Detecting axial heterogeneity of birefringence in layered turbid media using polarized light imaging

Abstract

The structural anisotropy of biological tissues can be quantified using polarized light imaging in terms of birefringence; however, birefringence varies axially in anisotropic layered tissues. This may present ambiguity in result interpretation for techniques whose birefringence results are averaged over the sampling volume. To explore this issue, we extended the polarization sensitive Monte Carlo code to model bi-layered turbid media with varying uniaxial birefringence in the two layers. Our findings demonstrate that the asymmetry degree (ASD) between the off-diagonal Mueller matrix elements of heterogeneously birefringent samples is higher than the homogenously birefringent (uniaxial) samples with the same effective retardance (magnitude and orientation). We experimentally verified the validity of ASD as a birefringence heterogeneity measure by performing polarized light measurements of bi-layered elastic and scattering polyacrylamide phantoms.

Review of the emerging role of optical polarimetry in characterization of pathological myocardium

“…20,37,[48][49][50] To facilitate the promotion of optical polarimetry in cardiac imaging clinics, the development of a flexible optical probe capable of intracardiac pathology assessment is desirable, which can in times be integrated with, for example, RF ablation catheter for the real time assessment of thermal lesion, similar to the recently reported combined RFA-optical coherence reflectometry catheters. 51 Indeed, the construction of flexible fiber-based probes for in vivo polarimetric studies is under way, 52 which, if successfully translated to the clinics, can possibly contribute in reducing the rate of unsuccessful ventricular arrhythmias treatments (∼10%). 53,54 Assessment of other cardiac pathologies such as the MI lesion (spatial extent, geometry, and position) and tacking the progress of stem cell therapy can also be made possible through the proposed optical probe, most likely delivered to the myocardial wall via catheter.…”

Polarized light imaging in biomedicine: emerging Mueller matrix methodologies for bulk tissue assessment

“…Simulation results from polarization-sensitive Monte Carlo code (Pol-MC) suggest that average pathlength of the polarization preserving photons is ∼6 mm (in the visible wavelength range and for typical tissue properties). [44][45][46] The interrogation depth then depends on the imaging geometry and the incident polarization state (circular, linear), and can be up to a few millimeters in transmission (∼4 mm) or in backscattering (∼2 mm). [44][45][46] The lateral resolution (FWHM of point spread function of the polarization preserving photons in tissue for an incident pencil beam) is ∼200 μm.…”

“…[44][45][46] The interrogation depth then depends on the imaging geometry and the incident polarization state (circular, linear), and can be up to a few millimeters in transmission (∼4 mm) or in backscattering (∼2 mm). [44][45][46] The lateral resolution (FWHM of point spread function of the polarization preserving photons in tissue for an incident pencil beam) is ∼200 μm. 44 These numbers need further experimental validation with well-controlled phantom studies.…”

“…[47][48][49] To test this hypothesis, using Pol-MC code, we recently modeled many bilayered Mueller matrices of heterogeneous birefringent turbid media, with different orientation or value of anisotropy in the layers. 46 The resultant Mueller matrices were then decomposed with both polar and differential decompositions. Our initial studies (manuscript in preparation) show that these two decompositions yield nearly identical results for a turbid medium that does not contain distinct layers of retarder/diattenuator (as is the case for biological tissues).…”

Retardance of bilayer anisotropic samples consisting of well-aligned cylindrical scatterers and birefringent media

“…8,9 It has been shown that for biological tissues containing several layers of different anisotropic properties, the axial variation in the birefringence can result in ambiguity when the measurement is averaged over the sampling volume. [10][11][12] In this study, we examined in detail how well-aligned cylindrical scatterers and birefringent media contributed to the value and direction of the total retardance of the media. Using Monte Carlo simulations, 13 we simulated how the total retardance and the equivalent extraordinary axis of the bilayer sample changed with the change in the value of the retardance and directions of the extraordinary axis of the two anisotropic layers, respectively.…”