Jones Derek K
Section on Tissue Biophysics and Biomimetics, Laboratory of Integrative Medicine and Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-5772, USA.
Magn Reson Med. 2004 Apr;51(4):807-15. doi: 10.1002/mrm.20033.
There are conflicting opinions in the literature as to whether it is more beneficial to use a large number of gradient sampling orientations in diffusion tensor MRI (DT-MRI) experiments than to use a smaller number of carefully chosen orientations. In this study, Monte Carlo simulations were used to study the effect of using different gradient sampling schemes on estimates of tensor-derived quantities assuming a b-value of 1000 smm(-2). The study focused in particular on the effect that the number of unique gradient orientations has on uncertainty in estimates of tensor-orientation, and on estimates of the trace and anisotropy of the diffusion tensor. The results challenge the recently proposed notion that a set of six icosahedrally-arranged orientations is optimal for DT-MRI. It is shown that at least 20 unique sampling orientations are necessary for a robust estimation of anisotropy, whereas at least 30 unique sampling orientations are required for a robust estimation of tensor-orientation and mean diffusivity. Finally, the performance of sampling schemes that use low numbers of sampling orientations, but make efficient use of available gradient power, are compared to less efficient schemes with larger numbers of sampling orientations, and the relevant scenarios in which each type of scheme should be used are discussed.
关于在扩散张量磁共振成像（DT - MRI）实验中使用大量梯度采样方向是否比使用少量精心选择的方向更有益，文献中存在相互矛盾的观点。在本研究中，假设b值为1000 smm(-2)，使用蒙特卡罗模拟来研究不同梯度采样方案对张量衍生量估计的影响。该研究特别关注独特梯度方向的数量对张量方向估计的不确定性以及对扩散张量的迹和各向异性估计的影响。结果对最近提出的一组六个二十面体排列方向对DT - MRI是最优的这一观点提出了挑战。结果表明，对于稳健估计各向异性，至少需要20个独特的采样方向，而对于稳健估计张量方向和平均扩散率，则至少需要30个独特的采样方向。最后，将使用少量采样方向但有效利用可用梯度功率的采样方案的性能与具有大量采样方向的效率较低的方案进行了比较，并讨论了应使用每种类型方案的相关场景。
