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PubMed2006

Contrast-detail analysis of three flat panel detectors for digital radiography.

In this paper we performed a contrast detail analysis of three commercially available flat panel detectors, two based on the indirect detection mechanism (GE Revolution XQ/i, system A, and Trixell/Philips Pixium 4600, system B) and one based on the direct detection mechanism (Hologic DirectRay DR 1000, system C). The experiment was conducted using standard x-ray radiation quality and a widely used contrast-detail phantom. Images were evaluated using a four alternative forced choice paradigm on a diagnostic-quality softcopy monitor. At the low and intermediate exposures, systems A and B gave equivalent performances. At the high dose levels, system A performed better than system B in the entire range of target sizes, even though the pixel size of system A was about 40% larger than that of system B. At all the dose levels, the performances of the system C (direct system) were lower than those of system A and B (indirect systems). Theoretical analyses based on the Perception Statistical Model gave similar predicted SNRT values corresponding to an observer efficiency of about 0.08 for systems A and B and 0.05 for system C.

Contrast Media↗

PubMed2005

Analysis and synthesis of the three-dimensional movements of the head, face, and hand of a speaker using cued speech.

In this paper we present efforts for characterizing the three dimensional (3-D) movements of the right hand and the face of a French female speaker during the audiovisual production of cued speech. The 3-D trajectories of 50 hand and 63 facial flesh points during the production of 238 utterances were analyzed. These utterances were carefully designed to cover all possible diphones of the French language. Linear and nonlinear statistical models of the articulations and the postures of the hand and the face have been developed using separate and joint corpora. Automatic recognition of hand and face postures at targets was performed to verify a posteriori that key hand movements and postures imposed by cued speech had been well realized by the subject. Recognition results were further exploited in order to study the phonetic structure of cued speech, notably the phasing relations between hand gestures and sound production. The hand and face gestural scores are studied in reference with the acoustic segmentation. A first implementation of a concatenative audiovisual text-to-cued speech synthesis system is finally described that employs this unique and extensive data on cued speech in action.

Acoustic Stimulation↗

PubMed2002

The mass disruption of Oort cloud comets.

We have calculated the number of dormant, nearly isotropic Oort cloud comets in the solar system by (i) combining orbital distribution models with statistical models of dormant comet discoveries by well-defined surveys and (ii) comparing the model results to observations of a population of dormant comets. Dynamical models that assume that comets are not destroyed predict that we should have discovered approximately 100 times more dormant nearly isotropic comets than are actually seen. Thus, as comets evolve inward from the Oort cloud, the majority of them must physically disrupt.

Journal Article↗

PubMed2002

Ecological predictions and risk assessment for alien fishes in North America.

Methods of risk assessment for alien species, especially for nonagricultural systems, are largely qualitative. Using a generalizable risk assessment approach and statistical models of fish introductions into the Great Lakes, North America, we developed a quantitative approach to target prevention efforts on species most likely to cause damage. Models correctly categorized established, quickly spreading, and nuisance fishes with 87 to 94% accuracy. We then identified fishes that pose a high risk to the Great Lakes if introduced from unintentional (ballast water) or intentional pathways (sport, pet, bait, and aquaculture industries).

Adaptation, Physiological↗

PubMed2001

Glaucoma in China: how big is the problem?

AIMS: To derive preliminary estimates for the number of adults in China suffering from glaucoma, and project the burden of visual morbidity attributable to primary and secondary glaucoma. METHODS: Age and sex specific data from two population surveys were applied to US Census Bureau population estimates for urban and rural China. It was assumed that data from Singapore were representative of urban China, and those from Mongolia were representative of rural China. RESULTS: It was estimated that 9.4 million people aged 40 years and older in China have glaucomatous optic neuropathy. Of this number, 5.2 million (55%) are blind in at least one eye and 1.7 million (18.1%) are blind in both eyes. Primary angle closure glaucoma (PACG) is responsible for the vast majority (91%) of bilateral glaucoma blindness in China. The number of people with the anatomical trait predisposing to PACG (an "occludable" drainage angle) is in the region of 28.2 million, and of these 9.1 million have significant angle closure, indicated by peripheral anterior synechiae or raised intraocular pressure. CONCLUSIONS: This extrapolation of data from two east Asian countries gives an approximate number of people in China suffering from glaucoma. It is unlikely that this crude statistical model is entirely accurate. However, the authors believe the visual morbidity from glaucoma in China is considerable. PACG is probably the leading cause of glaucoma blindness in both eyes, and warrants detailed investigation of strategies for prevention.

