PT  - JOURNAL ARTICLE
AU  - Fabio Raman
AU  - Yu-Hua Dean Fang
AU  - Sameera Grandhi
AU  - Charles F. Murchison
AU  - Richard E. Kennedy
AU  - John C. Morris
AU  - Parinaz Massoumzadeh
AU  - Tammie Benzinger
AU  - Erik D. Roberson
AU  - Jonathan McConathy
TI  - Dynamic Amyloid PET: Relationships to Flortaucipir Tau PET Measures
AID  - 10.2967/jnumed.120.254490
DP  - 2021 May 01
TA  - Journal of Nuclear Medicine
PG  - jnumed.120.254490
4099  - http://jnm.snmjournals.org/content/early/2021/05/27/jnumed.120.254490.short
4100  - http://jnm.snmjournals.org/content/early/2021/05/27/jnumed.120.254490.full
AB  - Rationale: Measuring amyloid and predicting tau status using a single amyloid positron emission tomography (PET) study would be valuable for assessing brain AD pathophysiology. We hypothesized that early-frame amyloid PET (efAP) correlates with the presence of tau pathology because the initial regional brain concentrations of radioactivity are primarily determined by blood flow, which is expected to be decreased in the setting of tau pathology. Methods: 120 participants (63 amyloid-positive/57 amyloid-negative) with dynamic 18F-florbetapir-PET and static 18F-flortaucipir-PET scans obtained within 6 months of each other were included. These subjects were predominantly cognitively intact in both the amyloid positive (63%) and amyloid negative (93%) groups. Parameters for efAP quantification were optimized for stratification of tau PET positivity, assessed by either a tauopathy score or Braak regions. The ability of efAP to stratify tau positivity was measured using receiver operating characteristics (ROC) analysis of area under the curve (AUC). Pearson’s r and Spearman’s ρ were used for parametric and non-parametric comparisons between efAP and tau PET, respectively. Standardized net benefit was used to evaluate improvement in utilizing efAP as an additional co-predictor over hippocampal volumes in predicting tau PET positivity. Results: Measuring efAP within the hippocampus and summing the first 3 minutes of brain activity post-injection showed the strongest discriminative ability to stratify for tau positivity (AUC 0.67-0.89 across tau PET Braak regions) in amyloid positive individuals. Hippocampal efAP correlated significantly with a global tau-PET tauopathy score in amyloid-positive participants (r = -0.57, P < 0.0001). Compared to hippocampal volumes, hippocampal efAP showed stronger association with tau PET Braak stage (ρ = -0.58 vs. -0.37) and superior stratification of tau PET tauopathy score (AUC: 0.86 vs. 0.66, P = 0.002). Conclusion: Hippocampal efAP can provide additional information to conventional amyloid-PET, including estimation of the likelihood of tau positivity in amyloid-positive individuals.