School of Brain and Behavioral Sciences, University of Texas at Dallas, Dallas, TX, USA.
Neuroimage. 2012 Apr 2;60(2):1127-38. doi: 10.1016/j.neuroimage.2011.12.062. Epub 2011 Dec 29.
Diffusion tensor tractography is increasingly used to examine structural connectivity in the brain in various conditions, but its test-retest reliability is understudied. The main purposes of this study were to evaluate 1) the reliability of quantitative measurements of diffusion tensor tractography and 2) the effect on reliability of the number of gradient sampling directions and scan repetition. Images were acquired from ten healthy participants. Ten fiber regions of nine major fiber tracts were reconstructed and quantified using six fiber variables. Intra- and inter-session reliabilities were estimated using intraclass correlation coefficient (ICC) and coefficient of variation (CV), and were compared to pinpoint major error sources. Additional pairwise comparisons were made between the reliability of images with 30 directions and NEX 2 (DTI30-2), 30 directions and NEX 1 (DTI30-1), and 15 directions and NEX 2 (DTI15-2) to determine whether increasing gradient directions and scan repetition improved reliability. Of the 60 tractography measurements, 43 showed intersession CV ≤ 10%, ICC ≥ .70, or both for DTI30-2, 40 measurements for DTI30-1, and 37 for DTI15-2. Most of the reliable measurements were associated with the tracts corpus callosum, cingulum, cerebral peduncular fibers, uncinate fasciculus, and arcuate fasciculus. These reliable measurements included factional anisotropy (FA) and mean diffusivity of all 10 fiber regions. Intersession reliability was significantly worse than intra-session reliability for FA, mean length, and tract volume measurements from DTI15-2, indicating that the combination of MRI signal variation and physiological noise/change over time was the major error source for this sequence. Increasing the number of gradient directions from 15 to 30 while controlling the scan time, significantly affected values for all six variables and reduced intersession variability for mean length and tract volume measurements. Additionally, while increasing scan repetition from 1 to 2 had no significant effect on the reliability for DTI with 30 directions, this significantly reduced the upward bias in FA values from all 10 fiber regions and fiber count, mean length, and tract volume measurements from 5 to 7 fiber regions. In conclusion, diffusion tensor tractography provided many measurements with high test-retest reliability across different fiber variables and various fiber tracts even for images with 15 directions (NEX 2). Increasing the number of gradient directions from 15 to 30 with equivalent scan time reduced variability whereas increasing repetition from 1 to 2 for 30-direction DTI improved the accuracy of tractography measurements.
弥散张量纤维束追踪技术越来越多地用于在各种情况下检查大脑的结构连通性，但它的测试-再测试可靠性研究还很少。本研究的主要目的是评估 1）弥散张量纤维束追踪技术定量测量的可靠性，以及 2）梯度采样方向数量和扫描重复次数对可靠性的影响。从 10 名健康参与者中获取图像。使用 6 个纤维变量对 9 条主要纤维束的 10 个纤维区域进行重建和量化。使用组内相关系数（ICC）和变异系数（CV）来估计内-间和间-内的可靠性，并比较以确定主要误差源。还对 30 个方向和 NEX 2（DTI30-2）、30 个方向和 NEX 1（DTI30-1）、15 个方向和 NEX 2（DTI15-2）之间的图像可靠性进行了额外的两两比较，以确定增加梯度方向和扫描重复次数是否可以提高可靠性。在 60 项追踪测量中，43 项在 DTI30-2 时的间-内 CV 值≤10%，ICC 值≥.70，或两者兼有，40 项在 DTI30-1 时符合要求，37 项在 DTI15-2 时符合要求。大多数可靠的测量值与胼胝体、扣带回、大脑脚纤维、钩束和弓状束等纤维束有关。这些可靠的测量值包括所有 10 个纤维区域的分数各向异性（FA）和平均扩散系数。DTI15-2 的 FA、平均长度和束体积测量的间-内可靠性明显优于间-内可靠性，表明 MRI 信号变化和生理噪声/随时间变化的组合是该序列的主要误差源。在控制扫描时间的情况下，从 15 个方向增加到 30 个梯度方向，显著影响了所有 6 个变量的值，并降低了平均长度和束体积测量的间-内可变性。此外，尽管将扫描重复次数从 1 次增加到 2 次对 DTI30 方向的可靠性没有显著影响，但这显著降低了所有 10 个纤维区域以及纤维计数、平均长度和束体积测量的 FA 值的向上偏差。总之，弥散张量纤维束追踪技术提供了许多具有高测试-再测试可靠性的测量值，跨越了不同的纤维变量和各种纤维束，即使对于 15 个方向（NEX 2）的图像也是如此。在等效扫描时间内从 15 个方向增加到 30 个方向可以减少变异性，而对于 30 个方向的 DTI，从 1 次增加到 2 次扫描可以提高纤维束追踪测量的准确性。
