Background and Purpose: High-intensity focused ultrasound (HIFU) is a noninvasive technology capable of inducing thermal coagulative necrosis of subsurface structures without injuring intervening tissues. We have previously reported on the feasibility of HIFU vasectomy in a canine model. In this study, we evaluated the feasibility of HIFU ablation of the canine epididymis as an alternative to vasectomy. The epididymis may be a better target than the vas deferens because it is larger, more easily positioned in the HIFU focal zone, and more susceptible to occlusive injury at lower energy levels, thus reducing collateral damage. Materials and Methods: A hand-held HIFU clamp was used to grasp the epididymides of anesthetized dogs (eight surgically exposed and six grasped transcutaneously). An ultrasound transducer in the clamp focused energy on a 1 × 3 × 8-mm target zone centered between the clamp jaws. Ultrasonic energy (6-19 W) was delivered to this target zone for various times (16-150 seconds). The vas, epididymis, and testis were harvested for histologic examination 2 weeks after ablation. Results: Seven of the eight epididymides ablated after surgical exposure demonstrated histologic findings associated with occlusion (fibrosis, hemorrhage, and proximal duct dilatation). Five of the six epididymides ablated transcutaneously also demonstrated histologic evidence of occlusion. Skin burns were evident overlying three epididymides, and one testicular injury was noted adjacent to an ablated region of the epididymis. Conclusion: High-intensity focused ultrasound ablation of the epididymis causes injury and histologic changes associated with epididymal occlusion. Further investigations are under way to optimize ablation parameters and to confirm azoospermia with ejaculate studies. Refinement of this technology may provide a rapid noninvasive alternative to conventional vasectomy.
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