Optical Coherence Tomography Method Research Articles

Evaluation of the standard test methods for optical coherence tomograph for the posterior segment of the human eye

Optical Coherence Tomography (OCT) has revolutionized retinal imaging by offering non-invasive high-resolution three-dimensional visualization capabilities. OCT has become the standard of care in routine ophthalmological practice, especially for the posterior segment. Given its widespread clinical applications, establishing standardized test devices and methods for key OCT parameters is imperative to ensure both optimal imaging performance and diagnostic accuracy and treatment effectiveness. As a widely applied standard, ISO 16971:2015 published by the International Organization for Standardization specifies the minimum requirements, test device, and methods for OCT for the posterior segment of the human eye. Notably, these standards lacked experimental validation. In the present study, we implement the test device according to ISO 16971:2015, and assess a commercially available ophthalmic OCT instrument with the suggested test device and methods. Results show that the test device and methods could facilitate a rudimentary evaluation of OCT key parameters. Nevertheless, refinements of the test device and methods are requisite to enhance measurement accuracy, reliability, traceability, and practicability, catering to the diverse needs of manufacturers, end-users, and regulatory entities.

Acquired Vitelliform Lesions in Intermediate Age-Related Macular Degeneration: A Cross Sectional Study

PurposeThis study aims to define the characteristics of acquired vitelliform lesions (AVLs) in patients with intermediate age-related macular degeneration (iAMD). DesignRetrospective, observational, cross-sectional study SubjectsThis study included 217 eyes with AVLs associated with iAMD, and an equivalent number of control patients. MethodsOptical coherence tomography (OCT) scans were evaluated for qualitative and quantitative parameters at both the eye and lesion level. Eye-level parameters included the presence of: hyporeflective core drusen, intraretinal hyperreflective foci (IHRF), subretinal drusenoid deposits, macular pachyvessels, central retinal thickness, and central choroidal thickness (CCT). Lesion-level qualitative parameters included the presence of ellipsoid zone (EZ) and external limiting membrane disruption overlying the AVL, IHRF overlying the AVL, AVL overlying drusen, pachyvessels under the AVL, a solid core within AVL, and AVL location. Lesion-level quantitative characteristics included AVL height and width, AVL distance from the fovea, and sub-AVL choroidal thickness. Main Outcome MeasuresThe primary outcomes assessed included the frequency of iHRF, the presence of macular pachyvessels, CCT, and the dimensions (both height and width) of AVLs. ResultsComparing the AVL and control groups, the frequency of IHRF (AVL: 49.3% vs. control: 26.3%) and macular pachyvessels (37.3% vs. 6.9%) was significantly higher in the AVL case group, and the CCT (256.8 ± 88 μm vs. 207.1± 45 μm) was thicker in the AVL group. AVL lesions located over drusen, with overlying IHRF, or situated subfoveally, and AVL lesions with EZ disruption were found to have a greater lesion height and width compared to AVL lesions lacking these characteristics (P-value < 0.001 for all). Additionally, a significant negative correlation was observed between the distance from the fovea and AVL height (Spearman's rho: -0.19, P = 0.002) and width (Spearman’s rho: -0.30, P = 0.001). ConclusionsThis study represents the largest reported cohort of AVL lesions associated with iAMD. Novel findings include the higher frequency of pachyvessels in addition to the presence of a thicker choroid in these eyes, as well as the greater height and width of AVL closer to the foveal center. These findings may offer insights into pathophysiologic mechanisms underlying the development of AVL.

Comparison of central corneal thickness measured by automatic and manual analysis of optical coherence tomography.

To compare central corneal thickness (CCT) measured with optical coherence tomography (OCT) using an automatic algorithm (A-OCT) vs. manual measurements (M-OCT) with respect to the gold standard ultrasound pachymetry (USP). CCT measurements were performed on both eyes of 28 healthy subjects at four times of the day. A-OCT used an automatic software analysis of the corneal image, M-OCT was performed by two operators by setting a digital calliper on the corneal borders, and USP was performed after corneal anesthesia. Measurements were compared using a three-way repeated measures ANOVA. Bland-Altman plots were used to evaluate the agreement between OCT measurements and USP. Both A-OCT and M-OCT significantly underestimated the USP measures, with the mean difference, i.e., the systematic error, being larger for A-OCT (- 19.0µm) than for M-OCT (- 6.5µm). Good reproducibility between the two operators was observed. Bland-Altman plots showed that both OCT methods suffered from proportional errors, which were not affected by time and eye. Measuring CCT with OCT yielded lower values than USP. Therefore, clinicians should be aware that corneal thickness values may be influenced by the measurement method and that the various devices should not be used interchangeably in following up a given patient. Intriguingly, M-OCT had less systematic error than A-OCT, an important outcome that clinicians should consider when deciding to use an OCT device.

