[Studies on the heterogeneity quotient of the sieve irradiation. Heterogeneity quotient of some kinds of sieves and their biological effect].
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Aluminum↗
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Results for “Heterogeneity”
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An antibody to a subpopulation of neutrophils demonstrates antigenic heterogeneity which correlates with response heterogeneity.
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Antibodies, Monoclonal↗
[Lipid heterogeneity in biological membranes. Biophysical approaches to function associated with this heterogeneity].
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Biophysical Phenomena↗
Nondiscrete heterogeneity of human blood cells. 1. Volume heterogeneity as a reflection of the quality of erythropoiesis.
Coefficient of variation (C.V.) of red cell volume is inversely proportional to red cell mass in hemoglobinopathies and thalassemias. Even a subject with markedly reduced red cell survival and abnormal hemoglobin had a normal C.V. associated with normal hemoglobin level. In contrast are patients with nutritional deficiency, who have increased C.V. whether or not there is anemia, and patients with hypoplastic anemia, who have normal to near-normal C.V. independent of anemia.
Analysis of Variance↗
Molecular heterogeneity: a clinical dilemma. Clinical heterogeneity: a molecular dilemma.
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Collagen↗
An examination of the measurement of flow heterogeneity in striated muscle.
This review leads us to a number of conclusions and suggestions for further study. First, we find wide differences in the meaning of flow heterogeneity, arising as a result of the different methods used. These differences will have to be reconciled to form a comprehensive view of the role of heterogeneity in determining vascular function. Second, in the future, the meaning of heterogeneity must be clearly defined and related to a particular microvascular component, and it is imperative that the differences in scale of heterogeneity be appreciated when comparing data from various laboratories. These heterogeneities have different implications for function, and failure to distinguish among them leads to confusion. Third, the degree to which perfusion heterogeneity is regulated in the microcirculation remains in doubt. Reports of variations in flow heterogeneity in response to physiological stimuli are for the most part based on highly questionable indirect methods. Fourth, the heterogeneity that can be demonstrated at the capillary level within striated muscle does not appear to be large relative to the capacity for the microcirculation to exchange most diffusible solutes. Thus, the inferences regarding heterogeneity, as evidenced by diffusible indicators, are likely to be the result of different preparations, damage to the preparations, or perhaps large-scale heterogeneities in the tissue. An alternate possibility would be that the heterogeneity occurs at the microvascular level but reflects some other aspect of microcirculatory function, such as length or hematocrit heterogeneities, but not flow heterogeneities. Fifth, flow heterogeneity within microvessels implies important consequences for capillary exchange and tissue oxygenation. Heterogeneities of velocity of a magnitude comparable to those observed by direct visualization of microcirculation can clearly produce reductions in oxygen supply to small tissue regions of a degree that may limit oxygen delivery, and thereby, tissue function. Sixth, flow heterogeneity may also influence capillary hematocrit and/or red cell spacing by producing cell separation at bifurcations and a resultant reduction in mean capillary tube hematocrit. There is as yet no agreement on why and how these hematocrits influence tissue oxygenation and function. Although several hypotheses are advanced to explain the distribution of blood flow and red cells within microcirculation, each lacks a critical experimental test at present.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Validation of Monte Carlo dose calculations near 125I sources in the presence of bounded heterogeneities.
