Application of optical coherence tomography in clinical diagnosis

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.

Depth of intact vascular plexus - visualized with optical coherence tomography - correlates to burn depth in thoracic thermic injuries in children

Objectives

Deep thermal injuries are among the most serious injuries in childhood, often resulting in scarring and functional impairment. However, accurate assessment of burn depth by clinical judgment is challenging. Optical coherence tomography (OCT) provides structural images of the skin and can detect blood flow within the papillary plexus. In this study, we determined the depth of the capillary network in healthy and thermally injured skin and compared it with clinical assessment.

Methods

In 25 children between 7 months and 15 years of age (mean age 3.5 years (SD±4.14)) with thermal injuries of the ventral thoracic wall, we determined the depth of the capillary network using OCT. Measurements were performed on healthy skin and at the center of the thermal injury (16 grade IIa, 9 grade IIb). Comparisons were made between healthy skin and thermal injury.

Results

The capillary network of the papillary plexus in healthy skin was detected at 0.33 mm (SD±0.06) from the surface. In grade IIb injuries, the depth of the capillary network was 0.36 mm (SD±0.06) and in grade IIa injuries 0.23 mm (SD±0.04) (Mann-Whitney U test: p<0.001). The overall prediction accuracy is 84 %.

Conclusions

OCT can reliably detect and differentiate the depth of the capillary network in both healthy and burned skin. In clinical IIa wounds, the capillary network appears more superficial due to the loss of the epidermis, but it is still present in the upper layer, indicating a good prognosis for spontaneous healing. In clinical grade IIb wounds, the papillary plexus was visualized deeper, which is a sign of impaired blood flow.

Effect of skin color on optical properties and the implications for medical optical technologies: a review

Significance

Skin color affects light penetration leading to differences in its absorption and scattering properties. COVID-19 highlighted the importance of understanding of the interaction of light with different skin types, e.g., pulse oximetry (PO) unreliably determined oxygen saturation levels in people from Black and ethnic minority backgrounds. Furthermore, with increased use of other medical wearables using light to provide disease information and photodynamic therapies to treat skin cancers, a thorough understanding of the effect skin color has on light is important for reducing healthcare disparities.

Aim

The aim of this work is to perform a thorough review on the effect of skin color on optical properties and the implication of variation on optical medical technologies.

Approach

Published in vivo optical coefficients associated with different skin colors were collated and their effects on optical penetration depth and transport mean free path (TMFP) assessed.

Results

Variation among reported values is significant. We show that absorption coefficients for dark skin are ∼ 6 % to 74% greater than for light skin in the 400 to 1000 nm spectrum. Beyond 600 nm, the TMFP for light skin is greater than for dark skin. Maximum transmission for all skin types was beyond 940 nm in this spectrum. There are significant losses of light with increasing skin depth; in this spectrum, depending upon Fitzpatrick skin type (FST), on average 14% to 18% of light is lost by a depth of 0.1 mm compared with 90% to 97% of the remaining light being lost by a depth of 1.93 mm.

Conclusions

Current published data suggest that at wavelengths beyond 940 nm light transmission is greatest for all FSTs. Data beyond 1000 nm are minimal and further study is required. It is possible that the amount of light transmitted through skin for all skin colors will converge with increasing wavelength enabling optical medical technologies to become independent of skin color.

Automated deep learning-based AMD detection and staging in real-world OCT datasets (PINNACLE study report 5)

Real-world retinal optical coherence tomography (OCT) scans are available in abundance in primary and secondary eye care centres. They contain a wealth of information to be analyzed in retrospective studies. The associated electronic health records alone are often not enough to generate a high-quality dataset for clinical, statistical, and machine learning analysis. We have developed a deep learning-based age-related macular degeneration (AMD) stage classifier, to efficiently identify the first onset of early/intermediate (iAMD), atrophic (GA), and neovascular (nAMD) stage of AMD in retrospective data. We trained a two-stage convolutional neural network to classify macula-centered 3D volumes from Topcon OCT images into 4 classes: Normal, iAMD, GA and nAMD. In the first stage, a 2D ResNet50 is trained to identify the disease categories on the individual OCT B-scans while in the second stage, four smaller models (ResNets) use the concatenated B-scan-wise output from the first stage to classify the entire OCT volume. Classification uncertainty estimates are generated with Monte-Carlo dropout at inference time. The model was trained on a real-world OCT dataset, 3765 scans of 1849 eyes, and extensively evaluated, where it reached an average ROC-AUC of 0.94 in a real-world test set.

