Small CEUS glossary

Some definitions and terms that apply to CEUS and to these guidelines (well, one definition so far...)

TCA

The first few seconds of arterial filling of an FLL are sometimes crucial for characterization. By general definition the arterial phase begins at the time of the bolus injection of UCA and lasts for 30 seconds. This is the generally accepted and most practical approach, but the time of injection is a blunt parameter since there is great variation in the time of circulation from the site of injection to the liver circulation among individuals and between different injection sites. Roughly the cannula-to-liver bolus time varies from almost immediately to 30 seconds or more between a young individual with a central injection site and an elderly person with the cannula in a foot. Moreover, at "zero seconds" no UCA can be seen in the liver by definition.
The ultrasound community should of course stick to a common terminology regarding the vascular phases: The arterial (0 - 30 seconds following injection), portal (30 - 120 seconds) and late (120 > seconds). This terminology is quite sufficient most of the time, but I believe it is easier to discuss the very initial events that take place in FLL's at the very beginning of enhancement if we introduce a term for the observation of the very first microbubbles entering the liver. In these guidelines I have taken the liberty of calling this very point the "TCA" (Time of Contrast Arrival) when applicable. Where mentioned in the text and protocols, TCA is considered zero seconds, and any time interval described refers to the time from this point. The timer of the US machine then becomes a relative time reference rather than an absolute one, which is a minor inconvenience in a workstation routine.