1. Department of Thoracic Surgery, The Sixth Affiliated Hospital, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China
2. Department of Esophageal Surgery, The Sixth Affiliated Hospital, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China
3. Department of Ultrasonography, Guangzhou First People’s Hospital, School of Medicine, South China University of Technology , Guangzhou, Guangdong, P. R. China