In vivo real-time assessment of developmental defects in enamel of anti-Act1 mice using optical coherence tomography

The purpose of this study was to explore the feasibility of using optical coherence tomography (OCT) for real-time and quantitative monitoring of enamel development in gene-edited enamel defect mice. NF-κB activator 1, known as Act1, is associated with many inflammatory diseases. The antisense oligonucleotide of Act1 was inserted after the CD68 gene promoter, which would cover the start region of the Act1 gene and inhibit its transcription. Anti-Act1 mice, gene-edited mice, were successfully constructed and demonstrated amelogenesis imperfecta by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy. Wild-type (WT) mice were used as the control group in this study. WT mice and anti-Act1 mice at 3 weeks old were examined by OCT every week and killed at eight weeks old. Their mandibular bones were dissected and examined by OCT, micro-computed tomography (micro-CT), and SEM. OCT images showed that the outer layer of enamel of anti-Act1 mice was obviously thinner than that of WT mice but no difference in total thickness. When assessing enamel thickness, there was a significant normal linear correlation between these methods. OCT could scan the imperfect developed enamel noninvasively and quickly, providing images of the enamel layers of mouse incisors.

In vivo characterization of cerebrovascular impairment induced by amyloid β peptide overload in glymphatic clearance system using swept-source optical coherence tomography

SIGNIFICANCE

Antiamyloid β ( A β ) immunotherapy is a promising therapeutic strategy for Alzheimer's disease (AD) but generates large amounts of soluble A β peptides that could overwhelm the clearance pathway, leading to serious side effects. Direct implications of A β in glymphatic drainage transport for cerebral vasculature and tissue are not well known. Studies are needed to resolve this issue and pave the way to better monitoring abnormal vascular events that may occur in A β -modifying therapies for AD.

AIM

The objective is to characterize the modification of cerebral vasculature and tissue induced by soluble A β abundantly present in the glymphatic clearance system.

APPROACH

A β 1 - 42 peptide was injected intracerebroventricularly and swept-source optical coherence tomography (SS-OCT) was used to monitor the progression of changes in the brain microvascular network and tissue in vivo over 14 days. Parameters reflecting vascular morphology and structure as well as tissue status were quantified and compared before treatment.

RESULTS

Vascular perfusion density, vessel length, and branch density decreased sharply and persistently following peptide administration. In comparison, vascular average diameter and vascular tortuosity were moderately increased at the late stage of monitoring. Endpoint density gradually increased, and the global optical attenuation coefficient value decreased significantly over time.

CONCLUSIONS

A β burden in the glymphatic system directly contributes to cerebrovascular structural and morphological abnormalities and global brain tissue damage, suggesting severe deleterious properties of soluble cerebrospinal fluid- A β . We also show that OCT can be used as an effective tool to monitor cerebrovascular dynamics and tissue property changes in response to therapeutic treatments in drug discovery research.

Retinal imaging using adaptive optics optical coherence tomography with fast and accurate real-time tracking

One of the main obstacles in high-resolution 3-D retinal imaging is eye motion, which causes blur and distortion artifacts that require extensive post-processing to be corrected. Here, an adaptive optics optical coherence tomography (AOOCT) system with real-time active eye motion correction is presented. Correction of ocular aberrations and of retinal motion is provided by an adaptive optics scanning laser ophthalmoscope (AOSLO) that is optically and electronically combined with the AOOCT system. We describe the system design and quantify its performance. The AOOCT system features an independent focus adjustment that allows focusing on different retinal layers while maintaining the AOSLO focus on the photoreceptor mosaic for high fidelity active motion correction. The use of a high-quality reference frame for eye tracking increases revisitation accuracy between successive imaging sessions, allowing to collect several volumes from the same area. This system enables spatially targeted retinal imaging as well as volume averaging over multiple imaging sessions with minimal correction of motion in post processing.

