Polarization-sensitive Optical Coherence Tomography Research Articles

Posterior scleral birefringence measured by triple-input polarization-sensitive imaging as a biomarker of myopia progression.

In myopic eyes, pathological remodelling of collagen in the posterior sclera has mostly been observed ex vivo. Here we report the development of triple-input polarization-sensitive optical coherence tomography (OCT) for measuring posterior scleral birefringence. In guinea pigs and humans, the technique offers superior imaging sensitivities and accuracies than dual-input polarization-sensitive OCT. In 8-week-long studies with young guinea pigs, scleral birefringence was positively correlated with spherical equivalent refractive errors and predicted the onset of myopia. In a cross-sectional study involving adult individuals, scleral birefringence was associated with myopia status and negatively correlated with refractive errors. Triple-input polarization-sensitive OCT may help establish posterior scleral birefringence as a non-invasive biomarker for assessing the progression of myopia.

Polarization coherency matrix tomography.

In this paper, a polarization-sensitive optical coherence tomography (PS-OCT) based polarization coherency matrix tomography (PCMT) combining polarization coherency matrix with Mueller matrix is proposed for the determination of complete polarization properties of tissue. PCMT measures the Jones matrix of biological sample based on similar transformation, in which four elements have initial random phase from different polarization states based on traditional PS-OCT. The results indicate that PCMT can eliminate the phase difference of incident lights with different polarization states. In addition, the polarization coherency matrix using three polarization states has complete information of the sample Jones matrix. Finally, the 16 elements of the sample Mueller matrix are applied for deriving fully polarized optical properties of the sample based on the elliptical diattenuator and the elliptical retarder. Thus, the method based on the PCM and Mueller matrix has the advantage over the traditional PS-OCT.

Characteristics of Henle's fiber layer in healthy and glaucoma eyes assessed by polarization-sensitive optical coherence tomography.

Using conventional optical coherence tomography (OCT), it is difficult to image Henle fibers (HF) due to their low backscattering potential. However, fibrous structures exhibit form birefringence, which can be exploited to visualize the presence of HF by polarization-sensitive (PS) OCT. We found a slight asymmetry in the retardation pattern of HF in the fovea region that can be associated with the asymmetric decrease of cone density with eccentricity from the fovea. We introduce a new measure based on a PS-OCT assessment of optic axis orientation to estimate the presence of HF at various eccentricities from the fovea in a large cohort of 150 healthy subjects. By comparing a healthy age-matched sub-group (N = 87) to a cohort of 64 early-stage glaucoma patients, we found no significant difference in HF extension but a slightly decreased retardation at about 2° to 7.5° eccentricity from the fovea in the glaucoma patients. This potentially indicates that glaucoma affects this neuronal tissue at an early state.

Determination of birefringence of biological tissues using modified PS-OCT based on the quaternion approach

Introduction: Polarization-sensitive optical coherence tomography (PS-OCT) is a functional extension of standard OCT. PS-OCT systems can be generally categorized into two categories based on the number of input polarization states on the sample: multi-input polarization state (multi-IPS) and single IPS. In addition, each category includes two configurations: fiber-based system and bulk optics-based system. However, there are complex and time-consuming steps to calibrate the polarization states of light among the reference, the sample, and detection arms for fiber-based system. And it is not compact and robust enough for bulk optics-based system.Methods: In the modified SD PS-OCT system with structural symmetry in both arms of the reference and sample, there are no bulk polarization optical elements in both arms of the reference and the sample. A circularly polarized light was used to incident on sample, and Stokes vector of backscattered light was employed to characterize the birefringence of biological tissues based on the quaternion approach, which directly establishes the relationship between Stokes vectors of backscattered light and Jones matrix of the sample.Results and discussion: The new algorithm provides the analytic solution of retardance and fast-axis orientation. To evaluate the performance of the developed system, an eighth-wave plate is used. Then, the polarization properties of the myocardial tissue in vivo are quantitatively reconstructed based on the quaternion approach. The results demonstrated that the proposed method has an advantage over Jones formalism based on a single input state and two polarization input states. In the future, the modified SD PS-OCT could be improved as a common path SD PS-OCT for clinical applications.

