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PubMed2001

Qualitative and quantitative evaluation of six algorithms for correcting intensity nonuniformity effects.

The desire to correct intensity nonuniformity in magnetic resonance images has led to the proliferation of nonuniformity-correction (NUC) algorithms with different theoretical underpinnings. In order to provide end users with a rational basis for selecting a given algorithm for a specific neuroscientific application, we evaluated the performance of six NUC algorithms. We used simulated and real MRI data volumes, including six repeat scans of the same subject, in order to rank the accuracy, precision, and stability of the nonuniformity corrections. We also compared algorithms using data volumes from different subjects and different (1.5T and 3.0T) MRI scanners in order to relate differences in algorithmic performance to intersubject variability and/or differences in scanner performance. In phantom studies, the correlation of the extracted with the applied nonuniformity was highest in the transaxial (left-to-right) direction and lowest in the axial (top-to-bottom) direction. Two of the six algorithms demonstrated a high degree of stability, as measured by the iterative application of the algorithm to its corrected output. While none of the algorithms performed ideally under all circumstances, locally adaptive methods generally outperformed nonadaptive methods.

Algorithms↗
PubMed1985

The angiogenesis of micrencephalic rat brains caused by methylazoxymethanol acetate. II. Superficial and basal arterial system.

The angioarchitecture of the superficial and basal arterial system of the hypoplastic rat brain caused by the administration of the neurotoxin, methylazoxymethanol acetate (MAMAc), at the time of neuroblast migration was studied. Increased variation of the arterial branching of the basal main stem of arteries and local vessel changes were observed. The findings suggest a close relationship between vascular and neuronal development, showing a generalized disturbance and local adaptation of vasculature to the altered neuronal architecture of the corresponding hypoplastic areas.

Animals↗
PubMed1988

Relationship of transmural electrical parameters to the luminal Na concentration in the colon of the fowl (Gallus domesticus).

Electrical parameters: PD, resistance, Isc and amiloride-sensitive-Isc across the fowl colon (in vitro) change in response to the Na content of the diet. On a low-Na diet these changes appear to reflect increases in ion transport, especially amiloride-inhibitable Na transport. In vitro the magnitudes of the changes are related to the Na concentration in the luminal (mucosal) fluid and in birds on a low-Na diet peak at a concentration of about 12.5 mM. Such Na concentrations are similar to those in the colonic fluid of Na-deprived birds. Typical Michaelis-Menten kinetics do not appear to apply, possibly reflecting a local adaptation of the ion transport process in response to its external Na concentration.

Animals↗
PubMed1992

Oculokinetic perimetry compared with standard perimetric threshold testing.

To calibrate oculokinetic perimetry (OKP) as developed by Damato in terms of conventional perimetric threshold values, 33 eyes with either glaucoma or ocular hypertension were tested with a standard Humphrey Field Analyzer using the Central 30-2 test and twice with a 26-point OKP chart. The frequency of seeing of the OKP test spot was plotted against 30-2 thresholds. This showed a weak relation between the two tests. Subsequently eyes that were considered to have had poor fixation were omitted, but false positive and false negative results still occurred in 19 remaining eyes. To check whether Troxler's effect (local adaptation) might have caused false positives, 6 subjects were tested with OKP, controlling the fixation times. Increasing the fixation time from 'very short' to 2 and 5 seconds yielded more 'not seen' responses in OKP. False negative data were found to occur preferentially in border areas of visual defects. The average frequency of seeing curve over all data showed a 50% frequency of seeing for the OKP stimulus at a 14.6 dB equivalent conventional threshold value. The spreading of the curve was 7 dB (95% confidence interval 28 dB).

Adult↗
PubMed1994

Protein quality of weaning foods based on locally available cereal and pulse combination.

Locally available cereals and pulses such as rice (Oryza sativa), kangini (Setaria italica), sanwak (Echinochloa frumentacea), green gram (Vigna radiata) and jaggery were used to formulate three weaning foods. Cereal, pulse and jaggery were mixed in the ratio of 70:30:25. Roasting was the main processing technique used in the formulation of these weaning foods. The developed weaning foods had 5.06 to 5.68 g moisture, 10.28 to 13.71 g protein, 2.91 to 3.77 g ash, 1.08 to 1.87 g fat, 14.42 to 14.98 mg iron, 1.03 to 1.27 g crude fibre, and 357 to 374 Kcal. The weaning foods had a nutrient composition within the range prescribed by the Indian Standard Institute for processed weaning foods. The study indicated that the weaning foods obtained from locally available food stuffs have the potential of being produced locally, adaptable for household consumption and can be good substitute for commercial formulae.

