SEARCH · PubMed Health

Results for “trajectory”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,081 records · Page 60Linked to original sources

PubMed2002

Application of the photon average trajectories method to real-time reconstruction of tissue inhomogeneities in diffuse optical tomography of strongly scattering media.

The possibility of application of the photon average trajectories (PAT) method to real-time reconstruction of tissue inhomogeneities in diffuse optical tomography of strongly scattering media has been substantiated. By this method, the inverse problem is reduced to solution of the integral equation with integration along a conditional PAT. Such an approach allows the standard fast algebraic algorithms commonly used in projection computed tomography to be applied to diffuse optical image reconstruction. To demonstrate the capabilities of the PAT method, a numerical experiment on cross-sectional reconstruction of cylindrical strongly scattering objects with absorbing inhomogeneities has been done. Relative shadows caused by inhomogeneities are simulated via numerical solution of the non-stationary diffusion equation. To solve the inverse problem, the QR-factorization least-squares algorithm and the multiplicative algebraic reconstruction technique are used. The results are compared with those obtained by a well-known software package for temporal optical absorption and scattering tomography based on multiple solution of the diffusion equation. It is shown that the PAT method allows reconstruction of the optical structure of objects with comparable accuracy while saving reconstruction time considerably.

Algorithms↗

PubMed2004

Investigation of saddle trajectories for cardiac CT imaging in cone-beam geometry.

This paper investigates cone-beam tomography for a wide class of x-ray source trajectories called saddles. In particular, a mathematical analysis of the number of intersections between a saddle and an arbitrary plane is given. This analysis demonstrates that axially truncated cone-beam projections acquired along a saddle can be used for exact reconstruction at any point in a large volume. The reconstruction can be achieved either using a new algorithm presented herein or using a formula recently introduced by Katsevich (2003 Int. J. Math. Math. Sci. 21 1305-21). The shape of the reconstructed volume and the properties of saddles make saddles attractive for cardiac imaging. Three examples of saddles are presented with a discussion of implementation on devices similar to modern C-arm systems and multislice CT scanners. Reconstruction with one of these saddles has been tested using computer-simulated data, with and without truncation. The imaged phantom for the truncated data is a FORBILD head phantom (representing the heart) that has been modified and embedded inside the FORBILD thorax phantom. The non-truncated data were generated by excluding the thorax. The reconstructed images demonstrate the accuracy of the mathematical results.

Algorithms↗

PubMed2005

An FDK-like cone-beam SPECT reconstruction algorithm for non-uniform attenuated projections acquired using a circular trajectory.

In this paper, Novikov's inversion formula of the attenuated two-dimensional (2D) Radon transform is applied to the reconstruction of attenuated fan-beam projections acquired with equal detector spacing and of attenuated cone-beam projections acquired with a flat planar detector and circular trajectory. The derivation of the fan-beam algorithm is obtained by transformation from parallel-beam coordinates to fan-beam coordinates. The cone-beam reconstruction algorithm is an extension of the fan-beam reconstruction algorithm using Feldkamp-Davis-Kress's (FDK) method. Computer simulations indicate that the algorithm is efficient and is accurate in reconstructing slices close to the central slice of the cone-beam orbit plane. When the attenuation map is set to zero the implementation is equivalent to the FDK method. Reconstructed images are also shown for noise corrupted projections.

Algorithms↗

PubMed2005

Learning discrimination trajectories in EEG sensor space: application to inferring task difficulty.

We describe a spatio-temporal linear discriminator for single-trial classification of multi-channel electroencephalography (EEG). No prior information about the characteristics of the neural activity is required, i.e., the algorithm requires no knowledge about the timing and spatial distribution of the evoked responses. The algorithm finds a temporal delay/window onset time for each EEG channel and then spatially integrates the channels for each channel-specific onset time. The algorithm can be seen as learning discrimination trajectories defined within the space of EEG channels. We demonstrate the method for detecting auditory-evoked neural activity and discrimination of task difficulty in a complex visual-auditory environment.