PURPOSE: Dose distributions around low energy (< 60 keV) brachytherapy sources, such as 125I, are known to be very sensitive to changes in tissue composition. Available 125I dosimetry data describe the effects of replacing the entire water medium by heterogeneous material. This work extends our knowledge of tissue heterogeneity effects to the domain of bounded tissue heterogeneities, simulating clinical situations. Our goals are three-fold: (a) to experimentally characterize the variation of dose rate as a function of location and dimensions of the heterogeneity, (b) to confirm the accuracy of Monte Carlo dose calculation methods in the presence of bounded tissue heterogeneities, and (c) to use the Monte Carlo method to characterize the dependence of heterogeneity correction factors (HCF) on the irradiation geometry. METHODS AND MATERIALS: Thermoluminescent dosimeters (TLD) were used to measure the deviations from the homogeneous dose distribution of an 125I seed due to cylindrical tissue heterogeneities. A solid water phantom was machined accurately to accommodate the long axis of the heterogeneous cylinder in the transverse plane of a 125I source. Profiles were obtained perpendicular to and along the cylinder axis, in the region downstream of the heterogeneity. Measurements were repeated at the corresponding points in homogeneous solid water. The measured heterogeneity correction factor (HCF) was defined as the ratio of the detector reading in the heterogeneous medium to that in the homogeneous medium at that point. The same ratio was simulated by a Monte Carlo photon transport (MCPT) code, using accurate modeling of the source, phantom, and detector geometry. In addition, Monte Carlo-based parametric studies were performed to identify the dependence of HCF on heterogeneity dimensions and distance from the source. RESULTS: Measured and calculated HCFs reveal excellent agreement (< or = 5% average) over a wide range of materials and geometries. HCFs downstream of 20 mm diameter by 10 mm thick hard bone cylinders vary from 0.12 to 0.30 with respect to distance, while for an inner bone cylinder of the same dimension, it varies from 0.72 to 0.83. For 6 mm diameter by 10 mm thick hard bone and inner bone cylinders, HCF varies 0.27-0.58 and 0.77-0.88, respectively. For lucite, fat, and air, the dependence of HCF on the 3D irradiation geometry was much less pronounced. CONCLUSION: Monte Carlo simulation is a powerful, convenient, and accurate tool for investigating the long neglected area of tissue composition heterogeneity corrections. Simple one dimensional dose calculation models that depend only on the heterogeneity thickness cannot accurately characterize 125I dose distributions in the presence of bone-like heterogeneities.
Iodine Radioisotopes↗
Scale-dependent interaction of fire and grazing on community heterogeneity in tallgrass prairie.
Natural disturbances affect spatial and temporal heterogeneity in plant communities, but effects vary depending on type of disturbance and scale of analysis. In this study, we examined the effects of fire frequency (1-, 4-, and 20-yr intervals) and grazing by bison on spatial and temporal heterogeneity in species composition in tallgrass prairie plant communities. Compositional heterogeneity was estimated at 10-, 50-, and 200-m2 scales. For each measurement scale, we used the average Euclidean Distance (ED) between samples within a year (2000) to measure spatial heterogeneity and between all time steps (1993-2000) for each sample to measure temporal heterogeneity. The main effects of fire and grazing were scale independent. Spatial and temporal heterogeneity were lowest on annually burned sites and highest on infrequently burned (20-yr) sites at all scales. Grazing reduced spatial heterogeneity and increased temporal heterogeneity at all scales. The rate of community change over time decreased as fire frequency increased at all scales, whereas grazing had no effect on rate of community change over time at any spatial scale. The interactive effects of fire and grazing on spatial and temporal heterogeneity differed with scale. At the 10-m2 scale, grazing increased spatial heterogeneity in annually burned grassland but decreased heterogeneity in less frequently burned areas. At the 50-m2 scale, grazing decreased spatial heterogeneity on 4-yr burns but had no effect at other fire frequencies. At the 10-m scale, grazing increased temporal heterogeneity only on 1- and 20-yr burn sites. Our results show that the individual effects of fire and grazing on spatial and temporal heterogeneity in mesic prairie are scale independent, but the interactive effects of these disturbances on community heterogeneity change with scale of measurement. These patterns reflect the homogenizing impact of fire at all spatial scales, and the different frequency, intensity, and scale of patch grazing by bison in frequently burned vs. infrequently burned areas.
Animals↗
Modeling blood flow heterogeneity.
