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PubMed2006

Quantitative measurement and visual assessment of ileal Crohn's disease activity by computed tomography enterography: correlation with endoscopic severity and C reactive protein.

BACKGROUND: Few studies have correlated computed tomography (CT) enterography findings with endoscopic severity and C reactive protein (CRP) concentrations. AIM: To examine whether small bowel inflammation at CT enterography correlates with endoscopic severity and CRP in patients with Crohn's disease (CD). METHODS: CT enterography datasets from 143 CD patients undergoing ileoscopy were examined for three different CT parameters: CT bowel enhancement, as defined by the ratio of terminal ileal versus control ileal loop attenuation; vascular enlargement of the vasa recta ("the comb sign"); and mesenteric fat density. Correlations between CT scan parameters, endoscopy, and histology severity scores, and CRP were assessed using Spearman's rank correlation and logistic regression. RESULTS: Endoscopic score was significantly correlated with CT bowel enhancement, comb sign, and fat density (Spearman correlation coefficients 0.33-0.39; p<0.001). Correlations with histological inflammation were strongest for bowel enhancement (r = 0.34-0.38; p<0.001). CRP was elevated in patients with increased fat density versus those with increased bowel enhancement only (median 0.96 v 0.23, p = 0.002). CRP did not differ significantly between patients without evidence of active Crohn's and those with bowel enhancement and endoscopic inflammation not involving the perienteric tissues by CT (median 0.24 v 0.36; p = 0.38). CONCLUSION: Quantitative measures of bowel enhancement at CT enterography correlate with endoscopic and histological severity. CRP correlates with radiological findings of perienteric inflammation (increased fat density), but not of inflammation limited to the small bowel wall, underscoring the potential role of perienteric inflammation in CRP response in CD.

Adolescent↗

PubMed2001

Relations between hypometabolism in the posterior association neocortex and hippocampal atrophy in Alzheimer's disease: a PET/MRI correlative study.

OBJECTIVES: Hippocampal atrophy and hypometabolism in the posterior association neocortex are two well known features of Alzheimer's disease. A correlation between these two features was reported twice previously, suggesting intriguing relations. This question has been reassessed, this time controlling for severity of dementia as well as assessing each side of the brain separately and using a voxel based image analysis in addition to the previously employed regions of interest (ROIs). PATIENTS AND METHODS: Eleven patients were studied with probable Alzheimer's disease and mild to moderate dementia in whom both volume MRI and PET assessed cerebral glucose consumption (CMRGlc) were available. Hypothesis driven correlations between hippocampal width (an index of atrophy) and CMRGlc were performed for two posterior association regions, the superior temporal and the inferior parietal (angular gyrus) cortices, using ROIs set separately for each hemisphere. To confirm significant correlations from the ROIs approach, if any, and to assess their specificity for the posterior association neocortex, CMRGlc image voxel based analysis of correlations with hippocampal width was then carried out. RESULTS: There was a significant correlation, in the positive-neurobiologically expected-direction, between right hippocampal width and right angular gyrus metabolism (p< 0.01, Spearman), which remained significant with Kendall partial correlation controlling for dementia severity (estimated by mini mental state scores). Statistical non-parametric mapping (SnPM) confirmed this correlation (p< 0.025), and showed a single additional correlation in the right middle temporal gyrus (p< 0.005), which is also part of the posterior association cortex. CONCLUSION: The findings with both ROIs and voxel based mapping replicate earlier reports of a relation between hippocampal atrophy and ipsilateral association cortex hypometabolism in Alzheimer's disease, and for the first time document that this relation is both region specific and independent of the dementing process itself. Why the correlation was significant only for the right hemisphere is unclear but may be related to the limited sample. Hippocampal-neocortical disconnection due to early and severe medial temporal lobe pathology may at least partly explain the posterior association cortex hypometabolism found in Alzheimer's disease.

Aged↗

PubMed2003

Hepatic flow parameters measured with MR imaging and Doppler US: correlations with degree of cirrhosis and portal hypertension.

