Fast large-tip-angle multidimensional and parallel RF pulse design in MRI.
Fast large-tip-angle multidimensional and parallel RF pulse design in MRI.
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DOI：
10.1109/tmi.2009.2020064
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发表时间：
2009-10
影响因子：
10.6
通讯作者：
Noll DC
中科院分区：
文献类型：
--
作者：
Grissom WA;Xu D;Kerr AB;Fessler JA;Noll DC
大顶角多维射频脉冲的设计是一个困难的问题，由于磁化的非线性响应施加的RF在大顶角。在并行激励中，多维RF脉冲设计由于发射场图案在受试者之间改变的可能性而进一步复杂化，这要求在受试者位于扫描仪中时快速设计脉冲。为了加速脉冲设计，我们介绍了一个快速版本的最优控制方法的大锥角并行激励。新方法是基于一种新的方法来分析线性化的布洛赫方程的大尖端角的RF脉冲，这导致在一个近似的线性模型的扰动所产生的小尖端角脉冲的大尖端角脉冲。使用非均匀快速傅立叶变换可以快速评估线性模型，并且我们迭代地应用它来产生提高激励精度的脉冲更新序列。与传统的最优控制相比，我们实现了设计时间和内存需求的大幅减少，同时产生类似精度的脉冲。新方法还可以补偿非理想性，如主场不均匀性。
Large-tip-angle multidimensional RF pulse design is a difficult problem, due to the nonlinear response of magnetization to applied RF at large tip-angles. In parallel excitation, multidimensional RF pulse design is further complicated by the possibility for transmit field patterns to change between subjects, requiring pulses to be designed rapidly while a subject lies in the scanner. To accelerate pulse design, we introduce a fast version of the optimal control method for large-tip-angle parallel excitation. The new method is based on a novel approach to analytically linearizing the Bloch equation about a large-tip-angle RF pulse, which results in an approximate linear model for the perturbations created by adding a small-tip-angle pulse to a large-tip-angle pulse. The linear model can be evaluated rapidly using non-uniform fast Fourier transforms, and we apply it iteratively to produce a sequence of pulse updates that improve excitation accuracy. We achieve drastic reductions in design time and memory requirements compared to conventional optimal control, while producing pulses of similar accuracy. The new method can also compensate for non-idealities such as main field inhomogeneties.