Institution: | 1. Department of Anatomy, Harbin Medical University, Harbin, China;2. Drs. Liu and Ma contributed equally to this work.;3. Ultrasonic Department, the Second Clinical Hospital, Harbin Medical University, Harbin, China;4. Department of Bioinformation, Harbin Medical University, Harbin, China;5. Fax: 86‐451‐86342900 |