Ga-68-FAPI-46 PET for CRC Recurrence Detection in Elevated CEA

Inclusion Criteria: * Age ≥ 20 years old * The surgical intervention for colorectal cancer aims for curative resection, with the goal of achieving a disease-free status that persists for six months or more, as assessed clinically and through imaging studies. * Elevated serum CEA levels: Exceeding the laboratory's normal range (5 ng/ml) or, but not surpassing 13 ng/ml; using the individual's post-surgery +/- adjuvant chemotherapy or targeted therapy minimum value as a baseline, a consecutive increase of more than 10% for two times or as determined by the attending physician suggests suspicion of recurrence. * Already performed or scheduled for FDG PET scanning examination. (5) Able to lie flat for at least 30 minutes. * Signing the subject consent form. * ECOG grade 0-2. * The timing of F-18-FDG usage in this trial follows the " 2023 - Colorectal Cancer Treatment Principles" of our institution. Exclusion Criteria: * pregnant woman and breastfeeding women * severe renal impairment (eGRF\< 30ml/min) * Known or suspected allergy to radiopharmaceuticals * Simultaneously or previously diagnosed with malignant tumors other than colorectal cancer. * Inability to undergo the necessary PET scan procedure * Refusal or unwillingness to sign the informed consent form * Severe medical conditions (severe disabilities, mental disorders)