Polarization Uniformity Research Articles

Evaluation of choroidal melanin-containing tissue in healthy Japanese subjects by polarization-sensitive optical coherence tomography

In this study, the choroidal melanin content in healthy eyes was evaluated with polarization-sensitive optical coherence tomography (PS-OCT). We evaluated 105 healthy eyes of 105 Japanese subjects. The mean thickness of melanin-containing tissue in the choroid (thickness of MeCh) and the choroidal melanin occupancy rate within a 5-mm circular region from the foveal center were calculated using the degree of polarization uniformity obtained by PS-OCT and compared with the choroidal thickness, patient age, and axial length. To evaluate regional variations, the 5-mm circular region was divided into a center area and an outer ring area, and the outer ring area was further divided into four areas (nasal, temporal, superior, and inferior). The mean thickness of MeCh showed a significant positive correlation with the choroidal thickness. The mean choroidal melanin occupancy rate showed a significant positive correlation with age. The mean choroidal melanin occupancy rate of the center area was significantly larger than that of the outer ring area. The mean thickness of MeCh and choroidal melanin occupancy rate of the nasal area were significantly lower than those of other areas. The distribution of melanin-containing tissue in the choroid varies significantly with age and location.

Objective evaluation of choroidal melanin loss in patients with Vogt\u2013Koyanagi\u2013Harada disease using polarization-sensitive optical coherence tomography

In this study, sunset glow fundus was evaluated in patients with Vogt–Koyanagi–Harada (VKH) disease using polarization-sensitive optical coherence tomography (PS-OCT). We evaluated 40 VKH eyes (20 patients) and 59 healthy eyes (59 age-matched controls). VKH eyes were divided into three groups according to color fundus images: sunset (17 eyes), potential sunset (13 eyes), and non-sunset (10 eyes). Choroidal melanin thickness (ChMeT) and the choroidal melanin thickness ratio (ChMeTratio) were calculated based on the degree of polarization uniformity from PS-OCT. ChMeT was significantly lower in sunset eyes than in non-sunset or control eyes (P = 0.003). The ChMeTratios of sunset or potential sunset eyes were significantly lower than those of non-sunset or control eyes (P = 0.04). Regional evaluation of ChMeT and the ChMeTratio showed that choroidal depigmentation predominantly occurred in the macula’s outer ring area (P = 0.002). The areas under receiver operating characteristic curves discriminating combined sunset (sunset and potential sunset) from non-sunset eyes were 0.983 and 0.997 for ChMeT and the ChMeTratio, respectively. Time course evaluation of 12 eyes from disease onset showed that ChMeT and the ChMeTratio significantly decreased over time. PS-OCT may be useful for objectively evaluating choroidal depigmentation in patients with VKH disease.

Multicontrast investigation of in vivo wildtype zebrafish in three development stages using polarization-sensitive optical coherence tomography.

.Significance: The scattering and polarization characteristics of various organs of in vivo wildtype zebrafish in three development stages were investigated using a non-destructive and label-free approach. The presented results showed a promising first step for the usability of Jones-matrix optical coherence tomography (JM-OCT) in zebrafish-based research.Aim: We aim to visualize and quantify the scatter and polarization signatures of various zebrafish organs for larvae, juvenile, and young adult animals in vivo in a non-invasive and label-free way.Approach: A custom-built polarization-sensitive JM-OCT setup in combination with a motorized translation stage was utilized to investigate live zebrafish. Depth-resolved scattering (intensity and attenuation coefficient) and polarization (birefringence and degree of polarization uniformity) properties were analyzed. OCT angiography (OCT-A) was utilized to investigate the vasculature label-free and non-destructively.Results: The scatter and polarization signatures of the zebrafish organs such as the eye, gills, and muscles were investigated. The attenuation coefficient and birefringence changes between 1- and 2-month-old animals were evaluated in selected organs. OCT-A revealed the vasculature of in vivo larvae and juvenile zebrafish in a label-free manner.Conclusions: JM-OCT offers a rapid, label-free, non-invasive, tissue specific, and three-dimensional imaging tool to investigate in vivo processes in zebrafish in various development stages.

Rapid non-destructive volumetric tumor yield assessment in fresh lung core needle biopsies using polarization sensitive optical coherence tomography.

