Acoustic Radiation Force Impulse Elastography for the Evaluation of Focal Solid Hepatic Lesions: Preliminary Findings

Abstract 

This study was designed to investigate the potential usefulness of acoustic radiation force impulse (ARFI) elastography to evaluate focal solid hepatic lesions. In total, 51 patients with 60 focal hepatic lesions, which included 17 hemangiomas, 25 hepatocellular carcinomas (HCCs), 15 metastases and three cholangiocarcinomas, underwent ARFI elastography. The lesions were classified into three groups: Group I consisted of metastatic liver tumors and cholangiocarcinomas, group II consisted of HCCs and group III consisted of hemangiomas. The stiffness and conspicuity of the tumors as depicted on ARFI elastography and the echogenicity and conspicuity of the tumors on corresponding B-mode images were analyzed. Shear wave velocity was obtained to quantify stiffness for 36 focal hepatic lesions: 11 hemangiomas, 17 HCCs and eight other malignant lesions.

On ARFI elastography images, group I tumors (n=18) appeared stiffer than the background liver for 13 lesions (72%), softer for two lesions and had identical stiffness in three lesions compared with the background liver. For group II tumors (n=25), 13 lesions (52%) appeared stiffer than the liver, six lesions appeared softer than the liver and the remaining six lesions showed the same stiffness as the liver. For group III tumors (n=17), six lesions (35%) appeared stiffer than the liver, seven lesions appeared softer and the remaining four lesions showed the same stiffness as the liver. There were no statistical differences among the three groups in terms of tumor stiffness as seen on ARFI elastography images (p>0.05). Of the 60 lesions, 41 (68%) displayed a clearer or equivalent margin on the ARFI elastography compared with that seen on B-mode images. The shear wave velocities were: Group I, 2.18±0.96m/s (mean value±SD); group II, 2.45±0.81m/s; group III, 1.51±0.71m/s (p=0.012). With a cut-off value of 2m/s for the shear wave velocity, the positive predictive value and specificity for malignancy were 89% and 81%, respectively.

Images obtained with ARFI elastography provided additional qualitative information regarding the stiffness and tumor margin of liver tumors. By measuring shear wave velocity, quantification of stiffness was made possible and showed the potential to differentiate malignant hepatic tumors from hepatic hemangiomas. (E-mail: leejy@radiol.snu.ac.kr)

Key Words: Acoustic radiation force impulse imaging, ARFI Imaging, Elastography, Ultrasonography, Liver neoplasm