Biomedical subjects

M Sibomana

Publications and source records attributed to M Sibomana.

9 recordsLinked to original sources

PubMed2001

Decreased benzodiazepine receptor density in the cerebellum of early blind human subjects.

As a first approach to study the effect of early visual deprivation in the GABA-ergic inhibitory system, the distribution of benzodiazepine receptors (BZR) was accurately estimated using [11C]flumazenil ([11C]FMZ). Measurements were carried out in five subjects who became blind early in life and in five sighted control subjects. The interactions between [11C]FMZ and BZR were described using a non-linear compartmental analysis which permitted to estimate the BZR synaptic density independently of other model parameters. The distribution of BZR in the visual areas and other cortical regions of blind subjects was qualitatively and quantitatively similar to that of controls. However, the BZR density in the cerebellum was significantly lower in blind than in control subjects (P<0.01). Our findings suggest that modifications of the cerebellar neural circuitry may be concomitant to the already observed compensatory reorganization in cerebral areas of blind subjects.

Adult↗

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

Attenuation correction in whole-body FDG oncological studies: the role of statistical reconstruction.

Whole-body fluorine-18 fluoro-2-d-deoxyglucose positron emission tomography (FDG-PET) is widely used in clinical centres for diagnosis, staging and therapy monitoring in oncology. Images are usually not corrected for attenuation since filtered backprojection (FBP) reconstruction methods require a 10 to 15-min transmission scan per bed position on most current PET devices equipped with germanium-68 rod transmission sources. Such an acquisition protocol would increase the total scanning time beyond acceptable limits. The aim of this work is to validate the use of iterative reconstruction methods, on both transmission and emission scans, in order to obtain a fully corrected whole-body study within a reasonable scanning time of 60 min. Five minute emission and 3-min transmission scans are acquired at each of the seven bed positions. The transmission data are reconstructed with OSEM (ordered subsets expectation maximization) and the last iteration is reprojected to obtain consistent attenuation correction factors (ACFs). The emission image is then also reconstructed with OSEM, using the emission scan corrected for normalization, scatter and decay together with the set of consistent ACFs as inputs. The total processing time is about 35 min, which is acceptable in a clinical environment. The image quality, readability and accuracy of uptake quantification were assessed in 38 patients scanned for various malignancies. The sensitivity for tumour detection was the same for the non-attenuation-corrected (NAC-FBP) and the attenuation-corrected (AC-OSEM) images. The AC-OSEM images were less noisy and easier to interpret. The interobserver reproducibility was significantly increased when compared with non-corrected images (96.1% vs 81.1%, P<0.01). Standardized uptake values (SUVs) measured on images reconstructed with OSEM (AC-OSEM) and filtered backprojection (AC-FBP) were similar in all body regions except in the pelvic area, where SUVs were higher on AC-FBP images (mean increase 7.74%, P<0. 01). Our results show that, when statistical reconstruction is applied to both transmission and emission data, high quality quantitative whole-body images are obtained within a reasonable scanning (60 min) and processing time, making it applicable in clinical practice.

Adult↗

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↗

PubMed1999

Exact rebinning methods for three-dimensional PET.

The high computational cost of data processing in volume PET imaging is still hindering the routine application of this successful technique, especially in the case of dynamic studies. This paper describes two new algorithms based on an exact rebinning equation, which can be applied to accelerate the processing of three-dimensional (3-D) PET data. The first algorithm, FOREPROJ, is a fast-forward projection algorithm that allows calculation of the 3-D attenuation correction factors (ACF's) directly from a two-dimensional (2-D) transmission scan, without first reconstructing the attenuation map and then performing a 3-D forward projection. The use of FOREPROJ speeds up the estimation of the 3-D ACF's by more than a factor five. The second algorithm, FOREX, is a rebinning algorithm that is also more than five times faster, compared to the standard reprojection algorithm (3DRP) and does not suffer from the image distortions generated by the even faster approximate Fourier rebinning (FORE) method at large axial apertures. However, FOREX is probably not required by most existing scanners, as the axial apertures are not large enough to show improvements over FORE with clinical data. Both algorithms have been implemented and applied to data simulated for a scanner with a large axial aperture (30 degrees), and also to data acquired with the ECAT HR and the ECAT HR+ scanners. Results demonstrate the excellent accuracy achieved by these algorithms and the important speedup when the sinogram sizes are powers of two.

Algorithms↗

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↗

PubMed1997

31P NMR saturation transfer study of the creatine kinase reaction in human skeletal muscle at rest and during exercise.

The creatine kinase reaction has been studied by 31P NMR in exercising human calf muscle. Quantitative analysis of high energy phosphates and saturation transfer study of the creatine kinase flux in the direction of ATP synthesis (Vfor) were performed at rest and during exercise. As expected, exercise induced a [PCr] decrease (from 28.5 +/- 0.9 to 21.9 +/- 1.5 mM, P < 0.01) matched by a Pi increase (from 4.5 +/- 0.2 to 8.9 +/- 1.8 mM, P = 0.06). pHi and [ATP] remained unchanged. Vfor did not change from rest (12.4 +/- 0.9 mM s(-1)) to moderate exercise and decreased at the highest exercise level (8.4 +/- 1.4 mM s(-1), P = 0.006). This observation differs from the prediction of the creatine kinase rate equation, showing an increase in the flux with exercise intensity. Computations suggest that this discrepancy arises from metabolite compartmentalization and/or from the reaction kinetics of a dead end complex stabilized by planar anions.

Adult↗

PubMed1997

Exact and approximate rebinning algorithms for 3-D PET data.

This paper presents two new rebinning algorithms for the reconstruction of three-dimensional (3-D) positron emission tomography (PET) data. A rebinning algorithm is one that first sorts the 3-D data into an ordinary two-dimensional (2-D) data set containing one sinogram for each transaxial slice to be reconstructed; the 3-D image is then recovered by applying to each slice a 2-D reconstruction method such as filtered-backprojection. This approach allows a significant speedup of 3-D reconstruction, which is particularly useful for applications involving dynamic acquisitions or whole-body imaging. The first new algorithm is obtained by discretizing an exact analytical inversion formula. The second algorithm, called the Fourier rebinning algorithm (FORE), is approximate but allows an efficient implementation based on taking 2-D Fourier transforms of the data. This second algorithm was implemented and applied to data acquired with the new generation of PET systems and also to simulated data for a scanner with an 18 degrees axial aperture. The reconstructed images were compared to those obtained with the 3-D reprojection algorithm (3DRP) which is the standard "exact" 3-D filtered-backprojection method. Results demonstrate that FORE provides a reliable alternative to 3DRP, while at the same time achieving an order of magnitude reduction in processing time.

Algorithms↗

PubMedDate not supplied

[Current data and perspectives on positron emission tomography oncology-radiotherapy].

Positron emission tomography (PET) is one of the most promising diagnostic procedures in oncology. Using the glucose analogue fluorodeoxyglucose, PET produces whole-body images and is highly sensitive for tumor diagnosis and staging. We review three particular clinical situations in which PET-FDG has proven not only its diagnostic accuracy, but also its impact on patient management, i.e., the staging of non-small cell lung cancer, diagnosis and staging of colo-rectal cancer and head and neck cancer recurrence. Image registration yields anatomo-metabolic images that could be used as additional information for the determination of radiation fields. Tracer and technical issues remain to be solved before PET can be routinely used for that purpose.

Bronchial Neoplasms↗