The Diffusion Diaries: Diffusible Iodine-Based Contrast-Enhanced Computed Tomography for Vertebrate Natural History Specimens

Diffusible iodine-based contrast-enhanced CT (diceCT) is commonly used to create three-dimensional (3D) representations of the soft tissue anatomy of preserved vertebrate specimens. While widely applied, there is currently no documentation of protocols that can be adapted to a morphological and taxonomically broad range of vertebrates. We present the most taxonomically and morphologically broad sampling of diceCT vertebrates, imaged for the openVertebrate Thematic Collections Network. Within this study, we document our methods, outcomes, and observations throughout the preparation, staining, scanning, and data processing steps. Larger specimens take a longer time to stain, but the final staining time depends on the taxon, whether there is dermal and/or bony armor present, and whether any internal structures (e.g., eggs, embryos, large fat deposits) require large amounts of iodine to become fully saturated. We established a scoring system for diceCT-imaged soft tissues that reflects the usefulness of the data. We also provide examples of datasets that demonstrate severe soft tissue damage, incomplete preservation, permanent specimen alteration, and understaining. Finally, we have made all the diceCT datasets produced here freely available to download via the data repository MorphoSource, and hope that our work can serve as a resource for scientists and the public to explore and study vertebrate anatomy.