Evaluating the impact of freeze-thaw protocols on tissue microstructural imaging features measured using optical coherence tomography

Cryopreservation is routine in biomedical research and clinical practice for various purposes, including sample transportation, RNA preservation, and long-term storage. However, freezing poses risks of tissue damage due to ice crystal formation and cell lysis. The effects of tissue freezing and thawing on microstructural image features are not fully understood, and determining a freezing protocol that best preserves tissue integrity is essential for maximizing the transferability of imaging studies using previously frozen tissues. This study investigates the impact of freeze-thaw protocols on tissue microstructure using optical coherence tomography (OCT), an imaging technique that provides detailed 3D images of biological structures. Tissue specimens from three organs - lung, liver, and duodenum - were collected from six mice and imaged before and after freeze-thawing using different protocols. We tested protocols including slow freezing to -20 °C, slow freezing to -80 °C, and liquid nitrogen submersion. We examined immersion in both phosphate buffered saline and routine cryopreservation compounds for all methods. Using images from each specimen before and after freeze-thawing, differences in structural features were analyzed qualitatively and by using texture analysis. Texture features were extracted from OCT images using Haralick's method, and statistical analysis was performed to compare the different protocols and tissue types. Results show that flash freezing methods and the use of cryopreservation compounds cause fewer alterations in tissue microstructure compared to slow freezing. This study provides insight into the effects of common freezing protocols on tissue integrity, which may inform the optimization of tissue preservation techniques across many disciplines.