梯度回波采样自旋回波序列测量脑R2＇及氧摄取分数值稳定性及重复性的研究

Initial study of stability and repeatability of measuring R2 ＇ and oxygen extraction fraction values in the healthy brain with gradient-echo sampling of spin-echo sequence

目的 通过梯度回波采样自旋回波序列（GESSE）测量脑组织R2＇值与传统梯度回波序列（GRE）间接测量R2＇值的方法在正常志愿者内进行比较,初步评价该序列的稳定性及重复性.方法 8名正常健康志愿者,平静状态下进行头颅单层GESSE序列和该层面T2图（T2 map）和有效横向弛豫时间图（T2＊map）扫描.1 d之后,再重复进行相同层面的上述序列扫描.应用北大医院和北京大学工学院生物医学工程系共同自主开发的软件对GESSE序列原始图像进行后处理得到R2＇图（R2＇map）及氧摄取分数图（OEF map）,将左、右大脑半球等分为前、中、后3个区域,测量该区域R2＇值和OEF值;T2 map及T2＊map的数据在Functool工作站上进行后处理得到自旋-自旋弛豫率图（R2 map）和表观自旋-自旋弛豫率图（R2＊map）,利用公式计算得到R2＇值（R2＇=R2＊-R2,R2＊=1/T2＊,R2=1/T2）,ROI测量方法及部位同GESSE序列.通过配对t检验比较GESSE序列及传统序列2次测得R2＇,初步评价该序列的稳定性,通过配对t检验比较GESSE序列前后2次扫描得到的OEF值,初步判断该序列测量OEF值的重复性.结果 GESSE序列前后2次扫描得到的R2＇值分别为（4.21±0.92）、（4.45±0.94）Hz,差异无统计学意义（t=-0.83,P＞0.05）.前后2次传统方法得到R2＇平均值分别为（7.37±1.47）、（6.42±2.33）Hz,差异有统计学意义（t=1.80,P＜0.05）,第1次GESSE序列和传统方法所测R2＇差异有统计学意义（t=1.71,P＜0.05）.GESSE序列前后2次所测OEF值分别为0.327±0.036和0.336±0.035,差异无统计学意义（t=-1.48,P＞0.05）.结论 在正常被试者中GESSE序列测量R2＇值与传统方法相比稳定性较好.GESSE序列测量的OEF值重复性较好.该技术有进一步临床应用的前景.

Objective To evaluate the stability and repeatability of gradient-echo sampling of spinecho （GESSE） sequence in measuring the R2＇value in volunteers, by comparison with traditional GRE sequence （T2＊ map and T2 map）. Methods Eight normal healthy volunteers were enrolled in this study and written informed consents were obtained from all subjects. MR scanning including sequences of GESSE,T2 map and T2 ＊ map were performed in these subjects at resting status. The same protocol was repeated one day later. Raw data from GESSE sequence were transferred to PC to conduct postprocessing with the software built in house. R2＇map and OEF map were got consequently. To obtain quantitative R2＇and OEF values in the brain parenchyma, six ROIs were equally placed in the anterior, middle and posterior part of bilateral hemispheres. Both mean and standard deviation of R2 ＇and OEF were recorded. All images from T2 ＊ map and T2 map were transferred to the Workstation for postprocessing. The ROIs were put at the same areas as those for GESSE sequence. R2＇is defined as R2＇ = R2 ＊ -R2,R2＊ = 1/T2＊. The R2＇value of GESSE sequence were compared with that of GRE sequence. Results The mean R2 ＇values of GESSE at the first and second scan and those of the GRE were （4.21 ±0.92）,（4.45 ±0. 94） Hz and （7.37 ±1.47）, （6. 42 ±2. 33） Hz 0. 035 respectively. The R2＇value and OEF value obtained from GESSE were not significantly different between the first and second scan （ t = - 0. 83, - 1.48, P ＞ 0. 05 ）. The R2＇ value of first GRE imaging had significantly statistical difference from that of second GRE inaging （ t = 1.80, P ＜ 0. 05 ）. The R2＇ value of GESSE sequence was less than that of GRE sequence, and there was significantly statistical difference between them（t = 1.71 ,P＜0. 05）. Conclusion The GESSE sequence has good stability and repeatability with promising clinical practicability.