The ultrasound waves stop sperm production in the testes

Scientists are beginning tests to see if ultrasound can be used as a reversible contraceptive for men.

Based on early work, University of North Carolina experts believe a blast of ultrasound to the testes can safely stop sperm production for six months.

With a grant of $100,000 from the Bill & Melinda Gates Foundation they will push ahead with more clinical trials.

The researchers ultimately hope it could offer a new birth control option to couples throughout the world.

Lead researcher Dr James Tsuruta said: "We think this could provide men with up to six months of reliable, low-cost, non-hormonal contraception from a single round of treatment.

"Our long-term goal is to use ultrasound from therapeutic instruments that are commonly found in sports medicine or physical therapy clinics as an inexpensive, long-term, reversible male contraceptive suitable for use in developing to first world countries."

Once the testis has stopped producing sperm and all "sperm reserves" have been depleted, explain the researchers, the man will be temporarily infertile.

Their Grand Challenges Exploration Grant project aims at fine-tuning this technique for maximum effect and safety.