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PubMed2005

Evaluation of a diode array for QA measurements on a helical tomotherapy unit.

A helical tomotherapy system is used in our clinic to deliver intensity-modulated radiation therapy (IMRT) treatments. Since this machine is designed to deliver IMRT treatments, the traditional field flatness requirements are no longer applicable. This allows the unit to operate without a field flatness filter and consequently the 400 mm wide fan beam is highly inhomogeneous in intensity. The shape of this beam profile is mapped during machine commissioning and for quality assurance purposes the shape of the beam profile needs to be monitored. The use of a commercial diode array for quality assurance measurements is investigated. Central axis beam profiles were acquired at different depths using solid water built-up material. These profiles were compared with ion chamber scans taken in a water tank to test the accuracy of the diode array measurements. The sensitivity of the diode array to variations in the beam profile was checked. Over a seven week period, beam profiles were repeatedly measured. The observed variations are compared with those observed with an on-board beam profile monitor. The diode measurements were in agreement with the ion chamber scans. In the high dose, low gradient region the average ratio between the diode and ion chamber readings was 1.000 +/- 0.005 (+/- 1 standard deviation). In the penumbra region the agreement was poorer but all diodes passed the distance to agreement (DTA) requirement of 2 mm. The trend in the beam profile variations that was measured with the diode array device was in agreement with the on-board monitor. While the calculated amount of variation differs between the devices, both were sensitive to subtle variations in the beam profile. The diode array is a valuable tool to quickly and accurately monitor the beam profile on a helical tomotherapy unit.

Evaluation Studies as Topic↗

PubMed1991

Inter-observer variability in the measurement of body composition.

The inter-observer variation in simple bedside assessments of body composition has been evaluated in 12 healthy adult subjects (6 male and 6 female) by 6 observers. Systematic bias between observers was found to be evident in each of the basic measurements (except height) and in each of the estimates of body composition (except those derived from weight and height alone). The largest residual coefficients of variation (rCV) for the basic measurements were found for skinfold thickness (11-18 per cent for individual skinfold thicknesses, and 9 per cent for the sum of four skinfold thicknesses), and the lowest for weight (0.01 per cent for digital scales, and 0.05 per cent for beam balance) and height (0.4 per cent). The rCV for whole-body resistance (1.2 per cent), forearm resistance (5.4 per cent) and near infra-red interactance (optical density 1: 5.6 per cent and optical density 2: 6.2 per cent) measurements were found to have intermediate values. The variability in the estimate of body fat obtained by skinfold thickness (rCV = 4.6 per cent) and near infra-red interactance methods (rCV = 4.2 per cent) was found to be greater than that from the resistance method (rCV = 2.6 per cent) and by methods based on weight and height alone (rCV = 1.1 per cent). The variability in the estimate of fat-free mass showed the same trend as that for body fat, but the rCVs were less due to the greater mass of the fat-free body compared to body fat.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2004

Inter-observer agreement in the assessment of endoscopic findings in ulcerative colitis.

BACKGROUND: Endoscopic findings are essential in evaluating the disease activity in ulcerative colitis. The aim of this study was to evaluate how endoscopists assess individual endoscopic features of mucosal inflammation in ulcerative colitis, the inter-observer agreement, and the importance of the observers' experience. METHODS: Five video clips of ulcerative colitis were shown to a group of experienced and a group of inexperienced endoscopists. Both groups were asked to assess eight endoscopic features and the overall mucosal inflammation on a visual analogue scale. The following statistical analyses were used; Contingency tables analysis, kappa analysis, analysis of variance, Pearson linear correlation analysis, general linear models, and agreement analysis. All tests were carried out two-tailed, with a significance level of 5%. RESULTS: The inter-observer agreement ranged from very good to moderate in the experienced group and from very good to fair in the inexperienced group. There was a significantly better inter-observer agreement in the experienced group in the rating of 6 out of 9 features (p < 0.05). The experienced and inexperienced endoscopists scored the "ulcerations" significantly different. (p = 0.05). The inter-observer variation of the mean score of "erosions", "ulcerations" and endoscopic activity index in mild disease, and the scoring of "erythema" and "oedema" in moderate-severe disease was significantly higher in the inexperienced group.A correlation was seen between all the observed endoscopic features in both groups of endoscopists. Among experienced endoscopists, a set of four endoscopic variables ("Vascular pattern", "Erosions", "Ulcerations" and Friability") explained 92% of the variation in EAI. By including "Granularity" in these set 91% of the variation in EAI was explained in the group of inexperienced endoscopists. CONCLUSION: The inter-observer agreement in the rating of endoscopic features characterising ulcerative colitis is satisfactory in both groups of endoscopists but significantly higher in the experienced group. The difference in the mean score between the two groups is only significant for "ulcerations". The endoscopic variables "Vascular pattern", "Erosions", "Ulcerations" and Friability" explained the overall endoscopic activity index. Even though the present result is quite satisfactory, there is a potential of improvement. Improved grading systems might contribute to improve the consistency of endoscopic descriptions.

