Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “spatial”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 469 records · Page 26Linked to original sources
PubMed1999

Spatial variation of anthropometric traits in Ireland.

To further elucidate the relationship between geography and genetics in Ireland, we considered variation in anthropometric traits of adult males by town using spatial autocorrelation methods. By describing and distinguishing significant patterns of anthropometric variation, we determined whether the anthropometric traits display a simple pattern of spatial variation, as predicted by the isolation by distance model, or other patterns of spatial variation. Several hypotheses were examined, including (1) whether there was spatial patterning of 20 anthropometric phenotypic distributions and 7 principal components of Irish males and (2) if there was, whether these phenotypic distributions could be explained by a simple isolation by distance model. The results of this study can be summarized by several key findings: (1) There is significant spatial patterning among towns, as detected in correlograms of 14 anthropometric traits and 2 principal component factor scores (values of Moran's I ranging from 0.7510 to -0.3616, p < or = 0.0071); (2) 4 spatial patterns were detected, including clinical patterns, long-distance differentiation, distance distinction, and regional patchiness. These results suggest several likely causes of the observed spatial patterns. First, in Ireland patterns of anthropometric variation could not be explained by a single spatial pattern (i.e., isolation by distance). Second, through an examination of the various combinations of statistical homogeneity or heterogeneity, spatial patterning or nonpatterning, and similarity or dissimilarity of spatial patterns, we conclude that several migrational events structured the genetic landscape of Ireland.

Adult↗
PubMed2003

[Quantification comparison of spatial pattern of soil seed bank of Fraxinus mandshurica in two stands].

The spatial pattern of soil seed bank of Fraxinus mandshurica were examined by geostatistics in two stands with different densities, tree species composition and ground plants, in the Northeast of China. A sampling grid of 559 points, at each point a sample was located, was established according to regular grid design at three spatial scales (cell size were 0.5 m x 0.5 m, 1 m x 1 m, and 2 m x 2 m) in each plot. Spatial pattern were quantified by using semivariance analysis, fractal dimension and Kriging maps. The object of this paper is to quantify the spatial pattern of seed bank, to compare its variations between two stands, and to explore what sort of mechanism would control its variations. The results indicated seed distribution showed appreciable heterogeneity within stand and clearly difference between the two stands. In plot 1 (mixed stand), seed bank, with a mean of 158.1 +/- 96.7 seeds.m-2, higher sill (C0 + C = 0.549) and 4.25 m scales, has a stronger spatial pattern. There were a high autocorrelated variation (89.4%) and lowly random variation (10.6%) at this scale. However, at scale from 5 m to 31.3 m, its autocorrelated variation ranged 51.4%-69.8% and random variation ranged 30.2%-47.6%, also has distinctly mosaic patterns. Fractal dimension (D) analysis showed that the D values was relatively lower(1.728-1.865), their coefficient of variation only about 26.7%-68.35%, indicated that there was a high self-similarity of patch shapes of seed bank. In plot 2 (pure stand), with a mean of 57.4 +/- 44.7 seed.m-2, and lower sill (C0 + C = 0.125), spatial patterns were not so strong as plot 1, which has a smaller scale (2.59 m). Its spatially autocorrelated variation was 56.8% and randomly variation was 43.2%. Over the scale there were no clearly autocorrelated spatial patterns. Fractal dimension analysis showed higher D value (1.906-1.960), and their coefficient of variation varying wildly (69.51%-134.14%), implying highly random variation and more complex patch shapes. The differences of spatial pattern of seed bank between the two stands were likely to be due to spatial heterogeneity at the level of stands.

Seeds↗
PubMed1985

Mutual spatial orientation of hexons in the adenovirus capsid by electron microscopy and modelling.

