Temperature Field Analysis for the Main Permanent Magnet of MRI

　　Temperature Field Analysis for the Main Permanent Magnet of MRI
　　Among the many methods of medical imaging, magnetic resonance imagine (MRI) is characterized for high resolution of tissues and clearity of dissection structure. H proton in human body can be detected and imaged by MRI, therefore, it is an important instrument for the doctor to diagnose before disease gets worsened. Made of Nd-Fe-B material, main magnet is the Neodymium Magnets biggest, heaviest and most expensive part of MRI device. Its stability of main magnet field is directly influenced by the stability of temperature, which is influential to the quality of image. Thus, the control of the temperature of main magnet is needed.An open and permanent MRI system is discussed in this paper.
　　During the control of temperature of main magnet, problems like uneven distribution and huge fluctuation of temperature and over heating time is encountered. Presently, control technology of domestic products is based on the experienced judgement. Due to the lack of scientific analysis, it is hard to be improved. Internationally, the temperature control technology is kept by MRI makers as a secret because of commerce interest.To control the temperature field of the main magnet system of open-permanent-magnet MRI device, so as to make temperature field reach the required value and uniformity, the ANSYS software is used to solve the 3D-transient temperature field of MRI device on the basis of energy conservation law and equation of thermal balance. The emphasis is on the analysis of the variation of the temperature field in two yokes and supporting posts. The path along which http://www.999magnet.com the heat is transmitted is researched and found.Several improvement schemes are presented in this paper. To compare the time that is taken for the energy emitting through the steel structure in different heater arrangement, the finite element analysis is implemented. Appropriate point is selected as the representative of average temperature of the main magnet which is feedback for temperature control. The different schemes are given to reduce the heating time and to promote the homogeneity of the resultant temperature field. The problem of un-uniformly temperature distribution between the upper- and lower magnets is solved by the methods proposed in this paper. To program the process with APDL language supplied by ANSYS, modeling is predigested with great efficiency and speed.