Mine-detecting equipment under development for the Royal Navy is being adapted to help NHS specialists improve ultrasound scans on their increasingly flabby patients.

Secret sonar technology, which will soon allow minesweepers to see further through the ocean waves, should also allow hospital radiographers to take clearer pictures of internal organs.

This will aid the diagnosis and treatment of the growing number of obese people, claim the technique's designers.

One in five adults in England (around 8 million people) is now said to be obese, and widening tissue between their bodies' surface and their organs can make it difficult to get decent images.

A two-year Treasury-funded scheme to harness medical uses to military ones, costing nearly £1m, is nearing completion, with the ideas company QinetiQ, the privatised successor to the defence evaluation and research agency, expecting to patent its invention next month.

It is in discussions with manufacturers of ultrasound scanners on licences to use the technology.

The equipment is said to change the way devices called transducers, moved across patients' bodies by radiographers, shape the high frequency soundwaves that bounce off internal organs. It also means better screen images can be produced, as the echoes are changed into electric signals.

Ross Gooding, healthcare sales manager for QinetiQ, said the present ultrasound scanners, which cost between £15,000 and £200,000, were limited by laws of physics. "Different transducers operate at different frequencies. The lower frequencies you use, the further they can penetrate, the deeper into the body you can see. But the lower the frequency, the poorer the resolution becomes".

The technology that had been developed meant relatively lower frequency transducers could still be used, but the resolution would be similar to that now produced by higher frequency equipment.

The principle is also important for spotting mines in the water, according to Mr Gooding. "It is nice to know there is a mine a kilometre away rather than 500 metres away. It gives you a little bit more time to do something about it."

Most pregnant women will have had at least one ultrasound scan to check the growing foetus, but scanners are widely used for other purposes too, such as examining soft tissues in the liver or fluid-filled structures such as the gall bladder.