Parameters extracted from time activity curves in contrast enhanced ultrasound images play an important role in independent or computer aided diagnosis of hepatic focal lesions. Due to noise and errors induced by movement of ultrasound probe and breathing of patients, reproducible extraction time activity curve parameters is challenging. In this paper we propose a new solution that combines filtering and tracking, in the theoretical framework of robust estimation and the mean shift. To cope with the gradual apparence changes of the tracked lesions, we propose a new dynamic scale selection method.