Selective RF pulses are commonly designed with the desired profile as a low pass filter frequency response. However, for many MRI and NMR applications, the spectrum is sparse with signals existing at a few discrete resonant frequencies. By specifying a multiband profile and releasing the constraint on “don’t-care” regions, the RF pulse performance can be improved to enable a shorter duration, sharper transition, or lower peak B1 amplitude. In this project, a framework for designing multiband RF pulses with improved performance was developed based on the Shinnar-Le Roux (SLR) algorithm and convex optimization. It can create several types of RF pulses with multiband magnitude profiles, arbitrary phase profiles and generalized flip angles. The advantage of this framework with a convex optimization approach is the flexible trade-off of different pulse characteristics. Designs for specialized selective RF pulses for balanced SSFP hyperpolarized (HP) 13C MRI, a dualband saturation RF pulse for 1H MR spectroscopy, and a pre-saturation pulse for HP 13C study were developed and tested.
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机译:通常将选择性RF脉冲设计为具有所需的轮廓,作为低通滤波器的频率响应。但是,对于许多MRI和NMR应用而言,频谱稀疏,并且存在几个离散谐振频率的信号。通过指定多频段配置文件并释放对“无关”区域的限制,可以改善RF脉冲性能,以实现更短的持续时间,更尖锐的过渡或更低的B1峰值幅度。在该项目中,基于Shinnar-Le Roux(SLR)算法和凸优化设计,开发了一种用于设计具有改进性能的多频带RF脉冲的框架。它可以创建具有多频带幅度分布,任意相位分布和广义翻转角的几种类型的RF脉冲。这种采用凸优化方法的框架的优点是可以灵活地权衡不同脉冲特性。用于平衡SSFP超极化(HP) 13 sup> C MRI的专用选择性RF脉冲,用于 1 sup> H MR光谱的双频饱和RF脉冲和用于HP的预饱和脉冲的设计 13 sup> C研究被开发和测试。
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