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At least 883 records · Page 49Linked to original sources

PubMed1995

Fuzzy sets for feature identification in biomedical signals with self-assessment of reliability: an adaptable algorithm modeling human procedure in BAEP analysis.

The analysis of biomedical signals has mostly been restricted to traditional signal-processing methods. This article proposes a different approach, applied to the evaluation of brainstem auditory evoked potentials. An automatic peak identification method is described which uses criteria applied by human evaluators in visual analysis. These criteria are defined as fuzzy sets and are combined using fuzzy operations, thus reflecting the weighting of different facts by humans. Membership values are interpreted as degrees of satisfaction which indicate the degree to which a sample satisfies a given criterion. The system judges its own performance in terms of degrees of reliability. Tests on a large set of clinical data showed high performance on good and average-quality curves. A substantial drawback was the assignment of too many peaks in poor potentials. The approaches presented here can easily be applied to similar one-dimensional (and higher) signal analysis tasks.

Algorithms↗

PubMed1993

Skill and hemispheric specialization in detecting featural differences in visual images.

Visual asymmetry patterns related to skill were examined during a target-probe matching task in 24 skilled medical technologists and 24 matched controls. On each of 240 test trials, digitized replicas of specimens commonly encountered in medical laboratory diagnostics were shown centrally for 500 msec. Each target was immediately followed by a lateralized probe item for 120 msec that was either an exact copy (positive probe) or a distorted version (negative probe) of the target. Difficulty level of target-probe matching was manipulated on negative probe trials; half of the negative items consisted of difficult discriminations which were selected to assess the effects of domain-specific experience on detecting small differences in salient morphological features. Medical technologists exhibited a right visual field advantage, but were not different from the control subjects in speed or accuracy to positive probes or to easy negative probes. The observed left-hemisphere advantage in skilled visual processing is attributed to the beneficial effects of experience on the development of domain-specific visual analysis skills.

Adult↗

PubMed1979

[Coding visual information in frogs by means of the latent periods of neuronal responses].

The difference between latencies of responses of the retina ganglionic cells and the neurons of the midbrain tectum in frogs seems to be a way of coding visual signals which indicates the probability of the coherent principle of visual information processing. In combination with the probability-statistical principle, this can serve as a basis for high reliability, plasticity, and polyfunctional character of neuronal mechanisms of the visual analysis.

Animals↗

PubMed1984

The qualitative comparative analysis of the visual field using computer assisted, semi-automated and manual instrumentation: III. Clinical analysis.

A comparative evaluation of the Octopus automated perimeter (Programmes 21 and 31), the Goldmann Bowl perimeter, the Bjerrum Screen and the Friedmann VFAs Mk I and Mk II was carried out on a heterogeneous sample of 75 patients. Field loss was categorized using a modification of the classifications proposed by Greve (1982). The results were analysed using the Level 4 analysis developed by Flanagan, Wild, Barnes, Gilmartin, Good and Crews (1984a). The performance of the various test logics was found to differ between the categories of field defect.

Computers↗

PubMedDate not supplied

Imaging analysis of platelet deposition on the extracardiac valved conduit in humans.

In 14 patients (aged 2-29 yr) with Hancock (n = 11) or Carpentier-Edwards extracardiac valved conduits (n = 3), platelet deposition (PD) was investigated using indium 111 (111In) platelet imaging. Repeated studies were performed in five patients. By visual analysis, 71% (5/7) of the imagings (7 images/5 patients) showed PD at early study 1-3 months after surgery, 9% (1/11) at intermediate study at 6-46 months (mean 21 mon) (11 images/10 patients) and 0% at late study at 81-132 months (3 images/3 patients). Quantitative analysis was made using relative ratio of radioactivity at the graft area to the area of the brachiocephalic artery (platelet accumulation index or PAI). The PAI was 1.85 +/- 0.47 (mean +/- SD) at early study, 1.51 +/- 0.23 at intermediate, and 1.36 +/- 0.37 at late study (NS). There was no significant difference in the late pressure gradients across the conduit (16-68 mon postoperatively) between the two groups with (n = 3) and without (n = 5) PD at the early stage (1-18 mon postoperatively, n = 8). The result may indicate that PD to the valved conduit in the right ventricular (RV) outflow tract occurs early postoperatively (mostly within 3 mon). The relationship of the PD detected by this method to late obstruction was not clarified in this study.

