Intracardiac echoes can be derived from the blood in the cardiac chambers, using pulsed echoranging techniques. The physiological origin of these echoes has been established by showing patterns of changing echo intensity that are related to the cardiac cycle. It appears that circulating microbubbles are the most likely source and that they are produced by stable cavitation.
No takes yet. Share an insight, caveat, or question.
Gramiak et al. (1971) studied this question.