Doctors can begin to use a simple test to diagnose post-traumatic stress disorder (PTSD).

The test delivers results with 90% accuracy, according to a recent US study.

The research team said that the excellent results vouched for its usefulness in making differential diagnoses, evaluating psychological treatments, and monitoring disease progression.

The test relies on a brain imaging technique called magnetoencephalography (MEG) to analyse the magnetic patterns created by people's brain cells.

For the purposes of the study, the research team recruited 74 US military veterans, all of whom had been diagnosed with PTSD.

The team also recruited 250 people who had never been diagnosed with the disorder.

The test the team used was based on synchronous neural interactions (SNIs).

SNIs are tiny fluctuations in the magnetic field of the brain during which many of the brain's neurons fire in synchrony, creating a kind of chain reaction of magnetic resonance.

Since the late 1960s, researchers working in magnetoencephalography have mapped the magnetic fields and SNIs in the brain.

Their research has already been used as a criterion for diagnosing other disorders, including Alzheimer's disease, chronic tinnitus, multiple sclerosis, and chronic alcoholism.

In the recent study, the subjects were asked to stare at a dot on a screen for up to a minute.

After they had finished staring at the dot, the researchers recorded the magnetic picture taken of their brain as being a measurement of the brain at rest.

Lead researcher Apostolos Georgopoulos of the University of Minnesota in the US said that scientists got signals that came directly from brain activity when they used the new technique.

There are 248 sensors on the scanner, all of which are able to record brain activity on a millisecond by millisecond basis, making the SNI-based technique much faster than functional magnetic resonance imaging (fMRI).

The research team is now attempting to confirm their findings in a larger study.

Neil Greenberg, a military psychiatry researcher at King's College London, said that the main challenge in PTSD was not diagnosis, but in getting people who had the disorder to recognise their need for treatment.

He said that, if scientists could one day use SNIs to identify sufferers, that would be useful, because many of the people who needed treatment did not come forward of their own accord.

Rajendra Morey, a neurological researcher at Duke University in the US, said she thought the SNI-based approach was something that the scientific community and mental health researchers would watch closely for signs of progress.