Biomedical subjects

S Bobroff

Publications and source records attributed to S Bobroff.

5 recordsLinked to original sources

PubMed1999

Variations on the slotted-tube resonator: rectangular and elliptical coils.

Two designs (one rectangular, one elliptical) are proposed as efficient alternatives to noncylindrical birdcage RF coils. These designs are based on the slotted-tube resonator and their performance relies on the natural current distribution in the conductors due to the eddy current effects at high frequencies. A Finite element method program, solving the full set of Maxwell's equations, has been employed to accurately characterize and optimize the field homogeneity of the proposed noncylindrical coils. The optimum configuration of each design is presented, taking into account the effect of the RF shield. The proposed designs are compared to several configurations presented in the literature. Two coils (one rectangular, one elliptical) have been constructed and tested in a 0.6 T imaging system. A rectangular coil has been built to operate at 300 MHz. MR images substantiate the usefulness of these coils.

Equipment Design↗

PubMed1996

Quantitative porosity profiles and wettability contrast visualisation in sandstone by CPMG imaging.

CPMG imaging is applied to the visualisation of porosity and wetting heterogeneities in water saturated sandstone samples at 0.1 T. Porosity profiles from NMR imaging are in agreement within 1% with the standard core analysis. T2 calculated profiles show a factor greater than two between water-wet and oil-wet samples; thus, wettability contrast can be easily visualised.

Magnetic Resonance Imaging↗

PubMed1996

Susceptibility contrast and transverse relaxation in porous media: simulations and experiments.

A numerical simulation of spin diffusion in inhomogeneous magnetic fields due to susceptibility contrast was developed to describe the transverse relaxation of fluids in porous media. The simulation results are in quantitative agreement with experimental measurements obtained on samples of simple geometry. They also confirm the interpretation of the 1H transverse relaxation observed in natural rocks either hydrophilic or hydrophobic for several deuterium oxide/oil saturations, based on the traditional description of water and oil arrangement.

Diffusion↗

PubMed1994

Characterisation of wetting heterogeneities in sandstone rocks by MRI.

MRI is applied to the visualisation of wetting heterogeneities evidenced by water proton T1 contrast at 0.1 T. Water saturated Fontainebleau sandstone samples were examined either in their original water-wet condition, or after silanation. T1, T2Hahn, and T2CPMG were measured for several porosities. T1 and T2CPMG of hydrophobic samples are both twice longer than those of hydrophilic ones. This good contrast allows us to observe wetting heterogeneities in T1-profiles and T1-weighted images.

Magnetic Resonance Imaging↗

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↗