The Early Perfusion Image Is Useful to Support the Visual Interpretation of Brain Amyloid-PET With 18F-Flutemetamol in Borderline Cases

Purpose: Visual interpretation of brain amyloid-beta (A beta) PET can be difficult in individuals with borderline A beta burden. Coregistration with individual MRI is recommended in these cases, which, however, is not always available. This study evaluated coregistration with the early perfusion frames acquired immediately after tracer injection to support the visual interpretation of the late A beta-frames in PET with F-18-flutemetamol (FMM). Patients and Methods: Fifty dual-time-window FMM-PET scans of cognitively normal subjects with 0 to 60 Centiloids were included retrospectively (70.1 +/- 6.9 years, 56% female, MMSE score 28.9 +/- 1.3, 42% APOE epsilon 4 carrier). Regional A beta load was scored with respect to a 6-point Likert scale by 3 independent raters in the 10 regions of interest recommended for FMM reading using 3 different settings: A beta image only, A beta image coregistered with MRI, and A beta image coregistered with the perfusion image. The impact of setting, within- and between-readers variability, region of interest, and A beta-status was tested by repeated-measure analysis of variance of the Likert score. Results: The Centiloid scale ranged between 2 and 52 (interquartile range, 7-19). Support of visual scoring by the perfusion image resulted in the best discrimination between A beta-positive and A beta-negative cases, mainly by improved certainty of excluding A beta plaques in A beta-negative cases (P = 0.030). It also resulted in significantly higher between-rater agreement. The setting effect was most pronounced in the frontal lobe and in the posterior cingulate cortex/precuneus area (P = 0.005). Conclusions: The early perfusion image is a suitable alternative to T1-weighted MRI to support the visual interpretation of the late A beta image in FMM-PET.