Analysis of Variance↗
PubMed1995

Genetic variation in locomotor activity rhythm among populations of Leptopilina heterotoma (Hymenoptera: Eucoilidae), a larval parasitoid of Drosophila species.

The locomotor activity rhythm of Leptopilina heterotoma, a parasitoid insect of Drosophila larvae, was investigated under laboratory conditions. Under LD 12:12, the locomotor activity of females shows a clear rhythm which persists under continuous darkness (circadian rhythm). However, comparative study of five populations indicates that both the rate of activity and the profile of the rhythm vary according to the origin of females. The Mediterranean populations (Tunisia and Antibes) show two peaks of activity, at the beginning and at the end of the photophase, whereas more northern populations (Lyon and the Netherlands) are mostly active during the afternoon. Females originating from the area of Lyon have a very low level of activity. Reciprocal crosses (F1 hybrids and backcrosses) between the French and the Tunisian strains demonstrated the genetic basis of these variations and the biparental inheritance of the trait. This genetic variability is interpreted as a consequence of selective pressures and suggests a local adaptation of natural populations in host foraging behavior. The selective factors which could act on the daily organization of parasitoid behaviors are discussed.

Activity Cycles↗
PubMed1989

Digital contrast enhancement for online portal imaging.

Seven digital contrast enhancement algorithms were implemented and evaluated for application to images obtained with an online video portal imaging system. An objective quantitative comparison shows that superior contrast enhancement is obtained using histogram modification techniques. Additional tests made on an image of a humanoid phantom indicate that local (adaptive) histogram modification methods can produce a better contrast in detail than their global counterparts, if the original image is nonuniform in intensity.

Algorithms↗
PubMed1995

Computer-aided detection of clustered microcalcifications on digital mammograms.

A computer-aided diagnosis scheme to assist radiologists in detecting clustered microcalcifications from mammograms is being developed. Starting with a digital mammogram, the scheme consists of three steps. First, the image is filtered so that the signal-to-noise ratio of microcalcifications is increased by suppression of the normal background structure of the breast. Secondly, potential microcalcifications are extracted from the filtered image with a series of three different techniques: a global thresholding based on the grey-level histogram of the full filtered image, an erosion operator for eliminating very small signals, and a local adaptive grey-level thresholding. Thirdly, some false-positive signals are eliminated by means of a texture analysis technique, and a non-linear clustering algorithm is then used for grouping the remaining signals. With this method, the scheme can detect approximately 85% of true clusters, with an average of two false clusters detected per image.

Breast Diseases↗
PubMed1989

Evaluation of a commercial mammography image-enhancement system.

A commercial mammography image-enhancement system manufactured by Damon Corporation (Needham, MA) is evaluated. Using a dedicated computer, the system implements a real-time video local adaptive image processing algorithm based on the Wallis equation. Radiographs of a mammographic QA phantom (Nuclear Associates Model 76-001-4) containing five groups of simulated breast microcalcifications ranging in diameter from 0.12 to 0.35 mm were viewed by four investigators under three viewing conditions: on a light box with the unaided eye, on the image enhancer in magnified "bypass" (unenhanced) mode, and on the enhancer using all features for optimum enhancement. A mammogram was then overlaid on the radiographs, and the composite images were viewed under the same three conditions. Using the enhancer, as compared to using a light box alone, average increases of 1.4 and 1.1 microcalcifications per radiograph were observed for the phantom and phantom-with-mammogram radiographs, respectively. High-contrast resolution and spatial distortion were also measured.

Computers↗
PubMed2004

Agonistic onset during development differentiates wild house mouse males (Mus domesticus).

