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At least 1,729 records · Page 96Linked to original sources
PubMed2006

18F-CPFPX PET: on the generation of parametric images and the effect of scan duration.

UNLABELLED: 8-cyclopentyl-3-(3-18F-fluoropropyl)-1-propylxanthine (18F-CPFPX) is a novel PET ligand for in vivo quantification of cerebral A1 adenosine receptors. The present study investigated the applicability of voxelwise graphical analysis to the generation of parametric images of the total volume of distribution (DVt) of 18F-CPFPX as a prerequisite for voxel-by-voxel statistical analysis. The benefit of spatial smoothing for reduction of noise-dependent negative bias in graphical analysis was examined. Additionally, the effect of scan duration on the accuracy of analyses based on volumes of interest (VOIs) and individual voxels was explored. METHODS: Ten healthy male volunteers underwent bolus-injection 18F-CPFPX PET (90 min). The data were analyzed using a 2-tissue-compartment model and graphical analysis. Voxelwise graphical analysis was performed with and without preceding spatial gaussian smoothing. RESULTS: Voxelwise graphical analysis yielded high-quality parametric images. However, voxelwise graphical analysis suffered from a negative bias (mean bias in cortical regions, -9.6% to -7.5%), which could be attenuated considerably by spatial smoothing (using a kernel of 5 mm in full width at half maximum, bias of -4.0% to -1.9%). Shortening the total scan duration to 60 min had minor effects on the accuracy of VOI-based analysis (15 VOIs x 10 subjects); the resulting error only occasionally exceeded +/-5% in individual regions (n = 6 for 2-tissue-compartment model, n = 10 for VOI-based graphical analysis, always within +/-7.5%). Quantification accuracy was acceptable with scan durations of 60 and 75 min in voxelwise graphical analysis with spatial smoothing (mean bias in cortical regions, -8.4% to -5.9%) and without spatial smoothing (bias, -9.2% to -11.6%), respectively. CONCLUSION: High-quality DVt parametric images of 18F-CPFPX can be generated by voxelwise graphical analysis. The noise-dependent negative bias of voxelwise graphical analysis is greatly reduced by spatial smoothing. A shortened scan of 60 min will enhance the clinical applicability of 18F-CPFPX PET.

Adult↗
PubMed2003

Detailed behavioral analysis reveals both task strategies and spatial memory impairments in rats given bilateral middle cerebral artery stroke.

Middle cerebral artery occlusion (MCAO) impairs performance in the water maze task by rats. The purpose was to evaluate the effect of bilateral MCAO in naive and strategies-pretrained rats using a detailed behavioral analysis to further develop a water maze model of stroke. Rats were trained in either a simple swim-to-visible platform task or in a conventional spatial version with a hidden platform in the pool. In the visible platform task naive stroked rats were impaired because of a marked tendency to swim thigmotaxically on most trials. For the spatial learning experiment, some rats received Morris' water maze strategies pretraining prior to MCAO and subsequent spatial training to familiarize them with the general behavioral strategies required in the task. In the spatial learning task naive stroked rats had both strategies and spatial learning impairments but pretrained stroked rats were indistinguishable from sham controls on all behavioral measures. All stroked rats had comparable bilateral brain damage measured using a computerized volumetric measuring technique. These results indicate that in naive rats bilateral MCAO causes behavioral strategies impairments in the visible and hidden platform versions of the water maze as well as specific spatial learning impairments in the hidden platform version. The results also indicate that behavioral strategies pretraining allows stroked rats to acquire and remember sufficient strategies skills and spatial information to perform as well as sham controls during subsequent spatial training. These techniques appear to be capable of quantifying the effects of potentially protective treatments for stroke.

Adaptation, Psychological↗
PubMed2004

Spatial interactions and resilience in arid ecosystems.

