单边核磁共振磁体梯度磁场设计的Gram-Schmidt正交化拟合方法  

The Gram-Schmidt orthogonal data fitting method for the designing of the gradient magnetic field of the unilateral NMR

作　　者：何为[1,2] 何晓龙 徐征[1,2] 郭盼 

机构地区：[1]重庆大学电气工程学院 [2]输配电装备及系统安全与新技术国家重点实验室,400044

出　　处：《重庆大学学报（自然科学版）》2013年第1期86-91,共6页Journal of Chongqing University

基　　金：中央高校基本科研业务经费资助项目(CDJZR10150021)

摘　　要：针对传统圆形Halbach磁体结构封闭难以应用于开放式核磁共振中的缺点,提出一种半椭圆形分布的开放式Halbach磁体结构。调节各磁体模块中心点所在椭圆曲线的长轴长度,计算YOZ平面内不同高度上磁场的平坦程度,使用Gram-Schmidt数据拟合方法,得到一种平坦程度最优的磁体结构。优化结果表明:该结构磁体可在YOZ平面上50mm×50mm范围内产生水平方向平坦,垂直方向近似梯度变化的磁场,梯度值为2mT/mm,且获得一个面积为4mm×4mm,均匀度为1.3×10-3,场强为0.073 9T的均匀磁场区域。根据优化设计结果,搭建了实际磁体系统,并对该磁体系统的磁场进行测量,测量结果与设计结果一致。该开放式磁体优点在于垂直方向的梯度磁场由永磁体结构自然形成,不需额外的梯度线圈,从而简化了梯度编码系统的设计。By considering the shortcomings of the traditional Halbach magnet structure which is closed and cannot be applied to the open NMR, an open and semi-circle Halbach magnet structure is proposed. Adjusting the semi-major axis of the elliptic curve which the center of magnets are placed on and calculating the flatness of the magnetic field on different heights, a magnet structure with best flatness is achieved by data fitting method. The optimizing result shows that the best magnet structure can generate a magnetic fields which flatly distributes in the horizontal direction of the 50 mm）〈 50 mm area in the YOZ plane. The gradient is distributed in the vertical direction with gradient of 2 mT/mm. Magnetic field is uniformly distributed in the area of 4 minX4 mm with uniformity of 1.3X10-3 and magnetic field of 0. 073 9 T. An actual magnet model is constructed based on the result of the optimal design; the measurement result is consistent with the design. The advantage of this magnet structure is that the gradient magnetic field is generated by the permanent magnet naturally, and the extra gradient coil isn＇t needed, so the designing of the gradient coding system is simplified.

关 键 词：核磁共振 曲线拟合 单边磁体 梯度磁场 

分 类 号：TM153.1[电气工程—电工理论与新技术]