Optical Coherence Tomography Technique Research Articles

Conquering surfactant-induced partial wetting of commercial membrane in membrane distillation through in-situ water flushing

Surfactant-induced wetting impedes the practical implementation of membrane distillation (MD). Addressing this issue demands the development of an effective membrane cleaning strategy that can eliminate surfactants adhering to the membrane surface and restore the membrane hydrophobicity. However, current cleaning methods, such as direct drying and pressurized air backwashing, encounter challenges in thoroughly removing surfactants trapped within the pores while preserving the structural integrity of the membrane. This work presents a refined approach to conquer surfactant-induced wetting in MD by water flushing. Utilizing ultrasonic time domain reflectometry and optical coherence tomography techniques, we identified a critical cleaning depth and showed that the hydrophobicity of a partially wetted membrane can be fully recovered by water flushing when the wetting depth is below the critical threshold. Theoretical models evidenced that in instances of low water temperature and low flow rate conditions, relatively high critical cleaning depths can be realized, thereby expanding the operational scope for achieving complete hydrophobicity recovery. Our results demonstrated the applicability of water flushing to commercial membrane modules without necessitating any modification, emphasizing its substantial potential for advancing MD applications.

Phase-sensitive optical coherence tomography reveals droplet penetration into a powder bed

Understanding the mixing behavior that unfolds when liquid droplets impact on powder beds requires a sub-surface dynamic imaging method that provides high spatial and temporal resolution. In this study, a high-resolution phase-sensitive optical coherence tomography (PhS-OCT) technique was introduced to provide in-depth insights into the interaction of droplets and powder beds. A theoretical model correlating changes in the optical path differences (OPD) of the OCT signal with physical properties of the powder bed was presented. Experiments were conducted on three powders with median particle diameters, i.e., the size corresponding to the 50th percentile of the cumulative volume distribution, of 3 µm (mannitol), 4 µm (mannitol) and 109 µm (SV010). Water and ethanol droplets were used to illustrate the technique. The results demonstrated that OPD maps can qualitatively resolve the liquid-powder mixture region, both temporally and spatially, as the droplet diffuses into the powder bed, allowing for a quantitative description of diffusion behavior. A comparison of lactose and mannitol powder samples revealed varying diffusion rates, potentially attributed to differences in porosity, particle size, and agglomeration. Additionally, water and ethanol droplets exhibited significantly different (p = 0.005) diffusion profiles for the same powder properties. In general, the findings indicate the potential of the proposed PhS-OCT technique for evaluating the mixing behavior of multi-phase mixtures, holding promise in applications such as pharmaceutical drug formulations and additive manufacturing.

Mid-infrared optical coherence tomography with MHz axial line rate for real-time non-destructive testing

Non-destructive testing (NDT) is crucial for ensuring product quality and safety across various industries. Conventional methods, such as ultrasonic, terahertz, and x-ray imaging, have limitations in terms of probe-contact requirement, depth resolution, or radiation risks. Optical coherence tomography (OCT) is a promising alternative to solve these limitations, but it suffers from strong scattering, limiting its penetration depth. Recently, OCT in the mid-infrared (MIR) spectral region has attracted attention with a significantly lower scattering rate than in the near-infrared region. However, the highest reported A-scan rate of MIR-OCT has been 3 kHz, which requires long data acquisition time to take an image, unsatisfying industrial demands for real-time diagnosis. Here, we present a high-speed MIR-OCT system operating in the 3–4 µm region that employs the frequency-swept spectrum detection in OCT technique based on time-stretch infrared spectroscopy. By integrating a broadband femtosecond MIR pulsed laser operating at a repetition rate of 50 MHz, we achieved an A-scan rate of 1 MHz with an axial resolution of 11.6 µm, a 10 dB roll-off depth of about 700 µm, and a sensitivity of 55 dB. As a proof-of-concept demonstration, we imaged the surface of substrates covered by highly scattering paint coatings. The demonstrated A-scan rate surpasses previous state of the art by more than two orders of magnitude, paving the way for real-time NDT of industrial products, cultural assets, and structures.