Adult↗

PubMed1989

Seasonal prevalence of major congenital malformations in the Fylde of Lancashire 1957-1981.

The seasonal prevalence of major congenital malformations was studied in a prospective survey of 88,449 children born in the circumscribed Fylde of Lancashire to residents there over 25 years. Ascertainment was thought to be as complete as was practically possible because cases were recorded daily by one, and for 17 years the only, paediatrician and a very high rate of necropsies was maintained. The number of malformations were classified by month of maternal last menstrual period and seasonal variation was assessed by three statistical models. Neural tube defects showed a significant seasonal variation in month of last menstrual period but not in month of birth. From May 1956 to April 1968, when the prevalence of neural tube defects was high (5.5 per 1000 total births), conceptions were significantly more common in December to May. For anencephaly alone the figures were not significant, but spina bifida and cranium bifidum were more common in March to May. From May 1968 to April 1981, when the prevalence of neural tube defects fell below the national average, the significant variations disappeared. Seasonality for spina bifida and cranium bifidum was seen only in "singles" (cases with no other major lesion), but for anencephaly it was seen only in "multiples" (cases with other lesions). The three types of cardiac septal defect and persistent ductus each showed a higher prevalence of conceptions at some time during May to October. In contrast the commonest group of cyanotic cases showed no such pattern but with greater numbers in winter. There was evidence of a seasonal variation for bilateral renal agenesis and for vesicoureteric reflux as ascertained. Seasonal prevalence in an aetiological factor for certain malformations of the central nervous system, cardiac and urinary systems.

Causality↗

PubMed1999

Cancer registry data based estimation of regional cancer incidence: application to breast and colorectal cancer in French administrative regions.

STUDY OBJECTIVE: In many countries, cancer registries cover only a small part of the national population. Cancer incidence for the rest of the country has therefore to be estimated. This can be done from mortality data using the relation between incidence and mortality observed in the cancer registry areas. Such an approach was used to study geographical variation and trend of colorectal and breast cancer incidence in France where 10% of the national population is covered by cancer registries. DESIGN: This study applies the incidence/mortality ratios of cancer registry areas to regional mortality data to obtain an estimation of cancer incidence at a given point in time. Age and period effects are included in the statistical models. MAIN RESULTS: The incidence estimations are given for 21 administrative regions and three time points (1985, 1990, 1995). The European standardised incidence rates for breast cancer ranged from 86.8 to 128.8. For colorectal cancer, these rates ranged from 48.2 to 79.6 for men, and from 32.5 to 48.8 for women. Breast cancer incidence has increased considerably between 1985 and 1995 with a higher increase in the north than in the south of France. The incidence of colorectal cancer has also increased, albeit to a lesser extent. CONCLUSION: The incidence estimation method proposed leads to regional incidence rates that are useful for planning health care services on a regional basis and may also be used to study regional differences in incidence. This method is useful when only partial incidence data are available.

Adult↗

PubMed2005

Handling over-dispersion of performance indicators.

OBJECTIVES: A problem can arise when a performance indicator shows substantially more variability than would be expected by chance alone, since ignoring such "over-dispersion" could lead to a large number of institutions being inappropriately classified as "abnormal". A number of options for handling this phenomenon are investigated, ranging from improved risk stratification to fitting a statistical model that robustly estimates the degree of over-dispersion. DESIGN: Retrospective analysis of publicly available data on survival following coronary artery bypass grafts, emergency readmission rates, and teenage pregnancies. SETTING: NHS trusts in England. RESULTS: Funnel plots clearly show the influence of the method chosen for dealing with over-dispersion on the "banding" a trust receives. Both multiplicative and additive approaches are feasible and give intuitively reasonable results, but the additive random effects formulation appears to have a stronger conceptual foundation. CONCLUSION: A random effects model may offer a reasonable solution. This method has now been adopted by the UK Healthcare Commission in their derivation of star ratings.

