扫描参数改变对FSE T_2WI序列金属伪影的影响

Experimental study about the effect of different scan parameters of FSE T_2WI sequences on MR metal artifacts

目的探讨不同扫描参数对FSE T_2WI序列金属伪影的影响,以通过调整扫描参数来减小金属伪影。方法选用镍铬合金制成左下6标准桩核冠模型,将模型固定于水模中。应用1. 5T MRI扫描仪,头线圈,对桩核冠模型行横断面FSE T_2WI序列扫描,扫描参数为西门子1. 5T MRI扫描仪的推荐值。在不影响图像质量的前提下保持其它参数与标准扫描序列参数一致,逐一改变以下各参数进行成像:TR、TE、ETL、NEX、FOV、Matrix、BW、Thk、FA。确定伪影最大的层面并测量伪影面积。应用SAS V8统计学软件进行统计学分析。结果调整不同ETL值,镍铬合金伪影大小差异有统计学意义(F=6. 19,P=0. 04 <0. 05)。调整不同NEX值,镍铬合金伪影大小差异有统计学意义(F=6. 98,P=0. 03 <0. 05)。结论在FSE T_2WI序列中,可以通过增加回波链长度和激励次数来减小金属伪影。

Objective To discuss the influence of different scanning parameters on the size of metal artifacts in FSE T2WI sequence, so as to reduce the artifacts by adjusting the scanning parameters. Methods Standard post-core-crown posterior tooth model made of Ni-Cr alloy was fixed in water phantom. The phantom was scanned by 1.5 T MR scanner with the head coil. Axial FSE T2WI sequence was scanned, with scan parameters recommended for Siemens 1.5 T MR scanner. Under the premise of not affecting the image quality, the other parameters were consistent with the recommended parameters, changing the following param- eters： TR, TE, ETL, NEX, FOV, Matrix, BW, Thk and FA one by one. Then, we determined the maximum level of artifact and measured the area of artifact. Statistical testing was performed using SAS V8 statistical software. Results There was statistically significant difference in size of Ni-Cr alloy artifacts by adjusting different ETL values （ F = 6.19, P = 0.04 〈 0.05 ）. There was statistically significant difference in size of Ni-Cr alloy artifacts by adjusting different NEX values （ F = 6.98, P = 0. 03 〈 0. 05）. Conclusion In the FSE T22I sequence, the metal artifacts can be reduced by increasing the ETL and NEX.