Non-Invasive Embolus Trap Using Histotripsy—An Acoustic Parameter Study

Abstract

Free-flowing particles in a blood vessel were observed to be attracted, trapped, and eroded by a histotripsy bubble cloud. This phenomenon may be used to develop a Non-Invasive Embolus Trap (NET) to prevent embolization. This study investigates the effect of acoustic parameters on the trapping ability of the NET generated by a focused 1.063MHz transducer. The maximum trapping velocity, defined by the maximum mean fluid velocity at which a 3–4 mm particle trapped in a 6 mm diameter vessel phantom, increased linearly with peak negative pressure (P−) and increased as the square root of pulse length and pulse repetition frequency (PRF). At 19.9 MPa P−, 1000 Hz PRF and 10 cycle pulse length, a 3 mm clot-mimicking particle could remain trapped under a background velocity of 9.7 cm/s. Clot fragments treated by NET resulted in debris particles < 75 μm. These results will guide the appropriate selection of NET parameters.

Histotripsy methods in mechanical disintegration of tissue: Towards clinical applications

“…Our study shows that clot lysis and blood flow restoration can be achieved at a speed an order of magnitude faster than any current method, without vessel penetration or hazardous embolization. We have investigated the in vitro and in vivo feasibility of using histotripsy for non-invasive thrombolysis [71-74]. …”

Trapping of embolic particles in a vessel phantom by cavitation-enhanced acoustic streaming

“…While ultrasound produces a direct radiation force on the particle through scattering or absorption of acoustic energy, the trapping effect was not observed during exposures in the absence of cavitation(Park et al 2013). Instead, the results indicated that focused ultrasound produced high-velocity streaming of the liquid through the focus, with the peak velocity as high as 120 cm/s.…”

“…Instead, the results indicated that focused ultrasound produced high-velocity streaming of the liquid through the focus, with the peak velocity as high as 120 cm/s. The streaming is greatly enhanced by the presence of a cavitation cloud at the focus (Park et al 2013). The behavior of cavitating bubble clouds generated by short, finite-amplitude, focused ultrasound pulses has been studied in the context of histotripsy for ultrasound tissue erosion (Xu et al 2007; Xu et al 2008).…”

“…Previously, we observed acoustic trapping of blood clot fragments during histotripsy, a noninvasive ultrasound therapy that uses short, focused, high amplitude pressure pulses to generate a cavitation cloud that mechanically breaks down targeted tissues(Xu et al 2004; Roberts et al 2006; Maxwell et al 2009; Park et al 2013). During in-vitro experiments investigating the use of histotripsy for thrombolysis, it was found that thrombus fragments inside a vessel-mimicking tube were attracted to the transducer focus.…”

“…1), and were broken down into sub-millimeter particles. The trapping phenomenon was only observed when the acoustic pressure amplitude was great enough to generate a cloud of cavitation bubbles at the focus (Park et al 2013). Based on these findings, it was suggested that trapping resulted not directly from ultrasound radiation force on the particle, but rather due to ultrasound- or cavitation-induced fluid streaming in the vessel.…”