Department of Electrical Engineering, Stanford University, Stanford, California, USA.
Department of Radiology, Stanford University, Stanford, California, USA.
Magn Reson Med. 2018 Aug;80(2):507-520. doi: 10.1002/mrm.27043. Epub 2017 Dec 19.
The purpose of this study is to develop double diffusion encoding (DDE) MRI methods for clinical use. Microscopic diffusion anisotropy measurements from DDE promise greater specificity to changes in tissue microstructure compared with conventional diffusion tensor imaging, but implementation of DDE sequences on whole-body MRI scanners is challenging because of the limited gradient strengths and lengthy acquisition times.
A custom single-refocused DDE sequence was implemented on a 3T whole-body scanner. The DDE gradient orientation scheme and sequence parameters were optimized based on a Gaussian diffusion assumption. Using an optimized 5-min DDE acquisition, microscopic fractional anisotropy (μFA) maps were acquired for the first time in multiple sclerosis patients.
Based on simulations and in vivo human measurements, six parallel and six orthogonal diffusion gradient pairs were found to be the minimum number of diffusion gradient pairs necessary to produce a rotationally invariant measurement of μFA. Simulations showed that optimal precision and accuracy of μFA measurements were obtained using b-values between 1500 and 3000 s/mm . The μFA maps showed improved delineation of multiple sclerosis lesions compared with conventional fractional anisotropy and distinct contrast from T -weighted fluid attenuated inversion recovery and T -weighted imaging.
The μFA maps can be measured using DDE in a clinical setting and may provide new opportunities for characterizing multiple sclerosis lesions and other types of tissue degeneration. Magn Reson Med 80:507-520, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
本研究旨在开发用于临床应用的双扩散编码（DDE）MRI 方法。与传统的扩散张量成像相比，DDE 测量的微观扩散各向异性有望对组织微观结构的变化具有更高的特异性，但由于梯度强度有限和采集时间长，在全身 MRI 扫描仪上实现 DDE 序列具有挑战性。
在 3T 全身扫描仪上实现了定制的单重聚焦 DDE 序列。基于高斯扩散假设，优化了 DDE 梯度方向方案和序列参数。使用优化的 5 分钟 DDE 采集，首次在多发性硬化症患者中获得了微观各向异性分数（μFA）图。
基于模拟和体内人体测量，发现六个平行和六个正交扩散梯度对是产生μFA 旋转不变测量的最小梯度对数量。模拟表明，使用 1500 到 3000 s/mm 之间的 b 值可以获得 μFA 测量的最佳精度和准确性。μFA 图与常规各向异性分数相比，可以更好地描绘多发性硬化症病变，并且与 T1 加权液体衰减反转恢复和 T1 加权成像具有明显的对比。
可以在临床环境中使用 DDE 测量 μFA 图，这可能为表征多发性硬化症病变和其他类型的组织退化提供新的机会。磁共振医学 80：507-520，2018。© 2017 国际磁共振学会。