Development of an intelligent full-field polarization sensitive optical coherence tomography for breast cancer classification.

Biopsy is the gold standard for cancer detection, however the surge in breast cancer cases has made manual haematoxylin and eosin stained histopathological image examination difficult. Automatic cancer diagnosis is vital for a healthy life. It allows fast diagnosis without specific skills. This research proposes an intelligent full-field polarization-sensitive optical coherence tomography (FF-PS-OCT) system for ex-vivo breast classification using ensemble model corroborated by technique for order preference by similarity to ideal solution (TOPSIS). 220 samples image were scanned using the FF-PS-OCT to extract the phase information. The multilevel ensemble classifier has 94.8% precision, 92.5% recall, 93.7% F-score and 82.3% Mathews correlation coefficient on the testing dataset. The developed ensemble model corroborated by TOPSIS, outperforms the single model in terms of performance metrics. The initial results indicate that the rapid, non-contact and label-free FF-PS-OCT imaging modality using birefringent information is beneficial for making interventional decisions by clinicians.

Development of polarization-sensitive optical coherence tomography imaging platform and metrics to quantify electrostimulation-induced peripheral nerve injury in vivo in a small animal model.

Neuromodulation devices are rapidly evolving for the treatment of neurological diseases and conditions. Injury from implantation or long-term use without obvious functional losses is often only detectable through terminal histology. New technologies are needed that assess the peripheral nervous system (PNS) under normal and diseased or injured conditions. We aim to demonstrate an imaging and stimulation platform that can elucidate the biological mechanisms and impacts of neurostimulation in the PNS and apply it to the sciatic nerve to extract imaging metrics indicating electrical overstimulation. A sciatic nerve injury model in a 15-rat cohort was observed using a newly developed imaging and stimulation platform that can detect electrical overstimulation effects with polarization-sensitive optical coherence tomography. The sciatic nerve was electrically stimulated using a custom-developed nerve holder with embedded electrodes for 1h, followed by a 1-h recovery period, delivered at above-threshold Shannon model -values in experimental groups: sham control (SC, , ), stimulation level 1 (SL1, , , and ), and stimulation level 2 (SL2, , , and ). The stimulation and imaging system successfully captured study data across the cohort. When compared to a SC after a 1-week recovery, the fascicle closest to the stimulation lead showed an average change of (SL1/SL2) in phase retardation and in optical attenuation relative to SC. Analysis of immunohistochemistry (IHC) shows a difference in myelin pixel counts and difference in axon pixel counts, and an overall increase in cell nuclei pixel count of . These metrics were consistent with IHC and hematoxylin/eosin tissue section analysis. The poststimulation changes observed in our study are manifestations of nerve injury and repair, specifically degeneration and angiogenesis. Optical imaging metrics quantify these processes and may help evaluate the safety and efficacy of neuromodulation devices.

Change of the polarization properties of the human dermis with directions of incident and observation

In this work, a simplified cylinder-birefringence optical model of the human skin dermis model is reported. The actual polarization parameters of human fingernail skin were measured. And the accuracy and stability of the Mueller matrix polarization decomposition (MMPD) and the direct Mueller matrix (DMM) methods were compared under different incident and scattering angles. One main novelty of the present work is that the value of birefringence of the skin dermis was obtained from images of living human index finger nails by using a polarization-sensitive optical coherence tomography device. The results obtained in this work provide a basis for the selection of incident and scattering angles when measuring biological samples containing fibrous structures in the future.

In vivo microstructural investigation of the human tympanic membrane by endoscopic polarization-sensitive optical coherence tomography.

