A new type of PET scan has been used to detect Alzheimer’s non-invasively. It gives results that are as good as doing an autopsy, a new research study suggests.
The research, which is published in the New England Journal of Medicine was carried out by a team of scientists from the David Geffen School of Medicine at the University of California, Los Angeles.
The brain of a person with Alzheimer’s contains abnormal proteins that form deposits and tangles (or more specifically, amyloid senile plaques and tau neurofibrillary tangles) in the cortical region. However, the most reliable method of finding these proteins while the patient is alive is by surgical removal of brain tissue, an invasive and potentially risky procedure. Some scanning methods exist but they are not as reliable.
Scientists have now come up with what appears to be a reliable non-invasive method of detecting these Alzheimer "markers" using a PET scan and a new tracer chemical called FDDNP that binds effectively to abnormal protein plaques and tangles.
PET stands for Positron Emission Tomography. A PET scan gives a three dimensional, computer enhanced and highly colourful "blurry-looking" image of the brain as it traces a positron emitting chemical (in this case FDDNP) after it is injected into the patient and travels through the tiny blood vessels in the brain. Any abnormal protein plaques and tangles show up because the FDDNP will stick to them.
Gary Small who led the study, and his team examined 83 volunteers who were psychiatrically evaluated and given cognitive tests (e.g. to detect memory and reasoning problems). 30 of the volunteers were classed as having no cognitive impairment (they were the "healthy controls"), 28 as having mild cognitive impairment, and 30 were classed as having Alzheimer’s disease.
All of the volunteers underwent a PET scan using FDDNP, and they were also scanned using another PET method based on another chemical tracer called FDG. MRI (magnetic resonance imaging) scans were also performed on 72 of the volunteers.
The results showed that it was possible to tell which of the 83 volunteers was "healthy", which had Alzheimer’s and which had the mild memory problems. The level of accuracy achieved was 98 per cent – significantly better than the FDG-PET method (87 per cent) and the MRI method (68 per cent accuracy).
Also, Small and his colleagues said the 3D PET traces showed that the pattern of protein clumps on the brain were very similar to those found by autopsy and suggested this method could be used to track the progress of the disease.
They conclude that "This (PET-FDDNP) technique is potentially useful as a noninvasive method to determine regional cerebral patterns of amyloid plaques and tau neurofibrillary tangles".
