Observing Diffusion-Diffraction Patterns in Heterogeneous Specimens Using the Double-PFG NMR Methodology

with the periodic excitation. The usual applications of MRE include a measurement of the shear modulus in a living tissue or gel-like substances. The goal of this project was to develop an MRI technique to image a periodic motion in fluids for studies of cavitation, turbulence, thermoacoustics, and fluid flow in media. Although a fluid does not have any shear strength that a gel does, it can still oscillate via a rotational motion in the eddy currents in a turbulent liquid, in a flow through granular/porous media, by a strong acoustic field in a gas or by the motion of cavitating bubbles. In this project, the concept of MRE was applied to measure the displacements at a range of gradient frequencies with the goal to obtain power spectra of the oscillations. We used a set of the oscillating gradient waveforms (16 Hz– 10 kHz) during the preparation part of the sequence with the Z-storage of Xand Y -components of the transverse magnetization with the subsequent use of the spiral SPRITE imaging as a readout sequence. A major problem with applying the ideas of MRE to liquids is the presense of flows that, in case of oscillating gradients, will contribute a non-zero phase. To cancel the flow effect, velocity-compensated symmetric oscillating gradient waveforms were used. The technique was applied to studies of cavitating liquids and a gas in a working thermoacoustical device.