Past and recent progress of molecular imaging probes for β-amyloid plaques in the brain

The deposition of β-amyloid (Aβ) plaques in the parenchymal and cortical brain is accepted as the main pathological hallmark of Alzheimer's disease (AD). According to the amyloid cascade hypothesis, the Aβ deposition in the brain appears to be a good diagnostic biomarker for AD and may also be a good predictive biomarker of this disease. Molecular imaging of Aβ plaques in the brain with positron emission tomography (PET), single photon emission computed tomography (SPECT) or molecular optical imaging represents a promising approach to the early diagnosis of AD and monitoring the effectiveness of novel therapies for this devastating disease. Our review focuses on the past and recent knowledge in this field with respect to small organic molecules that have been utilized for the development of Aβ imaging probes.