PURPOSE: The purpose of this study is to evaluate the effectiveness of monotherapeutic High-Intensity Focused Ultrasound (HIFU) for thrombolysis in highly occluded vessels using an in vitro model, with emphasis on thermal safety. Methods: HIFU was applied to vessel phantom with various occlusion ratios (60%, 70%, 80%, 90%, and 100%) of the lumen cross-sectional area, each with an equal clot length of 15 mm, under a pulsatile flow of 5 mL/min generated by a peristaltic pump operated at 70 rpm. The insonation was conducted at a frequency of 1.1 MHz, power (Pelect) of 180 W, duty cycle (DC) of 0.4%, pulse repetition frequency (PRF) of 1 Hz and total exposure time of 30 minutes. A step-by-step exposure technique was employed, where the focus of the HIFU beam was progressively moved from one end of the clot to the other. A multi-layer simulation model was used to estimate the acoustic pressure and temperature at the focal point, with temperature distribution monitored throughout the exposure to ensure thermal safety. Thrombolysis efficiency was assessed by measuring the pre- and post-treatment clot weights. Results: HIFU achieved a thrombolysis efficiency (defined as fractional reduction in clot weight) of 65.99% at 100% occlusion when high power and step-by-step exposure were used. This efficiency increased to 78.6% at 60% occlusion. These results were achieved while ensuring thermal safety by maintaining the temperature below 43°C. Conclusions: This study further confirms that HIFU is a promising non-invasive method for thrombolysis in highly occluded vessels while ensuring thermal safety by using high power and a step-by-step exposure method.
Mohammed et al. (Wed,) studied this question.