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PubMed1985

[Experience with the conversion from radium therapy to an afterloading procedure with special reference to spatial dose distribution].

In radium therapy, the spatial and temporal dose distribution have never been identical in the different hospitals. However, the healing results did not vary correspondingly despite the partly great methodical differences between German and foreign hospitals. Furthermore, the spatial and temporal dose distribution in radium therapy did not conform to theoretic considerations but were a result of the low specific activity of radium as well as of the technical standard of X-ray therapy units until the sixties. It is shown that all requirements valid for radium therapy are also fulfilled by the afterloading method using a linear ray emitter, if an adequate dosage and fractionation is chosen. Taking into account the radiation risk, we think that the radium must be replaced by an afterloading method using a less dangerous nuclide. In our opinion the high dose rate technique is the most favorable method.

Brachytherapy↗
PubMed2006

Ecological analysis of the distribution and socio-spatial context of homicides in Porto Alegre, Brazil.

Over the last decade, the number of homicides in Porto Alegre has increased to the point where external causes are now the main group of causes of death in the 5-34-year age group. Preventing these deaths depends fundamentally on identifying factors related to excess violence in population groups. The overall aim of this study is to analyse the spatial distribution of homicide victims by place of residence in Porto Alegre, the capital of the southernmost Brazilian State of Rio Grande do Sul, in 1996, in order to identify and understand the socio-spatial context. Demographic and socioeconomic indicators based on the 1991 census and 1996 population count were used to build a multivariate classification characterizing the 1851 census tracts. Homicides occurring in 1996 were located using the municipality's Geographic Information System. Four socioeconomic groups were identified, mainly differentiated by housing indicators. Small areas on the urban periphery in which slums (favelas) are concentrated presented higher homicide rates. Homicide rates were lower in the two groups with higher income and educational level. The second step was to classify the census tracts according to the homicide indicator. In this case, areas were differentiated by the number of household inhabitants per room, income, schooling, and median age. We conclude that the multivariate socioeconomic classification presents a limited capacity to identify populations exposed to homicides, suggesting that socioeconomic conditions themselves do not determine violent behaviour. On the other hand, the spatial methods allowed us to identify small areas where deaths are concentrated and whose populations should receive special attention in planning measures to prevent violent deaths.

Adolescent↗
PubMed2005

Tachistoscopic treatment of dyslexia changes the distribution of visual-spatial attention.

Twelve children with developmental dyslexia underwent a four-month treatment with tachistoscopic presentation of words, according to Bakker's methodology. One group received standard lateral presentation of words on a PC screen, while the other group received the same stimuli in random lateral position. The spatial distribution of visual attention was measured by means of the Form-Resolving Field (FRF; ), which was administered along with reading tests, before and after treatment. The FRF of children who received random presentation widened at -12.5 degrees on the left side, while the FRF in the group that received standard lateral presentation narrowed at that position. Both groups significantly improved in reading accuracy for both words and nonwords. Some hypotheses are proposed concerning the mechanisms responsible for the changes in the FRF and their correlation with improvements in word and nonword reading. The results of the present study are also compared with data suggesting a left "minineglect" in dyslexia.

Adolescent↗
PubMed2006

Spatial clustering analysis in neuroanatomy: applications of different approaches to motor nerve fiber distribution.

Spatial organization of the nerve fibers in the peripheral nerves may be important for the studies of axonal regeneration, the degenerative nerve diseases and the construction of interfaces with peripheral nerves, such as nerve prostheses. Functional topography of motor axons related to the gastrocnemius muscle was revealed in the ventral spinal roots by retrograde tracing. Gastrocnemius muscles of adult rats were injected with the tracer Fluoro-Gold. After 3 days of survival the animals were sacrificed and their ventral roots were harvested, sectioned, and imaged on a fluorescence microscope. Maps of the traced fibers were automatically analyzed using a novel approach, local spatial clustering statistics, that tested for occurrences of clusters of motor fibers and visualized them. Thresholds indicating the presence of clustering at various scales of observation were computed based on series of Monte Carlo simulations of random spatial point patterns. Clusters were visualized by kernel interpolation. The approach was tested on simulated data and subsequently applied to the motor fiber maps in the ventral roots. Results revealed clustering of the motor fibers innervating the gastrocnemius muscle at the level of the L6 ventral spinal root. The analysis was validated using Voronoi tessellation and nearest neighbor analysis.

Animals↗
PubMed1982

City size distributions and spatial economic change.

