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We present two new methods used to determine the optical properties in ovarian cancer, idiopathic pulmonary fibrosis and osteoarthritis. The bulk optical properties are determined by a combination of on axis attenuation, goniometry, and Monte Carlo simulations. The resulting wavelength dependent values delineates the importance of both μs’ and the fractal dimension. We also present a new method to determine μs’ on the SHG microscope. By measuring the depth dependence of the SHG emission directionality and performing Monte Carlo simulations, both the relative fibril size distribution and reduced scattering coefficient can be simultaneously determined without the need for bulk measurements.

Extensive remodeling of the extracellular matrix (ECM) occurs in many epithelial cancers. For example, in ovarian cancer, upregulation of collagen isoform type III has been linked to invasive forms of the disease, and this change may be a potential biomarker. To examine this possibility, we implemented wavelength-dependent second harmonic generation circular dichroism (SHG-CD) imaging microscopy to quantitatively determine changes in chirality in ECM models comprised of different Col I/Col III composition. In these models, Col III was varied between 0 and 40%, and we found increasing Col III results in reduced net chirality, consistent with structural biology studies of Col I and III in tissues where the isoforms comingle in the same fibrils. We further examined the wavelength dependence of the SHG-CD to both optimize the response and gain insight into the underlying mechanism. We found using shorter SHG excitation wavelengths resulted in increased SHG-CD sensitivity, where this is consistent with the electric-dipole-coupled oscillator model suggested previously for the nonlinear chirality response from thin films. Moreover, the sensitivity is further consistent with the wavelength dependency of SHG intensity fit to a two-state model of the two-photon absorption in collagen. We also provide experimental calibration protocols to implement the SHG-CD modality on a laser scanning microscope. We last suggest that the technique has broad applicability in probing a wide range of diseased states with changes in collagen molecular structure.

Visualizing whole cells at many scales Cells need to compartmentalize thousands of distinct proteins, but the nanoscale spatial relationship of many proteins to overall intracellular ultrastructure remains poorly understood. Correlated light and electron microscopy approaches can help. Hoffman et al. combined cryogenic super-resolution fluorescence microscopy and focused ion beam–milling scanning electron microscopy to visualize protein-ultrastructure relationships in three dimensions across whole cells. The fusion of the two imaging modalities enabled identification and three-dimensional segmentation of morphologically complex structures within the crowded intracellular environment. The researchers observed unexpected relationships within a variety of cell types, including a web-like protein adhesion network between juxtaposed cerebellar granule neurons. Science , this issue p. eaaz5357

Both ovarian cancer and idiopathic pulmonary fibrosis (IPF) are accompanied by significant collagen remodeling in the respective extracellular matrix (ECM). These diseases have similar attributes and collagen alterations can be probed with the same methods. Remodeling can be reflected in increased collagen concentration, changes in alignment within fibrils and fibers and/or up-regulation of different collagen isoforms. We used pixel-based SHG polarization analyses to discriminate the macro/supramolecular collagen structure in human tissues by: i) determination of the helical pitch angle via the single axis molecular model, ii) dipole alignment within fibrils via anisotropy, and iii) chirality via SHG circular dichroism (SHG-CD). For ovarian cancer, the largest differences were between normal stroma and benign tumors, consistent with gene expression showing Col III is up-regulated in the latter. The tissues also displayed differing SHG anisotropies and SHG-CD responses, consistent with randomization of Col I alignment in fibrils in all tumors. These results collectively indicate the fibril assemblies are distinct in all ovarian tissues and likely result from synthesis of new collagen rather than remodeling of existing collagen. For IPF, the largest change was in the SHG-CD response, indicating the fibrotic collagen has different helical structure than that of normal tissues. Interestingly, for both diseases, no increase in Col IIII was found, in contrast to previous reports by immunostaining. We suggest these polarization-based metrics could form the basis of a new classification scheme and complement conventional classification based on genetic profiles and conventional histology for these diseases as well as other cancers and fibroses.

