External ultrasonic valvuloplasty for the treatment of superficial venous insufficiency: a feasibility study

Deformations on the valvular tissues of the saphenous vein can cause an abnormal reflux of blood. This reflux is the main cause of superficial venous insufficiency (SVI) and varicose veins. Since high intensity focused ultrasound (HIFU) induces a strong rise in the temperature of biological tissue, and collagen in veins deforms when exposed to a high temperature, we conducted a study to demonstrate the feasibility of using HIFU to induce shrinkage of the collagen of the saphenous vein near the valvular tissue. This shrinkage should restore normal function of the valve. An experimental protocol was carried out where several in vitro segments of human saphenous vein were sonicated with HIFU. In order to better recreate in vivo conditions, the segment was inserted in porcine muscle. The segment of vein and the porcine muscle sample were placed into a PVC cylinder. After being degassed, the sample was inserted in a recipient filled with degassed-saline solution and sonicated with a real-time imaging HIFU probe. The probe has a focal length of 45 mm, a diameter of 52.5 mm and operates at 3 MHz. Ultrasonic imaging, obtained by an 9-MHz 128-element linear array placed in the center of the HIFU probe, was used to spot the focal zone on the wall of the vein. Individual sonications of the vein wall were performed for acoustic power values ranging between 8.75 and 35 W at a constant sonication duration of 5-s. Different sonication durations ranging between 3 and 7-s at constant power were also tested. Results showed that shrinkage of the vein wall was observed by echographic and macroscopic analysis for the cases of high-power sonication. Histological analysis showed that collagen of the vein wall was indeed altered for all cases of sonications but no signs of perforation were found. However, a macroscopic ablation was observed in the surrounding muscle. The observed shrinkage of the vein wall suggests that dysfunctional valves of the saphenous vein could be treated with HIFU since a significant shrinkage of collagen could restore competence of the abnormal valve.