"The concept of the city size distribution is criticized for its lack of consideration of the effects of interurban interdependencies on the growth of cities. Theoretical justifications for the rank-size relationship have the same shortcomings, and an empirical study reveals that there is little correlation between deviations from rank-size distributions and national economic and social characteristics. Thus arguments suggesting a close correspondence between city size distributions and the level of development of a country, irrespective of intranational variations in city location and socioeconomic characteristics, seem to have little foundation." (summary in FRE, ITA, JPN, )

Demography↗
PubMed1989

Spatial velocity distribution and acceleration in serial subvalve tunnel and valvular obstructions: an in vitro study using Doppler color flow mapping.

To evaluate the spatial distribution of flow velocities, turbulence and spatial acceleration in serial tunnel-valve obstruction, Doppler color flow mapping was performed in a pulsatile flow model with a tunnel obstruction (1.0 or 1.5 cm2) inserted at 2, 20 and 40 mm proximal to a mildly stenotic bioprosthetic valve studied at flow rates of 1, 2.7 and 4.9 liters/min. Measured pressure gradients were consistently higher across the tunnel (mean +/- SD 32.7 +/- 26.5 mm Hg) than across the tunnel plus valve (28.8 +/- 26.9 mm Hg, p less than 0.01). Doppler color flow map images were analyzed using a Sony RGB video-digitizing computer, providing numerical velocity assignments for the blue, red and green (variance) pixel components to allow the flow maps to be constructed into digital velocity maps and pseudo three-dimensional velocity maps. The maximal velocity stream extended distal to the tunnel (2 to 19 mm), and the length of this extension correlated well with the pressure gradient measured across the tunnel (r = 0.89), with a rapidly decelerating and turbulent spray area seen immediately distal to the valve. Pressure gradient calculated from the maximal velocity derived from the color flow map, which could only be estimated from the velocity maps for the 1.5 cm2 tunnel, correlated well with the gradient measured across the tunnel (18.0 +/- 14.1 versus 19.2 +/- 14.5 mm Hg, respectively, r = 0.98). Acceleration was seen proximal to both tunnels.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed2005

Towards biologically conformal radiation therapy (BCRT): selective IMRT dose escalation under the guidance of spatial biology distribution.

It is well known that the spatial biology distribution (e.g., clonogen density, radiosensitivity, tumor proliferation rate, functional importance) in most tumors and sensitive structures is heterogeneous. Recent progress in biological imaging is making the mapping of this distribution increasingly possible. The purpose of this work is to establish a theoretical framework to quantitatively incorporate the spatial biology data into intensity modulated radiation therapy (IMRT) inverse planning. In order to implement this, we first derive a general formula for determining the desired dose to each tumor voxel for a known biology distribution of the tumor based on a linear-quadratic model. The desired target dose distribution is then used as the prescription for inverse planning. An objective function with the voxel-dependent prescription is constructed with incorporation of the nonuniform dose prescription. The functional unit density distribution in a sensitive structure is also considered phenomenologically when constructing the objective function. Two cases with different hypothetical biology distributions are used to illustrate the new inverse planning formalism. For comparison, treatments with a few uniform dose prescriptions and a simultaneous integrated boost are also planned. The biological indices, tumor control probability (TCP) and normal tissue complication probability (NTCP), are calculated for both types of plans and the superiority of the proposed technique over the conventional dose escalation scheme is demonstrated. Our calculations revealed that it is technically feasible to produce deliberately nonuniform dose distributions with consideration of biological information. Compared with the conventional dose escalation schemes, the new technique is capable of generating biologically conformal IMRT plans that significantly improve the TCP while reducing or keeping the NTCPs at their current levels. Biologically conformal radiation therapy (BCRT) incorporates patient-specific biological information and provides an outstanding opportunity for us to truly individualize radiation treatment. The proposed formalism lays a technical foundation for BCRT and allows us to maximally exploit the technical capacity of IMRT to more intelligently escalate the radiation dose.

Dose-Response Relationship, Radiation↗
PubMed1992

Search patterns and neglect: a case study.

