Polarization-sensitive Optical Coherence Tomography Research Articles

Suppression of autocorrelation artifacts in PS-OCT images based on spectral phase interpolation

Polarization-maintaining (PM) fiber-based polarization-sensitive optical coherence tomography (PS-OCT) system has high stability and portability. However, PM fibers may introduce different kinds of artifacts. A spectral phase interpolation method is proposed to suppress the autocorrelation artifacts in this Letter, in which the reference phase is calculated based on each A-scan signal, and the calculated reference phase is used to perform phase interpolation in the original interference signal. Experimental results from the ex vivo porcine eye demonstrate that autocorrelation artifacts in PS-OCT images can be effectively eliminated and the original image information is perfectly recovered at artifacts.

Synthetic polarization-sensitive optical coherence tomography using contrastive unpaired translation

Polarization-sensitive optical coherence tomography (PS-OCT) measures the polarization state of backscattered light from tissues and provides valuable insights into the birefringence properties of biological tissues. Contrastive unpaired translation (CUT) was used in this study to generate a synthetic PS-OCT image from a single OCT image. The challenges related to extensive data requirements relying on labeled datasets using only pixel-wise correlations that make it difficult to efficiently regenerate the periodic patterns observed in PS-OCT images were addressed. The CUT model captures birefringence patterns by leveraging patch-wise correlations from unpaired data, which allows learning of the underlying structural features of biological tissues responsible for birefringence. To demonstrate the performance of the proposed approach, three generative models (Pix2pix, CycleGAN, and CUT) were compared on an in vivo dataset of injured mouse tendons over a six-week healing period. CUT outperformed Pix2pix and CycleGAN by producing high-fidelity synthetic PS-OCT images that closely matched the original PS-OCT images. Pearson correlation and two-way ANOVA tests confirmed the superior performance of CUT (p-value < 0.0001) over the comparison models. Additionally, a ResNet-152 classification model was used to assess tissue damage, which achieved an accuracy of up to 90.13% compared to the original PS-OCT images. This research demonstrates that CUT is superior to conventional methods for generating high-quality synthetic PS-OCT images and offers better improvements in most scenarios, in terms of efficiency and image fidelity.

From Cellular to Metabolic: Advances in Imaging of Inherited Retinal Diseases.

Background: Inherited retinal diseases (IRDs) are a genetically complex group of disorders, usually resulting in progressive vision loss due to retinal degeneration. Traditional imaging methods help in structural assessments, but limitations exist in early functional cellular-level detection that are crucial for guiding new therapies. Methods: This review includes a systematic search of PubMed and Google Scholar for studies on advanced imaging techniques for IRDs. Results: Key modalities covered are adaptive optics, fluorescence lifetime imaging ophthalmoscopy, polarization-sensitive optical coherence tomography, optoretinography, mitochondrial imaging, flavoprotein fluorescence imaging, and retinal oximetry. Each imaging method covers its principles, acquisition techniques, data from healthy eyes, applications in IRDs with specific examples, and current challenges and future directions. Conclusions: Emerging technologies, including adaptive optics and metabolic imaging, offer promising potential for cellular-level imaging and functional correlation in IRDs, allowing for earlier intervention and improved therapeutic targeting. Their integration into clinical practice may significantly improve IRD management and patient outcomes.

Visualization of the Scleral Structure Changes at Various Stages of Eyes With Myopic Maculopathy Using Polarization-Sensitive OCT