Adolescent↗

PubMed1986

[Image analysis in hip sonography. Classification criteria].

Based on 5000 ultrasound studies of infantile hips, Graf's classification and diagnostic criteria are reviewed with regard to their ability to discriminate between normal and pathological conditions. Additional criteria (delta angle and vector line) are presented, and the results compared. The proposed approach via visual analysis is explained as a flow chart. The consequences of the methodical limitations for use as a screening procedure are discussed.

Hip Dislocation, Congenital↗

PubMed1985

[Comparative scintigraphic analysis of 99mTc aerosol inhalation and 81m Kr ventilation in chronic obstructive bronchial disease].

The usefulness of 99mTc-labelled serum albumin aerosol as a ventilation agent was compared to that of 81mKr gas in normal subjects and in patients with a wide range of pathological pulmonary function. In addition to visual analysis of the scintigrams, lung activity distribution was quantified by an index. In healthy subjects aerosol distribution was very similar to that of 81mKr gas. In patients with persistent obstruction of bronchial air flow, the aerosol tended to penetrate less well than 81mKr gas to the lung periphery and to show a more uneven pulmonary tracer distribution. Consequently the 81mKr gas technique resulted in underestimating bronchial obstructive defects compared with the radioaerosol method. The results indicate that unlike 81mKr gas imaging, small-particle aerosol scintigraphy provides a useful diagnostic technique for the detection of even mild air flow obstructions.

Adult↗

PubMed1995

Detection of degradation of magnetic resonance (MR) images: comparison of an automated MR image-quality analysis system with trained human observers.

RATIONALE AND OBJECTIVES: The perceived need for magnetic resonance (MR) imaging quality control (QC) is occasionally minimized on the assumption that significant errors will be detected by the users. To evaluate the validity of this assumption, we compared the sensitivity of a test object and automated image analysis system for MR imaging QC with the sensitivity of trained human observers by evaluating images that were intentionally degraded. METHODS: Parameters for imaging the test object and normal human volunteers were set to values that decreased the signal-to-noise ratio (SNR), caused distortion, and increased the slice thickness and separation. RESULTS: The human observers were able to detect a 6-13% reduction in the SNR and distortions of more than 15% in human images. They were unable to identify 40% increases in the slice thickness. Automated analysis of test object images was able to detect all image degradations at the minimum levels applied. CONCLUSION: The poor sensitivity of the human observers indicated that degradation, especially spatial measurements, could be significantly in error before being detected through visual analysis of clinical images. These errors would be detected by automated analysis of the test object used. Further investigation is needed to better define the accuracy with which quantitative image-quality analysis predicts the effects of degraded image quality on the ability of human observers to detect subtle abnormalities in clinical images.

Contrast Sensitivity↗

PubMed1987

Automated sleep scoring: a comparative reliability study of two algorithms.

In the present study, deterministic and stochastic sleep staging (DSS and SSS) methods were compared with expert visual analysis in order to provide reliability estimates under strict conditions of comparison. Thirty polygraphic records (15 controls, 15 patients) have been investigated, including artefacts and doubtful periods. Average agreement rates of both methods compared to expert visual scoring were very similar, although a few specifics occasionally appeared for partial sleep stages. The comparison of more than 40,000 sleep decisions (on 20 sec epochs) yielded 75% absolute reliability for normal controls and 70% for pathological cases. However, if the agreement rate obtained for routine visual scoring (82%) in our sleep laboratory is considered as satisfactory, our system is then 90% satisfactory. Finally, complementary aspects outlined in the two automatic scoring systems suggested the development of a unique algorithm on the basis of these methods. Keeping in mind the size of the test sample and the strict procedure of comparison, the two automated staging systems described in this study can be used with reasonable confidence for large scale investigations of sleep in man.

