Non-Linear Analysis of Collagen in Murine Ovarian Samples Using Second Harmonic Generation
Hasina Shir, University of Arizona, Undergraduate Student
Title: Feasibility of Non-Imaging Second Harmonic Generation to Identify Early Ovarian Cancer in a Murine Model Analysis of Collagen in Murine Ovarian Samples Using Second Harmonic Generation
Ovarian cancer is the fifth leading cause of cancer death in women. Early detection can save lives, but no generally acceptable (accurate and inexpensive) method exists. Research conducted by us and others has shown that the morphology and density of collagen is altered in cancerous tissue. In this study, the ovaries of a transgenic (TAg) mouse model of ovarian cancer were quantitatively imaged, using second harmonic generation microscopy (SHG). SHG is a nonlinear optical technique that can provide information about collagen structure and organization, however, it utilizes complex and expensive scanning elements. We sought to determine if non-imaging, randomly sampled point intensity measurements could be used to distinguish TAg from normal wild type (WT) mice. Eighty four three-dimensional (3D) SHG image sets from 21 TAg mice and 72 3D image sets from 18 wild type (WT) mice were obtained and analyzed. 3D image sets were converted to two-dimensional (2D) images, with maximum intensity projection being the preferred method. Images were thresholded and masked to exclude non-collagen signal, and then image pixels were randomly chosen. We found that the average intensity of a random sampling of 1000 pixels was not significantly different than the average intensity of the entire 1 million pixel image. This finding indicates that a simple continuously sampling, point-measuring system may provide data equivalent to a scanning system. We also found that the 1000-random-pixel average intensities were significantly lower in the TAg than WT mice at 4 weeks of age, suggesting that collagen is being degraded in the cancerous ovaries. However, there was no significance between the average intensities at eight weeks of age, possibly because more advanced cancer is heterogenous in collagen content. Next steps include further investigating the collagen structure as a function of cancer type, and adding an endoscope to the SHG system, which would allow use in vivo without the need for scanning.