1. Department of Ultrasonic, The Second Affiliated Hospital of Mudanjiang Medical University, Mudanjiang 157009, China
2. Department of Anesthesiology, The Second Affiliated Hospital of Mudanjiang Medical University, Mudanjiang 157009, China
3. Department of Histology and Embryology, Mudanjiang Medical University, Mudanjiang 157011, China
4. Clinical Skills Center of The First Clinical College, Mudanjiang Medical University, Mudanjiang 157011, China