It has been known for some time that regional blood flows within an organ are not uniform. Useful measures of heterogeneity of regional blood flows are the standard deviation and coefficient of variation or relative dispersion of the probability density function (PDF) of regional flows obtained from the regional concentrations of tracers that are deposited in proportion to blood flow. When a mathematical model is used to analyze dilution curves after tracer solute administration, for many solutes it is important to account for flow heterogeneity and the wide range of transit times through multiple pathways in parallel. Failure to do so leads to bias in the estimates of volumes of distribution and membrane conductances. Since in practice the number of paths used should be relatively small, the analysis is sensitive to the choice of the individual elements used to approximate the distribution of flows or transit times. Presented here is a method for modeling heterogeneous flow through an organ using a scheme that covers both the high flow and long transit time extremes of the flow distribution. With this method, numerical experiments are performed to determine the errors made in estimating parameters when flow heterogeneity is ignored, in both the absence and presence of noise. The magnitude of the errors in the estimates depends upon the system parameters, the amount of flow heterogeneity present, and whether the shape of the input function is known. In some cases, some parameters may be estimated to within 10% when heterogeneity is ignored (homogeneous model), but errors of 15-20% may result, even when the level of heterogeneity is modest. In repeated trials in the presence of 5% noise, the mean of the estimates was always closer to the true value with the heterogeneous model than when heterogeneity was ignored, but the distributions of the estimates from the homogeneous and heterogeneous models overlapped for some parameters when outflow dilution curves were analyzed. The separation between the distributions was further reduced when tissue content curves were analyzed. It is concluded that multipath models accounting for flow heterogeneity are a vehicle for assessing the effects of flow heterogeneity under the conditions applicable to specific laboratory protocols, that efforts should be made to assess the actual level of flow heterogeneity in the organ being studied, and that the errors in parameter estimates are generally smaller when the input function is known rather than estimated by deconvolution.
Algorithms↗
Diagnostic and prognostic significance of genetic regional heterogeneity in meningiomas.
We analyzed the frequency and regional distribution of cells with genetic abnormalities of chromosomes 1, 14, and 22 in meningiomas. This data was evaluated for correlation to the clinical outcome of the patients. Eight defined areas of each of 77 paraffin-embedded meningioma samples (59 grade I, 13 grade II, and 5 grade III) were analyzed by fluorescent in situ hybridization using bacterial artificial chromosome probes localized to chromosomes 1p36.32, 1q25.3, 14q13.3, 14q32.12, 22q11.2, and 22q12.1-3. Chromosome deletion was considered to be regionally heterogeneous if 7 regions showed cells with chromosome deletions. Deletion of 1p occurred in 35% of the grade I tumors. Distribution of cells with 1p deletion was regionally heterogeneous in 25% and homogeneous in 10% of grade I tumors. Distribution of cells with deletion of 1p was regionally heterogeneous in 23% and homogeneous in 69% of the grade II tumors. All grade III meningiomas had homogeneous distribution of cells with deletion of chromosome 1p. Distribution of cells with deletion of 14q was regionally heterogeneous in 27% and homogeneous in 2% of the grade I meningiomas, heterogeneous in 31% and homogeneous in 62% of the grade II tumors, and heterogeneous in 40% and homogeneous in 60% of the grade III meningiomas. Distribution of cells with deletion of 22q was regionally heterogeneous in 15% and homogeneous in 3% of the grade I tumors, heterogeneous in 15% and homogeneous in 31% of grade II tumors, and homogeneous in 20% of the grade III meningiomas. Distribution of cells with trisomy 22q was regionally heterogeneous in 10% of grade I tumors, heterogeneous in 23% of grade II, and homogeneous in 80% of grade III meningiomas. The proportion of patients with a deletion of 22q (either homogeneous or heterogeneous) who had recurrence was greater than the proportion of those without 22q deletion who had recurrence, and deletion of 22q was significantly associated with radiologically detected recurrence (P < 0.05). We conclude that the appearance of chromosomal aberrations in different areas of the tumor demonstrates the importance of regional heterogeneity in the biological behavior of meningiomas.
Adolescent↗
Perfusion heterogeneity in human skeletal muscle: fractal analysis of PET data.