FMMAS-OCT: Aberration correction for high-resolution cellular imaging

In optical coherence tomography (OCT), spatial resolution and signal strength often suffer due to aberrations from both the imaging system and the sample. In this work, we introduce a novel method, FMMAS (Forward-Model Multiple Aperture Synthesis), which effectively compensates for these aberrations. It combines forward-model (FM) based method for transverse resolution restoration and multiple aperture synthesis (MAS) to mitigate depth domain aberrations. Our proof-of-concept experiment demonstrates a significant improvement in the mean transverse full width at half maximum (FWHM) of microparticles by 46.1 %. Compared to original OCT and FM method, FMMAS produces sharper, 'pencil beam'-like imaging, resolving cell nuclei in swine esophagus ex vivo and human blood cells in vivo, suggesting a potential for significant enhancements in OCT image quality.

Preliminary analysis of predicting the first recurrence in patients with neovascular age-related macular degeneration using deep learning

BackgroundTo predict, using deep learning, the first recurrence in patients with neovascular age-related macular degeneration (nAMD) after three monthly loading injections of intravitreal anti-vascular endothelial growth factor (anti-VEGF).MethodsOptical coherence tomography (OCT) images were obtained at baseline and after the loading phase. The first recurrence was defined as the initial appearance of a new retinal hemorrhage or intra/subretinal fluid accumulation after the initial resolution of exudative changes after three loading injections. Standard U-Net architecture was used to identify the three retinal fluid compartments, which include pigment epithelial detachment, subretinal fluid, and intraretinal fluid. To predict the first recurrence of nAMD, classification learning was conducted to determine whether the first recurrence occurred within three months after the loading phase. The recurrence classification architecture was built using ResNet50. The model with retinal regions of interest of the entire region and fluid region on OCT at baseline and after the loading phase is presented.ResultsA total of 1,444 eyes of 1,302 patients were included. The mean duration until the first recurrence after the loading phase was 8.20 ± 15.56 months. The recurrence classification system revealed that the model with the fluid region of OCT after the loading phase provided the highest classification performance, with an area under the receiver operating characteristic curve (AUC) of 0.725 ± 0.012. Heatmap analysis revealed that three pathological fluids, subsided choroidal neovascularization lesions, and hyperreflective foci were important areas for the first recurrence.ConclusionsThe deep learning algorithm allowed for the prediction of the first recurrence for three months after the loading phase with adequate feasibility. An automated prediction system may assist in establishing patient-specific treatment plans and the provision of individualized medical care for patients with nAMD.

A Conceptual Model of Dual-Mode Tomography Technique for Dental Diagnostics: Ultrasound and Light Propagation Analysis.

Many advanced imaging modalities, such as magnetic resonance imaging (MRI), X-ray Computed Tomography, Positron Emission Tomography (PET), Ultrasound, Single Photon Emission Computed Tomography (SPECT), and the most recent, Optical Coherence Tomography (OCT), have been developed for identifying dental tissues images and detecting changes in early carious lesions. Some modalities use high doses of radiation and energy to obtain more information, which may be harmful to patient’s health. Most early commercial OCTs had drawbacks such as its bulky size and limited image resolution. In order to overcome these concerns, this paper presents a dual-mode tomography technique that combines OCT and ultrasound method using the COMSOL Multiphysics. The application of an ultrasound device helps overcome the limitation of OCT in detecting the penetration depth of a caries lesion. Several simulations were performed to analyse the light and ultrasonic propagated waves with different diameters of carious lesions. In response to this goal, the combination data of OCT and ultrasound provide a 3D image which offers the best approach for displaying and examining changes in the oral cavity.

