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.

Inclusion Criteria:

1. Age 29 days to 18 years old;
2. The clinical diagnosis was abdominal space-occupying lesions, blunt abdominal trauma, ascites of unknown cause, and children with suspected abdominal disease but other examinations could not identify the cause.

Exclusion Criteria:

1. Allergic to sulfur hexafluoride or other components;
2. Heart disease with right-to-left shunt/severe pulmonary hypertension /uncontrolled systemic hypertension/respiratory failure/heart failure/severe arrhythmia;
3. Electrocardiogram, echocardiography or clinical manifestations of myocardial ischemia;
4. Patients with severe blood system diseases or infectious diseases;
5. Hypercoagulable state and recent history of thrombosis;
6. Severe hepatic and renal insufficiency;
7. Patients with respiratory tract infection or congenital respiratory malformation.

Patients in Children's Hospital Affiliated to Zhejiang University School of Medicine, Second Affiliated Hospital of Zhejiang University School of Medicine, Shenzhen Children's Hospital, West China Hospital of Sichuan University, Children's Hospital of Chongqing Medical University, Tianjin Children's Hospital, Xi 'an Children's Hospital, Yuying Children's Hospital Affiliated to Wenzhou Medical University, Kunming Children's Hospital.