Muscle blood flow has been shown to be heterogeneous at the voxel by voxel level in positron emission tomography (PET) studies using oxygen-15 labelled water. However, the limited spatial resolution of the imaging device does not allow direct measurement of true vascular flow heterogeneity. Fractal dimension (D) obtained by fractal analysis describes the relationship between the relative dispersion and the size of the region studied, and has been used for the assessment of perfusion heterogeneity in microvascular units. This study was undertaken to evaluate fractal characteristics of PET perfusion data and to estimate perfusion heterogeneity in microvascular units. Skeletal muscle blood flow was measured in healthy subjects using [15O]water PET and the fractal characteristics of blood flow in resting and exercising skeletal muscle were analysed. The perfusion heterogeneity in microvascular units was estimated using the measured heterogeneity (relative dispersion, RD = SD/mean) and D values. Heterogeneity due to methodological factors was estimated with phantoms and subtracted from the flow data. The number of aggregated voxels was inversely correlated with RD both in phantoms (Pearson r = -0.96-0.97) and in muscle (Pearson r = -0.94) when both parameters were expressed using a logarithmic scale. Fractal dimension was similar between exercising (1.13) and resting (1.14) muscles and significantly lower than the values in the phantoms with different activity levels (1.27-1.29). Measured flow heterogeneity values were 20% +/- 6% (exercise) and 27% +/- 5% (rest, P < 0.001), whereas estimated flow heterogeneity values in microvascular units (1 mm3) were 35% +/- 14% (exercise) and 49% +/- 14% (rest, P < 0.01). In conclusion, these results show that it is feasible to apply fractal analysis to PET perfusion data. When microvascular flow heterogeneity is estimated using fractals, perfusion appears to be more heterogeneous in microvascular units than when obtained by routine spatial analysis of PET data. Analysis of flow heterogeneity using PET and fractals could provide new insight into physiological conditions and diseases associated with changes in peripheral vascular function.
Adult↗
Intratumoral nuclear morphologic heterogeneity in prostate cancer.
OBJECTIVES: Tumor heterogeneity can be measured by quantifying variance of nuclear characteristics by image analysis. Heterogeneity of cell nuclear features correlated with increased local progression in prostate cancer. In the present study, the influence of tumor heterogeneity on prostate-specific antigen (PSA) recurrence after radical retropubic prostatectomy was analyzed and tumor heterogeneity was compared in patients with and without neoadjuvant hormonal therapy. METHODS: Retrospectively, radical prostatectomy material of 44 patients without and 12 patients with neoadjuvant hormonal treatment with a postoperative follow-up of at least 4 years was studied. Each prostatectomy specimen was systematically embedded in paraffin, and each tumor area within the prostate was marked and analyzed by an image analysis system for 32 nuclear features comprising nuclear shape, size, DNA content, and chromatin pattern. Several clinical features were available: preoperative serum PSA, hemoglobin concentration, Karnofsky score, tumor stage, and Gleason score. RESULTS: Increased tumor heterogeneity, as expressed by differences in karyometric values between tumor areas in nuclear shape and chromatin pattern within the tumor, was significantly correlated with earlier PSA recurrence rate. As compared with nonpretreated patients, hormonally pretreated specimens showed smaller and less heterogeneous tumors. In particular, chromatin pattern heterogeneity was decreased in patients who underwent preoperative hormonal treatment compared with patients who were not pretreated. However, decreased heterogeneity was accompanied by a higher percentage of aneuploid areas per tumor in the pretreated patients. Cox regression analysis showed that karyometric determination of nuclear shape heterogeneity in combination with preoperative PSA level could predict time to PSA recurrence after radical prostatectomy in patients without hormonal pretreatment. CONCLUSIONS: Increase in karyometric tumor heterogeneity in nuclear shape and chromatin pattern was correlated with a shorter PSA recurrence-free interval after radical prostatectomy. Preoperative PSA and karyometric tumor heterogeneity were the best predictors of PSA recurrence in a multivariate analysis. Intratumoral heterogeneity was decreased in patients with prostate cancer who underwent neoadjuvant hormonal therapy.
Adult↗
Intratumour heterogeneity in the uptake of macromolecular therapeutic agents in human melanoma xenografts.
