Contrast Enhancement of Cross-Polarization OCT Images of Breast Cancer by Optical Coefficient Calculation
The aim of the study was to develop the techniques for contrast enhancement of cross-polarization OCT (CP OCT) images of breast cancer (BC) by calculating optical attenuation coefficients of OCT signal to differentiate cancer subtypes and analyze polarization properties of tumor stroma. Materials and Methods. The study involved ex vivo breast tissue samples after radical mastectomy. Scattering and polarization properties were studied using a high-speed spectral OCT unit suitable for cross-scattering recording with higher specificity enabling to differentiate breast connective tissue in health and cancer. We presented the findings of qualitative and quantitative analysis of en face CP OCT images of non-tumor breast cancer and two the most common BC types, which differ fundamentally by tumor stroma condition - infiltrating ductal carcinoma of solid and sclerosing structures. Optical coefficients were calculated for contrast enhancement of CP OCT images: attenuation coefficient in a co-channel (coefficient 1) and a difference attenuation coefficient in co- and cross-channels (coefficient 2), which enabled both: to differ tumor tissue from non-tumor tissue, and differentiate two breast cancer types under study. Results. En face CP OCT images of breast tissue without tumor are characterized by heterogeneity due to different scattering capacity of fat, glandular and connective tissue with predominantly low values of both optical coefficients. Infiltrating ductal BC of a solid structure is characterized by homogenous distribution of lowest values of both optical coefficients. In case of infiltrating ductal BC of a sclerosing structure, CP OCT images have the most heterogeneous and contrast OCT signal related to the tumor stroma dominated over parenchyma, and various degenerative changes are in stroma (fibrosis or hyalinosis). Conclusion. The use of optical attenuation coefficients of OCT signal in two channels and en face color-coded mapping is an obvious example presenting CP OCT images of BC and an objective technique for OCT signal quantitative assessment. Moreover, imaging contrast enhances, it eases the differentiation of morphological BC subtypes and can be used in clinical settings.