Adolescent↗

PubMed2003

Probability in radiology.

In this article, a summary of the basic rules of probability using examples of their application in radiology is presented. Those rules describe how probabilities may be combined to obtain the chance of "success" with either of two diagnostic or therapeutic procedures or with both. They define independence and relate it to the conditional probability. They describe the relationship (Bayes rule) between sensitivity, specificity, and prevalence on the one hand and the positive and negative predictive values on the other. Finally, the two distributions most commonly encountered in statistical models of radiologic data are presented: the binomial and normal distributions.

Bayes Theorem↗

PubMed1997

Disorderly and nonstationary insulin secretion in relatives of patients with NIDDM.

To further explore the role of the beta-cell as a pathogenic factor behind non-insulin-dependent diabetes mellitus (NIDDM), insulin secretion at modest hyperglycemia was examined in 15 healthy first-degree relatives of NIDDM patients and 13 anthropometrically and age-matched controls. The oral glucose tolerance test was normal in all, but the relatives had impaired insulin-stimulated glucose uptake (P < 0.05). During a constant intravenous glucose infusion we performed a time-series analysis of serum insulin in samples obtained at 1-min intervals for 75 min (60-135 min). The recently introduced scale- and model-independent statistic approximate entropy (ApEn) and the coefficient of variation for a 6- (9 and 15) point moving average (MA) were applied to test regularity and stationarity, respectively, of insulin secretion. Both ApEn and 6-point MA were able to significantly discern the insulin time series of the two groups (P < 0.05), demonstrating a higher degree of irregularity and nonstationarity among the offspring. Moreover, when the two complementary sets of statistics were combined into a single "index of nonpulsatility," an even more notable distinction was available (P < 0.01). No relationship was found between altered insulin secretion and insulin resistance. In conclusion, this experimental and statistical model demonstrates that the stimulated insulin secretion of glucose-tolerant relatives of NIDDM patients is characterized by disorderliness. Whether the model can predict the risk for developing a clinically important beta-cell dysfunction remains to be clarified.

Adult↗

PubMed1998

Interactions between CO2 chemoreflexes and arterial baroreflexes.

We studied interactions between CO2 chemoreflexes and arterial baroreflexes in 10 supine healthy young men and women. We measured vagal carotid baroreceptor-cardiac reflexes and steady-state fast Fourier transform R-R interval and photoplethysmographic arterial pressure power spectra at three arterial pressure levels (nitroprusside, saline, and phenylephrine infusions) and three end-tidal CO2 levels (3, 4, and 5%, fixed-frequency, large-tidal-volume breathing, CO2 plus O2). Our study supports three principal conclusions. First, although low levels of CO2 chemoreceptor stimulation reduce R-R intervals and R-R interval variability, statistical modeling suggests that this effect is indirect rather than direct and is mediated by reductions of arterial pressure. Second, reductions of R-R intervals during hypocapnia reflect simple shifting of vagally mediated carotid baroreflex responses on the R-R interval axis rather than changes of baroreflex gain, range, or operational point. Third, the influence of CO2 chemoreceptor stimulation on arterial pressure (and, derivatively, on R-R intervals and R-R interval variability) depends critically on baseline arterial pressure levels: chemoreceptor effects are smaller when pressure is low and larger when arterial pressure is high.

Adult↗

PubMed2006

Remapping in human visual cortex.

