脉冲动脉自旋标记技术测量正常脑白质血流量的局限性

Limitation of pulsed arterial spin labeling technique in the measurement of normal white matter perfusion

目的 探讨脉冲动脉自旋标记（PASL）灌注技术测量正常脑白质血流量（CBF）的局限性.方法 选取31例颅脑肿瘤患者,使用3.0 T MR系统进行可一次多层采集的第2版本薄层连续饱和技术的单减影灌注定量（Q2TIPSⅡ）PASL和动态磁敏感对比（DSC）灌注成像.观察PASL和DSC-CBF图的脑灌注表现.取病灶对侧大脑半球正常脑白质区做正常脑白质测量.在PASL-CBF和DSC-CBF图上,测量近端基底节层面和远端半卵圆中心层面ROI内的脑白质信号强度值,分别对PASL-CBF和DSC-CBF图不同层面所测值进行配对t检验,并对同一层面两种技术所测值进行Pearson直线相关性分析.结果 在远端层面的深部白质区域,PASL-CBF图显示为黑色的灌注缺失,而DSC-CBF图相应层面末见白质血流的缺失,仍显示为蓝色的低血流区.远端深部白质灌注信号随反转时间的延长而明显改善,但仍可见到黑色的信号缺失区 而灰质灌注信号随着反转时间的延长却稍有下降.远端层面的正常脑白质平均PASL-CBF为（-22.1±55.5）ml·100 g-1·min-1,近端层面脑白质为（89.5±45.5）ml·100 g-1·min-1,两者差异有统计学意义（t=-9.512,P〈0.05）,而远端[（62.8±29.9）ml·100 g-1·min-1]和近端[（57.1±29.6）ml·100 g-1·min-1]层面脑白质的DSC-CBF差异无统计学意义（t=-1.607,P〉0.05） 两种技术测得的近端、远端层面脑白质信号强度无相关性（r值分别为-0.234、0.093,P值均〉0.05）.结论 PASL技术在定量测量正常脑白质血流量时仍存在不足,定量的准确性受到ASL技术自身的局限性和所选择不同参数的影响.

Objective To investigate the limitation of quantitative measurement of cerebral blood flow （CBF） of normal white matter by using a single subtraction with thin-slice TI1 periodic saturation （Q2TIPS Ⅱ ） pulsed arterial spin labeling （PASL）technique. Methods Thirty-one patients with brain tumors were examined at 3.0 T MRI system . A second version of quantitative imaging of perfusion using a single subtraction with additional thin-section periodic saturation after inversion and a time delay （Q2TIPS） technique of pulsed arterial spin labeling in the multisection mode and T2＊ dynamic susceptibility-weighted contrast-enhanced （T2＊ DSC）MR imaging were both implemented. Cerebral blood flow map obtained from PASL and DSC were reviewed. The regions of interest（ ROI ）were placed in the region of normal white matter contralateral to the lesion in the proximal and distal slices. In regions of interest, the signal intensity （SI）was measured from the maps of cerebral blood flow map obtained from PASL and DSC. Pair-t test was performed to determine if there were significant signal differences between proximal and distal slices. Pearson linear correlation analysis of signal intensity was performed for values from the same slices of PASL-CBF and DSC-CBF maps. Results In the deep white matter of distal slice, PASL-CBF map showed perfusion deficit while DSC-CBF map showed low CBF in the corresponding brain area. With the increased inversion time,the PASL-CBF map showed obviously improved perfusion signal in deep white matter （but still some perfusion deficit）and slightly decreased perfusion signal in grey matter. The mean signal of normal white matter measured from distal slices of PASL-CBF maps was（ -22.1 ±55.5） ml· 100 g-1 · min-1 while it was （89.5 ±45.5） ml. 100 g-1 · min-1 in proximal slices. There was a significant difference of signal intensity from PASL-CBF maps between distal and proximal slices （ t = - 9. 512, P 〈 0. 01 =, while no difference of signal intensity between distal[ （62. 8 ± 29.9） ml · 100 g-1 · min-1] and proximal slices [（57. 1 ±29.6） ml · 100 g-1 · min-1 ]was obtained from DSC-CBF maps（t= -1.607,P〉0.05）. There was no significant correlation between PASL-CBF and DSC-CBF in both distal （ r = 0. 093, P 〉 0. 05 ） and proximal slices （ r = - 0. 234, P 〉 0. 05）. Conclusions PASL has limitation in the accurate quantification of cerebral blood flow of normal white matter. The quantification of CBF was affected by the limitations of the technique itself and the different parameters chosen..