Ultrasound-Enhanced Thrombolysis Using Definity® as a Cavitation Nucleation Agent

Abstract

Ultrasound has been previously shown to act synergistically with a thrombolytic agent, such as recombinant tissue plasminogen activator (rt-PA) to accelerate thrombolysis. In this in vitro study, a commercial contrast agent, Definity ® , was used to promote and sustain the nucleation of cavitation during pulsed ultrasound exposure at 120 kHz. Ultraharmonic signals, broadband emissions, and harmonics of the fundamental were measured acoustically by using a focused hydrophone as a passive cavitation detector and utilized to quantify the level of cavitation activity. Human whole blood clots suspended in human plasma were exposed to a combination of rt-PA, Definity ® , and ultrasound at a range of ultrasound peak-to-peak pressure amplitudes, which were selected to expose clots to various degrees of cavitation activity. Thrombolytic efficacy was determined by measuring clot mass loss before and after the treatment and correlated with the degree of cavitation activity. The penetration depth of rt-PA and plasminogen was also evaluated in the presence of cavitating microbubbles using a dual antibody fluorescence imaging technique. The largest mass loss (26.2%) was observed for clots treated with 120 kHz ultrasound (0.32 MPa peak-to-peak pressure amplitude), rt-PA and stable cavitation nucleated by Definity ® . A significant correlation was observed between mass loss and ultraharmonic signals (r=0.8549, p<0.0001, n=24). The largest mean penetration depth of rt-PA (222 µm) and plasminogen (241 µm) was observed in the presence of stable cavitation activity. Stable cavitation activity plays an important role in enhancement of thrombolysis and can be monitored to evaluate the efficacy of thrombolytic treatment.

Combined Contrast-Enhanced Ultrasound and rt-PA Treatment is Safe and Improves Impaired Microcirculation after Reperfusion of Middle Cerebral Artery Occlusion

“…Our experimental setup does not allow the investigation of bubble dynamics, that is, whether destruction or oscillation of microbubbles in the sound field (stable cavitations) are most beneficial. An earlier in vitro study suggested that stable cavitation activity may result in strongest treatment effects (Datta et al, 2008). Further investigations need to address this interesting field of research.…”

Experimental demonstration of passive acoustic imaging in the human skull cavity using CT‐based aberration corrections

“…In FUS-induced BBB opening, 20,[32][33][34][35][36][37] sonothrombolysis, [38][39][40][41][42] and histotripsy 43,44 studies, correlations between the cavitation activity measured using a single-element passive cavitation detector (PCD) and treatment outcome have been reported. Moreover, microbubble emissions have been used to select treatment pressures 36 and modulate them in real-time between subsequent therapy pulses 35 during FUS-induced BBB opening.…”

Pulsed ultrasound enhances the delivery of nitric oxide from bubble liposomes to ex vivo porcine carotid tissue

“…Each frequency spectrum was scaled to account for the energy lost due to windowing. A frequency domain comb filter was applied to the power spectrum ( Figure 3C) to extract the ultraharmonic (100 kHz bands at odd multiples of 500 kHz) and broadband 38,39 This process is depicted graphically in Figure 3.…”