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At least 523 records · Page 29Linked to original sources
PubMed2000

Near-infrared study of fluctuations in cerebral hemodynamics during rest and motor stimulation: temporal analysis and spatial mapping.

We have noninvasively studied the motor cortex hemodynamics in human subjects under rest and motor stimulation conditions using a multichannel near-infrared tissue spectrometer. Our instrument measures optical maps of the cerebral cortex at two wavelengths (758 and 830 nm), with an acquisition time of 160 ms per map. We obtained optical maps of oxy- and deoxy-hemoglobin concentration changes in terms of amplitudes of folding average, power spectrum and coherence at the stimulation repetition frequency, and the phase synchronization index. Under periodic motor stimulation conditions, we observed coherence and frequency or phase synchronization of the local hemodynamic changes with stimulation. Our main findings are the following: (1) The amplitude of the hemodynamic response to the motor stimulation is comparable to the amplitude of the fluctuations at rest. (2) The spatial patterns of the oxy- and deoxy-hemoglobin responses to the stimulation are different. (3) The hemodynamic response to stimulation shows a spatial localization and a level of phase synchronization with the motor stimulation that depends on the stimulation period.

Adult↗
PubMed2002

Spatial coherence analysis applied to aberration correction using a two-dimensional array system.

Complex degree of coherence functions are computed using synthetic and measured ultrasound data to demonstrate noteworthy aspects of coherence analysis in the context of aberration correction. Coherence functions calculated from synthetic data illustrate the importance of proper normalization of the constituent cross-correlation integrals when weak elements and receiver directivity are significant factors. The synthetic data also show that a spike can occur at the zero-lag position of the coherence function when the signal-to-noise ratio is reduced by element directivity near the edges of a large aperture. The latter observation is confirmed by experimental data acquired through tissue-mimicking distributed aberration phantoms using a low f-number two-dimensional array system. The coherence of data acquired at neighboring elements is not changed by time-shift compensation of transmit and receive focusing, but time-shift compensation does improve the coherence of echoes measured over larger separations. The resulting increase in coherence widths evaluated at levels between 0.2 and 0.5 is correlated with narrower -10 dB and -20 dB effective widths in focuses visualized using single-transmit images. Iterative focus compensation methods may benefit from aberration estimation algorithms that take advantage of these longer-range correlations in random-scattering waveforms.

Artifacts↗
PubMed2004

Modification of spatial distribution of 2,4-dichlorophenoxyacetic acid degrader microhabitats during growth in soil columns.

Bacterial processes in soil, including biodegradation, require contact between bacteria and substrates. Knowledge of the three-dimensional spatial distribution of bacteria at the microscale is necessary to understand and predict such processes. Using a soil microsampling strategy combined with a mathematical spatial analysis, we studied the spatial distribution of 2,4-dichlorophenoxyacetic acid (2,4-D) degrader microhabitats as a function of 2,4-D degrader abundance. Soil columns that allowed natural flow were percolated with 2,4-D to increase the 2,4-D degrader abundance. Hundreds of soil microsamples (minimum diameter, 125 microm) were collected and transferred to culture medium to check for the presence of 2,4-D degraders. Spatial distributions of bacterial microhabitats were characterized by determining the average size of colonized soil patches and the average number of patches per gram of soil. The spatial distribution of 2,4-D degrader microhabitats was not affected by water flow, but there was an overall increase in colonized patch sizes after 2,4-D amendment; colonized microsamples were dispersed in the soil at low 2,4-D degrader densities and clustered in patches that were more than 0.5 mm in diameter at higher densities. During growth, spreading of 2,4-D degraders within the soil and an increase in 2,4-D degradation were observed. We hypothesized that spreading of the bacteria increased the probability of encounters with 2,4-D and resulted in better interception of the degradable substrate. This work showed that characterization of bacterial microscale spatial distribution is relevant to microbial ecology studies. It improved quantitative bacterial microhabitat description and suggested that sporadic movement of cells occurs. Furthermore, it offered perspectives for linking microbial function to the soil physicochemical environment.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1989

Component analysis of spatial and spectral patterns in multispectral images. II. Entropy minimization.