Intratumour heterogeneity in the uptake of blood-borne technetium-labelled human serum albumin ((99m)Tc-HSA) was studied in human melanoma xenografts in an attempt to identify transport barriers leading to inadequate and heterogeneous uptake of macromolecular therapeutic agents in tumours. The Bioscope imaging system, which can detect the distribution of (99m)Tc in 10-microm-thick tissue sections with a spatial resolution of just above 50 microm, was used to image the (99m)Tc-HSA uptake. Xenografted tumours of four human melanoma cell lines were included in the study. Significant intratumour heterogeneity in the uptake of (99m)Tc-HSA was detected. The heterogeneity had two distinctly different components, one random and one radial component. The uptake was lowest in the centre of the tumours and increased towards the tumour periphery. This radial heterogeneity was superimposed by a random heterogeneity, that is, spots with high uptake colocalised with spots with high vascular density and regions without significant uptake colocalised with necrotic regions. The magnitude of the heterogeneity did not change significantly with time after the administration of (99m)Tc-HSA. The tumours showed a random and a radial heterogeneity in blood perfusion similar to that in the uptake of (99m)Tc-HSA. The observations reported here suggest that the intratumour heterogeneity in the distribution of (99m)Tc-HSA was initiated primarily because of heterogeneity in the supply of (99m)Tc-HSA through the microvasculature, and that the presence of severe transport barriers in the tumour interstitium prevented significant equalisation of the initial heterogeneity with time. Consequently, strategies for improving the delivery of macromolecular therapeutic agents to tumours should focus on increasing the tumour blood perfusion to increase the total uptake and improving the diffusion conditions in the tumour interstitium to diminish the heterogeneity in the uptake.
Animals↗
[Spatial heterogeneity and forest regeneration].
The research on spatial heterogeneity is meaningful for forest regeneration dynamics, which is a critical part in the forest ecosystem dynamics. Traditionally, forestry scientists are mainly concentrated their attention to the studies on the process of regeneration. However forests are spatiotemporal heterogeneous. In regeneration, there exists an ecological dynamic process at temporal scale, but also a heterogeneous pattern at spatial scale. Almost of the factors influencing forest regeneration, including both botic and abotic environment, both natural and human disturbances, and both characteristics of tree species and response of tree species to different disturbance agents, are spatially heterogeneous. Discussion on spatial heterogeneity and its effect on regeneration is indispensable for the understanding of the pattern, process and mechanism of forest regeneration. Main research contents and viewpoints of spatial heterogeneity in forest regeneration were summarised on the basis of available literature, and sources of spatial heterogeneity in the process of regeneration were analysed. The response of species to spatial heterogeneity, small-scale spatial heterogeneity and regeneration dynamics, spatial heterogeneity of lights in stand and regeneration pattern, and correlative relationships between the scales of soil heterogeneity and regeneration heterogeneity were reviewed.
Trees↗
Are physiological changes in capillary tube hematocrit related to alterations in capillary perfusion heterogeneity?
Average capillary tube hematocrit is hypothesized to be reduced below the mean systemic value as a result of heterogeneous distribution of blood flow among microvessels. Furthermore, capillary tube hematocrit changes with vasomotor state and these have been proposed to be due to concomitant changes in perfusion heterogeneity. We reasoned that if alterations in average capillary tube hematocrit were related to changes in perfusion heterogeneity, then mean capillary tube hematocrit should be inversely related both to the heterogeneity of capillary blood flows and to the heterogeneity of capillary hematocrit. These inferences were tested by comparing estimates of average capillary tube hematocrit (Ht) and the heterogeneities of capillary blood flow and Ht in vasoconstricted and vasodilated hamster tibialis anterior muscles. Ht was estimated from the number of red blood cells per unit capillary length (n/l); heterogeneity of capillary blood flow and heterogeneity of Ht were estimated by calculating the coefficient of variation of capillary red blood cell velocities (vrbc) and n/l, respectively. Average Ht varied with vasomotor state. However, there was no correlation between average Ht and the heterogeneity of vrbc, our index of capillary blood flow: in fact, the heterogeneity of vrbc was constant under all experimental conditions. The heterogeneity of Ht varied with vasomotor state, but not in inverse proportion to average Ht as was expected. From these observations we conclude that alterations in average capillary tube hematocrit are not due to concomitant alterations in perfusion heterogeneity.
Animals↗
Heterogeneity testing in meta-analysis of genome searches.
