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G Guillot

Publications and source records attributed to G Guillot.

23 records · Page 2Linked to original sources
PubMedDate not supplied

NMR diffusion of hyperpolarised 3He in aerogel: a systematic pressure study.

Diffusion of hyperpolarised 3He in a silica aerogel sample with 98% porosity was measured by NMR, and systematically studied as a function of pressure P in the range 20 mbar -1 bar. Spin-echo amplitudes, recorded with pulsed gradients in the usual CMPG sequence, follow a monoexponential decay, and the decay rate varies quadratically with the gradient intensity: thus the apparent diffusion coefficient of the gas D can be evaluated. Our results show a power-law (1/D proportional to P(0.55)), which could be consistent with a fairly broad mean free path distribution, implying some inhomogeneity in the aerogel structure. We have observed a spatial non-uniformity of D, and some deviation to the quadratic dependence of the decay rate with the gradient intensity, possibly related to sample structure inhomogeneity.

Diffusion↗
PubMedDate not supplied

Trabecular bone characterization with low-field MRI.

Multiple-echo (ME) T2 measurements were performed in vitro at 0.1 T on a series of human trabecular bone samples filled with water and compared to site-matched bone density measurements. Multiple-echo T2 is strongly correlated to bone density and allows distinction between samples of equivalent bone density. Multiple-echo T2 is also dependent on the trabecular orientation with respect to the direction of the main field.

Bone Density↗
PubMedDate not supplied

Comparative measurements between a new logging tool and a reference instrument.

Measurements were performed on reference samples (D2O-H2O mixtures) and on highly heterogeneous rocks (Vosges sandstone) with a new logging tool designed to give access to a high spatial resolution, below 1.5 cm on the vertical scale, for a toroidal sensitive volume of 20 cm3. The results were compared to measurements obtained on a clinical magnetic resonance imaging (MRI) equipment working at the same frequency (4.3 MHz). T2 differences as high as 30% were observed for the reference samples; the shortest values were obtained with the logging tool. Porosity profiles of the rock samples were also compared to reference profiles obtained with a conventional computed tomography (CT) scanner. Both nuclear magnetic resonance (NMR) measurements underevaluate porosity by 2-4% for short T2 values (< 10 ms).

Equipment Design↗