|
|
|
| The Study of a 3 T Conduction-Cooled Superconducting Magnet for Animal Magnetic Resonance Imaging |
| Chen Shunzhong1,2, Wang Qiuliang1,2, Sun Wanshuo1,2, Sun Jinshui1,2, Cheng Junsheng1 |
1. Institute of Electrical Engineering Chinese Academy of Sciences Beijing 100190 China;
2. University of Chinese Academy of Sciences Beijing 100049 China |
|
|
|
Abstract Magnetic resonance imaging (MRI) is one of the most advanced imaging techniques and is widely used in clinical diagnosis and basic life science research, with advantages including noninvasiveness, high/multiple soft tissue contrast, parametric imaging, and the richness of information. Animal MRI which takes animals as the research object is widely used in life science research, medical research, and drug mechanism research. The superconducting magnet system which is usually adopted the cryogenic technology of bath-cooling with 4.2 K liquid helium is one of the core components of the MRI system. Since liquid helium (LHe) is a costly nonrenewable resource with a diminishing reserve and the prices have kept steadily increasing, a 3 T superconducting magnet adopting conduction-cooled technology that does not require LHe was developed for small-size and low-cost animal MRI systems.
An active-shielded magnet structure composed of six main coils and two shielding coils arranged coaxially was designed by using both linear programming and nonlinear programming algorithm. The magnet produces a 3 T central magnetic field in a ϕ 330 mm warm bore with theoretical homogeneity of 12×10-4 % in a ϕ 180mm DSV. In order to adapt to the condition that the coil’s temperature may be higher than 4.2 K in a conduction-cooled system, sufficient current-sharing temperature margins are reserved in the magnet design. The minimum current-sharing temperature margin is 2.05 K in coils 1 and 6. A finite element analysis on the stress in the magnet was carried out by using averaged model in which mechanical characteristics of the elements are averaged on different material components. We can see that the maximum hoop stress in the magnet is about 40.9 MPa which is located at coils 3 and 4, indicating that the magnet design is safe.
A passive protection method based on coil subdivision and quench propagation acceleration is a study to protect the magnet from damage caused by a quench. The superconducting coils are divided into three subdivisions to restrict the peak voltage. A heater can deliberately trigger the coil to quench to prevent the harmful concentration of heat in the confined normal zone. The outside interfaces of all coils are equipped with three heaters respectively. All heaters are made of nonmagnetic stainless-steel foils designed to go from one end of the coil to the other end and turn back for two turns. Each heater is made with the following characteristics width and thickness are 10 mm, and 0.2 mm, respectively. Each subdivision is in parallel with a pair of back-to-back diodes in series with eight heaters. Each heater is driven by the loop current in the subdivision.
The cryostat uses a two-stage GM cryocooler to cool the superconducting magnet from room temperature to operating temperature and no LHe is needed. The cryostat mainly consists of a vacuum vessel, thermal shields, a GM cryocooler, pull rods, thermal connections, and a thermal switch. The GM cryocooler is mounted on the vacuum vessel. The first stage is directly connected to the thermal shields. The second stage cools the magnet via a thermal connection braid made of high-purity copper. A pair of hybrid current leads each of which consists of a copper lead and a Bi2223 HTS lead is employed to power the magnet.
The cryostat and the superconducting coils were tested successively after the magnet system had been assembled. The final measured temperature at the first stage is 50 K. The final measured temperature at the second stage is 4.0 K. The maximum temperature of the magnet is 5.0 K in the shielded coil. The magnet was magnetized to 3.001 3 T after undergoing five training quenches and the measured peak-to-peak homogeneity in 180 mm DSV was about 1.33×10-2 %.
|
|
Received: 06 November 2021
|
|
|
|
|
|
[1] 高家红, 雷皓, 陈群, 等. 磁共振成像发展综述[J]. 中国科学: 生命科学, 2020, 50(11): 1285-1295.
Gao Jiahong, Lei Hao, Chen Qun, et al.Magnetic resonance imaging: progresses and perspective[J]. Scientia Sinica (Vitae), 2020, 50(11): 1285-1295.
[2] 冯焕, 姜晖, 王雪梅. 功能磁共振成像在肿瘤学领域的应用[J]. 电工技术学报, 2021, 36(4): 705-716.
Feng Huan, Jiang Hui, Wang Xuemei.Application of functional magnetic resonance imaging in the field of oncology[J]. Transactions of China Electrotechnical Society, 2021, 36(4): 705-716.
[3] 郭磊, 刘东钊, 黄凤荣, 等. 基于突触可塑性的自适应脉冲神经网络在高斯白噪声刺激下的抗扰功能研究[J]. 电工技术学报, 2020, 35(2): 225-235.
