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PubMed2006

Evaluation of four probability distribution models for speckle in clinical cardiac ultrasound images.

Segmenting cardiac ultrasound images requires a model for the statistics of speckle in the images. Although the statistics of speckle are well understood for the raw transducer signal, the statistics of speckle in the image are not. This paper evaluates simple empirical models for first-order statistics for the distribution of gray levels in speckle. The models are created by analyzing over 100 images obtained from commercial ultrasound machines in clinical settings. The data in the images suggests a unimodal scalable family of distributions as a plausible model. Four families of distributions (Gamma, Weibull, Normal, and Log-normal) are compared with the data using goodness-of-fit and misclassification tests. Attention is devoted to the analysis of artifacts in images and to the choice of goodness-of-fit and misclassification tests. The distribution of parameters of one of the models is investigated and priors for the distribution are suggested.

Algorithms↗
PubMed1986

Multivariate analysis of Kenya's urban system.

"The study analyzes the structure, spatial interaction, and dimension of the post-colonial urban systems of Kenya using component factor analysis and based on selected socio-cultural, economic, and demographic variables. The study identified seven major dimensions of variation accounting for 72.0%. The analysis of the urban spatial variation is compared and intertwined with studies done in other countries to find out the regional variation of the loadings. Finally, a seven-order characteristics of Kenya urban systems is suggested, based on the study. The accurate knowledge of these salient characteristics of Kenya urban sub-systems is important before any viable spatial planning should be implemented."

Africa↗
PubMed2005

Decomposing rhythmic hippocampal data to obtain neuronal correlates.

Characterizing hippocampal electrical rhythmic activities requires a broadly applicable methodology that lends itself to physiological interpretation. In the intact hippocampal preparation, spontaneous rhythmic field potentials are exhibited in the 3--4 Hz range which evidence suggests is due to discharges in the inhibitory interneuron population. Because field rhythms arise as a network effect and models must be built from the neuron up, we focus on developing a methodology to de-construct the non-stationary rhythms into its important constituents. This study uses 50 CA1/CA3 local field potentials to determine the important constituents, and an additional field recording and two intracellular recordings are examined subsequently. We determine the suitability of several time-frequency techniques. Distinct regions in the time-frequency domain which account for the signal behaviour are then characterized in terms of duration and frequency. These characteristics are interpreted as arising from a statistical mixture distribution. The decomposition of the 50 recordings yields three components whose patterns of activity match those of the intracellular recordings. We suggest that the statistical variability of the local field data can be linked to the variability of neuronal activities seen in intracellular data.

Action Potentials↗
PubMed2000

Absence of nutritional or clinical consequences of decentralized bulk food portioning in elderly nursing home residents with dementia in Montreal.

OBJECTIVES: To evaluate the nutritional and clinical consequences of changing from a centralized food delivery system to decentralized bulk food portioning; a system in which meal portioning occurs on residents' floors of a nursing home. DESIGN: A pilot study with a pre-post design SUBJECTS/SETTING: The study took place on one floor of a home for elderly persons with dementia. Of the 34 residents, 22 (1 man) participated in this study. Average age was 82 years (range = 55 to 94 years). Nutritional status was verified before introduction of the bulk food portioning system by 3 nonconsecutive days of observed food intakes, anthropometric measurements (height, weight, triceps skinfold thickness, mid-upper-arm circumference), and biochemical parameters (albumin, lymphocytes, glucose, sodium, potassium, transferrin, vitamin B-12, folate, hemoglobin). Trained dietitians collected the dietary and anthropometric data and validated the food intake estimates and anthropometric measurements. Data were also collected 10 weeks after implementation of the new food distribution system. STATISTICAL ANALYSES PERFORMED: Paired t tests adjusted by a Bonferroni correction assessed differences between values measured before and after introduction of the new food distribution system. RESULTS: Average food consumption increased substantially and significantly after introduction of the bulk food portioning system. Mean energy intakes rose from 1,555 to 1,924 kcal/day and most other nutrients also increased, many significantly, but there were no changes in anthropometric values or biochemical parameters, except for albumin level which decreased to the lower normal limit. APPLICATIONS: Portioning of food in the residents' dining room simulates a homelike atmosphere thereby encouraging increased food consumption. With well-trained and enthusiastic staff, this system could contribute to improved nutritional status in the very elderly, even those who have dementia. Dietitians have a key role to play in overseeing residents' nutritional needs and in training, supervising, and motivating foodservice personnel.

Aged↗
PubMed2004

Solvable null model for the distribution of word frequencies.

