Effect of observer experience in the differentiation between benign and malignant liver tumors after ultrasound contrast agent injection.

OBJECTIVE: The purpose of this study was to assess the impact of the observer level of experience on the diagnostic performance of contrast-enhanced ultrasound imaging (CEUS) for differentiation between benign and malignant liver tumors. METHODS: From a computerized search, we retrospectively identified 286 biopsy-proven liver tumors (105 hepatocellular carcinomas, 48 metastases, 7 intra-hepatic cholangiocarcinomas, 33 liver hemangiomas, and 93 nonhemangiomatous benign lesions) in 235 patients (140 male and 95 female; mean age +/- SD, 56 +/- 11 years) who underwent CEUS after sulfur hexafluoride-filled microbubble injection. The digital cine clips recorded during the arterial (10-35 seconds from injection), portal (50-120 seconds), and late (130-300 seconds) phases were analyzed by 6 independent observers without experience (group 1, observers 1-3) or with 2 to 10 years of experience in CEUS (group 2, observers 4-6). Specific training in the diagnostic and interpretative criteria was provided to the inexperienced observers. Each observer used a 5-point scale to grade diagnostic confidence: 1, definitely benign; 2, probably benign; 3, indeterminate; 4, probably malignant; or 5, definitely malignant on the basis of the enhancement pattern during the arterial phase and enhancement degree during the portal and late phases compared with the liver (hypoenhancement indicating malignant and isoenhancement to hyperenhancement indicating benign). RESULTS: The analysis of observer diagnostic confidence revealed higher intragroup (kappa = 0.63-0.83) than intergroup (kappa = 0.47-0.63) observer agreement. The experienced observers showed higher diagnostic performance in malignancy diagnosis than did inexperienced observers (overall accuracy: group 1, 63.3%-72.8%; group 2, 75.9%-93.1%; P < .05, chi(2) test). CONCLUSIONS: The diagnostic performance of CEUS in liver tumor characterization was dependant on the observer's level of experience.