Adequate tumor yield in core-needle biopsy (CNB) specimens is essential in lung cancer for accurate histological diagnosis, molecular testing for therapeutic decision-making, and tumor biobanking for research. Insufficient tumor sampling in CNB is common, primarily due to inadvertent sampling of tumor-associated fibrosis or atelectatic lung, leading to repeat procedures and delayed diagnosis. Currently, there is no method for rapid, non-destructive intraprocedural assessment of CNBs. Polarization-sensitive optical coherence tomography (PS-OCT) is a high-resolution, volumetric imaging technique that has the potential to meet this clinical need. PS-OCT detects endogenous tissue properties, including birefringence from collagen, and degree of polarization uniformity (DOPU) indicative of tissue depolarization. Here, PS-OCT birefringence and DOPU measurements were used to quantify the amount of tumor, fibrosis, and normal lung parenchyma in 42 fresh, intact lung CNB specimens. PS-OCT results were compared to and validated against matched histology in a blinded assessment. Linear regression analysis showed strong correlations between PS-OCT and matched histology for quantification of tumors, fibrosis, and normal lung parenchyma in CNBs. PS-OCT distinguished CNBs with low tumor content from those with higher tumor content with high sensitivity and specificity. This study demonstrates the potential of PS-OCT as a method for rapid, non-destructive, label-free intra-procedural tumor yield assessment.

Investigating the depolarization property of skin tissue by degree of polarization uniformity contrast using polarization-sensitive optical coherence tomography.

The depolarization property of skin has been found to be important for skin cancer detection. Previous techniques based on light polarization lack the capability of depth differentiation. Polarization-sensitive optical coherence tomography (PS-OCT) has the advantage of both depth-resolved 3D imaging and high sensitivity to polarization. In this study, we investigate the depolarization property of skin tissue using PS-OCT, especially with the degree of polarization uniformity (DOPU) contrast. Well designed skin phantoms with various surface roughness levels and optical properties mimicking skin are imaged by PS-OCT and the DOPU values are quantified. The result shows a correlation between DOPU and surface roughness, where a higher roughness corresponds to a lower DOPU value. An index matching experiment with a water layer confirms the impact of surface condition on light depolarization. Refraction of backscattered photons on the surface boundary is attributed to the broadening of backscattering angle and thus depolarization. To the best of our knowledge, this is the first time the impact of surface roughness on DOPU is reported and its mechanism explained. Furthermore, through preliminary in vivo skin imaging, the capability of DOPU in detecting depolarization in skin is demonstrated. By utilizing the 3D imaging from PS-OCT, DOPU can offer a high-resolution depth differentiation and quantification of depolarization in skin tissue.

Differentiation of breast tissue types for surgical margin assessment using machine learning and polarization-sensitive optical coherence tomography.

We report an automated differentiation model for classifying malignant tumor, fibro-adipose, and stroma in human breast tissues based on polarization-sensitive optical coherence tomography (PS-OCT). A total of 720 PS-OCT images from 72 sites of 41 patients with H&E histology-confirmed diagnoses as the gold standard were employed in this study. The differentiation model is trained by the features extracted from both one standard OCT-based metric (i.e., intensity) and four PS-OCT-based metrics (i.e., phase difference between two channels (PD), phase retardation (PR), local phase retardation (LPR), and degree of polarization uniformity (DOPU)). Further optimized by forward searching and validated by leave-one-site-out-cross-validation (LOSOCV) method, the best feature subset was acquired with the highest overall accuracy of 93.5% for the model. Furthermore, to show the superiority of our differentiation model based on PS-OCT images over standard OCT images, the best model trained by intensity-only features (usually obtained by standard OCT systems) was also obtained with an overall accuracy of 82.9%, demonstrating the significance of the polarization information in breast tissue differentiation. The high performance of our differentiation model suggests the potential of using PS-OCT for intraoperative human breast tissue differentiation during the surgical resection of breast cancer.

Improvement of spin polarization spatial uniformity in optically pumped atomic magnetometers based on counter-propagating pump beams and atomic diffusion

In an optically pumped alkali vapor cell with a high density of atoms, the attenuation of the pump light generates a spatially non-uniform distribution of the electronic spin polarization of alkali atoms, which is detrimental to biomagnetism applications of magnetometers as well as the hyperpolarization of noble gas atoms. Therefore, in this study, we propose a new scheme to generate a nearly uniform, unsaturated spin polarization region based on counter-propagating pump beams and atomic diffusion. A finite element method-based simulation is used to demonstrate the three-dimensional distribution of the spin polarization in a spherical cell. The effects of cell temperature and pump light power on the homogeneity of the spin polarization are studied. The distribution of spin polarization near the center of the cell is experimentally measured and a 1 cm uniform spin polarization region is achieved in the center of the cell. The uniformity of spin polarization in the center region of the cell increased by 50% compared with single beam pumping. The advantage of our proposed scheme is that it can generate an unsaturated uniform region of spin polarization in the center of a cell using a single species of alkali atoms.