On the basis of electron microscopic analysis of the virion and model experiments there are four hexon species in the adenovirus capsid which have different positional status and spatial orientation as compared to the six nearest neighbouring capsomers. The binding pattern of the polypeptide subunits according to their orientation is also different. The four hexon species are situated beside one another in the capsid and they form the capsid of 240 hexons besides the penton by repeating symmetrically 60 times, as a group of four hexons (GOF). Electron microscopic analysis and model experiments lead to the conclusion that the mutual spatial orientation of GOF hexons can be parallel (their longitudinal axes are parallel), or the direction of their longitudinal axes is different in one or two planes, thus they form different angles with the longitudinal axes of the neighbouring hexons. In the latter cases therefore, a bend and torsion of the bindings (connective elements) can be supposed as compared to the tendency-plane of parallel bindings. Based on the different combinations of the three kinds of rotational orientation of polypeptide subunits and of the different spatial orientation of hexons, six kinds of interhexonal bindings can be found in the adenovirus capsid. The distribution and characteristics of the 690 interhexonal bindings are the following; 240 bindings of "one-to-two" polypeptide orientation with parallel spatial orientation; 180 bindings of "one-to-two" polypeptide with spatial orientation divergent in two planes; 30 bindings of "one-to-one" polypeptide orientation with parallel spatial orientation; 60 bindings of "one-to-one" polypeptide orientation with spatial orientations divergent in one plane; 60 bindings of "one-to-one" polypeptide orientation with spatial orientation divergent in two planes; 120 bindings of "two-to-two" polypeptide orientation with spatial orientation divergent in two planes. The dissociational sequence of the capsid suggests that the firmest bindings are the ones having "one-to-two" polypeptide orientation and parallel spatial orientation. It may be supposed that any two hexons are able to connect to each other according to all three polypeptide orientations and the connections can tolerate the bends and torsions arising from the icosahedral structure. This suggests that only one kind of hexon is existing and the adenovirus capsid is formed by a homogeneous hexon population.

Adenoviridae↗
PubMed1998

The digital anatomist structural abstraction: a scheme for the spatial description of anatomical entities.

In this paper, we propose a generalized scheme for the symbolic description of the spatial attributes of anatomical entities. The power of the scheme lies in the ability to model the spatial objects at the highest level of granularity: information can be obtained at the desired level of detail needed for a given application. This scheme uses the topological classes of point, line, surface, and volume to represent zero-D, one-D, two-D and three-D objects. A spatial object participates as a node in three complementary networks; the topology network, the part-of network, and the spatial associations network. The topology network describes a spatial object in terms of its boundaries, the part-of network describes a spatial object in terms of its parts, and the spatial associations network describes the spatial object in terms of its relationships to other spatial objects. All three of the networks can be used in combination or alone to answer queries to the spatial information system. The Digital Anatomist Structural Abstraction together with the other components of the Digital Anatomist Foundational Model will provide the information for describing and reasoning about anatomical entities.

Anatomy↗
PubMed2005

Epidemiology of child pedestrian casualty rates: can we assume spatial independence?

Child pedestrian injuries are often investigated by means of ecological studies, yet are clearly part of a complex spatial phenomena. Spatial dependence within such ecological analyses have rarely been assessed, yet the validity of basic statistical techniques rely on a number of independence assumptions. Recent work from Canada has highlighted the potential for modelling spatial dependence within data that was aggregated in terms of the number of road casualties who were resident in a given geographical area. Other jurisdictions aggregate data in terms of the number of casualties in the geographical area in which the collision took place. This paper contrasts child pedestrian casualty data from Devon County UK, which has been aggregated by both methods. A simple ecological model, with minimally useful covaraties relating to measures of child deprivation, provides evidence that data aggregated in terms of the casualty's home location cannot be assumed to be spatially independent and that for analysis of these data to be valid there must be some accounting for spatial auto-correlation within the model structure. Conversely, data aggregated in terms of the collision location (as is usual in the UK) was found to be spatially independent. Whilst the spatial model is clearly more complex it provided a superior fit to that seen with either collision aggregated or non-spatial models. Of more importance, the ecological level association between deprivation and casualty rate is much lower once the spatial structure is accounted for, highlighting the importance using appropriately structured models.

Accidents, Traffic↗
PubMed2026

Scalable, generalizable and uncertainty-aware integration of spatial multiomics across diverse modalities and platforms with SCIGMA.