PurposeTo observe the detailed structures of the inner and outer sclera at various stages of myopic maculopathy using polarization-sensitive optical coherence tomography (PS-OCT). MethodsA PS-OCT system was developed for imaging the posterior eye using a swept laser. Data from highly myopic patients who underwent PS-OCT examination between May and June 2019 were used to generate birefringence images (showing scleral fiber density), optic axis images (visualizing the orientation of scleral fibers), and streamline images (providing 3D reconstructions to visualize scleral fiber stream). ResultsA total of 89 eyes of 65 patients with high myopia were examined and analyzed for this study. The mean axial length was 30.4 ± 1.8mm. In highly myopic eyes with a thin choroid, PS-OCT visualized the detailed structure of the sclera, and the optic axis images differentiated the direction of the inner and outer scleral fibers. In the optic axis and streamline images, the inner layer of the sclera contained radial fibers extending from the optic disc. In contrast, the outer layer of the sclera contained vertical fibers. With the progression of myopia, highly birefringent fibers first disappear in the inner scleral layer, followed by thinning of the inner layer itself. Subsequently, in the outer scleral layer, the number of highly birefringent fibers decreased. As myopic maculopathy worsened, the inner and outer layers of the sclera disintegrated. ConclusionsPS-OCT is useful for observing the structures of the inner and outer sclera in various conditions of myopic maculopathy.

In vivo retinal melanin detection with the calibrated depolarization index in polarization-sensitive optical coherence tomography.

A data-based calibration method with enhanced depolarization contrast in polarization-sensitive optical coherence tomography (PS-OCT) was developed and demonstrated effective for detecting melanin content in the eye. We aim to mitigate the dependence between the measured depolarization metric and the intensity signal-to-noise ratio (SNR) for improved visualization of depolarizing tissues, especially in low SNR regions, and to demonstrate the enhanced depolarization contrast to evaluate melanin presence. A function for calibrating the depolarization metric was experimentally derived from the young albino guinea pig, assuming depolarization free in the retina. A longitudinal study of guinea pigs (9 weeks) was conducted to assess the accumulation of melanin during early eye growth. Furthermore, the melanin content of the sub-macular choroid was compared in eyes with light and dark irides involving 14 human subjects in early middle adulthood. We observed an increase in the improved depolarization contrast, which indicates potential melanin accumulation in the early eye development with age in the pigmented guinea pig eyes. We found a significant difference in melanin content between human eyes with light and dark colors. Our proposed calibration method enhanced the visualization of depolarizing structures in PS-OCT, which can be generalized to all kinds of polarization-sensitive imaging and can potentially monitor melanin in healthy and pathological eyes.

Absolute depth-resolved optic axis measurement with catheter-based polarization sensitive optical coherence tomography.

Imaging depth-resolved birefringence and optic axis orientation with polarization sensitive optical coherence tomography (PS-OCT) unveils details of tissue structure and organization that can be of high pathophysiologic, mechanistic, and diagnostic value. For catheter-based PS-OCT, the dynamic rotation of the fiber optic probe, in addition to the polarization effects of the system components, complicates the reliable and robust reconstruction of the sample's optic axis orientation. Addressing this issue, we present a new method for the reconstruction of absolute depth-resolved optic axis orientation in catheter-based PS-OCT by using the intrinsic retardance of the protecting catheter sheath as a stable guide star signal. Throughout the paper, we rigorously inspect the retardance and optic axis orientation of the sheath and validate our method by imaging a birefringent phantom with known optic axis orientation. Reconstructing the optic axis orientation of the phantom, placed at different locations around the catheter, we measured an average absolute deviation (AAD) for the mean optic axis orientation over cross-sectional images of 3.28°, even with significant bending stress on the catheter. This corresponds to an almost three-fold improvement compared to our earlier method (optic axis AAD of 9.41°). We finally highlight the capability of our reconstruction with stereotactic catheter-based PS-OCT of a fresh sheep brain.

Accurately differentiating inflamed and healthy tissue samples by removing errors and noises in depth-resolved polarization parameter images

The fiber-optics-based Mueller matrix polarization sensitive optical coherence tomography (PSOCT) can measure the complete depth-resolved Mueller matrices of biological samples and is a choice for practical clinical applications. To quantitatively interpret the measurement results, the system errors and the detection noise in a fiber-optics-based PSOCT are analyzed, simulated and eliminated. The depth-resolved polarization parameter images of the skin of inflamed and healthy mice are presented to demonstrate that the system has the capability of accurately differentiating between normal and diseased tissues. In addition, the values of the polarization parameters after removing the noise and their changes with depth may be helpful quantitative diagnosis of the diseases and the evaluation of the treatment.

