Scientists in Singapore have found a way to examine people's brains to see if they have had small silent strokes, which are linked to a higher risk of dementia.
Previously, doctors could detect these small strokes only after death as they had to examine brain tissue under a microscope.
The new method involves using a 3-tesla (3T) magnetic resonance imaging (MRI) machine.
The 3T machines generate a stronger magnetic field than the more common 1.5T machines used in hospitals, so they yield greater detail in the scans.
In their research, scientists from the National University Health System (NUHS) recruited 238 Asian patients who were admitted between late 2010 and 2013 to the National University Hospital and St Luke Hospital's memory clinics.
The patients' ages ranged from 50 to 95, with the mean age at 72.5 years, and there were almost as many men as women.
The patients were divided into five groups, based on their memory test results and whether they had Alzheimer's disease, a history of stroke or vascular dementia.
Vascular dementia is the second-most common dementia type after Alzheimer's. It is caused by brain damage due to stroke and diseased blood vessels.
The NUHS scientists imaged the patients' brains with the 3T machines. They found that those with the small lesions comprised 24 per cent of dementia-free patients, 43 per cent of those who suffered from Alzheimer's and 62 per cent of those with vascular dementia.
Associate Professor Christopher Chen, director of the NUHS Memory Ageing and Cognition Centre, said that the lesions found were, in a sense, the tip of the iceberg. "People have calculated that if you see one, you probably have several hundred even smaller ones. If you see nine, you probably have several thousands," he said.
He added that the link between the lesions and vascular dementia means doctors could use them as a marker to identify at-risk people.
While there is no cure or treatment for Alzheimer's and vascular dementia, people could reduce their risk by exercising and managing their blood pressure, blood sugar and cholesterol.
Dr Nagaendran Kandiah, a senior consultant at the National Neuroscience Institute, said the NUHS findings were consistent with his own research, which showed that silent small strokes are associated with dementia.
Dr Nagaendran added: "Our findings also show that this problem may be more widespread among Asians compared with Western populations."
According to a recent Institute of Mental Health study, the prevalence of dementia here has risen to 10 per cent of people aged 60 or above.
Prof Chen of NUHS noted that the disease is likely to become more widespread in the future due to Singapore's ageing population.
This article was first published on September 12, 2015.
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