Ultrasound contrast agents (USCA) or echo enhancers consist of minute gas containing microbubbles that have a high reflectivity when exposed to an ultrasound field. The history of USCA started in the mid of the 1960s. The cardiologist Joyner performed echo cardiography during the injection of saline solution into the aortic root via a catheter. During the injection he observed bright signals on M-mode imaging. The first written publication of this phenomenon was by Gramiak and Shah and appeared in 19681. Small highly reflective air bubbles within the injected fluid where recognized to be the reason for the observed signals.