Helmer K G, Dardzinski B J, Sotak C H
Department of Biomedical Engineering, Worcester Polytechnic Institute, MA 01609, USA.
NMR Biomed. 1995 Nov-Dec;8(7-8):297-306. doi: 10.1002/nbm.1940080705.
Recent developments in solid-boundary porous-media theory have shown that useful structural information can be extracted from the time-dependent diffusion coefficient, D(t), of the fluid filling the interstitial space. This theoretical framework provides a basis from which to understand the results from diffusion experiments performed in other types of systems (e.g. biological). Structural information about porous media can be obtained from the short-time behavior of D(t) in the form of the ratio of the surface area to pore volume, S/V. The long-time behavior of D(t) in porous media provides an indirect measure of the macroscopic structure. In this case, the long-time diffusion coefficient, D(eff), reflects the tortuosity, T, of the medium; a property of both the connectivity of the diffusion paths and the volume fraction of the sample. Measurements of D(t) were performed in RIF-1 tumors, using both spectroscopy and imaging, and the data were used to calculate S/V and T. The results were compared with histological sections in order to correlate S/V and T with differences in tissue structure (i.e. necrotic vs non-necrotic tumor tissue). Based on spectroscopic measurements, there is a trend towards decreasing S/V and T with increasing tumor volume, consistent with the interpretation that water in necrotic tissue is experiencing relatively fewer restricting barriers (as compared to non-necrotic tumor tissue). Based on D(t) maps generated from RIF-1 tumors, D(eff), and hence T appears to be much more sensitive than S/V in differentiating between necrotic and non-necrotic tissue. In addition to characterizing diseased tissue, S/V and particularly T appear to be sensitive to structural changes that would accompany tumor treatment and should therefore provide a useful tool for monitoring the progress of therapeutic interventions.
固体边界多孔介质理论的最新进展表明，可以从填充间隙空间的流体的时间相关扩散系数D(t)中提取有用的结构信息。这一理论框架为理解在其他类型系统（如生物系统）中进行的扩散实验结果提供了基础。关于多孔介质的结构信息可以从D(t)的短时间行为中以表面积与孔隙体积之比S/V的形式获得。多孔介质中D(t)的长时间行为提供了宏观结构的间接度量。在这种情况下，长时间扩散系数D(eff)反映了介质的曲折度T；这是扩散路径连通性和样品体积分数的共同属性。使用光谱学和成像技术在RIF-1肿瘤中测量了D(t)，并将数据用于计算S/V和T。将结果与组织学切片进行比较，以便将S/V和T与组织结构差异（即坏死与非坏死肿瘤组织）相关联。基于光谱测量，随着肿瘤体积的增加，S/V和T有降低的趋势，这与坏死组织中的水经历相对较少限制屏障的解释一致（与非坏死肿瘤组织相比）。基于从RIF-1肿瘤生成的D(t)图，D(eff)以及因此的T在区分坏死和非坏死组织方面似乎比S/V更敏感。除了表征病变组织外，S/V尤其是T似乎对肿瘤治疗伴随的结构变化敏感，因此应该为监测治疗干预的进展提供一个有用的工具。
