伽玛刀治疗磁共振影像定位精度的影响因素

Influencing factors of geometrical accuracy in magnetic resonance imaging for gamma knife radiosurgery

目的通过对伽玛刀MRI定位像空间位置误差的研究，提高MRI定位像的几何精确度。方法将临床常用的NRI4种定位扫描序列输入伽玛刀治疗计划系统，测量各栅格节点坐标，比较各点坐标测量值与实际位置的误差，并分析坐标误差的空间分布。结果各序列定位影像的栅格节点空间位置坐标误差均小于1mm。平均误差值以3DFSPGR和sET1加权序列较小。比较4种不同序列像坐标的平均误差值，在横轴位各序列的差异具有统计学意义（F=1497．51、1873．63、2．87、3．00，P〈0．05），冠状位各序列的差别无统计学意义。随着节点距中心点距离的增大，误差值有增大的趋势。结论磁共振成像的空间位置误差与成像序列参数直接相关，在定位时应根据患者病灶的影像学特点及位置合理选择成像序列参数，以减小定位MRI的空间位置误差。

Objective To evaluate and improve the geometrical accuracy of the magnetic resonance imaging used for gamma knife radiosurgery localization. Methods Four common MRI scan programs were used in this study. The images were transferred to the Gamma Plan treatment planning system. Deviations between stereotactie coordinates based on MR images and real geometrical positions given by the construction of the phantom insert were evaluated for each study. The deviations were further investigated as a function of the spatial position of measured points in the investigated volume. Results The geometrical coordinate errors for axial and coronal images of the selected scan programs were all less than 1 mm. Optimal imaging procedure in terms of geometrical accuracy was observed using spin echo T1 and 3D FSPGR MRI sequences in the unit. Statistically significant differences were found in axial images amongSE T1,FSE T2,FRFSE Pd,FSPGR 3D sequences （F =1497.51, 1873.63, 2.87, 3.00,P 〈 0. 05）. The error increased along with the increase of the distance between node point and eentricity. Conclusions The geometrical coordinate errors is related with the imaging program in Mill. Proper imaging programs and parameters should be selected according to the imageology character of patients＇ lesions when the radiosurgery is performed.