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M Bentourkia

Publications and source records attributed to M Bentourkia.

8 recordsLinked to original sources
PubMed2000

Comparison of regional cerebral blood flow and glucose metabolism in the normal brain: effect of aging.

The regional cerebral blood flow (rCBF) and metabolic rate for glucose (rCMRGlc) are associated with functional activity of the neural cells. The present work reports a comparison study between rCBF and rCMRGlc in a normal population as a function of age. 10 young (25.9+/-5.6 years) and 10 old (65.4+/-6.1 years) volunteers were similarly studied at rest. In each subject, rCBF and rCMRGlc were measured in sequence, during the same session. Both rCBF and rCMRGlc values were found to decrease from young (mean rCBF=43.7 ml/100 g per min; mean rCMRGlc=40.6 micromol/100 g per min) to old age (mean rCBF=37.3 ml/100 g per min; mean rCMRGlc=35.2 micromol/100 g per min), resulting in a drop over 40 years of 14.8% (0.37%/year) and 13.3% (0.34%/year), respectively. On a regional basis, the frontal and the visual cortices were observed to have, respectively, the highest and the lowest reduction in rCBF, while, for rCMRGlc, these extremes were observed in striatum and cerebellum. Despite these differences, the ratio of rCBF to rCMRGlc was found to have a similar behavior in all brain regions for young and old subjects as shown by a correlation coefficient of 88%. This comparative study indicates a decline in rCBF and rCMRGlc values and a coupling between CBF and CMRGlc as a function of age.

Adult↗
PubMed1999

Energy dependence of nonstationary scatter subtraction--restoration in high resolution PET.

In previous works, the determination of object and detector scatter kernels from line source measurements was described and their application in scatter correction was investigated. It was also shown that low energy data contains a large fraction of useful events (true and detector scatter events). In the present work, data acquired in multispectral mode was summed in single broad energy windows of lower energy thresholds varying from 129 to 516 keV in steps of 43 keV and a constant upper energy threshold of 645 keV. Line-source projections were fitted by extracting the object and detector scatter kernels as a function of energy threshold. These kernels were then used to process scatter by the nonstationary convolution subtraction-restoration method in phantom images. After scatter correction, the sensitivity is found to increase by up to 64% at the lower threshold of 129 keV, relative to the conventional photopeak energy window (344-645 keV). Whereas contrast and spatial resolution are degraded as the energy discriminator is lowered, such degradation is fully recovered by the scatter correction. As a result of scatter correction, the noise increases insignificantly in hot regions but substantially in cold regions, in proportion of the amount of scatter.

Image Processing, Computer-Assisted↗
PubMed1999

A standardized blood sampling scheme in quantitative FDG-PET studies.

Quantitative estimation of brain glucose metabolism (rCMRGlc) with positron emission tomography and fluorodeoxyglucose involves arterial blood sampling to estimate the delivery of radioactivity to the brain. Usually, for an intravenous injection of 30 s duration, an accurate input curve requires a frequency of one sample every 5 s or less to determine the peak activity in arterial plasma during the first 2 min after injection. In this work, 13 standardized sampling times were shown to be sufficient to accurately define the input curve. This standardized input curve was subsequently fitted by a polynomial function for its rising part and by spectral analysis for its decreasing part. Using the measured, the standardized, and the fitted input curves, rCMRGlc was estimated in 32 cerebral regions of interest in 20 normal volunteers. Comparison of rCMRGlc values obtained with the measured and the fitted input curves showed that both procedures gave consistent results, with a maximal relative error in mean rCMRGlc of 1% when using the autoradiographic method and 2% using kinetic analysis of dynamic data. This input-curve-fitting technique, which is not dependent on the peak time occurrence, allows an accurate determination of the input-curve shape from reduced sampling schemes.

Adult↗
PubMed1998

Evolution of brain glucose metabolism with age in epileptic infants, children and adolescents.

