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PubMed1997

Visualization and analysis of chromatin by scanning force microscopy.

The use of the scanning force microscope (SFM) to visualize and analyze chromatin fiber structures is presented. Protocols to prepare chromatin fibers for SFM imaging of fibers in air and in buffer are first discussed. Next, the conditions for acquiring high-quality SFM images such as optimal instrumental parameters, appropriate deposition substrates, and adequate procedures of sample deposition are described. It is shown that analysis and quantitation of the SFM images support an irregular, three-dimensional arrangement of nucleosomes in the native chromatin fiber. This structure is lost in linker histone-depleted fibers, which show, instead, a beads-on-a-string structure. Molecular modeling of the chromatin fiber structures and computer simulation of the SFM imaging process indicate that the natural variability of the linker length may be the major determinant of the structural irregularity of the native chromatin fiber. Removal of linker histones (H1/H5) may change the amount of DNA wrapped around the histone octamer, which in turn may induce the transition from a three-dimensional irregular helix to an extended beads-on-a-string structure. Studies of trinucleosomes indicate that both the average successive nucleosome center-to-center distance and the average angle between two successive linkers increase upon the removal of linker histone.

Chromatin↗
PubMed1994

Enhanced maximal binding capacity (Bmax) of second messenger ligand in the acute phase of cerebral ischemia--direct visualization by digital image analysis.

Autoradiographic visualization of the Bmax (maximal binding capacity) and Kd (dissociation constant) of [3H]phorbol 12,13-dibutyrate (PDBu) and [3H]forskolin (FK) was performed after 30-min unilateral carotid artery occlusion in the gerbil brain. These parameters and the local cerebral blood flow (CBF) were measured at the level of the caudate-putamen in the same brain using a digital image processing technique developed in our laboratory. The local CBF was measured at the end of the experiment. [3H]PDBu and [3H]FK were utilized as specific ligands to assess the activities of protein kinase C (PKC) and adenylate cyclase (AC), respectively. The local CBF on the occluded side was severely reduced and ranged from 0.2 to 9.0 ml/100 g/min, whereas the local CBF on the non-occluded side exhibited a moderate reduction except in the midline regions. The Bmax values of PDBu and FK were significantly increased not only on the occluded side but also on the non-occluded side in the ischemia group as compared to the corresponding values in the sham group. In contrast, the Kd value of each ligand remained unchanged in the ischemia group. These findings suggest that both the adenylate cyclase and protein kinase C systems may be significantly and diffusely activated in the initial stage of brain ischemia. Thus, severe hemispheric cerebral ischemia in the acute phase may induce severe perturbation of the second messenger systems in extensive bilateral regions.

Acute Disease↗
PubMed1993

Quantitative same-day rest-stress technetium-99m-sestamibi SPECT: definition and validation of stress normal limits and criteria for abnormality.

Gender-matched stress normal limits and criteria for abnormality for rest-stress 99mTc-sestamibi same-day myocardial perfusion imaging were developed and validated in 160 patients who were imaged using previously developed optimized acquisition, processing and quantitative protocols. The gender-matched mean and standard deviation of the normal response were calculated using 35 male and 25 female patients with a < 5% likelihood of coronary artery disease. Receiver-operating curve analysis using expert visual interpretation as the "gold standard" was used to determine the optimal criteria for abnormality detection, in terms of standard deviations from the mean and minimum defect size for each of the four major zones of the polar map, in a pilot population consisting of an additional 35 male and 25 female patients with a variety of perfusion defects. The optimum standard deviations resulted in the following true-positive/true-negative rates when quantitative results were compared to visual analysis for the anterior, septal, lateral, and inferior segments in the combined male and female pilot populations: 84%/86%, 70%/75%, 86%/76% and 69%/76%, respectively. The final criteria were then applied to a prospective population consisting of 33 male and 7 female patients. This analysis resulted in the following true-positive/true-negative rates for overall perfusion abnormalities and abnormalities of the LAD, LCX and RCA vascular territories: 97%/67%, 94%/73%, 73%/90% and 72%/91%, respectively. The optimized 99mTc-sestamibi stress normal limits and criteria for abnormality correlate well with expert visual interpretation of stress myocardial perfusion defects.

Coronary Disease↗
PubMed1995

Neutral location cues and cost/benefit analysis of visual attention shifts.

