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

https://doi.org/10.1016/j.ultrasmedbio.2009.10.009Get rights and content

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: [email protected])

Introduction

Most elastographic imaging of ultrasonography to date has used manual or motorized compression with moving probes. Compression of the liver for elastographic imaging has always been difficult because it is surrounded by the rib cage, which limits using this procedure clinically.

Recently, ultrasound elastography with a short, high-intensity focused ultrasound beam has been introduced for target tissue displacement, i.e., acoustic radiation force impulse (ARFI) elastography (Fahey et al., 2006, Fahley et al., 2005, Nightingale et al., 2002, Walker et al., 2000). This technique has enabled in vivo liver elastography by transmission of the acoustic wave between the ribs or from the subcostal area (Fahey et al., 2008a, Fahey et al., 2008b). Until now, only one in vivo study has characterized liver tumors in humans using ARFI elastography (Fahey et al. 2008a) and that study only included seven liver tumors. Additionally, there are no studies that have evaluated ARFI elastography's usefulness in differentiating liver tumors and no studies have been reported on the quantification of tumor stiffness using shear wave velocity, which may help in the diagnosis of liver tumors.

The present study was performed to investigate the potential usefulness of ARFI elastography for evaluating focal solid hepatic lesions, assuming that different features can be shown on ARFI elastography images according to the type of liver tumor and that quantification of tumor stiffness may be helpful in the diagnosis.

Section snippets

Materials and Methods

Our hospital Institutional Review Board approved this study (IRB number: 0902-039-272) and informed consent was obtained from all patients prior to the ARFI elastography examinations.

Results

Table 1, Table 2 summarize the echogenicity, stiffness and conspicuity of the lesions in the three groups. Of the elastographic images of group I (metastatic tumors and cholangiocarcinomas), 13 of 18 lesions (72%) appeared darker, which indicated that they were stiffer than the surrounding liver parenchyma (Fig. 1, Fig. 2). The stiffer tumors included three cholangiocarcinomas, four metastatic tumors from colon cancer, one metastatic tumor from duodenal cancer, three from neuroendocrine tumors

Discussion

For the abdominal application of ARFI elastography, Fahey et al. first reported the usefulness of ARFI elastography for improving both the conspicuity and contrast of hepatic and renal tumors relative to the use of conventional B-mode images (Fahey et al. 2008a). According to this report, for all seven hepatic tumors that were analyzed including HCCs and metastases, the boundary definition on ARFI images was improved or equivalent to that on B-mode images. HCCs were softer than the regional

Acknowledgments

The authors wish to thank Chris Woo (Korea) and Bonnie Hami, M.A. (USA) for their assistance in preparing and editing this manuscript.

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