Effect of chronic magnesium supplementation on magnesium distribution in healthy volunteers evaluated by 31P-NMRS and ion selective electrodes.

AIMS: The role of magnesium (Mg) intake in the prevention and treatment of diseases is greatly debated. Mg biodistribution after chronic Mg supplementation was investigated, using state-of-the-art technology to detect changes in free ionized Mg, both at extra- and intracellular levels. METHODS: Thirty young healthy male volunteers participated in a randomised, placebo (P)-controlled, double-blind trial. The treated group (MgS) took 12 mmol magnesium lactate daily for 1 month. Subjects underwent in vivo 31P-NMR spectroscopy and complete clinical and biological examinations, on the first and last day of the trial. Total Mg was measured in plasma, red blood cells and 24 h urine ([Mg]U ). Plasma ionized Mg was measured by ion-selective electrodes. Intracellular free Mg concentrations of skeletal muscle and brain tissues were determined noninvasively by in vivo 31P-NMR at 3T. NMR data were automatically processed with the dedicated software MAGAN. RESULTS: Only [Mg]U changed significantly after treatment (in mmol/24 h, for P, from 4.2+/-1.4 before to 4.1+/-1.3 after and, for MgS, from 3.9+/-1.1 before to 5. 1+/-1.1 after, t=2.15, P=0.04). The two groups did not differ, either before or after the trial, in any other parameter, whether clinical, biological or in relation with the Mg status. CONCLUSIONS: Chronic oral administration of Mg tablets to young healthy male volunteers at usual pharmaceutical doses does not alter Mg biodistribution. This study shows that an adequate and very complete noninvasive methodology is now available and compatible with the organization of clinical protocols which aim at a thorough evaluation of Mg biodistribution.

Quantification of noisy MRS signals with the Pseudo-Wigner Distribution.

This paper investigates the estimation errors induced by noise in the quantification of damped sinusoids with the Pseudo-Wigner Distribution (PWD). A constant amplitude single frequency noise is first considered. This simple model shows how underestimation or overestimation errors depend on the relative phase between signal and noise for a fixed signal-to-noise ratio (SNR). In a second step, cross-terms and noise amplitude fluctuations are identified as the main sources of discrepancy between the theoretical model and a practical situation where wideband noise is linearly added to a synthetic free induction decay (FID) signal. Cross-terms can be attenuated by band-pass filtering noise or by using a weighting (or smoothing) window in the PWD. An original procedure is then derived to make an on-line and noise-specific estimation of the statistical error in the quantification step. This property of the Wigner distribution is a unique feature in quantitative MRS. Confidence intervals are evaluated for a single damped sinusoid corrupted by eight random noise sequences with three different SNR's, 20, 10 and 5 dB, respectively. They are shown to match the statistical ranges of quantification results obtained with linear regression, until the SNR drops below 10 dB. Estimation accuracy of amplitude and damping constant is finally evaluated from the comparison of the Cramér-Rao (CR) lower bounds with the variance of estimation errors. CR-bounds are shown to be nearly achieved at each SNR.