We present a mathematical analysis of the consequences of spatial interactions between vegetation patches by means of water flow for the functioning of arid systems. Our model results suggest that spatial exchange of water improved the resilience to disturbances and increased the resistance to human-induced loss of cover. Furthermore, spatial exchange of water allowed vegetation to persist at lower rainfall levels compared to systems that lack spatial interactions. Our analysis stresses the general importance of spatial interactions for the functioning of ecological systems.

Climate↗
PubMed2006

Cross-talk analysis in a telecentric adaptive free-space optical relay based on a spatial light modulator.

We present an analysis of the performance limit of an adaptive multichannel free-space optical interconnect based on a spatial light modulator (SLM). The SLM function is to provide an active alignment of the signal beam in the detector plane. A thorough cross-talk analysis based on the diffractive properties of an ideal SLM in an isoplanatic optical system is shown. We analyze the performance in terms of the bit-error rate (BER) due to cross talk between different channels in the optical interconnect for different alignment states and for different phase-modulation schemes.

Journal Article↗
PubMed2003

Image analysis can be used to detect spatial changes in the histopathology of pancreatic tumours.

Pancreatic cancer is frequently associated with intense growth of fibrous tissue at the periphery of tumours, but the histopathological quantification of this stromal reaction has not yet been used as a prognostic factor because of the difficulty of obtaining quantitative measures using manual methods. Manual histological grading is a poor indicator of outcome in this type of cancer and there is a clinical need to establish a more sensitive indicator. Recent pancreatic tumour biology research has focused upon the stromal reaction and there is an indication that its histopathological quantification may lead to a new prognostic indicator. Histological samples from 21 cases of pancreatic carcinoma were stained using the sirius red, light-green method. Multiple images from the centre and periphery of each tumour were automatically segmented using colour cluster analysis to subdivide each image into representative colours. These were classified manually as stroma, cell cytoplasm or lumen in order to measure the area of each component in each image. Measured areas were analysed to determine whether the technique could detect spatial differences in the area of each tissue component over all samples, and within individual samples. Over all 21 cases, the area of stromal tissue at the periphery of the tumours exceeded that at the centre by an average of 10.0 percentage points (P < 0.001). Within individual tumours, the algorithm was able to detect significantly more stroma (P < 0.05) at the periphery than the centre in 11 cases, whilst none of the remaining cases had significantly more stromal tissue at the centre than the periphery. The results demonstrate that semi-automated analysis can be used to detect spatial differences in the area of fibrous tissue in routinely stained sections of pancreatic cancer.

Carcinoma↗
PubMed1991

Methodological error and spatial variability of organ blood flow measurements using radiolabeled microspheres.

The quantitative analysis of the spatial variability of organ blood flow by means of radiolabeled microspheres (MS) requires that the methodological variability ("error") of the technique (RDmeth.) is known in each individual organ. Therefore, RDmeth. was quantified (eight to nine nuclides) in 6941 tissue samples from 13 organs of three anesthetized dogs, and the relative importance of errors originating from both the stochastic nature of MS distribution (RDtheo.) and the process of quantitation of MS radioactivity (RDcounting) was assessed under varying conditions (high/low specific MS activity (SAMS); inaccurate separation of gamma spectra; large sample size). At "minimized" methodological error (experiment 2), RDmeth. of samples trapping approximately 375 MS/nuclide was 5.8% and only slightly exceeded RDtheo. (5%). RDmeth. varied in the range 2.7-7.8% in individual organs and contributed little (3.5%) to the organs' observed spatial variability of flow. In contrast, RDmeth.--due to increased RDcounting--considerably exceeded RDtheo. when SAMS was low (experiment 3), overlap of two nuclides' main photopeaks was critical (experiment 1), or counting geometry was inappropriate (pulmonary tissue samples). At the same time, the contribution of RDmeth. to spatial flow variability rose to 7.9% (experiment 3), 26.9% (experiment 1), and 15-23% (lungs). Completely artifactual measurements, as indicated by an extremely high RDmeth. of sample flow, were rarely observed (less than 0.1%). In general, our data suggest that blood flow can be measured reproducibly and with low methodological error using up to 8 nuclides, RDmeth. does not essentially contribute to the observed spatial variability of organ blood flow, and, hence, organ flow variability may be accurately quantified using the MS technique. However, if sources of error as indicated above are present, the practice of using RDtheo. as a measure of RDmeth. (thereby neglecting RDcounting) may notably underestimate true MS error and result in an overestimation of spatial heterogeneity of organ blood flow. RDmeth., therefore, should be quantified separately in each region of interest prior to the onset of a new study.