Recent advances in spatial omics technologies have enabled simultaneous profiling of transcriptomic, proteomic, epigenomic, metabolomic and imaging data at high spatial resolution, offering unprecedented opportunities to dissect tissue complexity. However, integrating these diverse and large-scale spatial multimodal datasets remains a major computational challenge. We present SCIGMA, a scalable and generalizable deep learning framework for spatial multiomics integration. SCIGMA introduces an uncertainty-aware contrastive learning objective and multiview graph neural networks to preserve modality-specific signals while learning biologically meaningful joint representations. Unlike previous methods, SCIGMA provides spatially resolved uncertainty estimates, interpretably identifying regions of biological or technical heterogeneity. SCIGMA supports integration of up to five modalities, and its modular framework is extensible to future technologies with even more modalities. It also scales to more than 1 million spatial locations, enabling analysis of high-resolution datasets such as Visium HD and Xenium Prime. We evaluated SCIGMA across 19 datasets spanning 8 modalities, 10 tissues and 9 platforms. On benchmarkable datasets, SCIGMA outperformed other methods in spatial domain detection, modality preservation, feature reconstruction and reproducibility. SCIGMA identifies biologically meaningful structures, refined spatial domains and modality-specific regulatory programs, providing a robust, flexible and future-ready solution for scalable spatial multimodal integration.

Multiomics↗
PubMed2002

Acute ethanol administration and acute allopregnanolone administration impair spatial memory in the Morris water task.

BACKGROUND: Acute ethanol administration degrades performance on many learning and memory tasks, including tasks that are dependent on spatial information. One common test of spatial learning and memory is the Morris water task, a task that requires subjects to learn the spatial location of a submerged escape platform located in a pool of cloudy water. However, although some studies report that acute ethanol administration degrades spatial memory performance in the Morris task, other studies report no significant performance impairment. Acute ethanol administration also produces a dose- and time-dependent increase in the concentration of the endogenous neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in rat brain. Given that ethanol and allopregnanolone are both gamma-aminobutyric acid type A receptor modulators, both drugs should produce similar degradations in spatial learning and memory. METHODS: Adult male rats were trained with either the spatial version or the nonspatial version of the Morris water task. After 4 days of training, the spatial or nonspatial memory performance of subjects was assessed after either an ethanol (1.0, 1.5, or 2.0 g/kg) or allopregnanolone (12.5, 17.0, or 20.0 mg/kg) challenge. RESULTS: Acute ethanol administration and acute allopregnanolone administration impaired spatial memory performance in a dose-dependent manner in the Morris water task. In addition, the impairment was selective in that neither acute ethanol nor acute allopregnanolone administration impaired nonspatial memory performance in the Morris water task. CONCLUSIONS: Acute ethanol administration and acute allopregnanolone administration impaired spatial memory performance but did not impair nonspatial memory performance in the Morris water task. These results demonstrate that both ethanol and allopregnanolone produce selective cognitive deficits that are not due to general sensory or motor deficits.

Animals↗
PubMed1997

Hippocampal synaptic plasticity: role in spatial learning or the automatic recording of attended experience?

Allocentric spatial learning can sometimes occur in one trial. The incorporation of information into a spatial representation may, therefore, obey a one-trial correlational learning rule rather than a multi-trial error-correcting rule. It has been suggested that physiological implementation of such a rule could be mediated by N-methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation (LTP) in the hippocampus, as its induction obeys a correlational type of synaptic learning rule. Support for this idea came originally from the finding that intracerebral infusion of the NMDA antagonist AP5 impairs spatial learning, but studies summarized in the first part of this paper have called it into question. First, rats previously given experience of spatial learning in a watermaze can learn a new spatial reference memory task at a normal rate despite an appreciable NMDA receptor blockade. Second, the classical phenomenon of 'blocking' occurs in spatial learning. The latter finding implies that spatial learning can also be sensitive to an animal's expectations about reward and so depend on more than the detection of simple spatial correlations. In this paper a new hypothesis is proposed about the function of hippocampal LTP. This hypothesis retains the idea that LTP subserves rapid one-trial memory, but abandons the notion that it serves any specific role in the geometric aspects of spatial learning. It is suggested that LTP participates in the automatic recording of attended experience': a subsystem of episodic memory in which events are temporarily remembered in association with the contexts in which they occur. An automatic correlational form of synaptic plasticity is ideally suited to the online registration of context event associations. In support, it is reported that the ability of rats to remember the most recent place they have visited in a familiar environment is exquisitely sensitive to AP5 in a delay-dependent manner. Moreover, new studies of the lasting persistence of NMDA-dependent LTP, known to require protein synthesis, point to intracellular mechanisms that enable transient synaptic changes to be stabilized if they occur in close temporal proximity to important events. This new property of hippocampal LTP is a desirable characteristic of an event memory system.

