Routine brain scanning could improve dementia diagnosis for two thirds of patients, ending years of misdiagnosis, a study has found.
Currently the only way to determine whether Alzheimer's is present is to look at the brain of a patient after death.
For patients who are still alive, doctors usually use special cognitive tests which monitor memory and everyday skills such as washing and dressing, but the results are often be misleading or inaccurate.
Now new findings presented at the Alzheimer's Association International Conference in London show that Positron Emission Tomography (PET) scans altered the diagnoses for more than two thirds people.
Currently people with early stage Alzheimer's can wait up to four years to receive a correct diagnosis because PET scans are rarely carried out on the NHS as they cost up to £3,000 a time.
But PET scans show the build-up of sticky amyloid plaques in the brain which prevent neurons from communicating and eventually kill areas, wiping out memories and can help with a definitive diagnosis.
Not only do scans pick up problems early, when drugs or lifestyle changes could make a difference, but they could also help reassure people who are suffering mild memory problems that they do not have the disease.
Dr David Reynolds, Chief Scientific Officer at Alzheimer's Research UK said: "Diagnosing dementia is a complex challenge, and doctors have to gather a range of clues to create a picture of what is going on in the brain.
"This new research highlights that value that amyloid brain scans can bring in helping doctors make a more informed diagnosis, either by indicating or ruling out Alzheimer's as the possible cause of someone's dementia symptoms.
"The current drive for life-changing dementia treatments means that in the future, the use of amyloid PET scans or other innovative diagnostic methods will be important to ensure that new medicines reach the right people at the right time."
Positron Emission Tomography (PET) scans work by picking up how good parts of the brain are at sucking up glucose, which is injected into the body bound to a radioactive tracer which can be seen on screen. Parts of the brain that are clogged up and not functioning will not light up.
The new study by the Karolinska Institute in Sweden involving 135 people who had been referred for memory problems found that 68 per cent had a change in diagnosis, following the scans.
A separate study led by GE Healthcare in the UK analysed data from four previous studies looking at the use of brain amyloid PET scans in the process of dementia diagnosis, combining information from 1106 people, found the use of brain amyloid PET scans led to a change in diagnosis in 20 per cent of people.
"A negative brain PET scan indicating sparse to no amyloid plaques rules out Alzheimer's disease as the cause of dementia symptoms," said Dr James Hendrix, Alzheimer's Association Director of Global Science Initiatives.
"This makes it a valuable tool to clarify an uncertain or difficult diagnosis. Misdiagnosis is costly to health systems, and expensive and distressing to persons with dementia and their families."