Colitis, Ulcerative↗

PubMed1995

An evaluation of setup uncertainties for patients treated to pelvic sites.

PURPOSE: Successful delivery of conformal fields requires stringent immobilization and treatment verification, as well as knowledge of the setup reproducibility. The purpose of this study was to compare the three-dimensional distribution of setup variations for patients treated to pelvic sites with electronic portal imaging devices (EPID) and portal film. METHODS AND MATERIALS: Nine patients with genitourinary and gynecological cancers immobilized with custom casts and treated with a four-field whole-pelvis technique were imaged daily using an EPID and filmed once every five to seven treatments. The three-dimensional translational and rotational setup errors were determined using a technique that relies on anatomical landmarks identified on simulation and treatment images. The distributions of the translational and rotational variations in each dimension as well as the total displacement of the treatment isocenter from the simulation isocenter were determined. RESULTS: Grouped analysis of all patients revealed average unidirectional translational deviations of less than 2 mm and a standard deviation of 5.3 mm. The average total undirected distance between the treatment and simulated isocenters was 8.3 mm with a standard deviation of 5 mm. Individual patient analysis revealed eight of nine patients had statistically significant nonzero mean translational variations (p < 0.05). Translational variations measured with film were an average of 1.4 mm less than those measured with EPID, but this difference was not statistically significant. CONCLUSION: Translational variations measured in this study are in general agreement with previous studies. The use of the EPID in this study was less intrusive and may have resulted in less additional attention being given each imaging setup. This may explain the slightly larger average translational variations observed with EPID vs. film, and suggests that the use of EPIDs is a superior method for assessing the true extent of setup displacements. Although no statistically significant translational variations for the patient group overall were observed, 90% of patients had significant translational variations in at least one direction when analyzed separately. The margin to be added to the clinical target volume (CTV) to account for setup uncertainties will depend on whether it is possible to identify patients with significant translational variations, and to eliminate these displacements from routine treatments. The choice to eliminate these variations and to use a smaller CTV margin will have to be accompanied by stringent frequent position verification methods and repositioning.

Female↗

PubMedDate not supplied

[Visual evaluation of conventional roentgen pictures and dual x-ray absorptiometry in the diagnosis of osteopenia].

Routine radiographs and PA dual x-ray absorptiometry (DXA) of the lumbar spine were performed in 253 patients. A T-score of -2SD (approximately 20% reduction from young normal bone mineral density (BMD)) as measured by DXA, was used as threshold for the diagnosis of osteopenia. A lumbar spine index (LSI) as proposed by Barnett and Nordin was assessed by one radiologist. The correlation between LSI and bone mineral density, measured by DXA, was poor, and our results indicate that osteopenic patients cannot be differentiated from non-osteopenic patients by LSI. 100 radiographs of the lumbar spine were evaluated by 9 observers in order to determine observer variation in the detection of osteopenia. A complete agreement between the readers for the diagnosis of osteopenia was achieved in 43 percent of all radiographs. DXA and observers agreed in 68 to 76 percent of all cases. For a decrease of BMD of more than 60 percent compared to young normal adults, as determined by DXA, all readers agreed in the diagnosis of osteopenia, whereas for higher BMD values the agreement between readers and DXA worsened. The inconsistency between DXA and observer agreement was greatest for patients with a BMD reduction between 10 and 20 percent. The mean values of the kappa-coefficients were 0.574 +/- 0.06 for interobserver variation and 0.437 +/- 0.06 for the agreement between readers and DXA-results. An only moderate kappa-coefficient of 0.573 for the intraobserver variation as determined in one reader was found.

