Fig. 3

Study selection flowchart. By updating our search from July 2019 (right panel, n = 11,343 hits) through a new search in October 2022 (left panel, n = 1461), we identified 12,804 records. After removing duplicates and screening by title, abstracts, and full text, 48 records were selected (blue boxes). Of those, we further excluded 30 records because of the reasons listed in Additional file 1: Table S4. This gave a total of 18 studies for our qualitative synthesis and original analysis (orange ellipsoid). *The search in October 2022 used the same medical subject heading (MeSH) and free-text terms than in July 2019, but duplicates were removed automatically during the actual search strategy. PET positron emission tomography; FDG fluorodeoxyglucose; MRI magnetic resonance imaging; HC healthy control; SCD subjective cognitive decline, MCI mild cognitive impairment