OCT-based dynamic mechanical analysis of vitreous humour

The vitreous humour plays an important role in shock absorption, i.e. the damping of the mechanical movement, to protect the delicate tissues within the eye. However, this damping is different for movements with different frequencies/velocities. While the collective low-frequency (below 100 Hz) damping behaviour of the vitreous humour associated with the saccadic and lens movements is well-studied, to the best of our knowledge, the high-frequency damping behaviour of the vitreous humour, which represents the response of the microstructural components, is not exhaustively documented. Here, we utilise a non-destructive testing method called Optical Coherence Tomography (OCT) to measure the high-frequency (100–350 Hz, waves able to probe approximately 500 µm distances) biomechanical behaviour of the vitreous humour. We parametrise this behaviour by calculating the shear storage modulus, shear loss modulus and phase angle. We compare these parameters to their low-frequency counterparts obtained with a rheometer, providing a comprehensive mechanical spectrum of the vitreous humour behaviour. The processing method developed in this study and the data collected help better understand the vitreous humour shock absorption properties. Consequently, they could allow a development of better vitreous humour substitutes. The local probing of the high-frequency regime and the non-invasive character of the OCT method provide new qualities in mapping the damping behaviour.

Needle guidance with Doppler-tracked polarization-sensitive optical coherence tomography.

Optical coherence tomography (OCT) can be integrated into needle probes to provide real-time navigational guidance. However, unscanned implementations, which are the simplest to build, often struggle to discriminate the relevant tissues. We explore the use of polarization-sensitive (PS) methods as a means to enhance signal interpretability within unscanned coherence tomography probes. Broadband light from a laser centered at 1310nm was sent through a fiber that was embedded into a needle. The polarization signal from OCT fringes was combined with Doppler-based tracking to create visualizations of the birefringence properties of the tissue. Experiments were performed in (i)well-understood structured tissues (salmon and shrimp) and (ii)ex vivo porcine spine. The porcine experiments were selected to illustrate an epidural guidance use case. In the porcine spine, unscanned and Doppler-tracked PS OCT imaging data successfully identified the skin, subcutaneous tissue, ligament, and epidural spaces during needle insertion. PS imaging within a needle probe improves signal interpretability relative to structural OCT methods and may advance the clinical utility of unscanned OCT needle probes in a variety of applications.

Renal tubular function and morphology revealed in kidney without labeling using three-dimensional dynamic optical coherence tomography

Renal tubule has distinct metabolic features and functional activity that may be altered during kidney disease. In this paper, we present label-free functional activity imaging of renal tubule in normal and obstructed mouse kidney models using three-dimensional (3D) dynamic optical coherence tomography (OCT) ex vivo. To create an obstructed kidney model, we ligated the ureter of the left kidney for either 7 or 14 days. Two different dynamic OCT (DOCT) methods were implemented to access the slow and fast activity of the renal tubules: a logarithmic intensity variance (LIV) method and a complex-correlation-based method. Three-dimensional DOCT data were acquired with a 1.3 upmum swept-source OCT system and repeating raster scan protocols. In the normal kidney, the renal tubule appeared as a convoluted pipe-like structure in the DOCT projection image. Such pipe-like structures were not observed in the kidneys subjected to obstruction of the ureter for several days. Instead of any anatomical structures, a superficial high dynamics appearance was observed in the perirenal cortex region of the obstructed kidneys. These findings suggest that volumetric LIV can be used as a tool to investigate kidney function during kidney diseases.

Research progress of optical coherence tomography in the airway

Optical coherence tomography (OCT) is a specialized optical imaging technique with a history of more than 30 years, known as'optical biopsy' because of its high resolution and high sensitivity. OCT has been used in the airway for more than 20 years, and researchers have explored and improved the imaging methods of OCT in the airway, focusing mainly on expanding the imaging site and enriching the imaging content. In terms of broadening the imaging site, it covers the airway from generation 0 to 9. In terms of enriching imaging content, additional assessment of airway wall blood vessels, airway smooth muscle, fibrous tissue, and airway compliance can be performed. It plays an important role in the study of various respiratory diseases. Therefore, this paper mainly summarized the exploration of the imaging site and content of airway OCT as follows.

Visible wavelength time-stretch optical coherence tomography.

