1. Department of Engineering Physics, Tsinghua University, Beijing, China
2. Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing, China
3. Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland
4. Medical Imaging Center, Beijing TongRen Hospital, Capital Medical University, Beijing, China
5. Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland