Propagation velocity and attenuation of a shear wave pulse measured by ultrasound detection in agarose and polyacrylamide gels.

The aim of our research was to measure and analyze phase velocity and pulse attenuation of a shear wave in two media: well-known agarose-gelatin gel and seldom-used polyacrylamide gel. These quantities were determined at three temperatures by the method of transmission sonoelastography described by Catheline et al. (1999).

Detection of acoustic waves by NMR using a radiofrequency field gradient.

A B(1) field gradient-based method previously described for the detection of mechanical vibrations has been applied to detect oscillatory motions in condensed matter originated from acoustic waves. A ladder-shaped coil generating a quasi-constant RF-field gradient was associated with a motion-encoding NMR sequence consisting in a repetitive binomial 13;31; RF pulse train (stroboscopic acquisition). The NMR response of a gel phantom subject to acoustic wave excitation in the 20-200 Hz range was investigated.

MR detection of mechanical vibrations using a radiofrequency field gradient.

A new method for NMR characterization of mechanical waves, based upon radiofrequency field gradient for motion encoding, is proposed. A binomial B1 gradient excitation scheme was used to visualize the mobile spins undergoing a periodic transverse mechanical excitation. A simple model was designed to simulate the NMR signal as a function of the wave frequency excitation and the periodicity of the NMR pulse sequence.