Pediatric Intravenous Contrast-Enhanced Ultrasound(CEUS) in China

The goal of this clinical trial is to evaluate the application of intravenous contrast-enhanced ultrasound examination in children with intra-abdominal diseases that require clear diagnoses. The main questions it aims to answer are: * Is intravenous contrast-enhanced ultrasound helpful for the diagnosis of intra-abdominal diseases in children? * What medical problems do participants have when participating in intravenous contrast-enhanced ultrasound examination? * How can ultrasound doctors conduct intravenous contrast-enhanced ultrasound examinations in a standardized manner? Researchers will performing intravenous contrast-enhanced ultrasound examinations on participants and collecting research subjects to establish a multicenter clinical data database. Participants will: * Perform abdominal ultrasound examination to assess the condition. * At least conduct one intravenous contrast-enhanced ultrasound examination. Based on the result of the contrast examination, decide whether to conduct another examination. * Keep a diary of their symptoms and therapeutic process in 30 days.