FA阈值对磁共振弥散张量胼胝体纤维束重建的影响

The effect of fractional anisotropy threshold on diffusion tensor tractography of the callosal fiber tract

目的探讨FA阈值对MR弥散张量胼胝体纤维束重建的影响,并寻求最佳阈值。方法 20名健康成年人,男10例,女10例,分别行脑部常规MRI和DTI扫描。对DTI原始数据进行处理:调节不同FA阈值进行胼胝体纤维束重建,获得FDi和FA等参数,并对所得数据进行统计分析。结果①0.05～0.40间,每0.05取一个值作为FA阈值:FA阈值取0.05与0.1、0.3和0.35以及0.35和0.40时测得的FDi值统计分析无明显差别;其余各组之间FDi值均有统计学差异;②在0.10～0.30之间每0.01取一个值作为FA阈值:每组FA阈值下测得的FDi值均与相邻若干组之间无统计学差别—无差别组数较多的主要集中在0.16～0.24之间,其中以0.20时达到高峰;③不同FA阈值下测得的FDi值与FA值存在线性相关(r=-0.918)。结论①正常胼胝体纤维束成像时,FA阈值小于0.1或大于0.3时,纤维追踪将出现假阳性或假阴性结果;而0.16～0.24为正常胼胝体纤维追踪的适合阈值,其中0.20可能为最佳阈值;②FDi值是DTT的一个重要参数,与FA值存在密切的相关性。

Objective To explore the effect of different fractional anisotropy threshold on diffusion tensor tractography of the callosal fiber tract, and to find the optimal trackability FA threshold. Methods Twenty healthy adults （ten males and ten females） were enrolled and underwent conventional magnetic resonance imaging （MRI） and diffusion tensor imaging （DTI） respectively. The DTI source data were postprocassed as follows corpus callosum was chose as seeds to track fibers, by regulating different FA threshold to obtain FDi, FA values and some other coefficients of each region of interest （ROI） and made an analysis statistically. Results （i） We made fibers track under FA threshold by every 0.05 in the range from 0.05 to 0.4, measured FDi and FA values. Significant difference （ P d0.01） was found between different groups in the FDi value, except that when the FA threshold was between 0.05 and 0.10, between 0.30 and 0.35, and between 0.35 and 0.40; （2） We made fibers track under FA threshold by every 0.01 from 0.1 to 0.3, measured FDi values： there were no significant difference between each group and its several adjacent groups-the high figure of indifference groups were mainly concentrated in 0.16 to 0.24, especially when FA threshold was 0.20; （3） The FDi measured under different FA threshold had a linear correlation with FA value （ r =-0. 918）. Conclusion （1） when we perform diffusion tensor tractog- raphy of the normal corpus callosum fiber tract, it may occur false-positive or false-negaive results when the FA threshold was below 0.1 or higher than 0.3 ; And 0.16 to 0.24 were considered to be adaptive FA threshold for normal corpus callosum fiber tracting above of that, FA threshold of about 0.2 was found to be the optimal trackability threshold; （2） FDi value was one of the important parameters of DTT, and it was closely related to FA value.