AbstractRecent 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 ofD(t)in the form of the ratio of the surface area to pore volume,S/V. The long‐time behavior ofD(t)in porous media provides an indirect measure of the macroscopic structure. In this case, the longtime diffusion coefficient,Deff, 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 ofD(t)were performed in RIF‐1 tumors, using both spectroscopy and imaging, and the data were used to calculateS/VandT. The results were compared with histological sections in order to correlateS/VandTwith differences in tissue structure (i.e. necrotic vs non‐necrotic tumor tissue). Based on spectroscopic measurements, there is a trend towards decreasingS/VandTwith 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 onD(t)maps generated from RIF‐1 tumors,Deff, and henceTappears to be much more sensitive thanS/Vin differentiating between necrotic and non‐necrotic tissue. In addition to characterizing diseased tissue,S/Vand particularlyTappear to be sensitive to structural changes that would accompany tumor treatment and should therefore provide a useful tool for monitoring the progress of therap
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