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

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.