Endoscopic optical coherence tomography (OCT) is of growing interest for in vivo diagnostics of the tympanic membrane (TM) and the middle ear but generally lacks a tissue-specific contrast. To assess the collagen fiber layer within the in vivo TM, an endoscopic imaging method utilizing the polarization changes induced by the birefringent connective tissue was developed. An endoscopic swept-source OCT setup was redesigned and extended by a polarization-diverse balanced detection unit. Polarization-sensitive OCT (PS-OCT) data were visualized by a differential Stokes-based processing and the derived local retardation. The left and right ears of a healthy volunteer were examined. Distinct retardation signals in the annulus region of the TM and near the umbo revealed the layered structure of the TM. Due to the TM's conical shape and orientation in the ear canal, high incident angles onto the TM's surface, and low thicknesses compared to the axial resolution limit of the system, other regions of the TM were more difficult to evaluate. The use of endoscopic PS-OCT is feasible to differentiate birefringent and nonbirefringent tissue of the human TM in vivo. Further investigations on healthy as well as pathologically altered TMs are required to validate the diagnostic potential of this technique.

Synthesizing the degree of polarization uniformity from non-polarization-sensitive optical coherence tomography signals using a neural network.

Degree of polarization uniformity (DOPU) imaging obtained by polarization-sensitive optical coherence tomography (PS-OCT) has the potential to provide biomarkers for retinal diseases. It highlights abnormalities in the retinal pigment epithelium that are not always clear in the OCT intensity images. However, a PS-OCT system is more complicated than conventional OCT. We present a neural-network-based approach to estimate the DOPU from standard OCT images. DOPU images were used to train a neural network to synthesize the DOPU from single-polarization-component OCT intensity images. DOPU images were then synthesized by the neural network, and the clinical findings from ground truth DOPU and synthesized DOPU were compared. There is a good agreement in the findings for RPE abnormalities: recall was 0.869 and precision was 0.920 for 20 cases with retinal diseases. In five cases of healthy volunteers, no abnormalities were found in either the synthesized or ground truth DOPU images. The proposed neural-network-based DOPU synthesis method demonstrates the potential of extending the features of retinal non-PS OCT.

Online detection of orientation of cellulose nanocrystals in a capillary flow with polarization-sensitive optical coherence tomography

Significant importance in the stiffness of materials, such as filaments and films, made of elongated components, has been attributed to orientation. Thus, the control of orientation during the manufacturing of materials has been the target of process optimization for long time. Measuring orientation during the process allows to better grasp the means to control it. In fact, such online tools would enable on-fly process control and optimization improving the flexibility with regards to the raw materials used, and the application requirements. In this article, we will discuss a method based on polarization-sensitive optical coherence tomography utilized as a light-weight online measurement tool of particle (here cellulose nanocrystals) orientation for the purposes of manufacturing next generation products by providing the appropriate interpretation of the retardation images with the help of modelling.

Quantification of elastic anisotropy of human skin in vivo with dynamic optical coherence elastography and polarization-sensitive OCT

The complex structure of skin ensures a broad range of biological functions. The loss of a large skin area due to trauma or disease usually requires reconstructive surgery that often involves grafting or flapping. The clinical need for non-contact objective measurements of skin elasticity is necessary to guide grafting procedures to minimize complications such as secondary contracture or hypertrophic scars. Here, we report a non-contact and non-invasive method combining acoustic micro-tapping optical coherence elastography (AμT-OCE) with polarization-sensitive (PS-) optical coherence tomography (OCT) to quantify anisotropic elastic properties of skin. We show that all three elastic constants that define skin’s anisotropic elastic deformation and the orientation of collagen fibers in the dermis can be determined from propagating elastic waves over the skin surface. Measurements were performed on healthy volunteers in vivo. A nearly incompressible transverse isotropic model of skin elasticity was used to reconstruct the moduli from experimental data after being validated in extensive numerical simulations. Finally, we demonstrate that combining several OCT modalities (structural OCT, OCT angiography, PS-OCT, and AμT-OCE) may provide rich information about skin and demonstrate the potential for complex characterization of scar.

