Abstract
.Significance: Biological tissues are typically characterized by high anisotropic scattering and may also exhibit linear form birefringence. Both scattering and birefringence bias the phase shift between transverse electric field components of polarized light. These phase alterations are associated with particular structural malformations in the tissue. In fact, the majority of polarization-based techniques are unable to distinguish the nature of the phase shift induced by birefringence or scattering of light.Aim: We explore the distinct contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in turbid tissue-like scattering medium.Approach: The circularly polarized light in frame of Stokes polarimetry approach is used for the screening of biotissue phantoms and chicken skin samples. The change of optical properties in chicken skin is accomplished by optical clearing, which reduces scattering, and mechanical stretch, which induces birefringence. The change of optical properties of skin tissue is confirmed by spectrophotometric measurements and second-harmonic generation imaging.Results: The contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in biological tissues are distinguished by the locus of the Stokes vector mapped on the Poincaré sphere. The phase retardation of circularly polarized light due to scattering alterations is assessed. The value of birefringence in chicken skin is estimated as , which agrees with alternative studies. The change of birefringence of skin tissue due to mechanical stretch in the order of is detected.Conclusions: While the polarimetric parameters on their own do not allow distinguishing the contributions of scattering and birefringence, the resultant Stokes vector trajectory on the Poincaré sphere reveals the role of scattering and birefringence in the total phase retardation. The described approach, applied independently or in combination with Mueller polarimetry, can be beneficial for the advanced characterization of various types of malformations within biological tissues.
Highlights
The use of polarized light in various biomedical applications is rapidly growing in the recent years.[1]
While the polarimetric parameters on their own do not allow distinguishing the contributions of scattering and birefringence, the resultant Stokes vector trajectory on the Poincaré sphere reveals the role of scattering and birefringence in the total phase retardation
The aim of the current study is to explore how the variations of birefringence and scattering contribute to the overall phase retardation of circularly polarized light propagated in turbid tissue-like scattering medium, such as skin
Summary
The use of polarized light in various biomedical applications is rapidly growing in the recent years.[1] The advantages of polarization-based diagnostic modalities over the conventional optical techniques, as well as the features and challenges of the characterization of biological tissues using so-called optical polarization fingerprint, are widely described elsewhere.[2,3,4,5] Due to its unique properties, the polarized light is widely used as a considerable add-on to a number of conventional diagnostic and imaging techniques. Mueller-matrix polarimetry shows promising results, in particular, in screening of cancerous tissues[15,16,17,18] and characterization of other turbid tissue-like scattering media.[19,20,21] it has been demonstrated that utilizing circularly polarized light in frame of Stokes-vector polarimetry approach, complemented by the use of Poincaré sphere as a quantitative graphical tool, has a high potential for tissue characterization and evaluation of cancer aggressiveness.[22,23,24,25,26,27]
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