Animals↗
PubMedDate not supplied

Spatial context of residential moves by elderly persons.

This is a descriptive analysis of the spatial context of residential moves by the over age forty-five population in the United States. It utilizes residential mobility and state of birth statistics calculated from a 15 per cent sample of the United States population drawn for the U.S. Census. It specifically focuses on the likelihood that the age sixty-five and over white and black mover will relocate within his same county or state of residence. The paper reveals that the preponderance of residential moves by the elderly (whether black or white) are within the same county. Only a relatively small percentage make interstate moves. The majority of elderly live in the state of their birth. However, there is no evidence that as a consequence of aging moves become more spatially restricted until after age seventy-five. It is argued that greater emphasis be placed on not why elderly persons move, but why when they do, their residential relocations occur within varying spatial contexts.

Black or African American↗
PubMedDate not supplied

[Concerning a conflict nature of the "spatial delayed response" test].

Neuropsychological analysis of rats' performance of the spatial delayed response (SDR) in different testing conditions revealed a conflict nature of the indirect variation of the SDR task. It was found that the execution of the response based on the image short-term memory interferes with the response differentiation acquired during learning the rule of indirect SDR performance, i.e., during acquisition of the spatial discrimination. It is evident that the maximization of conditions, which promote the acquisition of response differentiation (additional training of animals for spatial discrimination), makes it difficult to perform the indirect variation of the SDR task, while the minimization of these conditions facilitates the correct task performance.

Animals↗
PubMedDate not supplied

[Spatial segregation of old people in West German cities].

The presented segregation analysis of the spatial segregation of the aged produces differentiated segregation data of eight large cities of the Federal Republic of Germany for the first time. The investigations confirms the hypothesis that people who are older than 65 are the mostly segregated age group of the population. There is a trend of a longitudinal rising of segregation between 1950 and 1970. The registered high concentration of old people of lower SES in renovation-needy town areas underlines an actual important problem of town-planning politics.

Adolescent↗
PubMed1995

Covert orienting biases in scene-based reference frames: orientation priming and visual field differences.

Performance advantages for stimuli presented in the right versus the left visual field have been found in a variety of attentional tasks. Such advantages were exploited in the present set of studies to examine orientation priming and directional biases in retinotopic and scene-based spatial coordinates. The results demonstrate that directional biases occur within spatial coordinates across orientation transformations that dissociate retinotopic from scene-based visual half fields. The results are discussed concerning the representation of spatial maps in higher visual analysis, the role of spatial coordinates in guiding covert orienting, and methods of presenting stimuli in the right or left visual field to test for functional hemispheric asymmetries.

Adult↗
PubMedDate not supplied

[Development of spatial orientation during pilot training].

The problem of spatial orientation of pilots flying high-altitude aircraft is in the focus of present-day aviation medicine because of a growing number of accidents in the air. One of the productive lines of research is to study spatial orientation in terms of active formation and maintenance of its imagery in a complex environment. However investigators usually emphasize the role of visual (instrumental) information in the image construction, almost ignoring the sensorimotor component of spatial orientation. The theoretical analysis of the process of spatial orientation has facilitated the development of the concept assuming that the pattern of space perception changes with growing professional experience. The concept is based on an active approach to the essence, emergence, formation and variation in the pattern of sensory perception of space in man's consciousness. This concept asserts that as pilot's professional expertise increases, the pattern of spatial orientation becomes geocentric because a new system of spatial perception evolves which is a result of the development of a new (instrumental) type of motor activity in space. This finds expression in the fact that perception of spatial position inflight occurs when man has to resolve a new motor task--movement along a complex trajectory in the three-dimensional space onboard a flying vehicle. The meaningful structure of this problem which is to be implemented through controlling movements of the pilot acts as a factor that forms this new system of perception. All this underlies the arrangement of meaningful collection of instrumental data and detection of noninstrumental signals in the comprehensive perception of changes in the spatial position of a flying vehicle.