PURPOSE: To determine the correlations between hemodynamic parameters of hepatic flow measured with magnetic resonance (MR) imaging and Doppler ultrasonography (US) and the severity of cirrhosis and portal hypertension. MATERIALS AND METHODS: Forty-six patients referred for measurements of portal venous pressure (three with normal liver, 12 with chronic hepatitis, and 31 with cirrhosis [10 with Child-Pugh class A cirrhosis; 13 with class B cirrhosis; and eight with class C cirrhosis]) were included in the study. Apparent liver perfusion, apparent arterial and portal perfusion, portal fraction, distribution volume, and mean transit time were measured with dynamic contrast material-enhanced MR imaging. Portal velocity, portal flow, congestion index, right hepatic artery resistance index, and modified hepatic index were measured with Doppler US. Results in patients with cirrhosis and those without cirrhosis were compared with the Wilcoxon rank sum test. Correlations were assessed with Spearman rank correlation coefficients. RESULTS: With MR imaging, all flow parameters except distribution volume were significantly different between patients with and those without cirrhosis (P <.05). There was a significant correlation between all flow parameters measured with MR imaging and portal pressure (P <.02). Apparent arterial (P =.024) and portal (P <.001) perfusion, portal fraction (P <.001), and mean transit time (P =.004) were correlated with Child-Pugh class. Flow parameters measured with Doppler US did not differ significantly between patients with and those without cirrhosis. Only right hepatic arterial resistance (P <.007) and portal flow (P <.043) were weakly (r < 0.7) correlated with portal pressure. No Doppler US parameter was correlated with Child-Pugh class. CONCLUSION: Hepatic flow parameters measured with MR imaging correlate with the severity of cirrhosis and portal hypertension. Doppler US parameters are only weakly correlated with portal pressure.

Adolescent↗

PubMed2004

Correlation of MR lumbar spine bone marrow perfusion with bone mineral density in female subjects.

PURPOSE: To prospectively assess lumbar spine bone marrow perfusion at dynamic magnetic resonance (MR) imaging and correlate perfusion with bone mineral density (BMD) in female subjects. MATERIALS AND METHODS: BMD measurement and dynamic MR imaging of the lumbar spine were performed in 69 female subjects (mean age +/- standard deviation, 57 years +/- 11). Subjects were stratified into premenopausal (n = 19) and postmenopausal (n = 50) groups, with the latter group including both women who were (n = 13) and women who were not (n = 37) receiving hormone replacement therapy. BMD (in grams per square centimeter) was measured with dual energy absorptiometry in the lumbar spine. Peak enhancement ratio, measured with time-signal intensity curves calculated from dynamic MR image data, represented bone marrow perfusion. Peak enhancement ratio was compared with age and BMD by using linear regression analysis and Pearson correlation. RESULTS: A significant positive correlation was found for BMD with peak enhancement ratio of lumbar vertebrae among all subjects (n = 69, r = 0.63, P <.001), all postmenopausal women (n = 50, r = 0.50, P <.001), and postmenopausal women without hormone replacement therapy (n = 37, r = 0.61, P <.001). However, the correlation between BMD and peak enhancement ratio was not significant (P >.05) in premenopausal women (n = 19) or postmenopausal women receiving hormone therapy (n = 13). Both BMD and peak enhancement ratio were inversely correlated with age (P <.001, Pearson correlation). Pearson partial correlation coefficient for peak enhancement ratio and mean in all subjects, with control for inverse correlation with age, was significant (r = 0.63, P <.001). CONCLUSION: Significant correlation was found between the peak enhancement ratio of vertebral bone marrow and BMD in postmenopausal female subjects. This result may suggest a vascular component in the pathogenesis of osteoporosis.

Absorptiometry, Photon↗

PubMed2005

Neoangiogenesis and sinusoidal capillarization in hepatocellular carcinoma: correlation between dynamic CT and density of tumor microvessels.

PURPOSE: To retrospectively evaluate the correlation between the degree of contrast enhancement on dynamic computed tomographic (CT) scans and the degree of neoangiogenesis and sinusoidal capillarization in hepatocellular carcinoma (HCC). MATERIALS AND METHODS: The institutional review board did not require approval or informed patient's consent for the review of medical records or images. Dynamic CT scans of 97 nodular HCCs in 97 patients (79 men, 18 women; age range, 29-73 years; mean age, 54 years) were evaluated in terms of the attenuation change in the arterial, portal venous, and delayed phases, and the results were correlated with the number of unpaired arteries and the degree of sinusoidal capillarization at histopathologic examination. The mean attenuation value of the nodular HCCs on triple-phase helical CT scans was correlated with the number of unpaired arteries and the degree of sinusoidal capillarization. Statistical analysis was performed with the Spearman rank correlation test. RESULTS: The number of unpaired arteries in the nodular HCCs was found to correlate with the degree of contrast enhancement in the arterial phase (r = 0.225, P = .027), but did not correlate with the degree of contrast enhancement in the portal and delayed phases. The degree of sinusoidal capillarization did not correlate linearly with the mean attenuation of the nodular HCCs in any phase of contrast enhancement. CONCLUSION: The degree of contrast enhancement of the nodular HCCs in the arterial phase tended to correlate with the number of unpaired arteries, but no correlation was evident between the degree of contrast enhancement and sinusoidal capillarization in any phase of CT imaging.