In vivo optical molecular imaging of inflammation and immunity

Inflammation is the phenotypic form of various diseases. Recent development in molecular imaging provides new insights into the diagnostic and therapeutic evaluation of different inflammatory diseases as well as diseases involving inflammation such as cancer. While conventional imaging techniques used in the clinical setting provide only indirect measures of inflammation such as increased perfusion and altered endothelial permeability, optical imaging is able to report molecular information on diseased tissue and cells. Optical imaging is a quick, noninvasive, nonionizing, and easy-to-use diagnostic technology which has been successfully applied for preclinical research. Further development of optical imaging technology such as optoacoustic imaging overcomes the limitations of mere fluorescence imaging, thereby enabling pilot clinical applications in humans. By means of endogenous and exogenous contrast agents, sites of inflammation can be accurately visualized in vivo. This allows for early disease detection and specific disease characterization, enabling more rapid and targeted therapeutic interventions. In this review, we summarize currently available optical imaging techniques used to detect inflammation, including optical coherence tomography (OCT), bioluminescence, fluorescence, optoacoustics, and Raman spectroscopy. We discuss advantages and disadvantages of the different in vivo imaging applications with a special focus on targeting inflammation including immune cell tracking.

Non-invasive three-dimensional thickness analysis of oral epithelium based on optical coherence tomography-development and diagnostic performance

Objectives

Evaluating structural changes in oral epithelium can assist with the diagnosis of cancerous lesions. Two-dimensional (2D) non-invasive optical coherence tomography (OCT) is an established technique for this purpose. The objective of this study was to develop and test the diagnostic accuracy of a three-dimensional (3D) evaluation method.

Methods

The oral lip mucosa of 10 healthy volunteers was scanned using an 870-nm spectral-domain OCT device (SD-OCT) with enhanced depth imaging (EDI). Four raters semi-automatically segmented the epithelial layer twice. Thus, eighty 3D datasets were created and analyzed for epithelial thickness. To provide a reference standard for comparison, the raters took cross-sectional 2D measurements at representative sites. The correlation between the 2D and 3D measurements, as well as intra- and inter-rater reliability, were analyzed using intraclass correlation coefficients (ICC).

Results

Mean epithelial thickness was 280 ± 64μm (range 178–500 μm) and 268 ± 49μm (range 163–425 μm) for the 2D and 3D analysis, respectively. The inter-modality correlation of the thickness values was good (ICC: 0.76 [0.626–0.846]), indicating that 3D analysis of epithelial thickness provides valid results. Intra-rater and inter-rater reliability were good (3D analysis) and excellent (2D analysis), suggesting high reproducibility.

Conclusions

Diagnostic accuracy was high for the developed 3D analysis of oral epithelia using non-invasive, radiation-free OCT imaging.

Clinical significance

This new 3D technique could potentially be used to improve time-efficiency and quality in the diagnosis of epithelial lesions compared with the 2D reference standard.

Utilization potential of intraluminal optical coherence tomography for the Eustachian tube

Imaging the Eustachian tube is challenging because of its complex anatomy and limited accessibility. This study fabricated a fiber-based optical coherence tomography (OCT) catheter and investigated its potential for assessing the Eustachian tube anatomy. A customized OCT system and an imaging catheter, termed the Eustachian OCT, were developed for visualizing the Eustachian tube. Three male swine cadaver heads were used to study OCT image acquisition and for subsequent histologic correlation. The imaging catheter was introduced through the nasopharyngeal opening and reached toward the middle ear. The OCT images were acquired from the superior to the nasopharyngeal opening before and after Eustachian tube balloon dilatation. The histological anatomy of the Eustachian tube was compared with corresponding OCT images, The new, Eustachian OCT catheter was successfully inserted in the tubal lumen without damage. Cross-sectional images of the tube were successfully obtained, and the margins of the anatomical structures including cartilage, mucosa lining, and fat could be successfully delineated. After balloon dilatation, the expansion of the cross-sectional area could be identified from the OCT images. Using the OCT technique to assess the Eustachian tube anatomy was shown to be feasible, and the fabricated OCT image catheter was determined to be suitable for Eustachian tube assessment.