Deep learning automatically assesses 2-µm laser-induced skin damage OCT images.

The present study proposed a noninvasive, automated, in vivo assessment method based on optical coherence tomography (OCT) and deep learning techniques to qualitatively and quantitatively analyze the biological effects of 2-µm laser-induced skin damage at different irradiation doses. Different doses of 2-µm laser irradiation established a mouse skin damage model, after which the skin-damaged tissues were imaged non-invasively in vivo using OCT. The acquired images were preprocessed to construct the dataset required for deep learning. The deep learning models used were U-Net, DeepLabV3+, PSP-Net, and HR-Net, and the trained models were used to segment the damage images and further quantify the damage volume of mouse skin under different irradiation doses. The comparison of the qualitative and quantitative results of the four network models showed that HR-Net had the best performance, the highest agreement between the segmentation results and real values, and the smallest error in the quantitative assessment of the damage volume. Based on HR-Net to segment the damage image and quantify the damage volume, the irradiation doses 5.41, 9.55, 13.05, 20.85, 32.71, 52.92, 76.71, and 97.24J/cm² corresponded to a damage volume of 4.58, 12.56, 16.74, 20.88, 24.52, 30.75, 34.13, and 37.32mm³. The damage volume increased in a radiation dose-dependent manner.

Descemet Membrane Endothelial Keratoplasty for Penetrating Keratoplasty

ABSTRACT Background: Descemet membrane endothelial keratoplasty (DMEK) has been utilized more frequently during recent years to treat penetrating keratoplasty (PKP) graft failures. The perioperative evaluation technique of anterior segment optical coherence tomography (AS-OCT) is increasingly significant. Our goal is to discuss DMEK surgical and clinical for subsequent PKP graft failure, along with significant surgical modifications and adjustments in accordance with preoperative assessment utilizing AS-OCT. Materials and Methods: Patients’ records who performed DMEK for PKP failure were retrospectively reviewed. Demographic information, PKP graft size determined by postoperative problems, corneal donor endothelial cell density (ECD), AS-OCT, central pachymetry, visual acuity (VA) evaluated in Snellen units, intraoperative surgical procedure modifications, and postoperative ECD were all included in the data collection. Results: The observation was conducted with 16 patients with 16 eyes, nine males and seven females. The observation period is 18 months. DMEK was performed at an average age of 63. Preoperative AS-OCT was performed on all patients, and based on cases, surgical plans were created. Before processing DMEK, the mean VA is 0.04, and central pachymetry is 685 m. They improved considerably to 0.3 (P value = 0.001) and 542 m (P value = 0.008) at the most recent follow-up. About 93.75% of the grafts were adhered to after the procedure. Late decompensation caused a 6.25% graft failure rate. Graft detachment rates and cases requiring rebubble rates were respectively 18.75%. Conclusion: In DMEK for failed PKP, a good case-specific preoperative assessment by AS-OCT is essential. As a result, it relies on developing a surgical strategy that can improve surgical outcomes, lower the risk of complications, and quicken visual recovery.

From the past to the present, optical coherence tomography in glaucoma: a practical guide to a common disease.

Glaucoma comprises a group of disorders of the optic nerve that cause degenerative optic neuropathy, characterised by failure of neuroretinal rim tissue in the optic nerve head, retinal nerve fibre layer, and retinal ganglion cells. Glaucoma imposes a serious epidemiological threat, with an steady increase in the global number of cases. In the current ophthalmological practice, glaucoma is diagnosed via a series of examinations, including routine funduscopic examination, ocular tonometry, gonioscopy, measurement of the visual field, and assessment using the optical coherence tomography (OCT) technique. Nowadays, the OCT technique helps in systematising the diagnostic pathway and is a basic diagnostic tool for detection of early glaucomatous eye changes. It is also vital in assessing progression and monitoring treatment results of patients. The aim of this review was to present the OCT technique as a main tool in diagnosing and monitoring glaucoma.

Advantages and Pitfalls of the Use of Optical Coherence Tomography for Papilledema.