Adult↗

PubMed1999

Acute pancreatitis: interobserver agreement and correlation of CT and MR cholangiopancreatography with outcome.

PURPOSE: To assess the correlation between and the interobserver agreement of contrast medium-enhanced computed tomography (CT) and nonenhanced and contrast-enhanced magnetic resonance (MR) imaging findings in patients with acute pancreatitis and to correlate these findings with outcome. MATERIALS AND METHODS: Two blinded reviewers separately assessed contrast-enhanced CT and nonenhanced and contrast-enhanced MR images in 30 patients with acute pancreatitis and established a severity index based on the presence of peripancreatic fluid collections and pancreatic necrosis. The Spearman rank correlation coefficient and weighted kappa statistic were used to assess the correlation between each imaging technique and the interobserver agreement, respectively. Correlation between hospitalization days, morbidity, and severity indexes were assessed by using linear correlation. RESULTS: A strong correlation existed for both reviewers when comparing contrast-enhanced CT with nonenhanced (r = 0.82, 0.79) or contrast-enhanced (r = 0.82, 0.79) MR cholangiopancreatography or when comparing nonenhanced and contrast-enhanced MR cholangiopancreatography (r = 0.99, 1.00). The interobserver agreement in staging was stronger with nonenhanced (kappa = 0.76) and contrast-enhanced (kappa = 0.78) MR cholangiopancreatography than with contrast-enhanced CT (kappa = 0.70). There was no linear correlation between the severity index for contrast-enhanced CT and outcome, while there was a linear correlation between nonenhanced or contrast-enhanced MR cholangiopancreatographic staging and the patient morbidity rate. CONCLUSION: MR cholangiopancreatography could be an alternative to contrast-enhanced CT for the initial staging of acute pancreatitis.

Acute Disease↗

PubMed2003

Estimating membrane voltage correlations from extracellular spike trains.

The cross-correlation coefficient between neural spike trains is a commonly used tool in the study of neural interactions. Two well-known complications that arise in its interpretation are 1) modulations in the correlation coefficient may result solely from changes in the mean firing rate of the cells and 2) the mean firing rates of the neurons impose upper and lower bounds on the correlation coefficient whose absolute values differ by an order of magnitude or more. Here, we propose a model-based approach to the interpretation of spike train correlations that circumvents these problems. The basic idea of our proposal is to estimate the cross-correlation coefficient between the membrane voltages of two cells from their extracellular spike trains and use the resulting value as the degree of correlation (or association) of neural activity. This is done in the context of a model that assumes the membrane voltages of the cells have a joint normal distribution and spikes are generated by a simple thresholding operation. We show that, under these assumptions, the estimation of the correlation coefficient between the membrane voltages reduces to the calculation of a tetrachoric correlation coefficient (a measure of association in nominal data introduced by Karl Pearson) on a contingency table calculated from the spike data. Simulations of conductance-based leaky integrate-and-fire neurons indicate that, despite its simplicity, the technique yields very good estimates of the intracellular membrane voltage correlation from the extracellular spike trains in biologically realistic models.

Action Potentials↗

PubMed2000

Progesterone receptor isoforms, PR-B and PR-A, in breast cancer: correlations with clinicopathologic tumor parameters and expression of AP-1 factors.

