FAP and brain neoplasm: In addition, as FAP expression was also found in glioblastoma tissues in the brain (Ebert et al., 2020), the development of blood–brain barrier-permeable FAP-targeted PET tracer is highly valuable for the detection of brain tumors and brain metastases (Zhang et al., 2021; Wei et al., 2022), but the hydrophilic chelating groups such as DOTA and NOTA made the conjugates less possible to penetrate the blood–brain barrier and reach the target in the brain.