This study aimed to apply magnetic resonance elastography (MRE) using micro-magnetic resonance imaging (micro-MRI) system for the measurements of viscoelastic modulus in soft matters. The rectangular specimens of 90 × 70 × 50 mm were made of agarose gel with five kinds of stiffness by changing concentrations. The specimens were oscillated with longitudinal waves transmitted by an elastic-bar from a vibration generator in a micro-MRI system. Since the viscoelastic properties depend on the excitation frequency and amplitude, the experimental conditions were selected in the range of 50-250 Hz and 0.1-0.5 mm. The viscoelastic modulus was expressed as storage shear modulus G′ and loss shear modulus G″. As a result, G′ increased with the frequency and amplitude, and the difference of G′ between hard and soft gels was obtained. The viscoelastic modulus of agarose gels was measured using the MRE system under the excitation conditions. Furthermore, double-layer specimens composed of 0.6 and 2.0 wt% gels were examined as an application of the MRE system. The difference of wave pattern between the hard and soft parts was observed. The values of G′ in the soft parts of the double-layer specimens corresponded to the value of the single-layer specimen, but the values of G′ in the hard parts were varied. and Klatt et al. (2010) have also measured the viscoelastic modulus of livers in vivo.The authors developed an MRE system consisting of a micro-magnetic resonance imaging (micro-MRI) with 0.3 T, a bar-type transmitter, and a vibration generator, which allowed the excitation frequency of 50-250 Hz and the amplitude of 0.1-0.5 mm (Tadano, et al., 2012). The bar-type transmitter and the vibration generator were used to generate strong excitation. In that study, it was confirmed that the distribution of displacement was obtained within the agarose gel of 1.2 wt% concentration under the excitation conditions. Furthermore, to decrease the error of viscoelastic modulus, the authors proposed a calculation method for the MRE measurements under the low magnetic field based on the integration of the displacement (Jiang and Nakamura, 2011). It is necessary to apply the MRE instrument and the calculation method to the measurements of viscoelastic modulus of soft matters and to discuss the availability of the system. Therefore, the present study aimed to investigate the effect of the excitation frequency of 50-250 Hz and the amplitude of 0.1-0.5 mm on the viscoelastic modulus of agarose gels with five kinds of stiffness by using the MRE system. Furthermore, the distributions of the displacement and viscoelastic modulus in the specimens consisting of hard and soft gel parts were investigated as an application of the MRE system. Three kinds of the double-layer specimen were examined in the study. MethodsWhen a specimen was excited with a sine wave in the MRI, local displacements in the specimen under a gradient magnetic field were calculated from the phase shift of MR signal (Muthupillai, et al., 1996;Manduca, et al., 2001). A complex...

This study aimed to measure a viscoelastic property of gelatin gels and porcine liver by the magnetic resonance elastography using micro-magnetic resonance imaging (micro-MRE). In the experiments, gelatin gel specimens (90 × 70 × 50 mm) made of gelatin solution with 5, 7, 10, 12, and 15 wt% concentration were examined under excitation with longitudinal waves in frequency of 50-250 Hz and amplitude of 0.5 mm. The viscoelastic modulus was obtained as storage shear modulus G' and loss shear modulus G". As a result, G' values increased with the concentration and the excitation frequency. G" value was much smaller than G'. Double-layer specimens composed of 5 and 15 wt% gelatin gels were also examined. The average of G' in each concentration gel in the double-layer specimens showed no significant difference from the single-material specimens with the same concentration. Furthermore, a porcine liver specimen (150 × 50 × 30 mm) were examined; however, the specimen were not vibrated and the displacement distribution in the specimen was not observed. When porcine liver specimens were embedded in the 15 wt% gel (70 × 70 × 50 mm), the specimens were vibrated deeply and G' and G" of the liver and gel regions were obtained. As a result, G' of the gel region was almost the same as the value of the gel specimens. G' of the liver region increased with the excitation frequency as well as the gel specimens. The viscoelastic modulus of the porcine liver could be measured by embedding it inside gelatin gel using the micro-MRE system. This study demonstrated the application of the MRE system as the dynamic viscoelasticity measurements of gelatin gel and liver specimen.