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At least 1,369 records · Page 76Linked to original sources
PubMed1981

Automatic recognition of nervous structures by image analysis. A pattern recognition method applied to the study of mouse cerebellum.

An automatic image pattern analysis method based on differential densitometry is presented. It is applied to histological sections of mouse cerebellum. This method allows an automatic recognition of any cerebellar microscopic field. After recognition, histological images are decomposed into homogeneous parts with respect to cerebellar cellular layers, and both densitometric patterns and partial areas of each of these layers are estimated. This method is accurate to within 94% for a learning sample and 75% for a test sample. This score can be improved by adjunct algorithms presently under study.

Animals↗
PubMed1993

Algorithm for semi-automatic sorting of objects to specified tissue domains. An aid for co-ordinating morphometric data with identified tissue components.

A personal computer-based technique was developed that reduces the extent of human efforts in obtaining data, like numerical density of profiles on area, describing the distribution of specific features of histological sections, e.g., density of synaptic profiles or of histochemical reaction products in specified tissue compartments. The procedure consists of (i) marking the objects to be counted, (ii) recording the borderlines of (reference) tissue domains of interest, and (iii) allocating the marked objects to the corresponding domains automatically. This automatic sorting of objects into defined tissue domains is achieved by an algorithm operating on two sets of coordinates: (i) coordinates of points that constitute the boundary of tissue domains (perimeter points) and (ii) coordinates of points marking the particular objects to be sorted. The principle of the sorting calculation is to construct 'segments' of the loop by lines parallel to the ordinate which pass through neighbouring perimeter points. The 'items' to be sorted are classified by the sign of marker flags allocated to each point depending on which side of the perimeter segment they are located. Segmentation and classification procedures are sequentially repeated along the entire perimeter of each domain specified by the operator which may result during the procedure in multiple changes of the sign of the flags. The internal or external location of each item finally is represented by the last sign of its flag. Objects, allocated to domains can be counted and processed further for numerical density determination.

Algorithms↗
PubMed1995

Application of polynomial regression modeling to automatic measurement of periods of EMG activity.

We have developed a new algorithm for automatic detection and measurement of on/off periods of EMG burst and examined validity and reliability of the measuring technique. Mean EMG amplitude (M) during a semi-stationary state of an EMG data array [EMG] is calculated. Because M was determined to be significantly correlated with g(T(on)) (or g(Tend)) which represent amplitude on a polynomial regression curve g(t) which best-fitted to the [EMG], the estimate ]g(T(on) (or ĝ(T(end)) is calculated by substituting M into a regressive equation f(M) which explains the association between the M and g(T(on)) (or g(T(end)). T(on) and T(end) are human-determined on/off burst times for the [EMG]. The on/off periods of the EMG burst are finally computed as roots of the g(t) when ĝ(T(on)) and ĝ(T(end)) are subtracted from the constant of the polynomial. Application of the current method to the human masticatory muscle activity during chewing revealed that the absolute differences between human- and computer-determined measurements were smaller than 10 ms, and these measurements did not differ significantly. We conclude that the proposed algorithm is useful and effective for automatic detection and measurement of on/off periods of EMG burst.

Adult↗
PubMed1996

Excitatory actions of adenosine on ventricular automaticity.

Due to its negative chronotropic and inotropic effects, adenosine has to date been considered as a cardiodepressant agent. However, adenosine increases ventricular automaticity. This review by Jesus Hernández and Alexandre Ribeiro discusses the experimental and clinical evidence for the excitatory effects of adenosine on ventricular automaticity, as well as the possible mechanisms involved in the ventricular dysrhythmias that occur during the diagnostic and therapeutic use of adenosine.

Adenosine↗
PubMed1986

Failure of idioventricular suppression in man by overdrive pacing as well as lidocaine: the role of abnormal automaticity.