Structural similarity assessment of an optical coherence tomographic image enhanced using the wavelet transform technique

We report on the quality assessment of an optical coherence tomography (OCT) image. A set of recent digital filters are used for denoising the interferometric signals. It is found that when a combination of continuous wavelet transform (WT) decomposition and the WT denoising techniques is imposed on raw signals, the highest signal-to-noise ratio of 17.8 can be reached. The structural similarity (SSIM) index is eventually employed to evaluate the modality of the reconstructed OCT image. Further, we found out that a SSIM value of about 0.95 can be reached, independent of the method used for envelope extraction.

[Enhanced imaging in urological endoscopy]

White light cystoscopy and the concise documentation of pathological findings are standard diagnostic procedures in urology. Additional imaging modalities and technical innovations may support clinicians in the detection of bladder tumors. Modern endoscopy systems provide ultra-high-resolution imaging and the option of digital contrast enhancement. Photodynamic diagnostics and narrow band imaging are well-established in clinical routine and have shown significant benefits in the detection of bladder cancer. By means of multispectral imaging, different modalities can now be combined in real-time. Probe-based procedures such as optical coherence tomography (OCT) or Raman spectroscopy can further contribute to advanced imaging through an "optical biopsy" which may primarily improve diagnostics in the upper urinary tract. The aim of all techniques is to optimize the detection rate in order to achieve a more accurate diagnosis, resection and lower recurrence rates. Current research projects aim to digitalize the documentation of endoscopy and also make it more patient- and user-friendly. In the future, the use of image processing and artificial intelligence may automatically support the surgeon during endoscopy.

New Approaches in the Study of the Pathogenesis of Urethral Pain Syndrome

INTRODUCTION

Urethral pain syndrome (UPS) is still a pathology in which the diagnosis is formulated as a "diagnosis of exclusion". The exact pathogenetic mechanisms are not yet fully understood and clear recommendations for the prevention and treatment of UPS are absent.

METHODS AND PARTICIPANTS

A clinical and laboratory evaluation of 55 patients with established UPS included history taking, basic laboratory tests (e.g., complete blood count and clinical urine test), physical examination, uroflowmetry, and cystourethroscopy. Additionally, transvaginal ultrasound (TVUS) with compression elastography and cross-polarization optical tomography (CP OCT) were performed in 24 and 33 patients with UPS, respectively. The control group consisted of 14 patients with no complaints from the urinary system.

RESULTS

TVUS showed an expansion in the diameter of the internal lumen of the urethra, especially in the proximal region compared with the norm. Compression elastography revealed areas with increased stiffness (presence of fibrosis) in urethral and surrounding tissues. The performed CP OCT study showed that in UPS, the structure of the tissues in most cases was changed: trophic alterations in the epithelium (hypertrophy or atrophy) and fibrosis of underlying connective tissue were observed. The proximal fragment of the urethra with UPS underwent changes identical to those of the bladder neck.

CONCLUSION

This paper showed that the introduction of new technology-CP OCT-in conjunction with TVUS will allow verification of structural changes in tissues of the lower urinary tract at the level of their architectonics and will help doctors understand better the basics of the UPS pathogenesis.

Traumatic Macular Hole: Clinical Management and Optical Coherence Tomography Features