Evaluating the effect of partially polarized light sources on the point spread function in optical coherence tomography

Leveraging the polarization property of light to evaluate the birefringence of tissues as well as changes due to pathological conditions has been gaining interest over the past two decades with the introduction of different variants of optical coherence tomography (OCT) including polarization-sensitive OCT (PS-OCT) and cross-polarization OCT (CP-OCT). Because OCT sources are partially polarized, PS-OCT and CP-OCT generally require a linear polarizer and polarization-maintaining fibers to enable a linearly polarized input beam into the interferometer. While recent studies have suggested using an unpolarized input beam to reduce the system’s complexity, the effect of unpolarized light on the point spread function (PSF) of OCT has not been fully studied. This work proposed a mathematical framework to evaluate the contribution of unpolarized light to the PSF of OCT. Simulation and experiments were performed for three OCT sources to assess the validity of the proposed model. Overall, simulations were in good agreement with experiments and revealed that unpolarized light introduced two additional reflectors into the reflectivity profile of the source, which were more pronounced in the cross-polarization configuration. This additional information can lead to misinterpretation of the birefringence of tissues in PS-OCT and CP-OCT. Their effect on image quality was evaluated in ex vivo corneal imaging of porcine eyeballs.

Association of polarimetric signatures with coronary plaque composition in patients with acute and chronic coronary syndrome: an intravascular polarization-sensitive optical coherence tomography study

Abstract Background Intravascular polarimetry with polarization-sensitive (PS-) optical coherence tomography (OCT) measures polarization properties, birefringence and depolarization, in parallel with structural features available with conventional OCT (Figure 1). Birefringence is elevated in collagen and collagen-synthesizing smooth muscle cells, which imparts mechanical integrity to fibrous caps. Depolarization is elevated in the presence of macrophages and lipid/necrotic core. Purpose This study aimed to investigate polarimetric signatures of coronary lesions in patients with acute coronary syndrome (ACS) and chronic coronary syndrome (CCS). Furthermore, we aimed to investigate diagnostic value for birefringence and depolarization of ACS culprit lesions discriminating from CCS target lesions. Methods This was the first-in-human study of intracoronary PS-OCT in Japan, consisting of 17 patients with ACS (n = 5) or CCS (n = 12) who underwent intravascular PS-OCT. ACS culprit lesions (ACS-lesions) and CCS target lesions (CCS-lesions) were included in the analysis, resulting in a total of 862 cross-sections. In the cross-sectional images, lumen segmentation and guidewire artifact were automatically segmented. The median value of birefringence and depolarization were automatically analyzed using depolarization cut-off value (cross-sectional level). Birefringence and depolarization of ACS- and CCS-lesions were compared by using a generalized estimating equation model. Receiver operating characteristic (ROC) analysis was used to investigate diagnostic performance of polarimetric signatures for the identification of ACS-lesions. Results Compared to CCS-lesions, ACS-lesions featured higher lipid-burden index and maximum lipid arc (both p &amp;lt; 0.05). Compared to the CCS-lesions, ACS-lesions exhibited significantly lower birefringence (p &amp;lt; 0.05) and higher depolarization (p &amp;lt; 0.05) (Figure 2). In the ROC analysis for differentiating ACS-lesions from CCS-lesions, area under the curves (AUC) for birefringence and depolarization were 0.712 and 0.672, respectively. In the multivariable ROC analysis in diagnosing ACS lesions, combination of birefringence with depolarization improved the AUC to 0.755 (p ＝ 0.025). Conclusions Intravascular PS-OCT provides quantitative compositional assessment of coronary lesions. Decreased birefringence and pronounced depolarization within the ACS-lesions indicate increased collagenolytic activity and the presence of macrophage infiltration, respectively. These results suggest that polarization properties may serve as quantitative imaging markers for assessing natural history of coronary atherosclerosis.