Adult↗

PubMed1996

Three-dimensional fluid particle trajectories in the human larynx and trachea.

A computational fluid dynamics software package (FIDAP) has been employed to obtain three-dimensional flow data, which are used herein to calculate the trajectories of fluid particles. Our computations have demonstrated that the flow fields inside the larynx are very complex including eddies in the lumen and reverse motion along the surface. The effects of such flow fields will be to increase the residence times of entrained drug particles. Our computations have also demonstrated that the larynx has pronounced effects on the motion of air in the trachea.

Aerosols↗

PubMed2004

Early environment and child-to-adult growth trajectories in the 1958 British birth cohort.

BACKGROUND: Genetics and environmental conditions early in life are known to influence height. However, evidence is restricted to studies conducted at a specific age, and thus the effect on the entire growth trajectory has been neglected. OBJECTIVE: The objective was to determine when parental height and factors early in offspring life start to affect offspring height, when these variables have the strongest effect, and whether these variables persist to adulthood. DESIGN: Longitudinal data from the 1958 British birth cohort (all of whom were born during 1 wk in March 1958), including height measurements at 7, 11, 16, and 33 y of age, were analyzed by using multivariate multilevel response models. RESULTS: Parental height, birth weight, maternal smoking during pregnancy, breastfeeding, parental divorce, and socioeconomic factors were all significantly associated with childhood height, but their effects differed thereafter. Parental height and birth weight were most strongly associated with offspring height, and their effects persisted (adjusted increase in adult height: 2 cm for 1 SD of maternal or paternal height, or 1 kg of birth weight). Socioeconomic disadvantage (manual social class, large family size, and overcrowded households) was associated with substantial deficits of 2-3 cm (adjusted estimates) in height at 7 y. Catch-up growth was apparent but was insufficient to overcome the initial insult on growth; the adjusted deficit was as high as 1 cm in adulthood. CONCLUSIONS: Children from disadvantaged backgrounds have a delayed pattern of growth before the pubertal spurt, which is followed by catch-up growth. The health consequences of this pattern of growth need to be examined in future studies.

Adolescent↗

PubMed2006

The illness trajectory of elderly cancer patients across cultures: SIOG position paper.

BACKGROUND: Due to the aging of the population, cancer has become a health priority worldwide. While the number of elderly cancer patients is rapidly increasing, many barriers still exist to their effective management. Compared with their younger counterparts, the elderly are less likely to receive optimal medical, psychological and spiritual treatment provided in a culturally competent manner. DESIGN: The scanty literature on cultural competence in elderly cancer patients has been reviewed. Additional material has been selected based on the authors' clinical research in medical oncology and psycho-oncology, and on their scholarly work in anthropology and bioethics. RESULTS: The aging process is a synergistic product of biological, behavioral and social issues within a cultural context. Knowledge about how older people understand, perceive and experience their illness trajectory and make choices is essential to the planning and delivering of effective cancer care. CONCLUSION: This position paper of the SIOG Task Force on Cultural Competence in the Elderly creates awareness of the influence of culture in geriatric oncology. Negotiating cross-cultural issues in geriatric oncology helps managing possible conflicts between patients, families and physicians over differing health care values, beliefs, or practices. Possible areas of future scholarly investigation and clinical research are identified.

Aged↗

PubMed2026

FIERCE: reconstructing dynamic trajectories from the differentiation potency of single cells.

