Special Section Guest Editorial: Antonello De Martino (1954-2014): in memoriam

Pramana, 2010

The polarization parameters of light scattered from biological tissues contain wealth of morphological and functional information of potential biomedical importance. But, in optically thick turbid media such as tissues, numerous complexities due to multiple scattering and simultaneous occurrences of many polarization events present formidable challenges, in terms of both accurate measurement and unique interpretation of the individual polarimetry characteristics. We have developed and validated an expanded Mueller matrix decomposition approach to overcome this problem. The approach was validated theoretically with a polarization-sensitive Monte Carlo light propagation model and experimentally by recording Mueller matrices from tissue-like complex random medium. In this paper, we discuss our comprehensive turbid polarimetry platform consisting of the experimental polarimetry system, forward Monte Carlo modelling and inverse polar decomposition analysis. Initial biomedical applications of this novel general method for polarimetry analysis in random media are also presented.

Society of Photo-Optical …, 2012

A novel spectroscopic Mueller matrix system has been developed and explored for both fluorescence and elastic scattering polarimetric measurements from biological tissues. The 4 × 4 Mueller matrix measurement strategy is based on sixteen spectrally resolved (λ = 400 -800 nm) measurements performed by sequentially generating and analyzing four elliptical polarization states. Eigenvalue calibration of the system ensured high accuracy of Mueller matrix measurement over a broad wavelength range, either for forward or backscattering geometry. The system was explored for quantitative fluorescence and elastic scattering spectroscopic polarimetric studies on normal and precancerous tissue sections from human uterine cervix. The fluorescence spectroscopic Mueller matrices yielded an interesting diattenuation parameter, exhibiting differences between normal and precancerous tissues.

Thin Solid Films, 2004

A new spectroscopic Mueller matrix polarimeter based on liquid crystal devices is presented. Fast spectroscopic measurements (approx. 1 s) of a complete Mueller matrix with 1 nm resolution in the range from the visible to the near infrared can be obtained by the use of a CCD array coupled to a dispersion grid. The optical set-up is based on a polarization states generator (PSG)sample-polarization states analyzer (PSA) configuration that can be adapted to work in transmission as well as in reflection mode. PSG and PSA are both identical and consist of a linear polarizer, two voltage driven liquid crystal devices and a waveplate. The liquid crystals were chosen to be ferroelectric, working essentially as retardation waveplates. The design of the polarimeter was based on an objective criterion that allowed to optimize the accuracy of the measurements. As a result, we measured a complete Mueller matrix with a relative error lower than 0.5%. The eigenvalue method previously reported provided a straightforward and robust way to calibrate the polarimeter without ambiguities using a small set of three simple reference samples (a linear polarizer, a waveplate and a reflecting surface). In this article, we present a detailed description of the optical setup, the calibration of the polarimeter and some examples of measurements. Whenever the polarimeter is used as an ellipsometer, it is possible to profit the redundant information given by the 16 Mueller matrix coefficients to enhance the accuracy and precision of the measured ellipsometric angles C and D. For illustration, we compare the measurements obtained with the spectroscopic polarimeter to those of a standard spectroscopic ellipsometer. ᮊ

Optics Letters, 2016

Optics express, 2013

A novel spectroscopic Mueller matrix system has been developed and explored for both fluorescence and elastic scattering polarimetric measurements from biological tissues. The 4 × 4 Mueller matrix measurement strategy is based on sixteen spectrally resolved (λ = 400 -800 nm) measurements performed by sequentially generating and analyzing four elliptical polarization states. Eigenvalue calibration of the system ensured high accuracy of Mueller matrix measurement over a broad wavelength range, either for forward or backscattering geometry. The system was explored for quantitative fluorescence and elastic scattering spectroscopic polarimetric studies on normal and precancerous tissue sections from human uterine cervix. The fluorescence spectroscopic Mueller matrices yielded an interesting diattenuation parameter, exhibiting differences between normal and precancerous tissues.

