Ex vivo sensing of primordial follicles in ovarian tissues by spectral-domain optical coherence tomography

Minimally invasive visualization of follicles in the ovaries of adolescent and young adult (AYA) patients with cancer is a promising technique for maintaining fertility by cryopreserving follicle-rich ovarian tissues. Optical coherence tomography (OCT) using near-infrared light, which is less invasive to the follicles, is a promising imaging technique for quantifying follicle density before cryopreservation. A spectral-domain OCT system equipped with a superluminescent diode with a central wavelength of 1300 nm was applied to visualize primordial follicles with a diameter of about 20 mu m, which are often found at depths of 100-1000 mu m in ovarian tissue. We used a 20x immersion objective to improve lateral image resolution and reduce ghost images due to surface reflections. OCT images of 30 mu m diameter glass beads mimicking primordial follicles embedded in a polyacrylamide gel containing scattering particles were visualized at the depth required for imaging the ovaries. Ovarian tissues of 3-day-old and 12-day-old mice were fixed between an originally designed hydrophobic silicone plate and a cover glass. The distribution of primordial follicles and the structure of mature follicles were visualized in ovaries of 3-day-old and 12-day-old mice, respectively. These results indicate that near-infrared OCT at a central wavelength of 1300 nm with an extended depth of light penetration can effectively visualize the structure of follicles and quantify their density at depths where follicles are abundant in ovarian tissues. Further improvements in spatial resolution and image processing are expected to accelerate the contribution to reproductive medicine in the future.