The effects of location cuing on target responses can be examined by comparing informative and neutral cuing conditions. In particular, the magnitudes of costs of invalid location cuing and of benefits of valid location cuing can be determined by comparing invalid and valid cue responses to location-nonspecific neutral cue responses. Cost/benefit analysis is based on the assumption that neutral baseline measures reflect a general warning effect about the impending target's onset but no other specific target information. The experiments we report were carried out to determine the appropriateness of two baseline measures for cost/benefit analyses of direct (nonsymbolic) location cuing effects. We found that a multiple-cue baseline attenuated the benefits of valid cuing, and that a background-flash baseline arbitrarily attenuated costs or benefits depending on flash intensity. It is proposed that a background flash is the more suitable neutral cue because it is target-location-nonspecific, but that its intensity should be adjusted to elicit a target-onset warning signal of the same magnitude as the location cues with which it will be compared.

Attention↗
PubMed1994

The primary treatment trial: changes in the visual field analysis by computer-assisted perimetry.

Computer-assisted perimetry was performed 6-monthly on patients entered into the Primary Treatment Trial using the 30-2 program. Those patients with a minimum of five visual fields had pointwise linear regression analysis (Progressor) carried out. Two consecutive slopes significant at the 0.05 level were taken as evidence for change, either improvement or worsening. Forty-eight patients in the surgery group, 40 in the medical group and 20 in the laser group were suitable for analysis. A comparison of the eyes showing 'improvement' or 'worsening' in the surgery and medicine groups showed no difference between them. This lack occurred despite a significant difference in intraocular pressure between the two groups. The reasons for this lack of difference are discussed.

Diagnosis, Computer-Assisted↗
PubMed1995

Psychovegetative syndrome diagnosis: an automated psychophysiological investigation and mathematical modeling approach.

1. INTRODUCTION. The main purpose of our work was to create the informational expert system of psychovegetative syndrome diagnosis by applying clinical data and estimating the functioning of the central and peripheral part of regulatory apparatus of the human organism, taking into consideration parallel and consecutive sensory, motor, associative, emotional drive systems, and internal body state. We used automatized psychophysiological investigation and mathematical models. For this purpose the following principal tasks have been prepared: the creation of database of quantifiable estimation patient state; the definition and automation of psychophysiological investigation; mathematical modeling of vegetative functions using a non-invasive sample and its connection with real psychophysiological experiment; mathematical modeling of organisms inner medium homeostasis; and the creation of an informational-expert system of psychovegetative syndrome diagnosis. 2. DATABASE OF ESTIMATION OF PATIENTS STATE. The medical records of the DB "PATIENT" contain data on patient psychic and somatoneurological status. 3. AUTOMATED PSYCHOPHYSIOLOGICAL INVESTIGATION. Psychophysiological investigation enables estimation of the functioning of several subsystems of the human organism and establishes an interrelationship between them by means of electrophysiological data and performance parameters. The study of psychophysiological provision of behavior by psychophysiological investigation enables us to get information about adaptational mechanisms of the patient under certain environmental loads. By means of special mathematical provision, the mathematical elaboration of biosignals as performance parameters has been realized; also realized were the formation of received parameters in the database, the estimation of separated parameters in the view of informativity, and the establishment of diagnostic patterns. 4. MATHEMATICAL MODELS FOR ESTIMATION INTERNAL BODY STATE. The proposed mathematical models allow investigation of homeostatic regulation in various intensities of the metabolic processes and external load. This approach in mathematical models allows us to characterize the relations between the central and peripheral parts of the regulatory mechanisms, using non-invasive samples under psychophysiological investigation and the simulation of different surroundings for brain cells functioning. 5. INFORMATION-EXPERT SYSTEM. Proceeding from the principle of psychoneural unity, we characterized the functioning mechanisms of CNS by means of automatized EEG analysis, visually evoked potential analysis, estimated psychic status, and the characteristics of neural system biochemical processes received by mathematical modeling. By using the indices of the viscero-vegetative and somatolocomotor system (as well as parameters received by automatized analysis of ECG), the EEG respiratory signal--from mathematical models of vegetative functions decision support system applied in estimation of a peripheral block of the regulatory system--is reflected in diagnosis of certain syndromes. The informational expert system, proceeding from the functioning of the human organism's regulatory apparatus, diagnosed psychovegetative syndrome and described the mechanisms of its development. 6. CONCLUSION. The informational expert system enables estimation of the functioning of a human organism as a whole and can be introduced in the sphere of practical medicine and professional orientation as well as in laboratories of experimental psychology and neurosciences.

