Chris Rowe preceded his presentation of initial data from his group’s PIB studies by deploring that the commercial licensing agreement for PIB has made it more difficult for academic scientists to test PIB more broadly. To date, only five out of many more qualified academic PET centers have joined the Swedish teams and the original Pittsburg team in testing PIB, said Rowe. They are in Toronto, London, Turku/Finland, Washington University in St. Louis, Missouri, and Austin Hospital in Heidelberg, Australia.
Working at this latter center on the outskirts of Melbourne, Rowe collaborated with others at Monash University and the University of Melbourne to start a prospective study comparing MRI, FDG-PET and PIB-PET in people with AD, DLB, and controls.
A neuropsychiatric test battery, as well as plasma Aβ and ApoE genotyping, are part of the study. Five patients with mild AD who have been imaged to date all have abnormal PIB scans with high PIB retention in the cortex, said Rowe. Of the five control subjects, four show low PIB binding. A 78-year-old woman, who complained about being “less sharp” than before but has an abnormally low score only in one verbal fluency test, retained moderate amounts of PIB in her cortex, said Rowe.
Four patients enrolled so far into the LBD group all have advanced dementia and show PIB retention in a pattern that appears distinct from that of AD, said Rowe. LBD patients have lower overall uptake levels than do AD patients at the same stage of disease. Moreover, they show more diffuse retention, with a significant PIB signal in areas that are relatively spared in AD, such as the occipital lobe and primary sensory and motor cortex.
By testing PIB and FDG-PET side-by-side, this study, as well as Nordberg’s, will try to find out whether amyloid PET or PET based on glucose metabolism is more sensitive at picking up early stages of AD.
No matter who wins this particular contest, both methods require that the patients agree to flood their veins with radioactive tracers for several hours. Researchers are trying to find other methods that dispense with this infusion. In Sorrento, Norbert Schuff of the University of California, San Francisco, introduced early data on arterial spin-labeling perfusion MRI, which lights up under-perfused brain areas without an injection. Schuff suggested that once the signal-noise ratio of this method has improved, it, too, could help the clinician perform a differential diagnosis, because it generated different anatomical patterns of insufficient perfusion between related neurodegenerative conditions (see also Johnson et al., 2005). A broad-based multinational initiative has begun to validate the best among the multitude of promising approaches that neuroimaging has produced in recent years. Check back tomorrow for a news story on this big-science slice of the broader biomarker story.—Gabrielle Strobel.