Evaluating the feasibility of creatine-weighted CEST MRI in human brain at 7 T using a Z-spectral fitting approach
Evaluating the feasibility of creatine-weighted CEST MRI in human brain at 7 T using a Z-spectral fitting approach
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DOI：
10.1002/nbm.4176
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发表时间：
2019-10-14
影响因子：
2.9
通讯作者：
Reddy, Ravinder
中科院分区：
文献类型：
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作者：
Singh, Anup;Debnath, Ayan;Reddy, Ravinder
本研究旨在通过优化饱和脉冲参数和使用Z-谱拟合方法计算对比度，评估7 T条件下肌酸（Cr）化学交换饱和转移（CEST）加权MRI在人脑中的可行性。根据体模数据计算Cr加权（Cr-w）CEST对比度。进行模拟以获得Cr-w CEST的最佳饱和参数，其中其他脑代谢物的贡献较低。CEST-w图像是从四个人类受试者的大脑中以不同的饱和度参数获得的。使用基于洛伦兹函数的不对称性分析和Z光谱拟合方法（分别为模型1和2）计算Cr-w CEST对比度。对于宽磁化转移（MT）效应，高斯和超洛伦兹线的形状也进行了评估。在体模研究中，Cr-w CEST对比度在生理范围内与浓度呈线性相关，与饱和度参数呈非线性相关。使用来自大脑的不对称分析生成的体内Cr-w CEST图代表了具有来自其他代谢物的贡献的混合对比度以及中继核Overhauser效应（rNOE）。模拟提供了用于获取脑CEST数据的饱和度参数的最佳范围的估计。用于脑数据的Cr-w CEST的最佳饱和参数为约B-1 rms = 1.45 μ T和持续时间= 2秒。Z-光谱拟合方法使得能够计算各个组分。这也导致减少MT和rNOE对Cr-w CEST对比度的贡献，这是不对称分析中低估的主要来源。与模型1相比，所提出的修改的z-谱拟合方法（模型2）对噪声更稳定。使用拟合获得的Cr-w CEST对比度在灰质中为6.98 +/- 0.31%，在白色物质中为5.45 +/- 0.16%。最佳饱和度参数减少了其他CEST效应对Cr-w CEST对比度的贡献，并且所提出的Z谱拟合方法能够计算大脑Z谱中的各个分量。因此，计算Cr-w CEST对比度是可行的，其他CEST和rNOE的贡献较低。
The current study aims to evaluate the feasibility of creatine (Cr) chemical exchange saturation transfer (CEST)-weighted MRI at 7 T in the human brain by optimizing the saturation pulse parameters and computing contrast using a Z-spectral fitting approach. The Cr-weighted (Cr-w) CEST contrast was computed from phantoms data. Simulations were carried out to obtain the optimum saturation parameters for Cr-w CEST with lower contribution from other brain metabolites. CEST-w images were acquired from the brains of four human subjects at different saturation parameters. The Cr-w CEST contrast was computed using both asymmetry analysis and Z-spectra fitting approaches (models 1 and 2, respectively) based on Lorentzian functions. For broad magnetization transfer (MT) effect, Gaussian and Super-Lorentzian line shapes were also evaluated. In the phantom study, the Cr-w CEST contrast showed a linear dependence on concentration in physiological range and a nonlinear dependence on saturation parameters. The in vivo Cr-w CEST map generated using asymmetry analysis from the brain represents mixed contrast with contribution from other metabolites as well and relayed nuclear Overhauser effect (rNOE). Simulations provided an estimate for the optimum range of saturation parameters to be used for acquiring brain CEST data. The optimum saturation parameters for Cr-w CEST to be used for brain data were around B-1rms = 1.45 mu T and duration = 2 seconds. The Z-spectral fitting approach enabled computation of individual components. This also resulted in mitigating the contribution from MT and rNOE to Cr-w CEST contrast, which is a major source of underestimation in asymmetry analysis. The proposed modified z-spectra fitting approach (model 2) is more stable to noise compared with model 1. Cr-w CEST contrast obtained using fitting was 6.98 +/- 0.31% in gray matter and 5.45 +/- 0.16% in white matter. Optimal saturation parameters reduced the contribution from other CEST effects to Cr-w CEST contrast, and the proposed Z-spectral fitting approach enabled computation of individual components in Z-spectra of the brain. Therefore, it is feasible to compute Cr-w CEST contrast with a lower contribution from other CEST and rNOE.