A low-field ceramic magnet design for magnetic resonance.

We describe the design of a low-field portable magnet, based on two ceramic magnets, separated by a distance, with their magnetic poles aligned to create a large homogeneous region with a field strength of 425 gauss. Ceramic magnets are an uncommon choice compared to Neodymium Iron Boron magnets for low-field magnetic resonance but are preferable for our purposes to create a homogeneous region at lower field strength. The low cost of large ceramic magnets results in an inexpensive design with a large measurement volume.

Diffusion tensor imaging of anisotropic inhomogeneous turbulent flow.

Inhomogeneous anisotropic turbulent flow is difficult to measure, and yet it commonly occurs in nature and in many engineering applications. This work aims to introduce a technique based on magnetic resonance imaging which can spatially map the degree of turbulence as well as the degree of anisotropy. Our interpretation relies on the eddy diffusion model of turbulence, and combines this with the technique of diffusion tensor imaging.

The Determination of Sucrose Content in Maple Sap Using Time-Domain Magnetic Resonance.

The natural variation of sucrose concentration in maple tree sap is investigated using time-domain magnetic resonance (MR). The current study, which includes a concise introduction to the relevant MR properties, is a demonstration of principle showing how the relaxation time constant and the self-diffusion coefficient relate to the amount of sucrose and ionic content present in the collected sap samples. and self-diffusion coefficient for maple saps from six different trees, each sampled weekly in the spring of 2019, were measured using MR.

Gas and Liquid Phase Imaging of Foam Flow Using Pure Phase Encode Magnetic Resonance Imaging.

Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented in this article focuses on the use of MRI to measure density and velocity of foam as it passes through a pipe constriction.

Velocity mapping of fast flows using a linearly ramped gradient waveform.

We report a new pure phase encoding measurement for velocity mapping. Velocity-sensitization is achieved using a repeating, linearly ramped gradient waveform instead of rectangular bipolar pulsed field gradients. This approach reduces eddy current effects and results in the sample experiencing a gradient waveform that more closely matches the ideal input.

Magnetic field gradient waveform correction of motion-sensitized SPRITE by pre-equalization.

Eddy currents caused by pulsed field gradients in magnetic resonance measurements of high-speed flow cause the magnetic field gradient amplitude waveform experienced by the sample to be different from the waveform demanded of the magnetic field gradient amplifiers. By measuring and using the system impulse response, pre-equalization magnetic field gradient waveform correction can be used to counteract the resulting errors in measured signal phase at the cost of minimal additional experimental time. The effectiveness of the pre-equalization method of magnetic field gradient waveform correction is tested with a motion-sensitized (pulsed field gradient) version of the SPRITE imaging pulse sequence which requires extreme gradient slew rates in excess of 1000 T/m/s in a 6.

Motion-sensitized SPRITE measurements of hydrodynamic cavitation in fast pipe flow.

The pressure variations experienced by a liquid flowing through a pipe constriction can, in some cases, result in the formation of a bubble cloud (i.e., hydrodynamic cavitation).

Purely phase-encoded MRI of turbulent flow through a dysfunctional bileaflet mechanical heart valve.

Object: We have used a purely phase-encoded magnetic resonance imaging (MRI) technique, single-point ramped imaging with T1 enhancement (SPRITE), to investigate the steady, turbulent flow dynamics through a bileaflet mechanical heart valve (BMHV).

Materials And Methods: We have measured in vitro the turbulent diffusivity and velocity downstream of the valve in two configurations (fully opened and partially opened), which mimic normal and dysfunctional operation. Our constant-time implementation of the MRI measurement is unusually robust to fast turbulent flows, and to artefacts caused by the pyrolytic carbon construction of the valve.

'Snap-shot' velocity vector mapping using echo-planar imaging.

A 'snap-shot' ultra-fast MRI velocimetry technique based upon the echo-planar imaging (EPI) pulse sequence is presented. The new technique is an extension of the GERVAIS pulse sequence previously developed by Sederman et al. (2004) and is capable of acquiring both reference and velocity encoded phase maps following a single excitation for generation of three-component velocity vectors in under 125 ms.

SPRITE MRI of bubbly flow in a horizontal pipe.

Bubble flow is characterised by numerous phase interfaces and turbulence, leading to fast magnetic resonance signal decay and artefacts in spin-warp imaging. In this paper, the SPRITE MRI pulse sequence, with its potential for very short encoding times, is demonstrated as an ideal technique for studying such dynamic systems. It has been used to acquire liquid velocity and relative intensity maps of two-phase gas-liquid dispersed bubble flow in a horizontal pipe at a liquid Reynolds number of 14,500.

Dynamics of dissolved gas in a cavitating fluid.

A strong acoustic field in a liquid separates the liquid and dissolved gases by the formation of bubbles (cavitation). Bubble growth and collapse is the result of active exchange of gas and vapor through the bubble walls with the surrounding liquid. This paper details a new approach to the study of cavitation, not as an evolution of discrete bubbles, but as the dynamics of molecules constituting both the bubbles and the fluid.

Flow imaging of fluids in porous media by magnetization prepared centric-scan SPRITE.

MRI has considerable potential as a non-destructive probe of porous media, permitting rapid quantification of local fluid content and the possibility of local flow visualization and quantification. In this work we explore a general approach to flow velocity measurement in porous media by combining Cotts pulsed field gradient flow encoding with SPRITE MRI. This technique permits facile and accurate flow and dispersion coefficient mapping of fluids in porous media.

Centric-scan SPRITE magnetic resonance imaging with prepared magnetisation.

The combination of contrast preparation with centric-scan SPRITE imaging readout is investigated. The main benefit of SPRITE, its ability to image objects with short T2, is retained. We demonstrate T1 and T2 mapping as examples of magnetisation preparation followed by magnetisation storage and spatially resolved encoding.

MRI measurements of an acoustically cavitated fluid in a standing wave.

Double-diffusive convection in a horizontally infinite layer of a unit height in a large-Rayleigh-number limit is considered. From linear stability analysis it is shown that the convection tends to have a form of traveling tall thin rolls with width about 30 times less than height. Amplitude equations of ABC type for vertical variations of the amplitude of these rolls and mean values of diffusive components are derived.

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.

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.