1. Key Laboratory of Optoelectronics Technology & System, Chongqing University, Ministry of Education, Chongqing, China
2. Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
3. Department of Medical Imaging, University of Arizona, Tucson, AZ, USA
4. Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA