J022035 micro-MRIによる2層アガロースゲルのMRE画像

Abstract

Magnetic resonance elastography (MRE) is a newly developed imaging technique that makes full use of the magnetic resonance imaging (MRI) visualization to measure the stiffness of tissue in the body organs using mechanical excitation. In this study, an excitation device for MRE by micro-MRI (0.3T) was constructed from a high power vibration generator and a bar type vibration transmitter made from GFRP. The stiffness was expressed by storage shear modulus G' and loss shear modulus G" of the modified stokes model for a viscoelastic medium. Using a micro-MRI system, the optimal excitation condition of frequency and amplitude of wave was examined using some gel specimens. Viscoelastic modulus distribution of two layered agarose gel specimens were measured in the excitation condition of amplitude (0.5, 1.0, and 1.5 mm) and frequency (62.5, 125, and 250 Hz). The distribution of G' was influenced by both the frequency and amplitude of excitation. The two layered specimen combined with two different concentration gel samples shows the same tendency of G' in the same concentration layer approaching similar values under the higher excitation amplitude and frequency conditions as the uniform agarose gel specimen. Clear differences of the wave propagation patterns were observed in the MR image and the difference of G' between each phase area could be measured quantitatively in this MRE system.