Investigation of Thrombolysis and Safety of Stand-Alone High-Intensity Focused Ultrasound Therapy in Partially Occluded Ex-Vivo Animal Models.

Abstract

OBJECTIVE: Stand-alone high-intensity focused ultrasound (HIFU) therapy is a promising non-invasive approach for treating thrombo-occlusive disease. The objective of this study was to investigate the ability of this approach to achieve safe thrombolysis in clinical treatment. METHODS: Two types of thrombo-occlusive models, utilizing plastic tubes (model-&#x2160;) and the abdominal aorta of rabbits (model-&#x2161;), were exposed to 1.1-MHz HIFU with a pulse repetition frequency (PRF) of 1-100 Hz and transducer power (P) up to 180 W. A duty cycle of 0.6% was set to maintain tissue temperature below 43&#x2103;. RESULTS: The experimental results from model-I demonstrated that extensive thrombolysis was seen at P&#x2265; 120 W and PRF &#x2264; 10 Hz. In the experiments using model-&#x2161; (P= 120-180 W, PRF = 1 Hz) a degree of thrombolysis of over 70% was found with treatment times between 12 and 33 minutes. Under these conditions the arteries appeared to have suffered only minor damage, with slight laceration of the intima/inner media and separation of medial lamellae. The mean damage score did not exceed the threshold for vascular rupture at any power level, with no significant differences observed (n = 3, p > 0.05), but slightly lower values were noted at lower power levels. The maximum diameter of the clot debris was < 8 &#x3bc;m, therefore comparable to that of a typical capillary, minimizing the danger of distal embolization. CONCLUSION: The results confirm the potential of stand-alone HIFU as an effective treatment of thrombo-occlusive disease without causing significant vascular damage.