Deep learning (DL) derived CT scan from an FDG PET image of the same section. NAC: non-attenuation corrected PET FDG scan, deepACpseudo-CT image: DL created CT image; Acquired CT image: actual CT scan of the same section. Adapted with permission from “A deep learning approach for 18 F-FDG PET attenuation correction.”, Liu, Fang, et al., EJNMMI physics 5.1 (2018): 1–15.