Quantitative multi-contrast in vivo mouse imaging with polarization diversity optical coherence tomography and angiography.

Retinal microvasculature and the retinal pigment epithelium (RPE) play vital roles in maintaining the health and metabolic activity of the eye. Visualization of these retina structures is essential for pre-clinical studies of vision-robbing diseases, such as age-related macular degeneration (AMD). We have developed a quantitative multi-contrast polarization diversity OCT and angiography (QMC-PD-OCTA) system for imaging and visualizing pigment in the RPE using degree of polarization uniformity (DOPU), along with flow in the retinal capillaries using OCT angiography (OCTA). An adaptive DOPU averaging kernel was developed to increase quantifiable values from visual data, and QMC en face images permit simultaneous visualization of vessel location, depth, melanin region thickness, and mean DOPU values, allowing rapid identification and differentiation of disease symptoms. The retina of five different mice strains were measured in vivo, with results demonstrating potential for pre-clinical studies of retinal disorders.

Depth-resolved investigation of multiple optical properties and wrinkle morphology in eye-corner areas with multi-contrast Jones matrix optical coherence tomography.

Multi-contrast Jones matrix optical coherence tomography (JM-OCT) can provide quantitative depth-resolved local optical properties by improving the measurement algorithm. We examined the relationship between depth-resolved local optical properties of eye-corner skin measured by JM-OCT and corresponding wrinkle morphology of aged women (n=21; age range, 71.7±1.7years). Wrinkle morphology was analyzed by measuring the surface topography of three-dimensional replicas. The same regions were measured three-dimensionally by JM-OCT, and the local optical properties at each depth were computed. Birefringence (BR) and mean wrinkle depth correlated significantly at a depth of 88.2-138.6µm from the skin surface, and attenuation coefficient (AC) and mean wrinkle depth correlated significantly at a depth of 12.6-18.9µm and 189-459.9μm from the skin surface, although a degree of polarization uniformity (DOPU) did not. Stepwise multiple regression analysis demonstrated that a significant regression equation (R2 =0.649, P<.001) for predicting mean wrinkle depth was determined by BR at 107.1µm depth (BR 107.1 µm ), DOPU at 170.1µm (DOPU 170.1µm ), and AC at 252µm (AC 252 µm ) as independent variables and that these standardized beta regression coefficients were-0.860, -0.593, and-0.440, respectively, suggesting that BR, DOPU, and AC sufficiently explained mean wrinkle depth. These results suggest that BR 107.1 µm , DOPU 170.1 µm, and AC 252 µm may indicate collagen-related structure in the papillary, upper-reticular dermis, and microstructure or tissue density in reticular dermis, respectively, and may be involved in wrinkle formation.

Demonstration of biaxially tensile-strained Ge/SiGe multiple quantum well (MQW) electroabsorption modulators with low polarization dependence

Abstract We demonstrate a novel biaxially tensile-strained Ge/SiGe multiple quantum well (MQW) electroabsorption modulator with low polarization dependence. The device is waveguide integrated and has a length of 900 μm. Suspended microbridge structure is utilized to introduce biaxial tensile strain to the Ge/Si0.19Ge0.81 MQWs. Light is coupled into and out of the waveguide through deeply etched facets at the ends of the waveguide. Both TE and TM polarized electroabsorption contrast ratios are tested by the use of polarization maintaining focusing lensed fiber and a linear polarizer. A polarization irrelevant contrast ratio of 4.3 dB is achieved under 0 V/2 V operation. Both simulations and experiments indicate that the demonstrated device has potential in waveguide integrated utilizations that have high requirements on polarization uniformity.

Automated noise estimation in polarization-sensitive optical coherence tomography.

Advanced signal reconstruction in polarization-sensitive optical coherence tomography (OCT) frequently relies on an accurate determination of the signal noise floor. However, current methods for evaluating the noise floor are often impractical and subjective. Here we present a method using the degree of polarization uniformity and known speckle intensity statistics to model and estimate the OCT noise floor automatically. We establish the working principle of our method with a series of phantom experiments and demonstrate the robustness of our noise estimation method across different imaging systems and applications in vivo.

Clinical multi-functional OCT for retinal imaging.

A compact clinical prototype multi-functional optical coherence tomography (OCT) device for the posterior human eye has been developed. This compact Jones-matrix OCT (JM-OCT) device integrates all components into a single package. Multiple image functions, i.e., scattering intensity, OCT angiography, and the degree of polarization uniformity, are obtained. The device has the capability for measuring local birefringence. Multi-functional imaging of several eyes with age-related macular degeneration is demonstrated. The compact JM-OCT device will be useful for the in vivo non-invasive investigation of abnormal tissues.

