This observational clinical study aims to investigate the spatiotemporal changes of the 18F-FDG PET neuro-metabolic network in patients with lung, gastrointestinal, or endocrine diseases. The study seeks to clarify :
1. the dynamic metabolic alterations of specific brain regions,
2. the spatiotemporal associations between cerebral metabolism and systemic disease progression,
3. the prognostic value of neuro-metabolic parameters. Participants will undergo 18F-FDG PET/CT imaging, clinical assessments, and longitudinal follow-up to evaluate outcomes such as tumor recurrence, metastasis, and survival.