中文摘要：

在磁共振成像系统的工作过程中,噪声主要是由梯度线圈系统产生的.梯度线圈置于高均匀度超导磁体的室温孔内,并工作于脉冲状态,频繁的开启和关闭会使线圈中电流急剧随时间变化,变化的电流导致线圈受到变化的洛伦兹力作用,从而产生振动,这种高频振动所发出的噪声会对病人产生刺激,严重时甚至会对病人的听觉神经产生损伤.梯度场的场强越强、切换速度越快,所产生的噪声就越大.降低噪声的最根本方法是通过有效的梯度线圈设计,降低洛伦兹力的空间分布.本文针对纵向梯度线圈,在原经典目标场设计方法基础上,加入对振动参量,从而能够有效地降低线圈工作时所产生的噪声.其具体方法是将振动控制函数作为约束条件,通过目标场法建立数学模型,利用MATLAB进行电磁验算.计算结果表明,所提数学模型可有效地降低线圈振动的最大振幅.

英文摘要：

During the scanning of magnetic resonance imaging（MRI） system,the main acoustic noise source comes from the gradient coils.The gradient coils are turned on and of repeatedly,thus producing noise within the coil.With increasing magnetic feld strength,the noise also increases.The primary method to reduce the noise is to decrease the distribution of the Lorentz forces.Target feld（TF） method is very important for designing gradient coils which have been used in MRI and other applications.Many works based on the Turner＇s traditional TF method have been proposed.In this paper,a target feld method combined with vibration control has been presented to analyze the defection of a cylindrical z-gradient coil because of the Lorentz forces.Simulation results via Matlab show that the maximum vibration amplitude can be reduced efectively by the new design method proposed in this paper.