Jean-François Goudemant

Comparison of Gadolinium-dtpa and Polylysine-gadolinium-dtpa - Enhanced Magnetic-resonance-imaging of Hepatocarcinoma in the Rat

RATIONALE AND OBJECTIVES.To compare the magnetic resonance (MR) imaging characteristics of gadolinium-DTPA (Gd-DTPA), a low-molecular-weight contrast agent, and polylysine-Gd-DTPA, a macromolecular contrast agent, in two types of hepatocarcinomas (HCC) in the rat. METHODS.T1-weighted spin-echo images were obtained in 13 rats with chemically induced HCC and 26 rats with Novikoff HCC before and 3 minutes to 60 hours after administration of either Gd-DTPA or polylysine-Gd-DTPA. RESULTS.Three minutes after polylysine-Gd-DTPA administration, the tumor-to-liver contrast of the two types of HCC increased significantly (positive contrast for chemically induced HCC and negative contrast for Novikoff HCC). At 30 minutes and 60 hours, the tumor-to-liver contrast remained above baseline values in chemically induced HCC and returned progressively to baseline values in Novikoff HCC. No significant increase in tumor-to-liver contrast was observed after Gd-DTPA administration. CONCLUSIONS.These results suggest that polylysine-Gd-DTPA provides a higher and more prolonged increase in tumorto-liver contrast than Gd-DTPA.

Amiodarone pretreatment effects on ischemic isovolumic rat hearts: a P-31 nuclear magnetic resonance study of intracellular pH and high-energy phosphates contents evolutions.

Effects of amiodarone injected intravenously (i.v.) at two doses (10 and 20 mg/kg) on perfused isovolumic rat heans were assessed by P-31 nuclear magnetic resonance (NMR). P-31 NMR is used to measure intra-cellular myocardial pH, phosphocreatine (PCr), and ATP contents time evolutions. Myocardial mechanical function is estimated by heart rate (HR), left ventricular developed pressure (LVP), and coronary flow (CF). In experimental procedure A (2-h retrograde perfusion), drug injection induced a dose-dependent bradycardia (10–20%) and a slight decrease in LVP but did not affect CF, pH, PCr, or ATP contents. Experimental procedure B consisted of 30-min stabilization, 18-min ischemia, and 72-min reperfusion. During ischemia, amiodarone did not preserve ATP and PCr pools and did not alleviate acidosis. ATP decreased to 30% of its control values, whereas the PCr peak was hardly detectable after 12 min of ischemia. After 24 min of reflow, HR, PCr, and pH of treated hearts recovered. LVP recovered after 36 min, whereas for control hearts, HR, PCr, and pH recovered after 42 min and LVP did not reach its control values at the end of reperfusion time. Faster pH recovery is explained by a preservation of Na+/K+ATPase due to the influence of amiodarone on membrane lipid dynamics.

Comparison of unenhanced and gadoxetate disodium-enhanced spin-echo magnetic resonance imaging for the detection of experimental hepatocellular carcinoma in the rat.

RATIONALE AND OBJECTIVES The authors compare the potential value of unenhanced and gadoxetate disodium-enhanced spin-echo images for the detection of hepatocellular carcinoma in a rat model. METHODS Eleven rats with chemically induced hepatocellular carcinoma underwent unenhanced T2-weighted fast spin-echo imaging followed by T1-weighted spin-echo imaging before and at 5 minutes, 30 minutes, 3 hours, 1 day, and 3 days after intravenous administration of 60 micromol/kg gadoxetate disodium at 4.7 tesla. Tumor and liver enhancement, and tumor-to-liver contrast-to-noise (C/N) ratio were calculated. RESULTS After gadoxetate disodium administration, the tumors showed less enhancement than the liver. Tumor-to-liver C/N ratio increased from 5.5 +/- 0.8% on unenhanced T1-weighted images to 12.9 +/- 2.4% on gadoxetate-enhanced T1-weighted images (P = 0.02). However, the C/N ratio on unenhanced T2-weighted images (23.5 +/- 3.6%) remained higher than that on gadoxetate-enhanced T1-weighted images, a difference that is statistically significant (P < 0.01). CONCLUSIONS In the experimental setting of our study, the higher tumor-to-liver C/N ratio on unenhanced T2-weighted spin-echo images suggests that unenhanced T2-weighted spin-echo images are superior to gadoxetate disodium-enhanced T1-weighted spin-echo images for the detection of hepatocellular carcinoma.

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

The hypothesis of magnesium deficiency in isoproterenol (ISO) induced myocardial injury has been investigated by 31P nuclear magnetic resonance spectroscopy. High energy phosphate concentrations, pHi, 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, pHi, [PCr], and [ATP] decreased, while [P(i)] increased. When it was stopped, [PCr] completely repleted, whereas only a partial restoration was observed for pHi 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

We present a project developed in our University in order to provide Medical Imaging Departments with efficient software tools for 3D medical image processing 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 for telediagnosis on narrow-band ISDN networks. IMIS is based on a set of tools allowing the handling of 3D medical images such as magnetic resonance images (MRI), positron emission tomography (PET), and computed tomography (CT) of functional MRI (fMRI).

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.

A gating and triggering system dedicated to nuclear magnetic resonance studies of isolated perfused heart

This work reports a low-cost and versatile electronic device designed to trigger NMR acquisitions from the cardiac cycle of an isolated perfused heart, or to perform electrical stimulation of the heart. The triggering is synchronised with the pressure curve of the perfused heart. The cardiac pacing is achieved from pulses of the NMR system, or by an internal pulse generator, in order to be operated separately from the NMR instrument.