Using ultrasound can speed up the process of liposuction, and make it less painful, according to specialist plastic surgeons using the technique.

In the traditional method, doctors make "tunnels" in fat and have to break it down manually in order to remove it.

It's like a knife through butter Mr George Lamberty, Bupa's Cambridge Lee Hospital

This can leave an uneven surface, and cause bruising and swelling to the patient.

But the ultrasound technique uses high frequency sound waves to break down the fat, and fluid to flush it out, meaning the patient can expect to lose more fat, and have a smoother end result.

Up to two litres of fluid is pumped in to make the fat more liquid, and make it easier to break.

Ultrasonic liposuction can also be used externally to break down fat cells.

'Yellow soup'

Mr George Lamberty, a consultant plastic surgeon at Bupa's Cambridge Lee Hospital, which uses ultrasonic liposuction, said: "One of the signs of standard liposuction is the rippling effect on the skin, the 'ploughed field' effect."

He said results of the procedure depended on how elastic their skin was.

"In ultrasonic liposuction, it's easier to push through the fat because the ultrasound breaks the fat down.

"It's like a knife through butter.

There are concerns that it could damage fat cells, leaving them intact but altering the genetic make up Professor David Sharp, British Association of Plastic Surgeons

"And it breaks it up more evenly, with no trouble."

He added: "I think you can get more out because you can break the fat down more easily.

"It comes out looking like yellow soup, rather than globules of fat."

Genetic danger

However, some doctors have expressed concerns over the potential effect of the treatment on fat cells.

They fear that instead of killing them, like the traditional technique, ultrasonic liposuction could genetically alter cells.

Professor David Sharp, spokesman for the British Association of Plastic Surgeons, told BBC News Online there was no scientific evidence to confirm or eliminate the concerns.

But he said: "If you don't have someone who's expert at it, you could get skin burns.

"There are also concerns that it could damage fat cells, leaving them intact but altering the genetic make up.

"It may be perfectly safe, but there doesn't seem to be the science to back up or allay these fears."

Liposuction is useful for getting rid of fat in specific areas, such as women's outer thighs or stomachs, or men's "love handles".

But doctors say it should not be used if a patient needs to lose weight from across their body.