Pioneering brain imaging that can detect the build-up of destructive proteins linked to Alzheimer's has been developed by Japanese scientists.

It could lead to new ways of diagnosing the condition and of testing the effectiveness of new drugs.

The technology, reported in the journal Neuron, can identify inside a living brain clumps of a protein called tau that is closely linked to the disease.

Alzheimer's Research UK said it was promising work.

Alzheimer's disease is a problem for researchers trying to come up with a cure. The brain starts to die years before any symptoms are detected, which means drugs are probably given too late.

A diagnosis of Alzheimer's cannot be made with absolute certainty until a patient has died and their brain is examined. It is also not 100% clear what is the cause of the dementia and what are just symptoms.

One protein, called tau, is very closely linked to the disease, with tangles of tau thought to be one way in which brain cells are killed.

The team, lead by the National Institute of Radiological Sciences in Chiba, used positron emission tomography to build a 3D picture of tau in the brain.

They developed a chemical that could bind to tau and then be detected during a brain scan.

Image caption Finding tau in the brain

Tests on mice and people with suspected Alzheimer's showed the technology could detect tau.

Dr Makoto Higuchi, from the National Institute of Radiological Sciences in Japan, said: "Positron emission tomography images of tau accumulation... provide robust information on brain regions developing or at risk for tau-induced neuronal death."

The research is at an early stage, but it could eventually lead to an actual test for Alzheimer's disease.

It might also allow researchers to closely follow the impact drugs that affect tau have on the brain.

Another protein - beta amyloid - is also linked to Alzheimer's and can be detected in similar tests.

Dr Eric Karran, director of research at Alzheimer's Research UK, said: "This promising early study highlights a potential new method for detecting tau - a key player in both Alzheimer's and frontotemporal dementia - in the living brain.

"With new drugs in development designed to target tau, scans capable of visualising the protein inside the brain could be important for assessing whether treatments in clinical trials are hitting their target.

"If this method is shown to be effective, such a scan could also be a useful aid for providing people with an accurate diagnosis, as well as for monitoring disease progression."