Zipf's law asserts that in all natural languages the frequency of a word is inversely proportional to its rank. The significance, if any, of this result for language remains a mystery. Here we examine a null hypothesis for the distribution of word frequencies, a so-called discourse-triggered word choice model, which is based on the assumption that the more a word is used, the more likely it is to be used again. We argue that this model is equivalent to the neutral infinite-alleles model of population genetics and so the degeneracy of the different words composing a sample of text is given by the celebrated Ewens sampling formula [Theor. Pop. Biol. 3, 87 (1972)]], which we show to produce an exponential distribution of word frequencies.

Algorithms↗
PubMed1995

A sensitive and semi-quantitative pediatric myoclonus evaluation scale.

One of the difficulties in evaluating myoclonus in childhood is the lack of a standardized scale which addresses the constraints of pediatric scoring. The scale needs to be simple and rapid as well as sensitive and semi-quantitative and applicable across different ages. We videotaped children and young adults with myoclonus of various etiologies, such as progressive myoclonus epilepsy, opsoclonus-myoclonus and other acquired etiologies, and scored the videotapes using a new scale. Each clinical type of myoclonus (spontaneous, action and sensory-evoked myoclonus) was graded separately on a five-point scale for severity, intensity and distribution. Data were evaluated as separate scores and also combined for a total score. Validity and reliability were tested using a judge panel of three blinded, trained observers. Action myoclonus was the predominant form of myoclonus in our patients, and was significantly greater than spontaneous and sensory-evoked myoclonus in frequency, intensity and distribution. Separate statistical analysis performed for progressive myoclonus epilepsy and for opsoclonus-myoclonus showed the same pattern. Total scores between etiologies of myoclonus for frequency and distribution categories were significantly different. Subscores and total scores were highly correlated. We found the new scale to be flexible and adaptable for children and there were few missing values due to non-applicability of a scale item. It was useful for all pediatric age groups. The scale and videotape instructions provide a reliable tool for use in pediatric myoclonic disorders.

Adolescent↗
PubMed2005

A note on comparing exposure data to a regulatory limit in the presence of unexposed and a limit of detection.

In some occupational health studies, observations occur in both exposed and unexposed individuals. If the levels of all exposed individuals have been detected, a two-part zero-inflated log-normal model is usually recommended, which assumes that the data has a probability mass at zero for unexposed individuals and a continuous response for values greater than zero for exposed individuals. However, many quantitative exposure measurements are subject to left censoring due to values falling below assay detection limits. A zero-inflated log-normal mixture model is suggested in this situation since unexposed zeros are not distinguishable from those exposed with values below detection limits. In the context of this mixture distribution, the information contributed by values falling below a fixed detection limit is used only to estimate the probability of unexposed. We consider sample size and statistical power calculation when comparing the median of exposed measurements to a regulatory limit. We calculate the required sample size for the data presented in a recent paper comparing the benzene TWA exposure data to a regulatory occupational exposure limit. A simulation study is conducted to investigate the performance of the proposed sample size calculation methods.

Algorithms↗
PubMed1995

Monitoring sodium methohexital distribution with [99mTc]HMPAO with single photon emission computed tomography during Wada test.

Twenty-five consecutive patients being considered for surgery for intractable epilepsy had intracarotid sodium methohexital procedures (ISM) as part of their evaluation. The lipophilic brain SPECT agent, [99mTc]hexamethylpropylene aminoxime (HMPAO), was administered intravenously during the procedure to determine the intracerebral distribution of methohexital. The validity of the ISM depends on consistent delivery of the anesthetizing agent to one hemisphere, including the mesial structures of the temporal lobe. To prevent postoperative language and memory deficits, correct interpretation of the test results supposes a reliable knowledge of which regions of the brain have been anesthetized. Currently, no absolute criteria allow determination of the level and topographical extent of the anesthesia. We compared results of HMPAO-SPECT with clinical and EEG video-monitoring data and with results of digital subtraction angiography (DSA) performed during the test. In all patients, the effect of SM was ipsilateral cerebral hypoperfusion on SPECT and crossed cerebellar diaschisis. The distribution of HMPAO varied from patient to patient. The delivery of SM to mesial temporal lobe structures was not constant. Using nonparametric tests, we demonstrated a statistically significant relationship between hypoperfusion on SPECT and duration of hemiplegia but not with the duration of aphasia. Hypoperfusion on SPECT was also related to the onset and duration of drug-induced delta activity on EEG. SPECT showed a statistically different distribution of SM in the brain from that predicted with DSA. We present our experience with HMPAO-SPECT use for mapping the distribution of methohexital's effects during the ISM (Wada test). We confirm the results of previous studies that SPECT assessment may be an excellent way of determining the distribution of barbiturate during the examination. It increases confidence in interpreting results of speech and memory testing by detecting either contralateral diffusion of the drug due to crossflow between hemispheres or insufficient quantitative delivery to the homolateral hemisphere.

