Stromal alterations in ovarian cancers via wavelength dependent Second Harmonic Generation microscopy and optical scattering

Abstract

BackgroundOvarian cancer remains the most deadly gynecological cancer with a poor aggregate survival rate; however, the specific rates are highly dependent on the stage of the disease upon diagnosis. Current screening and imaging tools are insufficient to detect early lesions and are not capable of differentiating the subtypes of ovarian cancer that may benefit from specific treatments.MethodAs an alternative to current screening and imaging tools, we utilized wavelength dependent collagen-specific Second Harmonic Generation (SHG) imaging microscopy and optical scattering measurements to probe the structural differences in the extracellular matrix (ECM) of normal stroma, benign tumors, endometrioid tumors, and low and high-grade serous tumors.ResultsThe SHG signatures of the emission directionality and conversion efficiency as well as the optical scattering are related to the organization of collagen on the sub-micron size scale and encode structural information. The wavelength dependence of these readouts adds additional characterization of the size and distribution of collagen fibrils/fibers relative to the interrogating wavelengths. We found a strong wavelength dependence of these metrics that are related to significant structural differences in the collagen organization and are consistent with the dualistic classification of type I and II serous tumors. Moreover, type I endometrioid tumors have strongly differing ECM architecture than the serous malignancies. The SHG metrics and optical scattering measurements were used to form a linear discriminant model to classify the tissues, and we obtained high accuracy (>90%) between high-grade serous tumors from the other tissue types. High-grade serous tumors account for ~70% of ovarian cancers, and this delineation has potential clinical applications in terms of supplementing histological analysis, understanding the etiology, as well as development of an in vivo screening tool.ConclusionsSHG and optical scattering measurements provide sub-resolution information and when combined provide superior diagnostic power over clinical imaging modalities. Additionally the measurements are able to delineate the different subtypes of ovarian cancer and may potentially assist in treatment protocols. Understanding the altered collagen assembly can supplement histological analysis and provide new insight into the etiology. These methods could become an in vivo screening tool for earlier detection which is important since ovarian malignancies can metastasize while undetectable by current clinical imaging resolution.

Peptide Nanophotonics: From Optical Waveguiding to Precise Medicine and Multifunctional Biochips

“…The SHG effect is an emerging field of biomedical microscopy, bioimaging and diagnostics for a wide range of diseases . For example, SHG microscopy was applied as a cancer diagnostic tool to probe the structural differences in the extracellular matrix of normal stroma, benign tumors, endometrioid tumors, and more . Furthermore, SHG microscopy was used to identifying articular osteochondrosis in pigs, and as an early diagnostic tool for corneal related diseases and imaging of collagen distributions in human sclera .…”

“…c) SHG images of representative and ovarian tumors obtained at 890 nm excitation, and its histology image. Reproduced under the terms of the CC‐BY 4.0 license ( https://creativecommons.org/licenses/by/4.0/) . Copyright 2017, the Authors, Published by BioMed Central Ltd. d) Collagen distributions in SHG images of a piece of human sclera.…”

Methods for the visualization and analysis of extracellular matrix protein structure and degradation

“…Knowledge of the TACS-3 has the potential to improve diagnostic capabilities (Conklin et al, 2011). Another recent application includes work using ECM properties as determined by SHG imaging as a biomarker to delineate different subtypes of ovarian cancer (Tilbury et al, 2017). …”

3D second harmonic generation imaging tomography by multi-view excitation

“…This is a significant limitation as the native ECM in most tissues has intrinsic 3D architecture, where not all the collagen fibers lie in the plane of incidence or at small tilt angles relative to the plane. For example, the dermis and ovarian stroma in normal tissues have 3D mesh-like morphologies [9,10], and SHG will not visualize the entire structure. We previously have shown that 3D texture analysis provides significantly improved discrimination between ovarian tumors over the analogous 2D approach even using the incomplete information in 3D stacks [8].…”

“…Second, this affords detection only of backward SHG emission, where retroreflected photons are collected by the excitation objective. This limits the SHG signal that can be collected, as the majority of photons are emitted in the forward direction, as well as precludes the use of directional-based metrics, which can be used for structural analysis [9,10]. …”