Brain↗
PubMed1985

Spatio-temporal EEG measures and their application to human intracranially recorded epileptic seizures.

We describe analysis methods which involve the computation of band-integrated, intrachannel spectral measures from the EEG. These measures require only very general assumptions, have a simple interpretation and achieve significant data reduction, while providing a quantitative assessment of significant EEG modification at seizure or onset or in the course of seizure evolution. In developing these measures, we experimented with various measures derived from spatio-temporal power spectra. Bandpass (8-30 Hz) integrated relative energy measures appear to be the most useful since they objectively measure paroxysmal modification. Two such measures are illustrated in this report: the band-integrated power z-score (BIPZ), which is a quantitative measure designed to allow significance testing, and the band-integrated power ratio (BIPR), which is a simply calculated qualitative measure that behaves very similarly to the BIPZ measure and may be useful for real-time data screening. In addition to developing these intrachannel measures, we have also developed methods of displaying these measures in a format appropriate to the analysis of interchannel relationships. In a general sense, the displays provide objective information regarding the spatio-temporal dynamics of the EEG in a condensed format which is still readily understandable to the electroencephalographer. This analysis was applied to 29 spontaneous, depth-recorded seizures in 14 patients with the aim of identifying the initial locus of seizure activity in each seizure episode. The initial locus was defined as that location (or set of locations) to first exhibit statistically significant values of the BIPZ measure. The method was very effective in this regard, as shown by correspondence between the conclusions of this automated analysis and conventional visual analysis.

Brain↗
PubMed1989

The implementation of an autoregressive model with exogenous input in a single sweep visual evoked potential analysis.

Based on a model of signal-noise interaction, we present a method for single-sweep analysis of Visual Evoked Potentials. The EEG is represented as an autoregressive process and the single-sweep VEP as a filtered version of a reference signal taken as the running average of 20 consecutive sweeps. The algorithm for model identification and filtering is an ARX (AutoRegressive with eXogenous input) which provides a fast and efficient solution by means of a least squares approach. The choice of reference signal, as well as the complexity of the model, is also discussed. A further advantage of this approach is parameter reduction: all the single-sweep information is contained in 18 model coefficients and the reference signal.

Evoked Potentials, Visual↗
PubMed1996

Sleep stage scoring using the neural network model: comparison between visual and automatic analysis in normal subjects and patients.

In this paper, we compare and analyze the results from automatic analysis and visual scoring of nocturnal sleep recordings. The validation is based on a sleep recording set of 60 subjects (33 males and 27 females), consisting of three groups: 20 normal controls subjects, 20 depressed patients and 20 insomniac patients treated with a benzodiazepine. The inter-expert variability estimated from these 60 recordings (61,949 epochs) indicated an average agreement rate of 87.5% between two experts on the basis of 30-second epochs. The automatic scoring system, compared in the same way with one expert, achieved an average agreement rate of 82.3%, without expert supervision. By adding expert supervision for ambiguous and unknown epochs, detected by computation of an uncertainty index and unknown rejection, the automatic/expert agreement grew from 82.3% to 90%, with supervision over only 20% of the night. Bearing in mind the composition and the size of the test sample, the automated sleep staging system achieved a satisfactory performance level and may be considered a useful alternative to visual sleep stage scoring for large-scale investigations of human sleep.

Adult↗
PubMed1990

Detection of mild coronary stenoses using the Dynamic Spatial Reconstructor.

The accuracy of the Dynamic Spatial Reconstructor (DSR) in the detection of moderate coronary artery stenoses was examined in 20 closed-chest dogs. Twenty-eight hollow plastic cylinders were embolized into the left coronary arteries and produced 25% to 56% reductions in arterial lumina diameter. For each dog, one three-dimensional (3-D) image of the heart was reconstructed from each DSR scan recorded during injection of contrast into the aortic root. Analysis involved blinded visual analysis by four independent observers of multiview projection images computed from the single 3-D image. Postmortem coronary angiograms of the isolated heart were considered definitive for location of the stenoses. Overall sensitivity of detection by DSR was 89% and specificity 81%. Sensitivity of detecting stenoses greater than or equal to 50% was 98%. Receiver operating characteristics (ROC) analysis showed that detection of stenoses in the left coronary arteries is of equal sensitivity and specificity.

Animals↗
PubMed1992

Postictal switch in blood flow distribution and temporal lobe seizures.

