title: Quantifying collagen structure in breast biopsies using second-harmonic generation imaging.
abstract: Quantitative second-harmonic generation imaging is employed to assess stromal collagen in normal, hyperplastic, dysplastic, and malignant breast tissues. The cellular scale organization is quantified using Fourier transform-second harmonic generation imaging (FT-SHG), while the molecular scale organization is quantified using polarization-resolved second-harmonic generation measurements (P-SHG). In the case of FT-SHG, we apply a parameter that quantifies the regularity in collagen fiber orientation and find that malignant tissue contains locally aligned fibers compared to other tissue conditions. Alternatively, using P-SHG we calculate the ratio of tensor elements (d(15)/d(31), d(22)/d(31), and d(33)/d(31)) of the second-order susceptibility χ(2) for collagen fibers in breast biopsies. In particular, d(15)/d(31) shows potential differences across the tissue pathology. We also find that trigonal symmetry (3m) is a more appropriate model to describe collagen fibers in malignant tissues as opposed to the conventionally used hexagonal symmetry (C6). This novel method of targeting collagen fibers using a combination of two quantitative SHG techniques, FT-SHG and P-SHG, holds promise for breast tissue analysis and applications to characterizing cancer in a manner that is compatible with clinical practice.
authors.affiliation: Photonics Research of Bio/nano Environments (PROBE), Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, 1206 W Green St, Urbana, IL 61801,  USA ; Department of Electrical and Computer Engineering, University of Illinois Urbana-Champaign, 1406 W Green St, Urbana, IL 61801,  USA.
authors.forename: Raghu
authors.initials: R
authors.lastname: Ambekar
authors.forename: Tung-Yuen
authors.initials: TY
authors.lastname: Lau
authors.forename: Michael
authors.initials: M
authors.lastname: Walsh
authors.forename: Rohit
authors.initials: R
authors.lastname: Bhargava
authors.forename: Kimani C
authors.initials: KC
authors.lastname: Toussaint