Minimize flow-induced uncertainty in polarization sensitive optical coherence tomography imaging using eigen decomposition.

Blood flow alters the scattering behavior of penetration light, causing instability in the polarization state to emerge at the underlying tissue during polarization-sensitive optical coherence tomography (PSOCT). We propose an eigen decomposition method to meet this challenge, where the static and dynamic scattering signals are separated for PSOCT to provide the polarization measurements of the tissue of interest that is located beneath the blood flow. Using flow phantoms made by Intralipid solution and 3D-printed birefringent material, we show the flow-induced effects on the measurements of sample birefringent properties of optical axis, phase retardation, and degree of polarization uniformity. We demonstrate the usefulness of the proposed method through in vivo imaging of the human nail fold.

Polarization-sensitive optical coherence tomography and scleral collagen fiber orientation in osteogenesis imperfecta

Osteogenesis imperfecta (OI), a rare genetic connective tissue disorder, primarily arises from pathogenic variants affecting the production or structure of collagen type I. In addition to skeletal fragility, individuals with OI may face an increased risk of developing ophthalmic diseases. This association is believed to stem from the widespread presence of collagen type I throughout various parts of the eye. However, the precise consequences of abnormal collagen type I on different ocular tissues remain unknown. Of particular significance is the sclera, where collagen type I is abundant and crucial for maintaining the structural integrity of the eye. Recent research on healthy individuals has uncovered a unique organizational pattern of collagen fibers within the sclera, characterized by fiber arrangement in both circular and radial layers around the optic nerve head. While the precise function of this organizational pattern remains unclear, it is hypothesized to play a role in providing mechanical support to the optic nerve. The objective of this study is to investigate the impact of abnormal collagen type I on the sclera by assessing the fiber organization near the optic nerve head in individuals with OI and comparing them to healthy individuals. Collagen fiber orientation of the sclera was measured using polarization-sensitive optical coherence tomography (PS-OCT), an extension of the conventional OCT that is sensitive to materials that exhibit birefringence (axial changes in light refraction). Birefringence was quantified and used as imaging contrast to extract collagen fiber orientation as well as the thickness of the radially oriented scleral layer. Three individuals with OI, exhibiting different degrees of disease severity, were assessed and analyzed, along with seventeen healthy individuals. Mean values obtained from individuals with OI were descriptively compared to those of the healthy participant group. PS-OCT revealed a similar orientation pattern of scleral collagen fibers around the optic nerve head between OI individuals and healthy individuals. However, two OI participants exhibited reduced mean birefringence of the radially oriented scleral layer compared to the healthy participant group (OI participant 1 oculus dexter et sinister (ODS): 0.34°/μm, OI participant 2: ODS 0.26°/μm, OI participant 3: OD: 0.29°/μm, OS: 0.28°/μm, healthy participants: ODS 0.38 ± 0.05°/μm). The radially oriented scleral layer was thinner in all OI participants although within ±2 standard deviations of the mean observed in healthy individuals (OI participant 1 OD: 101 μm, OS 104 μm, OI participant 2: OD 97 μm, OS 98 μm, OI participant 3: OD: 94 μm, OS 120 μm, healthy participants: OD 122.8 ± 13.6 μm, OS 120.8 ± 15.1 μm). These findings imply abnormalities in collagen organization or composition, underscoring the necessity for additional research to comprehend the ocular phenotype in OI.

Cartesian coordinates transformation for backscattering computational polarimetry.

