On the problem of diffusivity in biological materials: estimation of diffusion coefficients via X-ray radiography

The processing of histological samples, particularly biopsies, is a pivotal step in the medical histopathology, as it prepares the sample for the subsequent microscopic examination. During this examination, the morphological, functional and molecular characteristics of the tissue withdrawn from the patient are investigated. Histological evaluation of biopsies is a cornerstone of daily medical diagnosis, staging and grading of many diseases, especially cancers. All the phases of the specimen preparation process require the diffusion of a solvent within the sample mass. Therefore, having reliable knowledge regarding the diffusion in biological materials is of crucial importance. This article presents an experimental technique to determine the diffusion coefficient in biological specimens. This key physical quantity provides significant information about the rate at which a substance spreads within a given medium. The objective was accomplished through the acquisition of a sequence of radiographic images of biological samples having different geometries immersed in processing solvents. As X-ray attenuation is proportional to the solvent’s concentration, changes in radiograph intensity over time reflect the diffusion of the substance in the irradiated sample. The intensity data were therefore fitted using analytically derived mathematical models for the diffusion coefficients estimation.