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At least 721 records · Page 40Linked to original sources
PubMed2000

Possible mechanisms of muscle cramp from temporal and spatial surface EMG characteristics.

In this study, the initiation and development of muscle cramp are investigated. For this, we used a 64-channel surface electromyogram (EMG) to study the triceps surae muscle during both cramp and maximal voluntary contraction (MVC) in four cramp-prone subjects and during cramp only in another four cramp-prone subjects. The results show that cramp presents itself as a contraction of a slowly moving fraction of muscle fibers, indicating that either the spatial arrangement of the motoneurons and muscle fibers is highly related or that cramp spreads at a level close to the muscle. Spectral analyses of the EMG and peak-triggered average potentials show the presence of extremely short potentials during cramp compared with during MVC. These results can also be interpreted in two ways. Either the motoneurons fire with enlarged synchronization during MVC compared with cramp, or smaller units than motor units are active, indicating that cramp is initiated close to or even at the muscle fiber level. Further research is needed to draw final conclusions.

Adult↗
PubMed2004

On- and off-axis statistical behavior of adaptive-optics-corrected short-exposure Strehl ratio.

Statistical behavior of the adaptive-optics- (AO-) corrected short-exposure point-spread function (PSF) is derived assuming a perfect correction of the phase's low spatial frequencies. Analytical expressions of the Strehl ratio (SR) fluctuations of on- and off-axis short-exposure PSFs are obtained. A theoretical expression of the short SR angular correlation is proposed and used to derive a definition of an anisoplanatic angle for AO-corrected images. Several applications of the analytical expressions are proposed: AO performance characterization, postprocessing imaging, light coupling into fiber, and exoplanet detection from a ground-based telescope.

Journal Article↗
PubMed2004

Reduction of coherent artifacts in dynamic holographic three-dimensional displays by diffraction-specific pseudorandom diffusion.

An electroholographic display based on diffraction-specific computation can reduce speckle by electronic diffusion through selective addition of a pseudorandom sequence. Intensity fluctuation as a result of the introduction of pseudorandom noise does not affect three-dimensional (3-D) images significantly since spatial windows formed by diffused basis fringes do not widen noticeably at low pseudorandom spread, whereas the features of the fluctuation are much smaller than human visual resolution. Experimental results obtained on the Massachusetts Institute of Technology holographic video system confirmed that the diffusion smooths 3-D images and improves the intensity nonuniformity among horizontal holographic lines.

Journal Article↗
PubMedDate not supplied

Geographic Information Systems and travel health.

Questions dealing with space and/or location have always been integral to understanding and addressing health issues, such as charting the spread of a disease. Health researchers have traditionally used paper maps to explore the spatial dimensions of health. However, due to advances in technology, it is now possible to ask such questions using a suite of computer-based methods and tools that are collectively known as a Geographic Information System (GIS).

Geographic Information Systems↗
PubMed1992

Clearance of brain edema and macromolecules through the cortical extracellular space.

The transit routes of fluid and particulate matter through brain tissue remain unclear. The object of this study was to examine the movement of macromolecules through brain tissue to further clarify the clearance pathways of edema proteins as they migrate toward the cortex. For this purpose, albumin solution (20 microliters rat albumin diluted to 65 mg/ml with mock cerebrospinal fluid (CSF)) was intracerebrally infused into the caudate putamen, and the migration through brain tissue as well as through the ultrastructure of the cortical surfaces was explored using an immunocytochemical technique. The authors observed immunoreactive product on the glial limitans and pial lining as well as in the extracellular space of the cortical neuropil at 24 hours postinfusion, confirming that the protein had reached the cortical surface. To confirm the efflux of macromolecules into the subarachnoid CSF, 71,200 D fluorescein isothiocyanate-dextran (FITC-dextran 71,200) was infused; cortical surfaces of brains removed en bloc as well as coronal sections were macroscopically observed under ultraviolet illumination at 15 minutes and 24 hours postinfusion. It was observed that infused FITC-dextran 71,200 mainly localized in the cortical white matter and caudate putamen of the infusion site at 15 minutes postinfusion and by 24 hours was distributed in the entire cortex of the infused hemisphere. However, the dynamics of lower-molecular-weight substances was completely different. The spatial distribution of FITC-dextran 4400 diverged upward toward the cortical surface and spread more extensively than FITC-dextran 71,200. These observations were consistent with a diffusion process as the spread of the tracer was dependent upon molecular size. These studies provide compelling evidence that a process other than bulk flow was involved in the spread of macromolecules through the extracellular space of the normal cortical neuropil to sink into the subarachnoid space. It was concluded that the CSF pathway via the extracellular space of the cortical neuropil is a primary route for clearance of extracellular edema proteins to the subarachnoid space and that diffusion is involved in this process.

