Extracorporeal ultrasound angioplasty - effect of pulse repetition frequency of high-intensity focused ultrasound on thrombolysis

• Main Author: Yang, Wenjing
• Other Authors: Zhou Yufeng
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Bioengineering
• Online Access: http://hdl.handle.net/10356/68519
• Institution: Nanyang Technological University

The vascular occlusion by the thrombi is the main reason for ischemic stroke and deep vein thrombosis. High-intensity focused ultrasound (HIFU) and histotripsy or microtripsy pulses can effectively dissolve the blood clot with no use of thrombolytic agent and ultrasound contrast agent (microbubble). In this study, HIFU bursts at the same duty cycle (5%) but varied pulse repetition frequency (PRF) from 1 Hz to 1000 Hz were delivered to in vitro porcine blood clot for 30 s. Thrombolysis efficiency initially increases slightly with the PRF, 86.4±10.3%, 89.9±11.9, and 92.9±12.8% at PRF of 1 Hz, 10 Hz, and 100 Hz, respectively, without significant difference (p > 0.05), but then drops dramatically to 37.9±6.9% at PRF of 1000 Hz (p < 0.05). The particle size in the supernant of dissolution is 547.1±129.5 nm, which suggests the disruption of thrombi into subcellular level. Thrombi motion during HIFU exposure shows violent motion and significant curling at low PRF, rotation about its axis with occasional curling at medium PRF, and localized vibration at high PRF due to the generation of acoustic radiation force and streaming. Quantitative analysis of recorded motion shows the displacement decreases with the PRF of delivered bursts, from 3.9±1.5 mm at 1 Hz to 0.7±0.4 mm at 1000 Hz. In summary, the PRF of delivered HIFU bursts at the same output power has a significant effect on the thrombi motion, bubble cavitation activities, and subsequently thrombolysis efficiencies.