Quantitative discrimination of water and hydrocarbons in porous media by magnetization prepared centric-scan SPRITE

MRI has considerable potential as a non-destructive probe of porous media, offering the possibility of rapid quantification of local oil and water content. This potential has not yet, however, been completely realized. In this paper, we explore a general magnetization preparation approach to the discrimination of water and oil in a model, representative, porous medium. These measurements have, as a common element, a centric scan pure phase encode readout based on the SPRITE methodology. Magnetization preparation permits facile T1, T2 and diffusion coefficient mapping as the basis for oil and water discrimination. Diffusion coefficient mapping proved to be the most robust approach to discrimination of oil and water. These methods are illustrated through static experiments and a dynamic immiscible fluid displacement experiment.     

A comparison of three SPRITE techniques for the quantitative 3D imaging of the 23Na spin density on a 4T whole-body machine

Sodium density maps acquired with three SPRITE-based methods have been compared in terms of the resulting quantitative information as well as image quality and acquisition times. Consideration of factors relevant for the clinical implementation of SPRITE shows that the Conical-SPRITE variant is preferred because of a 20-fold reduction in acquisition time, slightly improved image quality, and no loss of quantitative information. The acquisition of a 3D data set (32x32x16; FOV=256x256x160 mm) for the quantitative determination of sodium density is demonstrated. In vivo Conical-SPRITE 23Na images of the brain of a healthy volunteer were acquired in 30 min with a resolution of 7.5x7.5x7.5 mm and a signal-to-noise ratio of 23 in cerebrospinal fluid and 17 in brain tissue.     

Spatially resolved measurement of rock core porosity

Density weighted, centric scan, Conical SPRITE MRI techniques are applied in the current work for local porosity measurements in fluid saturated porous media. The methodology is tested on a series of sandstone core samples. These samples vary in both porosity and degree of local heterogeneity due to bedding plane structure. The MRI porosity measurement is in good agreement with traditional gravimetric measurements of porosity. Spatially resolved porosity measurements reveal significant porosity variation in some samples. This novel MRI technique should have applications to the characterization of local porosity in a wide variety of porous media.     

Sectoral sampling in centric-scan SPRITE magnetic resonance imaging

A new approach to the construction of k-space trajectories for centric-scan SPRITE in both 2D and 3D is presented. All benefits of previous SPRITE methods are retained, most importantly the ability to image objects with short T*(2). This new approach gives more flexibility in the choice of number of interleaves with points more evenly distributed across k-space. All these improvements positively contribute to image quality and resolution, which can be also traded off against experimental speed. Sectoral sampling will have significant benefits for magnetisation preparation contrast imaging.     

SPIRAL-SPRITE: a rapid single point MRI technique for application to porous media.

This study presents the application of a new, rapid, single point MRI technique which samples k space with spiral trajectories. The general principles of the technique are outlined along with application to porous concrete samples, solid pharmaceutical tablets and gas phase imaging. Each sample was chosen to highlight specific features of the method.     

Velocity imaging of highly turbulent gas flow

We introduce a noninvasive, quantitative magnetic resonance imaging (MRI) wind-tunnel measurement in flowing gas (>10 m s(-1)) at high Reynolds numbers (Re>10(5)). The method pertains to liquids and gases, is inherently three dimensional, and extends the range of Re to which MRI is applicable by orders of magnitude. There is potential for clear time savings over traditional pointwise techniques. The mean velocity and turbulent diffusivity of gas flowing past a bluff obstruction and a wing section at realistic stall speeds were measured. The MRI data are compared with computational fluid dynamics.     

Thin film MRI-high resolution depth imaging with a local surface coil and spin echo SPI

A multiple echo, single point imaging technique, employing a local surface coil probe, is presented for examination of thin film samples. Depth images with a nominal resolution of 5 microm were acquired with acquisition times on the order of 10 min. The method may be used to observe dynamic phenomenon such as polymerization, wetting, and drying in thin film samples. It is readily adapted to spatially resolved diffusion coefficient and T2 relaxation time mapping.     

Phantom materials for single point imaging pulse sequences

The popularity of pure phase encode MRI techniques, including single point imaging (SPI), is steadily increasing, particularly in instances where the samples of interest are solid-like, or for other reasons possess short effective transverse relaxation times, T2*. As the interest in these techniques grows, so too does the need for a phantom material which is representative of this class of samples. The characteristics of such a phantom should include chemical and physical stability, straightforward preparation, high signal to noise ratio and relaxation times which are both easily manipulated and representative. To this end, we have developed a gelatin/sucrose-based gel which addresses the above criteria and behaves as a very flexible short T2* phantom. An order of magnitude variation in T1 and T2 can be achieved over a reasonable range of sucrose concentration. Even larger changes can be achieved with the addition of further doping agents.