Algorithms↗

PubMed2005

Distributed neural plasticity for shape learning in the human visual cortex.

Expertise in recognizing objects in cluttered scenes is a critical skill for our interactions in complex environments and is thought to develop with learning. However, the neural implementation of object learning across stages of visual analysis in the human brain remains largely unknown. Using combined psychophysics and functional magnetic resonance imaging (fMRI), we show a link between shape-specific learning in cluttered scenes and distributed neuronal plasticity in the human visual cortex. We report stronger fMRI responses for trained than untrained shapes across early and higher visual areas when observers learned to detect low-salience shapes in noisy backgrounds. However, training with high-salience pop-out targets resulted in lower fMRI responses for trained than untrained shapes in higher occipitotemporal areas. These findings suggest that learning of camouflaged shapes is mediated by increasing neural sensitivity across visual areas to bolster target segmentation and feature integration. In contrast, learning of prominent pop-out shapes is mediated by associations at higher occipitotemporal areas that support sparser coding of the critical features for target recognition. We propose that the human brain learns novel objects in complex scenes by reorganizing shape processing across visual areas, while taking advantage of natural image correlations that determine the distinctiveness of target shapes.

Form Perception↗

PubMedDate not supplied

[EEG-Expert automated diagnostic system].

The system is designed to describe and collect data of virtual analysis of electroencephalograms (EEG), as well as to make an expert conclusion on the functional status of the brain and its particular regions. The system includes three parallelly operating systems in the form of a EEC visual analysis schedule as a questionnaire. A programme provides recommendations for describing the level, pattern, and magnitude of the changes detected. Another programme automatically makes an EEC description and a conclusion on cerebral function in conformity with the signs given in the questionnaire and displays them on the screen and sends them to the print. The system may be used for practice in the in- and outpatient settings, for training and postgraduate training of young specialists, and for researches.

Adolescent↗

PubMed2000

Video manometry of the sphincter of Oddi: a new aid for interpreting manometric tracings and excluding manometric artefacts.

BACKGROUND AND STUDY AIMS: Endoscopic sphincter of Oddi manometry (ESOM) allows direct assessment of motor function in the sphincter of Oddi. However, variations in examination conditions and duodenal motility may have a critical effect on the results of ESOM. The aim of the present study was to develop a new method sphincter of Oddi video manometry-based on simultaneous ESOM and real-time endoscopic image analysis, and to investigate the usefulness of video manometry for detecting manometric artefacts during ESOM. PATIENTS AND METHODS: Seven consecutive patients who had undergone cholecystectomy and were referred with a suspicion of sphincter of Oddi dysfunction were investigated. Sphincter of Oddi pressure and endoscopic images (20 frames/s) were recorded simultaneously on a Synectics PC Polygraf computer system with a time-correlated basis, and then compared. RESULTS: On ESOM, 69 sphincter of Oddi phasic contractions were identified, with an average amplitude of 153.9+/-85.0 mm Hg and a duration of 7.9+/-1.2 seconds. Visual analysis of the real-time endoscopic images, replayed in cine loop by the computer, revealed 236 separate duodenal contractions, with an average frequency of 3.5+/-2.4/min (range: 1-12/min). On the ESOM tracing, 78% of the duodenal contractions had a corresponding pressure wave with an average duration of 2.8+/-0.4 seconds and an amplitude of 71.9+/-16.7 mm Hg. Other artefacts on the ESOM tracings, such as catheter movements, pseudocontractions, hyperventilation, or retching, were also easily recognized using simultaneous ESOM and real-time endoscopic image analysis. CONCLUSIONS: Video manometry of the sphincter of Oddi is a promising new method for improving the analysis and documentation of ESOM tracings. It has several advantages over the conventional technique, allowing visual detection of duodenal activity and enabling enhanced recognition of other manometric artefacts.