Albumins↗
PubMedDate not supplied

[Effect of coagulation of the reticular formation in the region of the NRP and NRT nuclei on the spread of brain biopotential synchronization in rabbits].

The influence of coagulation of NRP and NRT nuclei on the level of spatial synchronization of bioelectrical activity in the visual and motor cortical areas was studied in chronic experiments on alert rabbits. It was shown that elimination of these structures from activity diminishes the correlation of processes in the studied zones. The degree of the coagulation effect depends on the volume of destruction and on the degree of synchroneity of the background neocortical biopotentials. Destruction of the nuclei is attended with dominance of delta-frequencies in the power spectra and a drop of coherence function in the theta range. It is assumed that the NRP and NRT nuclei are functional links of the integral system which controls the level of spatial synchronization of bioelectrical processes in the rabbit cerebral cortex.

Animals↗
PubMedDate not supplied

[Scanning electron microscopy of the kidney glomerulus during development].

Consecutive stages of renal glomerulogenesis were studied in white rats using scanning electron microscopy of microvessel corrosion casts and specimens dried through critical point. The splitting of ingrowing capillaries was shown to be the leading mechanism of glomerulogenesis. The differentiation of endothelial and epithelial components of glomerular filter involves two main processes: progressive spreading and arborization of cells. A suggestion is put forward that the growth and spatial reorganization of cytoskeletal elements in the endothelial and epithelial cells are the basic mechanisms of their differentiation during glomerulogenesis.

Animals↗
PubMed1983

The role of ultrasound in the management of cervical carcinoma. A preliminary report.

Thirty-five cases of carcinoma of the cervix were examined ultrasonographically in order to assess the role of ultrasound in the management thereof. The method is not sufficiently reliable to detect spread beyond the cervix, but does provide useful information regarding pelvic anatomy and the spatial relationships of the cervix. It can be advantageously applied in the planning of therapy and its use in the day-to-day management of such cases is recommended.

Cervix Uteri↗
PubMed1983

Visual plasticity as revealed in the two-dimensional modulation transfer function of a meridional amblyope.

The mammalian visual system is known to have considerable maturational plasticity, since the characteristics of early visual experience can have lasting effects on the organization and functioning of the visual cortex. One example which reveals this property is meridional amblyopia, an abnormal dependence of visual contrast sensitivity on orientation; it is demonstrably neural in origin and is presumed to reflect the redistribution of orientation-selective mechanisms in the visual cortex in response to anisotropic visual input during development. An unusual case of this abnormality was studied with two-dimensional (2D) Fourier techniques in a meridional amblyope having no history of significant astigmatism since the age of five. Modulation transfer function and point-spread surfaces were computed for comparison with a normal subject in both the 2D spatial frequency domain and the 2D space domain, based on contrast sensitivity measurements spanning the Fourier plane by radial and angular cross-sections as well as a 2D Cartesian sampling lattice. Contrary to the generalization that meridional amblyopia is only found in continuing astigmats, this case suggests the potency of transient infant astigmatism to induce permanent neural anisotropy.

Adult↗
PubMed1995

Comparison of frequency-specific c-Fos expression and fluoro-2-deoxyglucose uptake in auditory cortex of gerbils (Meriones unguiculatus).

Induction of c-Fos in the auditory cortex of gerbils was investigated immunocytochemically 1 h after single, triple or 1 h continuous stimulation with a series of narrow band frequency-modulated tone bursts. With single stimulation c-Fos immunoreactive neurons were chiefly found in the primary auditory field (AI), where they formed a narrow frequency-specific column across layers II-VI. Side-band-like patterns adjacent to this column appeared characteristically with triple stimulation. Immunoreactive cell density in the anterior auditory field and the caudal fields was sparse and location not frequency specific with single or triple stimulation. Spatial comparisons of c-Fos immunoreactive neuron density with 2-deoxy-2-fluoro-D-glucose (FDG) autoradiography in the same animals after 1 h of stimulation revealed spreading of c-Fos expression in neurons across the tonotopic maps of the AI and in the rostral and caudal fields of the auditory cortex. The pattern of the highest density of c-Fos labelled cells in the AI still matched the peak labelling of FDG autoradiographs. The results show that the postsynaptic marker c-Fos reflects the frequency representation in the AI with single or triple stimulation yet with a higher spatial resolution than the deoxyglucose technique. Longer stimulation causes nontonotopic intracortical spreading of the c-Fos-inducing message, a phenomenon potentially reflecting the effects of cooperativity in the maps.

Animals↗
PubMed2005

Presampling, algorithm factors, and noise: considerations for CT in particular and for medical imaging in general.

