Development of HIFU Therapy System for Lower Extremity Varicose Veins

High-intensity focused ultrasound (HIFU) treatment utilizing microbubbles was investigated in the present study. It is known that microbubbles have the potential to enhance the heating effects of an ultrasound field. In this study, the heat accompanying microbubble oscillation was used to occlude varicose veins. Alteration of veins was observed after ultrasound irradiation. Veins were resected by stripping. In this study, two vein conditions were adopted during HIFU irradiation; non-compressed and compressed. Compressing the vein was expected to improve occlusion by rubbing the altered intima under compressed conditions. The frequency of the ultrasound was 1.7 MHz, the intensity at the focus was 2800 W/cm2, and the irradiation time was 20 s. In this study, the contrast agent Levovist registered was chosen as a microbubble source, and the void fraction (ratio of total gas volume to liquid) in the vein was fixed at 10-5. Under non-compressed conditions, changes were observed only at the adventitia of the vein anterior wall. In contrast, under compressed conditions, changes were observed from the intima to the adventitia of both the anterior and posterior walls, and they were partly stuck together. In addition, more experiments with hematoxylin-eosin staining suggested that the changes in the vein were more substantial under the latter conditions. From these results, it was confirmed that the vein was occluded more easily with vein compression.