Virtual optical biopsy of human adipocytes with third harmonic generation microscopy

Using the sectioning capability of third harmonic generation (THG) microscopy, we assessed the morphologic features of human adipocytes directly without fixation and labeling. At the plane of the largest cross-sectional area, both area-equivalent circular diameters (AECD) and perimeters of adipocytes were measured, and their statistical distributions were examined. We found, in patients with no cardiovascular risk factors, the average AECD of epicardial adipocytes were 70-90 μm with 11-17 μm standard deviations. In contrast, for patients with coronary artery disease, amounts of small-sized (AECD <40 µm) epicardial adipocytes were observed and the corresponding standard deviations of AECD were increased to 20-29 μm. Our results indicate that the THG tomography platform can be used to explore the histopathological features of adipocytes in clinical scenarios based on its superior resolution for virtual optical biopsy.