Papilledema refers to optic disc swelling caused by raised intracranial pressure. This syndrome arises from numerous potential causes, which may pose varying degrees of threat to patients. Manifestations of papilledema range from mild to severe, and early diagnosis is important to prevent vision loss and other deleterious outcomes.The purpose of this review is to highlight the role of optical coherence tomography (OCT) in the diagnosis and management of syndromes of raised intracranial pressure associated with papilledema. Ophthalmoscopy is an unreliable skill for many clinicians. Optical coherence tomography is a non-invasive ocular imaging technique which may fill a current care gap, by facilitating detection of papilledema for those who cannot perform a detailed fundus examination.Optical coherence tomography may help confirm the presence of papilledema, by detecting subclinical peripapillary retinal nerve fiber layer (pRNFL) thickening that might otherwise be missed with ophthalmoscopy. Enhanced depth imaging (EDI) and swept source OCT techniques may identify optic disc drusen as cause of pseudo-papilledema. Macular ganglion cell inner plexiform layer (mGCIPL) values may provide early signs of neuroaxonal injury in patients with papilledema and inform management for patients with syndromes of raised intracranial pressure. There are well-established advantages and disadvantages of OCT that need to be fully understood to best utilize this method for the detection of papilledema.Overall, OCT may complement other existing tools by facilitating detection of papilledema and tracking response to therapies. Moving forward, OCT findings may be included in deep learning models to diagnose papilledema.

Study of the ganglion cell complex of the macula by optical coherence tomography in the diagnosis of glaucoma progression

IntroductionThe aim of this work is to evaluate the usefulness of the study of the ganglion cell complex of the macula using the OCT technique to estimate the progression of glaucoma according to its severity. Material and methodsThis is a retrospective cross-sectional study. It includes 205 eyes of 131 patients with glaucoma or ocular hypertension followed for a mean of 5.7 years. The parameters and rates of three tests have been analyzed using the progression software of each instrument: visual field, optical coherence tomography (OCT) in the ganglion cell complex of the macula and in the nerve fiber layer of the optic nerve. The results of each test, the concordance between them and how they differ according to severity stage have been evaluated. ResultsVisual field classifies more cases of progression in moderate-advanced glaucoma, while in mild glaucoma its capacity is limited. Optic nerve fiber layer OCT classifies more cases of progression in mild glaucoma than in moderate-advanced glaucoma, as it is artifacted by the floor effect. OCT of the macular ganglion cell complex is the test that classifies more cases of progression and has the highest agreement with visual field, regardless of severity. ConclusionIn both mild and moderate-advanced glaucoma, OCT of the macula ganglion cell complex may be a better biomarker of progression than OCT of the macula ganglion cell complex.

Silicone oil emulsification: A literature review and role of widefield imaging and ultra-widefield imaging with navigated central and peripheral optical coherence tomography technology.

Silicone oil (SO) emulsification is a significant concern in vitreoretinal surgery, leading to various complications. Despite the high prevalence of SO emulsification within the eye, there is currently no standardized method for its early detection. The recent introduction of widefield (WF) imaging and ultra-WF (UWF) imaging with navigated central and peripheral optical coherence tomography (OCT) techniques have shown promising results in providing high-resolution images of the peripheral vitreous, vitreoretinal interface, retina, and choroid. This enhanced visualization capability enables the early identification of emulsified SO droplets, facilitating a proactive therapeutic approach, and mitigating associated adverse events. This comprehensive literature review aims to provide an updated overview of the topic, focusing on the role of WFimaging and UWF imaging and navigated central and peripheral swept-source OCT (SS-OCT) in the early detection and management of SO emulsification. The review discusses the current understanding of SO emulsification, its associated complications, and the limitations of existing detection methods. In addition, it highlights the potential of WF and UWF imaging and peripheral OCT as advanced imaging modalities for improved visualization of SO emulsification. This review serves as a valuable resource for clinicians and researchers, providing insights into the latest advancements in the field of vitreoretinal surgery and the promising role of WF imaging and UWF imaging and navigated central and peripheral SS-OCT in the management of SO.