Adult↗

PubMed1981

Toward the optimal lead system and optimal criteria for exercise electrocardiography.

To define the optimal lead system for exercise electrocardiography, data of the whole body surface potential distribution were analyzed in 25 normal subjects and in 25 patients with coronary artery disease at rest and during exercise. All patients had a normal electrocardiogram at rest. The sensitivity of the standard chest leads was 60 percent; it improved to 84 percent with the body surface map whereas both methods had a 100 percent specificity. On the basis of these data, and reports from other centers, it is concluded that a single bipolar lead from the right subclavian area to lead V5 is adequate in those laboratories that are restricted to testing subjects with a normal electrocardiogram at rest. In patients with a previous infarction or other abnormalities in the electrocardiogram at rest three (pseudo) orthogonal leads or several standard leads are necessary. Recommendations for optimal measurements from the exercise electrocardiogram are based on quantitative computer analysis of the selected leads in larger groups of patients. Best results were obtained with a combination of S-T amplitude, S-T slope and heart rate. The improvement in sensitivity from 50 percent with visual analysis to 85 percent with computer was similar to that obtained with body surface mapping. Changes of the P wave and QRS complex during exercise appeared to be of little diagnostic value. The pathophysiologic mechanisms that contribute to the changes of the electrocardiogram during exercise are discussed.

Adult↗

PubMed2001

Striatal and pontocerebellar hypoperfusion in Hallervorden-Spatz syndrome.

Hallervorden-Spatz syndrome is a group of rare and severe disorders marked by extrapyramidal symptoms and iron accumulation in the globi pallidi, usually visible by magnetic resonance imaging. To assist in determining the functional correlates of these structural abnormalities, positron emission tomography was used to measure regional cerebral blood flows and dopaminergic function in a patient with Hallervorden-Spatz syndrome that manifested as progressive generalized dystonia, optic atrophy, and bilateral pallidal "eye of the tiger" sign. Voxel-by-voxel analysis of positron emission tomography images revealed no pallidal abnormalities but demonstrated significant hypoperfusion of the head of the right caudate nucleus, pons, and cerebellar vermis. Dopaminergic function of the basal ganglia, which was assessed based on visual- analysis of fixation of 18F-labeled fluoro-levodopa, was normal. These data suggest that Hallervorden-Spatz syndrome pathogenesis is not confined to the globi pallidi, and these data also may help to generate new pathogenic hypothesis.

Brain↗

PubMed1984

[Long-term EEG monitoring in epilepsy diagnosis].

EEG long-term monitorings were carried out in 149 patients using a portable 4-channel miniature recorder system. In most cases EEG was recorded for 48 hours. In addition to preceding routine EEG controls, long-term EEG monitoring disclosed epileptic phenomena in 32.7% of patients suspected for epileptic seizures from their history. This gain of information was based mainly on the detection of abnormal potentials or epileptic seizures appearing during sleep. Using EEG long-term recording numerous EEG routine controls could be replaced which otherwise are often necessary for ensuring the diagnosis of epilepsy. If the patient's history, however, gives only poor reason to believe epileptic seizures, positive findings in EEG long-term monitorings are unlikely. Consequently, careful evaluation of the patient's history is crucial for the indication of this laborious examination. As the limited number of recorder channels may cause false negative results, normal findings should be utilized with caution. Only the sum of all clinical and neurophysiological data should be used for exclusion of suspected epilepsy. The second, even more important application of EEG long-term recordings is the special examination of patients with known epilepsy, such as studies of the circadian profiles of epileptic excitability, documentation of seizure frequency, and electrographic analysis of the course of seizure. Therapy control of epileptic patients can be improved by such informations. In view of the large amount of data which results from long-term recordings, computer assisted methods supporting the visual analysis are necessary. In this regard the continuous spectral analysis of the EEG long-term recordings proved to be highly useful.

Brain Diseases↗

PubMed2002

Visual receptive field modulation in the lateral intraparietal area during attentive fixation and free gaze.

