For the first time to our knowledge, an experimental evaluation of the Faraday effect–induced polarization rotation in a biological tissue phantom is reported. The rotation of the polarization plane produced in the optical beam propagating through an Intralipid solution was evaluated using polarization-sensitive optical coherence tomography (PS-OCT), and the experimental results closely matched the theoretical values. The angle of rotation is proportional to the traversed path length along the magnetic field and can potentially be used to estimate the actual penetration depth.
National Health Interview Survey (NHIS) estimates more than 1.1 million burn injuries per year in the United States, with nearly 15,000 fatalities from wounds and related complications. An imaging modality capable of evaluating burn depths non-invasively is the polarization-sensitive optical coherence tomography. We report on the use of a high-speed, fiber-based Mueller-matrix OCT system with continuous source-polarization modulation for burn depth evaluation. The new system is capable of imaging at near video-quality frame rates (8 frames per second) with resolution of 10 μm in biological tissue (index of refraction: 1.4) and sensitivity of 78 dB. The sample arm optics is integrated in a hand-held probe simplifying the in vivo experiments. The applicability of the system for burn depth determination is demonstrated using biological samples of porcine tendon and porcine skin. The results show an improved imaging depth (1 mm in tendon) and a clear localization of the thermally damaged region. The burnt area determined from OCT images compares well with the histology, thus proving the system's potential for burn depth determination.
A unique feature of polarization-sensitive Mueller optical coherence tomography (Mueller-OCT) is that it can reveal various polarization properties of biological samples that are not observable using conventional OCT. One of the most important polarization parameters is birefringence, which can be measured in its integrated form using existing Mueller-OCT systems. We present a new method that uses the least squares algorithm to differentiate measured integrated Jones matrices so that the samples can be observed layer-by-layer. We tested the algorithm using simulated data with variable additive white Gaussian noise (AWGN) levels. We further verified the algorithm using in vitro measurements of the porcine tendon and the septum of the rat heart. This least squares-based algorithm has the potential to reveal structures previously hidden by the inherent masking properties of the integrated images and provide localized phase retardation and orientation information.
A novel fiber-based Mueller-matrix optical coherence tomography system is demonstrated for acquiring polarization images of biological tissues in vivo. The system features a single broadband source, a rapid scanning optical delay line, and an electro-optical polarization modulator that modulates the polarization states of the source light continuously. A frame of a 200 by 1515 pixel 2D image can be acquired in half a second. The Jones matrix of a sample is calculated from two frequency components--the A-scan carrier frequency component and the beat frequency component between the modulation frequency and the carrier frequency. For samples having negligible diattenuation, the Jones matrix can be calculated from a single measurement of either the horizontal or the vertical interference signal. The system was first validated by imaging standard polarization elements and then applied to imaging biological samples.
A fast scanning fiber-based system of Mueller-matrix optical coherence tomography was built to characterize the polarization properties of biological tissues with high spatial resolution. A polarization modulator with its fast-axis oriented at 45° in the source arm of the Michelson interferometer, driven by a sinusoidal wave, was used to continuously modulate the incident polarization states of both the sample and the reference arms. Two detection channels were used to detect the horizontal and vertical polarization components of the interference signals, which were used to calculate the roundtrip Jones matrix of the sample. The roundtrip polarization parameters of the sample were calculated from the measured Jones matrix. The system was successfully tested for both standard optical polarization elements and various types of biological samples.
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