Quantification of amyloid beta and tau PET without a structural MRI

Abstract Introduction Relying on magnetic resonance imaging (MRI) for quantification of positron emission tomography (PET) images may limit generalizability of the results. We evaluated several MRI‐free approaches for amyloid beta (Aβ) and tau PET quantification relative to MRI‐dependent quantification cross‐sectionally and longitudinally. Methods We compared baseline MRI‐free and MRI‐dependent measurements of Aβ PET ([18F]florbetapir [FBP], N = 1290, [18F]florbetaben [FBB], N = 290) and tau PET ([18F]flortaucipir [FTP], N = 768) images with respect to continuous and dichotomous agreement, effect sizes of Aβ+ impaired versus Aβ– unimpaired groups, and longitudinal standardized uptake value ratio (SUVR) slopes in a subset of individuals. Results The best‐performing MRI‐free approaches had high continuous and dichotomous agreement with MRI‐dependent SUVRs for Aβ PET and temporal flortaucipir (R 2 ≥0.95; ± agreement ≥92%) and for Alzheimer's disease–related effect sizes; agreement was slightly lower for entorhinal flortaucipir and longitudinal slopes. Discussion There is no consistent loss of baseline or longitudinal AD‐related signal with MRI‐free Aβ and tau PET image quantification.