17 August 1994 Interference-based linear birefringence measurements of thermally induced changes in collagen
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Abstract
Linear birefringence (LB) is a polarization-specific property of many semi-crystalline structures in tissue. Specifically, collagen, with its triple helix conformation, exhibits LB in its native state. Rat tail tendon (RTT) was chosen for the LB experiments because it is > 90% collagen and the collagen fiber alignment is nearly parallel with the RTT length. This alignment results in RTT exhibiting uniaxial characteristics such that two properly chosen optical axes display differing refractive indices ((Delta) n equals nslow - nfast). RTT, which has an elliptical cross section, has its slow axis parallel to the tendon's length and a fast axes along the tendon's cross section. Native RTT has a refractive index difference of (Delta) n equals 1.5 X 10-3. For a typical tendon thickness of 200 micrometers , the phase shift, (delta) equals n*d (d, diameter), is approximately equal to 300 nm (transmission measurement). Heating of RTT results in a repeatable loss of (delta) . If monochromatic light is used the sample's output intensity is proportional to sin2((delta) (pi) /(lambda) ) where (lambda) is the wavelength of the light. Thus, given the native phase shift, the incident light's wavelength may be chosen such that the sample's loss of LB with heating is intensity- mapped on the sample's image.
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Duncan J. Maitland, Duncan J. Maitland, Joseph T. Walsh, Joseph T. Walsh, } "Interference-based linear birefringence measurements of thermally induced changes in collagen", Proc. SPIE 2134, Laser-Tissue Interaction V; and Ultraviolet Radiation Hazards, (17 August 1994); doi: 10.1117/12.182948; https://doi.org/10.1117/12.182948
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