An intravascular optical coherence tomography technique for in vivo carotid intima-media thickness measurement and mechanical characterization

Arterial characteristic parameters including the intima-media thickness (IMT), strain, strain rate, elastic modulus, and compliance may be unevenly distributed due to local lesion growth. Thus, a combination of the full-field distribution of these parameters may provide more effective guidance for the diagnosis and treatment of vascular diseases than either one of them. Here, we develop an intravascular coherence tomography (IVOCT) based full-field measurement method to characterize the mechanical properties of carotid artery in vivo. Image processing methods are proposed based on U-Net model and centroid detection for accurate IMT measurement. The strain, strain rate, incremental elastic modulus and volumetric compliance are obtained based on the geometric changes of intima-media. Ex vivo silica gel phantom tests demonstrate the accuracy of the vascular wall segmentation by the U-Net based method is greater than 92%, and the error for elastic modulus measurement is less than 2%. A porcine carotid artery was imaged by IVOCT in vivo, and the IMT and the mechanical characteristics during cardiac cycle were measured. The proposed method facilitates the study of the uneven pathological evolution of the vascular wall and provides an effective measurement method for the study of vascular mechanical properties in vivo.

Depth extension technique of spectral domain optical coherence tomography

Depth extension technique of spectral domain optical coherence tomography

Role of intravascular ultrasound and optical coherence tomography in intracoronary imaging for coronary artery disease: a systematic review.

Coronary angiography has long been the standard for coronary imaging, but it has limitations in assessing vessel wall anatomy and guiding percutaneous coronary intervention (PCI). Intracoronary imaging techniques like intravascular ultrasound (IVUS) and optical coherence tomography (OCT) can overcome these limitations. IVUS uses ultrasound and OCT uses near-infrared light to visualize coronary pathology in unique ways due to differences in temporal and spatial resolution. These techniques have evolved to offer clinical utility in plaque characterization and vessel assessment during PCI. Meta-analyses and adjusted observational studies suggest that both IVUS and OCT-guided PCI correlate with reduced cardiovascular risks compared to angiographic guidance alone. While IVUS demonstrates consistent clinical outcome benefits, OCT evidence is less robust. IVUS has progressed from early motion detection to high-resolution systems, with smaller compatible catheters. OCT utilizes near infrared light to achieve unparalleled resolutions, but requires temporary blood clearance for optimal imaging. Enhanced visualization and guidance make IVUS and OCT well-suited for higher risk PCI in patients with diabetes and chronic kidney disease by allowing detailed visualization of complex lesions and ensuring optimal stent deployment and positioning in PCI for patients with type 2 diabetes and chronic kidney disease, improving outcomes. IVUS and recent advancements in zero- and low-contrast OCT techniques can reduce nephrotoxic contrast exposure, thus helping to minimize PCI complications in these high-risk patient groups. IVUS and OCT provide valuable insights into coronary pathophysiology and guide interventions precisely compared to angiography alone. Both have comparable clinical outcomes, emphasizing the need for tailored imaging choices based on clinical scenarios. Continued refinement and integration of intravascular imaging will likely play a pivotal role in optimizing coronary interventions and outcomes. This systematic review aims to delve into the nuances of IVUS and OCT, highlighting their strengths and limitations as PCI adjuncts.

Utilidad del estudio del complejo de células ganglionares de la mácula mediante tomografía de coherencia óptica en el diagnóstico de progresión del glaucoma

IntroductionThe aim of this work is to evaluate the usefulness of the study of the ganglion cell complex of the macula using optical coherence tomography (OCT) to estimate the progression of glaucoma according to its severity. Material and methodsThis is a retrospective cross-sectional study. It includes 205 eyes of 131 patients with glaucoma or ocular hypertension followed for a mean of 5.7years. The parameters and rates of three tests have been analyzed using the progression software of each instrument: visual field, OCT in the ganglion cell complex of the macula and in the nerve fiber layer of the optic nerve. The results of each test, the concordance between them and how they differ according to severity stage have been evaluated. ResultsVisual field classifies more cases of progression in moderate-advanced glaucoma, while in mild glaucoma its capacity is limited. Optic nerve fiber layer OCT classifies more cases of progression in mild glaucoma than in moderate-advanced glaucoma, as it is artifacted by the floor effect. OCT of the macular ganglion cell complex is the test that classifies more cases of progression and has the highest agreement with visual field, regardless of severity. ConclusionThe study of the macula ganglion cell complex using OCT could be a better biomarker of progression than the study of the optic nerve fiber layer, at any stage of glaucoma.