Absorptiometry, Photon↗

PubMed1988

[Variations in the calcaneo-fibular ligament (lig. calcaneofibulare). Application to the kinematics of the ankle].

The authors observe variations in the calcaneo-fibular ligament because this ligament controls two articulations, the talo-crural and the subtalar. This study is based on the dissection of the ankle of 20 specimens. The calcaneo-fibular ligament is reinforced by the ventral and lateral talo-calcaneus ligaments with variations. 3 types of disposition have been described. Type A: A lateral talo-calcaneal ligament reinforces the calcaneo-fibular ligament. These two ligaments are divergent on the proximal, medial, or distal part. Type B: There is an independent lateral talo-calcaneal ligament forward of the calcaneo-fibular ligament. Type C: A ventral talo-calcaneal ligament is observed, parallel to the interosseous ligament. The authors consider the consequences of variation in the lateral ligaments of the ankle for the functioning of the tibio-tarsal articulation, the subtalar articulation and the astragalo-scaphoid articulation in order to propose specific radiographic examination of the kinematics of the ankle.

Ankle Joint↗

PubMed2004

Systematic changes in gene expression in postmortem human brains associated with tissue pH and terminal medical conditions.

Studies of gene expression abnormalities in psychiatric or neurological disorders often involve the use of postmortem brain tissue. Compared with single-cell organisms or clonal cell lines, the biological environment and medical history of human subjects cannot be controlled, and are often difficult to document fully. The chance of finding significant and replicable changes depends on the nature and magnitude of the observed variations among the studied subjects. During an analysis of gene expression changes in mood disorders, we observed a remarkable degree of natural variation among 120 samples, which represented three brain regions in 40 subjects. Most of such diversity can be accounted for by two distinct expression patterns, which in turn are strongly correlated with tissue pH. Individuals who suffered prolonged agonal states, such as with respiratory arrest, multi-organ failure or coma, tended to have lower pH in the brain; whereas those who experienced brief deaths, associated with accidents, cardiac events or asphyxia, generally had normal pH. The lower pH samples exhibited a systematic decrease in expression of genes involved in energy metabolism and proteolytic activities, and a consistent increase of genes encoding stress-response proteins and transcription factors. This functional specificity of changed genes suggests that the difference is not merely due to random RNA degradation in low pH samples; rather it reflects a broad and actively coordinated biological response in living cells. These findings shed light on critical molecular mechanisms that are engaged during different forms of terminal stress, and may suggest clinical targets of protection or restoration.

Adult↗

PubMed1986

Seasonal variation in food intake, pattern of physical activity and change in body weight in a group of young adult Dutch women consuming self-selected diets.

The effect of season on the energy balance was examined in 114 young adult Dutch women consuming self-selected diets. Energy intakes and patterns of physical activity were assessed monthly 14 times with the 24-h recall method. After this period of 14 months, in the second year the same estimates were made with intervals of 2-3 months to check if the seasonal variations observed were not accidental. The study did not demonstrate seasonal variations in the mean energy intake of the group under study. However, the intake of fat appeared to be higher in the winter and spring than in the summer and autumn, whereas for the intake of mono- and di-saccharides the reverse seemed to be true. The intake of dietary fibre was higher in the autumn than in the summer, with intermediate values for winter and spring. Small seasonal fluctuations were observed in body weight and time spent on various physical activities. On the one hand, these fluctuations are too small to indicate physiological significance, on the other hand they are wide enough to be taken into account in the design of many longitudinal studies on the relation between diet and disease.

