Etude des champs locaux dans les solides par RMN à faible champ détectée par rayonnement nucléaire

dissertn: Diss. Doct

Effect of exogenous creatine supplementation on muscle PCr metabolism

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Effet d'un supplément alimentaire en créatine sur la concentration intra-musculaire et sur la resynthèse de la phosphoryl-créatine mesurées par RMN du 31P

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Effect of Creatine Supplementation on Pcr Repletion

The purpose of this study was to test the effect of creatine supplementation on muscle [PCr] and on its repletion kinetics after exercise. Sixteen male subjects were divided into two groups in a double blind fashion. They were instructed to consume over 13 days, either creatine (3 × 7 g a day), or an equivalent amount of placebo. The [PCr] was measured in the calf muscle by 31P NMRS, the day before the beginning of the treatment and the day following its completion. During the same session, the half-repletion time (T1/2) was measured by means of an exercise performed in the magnet. The exercise consisted in 50 plantar fexions-extensions over a period of 1 min against a load equal to 70% of MVC. A spectrum was acquired every 15 s during the exercise and during 5 min of recovery. T1/2 was calculated by means of the fitting of an exponential function through the [PCr] measured during the recovery. The results showed that muscle [PCr] at rest increased from 18.7 ± 22.1 mmol.kg-1 to 22.4 ± 1.56 mmol.kg-1 after a period of creatine supplementation (P=0.002) whereas it remained unchanged in the placebo group. [Pi] and muscle pH were not influenced by exogenous creatine. After exercise, T1/2 was not either modified (34.6 ± 5.0 s versus 40.0 ± 13.0 s) by creatine supplementation. To conclude, faster [PCr] repletion does not appear to explain the effects of creatine supplementation observed during intermittent exercises

Free magnesium concentration in isolated rabbit hearts subjected to high dose isoproterenol infusion: a P-31 NMR study

The hypothesis of magnesium deficiency in isoproterenol (ISO) induced myocardial injury has been investigated by P-31 nuclear magnetic resonance spectroscopy. High energy phosphate concentrations, pH(i), and intracellular free magnesium concentration ([Mg2+](i)) were measured in isolated rabbit hearts perfused at constant flow and subjected to 10(-6) M isoproterenol during 30 min. Recent calibrations were used for [Mg2+](i) measurements, and uncertainties on [Mg2+](i) estimated values were calculated. During isoproterenol infusion, pH(i), [PCr], and [ATP] decreased, while [P-i] increased. When it was stopped, [PCr] completely repleted, whereas only a partial restoration was observed for pH(i) and [P-i]. A rise of end-diastolic pressure and perfusion pressure expressed a contracture, concomitant with a lack of [ATP] recovery, which remained at 59 +/- 13% of the rest value. These results establish that 10(-6) M isoproterenol caused severe myocardial injury. [Mg2+](i) increased from 0.70 mM at rest to 0.88 mM at the end of the isoproterenol period. Considering the estimated uncertainties on the [Mg2+](i) values, this increase was not significant. After isoproterenol infusion, [Mg2+](i) progressively decreased to reach 0.72 mM at 45 min recovery. It is concluded that isoproterenol myocardial toxicity may not be related to [Mg2+](i) deficiency

IMIS: A Multi-Platform Software Package for Telediagnosis and 3D Medical Image Processing

In this paper, we present a project developed in our University in order to provide Medical Imaging Departments with efficient software tools for 3D medical image processing, storage and transmission. In this context, the IMIS software package has been developed, combining, in a modular programming strategy, an easily upgradable graphical user interface, using the Tcl/Tk toolkit, with high performance image processing techniques, such as 3D lossless multiresolution image compression, transmission, and advanced 3D medical image processing tools. 1. INTRODUCTION Medical image transmission is becoming a crucial issue in today's medical imaging context. Image transmission systems on high speed networks, such as ATM, are in constant development [1]. Although they are very promising, they presently do not respond to many requests emanating from the medical teams, since they are still at an experimental stage and remain quite expensive. Moreover, these heavy techniques are not adapted to so..

Changes in tumor oxygenation/perfusion induced by the no donor, isosorbide dinitrate, in comparison with carbogen: monitoring by EPR and MRI

PURPOSE: In an effort to improve radiotherapy treatments, methods aimed at increasing the quantity of oxygen delivered to tumors were investigated. The aim of this study was to evaluate the effect of one nitric oxide (NO) donor (isosorbide dinitrate) on pO(2) and blood flow in a murine tumor model. The effect was compared to carbogen, used as a reference treatment. METHODS AND MATERIALS: Thirty-six liver tumors implanted in mouse thighs were imaged using magnetic resonance imaging (MRI) at 4.7 Tesla with dynamic Gd-DTPA and blood oxygen level-dependent (BOLD) contrast-enhanced imaging after administration of isosorbide dinitrate or carbogen. The effect on the pO(2) was also tested by EPR oximetry (1.1 GHz) on 52 mice. RESULTS: A significant increase in MRI intensity was observed for both treatments in comparison with the control group. EPR oximetry showed a dose-dependant increase in tumor pO(2) for isosorbide dinitrate (by 5.9 mmHg at 0.2 mg/kg) and a substantially greater change for carbogen breathing (by 23 mmHg). CONCLUSION: Both tumor blood flow and pO(2) were increased by isosorbide dinitrate and carbogen. Carbogen is more efficient than isosorbide dinitrate in increasing the BOLD image intensity, as well as the tumor pO(2), but as efficient as isosorbide dinitrate in the Gd-DTPA contrast-enhanced imaging. We conclude that the effects of carbogen on improving tumor pO(2) involve both improved blood flow and improved hemoglobin oxygenation, whereas the effects of isosorbide dinitrate are predominantly mediated by improved blood flow alone

Ferumoxides and Tc-99m sulfur colloid: comparison of the tumor-to-liver uptake in focal nodular hyperplasia

The tumor-to-liver uptake of two reticuloendothelial agents, namely ferumoxides and technetium-99m (Tc-99m) sulfur colloid, was compared in focal nodular hyperplasia (FNH). Twelve patients with FNH who had undergone ferumoxides-enhanced MR imaging and planar Tc-99m sulfur colloid scintigraphy within 1 year were included from the study. Fourteen patients with FNH with a diameter larger than 3 cm were selected for the comparison. The tumor-to-liver ferumoxides uptake was calculated and the Tc-99m sulfur colloid uptake was assessed visually. Fermuoxides uptake was observed in all but one patient with FNH (mean tumor-to-liver ratio = .36). The six tumors showing normal (n = 5) or increased (n = 1) radiocolloid uptake when compared to the liver accumulated more ferumoxides than the eight tumors showing decreased radiocolloid uptake (P < .01). However, in some tumors, no direct relation was observed between ferumoxides and Tc-99m sulfur colloid uptake. Our observations suggest that ferumoxides uptake might not exactly mimic Tc-99m sulfur colloid uptake in FNH

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