CT scanners acquire noisy data at discrete sample positions. Typically, a convention of how to continue these data from discrete integer positions to the continuous domain must be applied during processing. We study the properties of three typical one-dimensional spatial domain interpolation algorithms in terms of a cost or quality factor Q. This figure of merit Q is a function of spatial resolution, data noise, and dose and is used to optimize detector design. Spatial resolution R is defined as either mean square width delta or as the full width at half maximum W of the point spread function (PSF). Our results show that a trapezoidal interpolation algorithm is optimal for the high resolution domain (relative to the detector aperture size g) and should be replaced by a triangular or Gaussian interpolation function for spatial resolutions of about 1.3g or larger; these result in bell-shaped PSFs. Assuming such a hybrid algorithm we find a 1.5-fold increase of Q2-this is equivalent to 50% improved dose usage-when smoothing the data to a spatial resolution of 3g or more compared to a highest resolution reconstruction. Therefore it is advisable to use detectors of one-third of the size of the desired spatial resolution W and to compensate for the 1.5-fold increase in Q2 by reducing dose by 33%. Under the presence of moderately sized septa (e.g., 10% of the spatial resolution element size) the benefit of optimizing still lies in the order of 30% improved dose usage; in that case the detector size g should be on the order of W/2 and a dose reduction of 23% can be achieved. Again, bell-shaped PSFs show a better tradeoff between noise and resolution for a given dose than rectangular-shaped PSFs. The general interpretation of our results is that the degree of freedom of choosing the weighting or interpolation function for a given resolution is large for small detectors and small for large detectors. Thus systems with small g have a higher potential of optimization compared to systems with large g. Similarly, detector binning, which corresponds to replacing g by 2g, should be avoided. Note that the figures reported correspond to a one-dimensional interpolation. Two-dimensional detectors typically separate and resulting quality factors can be easily obtained by multiplication. Then, Q2 is expected to improve by a factor of 1.52 without septa and by a factor of 1.32 with septa. This indicates that dose can be reduced by about 56% and about 41%, respectively. Our findings are general and not restricted to CT. They can be readily applied to medical or nonmedical imaging devices and digital detectors and they may also turn out to be useful in other fields.

Algorithms↗
PubMed1987

Vertical and horizontal visual whole-field motion differently affect the metabolic activity of the rat medial terminal nucleus.

The metabolic activity of the medial terminal nucleus (MTN) of the Accessory Optic System was studied by means of the [14C]2-deoxyglucose (2-DG) method in Long-Evans rats exposed to moving and stationary visual stimuli. In particular we explored the rate of local cerebral glucose utilization (LCGU) and the spatial distribution of 2-DG uptake within MTN related to visual stimuli capable of triggering optokinetic nystagmus. It was found that increases in MTN metabolism accompanied the retinal slip signals evoked by whole-field visual patterns moving in the vertical as well as in the horizontal direction. At the same level of luminous flux neither the same but stationary pattern, nor constant, diffuse illumination were able to elicit comparable changes in MTN metabolic rates. The effects of vertical and horizontal motions differed, however, from each other. In binocular testing LCGU rates resulted significantly higher after vertically moving patterns and upon the same stimulus condition the spatial distribution of 2-DG matched very closely the spatial distribution of the retinal afferents and the cellular density within MTN, in sharp contrast with the diffuse spreading out of the label across the nucleus following horizontal motion. In monocular testings only the vertically moving patterns were able to increase LCGU rates significantly and then in contralateral MTN alone. However, comparison between the levels of glucose consumption measured in binocular and in monocular vision also showed the involvement of the uncrossed retinal path in relaying the retinal slip signals to MTN. No difference in LCGU and in spatial distribution of the label were finally observed in relation to the upward or to the downward direction of the moving pattern.

Animals↗
PubMed1977

[Spatial deployments of morphogenetic movements as elements of the oral field in anuran amphibians. I. Structurally stable morphogenetic movements].

The movements of cells in the oral field of anuran embryos were followed by means of orto- and heterotopic transplantations of the ectoderm fragments. To mark individual ectoderm regions, the embryos were used which differed from each other by colour. The cells polarize along the apical-basal layer axis and the polarization spreads along the layer as a waver embracing consecutively new and new cells. The waves of morphogenetic rearrangements from the spatial deploiments of morphogenetic movement, i. e. the transition between the local morphologies of the layer which replace one another in time is swept continuously in space. The presence of spatial sweep is the necessary condition for the structural stability of morphogenetic movements.

Amphibians↗
PubMed2002

Coevolution of pathogens and cultural practices: a new look at behavioral heterogeneity in epidemics.