Genome searches for identifying susceptibility loci for the same complex disease often give inconclusive or inconsistent results. Genome Search Meta-analysis (GSMA) is an established non-parametric method to identify genetic regions that rank high on average in terms of linkage statistics (e.g., lod scores) across studies. Meta-analysis typically aims not only to obtain average estimates, but also to quantify heterogeneity. However, heterogeneity testing between studies included in GSMA has not been developed yet. Heterogeneity may be produced by differences in study designs, study populations, and chance, and the extent of heterogeneity might influence the conclusions of a meta-analysis. Here, we propose and explore metrics that indicate the extent of heterogeneity for specific loci in GSMA based on Monte Carlo permutation tests. We have also developed software that performs both the GSMA and the heterogeneity testing. To illustrate the concept, the proposed methodology was applied to published data from meta-analyses of rheumatoid arthritis (4 scans) and schizophrenia (20 scans). In the first meta-analysis, we identified 11 bins with statistically low heterogeneity and 8 with statistically high heterogeneity. The respective numbers were 9 and 6 for the schizophrenia meta-analysis. For rheumatoid arthritis, bins 6.2 (the HLA region that is a well-documented susceptibility locus for the disease) and 16.3 (16q12.2-q23.1) had both high average ranks and low between-study heterogeneity. For schizophrenia, this was seen for bin 3.2 (3p25.3-p22.1) and heterogeneity was still significantly low after adjusting for its high average rank. Concordance was high between the proposed metrics and between weighted and unweighted analyses. Data from genome searches should be synthesized and interpreted considering both average ranks and heterogeneity between studies.
Arthritis, Rheumatoid↗
Influence of physical and chemical heterogeneity shape on thin film rupture.
It is known that the breakup times for thin liquid films on solid surfaces can be substantially smaller if the surface is heterogeneous, either chemically or physically. In this paper we explore issues related to the effect of the shape of the physical and chemical heterogeneities on the breakup time and the thinning behavior. We consider two shapes, sinusoidal and exponential, for both physical and chemical gradients and compare the breakup times for these two different forms of gradients. Furthermore, the wavelength of the sinusoidal gradients and the length scale of the exponential gradients are varied and the effects of these on the breakup times and the film evolution are determined. For the sinusoidal gradients, we also obtain analytical results for shape evolution that are valid at short times and for small amplitude perturbation of the physical/chemical heterogeneities. The fastest growing modes are determined for spinodal breakup and also for both shapes (sinusoidal and exponential) of physical and chemical heterogeneities. The breakup times for the fastest growing modes from the linear and the nonlinear studies are compared for spinodal breakup and these results are also compared with those for both chemical and physical heterogeneities, of both sinusoidal and exponential shapes. Results show that the presence of heterogeneities, in general, accelerates the breakup of the film. In the linear regime, the growth rates are the same for the chemical and physical heterogeneities and spinodal breakup, and the effect of the heterogeneities is manifested as increased amplitude of initial perturbation. The effect of the chemical and physical heterogeneities dominate the film dynamics at early times, becoming less important at later times. The growth rates and equivalently the breakup times for the films on heterogeneous surfaces depend on the length scale over which physical/chemical gradients occur, and as the length scale approaches zero, which implies that the gradients become very steep, the effect of the heterogeneities on the breakup times becomes small.
Chemical Phenomena↗
A novel two-dimensional model for colloid transport in physically and geochemically heterogeneous porous media.
A two-dimensional model for colloid transport in geochemically and physically heterogeneous porous media is presented. The model considers patchwise geochemical heterogeneity, which is suitable to describe the chemical variability of many surficial aquifers with ferric oxyhydroxide-coated porous matrix, as well as spatial variability of hydraulic conductivity, which results in heterogeneous flow field. The model is comprised of a transient fluid flow equation, a transient colloid transport equation, and an equation for the dynamics of colloid deposition and release. Numerical simulations were carried out with the model to investigate the colloid transport behavior in layered and randomly heterogeneous porous media. Results demonstrate that physical and geochemical heterogeneities markedly affect the colloid transport behavior. Layered physical or geochemical heterogeneity can result in distinct preferential flow paths of colloidal particles. Furthermore, the combined effect of layered physical and geochemical heterogeneity may result in enhanced or reduced preferential flow of colloids. Random distribution of physical heterogeneity (hydraulic conductivity) results in a random flow field and an irregularly distributed colloid concentration profile in the porous medium. Contrary to random physical heterogeneity, the effect of random patchwise geochemical heterogeneity on colloid transport behavior is not significant. It is mostly the mean value of geochemical heterogeneity rather than its distribution that governs the colloid transport behavior.
Colloids↗