Visible light optical coherence tomography (OCT) is an emerging non-invasive imaging modality that offers new opportunities for anatomical and functional imaging of biological tissues. Time-stretch dispersive Fourier transform, also known as photonic time-stretch, is an all-optical processing method that enables real-time Fourier transformation of ultrafast optical signals and allows for OCT at high A-scan rates. In this work, a working prototype of a photonic time-stretch OCT (TS-OCT) method in the visible wavelength region is proposed and experimentally demonstrated. The proposed visible-light TS-OCT system achieves unprecedented throughput of 100 giga voxels/second and OCT volume rate of 4,000 volumes/second and can be used to expand the range of applications of TS-OCT systems.

NOVEL METHOD FOR VISUALIZING PERIPHERAL RETINAL STRUCTURES WITH MICROSCOPE-INTEGRATED OPTICAL COHERENCE TOMOGRAPHY.

Visualization of peripheral retinal structures with optical coherence tomography (OCT) can be challenging but can offer valuable clinical information. We describe a method for intraoperative OCT of the peripheral retina. An investigational microscope-integrated OCT system with real-time 4D volumetric imaging was used in conjunction with a Goldmann style mirrored contact lens intraoperatively to capture peripheral images in three patients. We identified retinoschisis, a retinal break, and areas of focal retinal detachment using our peripheral OCT method. Use of a Goldmann lens in conjunction with intraoperative OCT offers surgeons the ability to resolve peripheral pathology that cannot be easily evaluated with OCT otherwise.

Effect of shape deprivation on retinal thickness in myopic mice using an OCT method.

The purpose of this study was to study in retina thickness changes in myopic mice using optical coherence tomography (OCT). There were 18 mice in the form-deprivation myopia (FDM) group，in which the left eye was not treated as a control;18 untreated mice served as a normal control group. The diopter of all mice was measured 21 days after birth (P21), before form deprivation. After 4 weeks of form deprivation (P49), the refraction, fundus, and retinal sublayer thickness of all mice were measured. After 4 weeks of form deprivation, the refractive power of the right eye in the FDM group was significantly higher than that in the left eye (p < 0.05). There was no significant change in the refractive power of the left eye in the FDM group compared with the normal control group. The retina, nerve fiber layer (NFL), inner nuclear layer (INL), and outer nuclear layer (ONL) in the right eye of the FDM group were significantly thinner than those of both the FDM and control groups (p < 0.05). There was no significant change in photoreceptor (PR). Our study highlights that the myopic mice have decreased R thickness, which might reflect the potential pathological mechanism of myopia.

Intravascular imaging modalities in coronary intervention: Insights from 3D-printed phantom coronary models

Introduction and objectivesSeveral studies comparing optical coherence tomography (OCT) and intravascular ultrasound (IVUS) have revealed that OCT consistently provides smaller area and diameter measurements. However, comparative assessment in clinical practice is difficult. Three-dimensional (3D) printing offers a unique opportunity to assess intravascular imaging modalities.We aim to compare intravascular imaging modalities using a 3D-printed coronary artery in a realistic simulator and to assess whether OCT underestimates intravascular dimensions, exploring potential corrections. MethodsA standard realistic left main anatomy with an ostial left anterior descending artery lesion was replicated using 3D printing. After provisional stenting and optimization, IVI was obtained. Modalities included 20 MHz digital IVUS, 60 MHz rotational IVUS (HD-IVUS) and OCT. We assessed luminal area and diameters at standard locations. ResultsConsidering all coregistered measurements, OCT significantly underestimated area, minimal diameter and maximal diameter measurements in comparison to IVUS and HD-IVUS (p<0.001). No significant differences were found between IVUS and HD-IVUS.A significant systematic dimensional error was found in OCT auto-calibration by comparing known reference diameter of guiding catheter (1.8 mm) to measured mean diameter (1.68 mm±0.04 mm). By applying a correction factor based on the reference guiding catheter area to OCT, the luminal areas and diameters were not significantly different compared to IVUS and HD-IVUS. ConclusionOur findings suggest that automatic spectral calibration method for OCT is inaccurate, with a systematic underestimation of luminal dimensions. When guiding catheter correction is applied the performance of OCT is significantly improved. These results may be clinically relevant and need to be validated.

Automated quantification of 3D wound morphology by machine learning and optical coherence tomography in type 2 diabetes.

