Alsop D C, Connick T J
Department of Radiology, University of Pennsylvania Medical Center, Philadelphia 19104, USA.
Magn Reson Med. 1996 Jun;35(6):875-86. doi: 10.1002/mrm.1910350614.
Local gradient coils can improve the performance of echo-planar, diffusion, and short TE imaging in the brain. A modified singular value decomposition algorithm, which allows the rapid optimization and comparison of designs, was employed to optimize head size gradient coils. A theoretical expression for the torque on a cylindrical coil is presented and used to design coils that are free from torque while pulsed within a magnetic field. Gradient coils of various lengths both with and without torque constraints were compared; although torque-free coils do not perform as well as unbalanced coils, asymmetric torque-balanced coils can achieve comparable homogeneity with only a modest increase in inductance and resistance. Both types of coils outperform body size gradient coils by a dramatic margin. A three-axis head gradient designed using these techniques was constructed and used for brain imaging on a clinical scanner.
局部梯度线圈可以改善脑部回波平面成像、扩散成像和短回波时间成像的性能。采用一种改进的奇异值分解算法（该算法可实现设计的快速优化和比较）来优化头部尺寸的梯度线圈。给出了圆柱线圈上扭矩的理论表达式，并用于设计在磁场中脉冲时无扭矩的线圈。比较了有无扭矩约束的各种长度的梯度线圈；尽管无扭矩线圈的性能不如不平衡线圈，但非对称扭矩平衡线圈仅在电感和电阻略有增加的情况下就能实现相当的均匀性。这两种类型的线圈在性能上都远远超过身体尺寸的梯度线圈。使用这些技术设计的三轴头部梯度线圈被制造出来，并用于临床扫描仪上的脑部成像。
