Development of High Intensity Focused Ultrasound (HIFU) Therapy for Lower Extremity Varicose Veins

HIFU treatment has been developed as a noninvasive therapeutic method in existing studies. In our study, a novel noninvasive therapeutic method with HIFU was proposed to occlude lower extremity varicose veins. The temperature rise caused by HIFU is used to occlude varicose veins. When veins were occluded, they become fibrotic and result in complete recovery. Our final goal is the medical application of HIFU treatment for varicose veins. In this study, we challenged to occlude the veins of rabbits. Prior to the vein occlusion experiments, the area heated by HIFU was investigated by using BSA gel, which denatures at over 70°C. The results indicate that the size of the heated area mainly depends on the intensity at focal point and the irradiation time. There was also a tendency that the heated area grew toward the transducer with the increase in irradiation time. In animal experiments, the skin burn during HIFU irradiation was a critical problem. Therefore, we examined the safety range of HIFU intensity through abdomen irradiation experiments before the vein occlusion experiments were conducted. The ultrasound frequency was 1.7 MHz. The intensity at focal point was 900 W/cm2, and the irradiation time was 20 seconds. Rabbits were dehaired by chemical hair remover and echo jelly was applied to the exposed skin in order to fill up the boundary gap. The veins were compressed during HIFU irradiation in order to avoid thermal dissipation, and hyaluronan water solution was injected between the veins and the skin to keep the distance between the skin and the vein. The distance between the veins and the skin was kept at 5 mm minimum. Then HIFU was irradiated on the veins, and the veins of rabbits were occluded. In the present study, we verified the capability of HIFU treatment to occlude lower extremity varicose veins.