Driven by increased prevalence of type 2 diabetes and ageing populations, wounds affect millions of people each year, but monitoring and treatment remain limited. Glucocorticoid (stress hormones) activation by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) also impairs healing. We recently reported that 11β-HSD1 inhibition with oral AZD4017 improves acute wound healing by manual 2D optical coherence tomography (OCT), although this method is subjective and labour-intensive. Here, we aimed to develop an automated method of 3D OCT for rapid identification and quantification of multiple wound morphologies. We analysed 204 3D OCT scans of 3mm punch biopsies representing 24 480 2D wound image frames. A u-net method was used for image segmentation into 4 key wound morphologies: early granulation tissue, late granulation tissue, neo-epidermis, and blood clot. U-net training was conducted with 0.2% of available frames, with a mini-batch accuracy of 86%. The trained model was applied to compare segment area (per frame) and volume (per scan) at days 2 and 7 post-wounding and in AZD4017 compared to placebo. Automated OCT distinguished wound tissue morphologies, quantifying their volumetric transition during healing, and correlating with corresponding manual measurements. Further, AZD4017 improved epidermal re-epithelialisation (by manual OCT) with a corresponding trend towards increased neo-epidermis volume (by automated OCT). Machine learning and OCT can quantify wound healing for automated, non-invasive monitoring in real-time. This sensitive and reproducible new approach offers a step-change in wound healing research, paving the way for further development in chronic wounds.

Classification of Tear Film Lipid Layer En Face Maps Obtained Using Optical Coherence Tomography and Their Correlation With Clinical Parameters.

The purpose of this study was to investigate the correlation between the pattern of optical coherence tomography (OCT) en face maps of the tear film lipid layer (TFLL) and lipid layer thickness (LLT), fluorescein breakup time (FBUT), and Schirmer I test values in healthy subjects. Measurements from four clinical data sets were retrospectively analyzed, and TFLL patterns were classified into 3 categories: homogeneous (HOM), wavy (WAV), or dotted (DOT) appearance. Linear mixed model analyses were performed. Intraclass correlation coefficients and index of qualitative variation were computed to investigate interrater and intrasubject variabilities. For the LLT, a significant difference between HOM and DOT ( P < 0.001, β HOMvsDOT = -6.42 nm) and WAV and DOT ( P = 0.002, β WAVvsDOT = -4.04 nm) was found. Furthermore, the difference between WAV and DOT regarding FBUT ( P < 0.001, β WAVvsDOT = -3.065 seconds) was significant, while no significant differences between any of the classes with respect to the Schirmer I test values were found. An intraclass correlation coefficient of 89.0% reveals a good interrater reliability, and an index of qualitative variation of 60.0% shows, on average, a considerable variability in TFLL pattern class for repeated measurements over 1 hour. A new classification method for OCT en face maps of the TFLL is presented. Significant differences between patterns were found with respect to LLT and FBUT. A dotted pattern on dark background appears to be the most stable type of TFLL. The analysis of OCT en face maps of the TFLL provides complimentary information to conventional imaging methods and might give new insights into the characteristics of the TFLL.

NCOG-15. A PILOT STUDY ON RETINAL FEATURES AND COGNITIVE FUNCTION IN PATIENTS WITH LOW GRADE GLIOMAS

Abstract BACKGROUND Retinal structure and vascular changes are used as biomarkers for preclinical Alzheimer disease. We conducted a cohort study to evaluate the feasibility of obtaining these data in patients with low-grade gliomas (LGGs) who completed chemoradiation therapy with and without self or family reported cognitive concerns. METHODS Optical coherence tomography (OCT) and angiography (OCTA, OptoVue, Inc.) images were obtained from 6 LGG patients and 2 healthy controls using 4.5 x 4.5 mm peripapillary and 6x6 mm macular scan patterns. We measured OCTA parameters including radial peripapillary capillary density for the peri-optic disc region, whole macular density, and foveal avascular zone (FAZ). RESULTS We analyzed two eyes of two control subjects, an LGG patient with normal cognition, and 5 LGG patients with cognitive impairment (mean age 45 years, range of 3 months to 10 years after chemoradiation). Both controls had normal eye exams. Average retinal nerve fiber layer thickness was thinner in patients with and without cognitive dysfunction (104 um and 106 um, respectively) than controls (123 um). A similar pattern was seen in macula thickness (283 um and 290 um vs. 325 um). The average peripapillary vessel densities were lower in patients with and without cognitive dysfunction (47.7% and 48.3%, respectively) than controls (51.9%). The whole macular vessel densities were similar in three groups (46.7 %, 48.0%, and 48.0 %). Average FAZs were larger in patients with cognitive dysfunction (0.254 mm2) than the patient with normal cognition (0.204 mm2) and controls (0.226 mm2). CONCLUSIONS Retinal architecture and microvascular changes measured by OCT/OCTA is feasible in LGG patients after chemoradiation. A larger prospective study is needed to investigate the role of OCT/OCTA in detecting peripapillary and perifoveal changes in brain tumor patients with treatment-associated cognitive dysfunction.

