Curtis Andrew Thomas, Anand Christopher Kumar
Department of Medical Biophysics, The University of Western Ontario, London, ON, Canada N6A 5C1.
Int J Biomed Imaging. 2008;2008:297089. doi: 10.1155/2008/297089.
A pseudorandom, velocity-insensitive, volumetric k-space sampling trajectory is designed for use with balanced steady-state magnetic resonance imaging. Individual arcs are designed independently and do not fit together in the way that multishot spiral, radial or echo-planar trajectories do. Previously, it was shown that second-order cone optimization problems can be defined for each arc independent of the others, that nulling of zeroth and higher moments can be encoded as constraints, and that individual arcs can be optimized in seconds. For use in steady-state imaging, sampling duty cycles are predicted to exceed 95 percent. Using such pseudorandom trajectories, aliasing caused by under-sampling manifests itself as incoherent noise. In this paper, a genetic algorithm (GA) is formulated and numerically evaluated. A large set of arcs is designed using previous methods, and the GA choses particular fit subsets of a given size, corresponding to a desired acquisition time. Numerical simulations of 1 second acquisitions show good detail and acceptable noise for large-volume imaging with 32 coils.
设计了一种伪随机、速度不敏感的体素k空间采样轨迹，用于平衡稳态磁共振成像。各个弧线是独立设计的，不像多激发螺旋、径向或回波平面轨迹那样相互契合。此前研究表明，可以为每个弧线独立定义二阶锥优化问题，将零阶及更高阶矩的归零编码为约束条件，并且各个弧线能够在数秒内完成优化。在稳态成像中使用时，预计采样占空比将超过95%。使用这种伪随机轨迹时，欠采样引起的混叠表现为不相干噪声。本文制定并对遗传算法（GA）进行了数值评估。使用先前方法设计了大量弧线，遗传算法选择给定大小的特定拟合子集，对应于所需的采集时间。1秒采集的数值模拟结果表明，对于32通道的大体积成像，具有良好的细节和可接受的噪声。
