Ozarslan Evren, Basser Peter J
Section on Tissue Biophysics and Biomimetics, NICHD, NIH, Bethesda, MD 20892, USA.
J Chem Phys. 2008 Apr 21;128(15):154511. doi: 10.1063/1.2905765.
We consider a general double pulsed field gradient experiment with arbitrary experimental parameters and calculate an exact expression for the NMR signal attenuation from restricted geometries, which is valid at long wavelengths, i.e., when the product of the gyromagnetic ratio of the spins, the pulsed gradients' duration, and their magnitude is small compared to the reciprocal of the pore size. It is possible to observe microscopic anisotropy within the pore space induced by the boundaries of the pore, which can be used to differentiate restricted from free or multicompartmental diffusion and to estimate a characteristic pore dimension in the former case. Explicit solutions for diffusion taking place between parallel plates as well as in cylindrical and spherical pores are provided. In coherently packed cylindrical pores, it is possible to measure simultaneously the cylinders' orientation and diameter using small gradient strengths. The presence of orientational heterogeneity of cylinders is addressed, and a scheme for differentiating microscopic from ensemble anisotropy is proposed.
我们考虑一个具有任意实验参数的一般双脉冲场梯度实验，并计算了受限几何形状下核磁共振信号衰减的精确表达式，该表达式在长波长时有效，即当自旋的旋磁比、脉冲梯度的持续时间及其幅度的乘积与孔径的倒数相比很小时。可以观察到由孔隙边界引起的孔隙空间内的微观各向异性，这可用于区分受限扩散与自由扩散或多隔室扩散，并在前一种情况下估计特征孔隙尺寸。提供了平行板之间以及圆柱孔和球形孔中扩散的显式解。在相干堆积的圆柱孔中，可以使用小梯度强度同时测量圆柱的取向和直径。讨论了圆柱取向异质性的存在，并提出了一种区分微观各向异性与整体各向异性的方案。