Image-based cross-calibration method for multiple spectrometer-based OCT.

A fast and practical computational cross-calibration of multiple spectrometers is described. A signal correlation matrix (CM) can be constructed from paired B-scans in a multiple-spectrometer optical coherence tomography (OCT), where the wavelength-corresponding pixels are indicated by high cross correlation. The CM can be used to either guide the physical alignment of spectrometers or to numerically match the spectra in the post-process. The performance is comparable to the previously reported optimization approach, as demonstrated by the mirror tests, qualitative comparison of OCT and optical coherence tomography angiography (OCTA) images, and quantitative comparison of image metrics.

Automated counting of cerebral penetrating vessels using optical coherence tomography images of a mouse brain in vivo.

Penetrating blood vessels emanating from cortical surface vasculature and lying deep in the cortex are essential vascular conduits for the shuttling of blood from superficial pial vessels to the capillary beds in parenchyma for the nourishment of neuronal brain tissues. Locating and counting the penetrating vessels is beneficial for the quantification of a course of ischemia in blood occlusive events such as stroke. This paper seeks to demonstrate and validate a method for automated penetrating vessel counting that uses optical coherence tomography (OCT). This paper proposes an OCT method that effectively identifies and grades the cortical penetrating vessels in perfusion. The key to the proposed method is the harnessing of vascular features found in the penetrating vessels, which are distinctive from those of other vessels. In particular, with an increase in the light attenuation and flow turbulence, the contrast in the mean projection of the OCT datacube decreases, whereas that in the maximum projection of the Doppler frequency variance datacube increases. By multiplying the inversion of the former with the latter, its binary thresholding is sufficient to highlight the penetrating vessels and allows for their counting over the projection image. A computational method that leverages the decrease in mean OCT projection intensity and the increase in Doppler frequency variance at the penetrating vessel is developed. It successfully identifies and counts penetrating vessels with a high accuracy of over 87%. The penetrating vessel density is observed to be significantly reduced in the mouse model of focal ischemic stroke. The OCT analysis is effective for counting penetrating blood vessels in mice brains and may be applied to the rapid diagnosis and treatment of stroke in stroke models of small animals.

Features for image processing of OCT images for seam tracking applications in laser welding

The coaxial integration of optical coherence tomography (OCT) enables the determination of surface topography and measurement of object features along the optical path within laser machining. The measurement of surface information from the processed workpiece allows for the identification of features from the joint configuration and the subsequent control of the welding process by seam tracking. State-of-the-art seam tracking approaches are based on monochromatic cameras or laser triangulation. Typically, these approaches apply line segmentations for the identification of the joint position. The interferometric measurement method of OCT gives rise to the identification of new features for image processing in seam tracking. In this work, we identify specific noise components and features based on the theoretical background of OCT for image processing in seam tracking applications. Two different features are derived for the detection of arbitrary joint configurations with corresponding systematic image processing approaches. In the first step, we show the applicability of line detection methods for feature detection of arbitrary joint configurations. The necessary evaluation algorithm for case sensitivity and limitations (e.g., chamfer) in detecting different joint geometries are discussed. In the second step, we show an approach in feature extraction with feature detectors (e.g., ORB, SURF) for a new image feature. Here, significant image space from (multiple) reflections at the joint position is used for joint detection. The detectability is discussed depending on the joint configuration. The results show good suitability of both features for seam tracking applications.