Experimental validation of a novel MRI-compatible HIFU device for the treatment of superficial venous insufficiency

A novel High Intensity Focused Ultrasound (HIFU) probe has been designed for minimally-invasive treatment of valvular dysfunction in the saphenous vein, which is known to be the cause of superficial venous insufficiency (SVI) and varicose veins. Treating SVI with HIFU is possible, since venous tissue undergoes localized partial shrinkage when subjected to high temperature elevation. In a previous study in vitro we demonstrated that diameter shrinkage should be sufficient to restore valvular function, as this is done in the more aggressive approach known as external valvuloplasty. Numerical optimization using fast simulations of pressure field have led to a non-spherically shaped probe design with two HIFU elements that focus ultrasound uniformly over a line of length 7 mm, at a depth of 15 mm from the skin. A MR-compatible prototype of the probe has been constructed and this was characterized 1). by electroacustical mapping of the pressure field in water, and 2). by fast, high resolution MR thermal mapping ex vivo on fresh meat samples. Results were in good agreement with those predicted by an analytical approach and numerical simulations. Available experimental data suggest that a short sonication (less than 10 sec duration) should permit sufficient temperature elevation to obtain vein shrinkage. Further studies will be performed on surgically excised samples of human veins under MR thermal mapping in order to determine the optimal sonication parameters (duration and power level).