Form-biattenuance in fibrous tissues measured with polarization-sensitive optical coherence tomography (PS-OCT)

Abstract

Form-biattenuance ( chi) in biological tissue arises from anisotropic light scattering by regularly oriented cylindrical fibers and results in a differential attenuation (diattenuation) of light amplitudes polarized parallel and perpendicular to the fiber axis (eigenpolarizations). Form-biattenuance is complimentary to form-birefringence (n) which results in a differential delay (phase retardation) between eigenpolarizations. We justify the terminology and motivate the theoretical basis for form-biattenuance in depth-resolved polarimetry. A technique to noninvasively and accurately quantify form-biattenuance which employs a polarization-sensitive optical coherence tomography (PS-OCT) instrument in combination with an enhanced sensitivity algorithm is demonstrated on ex vivo rat tail tendon (mean chi = 5.3.10-4, N = 111), rat Achilles tendon ( chi = 1.3.10-4, N = 45), chicken drumstick tendon ( chi = 2.1.10-4, N = 57), and in vivo primate retinal nerve fiber layer ( chi = 0.18.10-4, N = 6). A physical model is formulated to calculate the contributions of chi and n to polarimetric transformations in anisotropic media.

A review of some recent developments in polarization-sensitive optical imaging techniques for the study of articular cartilage

“…Note that δ can be complex, in which case the imaginary part represents the "diattenuance" of the tissue i.e. the differential absorption of light polarized along the direction SA relative to that of light polarized orthogonal to this direction 25 . We have used fluorescence polarimetry to quantify Im(δ) for both equine tendon and equine hyaline cartilage, finding apparent values of 2.65×10 −4 for tendon but significantly less for cartilage 50 .…”

“…Polaroid® is the classic example, in which directionally aligned long-chain polymers of polyvinyl alcohol are conjugated to iodine to produce a medium that strongly absorbs light linearly polarized along the long-chain axis but absorbs orthogonally polarized light more weakly. Recently Kemp et al introduced the term "biattenuance" to describe broadly the same phenomenon, but extending the physical interpretation to include the effects of polarization-dependent back-scattering efficiencies by anisotropic embedded particles 25 . In principle it has been demonstrated that PS-OCT has the ability to measure the dichroism/diattenuation of biological samples in addition to the birefringence 26 .…”

Optical coherence tomography—current technology and applications in clinical and biomedical research

“…Tissue can change the polarization state of the light by several mechanisms: birefringence [69], diattenuation [70], or polarization scrambling [71]. While early implementations of PS-OCT measured only reflectivity and phase retardation between the polarization axes [67,68], improved techniques developed in recent years can extract and image more information, such as Stokes vectors of the backscattered light [72], Müller and Jones matrix distribution [73,74], axis orientation [75], and diattenuation [70]. If diattenuation is neglected-it is very low in most biological tissues-the three most important parameters, reflectivity, retardation, and axis orientation ( Fig.…”

GDx-MM: An Imaging Mueller Matrix Retinal Polarimeter

“…Kemp et al [19] developed complementary expressions for form birefringence and a newly defined quantity, form biattenuance, which describes the differential attenuation of light components by either absorption (dichroism) or scattering, and which can be expressed on a per-unit-depth basis. The theory is developed by considering material composed of alternating anisotropic layers containing a single layer of embedded cylinders and isotropic layers containing water.…”

“…As the work of Kemp et al. is most recent and presents a general theory for the development of form-based retardance and diattenuation which is applicable to ocular tissues, this work is Reprinted with permission from [19].…”