Evaluation of the dependence of CEST-EPI measurement on repetition time, RF irradiation duty cycle and imaging flip angle for enhanced pH sensitivity.
Evaluation of the dependence of CEST-EPI measurement on repetition time, RF irradiation duty cycle and imaging flip angle for enhanced pH sensitivity.
复制标题
评估 CEST-EPI 测量对重复时间、射频辐射占空比和成像翻转角的依赖性，以增强 pH 灵敏度
DOI：
10.1088/0031-9155/58/17/n229
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发表时间：
2013-09-07
影响因子：
3.5
通讯作者：
Wu R
中科院分区：
文献类型：
--
作者：
Sun PZ;Lu J;Wu Y;Xiao G;Wu R
化学交换饱和转移（CEST）是一种MRI对比机制，可以检测稀释的CEST试剂和微环境特性，具有许多有前途的应用。CEST效应的实验测量是复杂的，并且不仅取决于CEST试剂浓度和交换速率，而且还取决于实验参数，例如RF照射幅度和方案。尽管回波平面成像（EPI）已越来越多地用于CEST MRI，但CEST效应与重复时间（TR）、RF辐射占空比（DC）和EPI翻转角（α）之间的关系尚未得到充分评估和优化，以提高CEST MRI灵敏度。此外，我们的研究通过量化CEST效应及其单位时间信噪比（SNRput）作为TR、占空比和α的函数来评估梯度回波CEST-EPI。我们发现CEST效应随TR和占空比的增加而增加，但随α的增加而减少。重要的是，我们发现SNRput在约为T1和α的两倍的中间TR处达到峰值，约为75°，并随着RF占空比的增加而增加。使用双pH肌酸凝胶CEST体模验证模拟结果。总之，我们的研究为优化CEST MRI实验提供了一个有用的框架。
Chemical exchange saturation transfer (CEST) is an MRI contrast mechanism that can detect dilute CEST agents and microenvironmental properties, with a host of promising applications. Experimental measurement of the CEST effect is complex, and depends on not only CEST agent concentration and exchange rate, but also experimental parameters such as RF irradiation amplitude and scheme. Although echo planar imaging (EPI) has been increasingly used for CEST MRI, the relationship between CEST effect and repetition time (TR), RF irradiation duty cycle (DC) and EPI flip angle (α) has not been fully evaluated and optimized to enhance CEST MRI sensitivity. In addition, our study evaluated gradient echo CEST-EPI by quantifying the CEST effect and its signal-to-noise ratio per unit time (SNRput) as functions of TR, duty cycle and α. We found that CEST effect increased with TR and duty cycle but decreased with α. Importantly, we found that SNRput peaked at intermediate TRs of about twice the T1 and α, at approximately 75°, and increased with RF duty cycle. The simulation results were validated using a dual-pH creatine-gel CEST phantom. In summary, our study provides a useful framework for optimizing CEST MRI experiments.