In the present study, we used Western blot analysis to determine the expression of the progesterone receptor (PR) isoforms, PR-B and PR-A, in breast tumors (n = 53), and correlated the expression patterns of the two isoforms with the clinicopathological parameters of these tumors and with expression of the AP-1 family of transcription factors. Expression of the two PR isoforms correlated significantly with each other, indicating that the expression of the two isoforms is probably regulated in a correlated fashion. Expression of both isoforms correlated significantly with expression of the estrogen receptor (ER). Furthermore, expression of PR-B was found to correlate significantly with the absence of ErbB2/neu. For the AP-1 factors, Fra-1 expression showed an inverse correlation with PR-B expression. In contrast, expression of FosB correlated significantly with expression of both isoforms, and the association was stronger with PR-B expression. An analysis of the ratio of expression of the two isoforms showed that most of the tumors expressed PR-A levels which were equal or higher than the corresponding PR-B expression levels (together 94% of the analyzed tumors) indicating that, in mammary carcinomas, a predominance of the PR-A isoform over the PR-B isoform seems to be the case. While there was no statistically significant correlation with age, staging and histological type, expression of both isoforms correlated with a more differentiated phenotype (G1/G2 grading). However, this association was stronger for PR-B. Also, a PR-A < or = PR-B expression level was associated with G1/G2 grading, while a PR-A > PR-B expression level showed an association with a more undifferentiated phenotype (G3 grading). The expression level of the two PR isoforms might prove to be of prognostic and/or predictive value, especially since the two isoforms have been shown to be functionally different and to modulate the response of tumor cells to progestins and antiprogestins differently.

Blotting, Western↗

PubMed2001

Familial correlation in the decline of forced expiratory volume in one second.

Studies have shown evidence of significant parent-offspring and sibling correlation in FEV1, but familial aggregation of decline of FEV1 over time has not been reported. Our study population comprised 392 families enrolled in the Tucson Epidemiological Study of Airway Obstructive Diseases. Subjects were older than 18 yr of age and performed at least 3 pulmonary function tests over 5 to 20 yr. The slope of FEV1 was calculated for each subject using simple linear regression. Multiple regression models were used to compute standardized residual slope values adjusted for possible confounders. Familial correlation analysis on residual slope values demonstrated no evidence of spousal or parent-offspring correlation. However, sibling pairs were highly correlated (r = 0.256, p < 0.001, n = 166), especially smoking-concordant pairs (r = 0.483, p < 0.01 for ever-smokers, and r = 0.280, p < 0.05 for never-smokers). The residual slopes of smoking-discordant siblings were not significantly correlated (r = 0.031, p < 0.77). Genetic susceptibility to an accelerated rate of decline associated with smoking may be evidenced in the increased correlation among smoking sibling pairs, and in the lack of correlation among smoking-discordant sibling pairs. High sibling correlation in the absence of parent-offspring correlation is compatible with a recessive model of inheritance.

Adult↗

PubMed2005

Computed tomography correlates with pulmonary exacerbations in children with cystic fibrosis.

RATIONALE: High-resolution computed tomography (HRCT) has been suggested as a potential outcome surrogate for cystic fibrosis (CF) lung disease. An important attribute of a valid outcome surrogate is that the surrogate reflects true clinical outcomes. OBJECTIVES: We performed this study to validate HRCT, a proposed surrogate outcome measure for CF lung disease, against a true clinical outcome, the number of respiratory tract exacerbations occurring in 2 yr, and to assess the correlation of CT scores and pulmonary function tests (PFTs) with this clinical outcome. METHODS: CTs and PFTs were performed on 6- to 10-yr-old children at the beginning and end of a 2-yr study during which the number of exacerbations were recorded. Spearman correlations and Poisson models were used to assess the correlation of the number of exacerbations with baseline values and changes in PFTs and CT scores. MEASUREMENTS AND MAIN RESULTS: Nine of 61 subjects had a total of 22 respiratory tract exacerbations. At baseline, PFTs and four CT scores showed significant correlation with number of exacerbations, but no variable by itself predicted exacerbations with high accuracy. For change over the 2-yr period, three CT scores showed significant correlation with exacerbations, whereas no PFTs showed significant correlation. CONCLUSION: This is the first study showing correlation between CT and a true clinical outcome. Change in CT scores correlates moderately well with the number of exacerbation. Poor correlation between change in FEV1 and exacerbations suggests that HRCT may be a more appropriate outcome surrogate for longitudinal studies of young children.

