The venous clot is described as being made of two regions: the red cell rich fibrin clot parallel to the endothelium and lines of platelet rich white thrombus commonly referred to as the lines of Zahn within the clot separating regions of red thrombus
. Genetic variants such as high levels of coagulation factor VIII, von Willebrand factor, factor Vii, and prothrombin are all linked to an elevated risk of thrombus formation.
In in vitro study, red thrombus aged 5 h and MBs were put in a static system and irradiated with a 1 MHz frequency TUS and 4 cm irradiation distance, a relatively lower intensity of 1W/[cm.sup.2], and lesser exposure time of 10 min could make a good fibrinolytic effect, while a higher power of 1.5W/[cm.sup.2] and longer irradiation time of 30 min in 2h obstructive FAT in rabbits also got a good performance in recanalized rates and scores, without the use of fibrinolytic agents.
In the control group, the surface and the inner fibrin structure of the red thrombus remained normal without micropores or clefts ((B1)-(B2), x100); in TUS group, a few tiny fractures and vacuoles were observed at the inner structure (black arrowheads) and loosened surface (blue arrowheads) of clots and a small amount of tiny clefts (black asterisks) was found in an almost intact fiber net within the clots ((B3)-(B4), x100); in TUS + MB group, there were more and larger vacuoles (black asterisks) at the loosened surface (blue arrowheads) area and more irregular clefts (black arrowheads) and tunnel-like disruption within the clots ((B5)-(B6), x100).