1. Department of Ultrasound Diagnosis, The Affiliated Hospital of Inner Mongolia Medical University, Hohot, Inner Mongolia Autonomous Region 010059, P.R. China
2. Department of Respiratory Medicine, The Affiliated Hospital of Inner Mongolia Medical University, Hohot, Inner Mongolia Autonomous Region 010059, P.R. China
3. Department of Ultrasound, Maternal and Child Health, Care Hospital of Linhe District, Bayanzhuoer, Inner Mongolia Autonomous Region 015022, P.R. China