An irregular and unsystematic search pattern may contribute to unilateral neglect. We examined the sequence of cancellations performed by a patient with unilateral neglect and found that she followed a systematic and stereotypic vertical search pattern. To overcome this vertical search pattern, foils were placed in rows. These foils induced slightly more horizontal movements, but did not alter her neglect. In another attempt to overcome her vertical search and tendency to cancel on the right, she was explicitly instructed to cancel targets alternating to and from the right and left sides of the array. This strategy overcame her vertical search, but, instead of modifying the severity of her neglect, this task only changed its spatial distribution. The altered spatial distribution of neglect is difficult to reconcile with current theories of neglect. We suggest that this patient demonstrates a limited capacity to sequentially be aware of or act upon stimuli.

Aged↗
PubMed2002

Biomechanical effects of intraspecimen variations in tissue modulus for trabecular bone.

Although recent nanoindentation studies have revealed the existence of substantial variations in tissue modulus within single specimens of trabecular bone, little is known regarding the biomechanical effects of such intraspecimen variations. In this study, high-resolution finite element modeling was used to investigate these effects. With limited literature information on the spatial distribution of intraspecimen variations in tissue modulus, two plausible spatial distributions were evaluated. In addition, three specimens (human femoral neck, human vertebral body, and bovine proximal tibia) were studied to assess the role of trabecular architecture. Results indicated that for all specimen/distribution combinations, the apparent modulus of the whole specimen decreased nonlinearly with increasing coefficient of variation (COV) of tissue modulus within the specimen. Apparent modulus decreased by <4% when tissue modulus COV was increased from 0% to 20% but decreased by 7-24%, depending on the assumed spatial distribution, for an increase in tissue modulus COV from 20% to 50%. For compressive loading to the elastic limit, increasing tissue modulus COV from 20% to 50% caused up to a 28-fold increase in the amount of failed tissue, depending on assumed spatial distribution and trabecular architecture. We conclude that intraspecimen variations in tissue modulus, if large, may have appreciable effects on trabecular apparent modulus and tissue-level failure. Since the observed effects depended on the assumed spatial distribution of the tissue modulus variations, a description of such distributions, particularly as a function of age, disease, and drug treatment, may provide new insight into trabecular bone structure-function relationships.

Adult↗
PubMed2005

Distribution of spatial complexity of EEG in idiopathic generalized epilepsy and its change after chronic valproate therapy.

The objective of this study was to investigate the global and regional spatial synchrony of the EEG background activity, and to assess the effect of chronic valproate therapy on spatial synchrony. 15 idiopathic generalized epilepsy (IGE) patients were examined and compared to 16 normal controls. Resting EEG with 19 channels was investigated before and during chronic administration of valproate (VPA). Omega, a single-valued measure of spatial covariance complexity, was calculated to assess the degree of spatial synchrony of EEG. Furthermore, a new parameter was defined to characterize the distribution of spatial synchrony (Antero-Posterior Complexity Ratio, APCR). Global Omega complexity was significantly lower in IGE compared to controls, while regional complexity showed significant differences only in the anterior region: the IGE group showed lower complexity. APCR was significantly lower in IGE. VPA therapy (1) lowered the global complexity, (2) increased regional complexity in the anterior region, but decreased it in the posterior region, and (3) increased APCR. In IGE lower complexity, i.e. enhanced spatial synchrony, was found, especially in the anterior cortical area. VPA modified the distribution of spatial synchrony in IGE patients towards that of normal controls, although the effect is not identical with full normalization of cortical bioelectric activity. Whether the observed change of spatial synchrony distribution may reflect the normalizing effect of valproate on the brain state is worth further investigation.

Adolescent↗
PubMed2004

Linkage disequilibrium as a signature of selective sweeps.

The hitchhiking effect of a beneficial mutation, or a selective sweep, generates a unique distribution of allele frequencies and spatial distribution of polymorphic sites. A composite-likelihood test was previously designed to detect these signatures of a selective sweep, solely on the basis of the spatial distribution and marginal allele frequencies of polymorphisms. As an excess of linkage disequilibrium (LD) is also known to be a strong signature of a selective sweep, we investigate how much statistical power is increased by the inclusion of information regarding LD. The expected pattern of LD is predicted by a genealogical approach. Both theory and simulation suggest that strong LD is generated in narrow regions at both sides of the location of beneficial mutation. However, a lack of LD is expected across the two sides. We explore various ways to detect this signature of selective sweeps by statistical tests. A new composite-likelihood method is proposed to incorporate information regarding LD. This method enables us to detect selective sweeps and estimate the parameters of the selection model better than the previous composite-likelihood method that does not take LD into account. However, the improvement made by including LD is rather small, suggesting that most of the relevant information regarding selective sweeps is captured by the spatial distribution and marginal allele frequencies of polymorphisms.

