Diagnosis of Alzheimer's disease, the most common type of dementia, is not easy for its overlapping signs with normal ageing. A collaborative research by City University of Hong Kong (CityU) and Johns Hopkins University has developed a new non-invasive molecular imaging approach based on Magnetic Resonance Imaging (MRI) to dynamically measure glucose level changes in the brain lymphatic system. Their discovery may help in identifying Alzheimer's disease at early stages so that treatments can start as soon as possible.
Dr Kannie Chan Wai-yan, Associate Professor of Department of Biomedical Engineering (BME) at CityU, and her team collaborated with scientists from the USA, Sweden and Hong Kong, in pioneering this pre-clinical study. Their findings were published in the latest issue of the scientific journal Science Advances, titled "Altered D-glucose in brain parenchyma and cerebrospinal fluid of early Alzheimer's disease detected by dynamic glucose enhanced MRI".
A hint of Alzheimer's disease
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"The tricky part of identifying Alzheimer's disease is that early abnormalities, such as the emergence of protein plaques, are similar to normal ageing in the human brain. Patients diagnosed with symptoms, in which deposition of plaques are found in their brain hampering the cognitive function, are most likely already in the middle or late stage of the disease. Actually, pathologies in the brain happened 15 or 20 years before the symptoms appear," said Dr Chan.
Recent findings have shown that abnormal clearance of waste in the glymphatic system - the lymphatic system in the brain - is one of the hallmarks of early Alzheimer's disease. The glymphatic system is a drainage-like system for cerebrospinal fluid to flow through the brain tissue called brain parenchyma, thus facilitating efficient clearance of solutes such as glucose and protein waste from the brain.
Currently, glucose uptake and metabolism can be assessed by imaging with positron emission tomography (PET) in hospitals. However, the PET scans with radioactive tracers are expensive, and its invasive nature has hindered its general clinical application. Moreover, patients cannot be scanned too frequently with radioactive tracers.
Dr Chan's team has spent almost two years looking for a better alternative. They have successfully developed a new imaging approach based on Chemical Exchange Saturation Transfer MRI (CEST MRI) to assess glucose uptake and clearance in the glymphatic system of the mice's brains non-invasively. "CEST MRI has been used in the diagnosis of brain tumors. This is the first time that it is used in assessing the function of glymphatic system," said Dr Chan.
