磁共振成像系统中射频线圈的优化设计

射频线圈是磁共振成像系统中拾取信号的核心元件。在线圈设计过程中，可以以优化信噪比为目标求解源电流的分布。文中利用磁偶极子的概念，将分布在有限的平面或圆柱面上的电流进行分解，构造基线圈，并引入一个环路基线圈处理圆柱面上的环形电流情况；然后通过源电流分布和基线圈电流分布之间的映射关系，求解使得来自空间某点信号的信噪比最优时的源电流分布。应用这一原理计算了一个源电流分布在圆柱表面上的实例以及工程实际中射频线圈信噪比的物理上限，并讨论如何利用这一结果对线圈的信噪比性能进行评估。

AN INVERSE METHOD TO DESIGN RF COILS WITH ARBITRARY CONDUCTOR PATTERNS FOR MRI SYSTEMS

Radio-frequency (RF) coils are used to pick up signals in the magnetic resonance imaging (MRI) systems. This paper presents an inverse design approach of RF coils with arbitrary conductor patterns to optimize the signal-to-noise ratio (SNR) at a point of interest. The source current is assumed to distribute in a specified plane area or a cylinder surface. Based on magnetic dipoles, it can be considered as a weighted current combination of an array of base coils. A single circular loop base coil is added in the array for the cylinder case to emulate the loop currents around cylinder. To achieve the best SNR at a given point in the object, the currents in the base coils are optimized and continuous current density distributions are then derived. By this method, the ultimate intrinsic SNR for various points inside a cylindrical object is estimated, and the method to evaluate the SNR performance of RF coils is discussed.