Polarization conversion of polarized white light-emitting diodes with wire-grid polarizer

The packaging structures of polarized white light-emitting diodes (PWLEDs) can be implemented with a reflective polarizer and a diffusive light source for enhancing transmittance. In this work, the polarization conversion mechanism of PWLEDs with wire-grid polarizers is studied. It was found that the Lambertian distribution function prevails for unpolarized 568 nm yellow emission of wavelength conversion, whereas for polarized blue light scattering, the Gaussian like scattering distribution gradually changes to Lambertian with increasing degree of scattering, owing to the enhanced surface scattering or phosphor concentration. The transverse magnetic polarized 474 nm blue light is preferentially scattered out with wider scatter, which is beneficial to the lower correlated color temperature (CCT) and high transmittance, and yields an increased degree of polarization and angular uniformity of radiance distribution.

Complementary use of polarization-sensitive and standard OCT metrics for enhanced intraoperative differentiation of breast cancer.

We report the development and implementation of an intraoperative polarization-sensitive optical coherence tomography (PS-OCT) system for enhancing breast cancer detection. A total of 3440 PS-OCT images were intraoperatively acquired from 9 human breast specimens diagnosed by H&E histology as healthy fibro-adipose tissue (n = 2), healthy stroma (n = 2), or invasive ductal carcinoma (IDC, n = 5). A standard OCT-based metric (coefficient of variation (CV)) and PS-OCT-based metrics sensitive to biological tissue from birefringence (i.e., retardation and degree of polarization uniformity (DOPU)) were derived from 398 statistically different and independent images selected by correlation coefficient analysis. We found the standard OCT-based metric and PS-OCT-based metrics were complementary for the differentiation of healthy fibro-adipose tissue, healthy stroma, and IDC. While the CV of fibro-adipose tissue was significantly higher (p<0.001) than those of either stroma or IDC, the CV difference between stroma and IDC was minimal. On the other hand, stroma was associated with significantly higher (p<0.001) retardation and significantly lower (p<0.001) DOPU as compared to IDC. By leveraging the complementary information acquired by the intraoperative PS-OCT system, healthy fibro-adipose tissue, healthy stroma, and IDC can be differentiated with an accuracy of 89.4%, demonstrating the potential of PS-OCT as an adjunct modality for enhanced intraoperative differentiation of human breast cancer.

The effect of time-of-flight and point spread function modeling on 82Rb myocardial perfusion imaging of obese patients

BackgroundThe effect of time-of-flight (TOF) and point spread function (PSF) modeling in image reconstruction has not been well studied for cardiac PET. This study assesses their separate and combined influence on 82Rb myocardial perfusion imaging in obese patients. MethodsThirty-six obese patients underwent rest-stress 82Rb cardiac PET. Images were reconstructed with and without TOF and PSF modeling. Perfusion was quantitatively compared using the AHA 17-segment model for patients grouped by BMI, cross-sectional body area in the scanner field of view, gender, and left ventricular myocardial volume. Summed rest scores (SRS), summed stress scores (SSS), and summed difference scores (SDS) were compared. ResultsTOF improved polar map visual uniformity and increased septal wall perfusion by up to 10%. This increase was greater for larger patients, more evident for patients grouped by cross-sectional area than by BMI, and more prominent for females. PSF modeling increased perfusion by about 1.5% in all cardiac segments. TOF modeling generally decreased SRS and SSS with significant decreases between 2.4 and 3.0 (P < .05), which could affect risk stratification; SDS remained about the same. With PSF modeling, SRS, SSS, and SDS were largely unchanged. ConclusionTOF and PSF modeling affect regional and global perfusion, SRS, and SSS. Clinicians should consider these effects and gender-dependent differences when interpreting 82Rb perfusion studies.

Visualization of interfacial adhesive defects at dental restorations with spectral domain and polarization sensitive optical coherence tomography

Abstract Restoration loss based on interfacial adhesive defects and associated caries at the restoration margin are the main causes for invasive replacement of dental restorations. Assessment of the interfacial quality based on clinical inspection and radiographic examination is often difficult and not reliable. In this work, we present spectral domain optical coherence tomography (SDOCT) and polarization sensitive optical coherence tomography (PSOCT) for the evaluation of tooth-composite bond failure. Imaging of two composite restorations at the occlusal surface are presented using intensity-based images obtained by SDOCT and PSOCT based degree of polarization uniformity (DOPU). Both modalities revealed several defects beneath the surface such as inhomogeneous adhesive layers, marginal gaps and bubbles. In addition, DOPU representation showed an inhomogeneous structure within the composite material. OCT based imaging of dental restorations could add a valuable diagnostic tool for the evaluation of structural defects in clinical practice. The representation of polarization characteristics with the DOPU algorithm provides further information on the homogeneity of the restoration.