Optics Express, 2015

A novel technique to measure the full 4 × 4 Mueller matrix of a sample through an optical fiber is proposed, opening the way for endoscopic applications of Mueller polarimetry for biomedical diagnosis. The technique is based on two subsequent Mueller matrices measurements: one for characterizing the fiber only, and another for the assembly of fiber and sample. From this differential measurement, we proved theoretically that the polarimetric properties of the sample can be deduced. The proof of principle was experimentally validated by measuring various polarimetric parameters of known optical components. Images of manufactured and biological samples acquired by using this approach are also presented.

Journal of Biomedical Optics, 2020

Significance: Mueller matrix polarimetry can provide useful information about the function and structure of the extracellular matrix. A portable and low-cost system could facilitate the clinical assessment of cervical anomalies in low-resource settings. Aim: We introduce a low-cost snapshot Mueller matrix polarimeter that does not require external power, has no moving parts, and can acquire a full Mueller matrix in ∼1 s, to conduct a feasibility study for cervical imaging in the low-resource setting. Approach: A snapshot system based on two sets of Savart plates, a ring illuminator with polarizing elements (generating four polarization states), and one camera is introduced. Stokes vectors are formulated to recover the polarization properties of the sample. Then, using Mueller matrix decomposition, the depolarization and retardance information is extracted. Results: We report the results on 16 healthy individuals (out of 22 patients imaged), whose Pap smear showed no malignant findings from mobile clinics in rural region of Mysore, India. The depolarization and retardance information was in agreement with previous reports. Conclusions: We introduce an imaging system and conducted a feasibility study on healthy individuals. This work could futurely translate into diagnostic applications to provide a quantitative platform in the clinical environment (e.g., cervical cancer screening).

Optics …, 2003

We demonstrate a Mueller polarimeter in which the polarization-state generator and analyzer are both composed of a linear polarizer and two liquid-crystal variable retarders. The polarimeter is designed to optimize the accuracy of the final results by minimization of the condition numbers of the modulation and analysis matrices. The polarimeter calibration, a difficult task by conventional procedures, is achieved easily by use of the eigenvalue method of Compain et al. [Appl. Opt. 38, 3490 (1999)]. The overall polarimeter performance is tested with a linear polarizer at various angles and a compensator at various retardations.

Optik, 2020

Mueller matrix polarimetry (MMP) is a fast and non-invasive optical technique for characterization of turbid media such as biological tissues, where the experimental Mueller matrix M contains the complete information of polarization properties of the sample. The individual optical properties in M are present in a complex interwoven way and need to be extracted; Mueller matrix polar decomposition (MMPD) and Mueller matrix transformation (MMT) are two widely used methods for this purpose. Here, we compared these two methods (i.e., MMPD and MMT) and assessed the possible correlation between their corresponding parameters in a comprehensive sample cohort containing different types of tissues and associated pathologies (n = 47), tissue phantoms (n = 21) and standard optical components (e.g., air, polarizer, quarter wave plate, etc.) (n = 09). Specifically, we calculated two sets of optical variables (Δ T , b) and (δ, t) representing depolarization and retardance for the MMPD and MMT methods, respectively. Qualitative correlation via graphical tools (i.e., violin, parallel coordinate, scatter, Bland and Altman plots) in tandem with correlation coefficients was investigated. The parameters of both methods are indicative of the structural features of the turbid samples; however, the MMT parameters (b, t) give higher values than the MMPD parameters (Δ T , δ) with moderate statistical correlation. This study assessed the link between the two methods and would provide a useful reference for such comparative analyses.

Optics Letters, 1999

A Mueller-matrix imaging polarimeter was developed to measure spatially resolved polarization properties in the living human eye. The apparatus is a double-pass setup that incorporates two liquid-crystal variable retarders and a slow-scan CCD camera in the recording stage. Series of 16 images for the combinations of independent polarization states in the f irst and second passages were recorded for two experimental conditions: with the camera conjugated either with the retina or with the eye's pupil plane. Spatially resolved collections of Mueller matrices and the degree of polarization were calculated from those images for both retinal and pupil planes.