1 Department of Ultrasound Diagnosis, Gansu Provincial Maternity and Child-care Hospital, Lanzhou, Gansu Province, People's Republic of China; Gansu Provincial Ultrasound Imaging Clinical Medicine Research Center, Lanzhou, Gansu Province, People's Republic of China. Electronic address: litiangang1981@126.com.
2 Department of Ultrasound Diagnosis, Gansu Provincial Maternity and Child-care Hospital, Lanzhou, Gansu Province, People's Republic of China; Gansu Provincial Ultrasound Imaging Clinical Medicine Research Center, Lanzhou, Gansu Province, People's Republic of China.
3 Department of Ultrasound Diagnosis, Gansu Provincial Maternity and Child-care Hospital, Lanzhou, Gansu Province, People's Republic of China; Department of Medical Imaging Center, Gansu Provincial Maternity and Child-care Hospital, Lanzhou, Gansu Province, People's Republic of China.