A simple 15-minute brain scan could help doctors diagnose people with autism by identifying structural differences in their brains. Scientists say the scans would speed up what is currently a long and emotional diagnostic procedure and allow the identification of at-risk children more rapidly.

"We know already that people with autism have differences in brain anatomy and some regions are just bigger and smaller or just different in shape," said Christine Ecker of King's College Institute of Psychiatry in London. "Our technique can use this information to identify someone with autism."

Autistic spectrum disorder (ASD) is a lifelong condition caused by abnormalities in the development of the brain that affects around half a million people in the UK. The vast majority of these are male, and diagnosis usually involves a lengthy process of interviews and personal accounts from family and friends close to the patient.

Medical researchers at the IoP compared the brain scans of 20 adults with autism against those of 20 adults without. They found significant differences in the thickness of tissue in parts of the grey matter in areas of the frontal and parietal lobes which are responsible for functions including behaviour and language.

In the experiment, Ecker showed that her imaging technique was able to detect which people in her group had autism, with 90% accuracy. "If we get a new case, we will also hopefully be 90% accurate," she said. The research, supported by the Medical Research Council, Wellcome Trust and National Institute for Health Research, is published today in the Journal of Neuroscience.

Declan Murphy, professor of psychiatry and brain maturation at the IoP said the new method would help people with ASD to be diagnosed more quickly and cost effectively. "Most importantly, their diagnosis will be based on an objective "biomarker" and not simply on the opinion of a clinician, which is formed after an interview. Simply being diagnosed means patients can take the next steps to get help and improve their quality of life."

Uta Frith, emeritus professor of cognitive development at University College London's Institute of Cognitive Neuroscience, said: "This study shows that the subtle brain abnormalities associated with autism show a distinctive pattern. However, it will need many more studies before the technique used in this study can be used for diagnosis. It is crucial that we learn more about what the brain abnormalities mean. The authors in the paper itself say their results are preliminary and serve as 'proof of concept' rather than a definitive means of diagnosis."

Ecker found there was a correlation between the severity of a person's autism and the amount of structural difference observed in their brain scans, compared with the control group. "We can see that, on the basis of the brain scan, some brains are simply located quite far away from the 'control' brain, whereas some are more like the controls, so the autism wouldn't be that severe."

The IoP team scanned the brains of 20 healthy men and 20 men with ASD, aged between 20 and 68 years. The men with ASD had already been diagnosed by traditional methods, which includes IQ tests, a psychiatric interview, physical examinations and a blood test. Once all the brains had been imaged using a standard clinical MRI scanner, the pictures were analysed for differences using a technique called pattern classification, which is widely used in facial recognition technology but has not, until now, been used on brain scans.

So far, Ecker's team has only looked at men but there are plans to extend the work to women and children. "We think this approach will work even better with kids because the brain abnormalities you see in autism develop over the life span and they're most prominent during childhood," she said. "If we can get up to 90% accuracy in adults, we think it'll be even better in kids."

Carol Povey, director of the National Autistic Society's Centre for Autism, said the study gave a valuable insight into the way people with autism process and understand the world around them. "Eventually, the researchers hope that brain scans might also be a useful diagnostic tool. While further testing is still required, any tools which could help identify autism at an earlier stage, have the potential to improve a person's quality of life by allowing the right support to be put in place as soon as possible."

She added: "However, diagnosis is only the first step. At the National Autistic Society, we frequently receive calls from people who have struggled to get support, leaving them anxious, frustrated and in some cases depressed or even suicidal. Research that improves our understanding of autism, is therefore part of a wider struggle to enable people with autism to access appropriate support at every stage of their life."