2-Amino-5-phosphonovalerate↗
PubMed2026

A High-Resolution Stereo-Seq Spatial Transcriptomic Resource for Adult Holstein Cattle Liver.

The bovine liver is a highly compartmentalized organ that plays essential roles in continuous gluconeogenesis and nitrogen recycling; however, its spatial molecular architecture has remained largely uncharacterized due to the limitations of traditional bulk and single-cell approaches. To address this gap, Spatial Enhanced Resolution Omics-sequencing (Stereo-seq) was utilized to generate a subcellular-resolution (500 nm) transcriptomic map of an adult Holstein cattle liver, and a refined reference-guided workflow was implemented to overcome standard annotation limitations in livestock. Raw sequencing data were processed using the Stereo-seq Analysis Workflow and analyzed with Stereopy, Seurat, SingleR, and reference-guided workflows. Spatial aggregation was evaluated at Bin20, Bin50, Bin100, Bin150, and Bin200. Increasing bin size increased molecular identifier counts and detected-gene complexity while progressively reducing spatial granularity. Bin50, corresponding to 50 &#xd7; 50 DNA nanoballs and an approximate nominal footprint of 25 &#xd7; 25 &#xb5;m, was therefore selected as a practical intermediate aggregation level for the primary analyses. Quality-control assessment, Leiden clustering, UMAP visualization, reference-based cell-type annotation, cluster-marker analysis, and spatial mapping of canonical hepatic genes demonstrated preservation of biologically interpretable liver transcriptional organization. Raw sequencing data processed spatial matrices, annotated objects, and analysis code are publicly available to support reanalysis and computational benchmarking. In summary, we present a Stereo-seq spatial transcriptomic resource generated from liver tissue of an adult Holstein cow. This initial resource provides a valuable foundation for future studies of bovine liver biology, comparative genomics, and the spatial basis of livestock health and production traits.

Animals↗
PubMed2002

Spatial working memory deficits in schizophrenia patients and their first degree relatives from Palau, Micronesia.

Spatial working memory deficits associated with dorsolateral prefrontal dysfunction have been found in Caucasian samples of schizophrenia patients and their first-degree relatives. This study evaluated spatial working memory function in affected and unaffected members of multiplex schizophrenia families from the Republic of Palau to determine whether the spatial working memory deficits associated with schizophrenia extend to this non-Caucasian population. Palau is an isolated island nation in Micronesia with an elevated prevalence of schizophrenia and an aggregation of cases in large multigenerational families. Our objective was to evaluate the potential for spatial working memory function to serve as one of multiple endophenotypes in a genetic linkage study of these Palauan schizophrenia families. A spatial delayed response task requiring resistance to distraction and a sensorimotor control task were used to assess spatial working memory in 32 schizophrenia patients, 28 of their healthy first-degree relatives, and 19 normal control subjects. Schizophrenia patients and their relatives were significantly less accurate than normal control subjects on the spatial delayed response task but not on the sensorimotor control task. On both tasks, patients and relatives were slower to respond than the normal controls. There were no age or gender effects on accuracy, and working memory performance in schizophrenia patients was not significantly correlated with medication dosage. In summary, spatial working memory deficits that have been found in Caucasian schizophrenia patients and relatives were confirmed in this isolated Pacific Island family sample. These results suggest that spatial working memory deficits may be a potentially useful addition to the endophenotypic characterization of family members to be used in a comprehensive genome wide linkage analysis of these Palauan families.