Anti-Bacterial Agents↗

PubMed1979

Morphologic-physiologic correlates of the severity of fibrosis and degree of cellularity in idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a progressive disease of lung parenchyma characterized by a chronic inflammatory cellular infiltration and varying degrees of interstitial fibrosis. Current data indicate that the severity of fibrosis and the degree of cellularity determine, in part, the prognosis of IPF and the response to therapy. Whereas lung biopsy gives the best assessement of fibrosis and cellularity, physiologic studies are used to stage and monitor the disease process. To determine which physiologic studies correlate best with severity of fibrosis and degree of cellularity, these parameters were graded in lung biopsies of 23 patients with IPF and compared with a variety of physiologic studies. Although vital capacity, total lung capacity, and diffusing capacity are commonly used as objective monitors of the disease process, none of these parameters correlated with either the severity of fibrosis or the degree of cellularity in biopsy specimens. In contrast, almost all parameters of lung distensibility correlated with the morphologic assessment of degree of fibrosis; compliance had the best correlation. Parameters of distensibility, however, correlated poorly with the degree of cellularity. In comparison, gas exchange during exercise correlated with both morphologic parameters; the exercise-induced changes in arterial oxygen pressure per liter of oxygen consumed had a high correlation with the degree of fibrosis (r = 0.89; P less than 0.001) and correlated to a lesser extent with the degree of cellularity (r = 0.56; P = 0.009). In contrast, neither the resting arterial oxygen tension nor the arterial oxygen tension at maximal exercise correlated with the morphologic assessment of degree of fibrosis or the degree of cellularity. These morphologic-physiologic comparisons suggest that (a) lung volumes and diffusing capacity are poor monitors of both the degree of fibrosis and the degree of cellularity; (b) the fibrotic process contributes, at least in part, to parameters of lung distensibility, and both fibrosis and cellularity contribute to gas exchange alterations during exercise; and (c) parameters of lung distensibility and exercise-induced gas exchange alterations may be useful in staging the severity of disease in IPF.

Adult↗

PubMed2005

Analysis of spatial correlation between 99mTc-Sestamibi uptake and radiographic breast density.

Breast scintigraphy is a technique by which the biological properties of breast lesions can be assessed using an injected radiopharmaceutical. It may be particularly useful for women with radiographically dense breasts, in whose mammograms, lesions are often obscured by breast tissue. We are evaluating a dual modality breast scanner developed at the University of Virginia for its ability to distinguish between benign and malignant lesions. The scanner obtains a digital mammogram and a gamma ray emission image in quick succession with the breast held under mild compression, resulting in a fused image in which structures in the digital mammogram can be directly correlated with those in the scintigram. Our experience has shown that radiopharmaceutical uptake by normal breast tissue can sometimes obscure uptake by small lesions. It would therefore be advantageous to correct for this background uptake if possible. One potential way of accomplishing this is to use the information from the digital mammogram to help predict the background radiopharmaceutical distribution. With this in mind, we retrospectively investigated the degree of spatial correlation between the distribution of background activity and the distribution of radiodense breast tissue in normal breasts. Using a histogram-based analysis, we have quantified the degree of correlation in 16 images obtained from a total of 8 patients. We also used the mammographic images to quantify the radiographic density of each breast. Our results suggest that spatial correlation between areas of high radiopharmaceutical uptake and parenchymal density exists in the most dense regions of the breast for either extremely dense or heterogeneously dense breasts. High correlation was also observed for some homogeneously fatty breasts. In the latter case however, variation in breast thickness appeared to be the cause of the increased correlation. Correlation properties are approximately equal in both right and left breasts for a particular patient, except in cases exhibiting focal radiotracer uptake in a lesion. Although our preliminary results suggest that correlation between radiopharmaceutical uptake and parenchymal density exists, the number of cases thus far is too small for definitive conclusions. In addition, the planar nature of the dual modality scans imposes an inherent limitation on our ability to take into account attenuation of the emitted gamma radiation, which thus constitutes an uncontrolled variable in the correlation analysis. In principle, this problem can be eliminated by 3-dimensional imaging.

Adipose Tissue↗

PubMed2004

The effect of correlation structure on treatment contrasts estimated from incomplete clinical trial data with likelihood-based repeated measures compared with last observation carried forward ANOVA.

