The effect of 220 kHz insonation scheme on rt-PA thrombolytic efficacyin vitro

Abstract

Ultrasound-enhanced recombinant tissue plasminogen activator (rt-PA) thrombolysis is under development as an adjuvant to ischemic stroke therapy. The goal of this study was to design a pulsed ultrasound (US) exposure scheme that reduced intracranial constructive interference and tissue heating, and maintained thrombolytic efficacy relative to continuous wave (CW) insonation. Three 220 kHz US schemes were evaluated, two pulsed insonation schemes (15 cycles, 68 µs pulse duration, 33% or 62.5% duty cycle) and an intermittent CW insonation scheme (50 s active, 30 s quiescent) over a 30-min treatment period. An in silico study using a finite-difference model of transcranial US propagation was performed to estimate the intracranial acoustic field and temperature rise in the skull for each insonation scheme. In vitro measurements with flow were performed to assess thrombolysis using time-lapse microscopy. Intracranial constructive interference was not reduced with pulsed US using a pulse length of 15 cycles compared to intermittent CW US. The 33.3% duty cycle pulsed US scheme reduced heating in the temporal bone as much as 60% relative to the intermittent CW scheme. All insonation schemes promoted sustained stable cavitation in vitro and augmented thrombolysis compared to rt-PA alone (p < 0.05). Ultraharmonic (UH) and harmonic cumulative energy over a 30 min treatment period was significantly higher (p < 0.05) for the intermittent CW US scheme compared to either pulsed US scheme. Despite the difference in cavitation emissions, no difference was observed in the clot lysis between the three US schemes. These findings demonstrate that a 33.3% duty cycle pulsed US scheme with a 15-cycle burst can reduce bone heating and achieve equivalent thrombolytic efficacy as an intermittent CW scheme.

Ultrasound-Responsive Cavitation Nuclei for Therapy and Drug Delivery

“…Goyal et al (2017) also measured a higher degree of thrombolysis with 1 MHz pulsed ultrasound at 1.0 MPa peak rarefactional pressure with inertial cavitation than at 0.23 MPa peak rarefactional pressure with stable cavitation in an in vitro model of microvascular obstruction using perfluorobutane-filled, lipid-shelled microbubbles (Weller et al 2002) as a nucleation agent. However, Kleven et al (2019) observed more than 60% fractional clot width loss for highly retracted human whole blood clots exposed to rt-PA, Definity and 220 kHz pulsed or continuous wave (CW) ultrasound at an acoustic output with sustained stable cavitation throughout the insonification periods (0.22 MPa peak rarefactional pressure) (Fig. 6).…”

“…Temperature rise was prominent in the ipsilateral bone along the transducer axis. The computational model is described in Kleven et al (2019).…”

Sonobactericide: An Emerging Treatment Strategy for Bacterial Infections

“…The presence of standing waves produces acoustic field variations that are sensitive to changes in transducer position, excitation frequency or temperature (Huber et al 2011). The acoustic intensity of the ultrasound field is proportional to the square of the pressure amplitude when the ultrasound wavelength is much smaller than the transducer aperture (Kleven et al 2019). Under the plane wave approximation, the acoustic pressure is related to the intensity as follows: I = P 2 /2pc, where P is the peak acoustic pressure, p is the density and c is the speed of sound (Kinsler et al 2000).…”

Nonlinear dynamics of acoustic bubbles excited by their pressure dependent subharmonic resonance frequency: oversaturation and enhancement of the subharmonic signal

“…In this paper, we have analyzed the nonlinear dynamics of the free bubble in the absence of coating (shell). Coated bubbles and most importantly lipid shell bubbles [76] are used in medical applications of ultrasound from SH imaging [40] to blood brain barrier opening [46] and thrombolysis [77]. The nonlinear behavior of lipid coating (e.g.…”