the primary histologic origin of extracranial solid tumors in children is malignant embryonic cells, including Neuroblastoma (NB) , Hepatoblastoma(HB), and kidney, wilms' tumor(WT). Their main clinical symptoms are large abdominal masses, the most common lymph node metastasis . NB accounts for 15% of childhood cancer deaths, but some low-risk NB can disappear on its own. The International Neuroblastoma Risk Group Staging System (INRGSS) was used to determine Risk before NB treatment, whereas the INRGSS was entirely based on the Neuroblastoma diagnosis, illustrating the importance of imaging in the assessment of NB.18F-FDG is the most commonly used agent in PET imaging of tumor. It can reflect the glucose metabolism of tumor and is widely used in the diagnosis, staging, evaluation of curative effect and prognosis prediction of tumor In this study, the investigators retrospectively analyzed 18F-FDG PET/CT or PET/MRI images from patients with NB, HB, and WT. The investigators sought to assess whether these images provide useful information for diagnosis and prognosis.

Inclusion Criteria:

1. age < 18 years,
2. have pathological results or definite clinical diagnosis as the gold standard.

Exclusion Criteria：

1. had surgery or chemotherapy before imaging,
2. accompanying other tumors,
3. diabetic patients or patients with fasting blood glucose ≥ 200 mg/dL.

We reviewed the electronic medical record and imaging data of 47 children who underwent 18F- FDG PET/CT or PET/MR for the diagnosis of suspected NB, HB or WT from Jan 1, 2013, to Aug 30, 2021.