title: Quantitative polarized Raman spectroscopy in highly turbid bone tissue.
abstract: Polarized Raman spectroscopy allows measurement of molecular orientation and composition and is widely used in the study of polymer systems. Here, we extend the technique to the extraction of quantitative orientation information from bone tissue, which is optically thick and highly turbid. We discuss multiple scattering effects in tissue and show that repeated measurements using a series of objectives of differing numerical apertures can be employed to assess the contributions of sample turbidity and depth of field on polarized Raman measurements. A high numerical aperture objective minimizes the systematic errors introduced by multiple scattering. We test and validate the use of polarized Raman spectroscopy using wild-type and genetically modified (oim/oim model of osteogenesis imperfecta) murine bones. Mineral orientation distribution functions show that mineral crystallites are not as well aligned (p<0.05) in oim/oim bones (28+/-3 deg) compared to wild-type bones (22+/-3 deg), in agreement with small-angle X-ray scattering results. In wild-type mice, backbone carbonyl orientation is 76+/-2 deg and in oim/oim mice, it is 72+/-4 deg (p>0.05). We provide evidence that simultaneous quantitative measurements of mineral and collagen orientations on intact bone specimens are possible using polarized Raman spectroscopy.
authors.affiliation: University of Michigan, Department of Biomedical Engineering, 930 North University Avenue, Room 4638, Ann Arbor, Michigan 48109, USA.
authors.forename: Mekhala
authors.initials: M
authors.lastname: Raghavan
authors.forename: Nadder D
authors.initials: ND
authors.lastname: Sahar
authors.forename: Robert H
authors.initials: RH
authors.lastname: Wilson
authors.forename: Mary-Ann
authors.initials: MA
authors.lastname: Mycek
authors.forename: Nancy
authors.initials: N
authors.lastname: Pleshko
authors.forename: David H
authors.initials: DH
authors.lastname: Kohn
authors.forename: Michael D
authors.initials: MD
authors.lastname: Morris
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000737:chemistry*; D024042:Collagen Type I / Q000737:chemistry; D004195:Disease Models, Animal; D004548:Elasticity; D005260:Female; D008027:Light; D051379:Mice; D008903:Minerals / Q000737:chemistry; D009391:Nephelometry and Turbidimetry; D010013:Osteogenesis Imperfecta / Q000235:genetics; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013977:Tibia / Q000737:chemistry*
chemical_list: D024042:Collagen Type I; D008903:Minerals