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

引言：磁场的均匀性是人们主要关注的问题。 光谱学以及其他成像应用。活体垫片 通常使用线性填补校正项来执行，并且虽然 许多扫描仪还配备了额外的阻性垫片线圈 可以提供二阶和三阶填充场，它们通常 由于需要额外的工作和扫描时间，因此不使用。方法 结果：我们测量了可实现的同质性改进 与线性垫片相比，使用附加的高阶垫片 单独用于化学位移成像的具体应用 人脑。本研究中开发的分析工具，以及 汇总数据可用于确定给定应用程序是否 保证额外的时间、精力和费用(如果额外 需要购买硬件)来实现更高阶的垫片 例行程序。15名正常志愿者在1.5T GE Signa上进行了研究 扫描仪，得到B0均匀度分析结果。AS 已证明，总体现场同质性有显著改善 是使用附加的非线性垫片获得的。例如， 中心频率在10.1ppm以内的脑体素分数 通过使用线性+增加了大约三分之一 与单独的线性填补校正相比，更高阶的填补。 使用更高的阶数也减少了体素内线展宽 然而，垫片的效果不那么明显。不出所料， 随着光谱的增加，腔内线宽效应更加严重 体素大小增加。结论：对于以下应用程序 体积CSI研究，使用额外非线性的好处 填充项是实质性的，情节可以用来决定是否给出了 应用程序需要努力实现更高阶的垫片。

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.