Computational Mueller matrix polarimetry holds great promise in biomedical studies and clinical applications, providing comprehensive polarization-related vectorial information within the sample. For backscattering polarization imaging systems aimed at in vivo tissue polarimetry, the measurement results can be affected by the Cartesian coordinates transformation due to the vectorial properties of polarized light and the non-collinear characteristics of the measurement system. It can influence the reliability of polarization information decoding and extraction. In this study, we elucidate the coupling effects of the photon and space coordinate systems on the backscattering computational polarimetry and provide complete solutions regarding the Cartesian coordinates transformation. We systematically derive the specific forms of the Mueller matrix elements under all combinations of Cartesian coordinates and demonstrate their interconversion relationships. From anisotropic modulus and direction perspectives, we further investigate the influence mechanism of Cartesian coordinates transformation on different polarization effects. Particularly, polarimetric parameters characterizing anisotropic direction exhibit sensitivity features of true negatives or false positives. Based on theoretical analysis and experimental results, we finally propose correction strategies based on photon and space coordinate system markers. Our study will provide significant insights and references for in vivo research and applications of biomedical optics and biophotonics involving coordinate system selection and transformation such as polarimetric endoscopes, full polarization biosensors, and polarization-sensitive optical coherence tomography.

Three-dimensional fiber orientation mapping of the human brain at micrometer resolution.

The accurate measurement of three-dimensional (3D) fiber orientation in the brain is crucial for reconstructing fiber pathways and studying their involvement in neurological diseases. Comprehensive reconstruction of axonal tracts and small fascicles requires high-resolution technology beyond the ability of current in vivo imaging (e.g. diffusion magnetic resonance imaging). Optical imaging methods such as polarization-sensitive optical coherence tomography (PS-OCT) and polarization microscopy can quantify fiber orientation at micrometer resolution but have been limited to two-dimensional in-plane orientation or thin slices, preventing the comprehensive study of connectivity in 3D. In this work we present a novel method to quantify volumetric 3D orientation in full angular space with PS-OCT. We measure the polarization contrasts of the brain sample from two illumination angles of 0 and 15 degrees and apply a computational method that yields the 3D optic axis orientation and true birefringence. We further present 3D fiber orientation maps of entire coronal cerebrum sections and brainstem with 10 μm in-plane resolution, revealing unprecedented details of fiber configurations. We envision that our method will open a promising avenue towards large-scale 3D fiber axis mapping in the human brain as well as other complex fibrous tissues at microscopic level.

Imaging of developing human brains with ex vivo PSOCT and dMRI.

The human brain undergoes substantial developmental changes in the first five years of life. Particularly in the white matter, myelination of axons occurs near birth and continues at a rapid pace during the first 2 to 3 years. Diffusion MRI (dMRI) has revolutionized our understanding of developmental trajectories in white matter. However, the mm-resolution of in vivo techniques bears significant limitation in revealing the microstructure of the developing brain. Polarization sensitive optical coherence tomography (PSOCT) is a three-dimensional (3D) optical imaging technique that uses polarized light interferometry to target myelinated fiber tracts with micrometer resolution. Previous studies have shown that PSOCT contributes significantly to the elucidation of myelin content and quantification of fiber orientation in adult human brains. In this study, we utilized the PSOCT technique to study developing brains during the first 5 years of life in combination with ex vivo dMRI. The results showed that the optical properties of PSOCT quantitatively reveal the myelination process in young children. The imaging contrast of the optic axis orientation is a sensitive measure of fiber orientations in largely unmyelinated brains as young as 3-months-old. The micrometer resolution of PSOCT provides substantially enriched information about complex fiber networks and complements submillimeter dMRI. This new optical tool offers great potential to reveal the white matter structures in normal neurodevelopment and developmental disorders in unprecedented detail.

Identification of pathological characteristics in pulmonary tuberculosis using polarization-sensitive optical coherence tomography

The low detection rate of Mycobacterium tuberculosis in clinical practice leads to a high rate of missed diagnosis for pulmonary tuberculosis (PTB). As a noninvasive, high-resolution, real-time imaging technology, polarization-sensitive optical coherence tomography (PS-OCT) may be feasible for the rapid identification of pathological feature. This study aimed to explore the feasibility of using PS-OCT to identify pathological features of PTB. In the experiments, PTB samples containing some surrounding lung tissues were imaged using PS-OCT. It is demonstrated that PS-OCT images showed good consistency with the corresponding pathological images and were able to identify PTB-related characteristic pathological regions. We think PS-OCT can serve as an effective supplement for the diagnosis of PTB, enabling rapid and accurate diagnosis, and aiding in the understanding of the pathological characteristics and pathophysiological processes of PTB.