Computer Simulation↗
PubMed1997

Additional thyroid dose factor from transportation sources in Russia after the Chernobyl disaster.

Beginning approximately 4 years after the Chernobyl nuclear accident a steady increase in the incidence of thyroid cancer was observed in children and adolescents of the Bryansk Oblast, which received the highest level of radionuclide contaminants in Russia. We examined the spatial relationship between the residence location of patients with identified thyroid cancer (0-18 years old at the time of the accident) and a number of geographic parameters to better account for the etiology of thyroid cancer spatial distribution. Geographic parameters analyzed included spatial distribution of 137Cs and 131I in soil, population demographics, measurements and reconstructions. of absorbed thyroid 131I doses in the population, and maps of major transportation arteries. An interesting finding is the lack of a consistent correlation between the spatial distribution of radionuclides in the soil and thyroid cancer incidence. Instead, most of the thyroid cancer cases were diagnosed in settlements situated on major railways and roads. Correlating population with thyroid cancer cases and transportation arteries reveals a much higher cancer rate on or near major roads and railways than at a distance from them, again independent of radionuclide soil concentration. There are other important factors, of course, that must be considered in future evaluations of this phenomenon. These include the influence of iodine endemic zones, genetic predisposition to thyroid cancer, and duration of residence time in contaminated areas. The feasibility of radionuclide transport on railways and roads is discussed, together with the vectors for transfer of the contaminants to the human population. Developing a model to reconstruct the radiation dose to the thyroid over time in this geographic region is proposed in light of the impact of transportation arteries. Specific studies are outlined to provide the data necessary to develop this model as well as to better characterize the feasibility and scientific validity of the contribution to human health effects of this transport factor. Transport factor refers to the transport of radionuclides on transportation arteries and the transfer of these agents to the human population residing in the vicinity of these arteries. If the impact on thyroid cancer of the transport of radionuclides on major railways and roads is indeed significant, a major reappraisal of the risk of large-scale radioactive release into the environment is necessary.

Adolescent↗
PubMed1992

The influence of spatial polarization distribution on spot poled PVDF membrane hydrophone performance.

The influence of spatial polarization distribution on spot poled PVDF membrane hydrophone performance was calculated and then experimentally verified using a one-dimensional model based on acoustic wave propagation through a layered medium. It is shown that the sensitivity of the hydrophone is markedly dependent on the spatial polarization distribution. It is also shown that there can be a significant difference between the voltage sensitivities measured in the same hydrophone probe depending on which electrode is actually facing the acoustic source. The measurements carried out in the frequency range 1-20 MHz indicate that this difference, while negligible below 2 MHz, may exceed 1.6 dB at higher frequencies. The model developed can also be used to determine the "effective" piezoelectric constant d33 of the PVDF material as a continuous function of frequency. Moreover, the model predicts the existence of a negative slope in the frequency response of the spot poled membrane hydrophone. The experimental confirmation of this prediction underscores the importance of using swept frequency methods during calibration measurements.

Electricity↗
PubMed2001

Methods of mortality (incidence) rates interpretation assessment in small populations.

Findings and procedures include in this article have been realized at Regional Public Health Office in Hradec Králové (Czech Republic) within the period from August 1999 to February 2000. The model sample used in this article dealed only with events of neoplasms incidence in men's population in the region of Eastern Bohemia within the period from 1986 to 1997. The original experimental part concerned to the use of procedures for demographical data standardization for target group of "small populations" including of their selection and spatial distribution. As the result of it, there are topical maps of spatial distribution of incidence (event. mortality) of selected diagnoses according to sex with target area units delimitated by methods of regional geography with around 120 km2 and total average number about 10000 inhabitants. Thanks to using of cluster analysis these maps include inside aggregated information about standardized ratio value, expression of its reliability rate. The original system has been tested thanks to software application and methodical procedures developed by author of this article in the connection with progressive information technology of geographical information system GIS SPANS which all allow quite easily to carry out the detection of another diagnoses spatial distribution within selected resolution and provided data. Mentioned above conclusions may be suggested as a basic descriptive method for the health risk assessment. Another analytical procedures can follow this original method in next phases. The method has brought essentially new view of the disease spatial distribution which has not been used in the Czech Republic in such a range and detail yet. There are being uncovered great possibilities that could in the end contribute to discovering of causal connections - mainly diseases with unfavourable development in time series. At the same time the introductory premise about spatial distribution of events to "skip" with the change of resolution has been confirmed.