Wild house mouse populations have been suggested to locally adapt to varying dispersal regimes by expressing divergent aggressivity phenotypes. This conjecture implies, first, genetic polymorphism for dispersive strategies which is supported by the finding of heritable variation for male dispersal tendency in feral house mice. Secondly, aggressivity is assumed to translate into dispersal rates. This speculation is reinforced by experimental evidence showing that non-agonistic males display lower dispersal propensity than same-aged males that have established agonistic dominance. However, the actual ontogenetic behavioural pattern and its variability among populations remain unknown. Hence, in this study the timing of agonistic onset is quantified within laboratory-reared fraternal pairs, and compared between descendants from two different feral populations. Males from the two populations (G and Z) differed strongly in agonistic development, as Z fraternal pairs had a 50% risk of agonistic onset before 23.5+/-2.7 days of age, while this took 57.3+/-5.4 days in males from population G. This difference coincided with significant genetic differentiation between the males of the two populations as determined by 11 polymorphic microsatellite markers. Furthermore, in population G, males from agonistic and amicable fraternal pairs exhibited significant genetic differentiation. These results corroborate the supposition of genetic variability for dispersive strategies in house mice, and identify the ontogenetic timing of agonistic phenotype development as the potential basis for genetic differentiation. This opens a unique opportunity to study the genetic determination of a complex mammalian behavioural syndrome in a life history context, using a simple laboratory paradigm.

Animals↗
PubMed2002

Mitochondrial DNA variation and RAPD mark oleasters, olive and feral olive from Western and Eastern Mediterranean.

The study of genetic diversity within the olive-tree (cultivated and wild forms) may be useful to reveal agronomic traits in the wild germplasm and to try to understand the history of the olive-tree domestication. In this way, a study of nuclear and mitochondrial DNAs of cultivated and wild olives from two Corsican and Sardinian Mediterranean islands was performed using RAPD and RFLP markers. Our results show that most of the varieties and most of the oleasters were separated using the UPGMA dendrogram based on the Nei and Li similarity index. Most of oleasters carried either the MOM or MCK mitotype, characteristic of olives in the Western Mediterranean, whereas most of the varieties carried the ME1 mitotype, characteristic of olives in the East Mediterranean. The results indicate that the combination of mitotype and RAPD markers can be used as a powerful tool for differentiating two groups in the wild forms: the Western true oleasters and the feral forms. The true oleasters are characterized by a Western mitotype and a Western RAPD pattern. Feral forms originate either from varieties or from hybridisation between a variety and an oleaster. Consequently, as expected, some of them aggregated with the varieties from which they were derived. The other feral forms are clustered with the oleasters and were detected only by their mitotype determination. This study has also permitted us to differentiate two populations of cultivated olives in Corsica: one with close relationships with Italian varieties (influenced by the East) and one selected from local oleasters probably due to a better local adaptation than foreign varieties.

Journal Article↗
PubMed2003

Molecular mapping of QTLs for Fusarium head blight resistance in spring wheat. II. Resistance to fungal penetration and spread.

Fusarium head blight (FHB, scab) causes severe yield and quality losses, but the most serious concern is the mycotoxin contamination of cereal food and feed. The cultivation of resistant varieties may contribute to integrated control of this fungal disease. Breeding for FHB resistance by conventional selection is feasible, but tedious and expensive. The aim of this work was to detect QTLs for combined type I and type II resistance against FHB and estimate their effects in comparison to the QTLs identified previously for type II resistance. A population of 364, F1 derived doubled-haploid (DH) lines from the cross 'CM-82036' (resistant)/'Remus' (susceptible) was evaluated for components of FHB resistance during 2 years under field conditions. Plants were inoculated at anthesis with a conidial suspension of Fusarium graminearum or Fusarium culmorum. The crop was kept wet for 20 h after inoculation by mist-irrigation. Disease severity was assessed by visual scoring. Initial QTL analysis was performed on 239 randomly chosen DH lines and extended to 361 lines for putative QTL regions. Different marker types were applied, with an emphasis on PCR markers. Analysis of variance, as well as simple and composite interval mapping, revealed that two genomic regions were significantly associated with FHB resistance. The two QTLs on chromosomes 3B (Qfhs.ndsu-3BS) and 5A (Qfhs.ifa-5A) explained 29 and 20% of the phenotypic variance, respectively, for visual FHB severity. Qfhs.ndsu-3BS appeared to be associated mainly with resistance to fungal spread, and Qfhs.ifa-5A primarily with resistance to fungal penetration. Both QTL regions were tagged with flanking SSR markers. These results indicate that FHB resistance was under the control of two major QTLs operating together with unknown numbers of minor genes. Marker-assisted selection for these two major QTLs appears feasible and should accelerate the development of resistant and locally adapted wheat cultivars.

Analysis of Variance↗
PubMed2005

Domestication patterns in common bean (Phaseolus vulgaris L.) and the origin of the Mesoamerican and Andean cultivated races.

