Actions for Polarization-Modulated Second Harmonic Generation Microscopy in Collagen [electronic resource].

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Polarization-Modulated Second Harmonic Generation Microscopy in Collagen [electronic resource].

Published
Washington, D.C. : United States. Dept. of Energy, 2002.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
PDF-FILE: 172 ; SIZE: 46.5 MBYTES pages
Additional Creators
Lawrence Livermore National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
Collagen is a key structural protein in the body; several pathological conditions lead to changes in collagen. Among imaging modalities that can be used in vivo, second harmonic generation (SHG) microscopy has a key advantage: it provides ≈1 {micro}m resolution information about collagen structure as a function of depth. A new technique--polarization-modulated SHG--is presented: it permits simultaneous measurement of collagen orientation, of a lower bound on the magnitude of the second order nonlinear susceptibility tensor, and of the ratio of the two independent elements in this tensor. It is applied to characterizing SHG in collagen and to determining effects of biologically relevant changes in collagen structure. The magnitude of the second harmonic signal in two dimensional images varies with position even in structurally homogeneous tissue; this phenomenon is due to interference between second harmonic light generated by neighboring fibrils, which are randomly oriented parallel or anti-parallel to each other. Studies in which focal spot size was varied indicated that regions where fibrils are co-oriented are less than ≈1.5 {micro}m in diameter. A quartz reference was used to determine the spot size as well as a lower limit (d{sub xxx} > 0.3 pm/V) for the magnitude of the second order nonlinear susceptibility. The ratio of the two independent tensor elements ranged between d{sub XYY}/d{sub XXX} = 0.60 and 0.75. SHG magnitude alone was not useful for identifying structural anomalies in collagenous tissue. Instead, changes in the polarization dependence of SHG were used to analyze biologically relevant perturbations in collagen structure. Changes in polarization dependence were observed in dehydrated samples, but not in highly crosslinked samples, despite significant alterations in packing structure. Complete thermal denaturation and collagenase digestion produced samples with no detectable SHG signal. Collagen orientation was measured in thin samples of several different tissues in transmission mode as well as at different depths (up to 200 {micro}m) in thick samples in reflection mode; birefringence had no effect on the measurement. These studies showed that SHG microscopy was capable of detecting pathophysiological changes in collagen structure, suggesting that this technique has potential clinical applications.
Report Numbers
E 1.99:ucrl-lr-150543
ucrl-lr-150543
Subject(s)
Other Subject(s)
Note
Published through SciTech Connect.
09/30/2002.
"ucrl-lr-150543"
Stoller, P C.
Funding Information
W-7405-ENG-48
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