The typical frequency of Tau PET scanning in Alzheimer's disease (AD) clinical trials can vary depending on the study's design, objectives, and phase of the trial. Most trials conduct an initial Tau PET scan at the beginning of the study (baseline) to assess the participant’s Tau pathology and establish a reference for future scans. For Phase 2 trials, follow-up scans are often conducted annually to assess the progression of tau pathology over time. Larger, long-term phase 3 trials may also have annual or semi-annual Tau PET scans, but some may include scans every 18 to 24 months depending on the study duration and budget.