The complex and uncertain prognosis of traumatic macular hole (TMH) makes it a difficult and challenging problem in clinical management. The features of spontaneously closed TMH and the time of vitrectomy remain unclear. This retrospective study aimed to demonstrate the optical coherence tomography (OCT) features of TMH, explore the relationship between OCT parameters and visual outcomes, and further evaluate the therapeutic effect of surgical management. Seventeen TMH patients were included in this study. 13 eyes of TMH received vitrectomy surgery and 4 eyes of TMH were closed spontaneously. Baseline patient characteristics, surgical details, and 6-month postoperative follow-up clinical assessment were recorded prospectively. There was a moderate rate (4/17 eyes, 23.5%) of spontaneous closure. The mean time of hole closure was 9.5 ± 9.9 weeks, and 75% occurred within three months. In the spontaneously closed TMH eyes (n = 4), an intact ellipsoid band was observed in all four patients with a mean age of 12.0 ± 1.6 years and a smaller preoperative basal diameter of 418.0 ± 283.6 μm. Small basal diameter of the macular hole at baseline (p = 0.02) was associated with spontaneous closure of TMH acuity. In the vitrectomy surgery group (n = 13), an intact ellipsoid band was observed in four patients (4/13) with a mean age of 27.0 ± 12.7 years and a larger preoperative basal diameter of 943.0 ± 444.2 μm (p = 0.02). Vitrectomy results in a better closure rate (11/13 eyes, 84.6%). Combined with the spontaneously closed TMH eyes, the overall hole closure rate was 88.2% (15/17 eyes). After 6-month treatment for all patients, the best-corrected visual acuity (BCVA) increased to 0.59 ± 0.40 (logMAR) compared to baseline 1.01 ± 0.50 (logMAR) (p < 0.001). The ellipsoid band integrity was found to be closely correlated with visual acuity (p = 0.03). In conclusion, vitrectomy is an effective treatment for TMH. Surgical management for TMH achieved better anatomical closure and improved visual outcomes. Observation for 3 months may be considered before deciding if surgical intervention is suitable.

Diagnostic accuracy of 870-nm spectral-domain OCT with enhanced depth imaging for the detection of caries beneath ceramics

OBJECTIVES

To evaluate the diagnostic accuracy of optical coherence tomography (OCT) for the non-invasive detection of caries adjacent to ceramic materials.

METHODS

Disks made from five ceramic materials (hybrid ceramic, feldspathic ceramic, zirconia-reinforced lithium silicate, lithium disilicate, and high-translucent zirconia) were ground to the recommended material thickness for single crown restorations and laminated with a 100 μm thick layer of one of three adhesive cements. The disks were fixed to extracted human molars with or without carious lesions of one of three standardized sizes. A total of 240 stacks of cross-sectional scans obtained using an 870-nm SD-OCT with enhanced depth imaging (EDI) were presented to five raters. Diagnostic accuracy was determined by rating the teeth beneath the cemented material as carious or healthy.

RESULTS

Carious samples were distinguished from sound teeth with high diagnostic accuracy, even for early stage caries. Sensitivity (SE) and specificity (SP) pooled over all raters and all materials were 0.9 and 0.97, respectively. When analyzing the effect of the ceramic and cement materials on detection rates, high SE and SP values of >0.96 and >0.91, respectively, were recorded for lithium disilicate, zirconia-reinforced lithium silicate, and high-translucent zirconia irrespective of the cement type. For hybrid and feldspathic ceramics, the cement material was found to have a significant effect on caries detection.

CONCLUSIONS

Given its high diagnostic accuracy, 870-nm SD-OCT with EDI might be useful for the detection of caries beneath restorative materials. The effect of the prescribed ceramic and cement material on optical penetration depth is substantial.

An enhanced OCT image captioning system to assist ophthalmologists in detecting and classifying eye diseases

Human eye is affected by the different eye diseases including choroidal neovascularization (CNV), diabetic macular edema (DME) and age-related macular degeneration (AMD). This work aims to design an artificial intelligence (AI) based clinical decision support system for eye disease detection and classification to assist the ophthalmologists more effectively detecting and classifying CNV, DME and drusen by using the Optical Coherence Tomography (OCT) images depicting different tissues. The methodology used for designing this system involves different deep learning convolutional neural network (CNN) models and long short-term memory networks (LSTM). The best image captioning model is selected after performance analysis by comparing nine different image captioning systems for assisting ophthalmologists to detect and classify eye diseases. The quantitative data analysis results obtained for the image captioning models designed using DenseNet201 with LSTM have superior performance in terms of overall accuracy of 0.969, positive predictive value of 0.972 and true-positive rate of 0.969using OCT images enhanced by the generative adversarial network (GAN). The corresponding performance values for the Xception with LSTM image captioning models are 0.969, 0.969 and 0.938, respectively. Thus, these two models yield superior performance and have potential to assist ophthalmologists in making optimal diagnostic decision.