Cross-sectional and en-face depolarization imaging for the assessment of dental lesions

Abstract Dental caries is one of the most widespread diseases and the early and non-invasive detection of carious lesions remains an ongoing topic in biomedical research. In contrast, optical coherence tomography (OCT) is an emerging, non-invasive imaging technique for near-surface structures, that has already proved its capability for manifold biomedical applications and can be extended by several modalities such as polarization sensitivity. We have recently shown that polarization sensitive OCT combined with an algorithm for depolarization imaging, visualizing the degree of polarization uniformity (DOPU), is a promising tool for the detection and assessment of carious lesions. In this paper, we evaluate different visualization approaches based on both the intensity and DOPU data with cross-sectional and en-face representations and discuss limitations and the potential of the proposed method for the assessment of dental lesions on the example of a molar tooth with a brown spot.

Measuring polarization changes in the human outer retina with polarization-sensitive optical coherence tomography.

Morphological changes in the outer retina such as drusen are established biomarkers to diagnose age-related macular degeneration. However, earlier diagnosis might be possible by taking advantage of more subtle changes that accompany tissues that bear polarization-altering properties. To test this hypothesis, we developed a method based on polarization-sensitive optical coherence tomography with which volumetric data sets of the macula were obtained from 10 young (<25 years) and 10 older (>54 years) subjects. All young subjects and 5 of the older subjects had retardance values induced by the retinal pigment epithelium and Bruch's membrane (RPE-BM) complex that were just above the noise floor measurement (5°-13° at 840 nm). In contrast, elevated retardance, up to 180°, was observed in the other 5 older subjects. Analysis of the degree of polarization uniformity (DOPU) demonstrates that reduced DOPU (<0.4) in the RPE is associated with elevated double pass phase retardation (DPPR) below the RPE-BM complex, suggesting that the observed elevated DPPR in older subjects is the result of increased scattering or polarization scrambling. Collectively, our measurements show that the outer retina can undergo dramatic change in its polarization properties with age, and in some cases still retain its clinically normal appearance.

Detection of carious lesions utilizing depolarization imaging by polarization sensitive optical coherence tomography.

As dental caries is one of the most common diseases, the early and noninvasive detection of carious lesions plays an important role in public health care. Optical coherence tomography (OCT) with its ability of depth-resolved, high-resolution, noninvasive, fast imaging has been previously recognized as a promising tool in dentistry. Additionally, polarization sensitive imaging provides quantitative measures on the birefringent tissue properties and can be utilized for imaging dental tissue, especially enamel and dentin. By imaging three exemplary tooth samples ex vivo with proximal white spot, brown spot, and cavity, we show that the combination of polarization sensitive OCT and the degree of polarization uniformity (DOPU) algorithm is a promising approach for the detection of proximal carious lesions due to the depolarization contrast of demineralized tissue. Furthermore, we investigate different sizes of the DOPU evaluation kernel on the resulting contrast and conclude a suitable value for this application. We propose that DOPU provides an easy to interpret image representation and appropriate contrast for possible future screening applications in early caries diagnostics.

Generation and optimization of superpixels as image processing kernels for Jones matrix optical coherence tomography.

Jones matrix-based polarization sensitive optical coherence tomography (JM-OCT) simultaneously measures optical intensity, birefringence, degree of polarization uniformity, and OCT angiography. The statistics of the optical features in a local region, such as the local mean of the OCT intensity, are frequently used for image processing and the quantitative analysis of JM-OCT. Conventionally, local statistics have been computed with fixed-size rectangular kernels. However, this results in a trade-off between image sharpness and statistical accuracy. We introduce a superpixel method to JM-OCT for generating the flexible kernels of local statistics. A superpixel is a cluster of image pixels that is formed by the pixels' spatial and signal value proximities. An algorithm for superpixel generation specialized for JM-OCT and its optimization methods are presented in this paper. The spatial proximity is in two-dimensional cross-sectional space and the signal values are the four optical features. Hence, the superpixel method is a six-dimensional clustering technique for JM-OCT pixels. The performance of the JM-OCT superpixels and its optimization methods are evaluated in detail using JM-OCT datasets of posterior eyes. The superpixels were found to well preserve tissue structures, such as layer structures, sclera, vessels, and retinal pigment epithelium. And hence, they are more suitable for local statistics kernels than conventional uniform rectangular kernels.