Gapped pulses for frequency-swept MRI
Gapped pulses for frequency-swept MRI
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DOI：
10.1016/j.jmr.2008.05.009
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发表时间：
2008-08-01
影响因子：
2.2
通讯作者：
Garwood, Michael
中科院分区：
文献类型：
--
作者：
Idiyatullin, Djaudat;Corum, Curt;Garwood, Michael
最近推出的一种称为SWIFT（傅里叶变换扫描成像）的方法是一种与MRI完全不同的方法，特别适合于对具有极快自旋-自旋弛豫速率的物体进行成像。该方法利用扫频激励脉冲，在分时模式下几乎同时采集信号。利用自旋系统响应与激励脉冲函数的相关性提取感兴趣的信号。在SWIFT中，图像质量高度依赖于产生均匀和宽带的自旋激发。通过使用双曲割线族的调频脉冲（HSn脉冲）来满足这些要求。本文描述了在SWIFT中正确实现HSn脉冲所需的实验步骤。此外，研究了HSn脉冲在快速通过线性区域的特性，然后分析了插入“间隙”后的脉冲，以实现分时激励和采集。最后，给出了HSn脉冲的幅值和翻转角以及SWIFT序列沉积的相对能量的紧凑表达式。(c) 2008爱思唯尔公司版权所有。
A recently introduced method called SWIFT (SWeep Imaging with Fourier Transform) is a fundamentally different approach to MRI which is particularly well suited to imaging objects with extremely fast spin-spin relaxation rates. The method exploits a frequency-swept excitation pulse and virtually simultaneous signal acquisition in a time-shared mode. Correlation of the spin system response with the excitation pulse function is used to extract the signals of interest. With SWIFT, image quality is highly dependent on producing uniform and broadband spin excitation. These requirements are satisfied by using frequency-modulated pulses belonging to the hyperbolic secant family (HSn pulses). This article describes the experimental steps needed to properly implement HSn pulses in SWIFT. In addition, properties of HSn pulses in the rapid passage, linear region are investigated, followed by an analysis of the pulses after inserting the "gaps" needed for time-shared excitation and acquisition. Finally, compact expressions are presented to estimate the amplitude and flip angle of the HSn pulses, as well as the relative energy deposited by the SWIFT sequence. (c) 2008 Elsevier Inc. All rights reserved.