The ictal increase of regional cerebral blood flow has yet to be fully utilised in the investigation of focal seizures. Although single photon emission tomography (SPECT) is being increasingly used in the localisation of epileptic foci, the evolution and time courses of the peri-ictal perfusion changes have yet to be clarified. We performed serial SPECT studies in the interictal, ictal and immediate postictal states in 12 patients with refractory temporal lobe epilepsy to define the patterns and duration of peri-ictal cerebral blood flow changes. Visual analysis showed a constant pattern of unilateral global increases in temporal lobe perfusion during seizures which suddenly switched to a pattern of relative mesial temporal (hippocampal) hyperperfusion and lateral temporal hypoperfusion in the immediate postictal period. Quantitative analysis confirmed the visual assessment. Lateral temporal cortex ictal/normal side to side ratios were increased by mean 35.1% (95% confidence interval 21.8% to 48.4%) more in the ictal studies than in the interictal studies and mesial temporal cortex ratios increased by mean 30.8% (22.4% to 39.2%). In the postictal state, however, lateral temporal ratios were reduced by mean 7.7% (-15.8% to 0.4%) compared with interictal values, whereas mesial temporal perfusion was maintained compared with the interictal studies. These observations provide critical information for interpreting scans which can be used in the localisation of epileptic foci. This postictal switch in blood flow patterns may reflect the underlying metabolic processes of neuronal activation and recovery and have implications for understanding the neurobiology of human epileptic seizures.

Basal Ganglia↗
PubMed1994

Effects of aging on amplitude-modulation following response.

Phase spectral analysis as developed by Fridman (1982) was used to detect amplitude-modulation following response (AMFR). The threshold of AMFR was determined with greater sensitivity and accuracy by phase spectral analysis than by visual analysis. Using this method, a modulation frequency (MF) of 80 Hz was found optimal for detecting AMFR in young children (ranging in age from 2 to 4 years) during sleep, for whom there is no advantage in recording 40-Hz steady-state responses. To determine the optimal MF for detecting AMFR during sleep in children less than 2 years of age and age limitation for using 80-Hz MAFR in objective audiometry, AMFR as a function of MF was investigated during sleep in 25 children with normal hearing ranging from 4 months to 15 years of age, and 10 normal hearing adults. The stimulus was a 1000 Hz, 50 dBnHL sinusoidally amplitude modulated tone with a modulation depth of 95%. MF was varied from 20 to 200 Hz in 20 Hz steps. Response was determined by phase spectral analysis and the S/N ratio calculated by spectral amplitude at the modulation frequency and noise level around the modulation frequency using fast Fourier transform. Phase spectral analysis showed AMFR at MF of 80 Hz to be the most stable and reliable in all children during sleep among MFs from 20 to 200 Hz. Spectral amplitude analysis demonstrated 80-Hz AMFR to have a high S/N ratio in all children.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMedDate not supplied

[Visual evoked potentials to illusory contours (Kanizsa's square)].

Visual evoked potentials (VEP) were studied in 10 subjects to presentation of illusory Kanizsa's square and control visual stimulus with similar spatial organization, which did not produce a visual illusion. The VEPs to the applied stimuli were expressed in the occipital, parietal, and inferiotemporal areas. It was shown that during presentation of the illusory configuration the amplitude of VEP variation between the N180 and P230 peaks was higher and the N300 latency lower than during presentation of stimuli with real configuration. The difference between VEPs in amplitude were observed in the left and right occipital and left inferiotemporal areas, and differences in latency were pronounced in the left occipital derivation. It is suggested that there exist two contour-encoding regions in the visual system which participate in different kinds of the visual analysis. First, associative visual fields which encode the information on single sings and their complexes and inferiotemporal fields which compare the sensory and memory codes.

Adult↗
PubMed1982

Thallium-201 myocardial scintigraphy: improved sensitivity, specificity and predictive accuracy by application of a statistical image analysis algorithm.

