S1PR1 and Alzheimer disease: The VT comparisons of [18F]TZ4877 (S1PR1: AD, n = 5; EA, n = 5; WT, n = 5) and [18F]AV45 (Aβ: AD, n = 5; EA, n = 5; WT, n = 3) in AD, WT, and EA groups at 30 minutes post‐injection.