Xiaomei Wu is with the Center for Biomedical Engineering, School of Information Science and Technology and Academy for engineering & technology, Fudan University; the Key Laboratory of Medical Imaging Computing and Computer Assisted Intervention (MICCAI) of Shanghai, CO 200433 China; Research Center of Assistive Devices, Shanghai, China. (corresponding author to provide phone: 86-21-65643709-801; e-mail: xiaomeiwu@fudan.edu.cn).