Adult↗

PubMed1999

Genetic structure, reproductive biology and ecology of isolated populations of asplenium csikii (Aspleniaceae, pteridophyta)

The potential for environmental heterogeneity to generate spatial structuring of genotypes in seed-plant populations that occupy patchy habitats has been demonstrated by several studies, but little is known about the population structure of pteridophytes occupying patchy environments. In this study we have examined the genetic structure of isolated populations of the rock fern Asplenium csikii, an ecological specialist, growing almost exclusively on perpendicular walls of natural rock outcrops. All genetic variation observed in this taxon was partitioned between localities; no allozyme variation was found within a site and each site was colonized by a single multilocus phenotype (MLP). In total, five different MLPs were recorded from the nine localities, with two MLPs present at more than one site. Previous examination of population structure and genetic diversity in another rock fern, A. ruta-muraria, showed that the genetic diversity increases through multiple colonization over time. However, we cannot find any such correlation for A. csikii. All populations are genetically uniform, despite the probably considerable age of the populations and sites. Earlier studies concluded that the ample production of wind-borne propagules would lead to multiple colonization of sites and that reproductive features, such as single-spore colonization and subsequent intragametophytic selfing, would lead to very little genetic structuring of fern populations. In contrast to this prediction, it appears that ecological specialization and the scarcity of the narrowly defined niche contribute strongly to the pronounced partitioning of genetic variability observed in populations of A. csikii.

Journal Article↗

PubMed1997

Topsoil (0-5 cm) composition in eight arctic catchments in northern Europe (Finland, Norway and Russia).

Frozen topsoil samples (0-5 cm) were collected during March/April 1994 in eight Arctic catchments in northern Europe (four in Russia, three in Finland, one in Norway), at different distances and in different wind directions from the emissions of the Russian mining, roasting and smelting industry on the Kola Peninsula. Between 14 and 25 sites were sampled in each of the eight catchments ranging in size from 12 to 35 km2. Results show that close to the smelters in Monchegorsk and Nikel, topsoil is clearly enriched in Ag, As, Bi, Cd, Co, Cr, Cu, Fe, Ni, Pb, Sb, Se, Te and V. Cu and Ni median contents in topsoils collected close to Monchegorsk are about 600 times higher than in the Finnish catchments. The effect of open-cast mining and waste dumps of alkaline rocks from the nephelinite industry near Kirovsk can be seen in the elevated contents of Al, Ba, K, La, Mn, Na, Sr, Ti, Y and Zn in topsoil collected in a nearby catchment. For many elements, however, variations observed in single catchments are as great as the total regional variation. Several elements (e.g. Cd, Hg, Cu, Ni, Pb, S, Zn) show strong positive correlation between the organic content of the sample and the element content observed. Thus it is necessary to determine the organic content of the samples and correct the element levels when using depth-related soil samples (here, the 0-5 cm topsoil layer) for regional mapping.

Journal Article↗

PubMed1978

Kinetics of digoxin stability in aqueous solution.

Digoxin hydrolysis was studied as a function of pH. Conversion of digoxin to digoxigenin was followed by high-pressure liquid chromatography and shown to proceed by the initial loss of one, two, or three sugars. The hydrolysis rate was directly proportional to parent drug concentration and hydrogen-ion activity. The individual hydrolysis rate constants of digoxin, digoxigenin bisdigitoxoside, and digoxigenin monodigitoxoside were determined by a simplex fitting procedure. Data are presented suggesting that at least some variation in the bioavailability of orally administered digoxin arises from observed variations in gastric pH; these variations influence the extent to which hydrolysis occurs and, thus, modify the composition of digoxin species available for absorption.

Chemical Phenomena↗

PubMed2003

Overcoming technical variation and biological variation in quantitative proteomics.

Quantitative proteomics investigates physiology at the molecular level by measuring relative differences in protein expression between samples under different experimental conditions. A major obstacle to reliably determining quantitative changes in protein expression is to overcome error imposed by technical variation and biological variation. In drug discovery and development the issue of biological variation often rises in concordance with the developmental stage of research, spanning from in vitro assays to clinical trials. In this paper we present case studies to raise awareness to the issues of technical variation and biological variation and the impact this places on applying quantitative proteomics. We defined the degree of technical variation from the process of two-dimensional electrophoresis as 20-30% coefficient of variation. On the other hand, biological variation observed experiment-to-experiment showed a broader degree of variation depending upon the sample type. This was demonstrated with case studies where variation was monitored across experiments with bacteria, established cell lines, primary cultures, and with drug treated human subjects. We discuss technical variation and biological variation as key factors to consider during experimental design, and offer insight into preparing experiments that overcome this challenge to provide statistically significant outcomes for conducting quantitative proteomic research.