Adolescent↗
PubMedDate not supplied

[Spatial risk distribution: modeling infant mortality in Porto Alegre, Rio Grande do Sul State, Brazil].

Estimation and mapping of risk profiles are the main concerns of epidemiology. This paper analyzes spatial distribution of infant mortality cases as compared to live-born controls from Porto Alegre, Rio Grande do Sul. The modeling framework adopted in this research work is a spatial point process. Under this structure, a risk measure which continuously varies over the study region is defined and estimated using generalized additive model methods. This approach has the advantage of allowing for risk factors that are simple and easy to interpret. The procedure also allows the construction of tolerance contours which help identify areas of significantly high/low risk and an overall test for the null hypothesis of constant risk over the region. Application of this method to infant mortality data showed a highly significant spatial variation in risk for neonatal mortality data and non-significant results for post-neonatal mortality data.

Brazil↗
PubMed2003

Spatial autocorrelation analysis offers new insights into gene flow in the Australian bush rat, Rattus fuscipes.

Dispersal is a fundamental process that influences the response of species to landscape change and habitat fragmentation. In an attempt to better understand dispersal in the Australian bush rat, Rattus fuscipes, we have combined a new multilocus autocorrelation method with hypervariable microsatellite genetic markers to investigate fine-scale (< or = 1 km) patterns of spatial distribution and spatial genetic structure. The study was conducted across eight trapping transects at four sites, with a total of 270 animals sampled. Spatial autocorrelation analysis of bush rat distribution revealed that, in general, animals occurred in groups or clusters of higher density (< or = 200 m across), with intervening gaps or lower density areas. Spatial genetic autocorrelation analysis, based on seven hypervariable microsatellite loci (He = 0.8) with a total of 80 alleles, revealed a consistent pattern of significant positive local genetic structure. This genetic pattern was consistent for all transects, and for adults and sub-adults, males and females. By testing for autocorrelation at multiple scales from 10 to 800 m we found that the extent of detectable positive spatial genetic structure exceeded 500 m. Further analyses detected significantly weaker spatial genetic structure in males compared with females, but no significant differences were detected between adults and sub adults. Results from Mantel tests and hierarchical AMOVA further support the conclusion that the distribution of bush rat genotypes is not random at the scale of our study. Instead, proximate bush rats are more genetically alike than more distant animals. We conclude that in bush rats, gene flow per generation is sufficiently restricted to generate the strong positive signal of local spatial genetic structure. Although our results are consistent with field data on animal movement, including the reported tendency for males to move further than females, we provide the first evidence for restricted gene flow in bush rats. Our study appears to be the first microsatellite-based study of fine-scale genetic variation in small mammals and the first to report consistent positive local genetic structure across sites, age-classes, and sexes. The combination of new forms of autocorrelation analyses, hypervariable genetic markers and fine-scale analysis (< 1 km) may thus offer new evolutionary insights that are overlooked by more traditional larger scaled (> 10 km) population genetic studies.

Animals↗
PubMed1982

[Spatial population distribution and development: notes on urban settlements in Latin America].

The relationship between population distribution and development trends is analyzed, with attention to the planning of spatial redistribution policies. Some shortcomings in the investigation of the causes and consequences of urbanization are discussed. The second part of the article "refers to some spatial demographic and socio-economic expressions of the urbanization process in Latin America, the population concentration trends and their relationships with changes in agrarian structure and industrialization, social stratification patterns and forms of urban space organization.... The paper concludes with some critical notes on the theses related to 'optimum' size of urban centres and to 'balanced development' of urban systems, on which some policy proposals have been based." (summary in ENG)

Agriculture↗
PubMed1997

Calcium waves in a model with a random spatially discrete distribution of Ca2+ release sites.

We study the propagation of intracellular calcium waves in a model that features Ca2+ release from discrete sites in the endoplasmic reticulum membrane and random spatial distribution of these sites. The results of our simulations qualitatively reproduce the experimentally observed behavior of the waves. When the level of the channel activator inositol trisphosphate is low, the wave undergoes fragmentation and eventually vanishes at a finite distance from the region of initiation, a phenomenon we refer to as an abortive wave. With increasing activator concentration, the mean distance of propagation increases. Above a critical level of activator, the wave becomes stable. We show that the heterogeneous distribution of Ca2+ channels is the cause of this phenomenon.

Animals↗