ANALYSIS OF IMPROVED HOMOGENEITY USING HIGHER ORDER SHINS FOR CSI OF BRAIN

简介：磁场均匀性是主要关注的问题， 光谱学以及其他成像应用。 体内匀场 通常使用线性匀场校正项进行，而 许多扫描器还配备有附加的电阻匀场线圈 可以提供二阶和三阶匀场，它们通常 由于需要额外的工作量和扫描时间而未使用。 方法 结果：我们测量了均匀性改善的可行性， 与线性插值相比， 单独用于化学位移成像的特定应用， 人脑 本研究中开发的分析工具，沿着 汇总的数据可以用于决定给定的应用程序是否 需要额外的时间、精力和费用（如果需要 需要购买硬件）来实现高阶匀场 例行公事 15名正常志愿者在1.5T GE Signa 扫描仪，并获得B0均匀性分析结果。 作为 已证明，整体场均匀性有显著改善 使用额外的非线性插值获得。 比如说 中心频率在10.1 ppm内的脑体素分数 增加了约三分之一，使用线性+ 与单独的线性匀场校正相比，更高阶的匀场校正。 使用更高阶也减少了体素内线加宽 填隙，但是效果不太明显。 正如所预料的那样， 由于光谱的变化， 体素尺寸增加。 结论：对于应用程序，如 体积CSI研究，使用额外的非线性 匀场项是实质性的，并且可以使用图来决定给定的 应用保证了实现更高阶匀场的努力。

Introduction: Magnetic field homogeneity is of major concern for spectroscopy as well as other imaging applications. In vivo shimming is routinely performed using linear shim correction terms, and while many scanners are also equipped with additional resistive shim coils that can provide second and third order shim fields, they are often not used due to the additonal effort and scan time required. Methods and Results: We measured the homogeneity improvement achieveable using additional higher order shims as compared to the linear shims alone for the specific application of chemical shift imaging of the human brain. The analysis tools developed in this study, along with the summarized data, can be useful in deciding if a given application warrants the additional time, effort, and expense (if additional hardware needs to be purchased) of implementing higher order shimming routines. 15 normal volunteers were studied on a 1.5T GE Signa scanner, and the B0 homogeneity analysis results were obtained. As demonstrated, a significant improvement in overall field homogeneity was obtained using the additional non-linear shims. For example, the fraction of brain voxels with center frequencies within 1 0.1 ppm increased by approximately one third with the use of the linear + higher order shims as compared to the linear shim corrections alone. Intravoxel line broadening was also reduced using higher order shimming, however the effect was less pronounced. As expected, intravovel linebroadening effects are more severe as the spectroscopic voxel size increases. Conclusions: For applications such as volumetric CSI studies, the benefits of using additional non-linear shim terms are substantial, and plots can be used to decide if a given application warrants the effort of implementing higher order shimming.