Adult↗
PubMed2003

LORETA imaging of P300 in schizophrenia with individual MRI and 128-channel EEG.

We investigated the characteristics of P300 generators in schizophrenics by using voxel-based statistical parametric mapping of current density images. P300 generators, produced by a rare target tone of 1500 Hz (15%) under a frequent nontarget tone of 1000 Hz (85%), were measured in 20 right-handed schizophrenics and 21 controls. Low-resolution electromagnetic tomography (LORETA), using a realistic head model of the boundary element method based on individual MRI, was applied to the 128-channel EEG. Three-dimensional current density images were reconstructed from the LORETA intensity maps that covered the whole cortical gray matter. Spatial normalization and intensity normalization of the smoothed current density images were used to reduce anatomical variance and subject-specific global activity and statistical parametric mapping (SPM) was applied for the statistical analysis. We found that the sources of P300 were consistently localized at the left superior parietal area in normal subjects, while those of schizophrenics were diversely distributed. Upon statistical comparison, schizophrenics, with globally reduced current densities, showed a significant P300 current density reduction in the left medial temporal area and in the left inferior parietal area, while both left prefrontal and right orbitofrontal areas were relatively activated. The left parietotemporal area was found to correlate negatively with Positive and Negative Syndrome Scale total scores of schizophrenic patients. In conclusion, the reduced and increased areas of current density in schizophrenic patients suggest that the medial temporal and frontal areas contribute to the pathophysiology of schizophrenia, the frontotemporal circuitry abnormality.

Adolescent↗
PubMed2005

Dental erosion in 12-year-old schoolchildren: a cross-sectional study in Southern Brazil.

OBJECTIVE: The aim of this study was to assess the prevalence and severity of dental erosion among 12-year-old schoolchildren in Joaçaba, southern Brazil, and to compare prevalence between boys and girls, and between public and private school students. METHODS: A cross-sectional study was carried out involving all of the municipality's 499, 12-year-old schoolchildren. The dental erosion index proposed by O'Sullivan was used for the four maxillary incisors. Data analysis included descriptive statistics, location, distribution, and extension of affected area and severity of dental erosion. RESULTS: The prevalence of dental erosion was 13.0% (95% confidence interval = 9.0-17.0). There was no statistically significant difference in prevalence between boys and girls, but prevalence was higher in private schools (21.1%) than in public schools (9.7%) (P < 0.001). Labial surfaces were less often affected than palatal surfaces. Enamel loss was the most prevalent type of dental erosion (4.86 of 100 incisors). Sixty-three per cent of affected teeth showed more than a half of their surface affected. CONCLUSION: The prevalence of dental erosion in 12-year-old schoolchildren living in a small city in southern Brazil appears to be lower than that seen in most of epidemiological studies carried out in different parts of the world. Further longitudinal studies should be conducted in Brazil in order to measure the incidence of dental erosion and its impact on children's quality of life.

Brazil↗
PubMed1999

Intron-exon structures of eukaryotic model organisms.

To investigate the distribution of intron-exon structures of eukaryotic genes, we have constructed a general exon database comprising all available intron-containing genes and exon databases from 10 eukaryotic model organisms: Homo sapiens, Mus musculus, Gallus gallus, Rattus norvegicus, Arabidopsis thaliana, Zea mays, Schizosaccharomyces pombe, Aspergillus, Caenorhabditis elegans and Drosophila. We purged redundant genes to avoid the possible bias brought about by redundancy in the databases. After discarding those questionable introns that do not contain correct splice sites, the final database contained 17 102 introns, 21 019 exons and 2903 independent or quasi-independent genes. On average, a eukaryotic gene contains 3.7 introns per kb protein coding region. The exon distribution peaks around 30-40 residues and most introns are 40-125 nt long. The variable intron-exon structures of the 10 model organisms reveal two interesting statistical phenomena, which cast light on some previous speculations. (i) Genome size seems to be correlated with total intron length per gene. For example, invertebrate introns are smaller than those of human genes, while yeast introns are shorter than invertebrate introns. However, this correlation is weak, suggesting that other factors besides genome size may also affect intron size. (ii) Introns smaller than 50 nt are significantly less frequent than longer introns, possibly resulting from a minimum intron size requirement for intron splicing.

Animals↗
PubMed1993

On human outmigration model.

"This paper provides a probability model for the total out-migration pattern from the rural areas [of India]. The suitability of [the] model [is] tested through observed data."

Asia↗