Five patients with third-degree atrioventricular block and an idioventricular escape rhythm who showed unusual responses to overdrive ventricular pacing and lidocaine are presented. In four cases, the idioventricular rhythm was not suppressed by overdrive; in one, the recovery time of the escape rhythm was shorter than the escape cycle length. Lidocaine did not affect the cycle lengths and recovery times of the idioventricular rhythms. These responses are characteristic of abnormal automaticity. The role of abnormal automaticity in human idioventricular escape rhythms has not been previously supported by these characteristic responses to overdrive pacing and lidocaine.

Aged↗
PubMed1994

Automatic field shaping for conformal radiation therapy.

A computer method has been developed to shape the radiation field to conform to the shape of the target as visualized through the beam's eye view (BEV) perspective for conformal radiation therapy. Initially, a series of 2D target contours to define the target size are input into the computer. These target contour data are mapped onto a 3D surface and thereafter projected onto a BEV plane. The projection's outer boundary of the target is auto-contoured. After auto-contouring, a margin is automatically added to define the radiation beam cross section. Since the BEV plane is arbitrarily oriented about the target, the beam orientation can be non-coplanar to the plane of the target contours. For a chosen beam orientation, the conformal treatment beam cross section can be generated automatically using this computer technique and output to either a laser printer, a plotter or stored on files for transfer to the linear accelerator computer system.

Humans↗
PubMed1995

A computer program for automatic measurement of respiratory mechanics in artificially ventilated patients.

A program for automatic and periodic determination of respiratory mechanics in artificially ventilated patients is described. Airway pressure and flow signals are obtained from the ventilator in the controlled ventilation mode with constant flow inflation and end-inspiratory pause. Periodically, the program records both signals for a given time and it delimits a ventilatory cycle and its components out of this record. Then, four mechanical parameters of the respiratory system are calculated: (1) Rinit, the resistance obtained with the end-inflation occlusion technique; (2) Ers, the elastance (inspiratory) calculated from the slope of the airway pressure profile during inflation; (3) tau, the expiratory time constant; (4) PEEP, the global positive end expiratory pressure. All parameter measurements have been evaluated in experimental conditions, and are in good agreement with reference values. The complete software includes the display of the signals and of the trends together with automatic disk file backups. An additional program allows one to display the trends again and to create table text files containing all the recorded data for further analysis. The system proved to work in ICU and anaesthesia patients with various ventilators.

Adult↗
PubMed1996

Automatic detection of breast border and nipple in digital mammograms.

Advances in the area of computerized image analysis applied to mammography may have very important practical applications in automatically detecting asymmetries (masses, architectural distortions, etc.) between the two breasts. We have developed a fully automatic technique to detect the breast border and the nipple, this being a necessary prerequisite for further image analysis. To detect the breast border, an algorithm that computes the gradient of gray levels was applied. To detect the nipple, three algorithms were compared (maximum height of the breast border, maximum gradient, and maximum second derivative of the gray levels across the median-top section of the breast). A combined method was also designed. The algorithms were tested on 156 digitized mammograms. The breast segmentation results were evaluated by two expert radiologists and one physicist. In 89% of the mammograms, the computed border was in close agreement with the radiologist's estimated border. Segmentation results were acceptable to be used in computer-aided diagnostic schemes. The mean distance between the position of the nipple indicated by two radiologists by consensus and the position calculated by the computer was 6 mm.

Algorithms↗
PubMedDate not supplied

Accuracy of an automatic impedance apparatus in a population with secretory otitis media: principles in the evaluation of tympanometrical findings.

