Introduction to the basic principles and clinical applications of contrast-enhanced ultrasonography

Contrast-enhanced ultrasonography (CEUS) is based on the application of echoenhancers, which are usually administered intravenously. Modern echo enhancers are suspensions of microbubbles of an inert gas with an elastic biocompatible cover. When insonated at low acoustic power, the microbubbles undergo non-linear oscillation and return pulses of harmonic frequencies (namely, multiples of the fundamental frequency). With dedicated, contrast-specific digital techniques the harmonic signals emitted from the microbubbles are detected with high sensitivity, while linear signals from the background tissues are cancelled. Thus, the presence of microbubbles can be accurately depicted in real time. With few exceptions, both normal and pathologic macro-and in micro-circulation can be studied with CEUS more efficiently than with any other currently available ultrasonographic technique. The majority of clinical applications of CEUS are related to the liver. CEUS plays a vital role in the diagnosis of hepatocellular carcinoma, (particularly in the context of cirrhosis), in the characterization of incidentally discovered liver lesions, in the screening of oncologic patients for liver metastases and as a monitoring tool of percutaneous interventions for tumor ablation. There is also an emerging role of CEUS in the diagnosis of various pancreatic, splenic, gastrointestinal, urogenital and vascular disorders.