Guo Lei, Liu Dongzhao, Huang Fengrong, et al.Research on disturbance rejection of adaptive spiking neural network based on synaptic plasticity under white Gaussian noise[J]. Transactions of China Electrotechnical Society, 2020, 35(2): 225-235.
[4] 李冬梅, 万春丽, 李继承. 小动物活体成像技术研究进展[J]. 中国生物医学工程学报, 2009, 28(6): 916-921.
Li Dongmei, Wan Chunli, Li Jicheng.Development of small living animal imaging technology[J]. Chinese Journal of Biomedical Engineering, 2009, 28(6): 916-921.
[5] 林良真. 我国超导技术研究进展及展望[J]. 电工技术学报, 2005, 20(1): 1-7.
Lin Liangzhen.Recent advances and prospect in the development of superconducting technology in China[J]. Transactions of China Electrotechnical Society, 2005, 20(1): 1-7.
[6] Chen Shunzhong, Dai Yinming, Zhao Baozhi, et al.Development of an 8-T conduction-cooled super-conducting magnet with 300-mm warm bore for material processing application[J]. IEEE Transactions on Applied Superconductivity, 2014, 24(2): 72-76.
[7] Liang Qing, Li Yi, Wang Qiuliang.Cryogenic oscillating heat pipe for conduction-cooled super-conducting magnets[J]. IEEE Transactions on Applied Superconductivity, 2018, 28(3): 1-5.
[8] Wang Qiuliang, Wang Chunzhong, Wang Hui, et al.Development of conduction-cooled superconducting magnet for baby imaging[J]. IEEE Transactions on Applied Superconductivity, 2010, 20(3): 726-731.
[9] 倪志鹏, 王秋良, 严陆光. 短腔、自屏蔽磁共振成像超导磁体系统的混合优化设计方法[J]. 物理学报, 2013, 62(2): 171-177.
Ni Zhipeng, Wang Qiuliang, Yan Luguang.A hybrid optimization approach to design of compact self-shielded super conducting magnetic resonance imaging magnet system[J]. Acta Physica Sinica, 2013, 62(2): 171-177.
[10] 张正硕, 郑金星, 宋云涛, 等. 中国聚变工程实验堆纵场超导磁体高性能Nb3Sn CICC导体稳定性分析[J]. 电工技术学报, 2020, 35(24): 5031-5040.
Zhang Zhengshuo, Zheng Jinxing, Song Yuntao, et al.Stability analysis of high-performance Nb3Sn CICC conductor in China fusion engineering testing reactor toroidal field superconducting magnets[J]. Transa-ctions of China Electrotechnical Society, 2020, 35(24): 5031-5040.
[11] 方进, 丘明, 范瑜, 等. 超导磁体失超检测电路的设计[J]. 电工技术学报, 2012, 27(8): 239-247.
Fang Jin, Qiu Ming, Fan Yu, et al.Design of the circuit in superconducting magnet quench detection[J]. Transactions of China Electrotechnical Society, 2012, 27(8): 239-247.
[12] Picaud V, Hiebel P, Kauffmann J M.Superconducting coils quench simulation, the Wilson's method revi-sited[J]. IEEE Transactions on Magnetics, 2002, 38(2): 1253-1256.
[13] Li Yi, Wang Qiuliang, Chen Shunzhong.Quench simulation for 9.4T MRI superconducting magnet[J]. Journal of Physics: Conference Series, 2014, 507(3): 032054.
[14] Whetstone C N, Roos C E.Thermal phase transitions in superconducting Nb-Zr alloys[J]. Journal of Applied Physics, 1965, 36(3): 783-791.
[15] Lorenzo J, Bajas H, Bajko M, et al.Quench pro-pagation velocity and hot spot temperature models in Nb3Sn racetrack coils[J]. IEEE Transactions on Applied Superconductivity, 2018, 28(3): 1-6.
[16] 谢伟, 杨征, 程显, 等. 环氧树脂材料热氧老化特性研究[J]. 电工技术学报, 2020, 35(20): 4397-4404.
Xie Wei, Yang Zheng, Cheng Xian, et al.Study on thermo-oxygen aging characteristics of epoxy resin material[J]. Transactions of China Electrotechnical Society, 2020, 35(20): 4397-4404.
[17] 李兰凯, 王厚生, 倪志鹏, 等. 超导线圈绕制过程的力学行为研究[J]. 物理学报, 2013, 62(5): 508-514.
Li Lankai, Wang Housheng, Ni Zhipeng, et al.Mechanical stress in superconducting coils during winding process[J]. Acta Physica Sinica, 2013, 62(5): 508-514.
[18] Wilson M N.NbTi superconductors with low ac loss: a review[J]. Cryogenics, 2008, 48(7/8): 381-395.
[19] Yunus M I.A.c. loss induced quenching in multicoil adiabatic superconducting magnets[J]. Cryogenics, 1995, 35(2): 93-100. |
|
|
|
2023, Vol. 38 
