Abstract
BackgroundIodine-based solutions have long been known to be effective in aiding the differentiation among soft tissues in both fundamental anatomical research and for clinical diagnoses. Recently the combination of this particular contrasting agent with micro-computed tomography (micro-CT) has resulted in an array of high-quality image data, in which anatomical structures not visible in conventional CT can be identified and quantified. However, there has been only limited data available to inform detailed protocols for staining large specimens. Further, modeling of the staining mechanism has focused on simple diffusion processes.ResultsA low concentration of iodine-based buffered formalin solution with a long staining period was used to visualize soft-tissue structures in a large goose head. The staining effect was analyzed by serially measuring the micro-CT profiles across coronal sections throughout the staining period. Regular replacement of the staining solution combined with a longer staining period significantly improved contrast within tissues. A simplified one-dimensional Diffusion-Sorption model with a three-zone domain was used to simulate the diffusion process by calculating the concentration profile of iodine across the adductor region, which fits well with the experiment data. Observations of changes in the concentration of the staining agent and simulation results suggest that the sorption of iodine by tissues significantly affects the effective diffusion coefficient for the contrasting agent.ConclusionsThe Diffusion-Sorption model better explains previously reported difficulties in staining large samples comprised of tissues with high partition coefficients (Kd). Differences in partition coefficient (Kd), bulk density (ρb), and porosity (θ) could further explain the observed variation in staining rate and maximal staining effect among different tissues. Recommended protocols for staining large specimens are detailed.
Highlights
Iodine-based solutions have long been known to be effective in aiding the differentiation among soft tissues in both fundamental anatomical research and for clinical diagnoses
Based on CT imaging of these stained specimens, accurate and detailed three-dimensional (3D) structures were reconstructed and assessed through comparison with histological data [9, 10]. Successful trials of this contrast-enhancing technique in micro-CT imaging have shown the importance of three conditions: (1) the effective and efficient penetration of iodine through organic tissues, (2) different X-ray attenuation for different tissues after the staining, and (3) the high resolution of CT images that derived from micro-CT scans (1–50 μm resolution) [6, 11]
The first round of immersion in the contrasting agent primarily resulted in staining of exterior regions directly in contact with the solution
Summary
Iodine-based solutions have long been known to be effective in aiding the differentiation among soft tissues in both fundamental anatomical research and for clinical diagnoses. Based on CT imaging of these stained specimens, accurate and detailed three-dimensional (3D) structures were reconstructed and assessed through comparison with histological data [9, 10]. Successful trials of this contrast-enhancing technique in micro-CT imaging have shown the importance of three conditions: (1) the effective and efficient penetration of iodine through organic tissues, (2) different X-ray attenuation for different tissues after the staining, and (3) the high resolution of CT images that derived from micro-CT scans (1–50 μm resolution) [6, 11]. Higher concentrations of iodine yielded higher rates of iodine penetration and cause higher degrees of tissue shrinkage [6, 12]
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