Visualization of the microstructure and distribution of follicles in deep human ovaries using speckle-modulated optical coherence microscopy

Abstract Ovarian tissue cryopreservation (OTC) and transplantation (OTT) are the only fertility preservation (FP) options for children, adolescents, and young adults (CAYA) who don’t enough time until treatment of primary disease. OTC is still unestablished FP options, but it is expected that selective preservation of ovarian tissue with high follicle density will enhance pregnancy efficiency. Despite its value as a noninvasive follicle visualization method, optical coherence microscopy (OCM) lacks sufficient spatial resolution, imaging depth, and noise suppression capabilities to resolve fine follicular structures in deep ovarian tissue. In this study, we applied speckle modulation to a wavelength-swept OCM optical system in the near-infrared region to visualize the fine structure of follicles distributed in deep tissues. OCM images of 4-day-old mice revealed dense superficial-layer distributions of primordial follicles. These follicles were distinguishable from primary follicles, which were surrounded by a single layer of granulosa cells. In 14-day-old ovarian tissue, secondary follicles exhibited spatial dominance, and the fine structures constituting the follicles were successfully visualized. In ovarian tissues extracted from a patient diagnosed with acute myeloid leukemia (AML), the fine structures of primordial follicles were visualized to a depth of 300 μm, and a comparison with HE staining revealed that follicle density varied significantly depending on the ovarian regions. Speckle modulation-assisted OCM visualized the microstructure of follicles with varying degrees of maturation in human ovaries at the depth necessary for clinical application. Overall, this technology enables quantitative ovarian reserve assessment and selective cryopreservation of ovarian tissue rich in immature follicles, supporting FP in CAYA diagnosed with cancer.