Focused ultrasound ablation of the epididymis with use of thermal measurements in a canine model

Abstract

Objective: To explore the epididymis as an alternative anatomical target to the vas deferens for noninvasive male sterilization using therapeutic focused ultrasound.

Design: Controlled preclinical study.

Setting: Canine animal model in an academic research environment.

Patient(s): Four healthy male mongrel dogs (30-35 kg).

Intervention(s): A transducer mounted on a plastic clip delivered ultrasound energy to the canine epididymis. Thermocouples placed transcutaneously into the epididymis, intradermally, and on the skin surface recorded temperatures during ablation with a wide range of acoustic powers and sonication times (control, 3 W/120 s, 5 W/90 s, 7 W/60 s).

Main outcome measure(s): Thermocouple temperature measurements determined the optimal range of ablation parameters that produced successful thermal occlusion of the epididymis without adverse effects (e.g., skin burns, testicular injury).

Result(s): A large "therapeutic window" was determined (power = 3-7 W, time = 20-120 seconds) over which noninvasive thermal occlusion of the epididymis can be achieved. Thermal occlusion rates were higher, and complications lower, than found previously with vas deferens ablation.

Conclusion(s): The epididymis represents a larger and easier target than the vas deferens for performing noninvasive male sterilization using focused ultrasound. Long-term azoospermia studies will be necessary to confirm permanent sterilization with this technique.