Crombe A, Alberti N, Hiba B, Uettwiller M, Dousset V, Tourdias T
From the Centre Hospitalier Universitaire de Bordeaux (A.C., V.D., T.T.), Service de NeuroImagerie Diagnostique de Thérapeutique, Bordeaux, France
Institut National de la Santé et de la Recherche Médicale U1215 (A.C., V.D., T.T.), Physiopathologie de la Plasticité Neuronale, Bordeaux, France.
AJNR Am J Neuroradiol. 2016 Nov;37(11):2163-2170. doi: 10.3174/ajnr.A4850. Epub 2016 Jun 30.
Reduced-FOV DTI is promising for exploring the cervical spinal cord, but the optimal set of parameters needs to be clarified. We hypothesized that the number of excitations should be favored over the number of diffusion gradient directions regarding the strong orientation of the cord in a single rostrocaudal axis.
Fifteen healthy individuals underwent cervical spinal cord MR imaging at 3T, including an anatomic 3D-Multi-Echo Recombined Gradient Echo, high-resolution full-FOV DTI with a NEX of 3 and 20 diffusion gradient directions and 5 sets of reduced-FOV DTIs differently balanced in terms of NEX/number of diffusion gradient directions: (NEX/number of diffusion gradient directions = 3/20, 5/16, 7/12, 9/9, and 12/6). Each DTI sequence lasted 4 minutes 30 seconds, an acceptable duration, to cover C1-C4 in the axial plane. Fractional anisotropy maps and tractograms were reconstructed. Qualitatively, 2 radiologists rated the DTI sets blinded to the sequence. Quantitatively, we compared distortions, SNR, variance of fractional anisotropy values, and numbers of detected fibers.
Qualitatively, reduced-FOV DTI sequences with a NEX of ≥5 were significantly better rated than the full-FOV DTI and the reduced-FOV DTI with low NEX (N = 3) and a high number of diffusion gradient directions (D = 20). Quantitatively, the best trade-off was reached by the reduced-FOV DTI with a NEX of 9 and 9 diffusion gradient directions, which provided significantly fewer artifacts, higher SNR on trace at = 750 s/mm and an increased number of fibers tracked while maintaining similar fractional anisotropy values and dispersion.
Optimized reduced-FOV DTI improves spinal cord imaging. The best compromise was obtained with a NEX of 9 and 9 diffusion gradient directions, which emphasizes the need for increasing the NEX at the expense of the number of diffusion gradient directions for spinal cord DTI contrary to brain DTI.
缩小视野的扩散张量成像（DTI）在探索颈髓方面颇具前景，但最佳参数组合仍需明确。我们推测，鉴于脊髓在单一头尾轴上的强烈方向性，激励次数相较于扩散梯度方向数应更为重要。
15名健康个体在3T条件下接受颈髓磁共振成像，包括一次解剖学三维多回波重组梯度回波成像、具有3次激励次数（NEX）和20个扩散梯度方向的高分辨率全视野DTI，以及5组在NEX/扩散梯度方向数方面平衡方式不同的缩小视野DTI：（NEX/扩散梯度方向数 = 3/20、5/16、7/12、9/9和12/6）。每个DTI序列持续4分30秒，这是一个可接受的时长，用于在轴位平面覆盖C1 - C4。重建了各向异性分数图和纤维束成像。定性方面，2名放射科医生在不知序列的情况下对DTI数据集进行评分。定量方面，我们比较了畸变、信噪比、各向异性分数值的方差以及检测到的纤维数量。
定性分析表明，NEX≥5的缩小视野DTI序列的评分显著优于全视野DTI以及NEX较低（N = 3）且扩散梯度方向数较多（D = 20）的缩小视野DTI。定量分析显示，NEX为9且扩散梯度方向数为9的缩小视野DTI实现了最佳权衡，其产生的伪影显著减少，在扩散时间为750 s/mm²时的迹线信噪比更高，同时在保持各向异性分数值和离散度相似的情况下，追踪到的纤维数量增加。
优化后的缩小视野DTI改善了脊髓成像。NEX为9且扩散梯度方向数为9时实现了最佳折衷，这强调了与脑DTI相反，在脊髓DTI中需要以牺牲扩散梯度方向数为代价来增加激励次数。
