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J Biomed Opt. 2014 Nov;19(11):117009. doi: 10.1117/1.JBO.19.11.117009.

Polarization gating enables sarcomere length measurements by laser diffraction in fibrotic muscle.

Author information

1
University of California San Diego, Department of Bioengineering, 9500 Gilman Drive, La Jolla, California 92093-0412, United StatesbVA San Diego Healthcare System, 3350 La Jolla Village Drive, San Diego, California 92161, United States.
2
VA San Diego Healthcare System, 3350 La Jolla Village Drive, San Diego, California 92161, United StatescUniversity of California San Diego, Department of Orthopaedic Surgery, 9500 Gilman Drive, La Jolla, California 92093-0863, United States.
3
University of California San Diego, Department of Bioengineering, 9500 Gilman Drive, La Jolla, California 92093-0412, United StatesbVA San Diego Healthcare System, 3350 La Jolla Village Drive, San Diego, California 92161, United StatescUniversity of Calif.

Abstract

Raman spectroscopy (RS) has been extensively used to characterize bone composition. However, the link between bone biomechanics and RS measures is not well established. Here, we leveraged the sensitivity of RS polarization to organization, thereby assessing whether RS can explain differences in bone toughness in genetic mouse models for which traditional RS peak ratios are not informative. In the selected mutant mice—activating transcription factor 4 (ATF4) or matrix metalloproteinase 9 (MMP9) knock-outs—toughness is reduced but differences in bone strength do not exist between knock-out and corresponding wild-type controls. To incorporate differences in the RS of bone occurring at peak shoulders, a multivariate approach was used. Full spectrum principal components analysis of two paired, orthogonal bone orientations (relative to laser polarization) improved genotype classification and correlation to bone toughness when compared to traditional peak ratios. When applied to femurs from wild-type mice at 8 and 20 weeks of age, the principal components of orthogonal bone orientations improved age classification but not the explanation of the maturation-related increase in strength. Overall, increasing polarization information by collecting spectra from two bone orientations improves the ability of multivariate RS to explain variance in bone toughness, likely due to polarization sensitivity to organizational changes in both mineral and collagen.

PMID:
25422904
PMCID:
PMC4242972
DOI:
10.1117/1.JBO.19.11.117009
[Indexed for MEDLINE]
Free PMC Article

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