With each eye movement, stationary objects in the world change position on the retina, yet we perceive the world as stable. Spatial updating, or remapping, is one neural mechanism by which the brain compensates for shifts in the retinal image caused by voluntary eye movements. Remapping of a visual representation is believed to arise from a widespread neural circuit including parietal and frontal cortex. The current experiment tests the hypothesis that extrastriate visual areas in human cortex have access to remapped spatial information. We tested this hypothesis using functional magnetic resonance imaging (fMRI). We first identified the borders of several occipital lobe visual areas using standard retinotopic techniques. We then tested subjects while they performed a single-step saccade task analogous to the task used in neurophysiological studies in monkeys, and two conditions that control for visual and motor effects. We analyzed the fMRI time series data with a nonlinear, fully Bayesian hierarchical statistical model. We identified remapping as activity in the single-step task that could not be attributed to purely visual or oculomotor effects. The strength of remapping was roughly monotonic with position in the visual hierarchy: remapped responses were largest in areas V3A and hV4 and smallest in V1 and V2. These results demonstrate that updated visual representations are present in cortical areas that are directly linked to visual perception.

Acoustic Stimulation↗

PubMed2006

Template-based spike pattern identification with linear convolution and dynamic time warping.

Pattern identification for spiking activity, which is central to neurophysiological analysis, is complicated by variability in spiking at multiple timescales. Incorporating likelihood tests on the variability at two timescales, we developed an approach to identifying segments from continuous neurophysiological recordings that match preselected spike "templates." At smaller timescales, each component of the preselected pattern is represented by a linear filter. Local scores to measure the similarities between short data segments and the pattern components are computed as filter responses. At larger timescales, overall scores to measure the similarities between relatively long data segments and the entire pattern are computed by dynamic time warping, which combines the local similarity scores associated with the pattern components, optimizing over a range of intercomponent time intervals. Occurrences of the pattern are identified by local peaks in the overall similarity scores. This approach is developed for point process representations and binary representations of spiking activity, both deriving from a single underlying statistical model. Point process representations are suitable for highly reliable single-unit responses, whereas binary representations are preferred for more variable single-unit responses and multiunit responses. Testing with single units recorded from individual electrodes within the robust nucleus of the arcopallium of zebra finches and with recordings from an array placed within the motor cortex of macaque monkeys demonstrates that the approach can identify occurrences of specified patterns with good time precision in a broad range of neurophysiological data.

Algorithms↗

PubMed2001

Intratumoral variations in DNA ploidy and s-phase fraction in human breast cancer.

To study intratumoral DNA ploidy heterogeneity and S-phase fraction (SPF) variability, we prospectively collected five different samples from 48 breast carcinomas and each sample was analysed separately by flow cytometry. Aneuploidy rate was 89.6% after analysis of four or five samples. DNA ploidy heterogeneity, i.e., different samples classified as either DNA euploid or DNA aneuploid in the same tumor was seen in 17%, and DNA index heterogeneity, i.e., tumor populations with different DNA indices (DIs) seen in different samples was 44%. A statistical model defining SPF heterogeneity is proposed. SPF heterogeneity as defined by us was 71%, and as expected the SPF heterogeneity rate increased significantly with increasing number of analysed samples. Four or more samples are needed to detect the most deviant (highest) SPF values. An unrecognized intratumor heterogeneity of DNA ploidy and SPF may partly explain the conflicting results reported in the literature on the above prognostic indicators.

Breast Neoplasms↗

PubMed2006

Thiazide diuretics, potassium, and the development of diabetes: a quantitative review.

National guidelines and a recent clinical trial have supported the use of thiazide diuretics as the preferred initial pharmacological treatment for hypertension. However, evidence from this and other clinical trials have also found an increased incidence of new onset diabetes among those patients receiving thiazide diuretics. The mechanisms responsible for the increased incidence of diabetes with thiazide diuretics have not been fully elucidated. This article provides a review of intervention studies that included data on the relation between thiazide-induced hypokalemia and glucose intolerance. We conducted a literature search from 1966 to June 2004 to identify clinical trials using thiazide diuretics where the metabolic effects on potassium and glucose are reported. A total of 59 clinical trials constituting 83 thiazide diuretic study arms were identified. Trial size, length, type of thiazide diuretic, and dose varied substantially among the studies. The association between average changes in potassium and glucose in the study arms is considered jointly in a weighted statistical model. The Pearson's correlation coefficient, weighted by study sample size, for the relationship between glucose and potassium was -0.54 (95% CI, -0.67 to -0.36; P < 0.01). A sensitivity analysis, which considered subset analyses and effect of covariates, as well as inverse-variance weighting, supported this finding. These data suggest that thiazide-induced hypokalemia is associated with increased blood glucose. Treatment of thiazide-induced hypokalemia may reverse glucose intolerance and possibly prevent the future development of diabetes.

