Nossin-Manor Revital, Duvdevani Revital, Cohen Yoram
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel.
Magn Reson Med. 2005 Jul;54(1):96-104. doi: 10.1002/mrm.20519.
The influence of diffusion time (delta), gradient duration (delta), and TE on the appearance of high b-value q-space diffusion MR images of excised rat spinal cord (SC) was evaluated. The water signal decays in the white (WM) and gray matter (GM) were analyzed when the diffusion was measured perpendicular ( perpendicular) and parallel to the fibers of the SC, using three different approaches: single-component q-space analysis, the biexponential model, and the bi-Gaussian fit of the displacement distribution profile. Probability and displacement contrast and anisotropy indices were calculated for the WM and GM. It was found that WM/GM contrast increases as the diffusion time is increased when diffusion is measured perpendicular to the long axis of the SC. At a diffusion time of 50 ms, when diffusion was measured parallel to the fibers of the SC, the displacement was found to be higher for GM as compared to WM. For this direction the WM/GM contrast increased when diffusion time was increased, although here the changes were much less pronounced than for the perpendicular direction. The WM/GM displacement contrast nearly disappears for a diffusion time of 150 ms, when diffusion is measured parallel to the fibers of the SC. As expected, the anisotropy indices were found to be higher in WM than in GM, and increased with the increase in diffusion time. Both delta and TE affected the extracted parameters. It was found that long delta and long TE overemphasizes the apparent slow-diffusing water component of the SC, which is also the more restricted one. It is demonstrated that the single-component q-space analysis best describes diffusion in WM when diffusion is measured perpendicular to the fibers of the SC. In other cases, a more complete description is obtained by using two-component models.
评估了扩散时间（δ）、梯度持续时间（δ）和回波时间（TE）对切除的大鼠脊髓（SC）高b值q空间扩散磁共振成像外观的影响。当扩散测量方向垂直于（⊥）和平行于脊髓纤维时，使用三种不同方法分析白质（WM）和灰质（GM）中的水信号衰减：单组分q空间分析、双指数模型和位移分布轮廓的双高斯拟合。计算了WM和GM的概率、位移对比度和各向异性指数。结果发现，当扩散测量方向垂直于脊髓长轴时，WM/GM对比度随扩散时间增加而增加。在扩散时间为50 ms时，当扩散测量方向平行于脊髓纤维时，发现GM的位移高于WM。对于该方向，当扩散时间增加时，WM/GM对比度增加，尽管此处的变化比垂直方向小得多。当扩散测量方向平行于脊髓纤维时，在扩散时间为150 ms时，WM/GM位移对比度几乎消失。正如预期的那样，发现WM中的各向异性指数高于GM，并且随扩散时间增加而增加。δ和TE均影响提取的参数。发现长δ和长TE会过度强调脊髓中表观扩散缓慢的水成分，这也是更受限制的成分。结果表明，当扩散测量方向垂直于脊髓纤维时，单组分q空间分析最能描述WM中的扩散。在其他情况下，使用双组分模型可获得更完整的描述。
