School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
J Am Chem Soc. 2011 Apr 20;133(15):6028-35. doi: 10.1021/ja200303h. Epub 2011 Mar 29.
Microarchitectural features of opaque porous media and biological tissues are of great importance in many scientific disciplines ranging from chemistry, material sciences, and geology to biology and medicine. Noninvasive characterization of coherently organized pores is rather straightforward since conventional diffusion magnetic resonance methods can detect anisotropy on a macroscopic scale; however, it remains extremely challenging to directly infer on microarchitectural features on the microscopic scale in heterogeneous porous media and biological cells that are comprised of randomly oriented compartments, a scenario widely encountered in Nature. Here, we show that the angular bipolar double-pulsed-field-gradient (bp-d-PFG) methodology is capable of reporting on unique microarchitectural features of highly heterogeneous systems. This was demonstrated on a toluene-in-water emulsion system, quartz sand, and even biological specimens such as yeast cells and isolated gray matter. We find that in the emulsion and yeast cells systems, the angular bp-d-PFG methodology uniquely revealed nearly an image of the pore space, since it conveyed direct microarchitectural information such as compartment shape and size. In two different quartz sand specimens, the angular bp-d-PFG experiments demonstrated the presence of randomly oriented anisotropic compartments. We also obtained unequivocal evidence that diffusion in interconnected interstices is restricted and therefore non-Gaussian. In biological contexts, the angular bp-d-PFG experiments could uniquely differentiate between spherical cells and randomly oriented compartments in gray matter tissue, information that could not be obtained by conventional NMR methods. The angular bp-d-PFG methodology also performs very well even when severe background gradients are present, as is often encountered in realistic systems. We conclude that this method seems to be the method of choice for characterizing the microstructure of porous media and biological cells noninvasively.
不透明多孔介质和生物组织的微观结构特征在许多科学领域都非常重要，这些领域涵盖了化学、材料科学、地质学、生物学和医学等多个学科。由于传统的扩散磁共振方法可以在宏观尺度上检测各向异性，因此对具有规则排列的孔的非侵入性特征进行描述相对较为简单；然而，在由随机取向的隔室组成的非均相多孔介质和生物细胞中，直接推断微观结构特征仍然极具挑战性，这种情况在自然界中非常普遍。在这里，我们展示了角双极扩散梯度（bp-d-PFG）方法能够对高度不均匀的系统的独特微观结构特征进行报告。我们在甲苯-水乳液体系、石英砂，甚至酵母细胞和分离的灰质等生物样本上验证了这一方法。我们发现，在乳液和酵母细胞体系中，角 bp-d-PFG 方法能够独特地揭示出近孔空间的图像，因为它传递了诸如隔室形状和大小等直接的微观结构信息。在两个不同的石英砂样本中，角 bp-d-PFG 实验证明了存在随机取向的各向异性隔室。我们还获得了明确的证据，证明了相互连接的空隙中的扩散受到限制，因此是非高斯的。在生物学背景下，角 bp-d-PFG 实验可以在灰质组织中区分球形细胞和随机取向的隔室，而这是常规 NMR 方法无法获得的信息。即使存在严重的背景梯度，角 bp-d-PFG 方法也能很好地发挥作用，这在实际系统中经常会遇到。我们得出的结论是，这种方法似乎是无创表征多孔介质和生物细胞微观结构的首选方法。
