Mechanical clot damage from cavitation during sonothrombolysis

Recent studies have shown that high intensity focused ultrasound (HIFU) accelerates thrombolysis for ischemic stroke. Although the mechanisms are not fully understood, cavitation is thought to play an important role. The goal of this paper is to investigate the potential for cavitation to cause mechanical damage to a blood clot. The amount of damage to the fiber network caused by a single bubble expansion and collapse is estimated by two independent approaches: One based on the stretch of individual fibers and the other based on the energy available to break individual fibers. The two methods yield consistent results. The energy method is extended to the more important scenario of a bubble outside a blood clot that collapses asymmetrically creating an impinging jet. This leads to significantly more damage compared to a bubble embedded within the clot structure. Finally, as an example of how one can apply the theory, a simulation of the propagation of HIFU waves through model calvaria of varying density is explored. The maximum amount of energy available to cause damage to a blood clot increases as the density of the calvaria decreases. (C) 2013 Acoustical Society of America.