MR Elastography of Liver Tumors: Preliminary Results

Abstract

OBJECTIVE. The purpose of this study was to evaluate the potential value of MR elastography (MRE) in the characterization of solid liver tumors. MATERIALS AND METHODS. Forty-four liver tumors (14 metastatic lesions, 12 hepatocellular carcinomas, nine hemangiomas, five cholangiocarcinomas, three cases of focal nodular hyperplasia, and one hepatic adenoma) were evaluated with MRE. MRE was performed with a 1.5-T system with a modified phase-contrast gradient-echo sequence to collect axial wave images sensitized along the through-plane motion direction. The tumors were identified on T2- and T1-weighted and gadolinium-enhanced T1-weighted images, and the MRE images were obtained through the tumor. A stiffness map (elastogram) was generated in an automated process consisting of an inversion algorithm. The mean shear stiffness of the tumor was calculated with a manually specified region of interest over the tumor in the stiffness map. The stiffness value of tumor-free hepatic parenchyma was calculated. Statistical analysis was performed on the stiffness values for differentiation of normal liver, fibrotic liver, benign tumors, and malignant tumors. RESULTS. Malignant liver tumors had significantly greater mean shear stiffness than benign tumors (10.1 kPa vs 2.7 kPa, p < 0.001), fibrotic liver (10.1 kPa vs 5.9 kPa, p < 0.001), and normal liver (10.1 kPa vs 2.3 kPa, p < 0.001). Fibrotic livers had stiffness values overlapping both the benign and the malignant tumors. A cutoff value of 5 kPa accurately differentiated malignant tumors from benign tumors and normal liver parenchyma in this preliminary investigation. CONCLUSION. MR elastography is a promising noninvasive technique for assessing solid liver tumors. Use of MRE may lead to new quantitative tissue characterization parameters for differentiating benign and malignant liver tumors.