Collagen remodeling occurs in many prostate pathologies; however, the underlying structural architecture in both normal and diseased prostatic tissues is largely unexplored. Here, we use second-harmonic generation (SHG) microscopy to specifically probe the role of the proteoglycan decorin (Dcn) on collagen assembly in a wild type (wt) and Dcn null mouse (Dcn − / − ). Dcn is required for proper organization of collagen fibrils as it regulates size by forming an arch-like structure at the end of the fibril. We have utilized SHG metrics based on emission directionality (forward–backward ratio) and relative conversion efficiency, which are both related to the SHG coherence length, and found more disordered fibril organization in the Dcn − / − . We have also used image analysis readouts based on entropy, multifractal dimension, and wavelet transforms to compare the collagen fibril/fiber architecture in the two models, where all these showed that the Dcn − / − prostate comprised smaller and more disorganized collagen structures. All these SHG metrics are consistent with decreased SHG phase matching in the Dcn − / − and are further consistent with ultrastructural analysis of collagen in this model in other tissues, which show a more random distribution of fibril sizes and their packing into fibers. As Dcn is a known tumor suppressor, this work forms the basis for future studies of collagen remodeling in both malignant and benign prostate disease.

The collagen structure throughout the patella has not been thoroughly investigated by 3D imaging, where the majority of the existing data come from histological cross sections. It is important to have a better understanding of the architecture in normal tissues, where this could then be applied to imaging of diseased states.To address this shortcoming, we investigated the combined use of collagen-specific Second-Harmonic Generation (SHG) imaging and measurement of bulk optical properties to characterize collagen fiber orientations of the histologically defined zones of bovine articular cartilage. Forward and backward SHG intensities of sections from superficial, middle and deep zones were collected as a function of depth and analyzed by Monte Carlo simulations to extract the SHG creation direction, which is related to the fibrillar assembly.Our results revealed differences in SHG forward-backward response between the three zones, where these are consistent with a previously developed model of SHG emission. Some of the findings are consistent with that from other modalities; however, SHG analysis showed the middle zone had the most organized fibril assembly. While not distinct, we also report bulk optical property values for these different zones within the patella.Collectively, these results provide quantitative measurements of structural changes at both the fiber and fibril assembly of the different cartilage zones and reveals structural information not possible by other microscope modalities. This can provide quantitative insight to the collagen fiber network in normal cartilage, which may ultimately be developed as a biomarker for osteoarthritis.

The collagen architecture in all human ovarian cancers is substantially remodeled, where these alterations are manifested in different fiber widths, fiber patterns, and fibril size and packing. Second harmonic generation (SHG) microscopy has differentiated normal tissues from high-grade serous (HGS) tumors with high accuracy; however, the classification between low-grade serous, endometrioid, and benign tumors was less successful. We postulate this is due to known higher genetic variation in these tissues relative to HGS tumors, which are genetically similar, and this results in more heterogeneous collagen remodeling in the respective matrix. Here, we examine fiber widths and SHG emission intensity and directionality locally within images (e.g., 10×10 microns) and show that normal tissues and HGS tumors are more uniform in fiber properties as well as in fibril size and packing than the other tissues. Moreover, these distributions are in good agreement with phase matching considerations relating SHG emission directionality and intensity. The findings show that in addition to average collagen assembly properties the intrinsic heterogeneity must also be considered as another aspect of characterization. These local analyses showed differences not shown in pure intensity-based image analyses and may provide further insight into disease etiology of the different tumor subtypes.