Aerospace Medicine↗
PubMed1997

Geographic information systems: their use in environmental epidemiologic research.

Advances in geographic information system (GIS) technology, developed by geographers, provide new opportunities for environmental epidemiologists to study associations between environmental exposures and the spatial distribution of disease. A GIS is a powerful computer mapping and analysis technology capable of integrating large quantities of geographic (spatial) data as well as linking geographic with nongeographic data (e.g., demographic information, environmental exposure levels). In this paper we provide an overview of some of the capabilities and limitations of GIS technology; we illustrate, through practical examples, the use of several functions of a GIS including automated address matching, distance functions, buffer analysis, spatial query, and polygon overlay; we discuss methods and limitations of address geocoding, often central to the use of a GIS in environmental epidemiologic research; and we suggest ways to facilitate its use in future studies. Collaborative efforts between epidemiologists, biostatisticians, environmental scientists, GIS specialists, and medical geographers are needed to realize the full potential of GIS technology in environmental health research and may lead to innovative solutions to complex questions.

Electromagnetic Fields↗
PubMed2004

Towards a standard analysis for functional near-infrared imaging.

Functional near-infrared spectroscopy (fNIRS) allows the ability to monitor brain activation by measuring changes in the concentration of oxy- and deoxy-hemoglobin. Until now no standardized approach for fNIRS data analysis has been established, although this has to be regarded as a precondition for future application. Hence, we applied the well-established general linear model to optical imaging data. Further, fNIRS data were analyzed in the frequency domain. Two visual tasks were investigated with optical imaging: a checkerboard paradigm supposed to activate the primary and secondary visual cortex, and a paradigm consisting of moving colored stimuli (rotating 'L's) additionally involving the motion area V5. Analysis with the general linear model detected the activation focus in the primary and secondary visual cortex during the first paradigm. For the second paradigm, a second laterally localized activated brain region was found, most likely representing V5. Spatially resolved spectral analysis confirmed the results by showing maxima of power spectral density and coherence in the same respective brain regions. Moreover, it demonstrated a delay of the hemodynamic response in the motion area. In summary, the present study suggests that the general linear model and spatially resolved spectral analysis can be used as standard statistical approaches for optical imaging data, particularly because they are almost independent of the assumed differential path length factors.

Adult↗
PubMed2005

Spatial phase-shift interferometry--a wavefront analysis technique for three-dimensional topometry.

We describe a new wavefront analysis method, in which certain wavefront manipulations are applied to a spatially defined area in a certain plane along the optical axis. These manipulations replace the reference-beam phase shifting of existing methods, making this method a spatial phase-shift interferometry method. We demonstrate the system's dependence on a defined spatial Airy number, which is the ratio of the characteristic dimension of the manipulated area and the Airy disk diameter of the optical system. We analytically obtain the resulting intensity data of the optical setup and develop various methods to accurately reconstruct the inspected wavefront out of the data. These reconstructions largely involve global techniques, in which the entire wavefront's pattern affects the reconstruction of the wavefront in any given position. The method's noise sensitivity is analyzed, and actual reconstruction results are presented.

Journal Article↗
PubMed2006

Imaging of peptides in the rat brain using MALDI-FTICR mass spectrometry.