The effect of heterogeneity within populations on the spread of infectious diseases has been a recent focus of research. Such heterogeneity may be, for example, spatial, temporal or behavioral in form. Generally, models that include population subdivision have assumed that individuals are permanently assigned to given behavioral states represented by the subpopulations. We consider a simple epidemic model in which a behavioral trait affects disease transmission, and this trait may be transferred among hosts as a consequence of social interaction. This creates a situation where the frequencies of different behavioral traits and disease states as well as their associations may change over time. We consider the impact of the culturally transmitted trait on the criterion for initial spread of the disease. We also explore the evolution of cultural traits in response to pathogen dynamics and show some conditions under which behavioral traits that reduce transmission evolve. We find that behaviors increasing the risk of infection can also evolve when they are inherently favored or when there is sufficient clustering of contacts between like behaviors.

Communicable Diseases↗
PubMed1986

Spatial and quantitative distribution of human peritumoural brain oedema in computerized tomography.

Computerized tomography (CT) was used to study the pathways of oedema spreading in man. Based on the assumption that local changes in CT numbers in oedematous white matter closely correspond to changes in tissue water content, CT numbers of consecutive tissue blocks of 3.0-3.6 mm were examined in the main directions of oedema spreading: towards the deep white matter, towards the cortex and towards the ventricle. Tumours with oedema grade II and III showed a reduction of CT number of 10 +/- 1.8. The corresponding increase in water content of about 10-12% seems to be an upper limit of fluid accumulation in the white matter. From this oedema centre, water content very slowly and gradually decreased along the oedema projection into the deep white matter. In contrast, if oedema reached the cortex of adjacent gyri, the decline in water content was very sharp. A similar observation was made in the external capsule where oedema sharply declined at the border to the adjacent grey matter, putamen and claustrum. Oedema projection towards the ventricle showed a nearly uniform magnitude from the centre to the ventricular lining, suggesting a certain resistance by a limited capacity of transependymal drainage of oedema fluid. It is assumed that the spatial distribution and extension of oedema around a brain tumour is determined by a system of differential resistance to fluid movement in the following order: grey matter--ventricular lining--white matter.

Brain Edema↗
PubMed2000

Three-dimensional organization of microtubules in tumor cells studied by confocal laser scanning microscopy and computer-assisted deconvolution and image reconstruction.

Confocal microscopy, image deconvolution and computer-assisted methods have been used to reconstruct the three-dimensional (3-D) distribution of tubulin in cells. The techniques were applied to tumor cells growing under regular culture conditions (planar cultivation) and those penetrating into reconstituted collagen matrices (spatial cultivation). As expected the application of deconvolution algorithms enhanced the resolution of results. The deconvolution using the maximum likelihood estimation included the measurement of the point spread function of the optical setup. The data visualization of the resulting data sets uses volume as well as surface rendering approaches. The 3-D reconstruction gives a clear image of the spatial arrangement of tubulin fibers in relation to cell shape and position of other cellular organelles, particularly the nucleus. The tubulin forms an intricate network of fibers of variable thickness. The highest tubulin concentrations appear in the cell periphery and particularly in pseudopodia/invadopodia. This is indicative of an enhanced transport of intracellular material facilitating cell movement and lysis of the extracellular matrix. The investigation is assumed to stimulate further experiments using a variety of techniques leading to the complete understanding of the spatial architecture of living cells.

Cell Movement↗
PubMed1984

The propagation of cancer, a process of tissue remodeling. Studies in histophysiologic gradient culture.

Effective study of the malignant phenotype at the tissue level requires model systems that are intelligible both to cell biologists and to pathologists, and that also observe the spatial imperatives intrinsic to tissues in nature. Malignant cells commonly appear in multicellular units, and growth of tumor tissue is seen as an increase in the number of cells and multicellular units. The supporting stroma frequently has an abnormal appearance, and this component of the tissue also increases in mass as the tumor enlarges and spreads. The direction of invasion is influenced by the direction of available metabolites. Histophysiologic gradient culture complies with nature's spatial rationale, since at the substrate-parenchymal interface three functions coincide. These are anchorage, initiation of epithelial renewal, and complete exchange of metabolites. Our model system provides a setting for reconstructing and manipulating many features of the malignant phenotype seen in cancer tissues in nature, such as abnormalities in the sequence of maturation of stratified epithelium, hyperplasias, dysplasias, interaction between different types of epithelium, aggregate formation, tumor angiogenesis, and neoplastic blockade.

Animals↗
PubMed1996

Point spread functions of photons in time-resolved transillumination experiments using simple scaling arguments.

Simple scaling arguments are used to determine spatial resolution achievable in time-resolved transillumination experiments involving highly diffuse media. These arguments allow us to obtain relationships linking target resolution at different planes inside an optically turbid slab to the gating times of the imaging system. We show that this approach yields the same results as those obtained previously from an approximate and rather complicated analytical derivation. In addition, we are now able to assess the effects of scattering anisotropy on spatial resolution attainable when gating times are so short that a constant scaling of photon transport scattering length is not appropriate. These results should enable one to devise more accurate and simpler image reconstruction algorithms.

Algorithms↗