MOTIVATION: Since the introduction of single-cell RNA sequencing (scRNA-seq), numerous computational approaches have been developed to reconstruct dynamic cellular processes from static transcriptional profiles. These methods order cells along continuous trajectories by assessing their similarity in the gene-expression space. However, they rely on several assumptions, such as prior knowledge of the structure and directionality of the expected genealogy. These assumptions can limit their application to complex cellular systems with poorly understood developmental paths. RESULTS: To address this challenge, we introduce FIERCE (Framework for InfERence of the veloCity of Entropy), a novel computational pipeline designed to predict the changes in the differentiation potency of single cells during dynamic processes. Through a fully unsupervised approach, FIERCE enables the inference of cell lineages directly on the differentiation landscape of the biological system, thus eliminating the need for prior specification of developmental parameters. We demonstrate the efficacy of FIERCE by reconstructing three well-known mouse differentiation systems and by quantifying its accuracy on simulated data. AVAILABILITY AND IMPLEMENTATION: The FIERCE R package is available on GitHub at https://github.com/bicciatolab/FIERCE.

Cell Differentiation↗

PubMed2000

The structure of L-amino acid oxidase reveals the substrate trajectory into an enantiomerically conserved active site.

The structure of L-amino acid oxidase (LAAO) from Calloselasma rhodostoma has been determined to 2.0 A resolution in the presence of two ligands: citrate and o-aminobenzoate (AB). The protomer consists of three domains: an FAD-binding domain, a substrate-binding domain and a helical domain. The interface between the substrate-binding and helical domains forms a 25 A long funnel, which provides access to the active site. Three AB molecules are visible within the funnel of the LAAO-AB complex; their orientations suggest the trajectory of the substrate to the active site. The innermost AB molecule makes hydrogen bond contacts with the active site residues, Arg90 and Gly464, and the aromatic portion of the ligand is situated in a hydrophobic pocket. These contacts are proposed to mimic those of the natural substrate. Comparison of LAAO with the structure of mammalian D-amino acid oxidase reveals significant differences in their modes of substrate entry. Furthermore, a mirror-symmetrical relationship between the two substrate-binding sites is observed which facilitates enantiomeric selectivity while preserving a common arrangement of the atoms involved in catalysis.

Amino Acid Oxidoreductases↗

PubMed2026

Dissecting contributions of directional and balancing selection to trajectories of mitochondrial haplotype evolution in Drosophila melanogaster.

Emerging evidence suggests mtDNA haplotypes contribute to fitness variation and local adaptation, with directional thermal selection and negative frequency-dependent selection shaping haplotype diversity. However, their interplay remains unexplored. We conducted experimental evolution using Drosophila melanogaster populations from opposite ends of an Australian latitudinal cline (Melbourne and Townsville), exposing them to contrasting temperatures (17°C versus 27°C) and varying starting frequencies of two mtDNA haplotypes (A1 and B1) that occur at appreciable frequencies in these populations. We paired this with population genetic simulations to estimate selection and its influence on haplotype trajectories. Haplotype frequencies were influenced by interactions involving temperature, starting frequency, and nuclear genomic background (Melbourne, Townsville, or admixed). Although prior work predicted A1 should be favoured at the warmer temperature and B1 at the cooler temperature, A1 was generally favoured across both temperatures. Simulations supported directional selection in populations evolving at 17°C in the Melbourne background; otherwise dynamics were best explained by balancing selection shaped by negative frequency-dependent fitness effects. Patterns also varied across nuclear backgrounds, suggestive of mito-nuclear epistasis. These findings challenge a simple thermal adaptation model of mtDNA dynamics, suggesting that mtDNA evolution is shaped by interacting effects of temperature, frequency-dependence, nuclear background and experimental environment.

adaptation↗

PubMed1994

The alternative fitness sets which preserve allele trajectories: a general treatment.

A general solution is presented of the problem of specifying all alternative, generally frequency-dependent, (absolute) fitness sets which give rise to the same allele frequency changes and population dynamics as a given fitness set. The one- and two-locus cases are analyzed in detail and the method is then extended to the n-locus case. It is shown that if biological constraints can be used to specify the mean fitness of the population and the relative fitnesses of the heterozygotes, then the allele frequency trajectories determine a unique fitness set.

Alleles↗

PubMed1997

Altering developmental trajectories in mice by restricted index selection.

