The study on non-human primates' brain function network and its advanced cognitive function by utilizing magnetic resonance imaging (MRI) stands for an important developing trend of neuroscience. However, the geometrical features of non-human primates' skull will lead to an inhomogeneity in the local magnetic field, and jeopardize the quality of MRI severely. In this study, a field map-based gradient shimming sequence protocol was optimized (including improval of the spatial resolution of the field map and shrink the adjustment volume) and then compared with the traditional shimming technique on a 3.0 T clinical MRI scanner. A MRI phantom with a geometrical structure inside and a non-human primate (one adult macaque) were scanned. Qualitative estimation was carried out by the phase difference imaging based on the gradient echo and the quantitative evaluation was performed by the full width at half maximum height (FWHM) of the spectrum. Results showed that the FWHM of the free-induction decay (FID) in the phantom's adjustment volume reduce by more than 34% (P<0.001) and the uniformity of the magnetic field could be improved profoundly, by using the optimized shimming protocol. Meanwhile, the geometrical distortion of the imaging of the non-human primate in vivo experiment had been significantly improved by the new method.Therefore,the optimized shimming protocol can effectively enhance the quality of shimming and diminish the imaging geometry distortion derived from the inhomogeneous magnetic field, which in turn meets the requirements of MRI of non-human primates' brain function.%利用磁共振成像技术研究非人灵长类动物的脑功能网络及其高级认知功能是神经科学发展的重要方向.然而,非人灵长类动物颅骨的几何特征会造成局部磁场不均匀,严重影响成像质量.本文采用3.0 T临床磁共振扫描仪,对基于场图的梯度匀场序列进行适当的参数优化(包括提高场图空间分辨率、缩小匀场范围),并与常规匀场方式对比,分别扫描了磁共振专用体模及非人灵长类动物大脑.通过基于梯度回波的相位图差值进行匀场效果的定性判断,并借助共振峰半高宽进行匀场效果的定量评估.结果表明,匀场序列经参数优化后,水模匀场区域内的自由感应衰减曲线半高宽降低超过34% (P<0.001),磁场均匀性提高,而非人灵长类动物活体实验的图像几何畸变得到显著改善.因此,经过优化后的匀场序列能够有效提高匀场质量,减小由于磁场不均匀导致的几何畸变,从而满足非人灵长类动物脑功能成像的匀场需要.
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