磁共振梯度涡流场的定量实验与分析

发布时间：2018-04-09 23:32

本文选题：磁共振成像　切入点：梯度　出处：《生物医学工程学杂志》2017年02期

【摘要】：脉冲梯度磁场由梯度线圈产生,广泛用于磁共振成像设备的信号定位系统中。但该脉冲也会同时在线圈周围导体结构中感应出涡流场,从而导致总磁场改变,使图像出现变形或伪影,影响临床诊断。本文通过实验测量了1.5 T超导磁共振成像设备中脉冲梯度导致的涡流场;根据电感-电阻串联模型,分析了其数学模型,该模型表明涡流磁场可以由独立项和交叉项组成;然后本文定量测定了每项指数函数的振幅和时间常数等关键参数,为设计数字滤波器以进行预加重和波形整形提供了依据。本文涉及的测量是在设计的专用工装上进行,它由基于中心对称的六个方向上的水模和各自的射频接收线圈构成,通过加载测试序列可以得到有无涡流的原始一维数据,经计算可将其转化为有意义的采样数据。根据本文研究提及的数学模型,将采样数据用最小二乘法拟合后表明,数据符合电感-电阻串联模型,涡流效应确实存在。通过对比实验同时也进一步证实,用数字滤波器对脉冲进行预加重后,涡流场被有效减小。本文建立了系统函数的数学模型,验证了预加重在减小涡流上的实用价值,提出了改进办法,为磁共振设备减轻涡流效应提供了参考。
[Abstract]:The pulsed gradient magnetic field is generated by gradient coil and is widely used in the signal location system of magnetic resonance imaging equipment.But the pulse also induces the eddy current field in the conductor structure around the coil at the same time, which results in the change of the total magnetic field and the distortion or artifact of the image, which affects the clinical diagnosis.In this paper, the eddy current field induced by pulse gradient in 1.5 T superconducting magnetic resonance imaging equipment is experimentally measured, and the mathematical model is analyzed according to the inductance resistance series model, which shows that the eddy current magnetic field can be composed of independent terms and cross terms.Then, the key parameters such as amplitude and time constant of each exponential function are quantitatively measured, which provides the basis for designing digital filter for pre-weighting and waveform shaping.The measurement in this paper is carried out on the designed special tooling. It consists of water modes based on central symmetry in six directions and their respective RF receiving coils. The original one-dimensional data with or without eddy current can be obtained by loading test sequences.It can be transformed into meaningful sampling data by calculation.According to the mathematical model mentioned in this paper, the sampling data are fitted with the least square method. It is shown that the data accord with the inductance resistance series model and the eddy current effect does exist.At the same time, the experimental results show that the eddy-current field is reduced effectively when the pulse is preaccented by digital filter.In this paper, the mathematical model of system function is established, and the practical value of preweighting in reducing eddy current is verified. The improved method is put forward, which provides a reference for magnetic resonance equipment to reduce eddy current effect.
【作者单位】：川北医学院医学影像学院;奥泰医疗系统有限公司;
【基金】：四川省教育厅科研项目(16ZB0237) 四川省教育厅教改课题(川教函[2014]156号-350)
【分类号】：R197.39

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