Liver investigations: Updating on US technique and contrast-enhanced ultrasound (CEUS)

Over the past few years, the cross sectional imaging techniques (Computed Tomography - CT and Magnetic Resonance - MR) have improved, allowing a more efficient study of focal and diffuse liver diseases. Many papers had been published about the results of a routinely clinical use of the dual source/dual energy CT techniques and the use of hepatobiliary contrast agents in MR liver studies. As a consequence, these new improvements have diverted the attention away from the Ultrasound technique and its technical and conceptual evolutions. In these years of disinterest, US and especially Contrast Enhanced Ultrasound (CEUS) have consolidated and grown in their application in clinical routine for liver pathologies. In particular, thanks to the introduction of new, dedicated software packages, CEUS has allowed not only qualitative, but also quantitative analysis of lesion microcirculation, thus opening a new era in the evaluation of lesion characterization and response to therapy. Moreover, the renewed interest in liver elastography, a baseline ultrasound-based imaging modality, has led to the development of a competitive technique to assess liver stiffness and then for the evaluation of the progression towards cirrhosis, and characterization of focal liver lesions, opening the way to avoid, in selected cases, liver biopsy. The aim of this review is to offer an up-to-date overview on the state of the art of clinical applications of US and CEUS in the study of focal and diffuse liver pathologies. Besides, it aims to highlight the emerging role of perfusion techniques in the assessment of local and systemic treatment response and to show how the liver evolution from steatosis to fibrosis can be revealed by elastography.