In Part I [J. Opt. Soc. Am. A 4, 2101 (1987)] of this series, we developed a method for estimating both spatial patterns and spectral curves of components in a multispectral scene. This method does not need spatial and spectral information about the components but only multispread imagery data. The estimation is given as a feasible solution set satisfying the nonnegativity constraint for density and spectral response for all components at all pixels. In this paper, we estimate unique solutions for both the component patterns and the spectra from the feasible solution set. The solution is given by optimizing an entropy minimization criterion. This criterion enhances the spectral or spatial features of individual components. Two experimental results are shown to demonstrate the effectiveness of this method with biological and cytochemical specimens. The limitations of this method for unique pattern estimation are also discussed.

Algorithms↗
PubMed2000

[Hospital system as a source of information to estimate stillbirth and neonatal mortality rates].

OBJECTIVE: Studies on the evolution of infant mortality rate are very relevant. Nevertheless, lack of vital statistics in Brazil limits the temporal and spatial analysis of this indicator. This study aims to investigate the possible use of the Brazilian Hospital Information System as an alternative information source for stillbirth and neonatal mortality rates by age group. METHODS: A new method to estimate the stillbirth and neonatal mortality rates is proposed. It was applied in a set of selected Brazilian states in the year of 1995. For comparative purposes, the Brazilian Death Information System was assessed to estimate the mortality rates under study, after adjusting the registered number of live births by using a demographic tool. RESULTS: By assessing the Hospital Information System a larger number of fetal and early neonatal deaths were observed when compared to data given by the death information system of the Northeastern states. Besides, in the Southern and Southeastern states, where death records are more thorough, the mortality rates calculated using both information sources were very similar. CONCLUSIONS: The results suggest that the proposed methodology could greatly contribute to the analysis of the spatial-time evolution of stillbirth and neonatal death rates in recent years in Brazil, as data on death registration in the majority of the Brazilian states are less thorough than those from the hospital information system.

Brazil↗
PubMed2004

Analysis of spatial and temporal expression patterns of bone morphogenetic protein family members in the rat uterus over the estrous cycle.

Recent studies have demonstrated that bone morphogenetic proteins (BMPs) play fundamental roles in female fertility. This is particularly evident in terms of the ovary. One major question that is just beginning to be addressed is the role of BMPs in the non-pregnant uterus. To help fill this gap, we used in situ hybridization to investigate the expression of BMP family members in the rat uterus over the estrous cycle. We found that the endometrial/uterine cycle is accompanied by the expression of several components of the BMP pathway - including ligands, receptors and antagonists. The mRNAs encoding BMP receptors are expressed in the epithelial (BMP-RIA, -RIB and -RII), periluminal stroma (BMP-RIA and -RII) and smooth muscle cells (BMP-RIA and -RII). The expression of all three receptors showed clear cyclic variations. The mRNAs encoding BMP ligands were highly expressed in the periluminal stroma (BMP-2 and -7) and glandular epithelium (BMP-7). The expression of BMP-2, but not BMP-7, was cyclical. Notably, the periluminal stroma expressed noggin mRNA. In the blood vascular system, BMP-4, -6 and -RII mRNAs were expressed in myometrial endothelial cells. Interestingly, follistatin, noggin, and BMP-4, -6 and -7 mRNAs were expressed in eosinophilic leukocytes, suggesting unexpected roles for eosinophil-derived BMPs in uterine function. We conclude that BMP ligands, receptors and antagonists are expressed in spatially and temporally restricted patterns that are consistent with a physiological role for these regulatory molecules in promoting uterine cellular processes including cell proliferation, differentiation and apoptosis during the cycle.

Animals↗