Inclusion Criteria:  unresectable or metastatic adenocarcinoma of the gastroesophageal junction confirmed by pathology and imaging; Subjects had measurable lesions according to recist1.1, or unmeasurable but evaluable lesions; HER2 (1 +) or HER2 (2 +) or HER2 (3 +) was found in primary or metastatic lesions; Age: over 18 years old; ECOG was 0-2; Voluntary participation and written informed consent;  Exclusion Criteria:  The inclusion criteria were not met; The function of liver and kidney was abnormal; Cardiac insufficiency; Preparation of pregnant, pregnant and lactating women; Unable to lie on your back for 30 minutes; Those who refused to join the clinical study; Those who have no legal capacity or whose medical or ethical reasons affect the continuation of the research; Refuse to provide tissue or hematological samples. 9）Allergic to both of the contrast agents used in the study