Dual-Frequency Intravascular Sonothrombolysis: An In Vitro Study

Abstract

Thrombo-occlusive disease is one of the leading causes of death worldwide. There has been active research on safe and effective thrombolysis in preclinical and clinical studies. Recently, the dual-frequency transcutaneous sonothrombolysis with contrast agents [microbubbles (MBs)] has been reported to be more efficient in trigging the acoustic cavitation, which leads to a higher lysis rate. Therefore, there is increasing interest in applying dual-frequency technique for more significant efficacy improvement in intravascular sonothrombolysis since a miniaturized intravascular ultrasound transducer typically has a limited power output to fully harness cavitation effects. In this work, we demonstrated this efficacy enhancement by developing a new broadband intravascular transducer and testing dual-frequency sonothromblysis in vitro. A broadband intravascular transducer with a center frequency of 750 kHz and a footprint size of 1.4 mm was designed, fabricated, and characterized. The measured -6-dB fractional bandwidth is 68.1%, and the peak negative pressure is 1.5 MPa under the driving voltage of 80 V_pp. By keeping one frequency component at 750 kHz, the second frequency component was selected from 450 to 650 kHz with an interval of 50 kHz. The in vitro sonothrombolysis tests were conducted with a flow model and the results indicated that the MB-mediated, dual-frequency (750+500 kHz) sonothrombolysis yields an 85% higher lysis rate compared with the single-frequency treatment, and the lysis rate of dual-frequency sonothrombolysis increases with the difference between the two frequency components. These findings suggest a dual-frequency excitation technique for more efficient intravascular sonothrombolysis than conventional single-frequency excitation.

Fig. 1.

Fabrication process of the stacked transducer (a)-(f) and the fabricated transducer before and after the wire connection (g)

Fig. 2.

Schematic for the experiment setup (a) the pulse-echo test and (b) the pressure output test

Fig. 3.

Experiment setup for the in-vitro MBs mediated intravascular sonothrombolysis tests.

Fig. 4.

Simulated pressure output with COMOSOL simulation (a) Structure of the transducer with symmetric simulation methods (b) Sound pressure 80 V input.

Fig. 5.

(a) Impedance and phase angle for the transducer (Solid line: Measured results; Dash line: Simulated results) (b) Measured pulse-echo results from the stacked transducer

Fig. 6.

Measured PTP and PNP with different frequency combinations under 80 V input (a) Single-frequency (b) Dual-frequency with component ratio of 1:1. (* and ** represented the maximum PTP and PNP from previously reported work [15])

Fig. 7.

(a) Mass reduction ratio for the un-retracted and retracted clots after 30 min treatment under various frequency combinations (b) Dual-frequency treatment improvement (I_d) compared with single frequency treatment (*, p<0.01;**, p<0.05)

Fig. 8.

Tested passive cavitation dose under various frequency combinations