Imaging pathological stomach tissue using polarization second harmonic generation microscopy

Abstract

Collagen is one of the main macromolecular components in the extracellular matrix (ECM), and its structure undergoes changes during cell differentiation and cancer progression in the tumour microenvironment. The main goal of the current study was to determine if polarization second harmonic generation (PSHG) analysis can be used to distinguish collagen structures in pathological from normal stomach tissue, and if it can be used to characterize the varying levels of adenocarcinoma differentiation. Using PSHG, we imaged normal and pathological stomach tissue samples which included well differentiated, moderately differentiated, and poorly differentiated gastric adenocarcinomas. Second harmonic generation (SHG) imaging is a non-linear optical microscopy technique that does not require staining of tissue samples due to the emission of SHG signals from intrinsic collagen fibers in the ECM. Therefore, it is less susceptible to observer variability compared to standard empirical staining techniques. For each sample image, PSHG analysis was performed to obtain 𝜌, a structural parameter associated with the degree of collagen disorder. Results showed that the mean 𝜌 value was significantly greater in pathological tissue in patients compared to their adjacent normal tissue, which indicated a higher degree of structural disorder in cancerous tissue. There was a significant increase in mean 𝜌 values from well differentiated to poorly differentiated adenocarcinoma. There was no significant difference in mean 𝜌 values for groups that were closer to their degrees of tissue differentiation, such as between well differentiated and moderately differentiated, and between moderately differentiated and poorly differentiated adenocarcinomas. These findings suggest that there is greater disorder of collagen structure in the tumour microenvironment compared to adjacent normal tissue. Patients with poorly differentiated gastric adenocarcinoma are potentially ideal candidates for PSHG as a diagnostic technique.