Blood Glucose↗

PubMed2003

Effect of age on clinical and morphological characteristics in patients with brain arteriovenous malformation.

BACKGROUND AND PURPOSE: The goal of this work was to determine the effect of age at initial presentation on clinical and morphological characteristics in patients with brain arteriovenous malformation (AVM). METHODS: The 542 consecutive patients from the prospective Columbia AVM database (mean+/-SD age, 34+/-15 years) were analyzed. Univariate statistical models were used to test the effect of age at initial presentation on clinical (AVM hemorrhage, seizures, headaches, neurological deficit, other/asymptomatic) and morphological (AVM size, venous drainage pattern, AVM brain location, concurrent arterial aneurysms) characteristics. RESULTS: Hemorrhage was the presenting symptom in 46% (n=247); 29% (n=155) presented with seizures, 13% (n=71) with headaches, 7% (n=36) with a neurological deficit, and 6% (n=33) without AVM-related symptoms. Increasing age correlated positively with intracranial hemorrhage (P=0.001), focal neurological deficits (P=0.007), infratentorial AVMs (P<0.001), and concurrent arterial aneurysms (P<0.001); an inverse correlation was found with seizures (P<0.001), AVM size (P=0.001), and lobar (P<0.001), deep (P=0.008), and borderzone (P=0.014) location. No age differences were found for sex, headache, asymptomatic presentation, and venous drainage pattern. CONCLUSIONS: Our data suggest a significant interaction of patient age and clinical and morphological AVM features and argue against uniform AVM characteristics across different age classes at initial presentation. In particular, AVM patients diagnosed at a higher age show a higher fraction of AVM hemorrhage and are more likely to harbor additional risk factors such as concurrent arterial aneurysms and small AVM diameter. Longitudinal population-based AVM data are necessary to confirm these findings.

Adolescent↗

PubMed2001

Association of surgical specialty and processes of care with patient outcomes for carotid endarterectomy.

BACKGROUND AND PURPOSE: Because there is considerable variation in practice patterns and outcomes for carotid endarterectomy (CE), there is a need to study the processes of care that are associated with adverse outcomes. The purpose of this study was to examine the impact of processes of care and surgical specialty on adverse outcomes for CE. METHODS: A retrospective cohort study based on a voluntary CE registry containing 3644 patients undergoing CE between April 1, 1997, and March 31, 1999, in New York hospitals was used in the study. A multivariable statistical model was used to identify significant independent patient risk factors and to examine the association of processes of care and surgical specialty with outcomes after adjustment for differences in patient risk factors. RESULTS: The overall adverse outcome (in-hospital death or stroke) rate was 1.84%. After adjustment for differences in 7 patient risk factors that were significantly related to adverse outcomes, the use of >/=1 specific processes of care (eversion endarterectomy, protamine, or shunts) was found to be associated with lower odds of an adverse outcome relative to patients undergoing CE without the processes (OR=0.42, P=0.006). Similarly, patients undergoing surgery performed by vascular surgeons had lower odds of experiencing an adverse outcome (OR=0.36, P=0.009). Processes of care and surgical specialty were highly correlated with one another. CONCLUSIONS: Processes of care and surgical specialty are significant interrelated determinants of adverse outcome for CE.

Aged↗

PubMed2000

Statistical procedures for spatiotemporal neuronal data with applications to optical recording of the auditory cortex.

This article presents new procedures for multisite spatiotemporal neuronal data analysis. A new statistical model - the diffusion model - is considered, whose parameters can be estimated from experimental data thanks to mean-field approximations. This work has been applied to optical recording of the guinea pig's auditory cortex (layers II-III). The rates of innovation and internal diffusion inside the stimulated area have been estimated. The results suggest that the activity of the layer balances between the alternate predominance of its innovation process and its internal process.

Animals↗