INTRODUCTION: The primary demand for a screening procedure for secretory otitis media (SOM) is to identify an objective test with sufficient sensitivity and specificity to meet the needs of the screening program. This study was designed to estimate the value of a portable automatic impedance apparatus to meet these needs. SUBJECTS AND METHODS: Two hundred twenty children with unilateral or bilateral SOM were evaluated in a double-blind, cross-sectional study. All have fulfilled two of the following three criteria for surgical intervention: (1) SOM by physical examination, (2) greater than 20 dB hearing impairment, and/or (3) adenoid symptoms. All ears were evaluated using tympanometry, following which myringotomy was performed. RESULTS: Otomicroscopy showed fluid behind the tympanic membrane in 393 ears. All underwent myringotomy. Thirteen percent (51 ears) were empty. Of the otomicroscopic findings consistent with SOM, 82% had B curves, 6% had C2 curves, 8% had C1 curves, and 4% had A curves. Both C2 and B curves were considered abnormal. Sensitivity of the apparatus is 94.4% and of the specificity is 52.9%. There was no statistical correlation between tympanometrical findings and fluid viscosity. RESULTS: A test intended for screening has to be simple, easy, and quick to perform. Furthermore, the test should have high sensitivity. The automatic impedance apparatus is able to meet these demands; however, the individual results have to be confirmed by another method, eg, otomicroscopy, pure-tone audiometry, and/or manual tympanometry.

Acoustic Impedance Tests↗
PubMed1988

Automatic and effortful processing after severe closed head injury.

To investigate the automatic versus effortful distinction following severe closed head injury (CHI), we administered free recall and frequency of occurrence tasks to patients and controls. In Experiment 1 we found that both free recall (an effortful task) and judgment of relative frequency of occurrence (an automatic task) were impaired in 15 CHI patients as compared to 14 controls. In Experiment 2 we corroborated this finding and showed that absolute estimates of frequency were also impaired in new samples of 16 patients and 16 controls. We infer that cognitive tasks which normal individuals can perform without practice, feedback, or instructions may demand more effortful strategies following severe CHI.

Adult↗
PubMed1993

Comparative assessment of the ventricular fibrillation detection algorithms in five semi-automatic or advisory defibrillators.

The sensitivity and specificity of ventricular fibrillation (VF) detection in three semi-automatic defibrillators (Laerdal Heartstart 3000, Spacelabs First Medic 610, Physio-Control Lifepak 300) and two advisory defibrillators (S&W DMS940, Marquette Responder 1500) were assessed with 25 ECG recordings, each of length 40 s. Of the 25 ECG recordings, 12 contained VF requiring defibrillation, three contained a tachyarrhythmia with a waveform similar to VF but which self-terminated, and 10 were selected from abnormal rhythms and artefacts which contained some features similar to VF. Sensitivity was assessed from the VF data. Specificity was assessed from both the rhythm preceding VF or the tachyarrhythmias, and from the VF-like data. The response to a changing rhythm was assessed from the self-terminating tachyarrhythmias. Each recording was replayed to the defibrillators at three signal amplitudes (normal, half and double). For each defibrillator, requests to check the patient and advice to shock were noted separately. The sensitivity for recommending a shock when a shock was required varied from 81 to 97%. The sensitivity for drawing attention to VF, either through requesting the patient to be checked or advising a shock, varied from 92% to 100%. There were no false detections in the rhythms preceding VF or the tachyarrhythmias (specificity with good quality signals 100%). The specificity with the VF-like data ranged from 63 to 90% for recommending a shock, and from 63% to 70% for requesting the patient be checked or shocked. There was no difference between the defibrillators for VF detection, but there was a significant difference between the semi-automatic and advisory defibrillators (P < 0.05) for the specificity of the final recommendation.

Algorithms↗
PubMed1988

Assessing the development of automatic processing: an application of dual-task and event-related brain potential methodologies.

