Towards compression-sensitive magnetic resonance elastography of the liver: sensitivity of harmonic volumetric strain to portal hypertension.

PURPOSE To assess induced oscillating volumetric strain as a biomarker for intrahepatic blood pressure abnormalities. MATERIALS AND METHODS Harmonic vibrations of 25 and 50 Hz frequency were induced in the liver and measured by fast 3D vector field magnetic resonance elastography (MRE), followed by processing of the decomposed curl (shear) and divergence (compression) fields. After an initial study on an excised sheep liver, a group of 13 patients with hepatic hypertension were examined before and after implantation of a transjugular intrahepatic portosystemic shunt (TIPS). RESULTS In the sheep liver specimen, volumetric strain decreased with excess portal pressure, whereas shear strain was not sensitive to portal pressure. In the patient cohort, volumetric strain was significantly higher after TIPS placement (P = 1.38·10(-5) ), while neither shear strain nor the shear modulus were affected. Normalized changes in volumetric strain were significantly correlated with the hepatic venous pressure gradient (R(2) = 0.7258, P = 6.95·10(-5) ) and portal venous pressure (R(2) = 0.5028, P = 0.0016). CONCLUSION These results indicate for the first time the sensitivity of volumetric strain to symptomatically high values of tissue pressure and motivate further developments in compression-sensitive MRE and poroelastography towards image-based and noninvasive markers of tissue pressure.