By Kate Kelland

LONDON (Reuters) - British scientists say they have found the best way yet to analyze the effects of smoking on the brain -- by taking functional magnetic resonance imaging (fMRI) scans of people while they puff on e-cigarettes.

In a small pilot study, the researchers used electronic cigarettes, or e-cigarettes, to mimic the behavioral aspects of smoking tobacco cigarettes, and say future studies could help scientists understand why smoking is so addictive.

E-cigarettes use battery-powered cartridges to produce a nicotine-laced vapor to inhale -- hence the new term "vaping".

Their use has rocketed in recent years, but there is fierce debate about the risks and benefits. Some public health experts say they could help millions quit tobacco cigarettes, while others argue they could "normalize" the habit and lure children into smoking.

While that argument rages, tobacco kills some 6 million people a year, and the World Health Organization estimates that could rise beyond 8 million by 2030.

Matt Wall, an imaging scientist at Imperial College London who led the study using e-cigarettes, said he was not aiming to pass judgment on their rights or wrongs, but to use them to dig deeper into smoking addiction.

The fact that other forms of nicotine replacement therapy, such as patches or gum, have had only limited success in getting hardened smokers to quit suggests they are hooked on more than just nicotine, he noted.

"There's something unique about the drug (nicotine) and the delivery system -- the smoking -- combined which makes it really, really addictive," he told Reuters.

And by analyzing the brains of people "smoking" or "vaping" e-cigarettes, scientists can study the brain effects of what he called the "the behavioral and sensory repertoire of smoking".

Until now, it was impossible to monitor these effects with conventional cigarettes due to the difficulty of having people smoke in the confined space of an MRI scanner.

But because e-cigarettes produce water vapor and do not burn, Wall's team could record brain activity with each drag.

Wall said the study was not large enough to draw any firm conclusions yet, although it did show interesting activity in brain areas linked to reward and addiction, and in areas involved in perception of taste and smell.

"E-cigarettes ... provide a very good simulation of traditional smoking (and) we have shown that using e-cigarettes with fMRI is an excellent paradigm for direct evaluation of the effects of smoking on human neurophysiology," he said.

The plan now is to conduct larger studies using "vapers".

Wall's findings were due to be presented on Tuesday at the Global Addiction Conference in Rio de Janeiro.

(Editing by Kevin Liffey)