Exercise and 3 hour delayed redistribution thallium-201 myocardial perfusion imaging was performed in 107 patients including 87 patients with documented coronary artery disease and 20 patients with normal coronary arteriograms. A computer algorithm for statistical analysis and redisplay of the analog scintillation data was developed to augment the visual analysis of the standard analog image. The basic algorithm identified the myocardial area (pixel) with the most absolute counts and developed an appropriate standard deviation range from a table. All pixels in the area of the myocardium containing absolute counts below three standard deviation ranges (or approximately 6 standard deviations) were deleted from the final image. The remaining pixels were redisplayed in a digitized bimodal format and the image photographed. Two experienced observers compared visual analysis of the analog image alone and the analog image in conjunction with the computer-analyzed image for sensitivity, specificity and predictive accuracy in the detection of perfusion defects in patients with coronary artery disease and in normal subjects. Sensitivity in patients with coronary artery disease and in normal subjects. Sensitivity in patients with coronary artery disease for the analog scintillation image alone was 79 percent (69 of 87) and with computer analysis 95 percent (83 of 87). Specificity in the patients with no coronary disease was 100 percent (20 of 20) for both techniques. The predictive accuracy of the test was 83 percent (89 of 107) for the analog image alone and 96 percent (103 of 107) for the two images combined. It is concluded that use of a computer statistical analysis algorithm of thallium-201 analog myocardial perfusion images improves the accuracy of detection of perfusion defects in patients with coronary artery disease.

Computers↗
PubMed2000

Comparison of frequency doubling perimetry with humphrey visual field analysis in a glaucoma practice.

PURPOSE: To determine the sensitivity and specificity of frequency doubling perimetry with Humphrey visual field testing used as the gold standard. METHODS: Frequency doubling perimetry and Humphrey visual field testing (24-2) were performed on 29 consecutive patients in a glaucoma practice. Data for the right eye were used to calculate sensitivity, specificity, and receiver operating characteristic curves. RESULTS: For the frequency doubling perimetry in screening mode, and with an abnormal glaucoma hemifield test used as the gold standard, the area under the receiver operating characteristic curve was 89.3%, 81.5%, or 75.0% for the presence of mild, moderate, or severe relative defects, respectively. Similar results were found with the use of mean deviation (P <.05) to define Humphrey visual field defects. For frequency doubling perimetry in threshold mode, the area under the receiver operating characteristic curve was 93.4% with the presence of any defect (P <.05) used as the criterion for an abnormal case, and an abnormal glaucoma hemifield test as the gold standard. In all cases, the threshold mode detected defects better than the screening mode.

Adolescent↗
PubMed1983

Sharp targets are detected better against a figure, and blurred targets are detected better against a background.

There is growing evidence that the performance of perceptual tasks is often facilitated by perceived "figureness." Accuracy in detection and discrimination of targets is higher when the targets are presented in figural regions than when they are presented in ground regions of an image. This "figure superiority" might be a result of a functional specialization in the visual analysis of figure; recent theories have also assumed a functional specialization in the visual analysis of ground. If so, we might expect "ground superiority" in situations where task performance requires information available primarily through analysis of ground. We manipulated the spatial frequency of a small line segment and found that when it was sharp (i.e., the high-spatial-frequency components were present), it was detected better in figural regions, but when we blurred it (only the low-to-medium spatial frequencies were present) it was detected better in ground regions. These findings support the view that figure and ground analyses involve different specialized functions.

Adolescent↗
PubMed1998

Visual gait analysis: the development of a clinical assessment and scale.

OBJECTIVES: To develop and evaluate a four-point scale visual gait assessment form, the Rivermead Visual Gait Assessment (RVGA), for clinical use with patients with neurological deficits. DESIGN: Preliminary clinical testing of reliability, validity and sensitivity to change. SETTING: Patients were recruited from the Rivermead Rehabilitation Centre (RRC), a centre specializing in rehabilitation for patients with neurological disease. PATIENTS: Ten inpatients were assessed by up to seven physiotherapists for the main reliability study, and eight different patients were also assessed by two raters one week apart. Twenty outpatients with multiple sclerosis (MS) who were receiving physiotherapy to improve their mobility and 27 inpatients with various neurological conditions were also assessed and the data used to examine validity, re iability and sensitivity to change. OUTCOME: The other comparative measures used were walking time, stride length, step length asymmetry, balance and the Rivermead Mobility Index. RESULTS: Inter-rater reliability between multiple raters was reasonable both for the global scores from the gait assessment form (Kendall's coefficient of concordance; p < 0.001), and for individual items (complete agreement occurred on 63.8% of all observations). There was a significant correlation between the global RVGA score and the various criterion measures (r = 0.53-0.79; p < 0.001) and between change in the RVGA score and change in walking time in patients who received treatment (r = 0.68; p < 0.01). CONCLUSIONS: The RVGA provides the clinician with a clinical assessment of the quality of gait which may be used in conjunction with other measures to inform and monitor the value of physiotherapy treatment for people with MS and stroke, and possibly other neurological deficits.

Central Nervous System Diseases↗