Analytical methods are pursued to measure the identity and location of biomolecules down to the subcellular (microm) level. Available mass spectrometric imaging methods either compromise localization accuracy or identification accuracy in their analysis of surface biomolecules. In this study, imaging FTICR-MS is applied for the spatially resolved mass analysis of rat brain tissue with the aim to optimize protein identification by the high mass accuracy and online MS/MS capabilities of the technique. Mass accuracies up to 6 ppm were obtained in the direct MALDI-analysis of the tissue together with a spatial resolution of 200 microm. The spatial distributions of biomolecules differing in mass by less than 0.1 Da could be resolved, and are shown to differ significantly. Online MS/MS analysis of selected ions was demonstrated. A comparison of the FTICR-MS imaging results with stigmatic TOF imaging on the same sample is presented. To reduce the extended measuring times involved, it is recommended to restrict the FTICR-MS analyses to areas of interest as can be preselected by other, faster imaging methods.

Animals↗
PubMed2006

Effect of temporal constraints on hemispheric asymmetries during spatial frequency processing.

Studies on functional hemispheric asymmetries have suggested that the right vs. left hemisphere should be predominantly involved in low vs. high spatial frequency (SF) analysis, respectively. By manipulating exposure duration of filtered natural scene images, we examined whether the temporal characteristics of SF analysis (i.e., the temporal precedence of low on high spatial frequencies) may interfere with hemispheric specialization. Results showed the classical hemispheric specialization pattern for brief exposure duration and a trend to a right hemisphere advantage irrespective of the SF content for longer exposure duration. The present study suggests that the hemispheric specialization pattern for visual information processing should be considered as a dynamic system, wherein the superiority of one hemisphere over the other could change according to the level of temporal constraints: the higher the temporal constraints of the task, the more the hemispheres are specialized in SF processing.

Adult↗
PubMed2006

Statistical inference using the g or K point pattern spatial statistics.

Spatial point pattern analysis provides a statistical method to compare an observed spatial pattern against a hypothesized spatial process model. The G statistic, which considers the distribution of nearest neighbor distances, and the K statistic, which evaluates the distribution of all neighbor distances, are commonly used in such analyses. One method of employing these statistics involves building a simulation envelope from the result of many simulated patterns of the hypothesized model. Specifically, a simulation envelope is created by calculating, at every distance, the minimum and maximum results computed across the simulated patterns. A statistical test is performed by evaluating where the results from an observed pattern fall with respect to the simulation envelope. However, this method, which differs from P. Diggle's suggested approach, is invalid for inference because it violates the assumptions of Monte Carlo methods and results in incorrect type I error rate performance. Similarly, using the simulation envelope to estimate the range of distances over which an observed pattern deviates from the hypothesized model is also suspect. The technical details of why the simulation envelope provides incorrect type I error rate performance are described. A valid test is then proposed, and details about how the number of simulated patterns impacts the statistical significance are explained. Finally, an example of using the proposed test within an exploratory data analysis framework is provided.

Data Interpretation, Statistical↗
PubMed2001

Spatial averaging in the beam of a piston transducer.

This paper presents a theoretical analysis of the spatially averaged free-field responses of phase-sensitive and phase-insensitive receivers centered in the beam of a harmonically excited piston transmitter. The responses of unfocused circular plane piston receivers are analyzed, and both unfocused and spherically focused piston transmitters are considered. A set of closed-form expressions figures prominently in the analysis. The expressions are based on the Lommel diffraction formulation which is, in turn, based on the Fresnel approximation. Although approximate, the expressions allow for quick and easy estimation of phase-sensitive or phase-insensitive unfocused piston receiver responses. It is shown that the spatial averaging effects associated with phase-sensitive and phase-insensitive receivers are virtually identical when gamma < or = 0.1, where gamma = b/a is the ratio of receiver radius b to transmitter radius a. In addition, numerical results obtained from the closed-form expressions are compared with previously reported results. The comparisons indicate that the approximate results are valid from the m = 3 maxima forward under the assumption of linear propagation when ka > 58, where k is the circular wave number. Finally, it is pointed out that the closed-form expressions may prove useful in the estimation of the potential for bioeffects associated with diagnostic ultrasound.

Mathematical Computing↗