Grissom William, Yip Chun-yu, Zhang Zhenghui, Stenger V Andrew, Fessler Jeffrey A, Noll Douglas C
Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2108, USA.
Magn Reson Med. 2006 Sep;56(3):620-9. doi: 10.1002/mrm.20978.
Parallel excitation has been introduced as a means of accelerating multidimensional, spatially-selective excitation using multiple transmit coils, each driven by a unique RF pulse. Previous approaches to RF pulse design in parallel excitation were either formulated in the frequency domain or restricted to echo-planar trajectories, or both. This paper presents an approach that is formulated as a quadratic optimization problem in the spatial domain and allows the use of arbitrary k-space trajectories. Compared to frequency domain approaches, the new design method has some important advantages. It allows for the specification of a region of interest (ROI), which improves excitation accuracy at high speedup factors. It allows for magnetic field inhomogeneity compensation during excitation. Regularization may be used to control integrated and peak pulse power. The effects of Bloch equation nonlinearity on the large-tip-angle excitation error of RF pulses designed with the method are investigated, and the utility of Tikhonov regularization in mitigating this error is demonstrated.
并行激发已被引入，作为一种使用多个发射线圈加速多维、空间选择性激发的方法，每个发射线圈由独特的射频脉冲驱动。先前并行激发中射频脉冲设计的方法要么是在频域中制定的，要么局限于回波平面轨迹，或者两者皆是。本文提出了一种在空间域中被制定为二次优化问题的方法，并允许使用任意的k空间轨迹。与频域方法相比，新的设计方法具有一些重要优势。它允许指定感兴趣区域（ROI），这在高加速因子下提高了激发精度。它允许在激发过程中进行磁场不均匀性补偿。正则化可用于控制积分和峰值脉冲功率。研究了布洛赫方程非线性对用该方法设计的射频脉冲大翻转角激发误差的影响，并证明了蒂霍诺夫正则化在减轻该误差方面的效用。