A restricted index selection experiment on mice was carried out for 1-4 generations on rate of early postnatal development (growth rate from birth to 10 days of age) vs. rate of development much later in ontogeny (growth rate from 28 to 56 days of age). Early rate of development (E) approximates hyperplasia (changes in cell number) and later rate (L) reflects hypertropy (changes in cell size). The selection criteria were as follows; E+LO was selected to increase early body weight gain while holding late body weight gain constant; E-LO was selected to decrease early body gain while holding late gain constant; EOL+ was selected to increase late gain holding early gain constant; and EOL- was selected to decrease late gain holding early gain constant. After 14 generations of selection, significant divergence among lines has occurred and the changes in the growth trajectories are very close to expectation. The genetic and developmental bases of complex traits are discussed as well as the concept of developmental homoplasy.

Animals↗

PubMed2000

Differential longevity in mouse stocks selected for early life growth trajectory.

Small body size is associated with superior longevity in several intraspecies comparisons, including dogs bred for specific forms of work, mice and rats fed diets low in calories, rats fed diets low in methionine, and mutant mice whose levels of growth hormone and thyroid hormone are atypically low. To further investigate the interactions among body size, genetic endowment, and longevity, we measured the life span of female mice selectively bred from Institute for Cancer Research stock for differences in rate of body weight gain. These mice were selected for differential rates of growth either early (0-10 days) or later (26-56 days) in the first 2 months of life. The data show a good correlation between the average weight of the stock and its mean longevity, with low body size associated, as predicted, with longer life span. Weight at 3, 6, and 12 months, and weight at peak body weight, are all significant predictors of longevity (among stocks) in univariate regressions; weight at 6 months has the strongest association in stepwise multiple regression. There is no significant correlation between the life span for the stock and the proportion of deaths attributable to neoplasia in this group of mice. The data provide support for the hypothesis that genetic factors that influence early life growth trajectories can have a strong influence on life span. These size-selected mice provide useful tools for analysis of the genetic factors that influence life history parameters, including maturation and aging rates.

Adenocarcinoma↗

PubMed2003

Trajectories of leg strength and gait speed among sedentary older adults: longitudinal pattern of dose response.

BACKGROUND: Current theory about how an older adult's leg strength influences walking speed is based primarily on nonlinear patterns of association observed in cross-sectional data. Compared with adults with normal or high levels of leg muscle strength, weak older adults are thought to have a greater capacity for functional change in response to changes in lower extremity strength. Longitudinal data, however, have not been applied to study this putative pattern of dose response. METHODS: Three repeated measures of leg strength, gait speed, and covariates were evaluated in a cohort of 134 sedentary, community-dwelling male and female participants (aged >64 years) of a randomized exercise intervention. Empirical Bayes methods were used to evaluate the association between trajectories of strength and gait speed during the course of the study. RESULTS: We observed a potentially clinically important, positive linear association between strength change and gait speed change. Each additional unit increase in the monthly rate of strength change increased the rate of gait speed change by 0.29 meters/minute/month (95% CI [confidence interval] = 0.03, 0.55 m/min/mo). Absolute change in walking velocity due to strength changes in the cohort ranged from a gain of approximately 15 m/min to a loss of approximately 13 m/min over the 9-month period (changes of -18% to +20% relative to a normal walking speed of 72 m/min). CONCLUSIONS: In this cohort, change in functional walking speed depended more on the rate of strength change observed than on the amount of muscle weakness present at baseline. These results have important implications for screening and intervention programs designed to change functional walking ability among sedentary older adults.

Aged↗

PubMed2005

Trajectories of cognitive decline and social relations.

