Multi-Energy Computed Tomography (CT) for Quantification of CPA Diffusion

Vitrification is of interest for its potential to enable indefinite cryopreservation of biological tissues. Vitrification uses an aqueous solution containing cryoprotective agents (CPAs) that penetrate tissues and lower the critical cooling rate needed to form a glass (vitreous) phase instead of ice, which can damage tissue. The dynamic diffusion behavior of individual CPAs affects cryopreservation outcomes. Standard X-ray CT methods, previously used to study CPA permeation, usually assume all CPAs diffuse at the same rate. Building off our prior work on the use of standard X-ray computed tomography for visualizing and demonstrating the possibility of ice-free and cavity-free vitrification, we introduce multi-energy CT to non-invasively track individual CPA diffusion. Despite having similar densities and elemental compositions, we measure CPA concentration without the use of contrast agents which may alter diffusion rates. Initially, we calibrate our system using multi-energy reconstructions of each CPA to quantify their specific attenuations and assess system noise. We apply this technique to a known three-component CPA solution for validation. Then, we measure the diffusion of this solution into a hydrogel that has comparable diffusion rates to biological tissue. We acquire multiple scans over time to track unsteady diffusion. In addition to vitrification, our method has potential to be extended to other applications requiring non-invasive, time-resolved analysis of fluid composition.