Amyloid PET imaging in Alzheimer’s disease: a comparison of three radiotracers

Abstract

Purpose The increasing use of amyloid PET in Alzheimer’s disease research and clinical trials has motivated efforts to standardize methodology. We compared tracer retention for 11C radiotracer Pittsburgh Compound B (PiB) with two 18F amyloid radiotracers (florbetapir and flutemetamol) using two study populations. We also examined the feasibility of converting between tracer-specific measures, using PiB as the common link between the two 18F tracers. Methods One group of subjects (N=40) underwent PiB and flutemetamol imaging sessions and a separate group (N=32) underwent PiB and florbetapir imaging sessions. We compared cortical and white matter retention for each F18 tracer relative to PiB, as well as several reference regions and image analysis methods. Associations between tracer pairs were used to convert thresholds for amyloid positivity between tracer-specific values. Results Cortical retention for each pair of tracers was strongly correlated regardless of reference region (flutemetamol-PiB, ρ=0.84–0.99; florbetapir-PiB, ρ=0.83–0.97) and analysis method (ρ=0.90–0.99). Compared to PiB, flutemetamol had higher white matter retention, while florbetapir had lower cortical retention. Two previously established independent thresholds for amyloid positivity were highly consistent when values were converted between tracer pairs. Conclusions Despite differing white and grey matter retention characteristics, cortical retention for each F18 tracer was highly correlated with PiB, enabling conversion of thresholds across tracer measurement scales with a high level of internal consistency. Standardization of analysis methods and measurement scales may facilitate the comparison of amyloid PET data obtained using different tracers.

Cognitive and neuroimaging features and brain β-amyloidosis in individuals at risk of Alzheimer's disease (INSIGHT-preAD): a longitudinal observational study

“…This strategy was previously used to study any relationships between different tracers or methods 37 .…”

Amyloid negativity in patients with clinically diagnosed Alzheimer disease and MCI

“…[12][13][14] Florbetapir scans for each participant were coregistered to baseline structural MRI scans, which were subsequently used to extract weighted cortical retention means (standardized uptake value ratios [SUVRs]) from frontal, cingulate, parietal, and temporal regions that were averaged and divided by a whole cerebellum reference region to create a SUVR with a positivity threshold of 1.11 as described in greater detail elsewhere 12,13 and online. 15 We also investigated several alternative reference regions and applied positivity thresholds that were derived using a linear transformation of the whole-cerebellum normalized SUVRs as described previously 16 FDG-PET image processing. FDG image data were acquired 30-60 minutes postinjection, and fully preprocessed images were downloaded from the ADNI Web site (adni.loni.usc.edu).…”

The role of PET quantification in neurological imaging: FDG and amyloid imaging in dementia

“…The literature comparing in vivo binding among various tracers with high affinity for amyloid is still limited, but publications generally demonstrate a very close relation with correlation coefficients above 0.8 of relative uptake values [66,67]. As is to be expected, tracers having similar affinity for amyloid and tau deposits, such as 18 F-FDDNP, produce different results with respect to regional distribution and uptake values [68].…”