Determining Gender-Based Differences in Retinal and Choroidal Thickness in Underweight Individuals via Swept-Source Optical Coherence Tomography.

Despite improvements in reducing hunger in recent years, undernutrition remains a global public health problem. This study utilizes the swept-source optical coherence tomography (SS-OCT) technique to assess changes in retinal and choroidal thickness in underweight subjects. Ophthalmic examinations were conducted on all adults participating in this cross-sectional research. Depending on their body mass index (BMI), the participants were divided into two groups: the underweight group and the normal group. The study included the right eyes of the underweight adults and an equal number of age- and gender-matched normal-weight subjects. The retinal thickness showed no significant difference between the underweight and normal groups (P > 0.05 for all). In males, the retina of the center and inner ring in the underweight group was significantly thinner than that in the normal group, while no such results were found in females. The choroid in the underweight group was significantly thinner compared to that in the normal group (all P < 0.05). Being underweight may affect choroidal thickness in both males and females. In comparison with underweight females, underweight males may experience more retinal damage. These findings contribute to a better understanding of the pathogenesis underlying specific ocular diseases in malnourished individuals.

Clinical Findings and Optical Coherence Tomography Measurements of Pediatric Patients with Papilledema and Pseudopapilledema.

To compare the clinical findings and multimodal imaging of pediatric patients diagnosed with papilledema and pseudopapilledema with those of healthy individuals. Ninety children (<18 years of age) referred for suspected papilledema were included in this study. All patients underwent optical coherence tomography (OCT) imaging and were compared with normal control subjects. Fifty-eight children diagnosed with pseudopapilledema, 32 children with mild-to-moderate papilledema, and 40 controls were evaluated. The average and all quadrants of retinal nerve fiber layer (RNFL) thickness were significantly higher in the papilledema group than in the pseudopapilledema and control groups (p<0.001). Bruch's membrane opening (BMO) measurements were similar in both groups (p>0.05). The average, nasal, and temporal RNFL thicknesses were significantly higher in the pseudopapilledema group compared with the controls (p<0.001). Area under the receiver operating characteristic (ROC) curve showed high diagnostic ability for RNFL thickness in all quadrants to differentiate papilledema from pseudopapilledema (p<0.001). In the pseudopapilledema group, average, temporal, and inferior RNFL thickness and BMO measurements were significantly higher in eyes with optic nerve head drusen (n=28) compared with those without drusen (n=88) (p=0.035, p=0.022, p=0.040 and, p=0.047 respectively). Papilledema and pseudopapilledema show great differences in evaluation, follow-up, and prognosis. Using non-invasive methods such as newly developed OCT techniques in differential diagnosis can relieve patients with pseudopapilledema from the stress and financial burden of expensive, extensive, and invasive procedures.

An innovative multi-modal retinal imaging system for in vivo retinal detection in small animals.

This paper presents an innovative retinal imaging system tailored for in vivo fundus detection in small animals. This system integrates Scanning Laser Ophthalmoscopy (SLO) and optical Coherence Tomography (OCT) techniques, enabling the simultaneous generation of images from various modalities, including SLO reflectance, SLO fluorescein angiogram, OCT, and OCT angiogram. The existing multi-modal retinal imaging systems generally encounter limitations such as the inability to detect peripheral lesion areas attributed to small Field of View (FOV) design and susceptibility to sample motion due to slow data acquisition speed. To address these challenges, it's essential to underscore that this proposed system offers a range of notable advantages, including its compact design, the capacity for widefield imaging with a FOV of up to 100°, and a rapid OCT A-scan rate of 250 kHz, notably exceeding the capabilities of pre-existing multi-modal retinal imaging systems. Validation of the system involved imaging the eyes of normal wild-type mice and diseased mice afflicted with retinal detachment and choroidal neovascularization (CNV). The favorable imaging results demonstrate the system's reliability in identifying retinal lesions in small animals.

