Optimal Design of Multiple-Channel RF Pulses Under Strict Power and SAR Constraints
Optimal Design of Multiple-Channel RF Pulses Under Strict Power and SAR Constraints
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DOI：
10.1002/mrm.22330
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发表时间：
2010-05-01
影响因子：
3.3
通讯作者：
Pruessmann, Klaas P.
中科院分区：
文献类型：
--
作者：
Brunner, David O.;Pruessmann, Klaas P.
并行射频传输最近被探索为一种定制MR激励的空间响应的方法。特别是，并行传输越来越多地被用于加速依赖于时变梯度场以实现多维选择性的射频脉冲。基本的多通道射频波形的设计大多基于正则化最小二乘优化，这与并行成像中的图像重建非常相似。然而，这种类比有很大的局限性。与图像重建不同，射频波形的设计受到多个严格的限制，这些限制来自技术功率限制，以及体内局部和全球能量沉积的安全限制。为了在这样严格的约束条件下优化激励曲线，建议背离正则化策略，而依赖于半定规划。为了使该方法更快，它在初始Lanczos迭代获得的缩小的搜索空间中执行。所提出的算法被证明能够在给定的约束下实现有效的脉冲优化，包括多个隔室的局部特定吸收速率限制。结果还表明，所提出的方法很容易适应激励过程的高级正演模型，包括局部非共振和横向弛豫的影响。《医学评论》63：1280-1291,2010。(C)2010年Wiley-Liss公司
Parallel radio frequency transmission has recently been explored as a means of tailoring the spatial response of MR excitation. In particular, parallel transmission is increasingly used to accelerate radio frequency pulses that rely on time-varying gradient fields to achieve selectivity in multiple dimensions. The design of the underlying multiple-channel radio frequency waveforms is mostly based on regularized least-squares optimization in close analogy with image reconstruction in parallel imaging. However, this analogy has important limitations. Unlike image reconstruction, the design of radio frequency waveforms is subject to multiple strict constraints, which arise from technical power limits, as well as safety limits on local and global energy deposition in vivo. To optimize excitation profiles under such strict constraints, it is proposed to depart from the regularization strategy and rely on semidefinite programming instead. To render this approach fast, it is performed in a reduced search space, which is obtained by initial Lanczos iteration. The proposed algorithm is demonstrated to enable efficient pulse optimization within exactly the given constraints, including local specific absorption rate limits for multiple compartments. It is also shown that the proposed approach readily accommodates advanced forward models of the excitation process, including the effects of local off-resonance and transverse relaxation. Magn Reson Med 63:1280-1291, 2010. (C) 2010 Wiley-Liss, Inc.