Baete Steven H, Cho Gene Y, Sigmund Eric E
Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, NYU Langone Medical Center, New York, NY, USA.
Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, USA.
NMR Biomed. 2015 Jun;28(6):667-78. doi: 10.1002/nbm.3296. Epub 2015 Apr 22.
When diffusion biomarkers display transient changes, i.e. in muscle following exercise, traditional diffusion-tensor imaging (DTI) methods lack the temporal resolution to resolve the dynamics. This article presents an MRI method for dynamic diffusion-tensor acquisitions on a clinical 3T scanner. This method, the Single-Line Multiple-Echo Diffusion-Tensor Acquisition Technique (SL-MEDITATE), achieves a high temporal resolution (4 s) by rapid diffusion encoding through the acquisition of multiple echoes with unique diffusion sensitization and limiting the readout to a single line volume. The method is demonstrated in a rotating anisotropic phantom, a flow phantom with adjustable flow speed and in vivo skeletal calf muscle of healthy volunteers following a plantar flexion exercise. The rotating and flow-varying phantom experiments show that SL-MEDITATE correctly identifies the rotation of the first diffusion eigenvector and the changes in diffusion-tensor parameter magnitudes, respectively. Immediately following exercise, the in vivo mean diffusivity (MD) time courses show, before the well-known increase, an initial decrease that is not typically observed in traditional DTI. In conclusion, SL-MEDITATE can be used to capture transient changes in tissue anisotropy in a single line. Future progress might allow for dynamic DTI when combined with appropriate k-space trajectories and compressed sensing reconstruction.
当扩散生物标志物呈现短暂变化时，例如运动后肌肉中的变化，传统的扩散张量成像（DTI）方法缺乏解析动力学的时间分辨率。本文介绍了一种在临床3T扫描仪上进行动态扩散张量采集的MRI方法。这种方法，即单线多回波扩散张量采集技术（SL-MEDITATE），通过采集具有独特扩散敏感化的多个回波并将读出限制在单个线体积内进行快速扩散编码，从而实现了高时间分辨率（4秒）。该方法在旋转各向异性体模、流速可调的流动体模以及健康志愿者进行跖屈运动后的体内小腿骨骼肌中得到了验证。旋转和流动变化的体模实验表明，SL-MEDITATE分别正确识别了第一扩散特征向量的旋转和扩散张量参数大小的变化。运动后立即进行的实验显示，体内平均扩散率（MD）随时间的变化过程在众所周知的增加之前，出现了传统DTI中通常未观察到的初始下降。总之，SL-MEDITATE可用于捕获单线组织各向异性的短暂变化。未来的进展可能会在结合适当的k空间轨迹和压缩感知重建时实现动态DTI。