Valid analyses of longitudinal data can be problematic, particularly when subjects dropout prior to completing the trial for reasons related to the outcome. Regulatory agencies often favor the last observation carried forward (LOCF) approach for imputing missing values in the primary analysis of clinical trials. However, recent evidence suggests that likelihood-based analyses developed under the missing at random framework provide viable alternatives. The within-subject error correlation structure is often the means by which such methods account for the bias from missing data. The objective of this study was to extend previous work that used only one correlation structure by including several common correlation structures in order to assess the effect of the correlation structure in the data, and how it is modeled, on Type I error rates and power from a likelihood-based repeated measures analysis (MMRM), using LOCF for comparison. Data from four realistic clinical trial scenarios were simulated using autoregressive, compound symmetric and unstructured correlation structures. When the correct correlation structure was fit, MMRM provided better control of Type I error and power than LOCF. Although misfitting the correlation structure in MMRM inflated Type I error and altered power, misfitting the structure was typically less deleterious than using LOCF. In fact, simply specifying an unstructured matrix for use in MMRM, regardless of the true correlation structure, yielded superior control of Type I error than LOCF in every scenario. The present and previous investigations have shown that the bias in LOCF is influenced by several factors and interactions between them. Hence, it is difficult to precisely anticipate the direction and magnitude of bias from LOCF in practical situations. However, in scenarios where the overall tendency is for patient improvement, LOCF tends to: 1) overestimate a drug's advantage when dropout is higher in the comparator and underestimate the advantage when dropout is lower in the comparator; 2) overestimate a drug's advantage when the advantage is maximum at intermediate time points and underestimate the advantage when the advantage increases over time; and 3) have a greater likelihood of overestimating a drug's advantage when the advantage is small. In scenarios in which the overall tendency is for patient worsening, the above biases are reversed. In the simulation scenarios considered in this study, which were patterned after acute phase neuropsychiatric clinical trials, the likelihood-based repeated measures approach, implemented with standard software, was more robust to the bias from missing data than LOCF, and choice of correlation structure was not an impediment to its implementation.

Analysis of Variance↗

PubMed2002

Spleen size: how well do linear ultrasound measurements correlate with three-dimensional CT volume assessments?

Ultrasound measurement of splenic length is standard practice, but it is not known how well this represents the true size of the spleen. Previous studies, using a combination of measurements from in vivo and resected spleens, were subject to error because of changes in splenic size. The aim of this study was to correlate the dimensions of the spleen measured by ultrasound with the splenic volume measured by helical CT. Ultrasound examination was performed on 50 adult patients at the time of their attendance for abdominal CT. Linear dimensions of the spleen were measured with the patient first in the supine and then in the right lateral decubitus (RLD) position. The splenic volume was calculated from a three-dimensional reconstruction of the CT images. There was good correlation, using Spearman's rank correlation, between ultrasound measurements and CT volumes with correlation coefficients exceeding 0.7 for all parameters except one. The linear measurement that correlated most closely with CT volume was the spleen width measured on a longitudinal section with the patient in the RLD position (correlation coefficient (r)=0.89, p<0.001). There was also good correlation between splenic length measured in the RLD position and CT volume (r=0.86, p<0.001). We conclude that a good correlation exists between in vivo ultrasound assessment of splenic size and true splenic volume. The most accurate single measurement is spleen width measured on a longitudinal section with the patient in the RLD position. However, measurement of splenic length, which is the most commonly used in clinical practice, also correlates well with splenic volume, particularly when performed with the patient in the RLD position.

Adult↗

PubMed2004

Fine-scale genetic structure and gene dispersal in Centaurea corymbosa (Asteraceae). II. Correlated paternity within and among sibships.

The fine-scale pattern of correlated paternity was characterized within a population of the narrow-endemic model plant species, Centaurea corymbosa, using microsatellites and natural progeny arrays. We used classical approaches to assess correlated mating within sibships and developed a new method based on pairwise kinship coefficients to assess correlated paternity within and among sibships in a spatio-temporal perspective. We also performed numerical simulations to assess the relative significance of different mechanisms promoting correlated paternity and to compare the statistical properties of different estimators of correlated paternity. Our new approach proved very informative to assess which factors contributed most to correlated paternity and presented good statistical properties. Within progeny arrays, we found that about one-fifth of offspring pairs were full-sibs. This level of correlated mating did not result from correlated pollen dispersal events (i.e., pollen codispersion) but rather from limited mate availability, the latter being due to limited pollen dispersal distances, the heterogeneity of pollen production among plants, phenological heterogeneity and, according to simulations, the self-incompatibility system. We point out the close connection between correlated paternity and the "TwoGener" approach recently developed to infer pollen dispersal and discuss the conditions to be met when applying the latter.

Centaurea↗

PubMed2000

High-resolution correlation in apparently monotonous rocks: upper Ordovician Kope Formation, Cincinnati Arch.

