MR elastography is a clinical imaging technique for the mapping of viscoelastic tissue properties on the millimeter scale. However, basic studies in tissue samples require a compact MRE setup which provides sub-millimeter resolution. We here introduce compact 0.5-Tesla tabletop multifrequency MRE for high-resolution mapping of viscoelasticity and water diffusion in VX2-liver tumors and surrounding liver tissue. Ex-vivo tumors were stiffer, more viscous and showed higher water diffusivity than adjacent tissue. In tumors, viscosity was inversely correlated with water diffusion while in liver tissue, stiffness was inversely correlated with diffusion.
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Tabletop MRI and MRE setup: (A) and (B) show two different tissue samples of VX2 tumor (white arrow) and surrounding liver tissue (black arrow). Tissue is placed within a rigid glass tube of 7 mm diameter. (C) Tabletop MRE setup: the glass tube (white arrow) is placed into the tabletop MRI device and mounted on a 3D printed scaffold for the piezoelectric actuator. Harmonic mechanical frequencies are induced along the tube direction.
High-resolution stiffness and fluidity mapping of VX2 liver tumors. Magnitude of MRE, stiffness maps (shear wave speed c in m/s), phase angle of the complex shear modulus φ (fluidity) and apparent diffusion coefficient (ADC) are shown for two cases. VX2 (red region of interest) is stiffer and more fluid than surrounding liver tissue (green region of interest). ADC is elevated compared to the surrounding liver tissue.
Mean values of mechanical and apparent diffusion coefficient (ADC) parameters of VX2 tumor and surrounding liver tissue. * P< 0.05, **P < 0.01, ***P < 0.001.
Correlation analysis of mechanical parameters shear wave speed c (stiffness) and phase angle φ (fluidity) and the apparent diffusion coefficient (ADC) for tumor and liver tissue. Tumor fluidity shows a negative correlation with tumor ADC. A similar correlation is observed for liver stiffness versus liver ADC. R, Pearson's correlation coefficient.
Table 1: Mechanical properties and ADC of VX2 and liver
VX2 tumors show increased mechanical values as well as increased ADC compared to the surrounding liver. c, shear wave speed; φ, phase angle of the complex shear modulus; ADC, apparent diffusion coefficient.