Update on amyloid imaging: from healthy aging to Alzheimer's disease

Abstract

We report on the current state of in vivo amyloid imaging. Although this technique is less than a decade old, a wealth of information is emerging as the initial clinical studies are being reported. Imaging of patients with Alzheimer's disease has allowed quantitative exploration of the natural history of amyloid deposition and its relationship to neurodegeneration. Amyloid imaging also shows significant promise in the differential diagnosis of mild cognitive impairment or atypical dementias. However, amyloid detection may be of greatest utility in healthy elderly persons; consistent with prior autopsy studies, a significant proportion of asymptomatic individuals display increased levels of amyloid by in vivo imaging. Understanding the relationship between this pathology and future cognitive status has significant implications for the application of disease-modifying medications in the "preclinical" phase of disease. Given the considerable clinical experience compared with other tracers, this review focuses on the literature involving Pittsburgh compound B positron emission tomography.

Figure 1

PiB retention by region in healthy controls, patients with mild cognitive impairment, and patients with Alzheimer's disease. PiB distribution volume ratio (DVR) values based on 90 minutes of scanning with cerebellum as reference quantified for frontal cortex (FRC), precuneus (PRC), and subcortical white matter (SWM). The white bars represent University of Pittsburgh cut-off values for dichotomous determination of “amyloid-positive” versus “amyloid-negative” scans. Red triangles: healthy controls; black circles: mild cognitive impairment patients; blue squares: Alzheimer's disease patients.

Figure 2

Axial and mid-sagittal PiB PET images of amyloid-positive (NC+) and amyloid-negative (NC-) healthy controls and patients with mild cognitive impairment (MCI+ and MCI-, respectively) compared with a typical patient with Alzheimer's disease. Images are quantified by distribution volume ratio (DVR).