Short stratigraphic sections in apparently monotonous strata pose several challenges to high-resolution (<l m) correlation. A lack of distinctive marker horizons can prevent obvious visual correlations between the sections. The stratigraphic shortness of the outcrops further reduces the likelihood of any given section having a recognizable marker horizon. The Upper Ordovician Kope Formation of the Cincinnati, Ohio, area exhibits both of these problems and correlation within the Kope has not been accomplished easily, to date. However, cross-correlation of meter-scale cycles in the Kope can be used to identify potential correlations of small outcrops to larger, well-described outcrops. If multiple correlations are equally plausible, large-scale faunal transitions among facies fossils can then be used to select the best correlation. In this pilot study, two sections separated by 9 km are correlated successfully using these methodologies, which show promise for the correlation of numerous outcrops in the Cincinnati area. In addition, the methods described here may be applied easily to other areas of limited outcrop in which the rocks are so complexly cyclic that they, likewise, appear to be monotonous.

Animals↗

PubMed1996

Plasma leptin levels correlate to islet function independently of body fat in postmenopausal women.

It has previously been demonstrated that plasma leptin correlates to body fat content. Increased body fat content is accompanied by low insulin sensitivity, which is compensated with increased insulin secretion. We therefore studied whether plasma levels of leptin also correlate to insulin secretion and sensitivity in humans. Therefore, we examined insulin sensitivity by the euglycemic-hyperinsulinemic clamp technique and measured the insulin response to intravenous arginine (5 g) at fasting and 14 mmol/l glucose in postmenopausal women. Percent body fat content was determined with impedance measurements. Log plasma leptin significantly correlated to percent body fat (r = 0.84, P < 0.001). In women with normal glucose tolerance (n = 36), partial correlation studies controlling for body fat content revealed significant correlations between log plasma leptin and fasting insulin levels (r = 0.39, P = 0.029), the insulin response to arginine at both glucose levels (r = 0.38 and r = 0.37, P < 0.036 for both), and the glucose potentiation of arginine-stimulated insulin secretion (r = 0.40, P = 0.025). In contrast, in women with impaired glucose tolerance (n = 17), these correlations were not significant. Plasma leptin did not correlate with insulin sensitivity independently of body fat content. To study whether the correlation between leptin and insulin would be explained by insulin stimulating leptin secretion, we examined plasma leptin during hyperinsulinemic conditions (689 +/- 41 pmol/l), under both euglycemia (5.0 mmol/l, n = 10) and hypoglycemia (2.5 mmol/l, n = 7). However, under both these conditions, plasma leptin was unaltered. In conclusion, plasma leptin 1) reflects body fat content and 2) correlates to insulin secretion independently of percent body fat in postmenopausal women with normal glucose tolerance.

Adipose Tissue↗

PubMed2006

Genetic correlations among fatty acid compositions in different sites of fat tissues, meat production, and meat quality traits in Duroc pigs.

This study estimated genetic parameters for fatty acids of different sites of fat tissue, meat production, and meat quality traits of Duroc pigs selected during 7 generations for ADG, LM area, backfat thickness (BF), and intramuscular fat (IMF). For this study, 394 barrows and 153 gilts were slaughtered at 105 kg of BW. High heritabilities for C18:0 of outer and inner subcutaneous fat tissue were estimated, respectively, as 0.54 and 0.51; those of intermuscular and intramuscular fat were 0.40 and 0.51, respectively. Genetic and phenotypic correlations of ADG and BF with saturated fatty acids of outer and inner subcutaneous fat were positive, but those with C16:1 and C18:2 were negative, and those with C18:1 were nearly zero. Genetic and phenotypic correlations between LM area and respective fatty acids showed opposite results. Respective genetic and phenotypic correlations of melting points with C18:0 and C18:1 were positive and high, and negative and high, respectively. Genetic correlations between cooking loss and SFA (C14:0, C16:0, and C18:0) of IMF were positive and moderate: 0.56, 0.47, and 0.47, respectively. On the other hand, monosaturated fatty acid of C18:1 was highly and negatively correlated with cooking loss (-0.61). Moreover, high genetic correlation between meat color (pork color standard and lightness) and fatty acid compositions of IMF suggest that the SFA (C14:0, C16:0, and C18:0) were correlated genetically with meat lightness and that unsaturated fatty acid compositions (C18:1 and C18:2) were correlated with meat darkness. Results of this study suggest that the fatty acid composition of adipose tissue is correlated genetically with meat production and meat quality traits.

Adipose Tissue↗