Multimodal imaging analysis of autosomal recessive bestrophinopathy: Case series.

Autosomal recessive bestrophinopathy (ARB) is a subtype of bestrophinopathy caused by biallelic mutations of the BEST1 gene, which affect the retinal pigment epithelium (RPE). Studying RPE abnormalities through imaging is essential for understanding ARB. This case series involved the use of multimodal imaging techniques, namely autofluorescence (AF) imaging at 488 nm [short-wavelength AF] and 785 nm [near-infrared AF (NIR-AF)] and polarization-sensitive optical coherence tomography (PS-OCT), to investigate RPE changes in 2 siblings with ARB. Two Japanese siblings (Case 1: male, followed for 20-23 years; Case 2: female, followed for 13-17 years) carried compound heterozygous mutations of the BEST1 gene. Both siblings were diagnosed with ARB. Multimodal imaging techniques were used to evaluate RPE changes. Both siblings had funduscopic changes similar to those seen in the vitelliruptive stage of Best vitelliform macular dystrophy during the follow-up period. NIR-AF imaging showed hypo-AF of the entire macular lesion in both cases, and this hypo-AF remained stable over time. PS-OCT confirmed reduced RPE melanin content in these hypo-AF areas. Additionally, hyper-NIR-AF dots were observed within hypo-NIR-AF areas. Concomitant identification of focally thickened RPE melanin on PS-OCT imaging and hyper-AF on short-wavelength AF imaging at the sites containing hyper-NIR-AF dots indicated that the hyper-NIR-AF dots had originated from either stacked RPE cells or RPE dysmorphia. We confirmed RPE abnormalities in ARB, including diffuse RPE melanin damage in the macula alongside evidence of RPE activity-related changes. This case series demonstrates that multimodal imaging, particularly NIR-AF and PS-OCT, provides detailed insights into RPE alterations in ARB.

Polarization-resolved analysis of outer retinal bands: investigating ballistic and multiply scattered photons using full-field swept-source optical coherence tomography.

Precise interpretation of the anatomical origins of outer retinal optical coherence tomography (OCT) presents technical challenges owing to the delicate nature of the retina. To address this challenge, our study introduces a novel polarization-sensitive full-field swept-source OCT (FF-SS-OCT) that provides parallel-polarization and cross-polarization OCT measurements, predominantly capturing ballistically reflected photons and multiply scattered photons, respectively. Notably, parallel-polarization OCT unveils layer-like structures more effectively, including the inner plexiform layer (IPL) sub-layers, outer plexiform layer (OPL) sub-layers (in rod-dominant regions), and rod/cone outer segment (OS) tips, compared to cross-polarization OCT, where such sub-layers are not visible. Through a comparative analysis of parallel-polarization and cross-polarization OCT images of the outer retina, we discovered that the 2nd outer retinal OCT band results from contributions from both the ellipsoid zone (EZ) and the inner segment/outer segment (IS/OS) junction. Similarly, the 3rd outer retinal OCT band appears to reflect contributions from both the interdigitation zone (IZ) and photoreceptor OS tips. This polarization-sensitive approach advances our understanding of the origins of outer retinal OCT signals and proposes potential new biomarkers for assessing retinal health and diseases.

Insights into atypical segmental layer thicknesses and phase retardation in thick corneas using ultrahigh-resolution polarization-sensitive optical coherence tomography