Remodeling of the extracellular matrix in human ovarian cancer, can be reflected in increased collagen concentration, changes in alignment and/or up-regulation of different collagen isoforms, including Col III. Using fibrillar gel models, we demonstrate that Col I and Col III can be quantitatively distinguished by 3 distinct SHG polarization specific metrics: i) determination of helical pitch angle via the single axis molecular model, ii) dipole alignment via anisotropy, and iii) chirality via SHG circular dichroism (SHG-CD). These sub-resolution differentiations are possible due to differences in the α helix angles of the two isoforms, which co-mingle in the same fibrils. We also investigated the mechanism of the SHG-CD response and show that unlike conventional CD, it is dominated by electric dipole interactions and is consistent with the two state SHG model. We further applied these 3 polarization resolved analyses to human normal, high risk, benign tumors, and malignant human ovarian tissues. We found that these tissues could all be differentiated by these metrics, where high grade tissues had analogous α-helical pitch angles to the in the Col I/Col III gel model. This confirms literature suggestions based on immunofluorescence and gene expression that Col III is up-regulated in high grade ovarian cancers. The different tissues also displayed differing anisotropies, indicating the fibril assemblies are distinct and likely do not result from remodeling of existing collagen but synthesis of new collagen. Importantly, these SHG polarization methods provide structural information not otherwise possible and can serve as label-free biomarkers for ovarian and other cancers.

Ovarian cancer remains the most deadly gynecological cancer with a poor aggregate survival rate. To improve upon this situation, we utilized collagen-specific Second Harmonic Generation (SHG) imaging microscopy and optical scattering measurements to probe structural differences in the extracellular matrix of normal stroma, benign tumors, endometrioid tumors, and low and high-grade serous (LGS and HGS) tumors. The 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. 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 strong wavelength dependent dependencies of these metrics that were different between the different tumors that are related to respective structural attributes in the collagen organization. These sub-resolution determinations are consistent with the dualistic classification of type I and II serous tumors. However, type I endometrioid tumors have strongly differing ECM architecture than the serous malignancies. Moreover, our analyses are further consistent with LGS and benign tumors having similar etiology. We identified optimal wavelengths for the SHG metrics as well as optical scattering measurements. The SHG metrics and optical scattering measurements were then used to form a linear discriminant model to classify the tissues, and we obtained high accuracy (~90%) between the tissue types. This delineation is superior to current clinical performance and has potential applicability in supplementing histological analysis, understanding the etiology, as well as development of an in vivo screening tool.

Background Ovarian 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. Method As 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. Results The 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. Conclusions SHG 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.

PURPOSE: Significant remodeling of the extracellular matrix (ECM) occurs in human ovarian cancer and has been observed in both high grade and low grade tumors as well as ovaries from high risk patients with BRCA mutations. Uniquely quantifying alterations in the tumor microenvironment (TME) could be used as a new diagnostic tool, e.g. to complement histology; provide insight into disease etiology; and assess treatment efficacy through minimally invasive in vivo imaging. Current clinical modalities (CT, MRI, PET) lack the resolution for this purpose. Our efforts have focused on examining collagen alterations across a spectrum of human ovarian tumors, where the changes can serve as quantitative biomarkers. Alterations can be reflected in increased collagen concentration, changes in alignment of collagen molecules within fibrils and/or fibers and/or up-regulation of different collagen isoforms, e.g. Col III. METHODS AND RESULTS: We used the collagen specific/sensitive Second Harmonic Generation (SHG) imaging microscopy to probe collagen architecture over size scales that range from the macromolecular structural properties to fibril/fiber morphology. First, we used SHG polarization analyses to probe collagen macromolecular/supramolecular properties to discriminate ex vivo human tissues (normal stroma, benign tumors, and high grade serous tumors) by determination of: i) collagen alpha helical pitch angle, ii) alignment of collagen molecules within fibrils, and iii) collagen helical chirality via SHG circular dichroism (SHG-CD). The largest differences were between normal stroma and benign tumors, consistent with gene expression data showing Col III is up-regulated in the latter. The different tissues also displayed differing collagen alignment within fibrils and SHG-CD responses, consistent with either Col III incorporation or randomization of Col I alignment within benign and high-grade tumors fibrils. These results collectively indicate the fibril assemblies are distinct in all tissues and likely result from synthesis of new collagen rather than remodeling of existing collagen. Importantly, these techniques do not require exogenous labels, and additionally, provide sub-resolution structural information previously obtained through ultrastructural analysis that cannot be performed on intact tissues. We next implemented a novel form of 3D texture analysis and machine learning to delineate the fibrillar morphology observed in SHG images of normal stroma, high risk stroma, benign tumors, and a spectrum of malignant tumors (high grade serous, low grade serous, and endometrioid). We extracted textural features in the 3D image sets to build statistical models of each class and we achieved clinically significant 83-91% classification accuracies for the six classes. Importantly, the 3D analysis significantly outperformed our prior 2D methods. This classification based on collagen morphology will complement conventional classification based on genetic profiles and can serve as an additional biomarker. CONCLUSIONS: Taken together, the combination of the macro/supramolecular probes and the fiber morphology classification will greatly increase our understanding of the TME evolution in human ovarian cancer. These methods and their findings have clinical translational significance in terms of understanding disease etiology, and also by enhancing prognostic and diagnostic capabilities. Citation Format: Kirby R. Campbell, Rajeev Chaudhary, Julia Handel, Bruce Wen, Vikas Singh, Manish Patankar and Paul J. Campagnola. COLLAGEN ALTERATIONS IN HUMAN OVARIAN CANCER PROBED BY SECOND HARMONIC GENERATION (SHG) IMAGING MICROSCOPY [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr AP19.