Previous research has found that properties of automatic processing do not always co-occur, suggesting that the acquisition rates may differ. The present study investigated the acquisition rate of several of these properties by employing additive factors logic, dual task methodology, and event-related brain potentials. Seven subjects participated in a ten session experiment in which they performed two tasks, a visual/memory search task and a pursuit step tracking task, both together and separately. RT and P300 latency measures indicated that parallel processing of the display was achieved early in training in the consistent mapping condition. This processing was unaffected by dual task demands. An analysis of RT/P300 ratios suggests that another form of perceptual efficiency was achieved later in practice in both the varied and consistently mapped search tasks. This effect was larger in the consistent mapping condition. Reductions in the slope of the memory set function occurred significantly earlier for P300 latency than for RT, suggesting that the stimulus evaluation processes became automated more rapidly than the response selection components of memory search. Consistent with an analysis of the processing demands of the two tasks, the introduction of the tracking task and an increase in tracking difficulty produced equivalent interference during consistent and varied mapping conditions. Results are discussed in terms of models of skill, skill acquisition and component task automaticity.

Adult↗
PubMed1990

Automatic vessel tracking and measurement for Doppler studies.

In this initial report, an imaging technique is described for automatically recognising the walls of a blood vessel during Doppler measurements, and hence automatically adjusting the position of the sample volume. The method reduces the inherently two-dimensional edge detection problem to a one-dimensional one, and iterates over several imaging frames to optimise the information. The orientation and diameter of the vessel are also measured. The technique has been clinically tested off-line and is particularly applicable to Doppler volumetric flow studies.

Algorithms↗
PubMed1995

Intravascular ultrasound image subtraction: a contrast enhancing technique to facilitate automatic three-dimensional visualization of the arterial lumen.

At 30 MHz, the intravascular ultrasound backscatter of blood confounds the discrimination of the lumen from the arterial wall. This study validates a subtraction method which creates a still-frame image with a sharp demarcation of the lumen. The method involves subtraction of consecutive images and 2D ensemble averaging of the absolute pixel values. Subtraction exploits the dynamic properties of flowing red blood cells. Three phantom arteries were used, with erythrocytes in their lumens and wall. For this reason, it was not possible, in one single original image, to discriminate the blood in the lumen from the phantom wall. Based on 26 consecutive original images, in the mean subtraction image contrast between lumen and phantom wall grey values increased eightfold from 10.9 (5.3-19.2) (mean and range) in the original image to 87.7 (73.6-107.0) (P < 0.001). A sufficiently large contrast increase to allow automatic segmentation was obtained by using five original images (0.3-s acquisition time) for any single mean subtraction image. Low blood flow velocities (down to 0.5 cm/s) did not alter this result. Automatic segmentation of the lumen allowed fast 3D reconstruction of the lumen in all three phantom arteries. In phantom arteries, the intravascular ultrasound image subtraction technique improved contrast between lumen and wall which enabled automated lumen segmentation and fast 3D visualization of both the lumen and defects in the wall.

Arteries↗
PubMed1979

An automatic device for forced wakefulness in dogs.

An automatic device is described which maintains sustained wakefulness of 12 h or more in dogs with chronically implanted electrodes for sleepwaking recording. The procedure consists of automatic sleep detection using EEG, EMG and body movement (BM), and of avoidance conditioning to arouse the animal with sound as conditioned stimulus, and with electroshock as unconditioned stimulus. The procedure does not disturb feeding, drinking and freely moving, and is not associated with forced exercise, or with a marked stress reaction as measured with cortisol and growth hormone. These advantages enable us to maintain 12 h of forced wakefulness in the same animal for 7 or more consecutive days.

Animals↗
PubMed1991

Physicochemical characteristics of the terbium-adriamycin complex and its effects on the sinus node automaticity.