During the first years of life, the human brain undergoes repetitive modifications in its anatomical, functional, and synaptic construction to reach the complex functional organization of the adult central nervous system. As an attempt to gain further insight in those maturation processes, the evolution of cerebral metabolic activity was investigated as a function of age in epileptic infants, children and adolescents. The regional cerebral metabolic rates for glucose (rCMRGlc) were measured with positron emission tomography (PET) in 60 patients aged from 6 weeks to 19 years, who were affected by complex partial epilepsy. They were scanned at rest, without premedication, in similar conditions to 20 epileptic adults and in 49 adult controls. The distribution of brain metabolic activity successively extended from sensorimotor areas and thalamus in epileptic newborns to temporo-parietal and frontal cortices and reached the adult pattern after 1 year of age. The measured rCMRGlc in the cerebral cortex, excluding the epileptic lesions, increased from low values in infants to a maximum between 4 and 12 years, before it declined to stabilize at the end of the second decade of life. Similar age-related changes in glucose metabolic rates were not observed in the adult groups. Despite the use of medications, the observed variations of rCMRGlc with age in young epileptic humans confirm those previously described in pediatric subjects. These metabolic changes are in full agreement with the current knowledge of the synaptic density evolution in the human brain.

Adolescent↗
PubMed1996

Nonstationary scatter subtraction-restoration in high-resolution PET.

UNLABELLED: Although removal of object scatter has been shown to improve both contrast and quantitation accuracy, subtraction of detector scatter leads to marginal contrast enhancement and negligible resolution recovery at the expense of reduced sensitivity and increased statistical noise. Since detector scatter has correct information about radioactivity but slightly erroneous information about source location, we suggest that this component should be restored to preserve sensitivity and improve resolution. METHODS: A scatter correction model that consecutively removes object scatter and restores detector scatter is proposed. The scatter components are processed in the spatial domain using nonstationary scatter kernels. The detector scatter restoration kernel is obtained by piecewise inversion in the Fourier space. The model was tested using line source and hot spot phantom measurements. RESULTS: Object scatter subtraction increased contrast substantively with no effect on resolution. Detector scatter restoration recovered resolution almost completely with modest contrast enhancement in small lesions. Spillover effects were reduced to less than 5% for hot spots > or = 3 x FWHM, at the expense of moderate noise amplification. CONCLUSION: While subtraction of object scatter is necessary for contrast enhancement and quantitation accuracy, restoration of detector scatter preserves sensitivity and improves quantitation accuracy by reducing spillover effects in high-resolution PET.

Image Enhancement↗
PubMed1995

Assessment of scatter components in high-resolution PET: correction by nonstationary convolution subtraction.

UNLABELLED: This paper describes a new approach to determine individual scatter kernels and to use them for scatter correction by integral transformation of the projections. METHODS: Individual scatter components are fitted on the projections of a line source by monoexponentials. The position-dependent scatter parameters of each scatter components are then used to design non-stationary scatter correction kernels for each point in the projection. These kernels are used in a convolution-subtraction method which consecutively removes object, collimator and detector scatter from projections. This method is based on a model which assumes that image degradation results exclusively from Compton interactions of annihilation photons, thus neglecting further Compton interactions of object scatters with collimator and detector. RESULTS: Subtraction of the object scatter component improved contrast typical of what is obtained with standard convolution-subtraction methods. The collimator scatter component is so weak that it can be safely combined with object scatter for correction. Subtraction of detector scatter from images did not improve contrast because statistical accuracy is degraded by removing counts from hot regions while cold regions (background) remain unchanged. CONCLUSION: Subtraction of object and collimator scatter improves contrast only. The slight gain in image sharpness resulting from the subtraction of detector scatter does not justify removal of this component at the expense of sensitivity.

Humans↗
PubMedDate not supplied

A flexible image segmentation prior to parametric estimation.

A flexible method based on spatial and temporal pixel variance to compute parametric images in positron emission tomography (PET) is reported. For [(18)F]fluorodeoxyglucose and [(15)O]water brain studies, images were segmented based on coefficients of variation and correlation coefficients of neighboring pixels, and kinetic parameters were estimated by dynamic (DYN) and autoradiographic (ARG) fitting. For comparison, regional glucose metabolism (rCMRGlc) and blood flow (rCBF) in both DYN and ARG were estimated from segmented and usual images. The maximal relative error was found to be 4, 10 and 17% for ARG and DYN rCMRGlc and DYN rCBF, respectively.

Autoradiography↗