Remodeling of the collagen architecture in the extracellular matrix (ECM) has been implicated in ovarian cancer. To quantify these alterations we implemented a form of 3D texture analysis to delineate the fibrillar morphology observed in 3D Second Harmonic Generation (SHG) microscopy image data of normal (1) and high risk (2) ovarian stroma, benign ovarian tumors (3), low grade (4) and high grade (5) serous tumors, and endometrioid tumors (6). We developed a tailored set of 3D filters which extract textural features in the 3D image sets to build (or learn) statistical models of each tissue class. By applying k-nearest neighbor classification using these learned models, we achieved 83–91% accuracies for the six classes. The 3D method outperformed the analogous 2D classification on the same tissues, where we suggest this is due the increased information content. This classification based on ECM structural changes will complement conventional classification based on genetic profiles and can serve as an additional biomarker. Moreover, the texture analysis algorithm is quite general, as it does not rely on single morphological metrics such as fiber alignment, length, and width but their combined convolution with a customizable basis set.

Multi-wavelength excitation SHG microscopy with circular dichroism probes decreasing chirality in fibrillary models of ovarian stroma comprised of collagen I and III isoforms. Results show increased sensitivity with shorter excitation wavelength.

Remodeling of the extracellular matrix in human ovarian cancer can be manifested in increased collagen concentration, changes in alignment within fibrils/fibers and/or up-regulation of different collagen isoforms. We used pixel-based second harmonic generation (SHG) polarization microscopy analyses to probe these molecular changes in human ovarian tissues [normal stroma, benign tumors, and high-grade serous (HGS) tumors] by: (i) determination of the [Formula: see text]-helical pitch angle via the single-axis molecular model, (ii) collagen alignment within fibrils via SHG anisotropy, and (iii) chirality via SHG circular dichroism (SHG-CD). Pixel approaches are required due to the complex structure of the matrix that lacks a high degree of fiber alignment. The largest differences in the helical pitch angle were between normal stroma and benign tumors, consistent with gene expression showing the Col III isoform is up-regulated in the latter. The data were not consistent with up-regulation of Col III in HGS tumors as previous reports have suggested. The different tissues also displayed differing SHG anisotropies and SHG-CD responses, consistent with either Col III incorporation or randomization of Col I alignment within benign and malignant tumors. Additionally, the high-grade tumors displayed higher collagen concentration, where this desmoplasia is consistent with the higher fiber density in these tissues. These results collectively indicate that the fibril assemblies are distinct in all tissues, where these differences likely result from the synthesis of collagen rather than remodeling of existing collagen. Importantly, these analyses are label-free and interrogate subresolution collagen structure on intact tissues, without the need for conventional structural biology tools.

