Incisionless vasectomy using focused ultrasound

Surgical vasectomy may lead to complications including bleeding, infection, and scrotal pain. Noninvasive transcutaneous delivery of therapeutic focused ultrasound has previously been shown to thermally occlude the vas deferens. However, skin bums and inconsistent vas occlusion have presented complications. This study uses bioheat transfer simulations and thermocouple measurements to determine the optimal ablation dosimetry for vas occlusion without skin burns. A two-radian ultrasound transducer clip delivered 4 MHz ultrasound energy to the canine vas deferens co-located at the focus between the clip jaws. Chilled, degassed water was circulated through an attached balloon, providing efficient ultrasound coupling into the tissue and applied cooling to prevent skin burns. Temperatures were recorded at the vas, intradermal, and skin surface during ablation. Acoustic powers of 3-7 W and sonication times of 60-120 sec were used on both the left and right vas (n=2) in a total of four dogs (Control, 3W/120s, 5W/90s, 7W/60s). Measurements were compared with bio-heat transfer simulations modeling the effects of variations in power and sonication time on tissue temperatures. Simulations and experiments suggest that a therapeutic window exists in which vas occlusion may be achieved without skin burns (P = 5-7 W, SI = 1.4-1.9 W/cm², t = 20-50 sec). This dosimetry will guide future vasectomy experiments using focused ultrasound.