Neuroimaging

The AIBL study is the largest study in the world involving Positron Emission Tomography (PET) scans using Pittsburgh Compound-B (PIB), a PET amyloid-imaging agent.

PIB is a radioactive marker used for in vivo imaging of Aß deposits using PET and is derived from Thioflavin T, a dye used to stain Aß plaques in histology.

PIB has several properties that make it attractive for PET imaging: it bounds to insoluble species of Amyloid with high affinity, it crosses the blood-brain barrier and enters brain in sufficient amount to be imaged using PET, and it clears rapidly from normal tissues as shown by several animal and human studies.

287 AIBL study participants have been imaged using Magnetic Resonance Imaging and PET.

In addition to PET-PIB, participants are undergoing several scans, including PET-FDG, to assess brain function, and a series of Magnetic Resonance Imaging contrasts for anatomical characterisation (T1W, PDW, T2W), structural integrity of the white matter (DWI), and pathological imaging (FLAIR, SWI).

MRI is a powerful method to image with exquisite anatomical details the different tissues of the brain. It has become an essential tool to assess Alzheimer’s because of the cortical atrophy associated with neuro-degenerescence, which can be measured by MRI. In particular, relatively fast T1W acquisitions offer very good contrast between white and gray matters allowing the precise delineation of the outer cortical mantel. Using algorithms developed at the CSIRO Australian e-Health Research Centre, fast and accurate automatic segmentation of the brain into its main tissue types and estimates of the thickness of the gray matter can be achieved in 3D.

Neuroimaging Research Stream Highlights

The neuroimaging research stream has pursued a better understanding of the natural history of Alzheimer’s disease. Using PET imaging to detect β-amyloid protein and AIBL’s sophisticated battery of psychological and cognitive assessments, these landmark studies have demonstrated that:

• 15 years before the typical levels of amyloid found in patients with Alzheimer’s disease dementia are reached, the levels of β-amyloid in the brain become abnormal on PiB PET scan. The total accumulation time for β-amyloid from none to typical amounts found in AD occurs over a 25-30 year period.
• 4 years before the onset of dementia, hippocampal atrophy becomes detectable on MRI.
• 3 years before onset of dementia memory impairment becomes abnormal on neuropsychology tests.

These findings are shown graphically in Figure 1.

Figure 1: A-beta deposition over time.