Here, we examine ovarian cancer extracellular matrix (ECM) modification by measuring the wavelength dependence of optical scattering measurements and quantitative second-harmonic generation (SHG) imaging metrics in the range of 800-1100 nm in order to determine fibrillary changes in ex vivo normal ovary, type I, and type II ovarian cancer. Mass fractals of the collagen fiber structure is analyzed based on a power law correlation function using spectral dependence measurements of the reduced scattering coefficient μ s ′ where the mass fractal dimension is related to the power. Values of μ s ′ are measured using independent methods of determining the values of μ s and g by on-axis attenuation measurements using the Beer-Lambert Law and by fitting the angular distribution of scattering to the Henyey-Greenstein phase function, respectively. Quantitativespectral SHG imaging on the same tissues determines F SHG /B SHG creation ratios related to size and harmonophore distributions. Both techniques probe fibril packing order, but the optical scattering probes structures of sizes from about 50-2000 nm where SHG imaging – although only able to resolve individual fibers – builds contrast from the assembly of fibrils. Our findings suggest that type I ovarian tumor structure has the most ordered collagen fibers followed by normal ovary then type II tumors showing the least order.

Biological tissues have complex 3D collagen fiber architecture that cannot be fully visualized by conventional second harmonic generation (SHG) microscopy due to electric dipole considerations. We have developed a multi-view SHG imaging platform that successfully visualizes all orientations of collagen fibers. This is achieved by rotating tissues relative to the excitation laser plane of incidence, where the complete fibrillar structure is then visualized following registration and reconstruction. We evaluated high frequency and Gaussian weighted fusion reconstruction algorithms, and found the former approach performs better in terms of the resulting resolution. The new approach is a first step toward SHG tomography.

We report on the wavelength dependence of second harmonic generation (SHG) of collagen in scattering tissues over the wavelength range of 800-1200 nm. The study incorporates inclusion of the molecular hyperpolarizability β of collagen and optical scattering, both of which are wavelength dependent. Using 3D SHG imaging and Monte Carlo simulations, we find the wavelength dependence of β is not well described by a two-state model based on known absorption bands. We further find that longer wavelength excitation is inefficient as the reduction in scattering is overcome by the decreased β far from resonance and the optimal excitation is within the 800-900 nm range. The impact is larger for backward collected SHG.

SHG imaging microscopy and tissue spectroscopy are used to quantitatively study structural changes in the collagen organization in the ECM in ovarian cancer using in in vitro models and ex vivo human tissues.

Here we experimentally show that second-harmonic generation (SHG) imaging is not sensitive to collagen fibers oriented parallel to the direction of laser propagation and, as a consequence, can potentially miss important structural information. As an alternative approach, we demonstrate the use of reflective micro-prisms to enable multi-view SHG imaging of mouse tail tendon by redirecting the focused excitation and collection of subsequent emission. Our approach data corroborates the theoretical treatment on vanishing and nonvanishing orientations, where fibers along the laser direction are largely transparent by SHG. In strong contrast, the two-photon excited fluorescence of dye-labeled collagen fibers is isotropic and is not subject to this constraint. We utilized Pearson correlation to quantify differences in fluorescent and backward detected SHG images of the tendon fiber structure, where the SHG and TPEF were highly statistically correlated (0.6–0.8) for perpendicular excitation but were uncorrelated for excitation parallel to the fiber axis. The results suggest that improved imaging of 3D collagen structure is possible with multi-view SHG microscopy.

Multi-wavelength SHG imaging microscopy is used to quantitatively probe alterations of the supramolecular structure of collagen in the ECM of human ovarian cancer further developing the potential of collagen as a biomarker.