Chloroplast DNA polymorphisms were studied by PCR sequencing and PCR-restriction fragment length polymorphism in 165 accessions of domesticated landraces of common bean from Latin America and the USA, 23 accessions of weedy beans, and 134 accessions of wild beans covering the entire geographic range of wild Phaseolus vulgaris. Fourteen chloroplast haplotypes were identified in wild beans, only five of which occur also in domesticated beans. The chloroplast data agree with those obtained from analyses based on morphology and isozymes and with other DNA polymorphisms in supporting independent domestications of common bean in Mesoamerica and the Andean region and in demonstrating a founder effect associated with domestication in each region. Andean landraces have been classified into three different racial groups, but all share the same chloroplast haplotype. This suggests that common bean was domesticated once only in South America and that the races diverged post-domestication. The haplotype found in Andean domesticated beans is confined to the southern part of the range of wild beans, so Andean beans were probably domesticated somewhere within this area. Mesoamerican landraces have been classified into four racial groups. Our limited samples of Races Jalisco and Guatemala differ from the more widespread and commercially important Races Mesoamerica and Durango in types and/or frequencies of haplotypes. All four Mesoamerican races share their haplotypes with local wild beans in parts of their ranges. Independent domestications of at least some of the races in Mesoamerica and/or conversion of some locally adapted wild beans to cultigens by hybridization with introduced domesticated beans, followed by introgression of the "domestication syndrome" seem the most plausible explanations of the chloroplast and other molecular data.

Base Sequence↗
PubMed1998

Postural reorganization of weight-shifting in below-knee amputees during leg raising.

The position of the center of gravity (CG) is a reference value that is controlled by the nervous system during the performance of movements. In order to maintain equilibrium, leg movement is preceded by a shift of the CG towards the supporting side. This CG shift is initiated by an early displacement of the center of pressure (CP) towards the moving leg. This characteristic CP thrust partly results from the activity of a distal muscle in the leg to be moved: the gastrocnemius medialis (GM). The aim of this study was to determine how this weight-shifting is initiated when the distal muscles are missing, as in amputees, and to identify any change in the central command. Experiments were performed on ten subjects: five below-knee amputees with no pathology and five control subjects. While standing, the subjects were instructed to raise one leg laterally as fast as possible to an angle of 45 degrees and to maintain the final position. The same weight-shifting strategy was used by both groups, whereas local adaptations associated with the behavior occurred. When the GM is lacking, an early tensor-fasciae-latae (TFL) burst is observed just prior to and associated with the onset of the lateral CP change. This moving-leg abductor may be responsible for initiating the thrust at a proximal level when that leg is still on the ground. In addition, upon analyzing the lateral displacement of the CP, two modes of CP shift were detected. The first CP-shift mode has been previously described and the second mode (which we term here the pre-pushing mode) was used by both amputees and controls. The prepushing mode consisted of two thrusts: an early thrust onto the ground was exerted by the leg about to become the supporting leg followed by the previously described thrust exerted by the leg about to be raised. The early thrust, which could be exerted by either the sound or prosthetic leg, may have increased the efficiency of the second, classical thrust by initiating a swing.

Adult↗
PubMed2004

Respiratory and reproductive characteristics of eastern mosquitofish (Gambusia holbrooki) inhabiting a coal ash settling basin.

Coal fly ash and effluent from coal ash settling basins negatively affects metabolism and reproduction in a variety of organisms, including a number of fish species. Some species, most notably the eastern mosquitofish (Gambusia holbrooki), are known to maintain viable populations in areas contaminated by coal ash. While eastern mosquitofish are present in these systems, their degree of tolerance to coal ash has not been investigated using sublethal metrics of exposure. It is possible that eastern mosquitofish persist in habitats affected by coal ash, but experience significant costs such as changes in metabolism and fecundity. Thus, we investigated the effects of coal ash on standard metabolic rate and reproduction of eastern mosquitofish inhabiting a coal-ash contaminated settling basin. Standard metabolic rates of mosquitofish from the ash contaminated site and a reference site (mean O2 consumption = 0.286 mL/g x h +/- 0.007 and 0.291 +/- 0.008 mL/g x h, respectively) were not significantly different. Despite elevated contaminant concentrations in ash basin females (selenium, arsenic, copper, and cadmium) and their offspring (selenium), brood sizes and offspring viability did not differ between clutches collected from ash basin and reference site females. Our data provide further evidence of the high degree of tolerance of eastern mosquitofish to exposure to aquatic coal ash disposal generated by power plants. However, the basis for such tolerance to ash remains unclear. Further investigations are required to determine whether such tolerance is a result of species-specific characteristics or population characteristics due to local adaptation.