BackgroundAccurately assessing corneal structural status is challenging when thickness deviates from the average. Polarization-sensitive optical coherence tomography (PS-OCT) measures tissue-specific polarization changes, providing additional contrast for accurate segmentations and aids in phase retardation (PR) measurements. Previous studies have shown PR's effectiveness in identifying sub-clinical keratoconus (KC) in asymmetric cases. Thus, this study aims to assess PR distribution in thick corneas with and without KC.MethodsIn this retrospective and cross-sectional study, 45 thick corneas from 30 Asian-Indian subjects, categorized into healthy (n = 26) and KC (n = 19) groups were analyzed. All eyes underwent standard clinical evaluations, tomographic assessments, and corneal biomechanics measurements. PR and individual layer thicknesses were measured using custom-designed ultrahigh-resolution PS-OCT. PR en-face maps were generated. Individual layer thicknesses and PR analysis was conducted across multiple zones, extending up to 8–10 mm in diameter. All eyes in the study had not undergone interventions, received topical medications, or had previous corneal disease history.ResultsSignificant differences were found in spherical and cylindrical powers, keratometry, pachymetry, and biomechanical indices (all P < 0.01). Thickness profiles from PS-OCT showed significant differences in the 4–8 mm zones only. Bowman's layer thickness significantly differed only in the central 2 mm zone (P = 0.02). The median PR values showed marginal differences in the central 2 mm zone (P = 0.0565). Additionally, there were significant differences observed in the 2–4 mm and 4–6 mm zones (P = 0.0274 and P = 0.0456, respectively). KC eyes exhibited an atypical PR distribution and corneal thinning, while normal eyes maintained a uniform Bowman’s layer thickness and PR maps with larger areas of higher PR.ConclusionThe study revealed distinctive PR distribution in thick corneas among healthy and KC groups. Using an ultrahigh-resolution PS-OCT the significance of Bowman's layer thickness in these groups was also emphasized. The study offered potential improvements in clinical diagnostics by enhancing our understanding of corneal structure and its altered function.

Light-scattering-induced retardation as a high-sensitivity image contrast revealing collagen fibers.

Retardation induced by media can be used as an image contrast to depict the cumulative birefringent features and local variations of the sample, respectively. It is commonly assumed that the retardation is induced by the light propagation; however, the light scattering would generate the retardation as well. In our work, the scattering-induced retardation as a high-sensitivity image contrast for revealing collagen fibers is presented. First, it is shown that the retardation induced by fiber scattering is equal to π when modeled as cylinders. Using the data for the chicken breast and the palm measured by the polarization-sensitive optical coherence tomography system as an example, the scattering-induced retardation is calculated. The measured value of π is in complete agreement with the theory, and the corresponding retardation per unit distance is two orders of magnitude greater than the light-propagation-induced retardation, demonstrating its predominant role on the overall retardation and providing a possibility for highly sensitive displays. Compared with the accumulated retardation image and the differential retardation image, the scattering-induced retardation images could exhibit sharper fiber structures even in deeper regions. This work might be helpful for the early diagnosis of collagen-related diseases.

Assessing Lung Fibrosis with ML-Assisted Minimally Invasive OCT Imaging.

This paper presents a combined optical coherence tomography (OCT) imaging/machine learning (ML) technique for real-time analysis of lung tissue morphology to determine the presence and level of invasiveness of idiopathic lung fibrosis (ILF). This is an important clinical problem as misdiagnosis is common, resulting in patient exposure to costly and invasive procedures and substantial use of healthcare resources. Therefore, biopsy is needed to confirm or rule out radiological findings. Videoscopic-assisted thoracoscopic wedge biopsy (VATS) under general anesthesia is typically necessary to obtain enough tissue to make an accurate diagnosis. This kind of biopsy involves the placement of several tubes through the chest wall, one of which is used to cut off a piece of lung to send for evaluation. The removed tissue is examined histopathologically by microscopy to confirm the presence and the pattern of fibrosis. However, VATS pulmonary biopsy can have multiple side effects, including inflammation, tissue morbidity, and severe bleeding, which further degrade the quality of life for the patient. Furthermore, the results are not immediately available, requiring tissue processing and analysis. Here, we report an initial attempt of using ML-assisted polarization sensitive OCT (PS-OCT) imaging for lung fibrosis assessment. This approach has been preliminarily tested on a rat model of lung fibrosis. Our preliminary results show that ML-assisted PS-OCT imaging can detect the presence of ILF with an average of 77% accuracy and 89% specificity.