分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-02
Mou, Hongjin
Mao, Guangbo
Zhang, Jinquan
Zhao, Can
Guo, Jinlong
Liu, Wenjintg
Wu, Ruqun
Shen, Cheng
Zhang, Lei
Li, Junshuai
Du, Guanghua
摘要： High-energy proton microbeam facilities are powerful tools in space science, biology, and cancer therapystudies. The primary limitationsof the 50 MeV proton microbeam system are the poor beam quality provided by the cyclotron and the problem of intense scattering in the slit position. Here, we present an optical design for a cyclotron-based 50 MeV high-energy proton microbeam system with a micron-sized resolution. The microbeam system,which hasan Oxford triplet lens configuration,has relatively small spherical aberrations and is insensitive to changes in the beam divergence angle and momentum spread. In addition, the energy filtrationincluded in the system can reducethe beam momentum spread from 1% to 0.02%. The effects of lens parasitic aberrations and the lens fringe fieldon the beam spot resolution are also discussed. In addition, owing to the severe scattering of 50 MeV protons in slit materials, a slit system model based on the Geant4 toolkit enables the quantitative analysis of scattered protons and secondary particles. For the slit system settings under a 10-micron final beam spot, very few scattered protons can enter the quadrupole lens system and affect the focusing performance of the microbeam system, but thesecondary radiation of neutrons and gamma rays generatedat the collimationsystem should be considered for the 50 MeV protonmicrobeam. These data demonstrate thata 50 MeV proton microbeam system with a micron-sized beam spot based on a cyclotron is feasible.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
Rao, Jia-Sheng
Zhao, Can
Liu, Zuxiang
Yang, Zhao-Yang
Li, Xiao-Guang
Ma, Manxiu
Liu, Zuxiang
Yang, Zhao-Yang
Li, Xiao-Guang
摘要： Purpose: To investigate the longitudinal brain regional homogeneity (ReHo) changes in nonhuman primate after spinal cord injury (SCI) by resting-state functional magnetic resonance imaging (fMRI). Methods: Three adult female rhesus monkeys underwent unilateral thoracic cord injury. A resting-state fMRI examination was performed in the healthy stage and 4, 8, and 12 weeks after the injury. The ReHo value of each voxel in the monkey brain was calculated and compared between pre- and post-SCI monkeys with paired t test. The regions of interest (ROIs) in the significantly changed ReHo regions were set. The correlations between the ReHo change and the time after injury were also determined. Results: Compared with those in healthy period, the ReHo values of the left premotor cortex and the anterior cingulate cortex (ACC) in post-SCI rhesus monkeys significantly increased in 4-week follow-up examinations. The ReHo values of posterior cingulate cortex, left precuneus, left temporal parietooccipital area, and bilateral superior parietal lobules decreased at 8-week follow-up examinations. In 12-week follow-up examinations, the ReHo values of the left postcentral gyrus, right caudate nucleus, and superior temporal gyrus increased. Correlation analysis showed positive correlations between left ACC and the postoperative time. Conclusion: SCI can change the regional synchronism of brain activity in sensorimotor system and the default mode network. These findings may help us to understand the potential pathophysiological changes in the central nervous system after SCI. (C) 2015 Elsevier Inc. All rights reserved.
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