Adult↗
PubMed1991

Equivalent impairment of spatial and nonspatial memory following damage to the human hippocampus.

The hippocampus has sometimes been proposed to function as a cognitive map, a memory system that stores information about allocentric space. Work with experimental animals and memory-impaired patients has raised difficulties with this view by showing that the hippocampus is not performing an exclusively spatial function. However, the possibility has remained that the hippocampus plays a special role in spatial memory or a disproportionately large role in spatial memory compared to other kinds of memory. This study compared spatial and nonspatial memory in amnesic patients with lesions of the hippocampal formation or diencephalon. Subjects studied an array of 16 toy objects and were subsequently tested for object recall, object recognition, and memory for the location of the objects. Control subjects were tested after long retention intervals in order to equate their object memory performance with that of the patients. The main finding was that, when the performance of amnesic patients on the object memory tests was matched to the object memory performance of control subjects, spatial memory performance of the amnesic patients also matched the spatial memory performance of the control subjects. The results were the same for the two groups of patients. These findings suggest that the hippocampus is not especially involved in spatial memory. Spatial memory is simply one instance of a broader category of memory that requires the hippocampus. While cognitive mapping in its most abstract sense may describe hippocampal function, our results support alternative formulation, suggesting that the hippocampus is necessary for the rapid acquisition of relational, configural, or declarative (as opposed to purely spatial) information.

Adult↗
PubMed1995

Gonadal hormone levels and spatial learning performance in the Morris water maze in male and female meadow voles, Microtus pennsylvanicus.

The present study examined the relationships between spatial learning and circulating levels of plasma estradiol and testosterone in adult male and female meadow vole, Microtus pennsylvanicus. Meadow voles are induced ovulators and most females that are housed with females or in isolation are in constant diestrus, whereas most females that are housed with males are in constant behavioral estrus. In this study sexually mature, adult male and female meadow voles housed with either females (constant diestrus) or males (constant behavioral estrus) were required to learn the spatial position of a hidden, submerged platform in the Morris water maze. Individual voles were tested using two blocks of four trials twice a day for 3 days for a total of six blocks. Task retention was examined with a probe trial 1 day after the last acquisition trial. Females were divided into two groups based on the median level of plasma estradiol [High Estradiol (15.79 +/- 1.20 pg/ml) and Low Estradiol (6.22 +/- 2.79 pg/ml) Females]. Males were similarly divided on the basis of median plasma testosterone levels [High (2.53 +/- 0.96 ng/ml) and Low Testosterone (0.45 +/- 0.08 ng/ml) Males]. High Estradiol females exhibited significantly longer latencies to reach the hidden platform, indicating poorer acquisition, than did either males (P = 0.025) or Low Estradiol females (for Blocks, 2, 3, 4, and 6, P = 0.037). Male superiority in spatial learning performance was evident only when High Estradiol females were compared to males. There were no significant performance differences between High and Low Testosterone males. There were also no group differences in retention, with all voles displaying significant retention of the spatial task. There was, however, a significant correlation between plasma estradiol levels in females and retention, with higher estradiol levels being associated with poorer retention. These results suggest that levels of estradiol in adult female meadow voles are significantly related to spatial learning, with low levels of estradiol being associated with better spatial learning. There was no evidence that levels of testosterone were related to spatial performance in adult male meadow voles. The results suggest that estradiol may have activational effects on spatial learning in the adult meadow vole and that sex differences in spatial learning are evident only when High Estradiol females are compared to adult males.

Animals↗
PubMed1997

Using Moment Equations to Understand Stochastically Driven Spatial Pattern Formation in Ecological Systems

Spatial patterns in biological populations and the effect of spatial patterns on ecological interactions are central topics in mathematical ecology. Various approaches to modeling have been developed to enable us to understand spatial patterns ranging from plant distributions to plankton aggregation. We present a new approach to modeling spatial interactions by deriving approximations for the time evolution of the moments (mean and spatial covariance) of ensembles of distributions of organisms; the analysis is made possible by "moment closure," neglecting higher-order spatial structure in the population. We use the growth and competition of plants in an explicitly spatial environment as a starting point for exploring the properties of second-order moment equations and comparing them to realizations of spatial stochastic models. We find that for a wide range of effective neighborhood sizes (each plant interacting with several to dozens of neighbors), the mean-covariance model provides a useful and analytically tractable approximation to the stochastic spatial model, and combines useful features of stochastic models and traditional reaction-diffusion-like models. Copyright 1997 Academic Press. Copyright 1997 Academic Press

Journal Article↗
PubMed1985

Spatial contrast sensitivity in macular disorder.

Spatial contrast sensitivity functions were evaluated in 30 patients with macular disorders and 16 age-matched control subjects. Eighteen of the affected eyes had macular holes and the rest had isolated macular problems. A loss in spatial contrast sensitivity in the central visual field indicated a relative scotoma resulting from macular dysfunctions. The nature and size of a localized scotoma such as the type caused by a macular lesion was estimated by measuring spatial contrast sensitivity as a function of retinal area centered on the fovea. Such spatial-contrast-threshold perimetry was found to be helpful in differential classification of macular holes. Spatial contrast sensitivity and visual resolution improved with increasing retinal area even in the eyes with macular holes, but never reached normal sensitivity for spatial frequencies above 5 cycles per degree (cpd) within our experimental conditions. The loss in sensitivity to low spatial frequencies (less than or equal to 5 cpd) was found to be apparent and a function of the retinal area stimulated. The summation curves (contrast sensitivity vs. stimulus size) were abnormal for all spatial frequencies. The 'critical' sizes (i.e. the stimulus size above which no increase in sensitivity occurred) were always larger in the affected eyes than those in the normal. Thus 'critical' areas of complete summation in the parafovea may be a better measure of functional integrity of central retina in the presence of a foveal lesion than the visual resolution that varies with the retinal area and location activated. Evaluation of contrast sensitivity of the parafoveal regions with nonfunctional fovea also indicated existence of similar mechanism of spatial vision in the fovea and the parafovea.

Aged↗
PubMed1991

Interocular mismatch in spatial frequency and directionality characteristics of striate cortical neurones.

Spatial-frequency dependence of directional tuning and directional bias was compared, for both eyes, in four previously established discrete classes of binocular feline striate cortical neurones. Two classes (respectively direction-selective or bidirectional at optimal spatial frequency) were directionality invariant at all spatial frequencies. In the remaining two classes, both direction-biased at optimal spatial frequency, directional bias either altered or reversed with change in spatial frequency. In all four classes, the directional tuning of a majority of neurones sharpened at high spatial frequency through either eye, although the bandpass characteristics were sometimes dissimilar for the two eyes. All neurones were of the same type through either eye. Amongst the two classes of direction-biased neurones, the strength of bias was commonly different through the two eyes. Where reversal of bias occurred, that reversal took place at different spatial frequencies for each eye. Thus, the direction and orientation preferences of cortical neurones are fixed at optimal spatial frequency, but their envelope of tuning to a gamut of spatial frequencies is not. These differences are potentially related to binocular coding of visual perspective, including dynamic object rotation in visual space.

Animals↗
PubMed1983

Two spatio-temporal filters in human vision. 1. Temporal and spatial frequency response characteristics.

