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. The preliminary results were obtained on a gel phantom at low vibration frequencies (0-200 Hz) by using a ladder-shaped coil generating a nearly constant RF field gradient along a specific known direction. For very small displacements and/or B1 gradients, the NMR signal measured on a gel phantom was proportional to the vibration amplitude and the pulse sequence was shown to be selective with respect to the vibration frequency. A good estimation of the direction of vibrations was obtained by varying the angle between the motion direction and the B1 gradient. The method and its use in parallel to more conventional MR elastography techniques are discussed. The presented approach might be of interest for noninvasive investigation of elastic properties of soft tissues and other materials.
Baril
Nathalie
N
Magnetic Resonance Centre, CNRS-Université Victor Segalen Bordeaux 2, Bordeaux, France.
Lewa
Czeslaw Jozef
CJ
de Certaines
Jacques Donald
JD
Canioni
Paul
P
Franconi
Jean-Michel
JM
Thiaudière
Eric
E
D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008962:Models, Theoretical; D014732:Vibration