The receptive field (RF) of neurons recorded from the lateral intraparietal area (LIP) was quantified using a rapid, computer-driven mapping procedure. For each neuron, the RF was mapped: (1) during attentive fixation and (2) during free visual exploration. RF location, size and internal structure were modulated by the mapping context in over two-thirds of the recorded neurons. The major trend was a proportionally larger amount of neuronal visual resources allocated to central space during fixation, and an attenuated center-to-periphery gradient in the visual field representation during free gaze. A population approach shows that these spatial modulations are accompanied by changes in the signal-to-noise ratio of the information carried in the RF substructure. We related these neurophysiological observations to behavior, by comparing the characteristics of saccades elicited during fixation and free gaze. Together, the results suggest that the dynamics of LIP visual RFs may characterize both the state of engagement of attention and the power of resolution of visual analysis: during fixation, the neural population is locked in a filter state concentrating the processing resources at the fovea, while during free gaze, the population shifts to a detector state spreading the resources more evenly across the visual field.

Animals↗

PubMed1990

Characterization of underivatized lipid biomarkers from microorganisms with pyrolysis short-column gas chromatography/ion trap mass spectrometry.

A microvolume Curie-point pyrolysis short-column (5 m) gas chromatography/mass spectrometry (Py-GC/MS) procedure was developed for the characterization of various lipid moieties in microorganisms. High linear flow rates (approximately 175 cm/s) characterized the GC conditions in order to effect an efficient chromatographic transfer and elution of the underivatized diglycerides and monoglycerides, and small modifications were necessary to the ion trap MS system in order for it to accommodate the relatively high gas load. During a typical analysis run anhydrodiacylglycerides eluted within a 5-6-min time frame. Gram-positive bacilli and Gram-negative species were differentiated from each other by the pyrolysis patterns of their lipid components. In spite of the complexity of the analyte, a straightforward visual analysis was achieved with the aid of simple computerized data display procedures. These procedures included examination of (1) total ion current (TIC) profiles of the lipid region of the reconstructed chromatogram, (2) the integrated mass spectrum of this region, (3) selected reconstructed ion chromatograms (RICs), (4) RIC intensity distributions, and (5) corresponding mass spectra. An appealing aspect of the lipid data reduction procedure is that most of it can be accomplished visually without requiring computerized pattern recognition techniques.

Bacteria↗

PubMed2003

Detection of glaucomatous visual field defect by nonconventional perimetry.

PURPOSE: To report the correlations among Humphrey Field Analyzer 750 (HFA), high-pass resolution perimetry (HRP), and frequency-doubling technology (FDT) perimetry in glaucoma patients and ocular hypertensive patients. DESIGN: Cross-sectional study. METHODS: Eighty-two eyes of 82 consecutive patients with primary open-angle glaucoma (POAG) or ocular hypertension were included in this study. One eye of each patient was randomly selected for data analysis. Visual fields were assessed by HFA, HRP, and FDT perimetry. HRP global deviation (HRP-GD), HRP local deviation (HRP-LD), FDT-mean deviation (FDT-MD), and FDT-pattern standard deviation (FDT-PSD) were considered for the analysis. Clinical agreement between HRP and FDT was evaluated. All data were analyzed by Pearson r coefficient when the distribution of the data was normal and by Spearman coefficient correlation when the distribution of the data was not normal. A P <.05 was considered statistically significant. RESULTS: Fifty-two eyes (52 patients) were classified as glaucoma and 30 eyes (30 patients) as ocular hypertension. In the entire group, a significant (P >.001) correlation was found between the HFA indices and those of either HRP or FDT. A significant (P <.001) correlation was found between HRP-GD and FDT-MD as well as between HRP-LD and FDT-PSD. In 14% of the glaucomatous patients and in 33% of the subjects with ocular hypertension, FDT and HRP showed different clinical features. CONCLUSIONS: Our data suggest that FDT and HRP are useful for detection of early glaucomatous visual field damage.

Aged↗