Echo-Planar-Imaging Studies of Turbulent Flow

Two-Dimensional PFG NMR for Encoding Correlations of Position, Velocity, and Acceleration in Fluid Transport

“…Applications range from the monitoring of laminar and turbulent flow through simple geometries (1)(2)(3)(4) to the characterization of flow in random, artificial, or natural porous systems (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). The techniques developed so far have mainly focused either on a purely statistical description of the fluid dispersion by obtaining the probability density of displacements, or propagator (15), averaged over a certain portion of the sample or on combining velocity encoding with imaging sequences to map average velocities with spatial resolution.…”

Magnetic Resonance Signal Loss in Turbulent Shear Flow

“…At the same flow rate, the image of water exhibits much greater signal loss than that of glycerol-water mixture; how ever, it does not imply a linear relation between the Reynolds number and the signal loss. Gatenby & Gore [25] measured the characteristic time of the turbulent eddies using pulsed-gradient NMR. They concluded that the characteristic time at the center of the pipe was longer than that near the wall.…”

‘Snap-shot’ velocity vector mapping using echo-planar imaging

“…ssG overcomes some of the limitations of standard implementations of EPI for velocity measurement in chaotic systems. In particular, EPI is known to exhibit spatially local signal attenuation in the presence of excessive fluid shear [19]. This is partially because the train of phase increment blips used for imaging is not velocity compensated, and thus, in the presence of high fluid velocities, phase shifts will be introduced that can compromise image integrity and contribute to the first gradient moment, thereby introducing error into the calculation of fluid velocity.…”