Improved detection and characterisation of liver tumors with echo-enhanced ultrasound

Contrast-enhanced ultrasound techniques represent the most challenging efforts in recent ultrasound developments. Contrast-enhanced imaging of the liver will be reviewed with respect to the literature and our own experience. Echo enhancing agents, also known as ultrasound contrast media, have improved the accuracy of liver ultrasound within recent years. The characterisation of focal liver lesions which is possible by flow characteristics and the improved detection of liver tumors give special importance to the contrast agents. The agents consist of air or gas bubbles coated with different shell media. These micro-bubbles act as strong reflectors to the ultrasound beam enhancing the backscatter signal up to 30 dB. There are differences between blood pool agents and agents with a liver-specific late phase. The agents remain in the vessels during the vascular phase and lead to enhancement of different structures (arterial, capillary, portal venous, and sinusoidal perfusion). This is the first real-time imaging technique of liver lesions that allows a unique analysis of tumor perfusion. Liver tumors known to be hyperperfused in the arterial phase (e.g., focal nodular hyperplasia, hepatocellular carcinoma, and hyperperfused metastases) can be detected and characterised. Hypoperfused tumours (e.g., liver metastases of the gastrointestinal tract) can be recognised in the portal venous phase as less perfused "black spots". Due to of the recently available improved ultrasound technology and affordable ultrasound systems, a reduction in the use of computed tomography (CT) and magnetic resonance imaging (MRI) may be possible, allowing these important technologies to be available for other indications (e.g., brain, thorax).