Fig. 4.

Schematic and in vivo visualization of rotational flow parameters (vorticity and helicity). a A schematic representation of vorticity ($\underset{\omega }{\to }$). The upper particle moves in space without rotating. The bottom particle moves in the same direction but also spins around its own axis, resulting in a curl. b Vorticity is clearly seen when looking at the in-plane vectors. This plane is located in the aortic arch where secondary flow patterns are physiological. In this case, two counter-rotating vortices are seen. c An example of helical flow (red circle)