Animals↗
PubMed2005

Evaluating the effect of a wavelet enhancement method in characterization of simulated lesions embedded in dense breast parenchyma.

Presence of dense parenchyma in mammographic images masks lesions resulting in either missed detections or mischaracterizations, thus decreasing mammographic sensitivity and specificity. The aim of this study is evaluating the effect of a wavelet enhancement method on dense parenchyma for a lesion contour characterization task, using simulated lesions. The method is recently introduced, based on a two-stage process, locally adaptive denoising by soft-thresholding and enhancement by linear stretching. Sixty simulated low-contrast lesions of known image characteristics were generated and embedded in dense breast areas of normal mammographic images selected from the DDSM database. Evaluation was carried out by an observer performance comparative study between the processed and initial images. The task for four radiologists was to classify each simulated lesion with respect to contour sharpness/unsharpness. ROC analysis was performed. Combining radiologists' responses, values of the area under ROC curve (Az) were 0.93 (95% CI 0.89, 0.96) and 0.81 (CI 0.75, 0.86) for processed and initial images, respectively. This difference in Az values was statistically significant (Student's t-test, P<0.05), indicating the effectiveness of the enhancement method. The specific wavelet enhancement method should be tested for lesion contour characterization tasks in softcopy-based mammographic display environment using naturally occurring pathological lesions and normal cases.

Breast↗
PubMed2004

Local distribution and thermal ecology of two intertidal fishes.

Geographic variability in the physiological attributes of widely distributed species can be a result of phenotypic plasticity or can reflect evolutionary responses to a particular habitat. In the field, we assessed thermal variability in low and high intertidal pools and the distribution of resident fish species Scartichthys viridis and transitory Girella laevifrons along this vertical intertidal gradient at three localities along the Chilean coast: Antofagasta (the northernmost and warmest habitat), Carrizal Bajo (central coast) and Las Cruces (the southernmost and coldest habitat). In the laboratory, we evaluated the thermal sensitivity of fish captured from each locality. The response to temperature was estimated as the frequency of opercular movements and as thermal selectivity in a gradient; the former being a indirect indicator of energy costs in a particular environment and the latter revealing differential occupation of habitat. Seawater temperature in intertidal pools was greatest at Antofagasta, and within each site was greatest in high intertidal pools. The two intertidal fish species showed opposite patterns of local distribution, with S. viridis primarily inhabiting the lower sectors of the intertidal zone, and G. laevifrons occupying the higher sectors of the intertidal zone. This pattern was consistent for all three localities. Locality was found to be a very important factor determining the frequency of opercular movement and thermal selectivity of both S. viridis and G. laevifrons. Our results suggest that S. viridis and G. laevifrons respond according to: (1) the thermal history of the habitat from which they came, and (2) the immediate physical conditions of their habitat. These results suggest local adaptation rather than plasticity in thermoregulatory and energetic mechanisms.

Adaptation, Physiological↗
PubMed2006

Are bottlenecks associated with colonization? Genetic diversity and diapause variation of native and introduced Rhagoletis completa populations.

The success of invasive species appears to be a paradox: despite experiencing strong population bottlenecks, invasive species are able to successfully establish in new environments. We studied how the walnut husk fly, Rhagoletis completa, was able to successfully colonize California from the Midwestern United States, by examining genetic diversity and diapause variation of native and introduced fly populations. Climate plays an important role in the successful establishment of introduced insects, because insect diapause is highly dependent upon external climatic conditions. We examined if: (1) fly populations show signs of a population bottleneck, (2) native and introduced flies differ in diapause length when exposed to California and Midwestern climatic conditions, and (3) population genetic diversity is related to variation in diapause length. We assessed if fly diapause conformed more to a model of establishment by local adaptation or to a model of a highly plastic "general-purpose genotype". Our results indicate that only two populations close to the original introduced location showed signs of a population bottleneck, and native and introduced populations did not differ in genetic diversity. Genetic diversity increased in the northern introduced populations, suggesting that multiple introductions have occurred. Flies emerged about 2 weeks earlier under the Midwestern treatment than the California treatment, and introduced flies emerged about a week earlier than native flies. All flies emerged when walnuts are typically available in California. Although variance in diapause length differed between populations, it did not vary between populations or regions. Furthermore, genetic diversity was not associated with diapause variation. Therefore, multiple introductions and a "general-purpose genotype" appear to have facilitated the fly's invasion into California.

Animals↗