We have studied visual detection of a circular target moving across a spatially and/or temporally modulated background. Illumination, It, for threshold detection of the target has been measured as a function of background modulation frequency and changes in It associated with background modulation provide a means of determining the frequency response characteristics of visual channels. Temporal frequency responses obtained with temporally modulated, spatially uniform backgrounds have pass-band characteristics and the temporal frequency for peak response increases with increase in mean background illumination. These temporal frequency responses resemble those of the de Lange (1954) filter, but the latter incorporates the incremental thresholds for steady backgrounds. The amplitude of this temporal response saturates at low (approximately 40%) background modulation, decreases to zero as the target velocity falls to zero, and is maximum for a circular target of diameter 2 degrees. The spatial characteristics of this temporal filter were measured with a background field consisting of alternate steady and flickering bars. The resulting spatial frequency curve peaks at 1 cycle deg-1 for all background illuminations and is independent of the background grating orientation. This spatial response differs significantly from the IMG spatial functions observed with a background grating (Barbur and Ruddock, 1980). The spatial and temporal responses reviewed above exhibit similar parametric variations and we therefore associate them with a single spatio-temporal filter, ST2. A second temporal response, with low-pass frequency characteristics, was observed with a background field consisting of two matched gratings, presented in spatial and temporal antiphase. This response has parametric properties similar to those of the IMG spatial response described previously by Barbur and Ruddock (1980), thus we associated the two sets of data with a single spatio-temporal filter, ST1. We show that the ST2 responses can be obtained by combining ST1 responses, and we present a network incorporating the two filters. We review other psychophysical studies which imply the activity of two spatio-temporal filters with properties of the kind revealed in our studies. We argue that filter ST1 has properties equivalent to those of X-type and filter ST2 has properties equivalent to those of Y-type electrophysiological mechanisms.

Adult↗
PubMed1993

Comparison of spatial thresholds and intensity thresholds in glaucoma.

Spatial resolution perimetry and conventional perimetry measure different qualities of the functional performance of the eye. Theoretically, spatial resolution is directly related to the density of intact sensory units, but the relation of intensity to the density of intact sensory units is unknown. Previous studies indicated an almost linear relationship of global indices of spatial thresholds and intensity thresholds. The purpose of our study is to look at any difference in the behaviour of local threshold values and their precise relation. We examined 41 eyes of 23 patients with open angle glaucoma. Perimetry was carried out using the Humphrey Field Analyzer, and program 30-S or program 30-2 and the ring perimeter and standard program. Because test point patterns of the two examinations were different, the best matching points were calculated. If the distance between next points in both examinations was more than 5 degrees, the location was excluded. The Humphrey program 30-2 provided 47 matching points, the Humphrey program 30-S furnished 49 matching points for 50 locations. For the range of 20..36 dB in conventional perimetry, linearity could be verified in relation to the local thresholds in ring perimetry. The spatial threshold units used in the ring perimeter are the logarithm of spatial extend. Vice versa, spatial resolution is a power function of spatial thresholds. Based on the linear relationship of both thresholds, spatial resolution is a power function of intensity thresholds. In other words, if the intensity threshold is reduced from 36 to 30 dB, the spatial resolution is nearly half.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Positron flight in human tissues and its influence on PET image spatial resolution.

The influence of the positron distance of flight in various human tissues on the spatial resolution in positron emission tomography (PET) was assessed for positrons from carbon-11, nitrogen-13, oxygen-15, fluorine-18, gallium-68 and rubidium-82. The investigation was performed using the Monte Carlo code PENELOPE to simulate the transport of positrons within human compact bone, adipose, soft and lung tissue. The simulations yielded 3D distributions of annihilation origins that were projected on the image plane in order to assess their impact on PET spatial resolution. The distributions obtained were cusp-shaped with long tails rather than Gaussian shaped, thus making conventional full width at half maximum (FWHM) measures uncertain. The full width at 20% of the maximum amplitude (FW20M) of the annihilation distributions yielded more appropriate values for root mean square addition of spatial resolution loss components. Large differences in spatial resolution losses due to the positron flight in various human tissues were found for the selected radionuclides. The contribution to image blur was found to be up to three times larger in lung tissue than in soft tissue or fat and five times larger than in bone tissue. For (18)F, the spatial resolution losses were 0.54 mm in soft tissue and 1.52 mm in lung tissue, compared with 4.10 and 10.5 mm, respectively, for (82)Rb. With lung tissue as a possible exception, the image blur due to the positron flight in all human tissues has a minor impact as long as PET cameras with a spatial resolution of 5-7 mm are used in combination with (18)F-labelled radiopharmaceuticals. However, when ultra-high spatial resolution PET cameras, with 3-4 mm spatial resolution, are applied, especially in combination with other radionuclides, the positron flight may enter as a limiting factor for the total PET spatial resolution--particularly in lung tissue.

Adipose Tissue↗