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.

Fig. 1

39-year-old man with incidental liver tumor. A large tumor in the right lobe of the liver was incidentally detected during an ultrasound examination. The tumor (white arrow) is hyperintense on the T2-weighted image (a) and seen to intensely enhance in arterial phase of gadolinium enhanced T1-weighted image (b). Axial MRE wave image (c) showing good illumination of the tumor (ROI). Note that the waves in the tumor have slightly longer wavelength as compared to those in surrounding normal liver parenchyma. Elastogram (d) with ROI corresponding to the tumor. The shear stiffness value of the tumor was 3.1kPa and the surrounding liver, 2.4kPa. Patient underwent right hepatectomy and final diagnosis was hepatic adenoma.

Fig. 2

78-year-old man with cryptogenic cirrhosis and biopsy proven hepatocellular carcinoma. Post gadolinium-enhanced T1-weighted images showing an enhancing tumor (white arrow) in right lobe of the liver during arterial phase (a) with washout in the portal venous phase (b). The MRE wave image (c) shows shear waves with long wavelength within the tumor. The waves in the surrounding liver also have longer wavelength than normal. The mean stiffness of the tumor was 14.2kPa. Note the fat containing region within the tumor (arrowhead) which appears less stiff on the elastogram. The liver parenchyma had a stiffness of 4.1kPa consistent with liver fibrosis.

Fig. 3

51-year-old female with hemangioma in the liver. T1-weighted images in the arterial phase (a) and delayed phase (b) showing a typical hemangioma (black arrow). The stiffness of the hemangioma was 3.2kPa calculated with the ROI placed on the elastogram (c). The normal liver parenchyma had stiffness value of 2.3kPa

Fig. 4

55-year-old female with fatty liver and a focal lesion in right lobe. T2-weighted image (a) showing a single hyperintense lesion in the periphery of right lobe of the liver (arrow). Elastogram shows the tumor as a “hot spot” with stiffness value of 6.2kPa suggestive of a malignant tumor. A subsequent colonoscopy revealed a carcinoma in the recto-sigmoid region. Patient underwent surgical resection of the liver tumor and confirmed to be metastases.

Fig. 5

77-year-old man with intrahepatic cholangiocarcinoma. Gadolinium enhanced T1-weighted image (a) showing an enhancing tumor involving the left hepatic duct and invading into surrounding left lobe of liver. The mean stiffness of tumor is 15.5kPa and that of liver parenchyma 4.3kPa. Patient underwent biliary stenting and currently on follow-up.

Fig. 6

Graph showing box plots of shear stiffness of different tissues. A cut-off value of 5kPa separates malignant tumors from benign tumors and normal liver. Note that the stiffness values of fibrotic liver overlaps both benign and malignant tumor.