It all started in the late eighties of the last century. Real time 2D medical ultrasound imaging was established and color Doppler turned out to have excellent diagnostic utility in the larger vessels and cavities like the atria and ventricles of the heart. For visualising smaller vessels, however, there was a clear need for a contrast agent to rescue the Doppler signal. Microbubbles were the obvious candidates, since it was known that small bubbles reflect ultrasound strongly. Very quickly, several pharmaceutical and start-up companies introduced gas filled microbubbles for intravenous administration.