Animals↗

PubMed1991

The use of national sample surveys for nutritional surveillance: lessons from Malawi's National Sample Survey of Agriculture.

National sample surveys, containing measurements of the weights and heights of children along with other socioeconomic modules, represent one of the important sources of information for nutritional surveillance. The potential uses of such information are political sensitization, targeting by geographic area, targeting by socioeconomic group, and identifying the most promising intervention options according to the presumed causes of malnutrition. The latter two applications depend upon the ability to detect stable associations between nutritional status and socioeconomic factors. This paper examines the extent to which these planning applications are affected by variation in the ecology of malnutrition across different segments of society, using Malawi's National Sample Survey of Agriculture (NSSA). The NSSA is nationally representative of Malawi's smallholder sector and contains information on anthropometrics of underfives and various socioeconomic characteristics of their households. This analysis is based upon 3000 households containing at least one underfive, with one child per household being selected for analysis. Height-for-age Z-scores (HAZ) are calculated using WHO standards, and analyzed using analysis of variance (ANOVA). Variation in nutritional ecology is investigated by examining statistical interactions among socioeconomic variables as they relate to HAZ and by comparing ANOVA models constructed within several sample strata. These strata are defined according to geographic region, size of cultivated area, child's sex, child's age and, for a subsample, ethnic/religious identification. The results demonstrate that significant two-way interactions exist between region, cultivated area, household labor availability and age of the child. For the total sample HAZ declines with increasing cultivated area among young children (less than 24 months) but improves with increasing cultivated area among older children (greater than or equal to 24 months). The overall trend for young children is region-specific, however, such that no generalizations can be made concerning the effects of region and cultivated area without taking the other factor and child's age into account. Similarly, cultivated area interacts with household labor availability among young children, such that more labor is associated with lower HAZ on plots less than 0.7 ha, but more labor is associated with higher HAZ on plots above 1.5 ha. The existence of variation in nutritional ecology is further borne out by the observed variation in multivariable ANOVA models constructed within various sample strata. It is concluded that significant variation in nutritional ecology does exist between various segments of society. This limits the usefulness of national sample surveys for selecting intervention options and for targeting interventions according to socioeconomic characteristics.

Age Factors↗

PubMed2004

Seasonal variation in morbidity and mortality related to atrial fibrillation.

OBJECTIVE: To determine whether there is seasonal variation in hospitalisations and deaths due to atrial fibrillation (AF) and to examine possible contributors to such variability. METHODS: We used the linked Scottish Morbidity Record scheme, which provides individualised morbidity and mortality data for the entire Scottish population. RESULTS: Between 1990 and 1996, there were a total of 33,582 male and 34,463 female hospitalisations related to AF. Significantly more admissions occurred in winter compared to summer (P<0.0001). In women, the peak number of admissions (106 per day) occurred in December (12% more than average) and the lowest number (89) in June (6% less than average). The respective figures for men were 10% more (101), 2% less (90). In both sexes, the greatest variation occurred in those aged >85 years-peak winter rates being 35-39% higher than average. A similar phenomenon was evident in relation to mortality in these patients. The average number of men who died during December was 22% higher, and in August 12% lower, than average, P<0.001. In women, the equivalent figures were 28% higher (December) and 14% lower (August), P<0.001. The winter peak of AF admissions did not, however, coincide with the lowest temperatures, and other factors such as seasonal variation in respiratory infection, may account for the monthly variation observed in hospitalisations for AF. CONCLUSIONS: There is substantial seasonal variation in AF hospitalisations and deaths, particularly in the elderly.

Age Distribution↗

PubMed2002

Critical Eotvos numbers for buoyancy-induced oil drop detachment based on shape analysis.