Automated analysis framework for in vivo cardiac ablation therapy monitoring with optical coherence tomography.

Radiofrequency ablation (RFA) is a minimally invasive procedure that is commonly used for the treatment of atrial fibrillation. However, it is associated with a significant risk of arrhythmia recurrence and complications owing to the lack of direct visualization of cardiac substrates and real-time feedback on ablation lesion transmurality. Within this manuscript, we present an automated deep learning framework for in vivo intracardiac optical coherence tomography (OCT) analysis of swine left atria. Our model can accurately identify cardiac substrates, monitor catheter-tissue contact stability, and assess lesion transmurality on both OCT intensity and polarization-sensitive OCT data. To the best of our knowledge, we have developed the first automatic framework for in vivo cardiac OCT analysis, which holds promise for real-time monitoring and guidance of cardiac RFA therapy..

Improved in vivo optical coherence tomography imaging of animal peripheral nerves using a prism nerve holder.

Modern optical volumetric imaging modalities, such as optical coherence tomography (OCT), provide enormous information about the structure, function, and physiology of living tissue. Although optical imaging achieves lateral resolution on the order of the wavelength of light used, and OCT achieves axial resolution on a similar micron scale, tissue optical properties, particularly high scattering and absorption, limit light penetration to only a few millimeters. In addition, in vivo imaging modalities are susceptible to significant motion artifacts due to cardiac and respiratory function. These effects limit access to artifact-free optical measurements during peripheral neurosurgery to only a portion of the exposed nerve without further modification to the procedure. We aim to improve in vivo OCT imaging during peripheral neurosurgery in small and large animals by increasing the amount of visualized nerve volume as well as suppressing motion of the imaged area. We designed a nerve holder with embedded mirror prisms for peripheral nerve volumetric imaging as well as a specific beam steering strategy to acquire prism and direct view volumes in one session with minimal motion artifacts. The axially imaged volumes from mirror prisms increased the OCT signal intensity by over a 1.25-mm imaging depth in tissue-mimicking phantoms. We then demonstrated the new imaging capabilities in visualizing peripheral nerves from direct and side views in living rats and minipigs using a polarization-sensitive OCT system. Prism views have shown nerve fascicles and vasculature from the bottom half of the imaged nerve which was not visible in direct view. We demonstrated improved OCT imaging during neurosurgery in small and large animals by combining the use of a prism nerve holder with a specifically designed beam scanning protocol. Our strategy can be applied to existing OCT imaging systems with minimal hardware modification, increasing the nerve tissue volume visualized. Enhanced imaging depth techniques may lead to a greater adoption of structural and functional optical biomarkers in preclinical and clinical medicine.

Local polarization properties extraction using single incident state, single-mode-fiber-based spectral domain polarization-sensitive optical coherence tomography.

We showed the local polarization properties extraction method for the single incident state, all-single-mode-fiber-based spectral domain polarization-sensitive optical coherence tomography (SD-PS-OCT) system that uses the single linear-in-wavenumber spectral camera. Polarization controllers are used in the single-mode-fiber-based SD-PS-OCT system to provide a compact structure with polarization state stability. The local polarization properties of the birefringent sample are extracted from the cumulative polarization properties iteratively. The reconstructed polarization images demonstrate the local polarization properties extraction ability of the system.

Quantifying airway remodelling for research or clinical purposes: How should we normalize for airway size?

Quantifying airway remodelling for research or clinical purposes: How should we normalize for airway size?

Measurement Method of Keyhole Depth in Laser Welding Based on Polarization Sensitive OCT

Measurement Method of Keyhole Depth in Laser Welding Based on Polarization Sensitive OCT

Quantitative assessment of depolarization by the retinal pigment epithelium in healthy and glaucoma subjects measured over a large field of view.

We present measurements of depolarization introduced by the retinal pigment epithelium (RPE) over a 45° field of view using polarization sensitive optical coherence tomography. A detailed spatial distribution analysis of depolarization caused by the RPE is presented in a total of 153 subjects including both healthy and diseased eyes. Age and sex related differences in the depolarizing character of the RPE are investigated.