The physicochemical characteristics of the terbium-adriamycin complex (terbomycin) were studied. Perturbations in the visible absorption spectrum of adriamycin by terbium (Tb3+) was indicative of formation of the terbomycin complex. The absorption maximum of free adriamycin at 479 nm shifted towards the absorption maximum of terbomycin at 539 nm. The binding of Tb3+ to adriamycin was negligible at acidic pH. At alkaline pH, the affinity of Tb3+ for adriamycin increased. The stoichiometry of binding was estimated to be 0.5; one Tb3+ ion per two adriamycin molecules. Thermodynamic analysis revealed that the spontaneous formation of terbomycin was due to an increase in the entropy of the system. The effects of adriamycin, Tb3+ and terbomycin on sinus node automaticity were studied using sinus node from rats, superfused with modified mammalian Tris-Tyrode's solution (37 degrees C). The sinus node rate was monitored with intracellular microelectrodes. 25 microM Tb3+ increased the sinus node rate. Adriamycin (50 microM) depressed sinus node automaticity. Terbomycin also reduced the sinus node rate. There was no difference between the effects of adriamycin and terbomycin. The chronotropic effect of terbomycin persisted in the presence of atropine.

Animals↗
PubMed1977

Oscillating contractions in protoplasmic strands of Physarum: effects of external Ca++-depletion and Ca++-antagonistic drugs on intrinsic contraction automaticity.

1. The minimal requirement of external Ca-concentration for continuance of contraction activity lies in the range of 10(-4) M. 2. As in mammalian smooth muscle, the Ca antagonistic drugs verapamil and D 600 (5.10(-4) M) suppress the minute-rhythms. The action of the drugs is inhibited by 5mM Ca, La or Mn. De novo generation of contraction automaticity is not inhibited by external Ca depletion or by Ca antagonists. 3. It is concluded that rhythmical Ca fluxes across the cortical plasmalemma are not a precondition for triggering continuance or de novo generation of contraction automaticity.

Calcium↗
PubMed1996

Monte Carlo-based treatment planning for boron neutron capture therapy using custom designed models automatically generated from CT data.

PURPOSE: A Monte Carlo-based treatment planning code for boron neutron capture therapy (BNCT), called NCTPLAN, has been developed in support of the New England Medical Center-Massachusetts Institute of Technology program in BNCT. This code has been used to plan BNCT irradiations in an ongoing peripheral melanoma BNCT protocol. The concept and design of the code is described and illustrative applications are presented. METHODS AND MATERIALS: NCTPLAN uses thin-slice Computed Tomography (CT) image data to automatically create a heterogeneous multimaterial model of the relevant body part, which is then used as input to a Monte Carlo simulation code, MCNP, to derive distributions within the model. Results are displayed as isocontours superimposed on precisely corresponding CT images of the body part. Currently the computational slowness of the dose calculations precludes efficient treatment planning per se, but does provide the radiation oncologist with a preview of the doses that will be delivered to tumors and to various normal tissues, and permits neutron irradiation times in Megawatt-minutes (MW-min) to be calculated for specific dose prescriptions. The validation of the NCTPLAN results by experimental mixed-field dosimetry is presented. A typical application involving a cranial parallel-opposed epithermal neutron beam irradiation of a human subject with a glioblastoma multiforme is illustrated showing relative biological effectiveness-isodose (RBE) distributions in normal CNS structures and in brain tumors. Parametric curves for the MITR-II M67 epithermal neutron beam, showing the gain factors (gain factor = minimum tumor dose/maximum normal brain dose) for various combinations of boron concentrations in tumor and in normal brain, are presented. RESULTS: The NCTPLAN code provides good computational agreement with experimental measurements for all dose components along the neutron beam central axis in a head phantom. For the M67 epithermal beam the gain factor for 1, boronophenylalanine for a small midline brain tumor under typical distribution assumptions is 1.4-1.8 x . Implementation of the code under clinical conditions is demonstrated. CONCLUSION: The NCTPLAN code has been shown to be well suited to treatment-planning applications in BNCT. Comparison of computationally derived dose distributions in a phantom compared with experimental measurements demonstrates good agreement. Automatic superposition of isodose contours with corresponding CT image data provides the ability to evaluate BNCT doses to tumor and to normal structures. Calculation of gain factors suggests that for the M67 epithermal neutron beam, more advantage is gained from increasing boron concentrations in tumor than from increasing the boron tumor-to-normal brain ratio.

Boron Neutron Capture Therapy↗