Critical values of the Eotvos number, which is half the Bond number, above which buoyancy induced drop detachment occurs, are estimated based on force balance equations available in the literature [Colloids Surf. A: Physicochem. Eng. Aspects 178 (2001) 249]. Since there are two significantly different expressions of the capillary retention force responsible for holding oil drops on a solid substrate in an aqueous phase, the critical dimensionless number is estimated with these two distinct equations. The differential equation defining the drop shape, with the constraints of the drop volume and the 'pinned' or 'receding' contact line, is numerically solved. The equilibrium drop shapes predicted are shown to match the experimentally observed variations in drop shape. From the numerical solution, it is observed that for interfacial tension (IFT) values lower than a certain limit for a given drop size, no numerically estimated drop shape can fulfil the drop volume constraint. Similarly, for the dimensionless number above a critical value, no shape can meet all the constraints. These critical Eotvos numbers are estimated, based on the above numerical approach, for initial contact angles measured in oil varying from 20 degrees to 90 degrees. It is found that the critical Eotvos numbers estimated from the numerical shape analysis are between the critical values estimated from the two force-balance equations. Near 90 degrees, the critical values estimated from the drop shape analysis matches the values from one of the force balance estimates, but merges with the critical values of the dimensionless number, estimated from the other force balance model near 10 degrees. From this analysis, it appears that a combination of the two equations for the capillary retention force is required, with one dominating when the contact angles are high, while the other applies for low values of the contact angle.

Algorithms↗

PubMed2002

Continuum secondary structure captures protein flexibility.

The DSSP program assigns protein secondary structure to one of eight states. This discrete assignment cannot describe the continuum of thermal fluctuations. Hence, a continuous assignment is proposed. Technically, the continuum results from averaging over ten discrete DSSP assignments with different hydrogen bond thresholds. The final continuous assignment for a single NMR model successfully reflected the structural variations observed between all NMR models in the ensemble. The structural variations between NMR models were verified to correlate with thermal motion; these variations were captured by the continuous assignments. Because the continuous assignment reproduces the structural variation between many NMR models from one single model, functionally important variation can be extracted from a single X-ray structure. Thus, continuous assignments of secondary structure may affect future protein structure analysis, comparison, and prediction.

Computer Systems↗

PubMed2000

Adaptable multivariate calibration models for spectral applications

Multivariate calibration techniques have been used in a wide variety of spectroscopic situations. In many of these situations, spectral variation can be partitioned into separate classes. For example, suppose that multiple spectra are obtained from each of a number of different objects wherein the level of the analyte of interest varies within each object over time. In such situations, the total spectral variation observed across all measurements has two distinct general sources of variation: intraobject and interobject. One might want to develop a global multivariate calibration model that predicts the analyte of interest accurately both within and across objects, including new objects not involved in developing the calibration model. However, this goal might be hard to realize if the interobject spectral variation is complex and difficult to model. If the intraobject spectral variation is consistent across objects, an effective alternative approach might be to develop a generic intraobject model that can be adapted to each object separately. This paper contains recommendations for experimental protocols and data analysis in such situations. The approach is illustrated with an example involving the noninvasive measurement of glucose using near-infrared reflectance spectroscopy. Extensions to calibration maintenance and calibration transfer are discussed.

Journal Article↗

PubMed2001

Seasonal and population variation in flavonoid and alliarinoside content of Alliaria petiolata.

Pieris napi oleracea, an indigenous butterfly in North America, lays eggs on Alliaria petiolata, an invasive weed that was introduced from Europe. However, larval development on plants from different sources varies considerably. A. petiolata is a compulsive biennial, and its foliage is rich in apigenin flavonoids. We compared the chemistry of different vegetative forms from different populations in the vicinity of Ithaca, NY throughout the year. Significant differences occurred in the number of apigenin derivatives in different populations and vegetative forms, and seasonal variations in the amounts of these compounds were found. We have previously isolated two major compounds, alliarinoside [(2Z)-4-(beta-D-glucopyranosyloxy)-2-butenenitrile] (1) and isovitexin-6-O"-beta-D-glucoside (3), which negatively affect development of P. napi oleracea larvae. Comparative analyses of these compounds in two populations throughout the year showed that their concentrations reached maxima twice annually. Foliage is almost devoid of flavonoids in June-July. Thus, variation in the chemistry of the plant may account for observed variation in development rates and survival of the larvae. Several apigenin compounds were isolated and identified by spectral studies.

Animals↗