the extent and rate of shortening of isolated cardiac myocytes are discussed. Construction of the motion detector is relatively inexpensive. It is easy to use because edge selection is simple and the video images of contracting cells can be analyzed at the experimenter's convenience. The device also exhibits high spatial and adequate temporal resolution. The physiologic application of the motion detector was examined by measuring overall shortening in enzymatically dispersed adult guinea pig and rabbit cardiac myocytes bathed in Tyrode's solution containing 2.7 mm calcium at 36 degrees C (pH/sub 0/ 7.4). When stimulated at 0.5 Hz, myocytes shortened an average of 8.1% (guinea pig) and 9.0% (rabbit) of cell length. respectively. The corresponding mean maximum rates of shortening were 81.7% (guinea pig) and 97.5% (rabbit) of cell length/s, respectively. The motion detector was also used to measure shortening between closely spaced markers on the cell surface. >

Theory of ultrasound Doppler-spectra velocimetry for arbitrary beam and flow configurations

Abstract: In conventional ultrasound Doppler systems, the velocity component along the beam axis is derived from the observed frequency shift. Recently, it was verified that by using a pulsed-Doppler system with the beam transversely oriented with respect to the flow, the velocity component transverse to the beam can be derived from the edges of the spectrum. These results are generalized to take into account arbitrary angles of incidence, effects of velocity gradients, arbitrary apertures, and arbitrary source pulses. For uniform apertures and transverse flow, it has been previously shown that the Doppler output spectrum is symmetrical about zero frequency, with its width depending on the Doppler effect due to the transverse velocity and the geometry of the problem. For a beam direction oblique to the velocity, it is shown that the spectrum is now shifted, and is centered about the classical Doppler frequency. For velocity gradients and transverse flows the spectrum remains symmetrical, with the edges corresponding to the maximal velocity; however, the profile becomes peaked at the center. For oblique incidence, an asymmetrical spectrum is obtained and its edges are related to the maximal and minimal velocities within the sampling volume. >

Suppression of stimulation artifacts from myoelectric-evoked potential recordings

Abstract: A system that allows detection of single and double differential surface myoelectric signals during electrical stimulation of either the nerve or the muscle motor point, using surface electrodes, is described. The input referred stimulation artifact is limited to less than 24 mu V/sub pp/ by a switching constant current/constant voltage output stage, slew rate limiting, and time windowing of the detected signal. The system is suitable for muscle crosstalk and for muscle fatigue investigation during functional electrical stimulation, in addition to measuring muscle or nerve conduction velocity. >

The electromyogram (EMG) as a control signal for functional neuromuscular stimulation. I. Autoregressive modeling as a means of EMG signature discrimination

Abstract: The successful application of functional neuromuscular stimulation to the muscles of paraplegics depends to a large extent on the adequate provision of a means by which the subject can exercise control over the resulting movement. The use of above-lesion electromyographic signals as a solution to the control problem is considered. A number of criteria for such a control system are defined. The general concepts underlying time-series analysis are described and the suitability of this method as a means of processing electromyographic signals is investigated. The electromyogram, which exhibits weak stationarity over short time intervals, is represented by a fourth-order autoregressive model. A sequential least-squares algorithm is used to determine the model parameters, which are then used to achieve signature discrimination. >

Estimation of single-evoked cerebral potentials by means of parametric modeling and Kalman filtering

Abstract: A method is presented for the investigation of stimulus evoked cerebral potentials (EPs) in single-trial EEG recordings which separates the measured activity into its evoked and spontaneous parts A compound state-space model trying to incorporate the observable properties of both parts is formulated on the basis of additivity of the two components Within this model, spontaneous activity is described as an autoregressive process, while the EP is modeled by an impulse response of a parametrically described system Based on the state-space representation of the model, a Kalman filter for the observation of the system's state can be designed which yields optimal estimates for both activities The properties of the proposed method are tested by application to stimulated data, in which preset EPs are added to measured spontaneous EEG segments The relative mean squared error and the bias are used to judge the accuracy of the EPs retrieved by the filter Finally, the method is applied to data where rapid drug-induced effects can be monitored with high time-resolution by means of estimated somatosensory evoked potentials >

Spectral analysis interpretation of electro-surgical generator nerve and muscle stimulation

Abstract: The frequency spectra of two commercial electrosurgical generators were examined during stimulated tissue cutting and compared to radio-frequency animal nerve and muscle stimulation curves generated from high-frequency sinusoidal current. During electrosurgical cutting, significant energy can exist at the fundamental frequency, as well as at frequencies lower and greater than the fundamental, which may be stimulatory to both nerve and muscle tissue. Different types of biological loads did not seem to significantly affect the spectra of each individual electrosurgical unit (ESU). However, the interaction of a specific ESU output with the biological load when compared to a pure resistive load accounts for varying impedances and resultant modulations of the fundamental frequency. Reducing electrosurgical side effects and hazards may depend, in part, on a better understanding of these underlying mechanisms. >

A flexible, portable system for neuromuscular stimulation in the paralyzed upper extremity

Abstract: A portable functional neuromuscular stimulation (FNS) system for control of the muscles of the paralyzed upper extremity has been developed and evaluated for outpatient use. The system, which has been tested over a five-year period, incorporates an 8-bit CMOS microprocessor which can be programmed to accept and process a variety of user-generated commands and to output complex stimulus patterns. Eight channels of analog input can be used to control four channels of constant-current-compensation monophasic stimulus output. The portable FNS system is programmed using a multichannel laboratory stimulation system. >

Modeling the excitation of fibers under surface electrodes

Abstract: It was demonstrated previously by the author (see J. Theor. Biol., vol.125, p.339-49, 1987) that the electrostimulation of nerve or muscle fibers is caused by the activating function, which is the second differential quotient of the extracellular potential along with fiber. To find the activating function, a simple model is used to approximate the potential distribution produced by a surface electrode in a homogeneous medium. Data from classical space-clamped experiments allow calculation of fiber response as a function of geometry and stimulating signal shape. >