From the past to the present, optical coherence tomography in glaucoma: a practical guide to a common disease

Glaucoma comprises a group of disorders of the optic nerve that cause degenerative optic neuropathy, characterised by failure of neuroretinal rim tissue in the optic nerve head, retinal nerve fibre layer, and retinal ganglion cells. Glaucoma imposes a serious epidemiological threat, with an steady increase in the global number of cases. In the current ophthalmological practice, glaucoma is diagnosed via a series of examinations, including routine funduscopic examination, ocular tonometry, gonioscopy, measurement of the visual field, and assessment using the optical coherence tomography (OCT) technique. Nowadays, the OCT technique helps in systematising the diagnostic pathway and is a basic diagnostic tool for detection of early glaucomatous eye changes. It is also vital in assessing progression and monitoring treatment results of patients. The aim of this review was to present the OCT technique as a main tool in diagnosing and monitoring glaucoma.

An Evaluation of Lymphedema Using Optical Coherence Tomography: A Rat Limb Model Approach.

Lymphedema is a pathology caused by poor lymphatic flow which may lead to complete disability. Currently, precise, non-invasive techniques for quantifying lymphedema are lacking. In this paper, the results of an in vivo assessment of lymphedema via a developed small-animal model using the hindlimbs of rats and an optical coherence tomography (OCT) technique are presented. This model of lymphedema was based on a surgical lymph node resection and subsequent two-step X-ray exposure. The development of lymphedema was verified via the histological examination of tissue biopsies. The properties of the lymphedematous skin were analyzed in vivo and compared with healthy skin via OCT. The main differences observed were (1) a thickening of the stratum corneum layer, (2) a thinning of the viable epidermis layer, and (3) higher signal attenuation in the dermis layer of the lymphedematous skin. Based on the distribution of the OCT signal's intensity in the skin, a machine learning algorithm was developed which allowed for a classification of normal and lymphedematous tissue sites with an accuracy of 90%. The obtained results pave the way for in vivo control over the development of lymphedema.

Fabrication and development of novel micromachined parylene-based electroactive membranes with embedded microfluidic architectures

This work describes the design, fabrication, modeling, and testing of monolithic micromachined parylene-based electroactive membranes (µPEMs) with embedded microfluidic channels. The design and modeling employed analytical plate theory to determine the optimal membrane dimensions and structural shapes for various microsystem designs. The µPEMs were fabricated using a combination of surface and bulk micromachining techniques incorporating Parylene C as a biocompatible polymeric structural material combined with patterned electrodes for actuation. Experimental actuation of the electroactive membranes demonstrated reliability with minimal voltage shifts, and theoretical pull-in voltages closely matching experimental results. Different structural parameters of the µPEMs were also tested, such as varying the overall membrane thickness/structural rigidity and actuation chamber depth. Dynamic actuation of the membrane, including, the deflection and system response to various actuation frequencies, was observed and quantified via optical coherence tomography techniques. Microfluidic architectures were monolithically integrated with the membrane actuator and successfully perfused, with no signs of leakage. This compact microsystem has potential applications in microfluidics and Lab/System-On-a-Chip devices, for use in micromixers, particle manipulators, and applying strain to adherent cells cultured on top of the membrane.

Observation of viscous liquid flow in tobacco substrate during heating using optical coherence tomography.

The present study used optical coherence tomography (OCT) to monitor the dynamics of a highly viscous liquid in a porous tobacco substrate during heating. The OCT technique was integrated with a specially designed heating chamber and an air pump for measuring. Two transitional points in the liquid behaviours at different temperatures were estimated using OCT and statistical analysis of the attenuation coefficient. The first point, 'A', shows the time approximation at which the penetration-dominant zone transitions into the evaporation-dominant zone. The second point, 'B', indicates the time approximation at which rapid evaporation of free liquid transitions into slow evaporation of trapped and bound liquid. This analytical system is an alternative for tracking liquid transport in porous biomass during heating.