We assessed conjoint trajectories of cognitive decline and social relations over 7 years on a representative sample of community-dwelling elderly persons. We analyzed data using repeated measurement models. Social integration, family ties, and engagement with family were associated with cognitive function at advanced ages, controlling for education and introducing depressive symptoms, functional limitations, and chronic conditions as intervening variables. Association of social integration, through participation in community activities, with change in cognitive decline was more significant at advanced ages. Having friends was significantly associated with change in cognitive function in women only. Our findings have important implications for clinical medicine and public health because associations of social relations with cognitive function suggests that they may help to maintain cognitive function in old age.

Activities of Daily Living↗

PubMed2006

Longitudinal trajectories in Guilford-Zimmerman temperament survey data: results from the Baltimore longitudinal study of aging.

We examined developmental trends in personality traits over a 42-year time period by using data from the Baltimore Longitudinal Study on Aging (N = 2,359; individuals aged 17-98), collected from 1958 to 2002. Hierarchical linear modeling analyses revealed cumulative mean-level changes averaging about 0.5 SD across adulthood. Scales related to extraversion showed distinct developmental patterns: General Activity declined from age 60 to 90; Restraint increased; Ascendance peaked around age 60; and Sociability declined slightly. Scales related to neuroticism showed curvilinear declines up to age 70 and increases thereafter. Scales related to agreeableness and openness changed little; Masculinity declined linearly. We found significant individual variability in change. Although intercepts differed, trajectories were similar for men and women. Attrition and death had no effect on slopes. This study highlights the use of lower order traits in providing a more nuanced picture of developmental change.

Adult↗

PubMed2002

Health and long-term care use trajectories of older disabled women.

PURPOSE: I examined health and long-term care use trajectories of a sample of chronically disabled older women eligible for both Medicare and Medicaid by exploring their use data in order to understand and anticipate the increasing demand on the health and long-term care delivery systems as aging female baby boomers reach age 65 and older. DESIGN AND METHODS: A sample of older disabled women in Ohio who completed preadmission review was divided into three groups on the basis of the setting in which they received their initial long-term care services. RESULTS: I was able to establish a long-term care career for the sample members beginning with receiving long-term care in the community, followed by a transition stage in which care was received in the community and in a nursing home, and finally by a stage at which they entered and remained in a nursing home. As the sample members proceeded along their long-term care career and their health and disability status worsened, I found a clear shift in the kind of care needed from hospital and home care to nursing home care. There was also a shift in the major payer, from Medicare to Medicaid. IMPLICATIONS: As the baby boomers age, a much larger number of women will be disabled and need health and long-term care services. For a considerable number of these women, Medicaid gradually becomes the major payer for care, an issue that needs close observation.

Aged↗

PubMed2002

Prenatal factors, childhood growth trajectories and age at menarche.

BACKGROUND: In recent studies a larger birth size has been shown to delay the timing of menarche. The mechanisms underlying this association are not clear, however, as birthweight is a predictor of body size in childhood, and a large body size is known to be associated with an early onset of menarche. METHODS: Data from a representative British cohort of 2547 girls born in 1946 who were followed prospectively throughout childhood were used. Information was available on prenatal characteristics, birthweight, height, weight and social circumstances during childhood, and on age at menarche. Random coefficients models were used to estimate the individual trajectories in height and body mass index (BMI) up to age 7 years. The parameters identified by these models were then included in Weibull survival models for the timing of menarche together with birthweight. RESULTS: Birthweight was found to positively influence height and BMI values at age 2 years, but not to affect their rates of change from age 2 to 7 years. Initial analyses showed low birthweight to be associated with an early onset of menarche, but after controlling for growth in infancy this effect was reversed, with girls who were heavy at birth reaching menarche earlier than others with similar infant growth. Rapid growth in infancy was also related to early pubertal maturation. The effects of birthweight and infant growth disappeared, however, when further controlled for growth from age 2 to 7 years. CONCLUSIONS: The effects of birthweight and growth in infancy on the timing of menarche seem to be mediated through growth in early childhood. These findings are consistent with the possibility that timing of menarche may be set in utero or early in life, although it may be modified by changes in body size and composition in childhood.

Birth Weight↗