Cavitation enhanced ultrasound thrombolysis

Application of ultrasound (US) has been demonstrated as an effective way to realize thrombus dissolution. Cavitation is hypothesized to be an important mechanism of US thrombolysis, but the relationship between quantified cavitation and thrombolysis efficiency has not been studied extensively. The purpose of this work was to study focused US thrombolysis feasibility and the relationship between cavitation dose and thrombolysis efficiency. Porcine clots were cut into small pieces and inserted into small rubber tubes, then placed in the focal zone of a 1.2 MHz source transducer in a water tank. At the same time, a passive cavitation detection method was used to investigate the role of both inertial and stable cavitation during thrombolysis. After thrombolysis, the debris of clots was microscopically observed, and the distribution of particles´ sizes was measured by Coulter Counter. The thrombolysis efficiency, inertial cavitation dose (ICD) and stable cavitation dose (SCD) were calculated with varying pulse length and duty cycle for 120 s at ISAL of 4243 W/cm². The differences of ICD and SCD in focal zone from when US was exposed to clot (thrombolysis) and when US was merely exposed to water (control) were calculated. According to the results, a high efficiency (90.83 plusmn 3.72%) could be achieved at duty cycle of 1:10 and pulse length of 2 ms. The debris diameters were mostly under 8 um (>99.69%). The subharmonic and broadband noise were both present during US thrombolysis. ICD and SCD generated by pulsed US increased significantly with increasing duty cycle, pulse length, which showed almost the same trends with thrombolysis efficiencies. SCD in thrombolysis was more than 9 times higher than that in control during the first recorded 132 ms. The preliminary experimental results indicated that stable cavitation may play a more important role in US thrombolysis.