PURPOSE : The aim of this prospective study was to evaluate the potential usefulness of contrast enhanced ultrasound in combination with uantitative parametric analysis for characterization of focal liver lesions. METHOD AND MATERIALS : One hundred forty five patients with 146 liver lesions were examined following a bolus injection of ultrasound contrast agent (2,5 ml Sonovue©, Bracco, Milano), using non linear imaging modes at low MI. Real time visualization of arterial, portal and late phase enhancement were recorded and subsequently analyzed with a dedicated software (Sonoliver®, Bracco Research, Geneva) in order to calculate parametric images. Processed signals were computed by subtracting a reference signal from the original signals and parametric images coded by color were obtained. The presence of wash-out and the following parameters were qualitatively evaluated in all tumors : time to peak, rise time, wash in rate, maximum intensity and wash out rate. The wash-out phase was quantitatively assessed by using a receiver operating characteristic (ROC) analysis, also sensitivity, specificity, negative and predictive values were calculated. The final diagnosis was obtained by CT, MRI or biopsy. RESULTS: One hundred forty five patients with 113 malignant (36 HCC, 10 cholangiocarcinoma, 65 metastasis, 2 lymphoma) et 33 benign (15 hemangioma, 12 FNH, 1 adenoma, 1 abscess, 1 focal steatosis, 3 other benign lesions) tumors were included. On qualitative analysis, 110 of the 113 malignant tumors were classified as true positive with 3 false negative. Thirty of the 33 benign tumors were classified as true negative with 3 false positive. This resulted in an overall sensitivity of 97,3 %, a specificity of 90,9 %. ROC analysis of the wash out phase revealed improved discrimination of benign and malignant lesions with a specificity of 93,9 %, positive predictive value of 98,2 % and negative predictive value of 91,2 %, with no loss of sensibility. Also, our data showed a significant difference in the contrast enhancement kinetic parameters between benign and malignant tumor. CONCLUSION: Contrast enhanced ultrasound in combination with quantitative parametric analysis is an accurate tool for the characterization of focal liver lesions. CLINICAL RELEVANCE/APPLICATION: Patterns of enhancement of FLL are usually difficult to analyze in real time. The addition of computerized analysis improves the specificity of contrast enhanced ultrasound.