Endoscopic imaging of white matter fiber tracts using polarization-sensitive optical coherence tomography

Polarization sensitive optical coherence tomography (PSOCT) has been shown to image and delineate white matter fibers in a label-free manner by revealing optical birefringence within the myelin sheath using a microscope setup. In this proof-of-concept study, we adapt recent advancements in endoscopic PSOCT to perform depth-resolved imaging of white matter structures deep inside intact porcine brain tissue ex-vivo, through a small, rotational fiber probe. The probe geometry is comparable to microelectrodes currently used in neurosurgical interventions. The presented imaging system is mobile, robust, and uses biologically safe levels of optical radiation making it well suited for clinical translation. In neurosurgery, where accuracy is imperative, endoscopic PSOCT through a narrow-gauge fiber probe could provide intra-operative feedback on the location of critical white matter structures.

Birefringent Properties of the Peripapillary Retinal Nerve Fiber Layer in Healthy and Glaucoma Subjects Analyzed by Polarization-Sensitive OCT.

To study the circumpapillary retinal nerve fiber layer (RNFL) birefringence (BIR) of early glaucoma and age-matched healthy eyes using polarization-sensitive optical coherence tomography (PS-OCT). In this prospective cross-sectional study, we compared virtual circular PS-OCT B-scans with a diameter of 3.5 mm centered on the optic disc (OD) acquired with a PS-OCT prototype (860 nm center wavelength). Early glaucoma was defined by the glaucomatous appearance of the OD and a pathologic visual field test with a mean deviation (MD) better than -6 dB. The main outcome parameters were BIR, RNFL-thickness (RNFL-T), and phase retardation (RET). The BIR value at each virtual A-scan position was the quotient of the RET measured at the inner segment/outer segment junction divided by the RNFL-T. The dataset comprised 49 early glaucoma patients (mean ± standard deviation [SD]: 64 ± 10 years) and 49 healthy control subjects (61 ± 9 years). Glaucomatous eyes showed a statistically significant lower BIR globally (mean ± SD: 0.108 ± 0.008°/µm vs. 0.112 ± 0.009°/µm, P = 0.033), superiorly (0.116 ± 0.017°/µm vs. 0.126 ± 0.013°/µm, P = 0.0001), and inferiorly (0.112 ± 0.011°/µm vs. 0.121 ± 0.011°/µm, P < 0.0001), and increased BIR in the temporal quadrant (0.088 ± 0.015°/µm vs. 0.078 ± 0.014°/µm, P = 0.0001) compared to healthy eyes. We report a reduced BIR of the RNFL in early perimetric glaucoma, which can be interpreted as a sign of loss or change of intracellular microtubules and may contribute to a better understanding of early disease development. Prospective longitudinal studies are needed to determine whether BIR is altered in pre-perimetric human glaucoma before RNFL-T decline.

Front Cover

Histological analysis is widely used to evaluate injured tendons; however, it has the limitation of being semi‐quantitative. Hence, a quantification method to objectively evaluate the fibrous structure of tendons was developed with exhibiting the optical property of birefringence by using polarization‐sensitive optical coherence tomography (PS‐OCT). The phase retardation images was quantified according to the degree of repetition of the period. The obtained frequency value of the peak from the Fourier transform of the periodic pattern in the phase retardation image indicates the degree of the structural arrangement of collagen fibers. The better the arrangement of the collagen fibers results the higher the frequency values, and a disordered collagen fiber architecture results in a lower repetition frequency value. The scoring method well represented the fibrous structural changes of the injured Achilles tendon according to the wound healing state with a partial‐rupture rat model. Further details can be found in the article by Yong‐Jae Lee, Eunwoo Park, Kwan Seob Park, Jun‐Hyuk Lim, Sungmin Kim, Myung‐Sun Kim, and Tae Joong Eom (e202200065).image