Illumination System Research Articles

Design of illumination system using characterized illuminances for smartphone-based fundus camera

Recently, smartphone-based fundus camera (SBFC) research has been actively conducted in response to the need to expand medical infrastructure in underdeveloped countries and the increased telemedicine since the COVID-19 pandemic. Compared to the conventional table-top system, SBFCs have technical challenges that make it difficult to guarantee uniform illumination and avoid back-reflection because of the design constraints of minimizing the form factor and cost. This paper proposes a novel illumination design methodology using characterized illuminance to obtain high-quality fundus images for SBFCs. Key performance indicators (KPIs), such as retinal uniformity, back-reflection suppression, and optical efficiency, were defined to evaluate the performance of the illumination system. Each KPI was calculated using optical simulation software based on Monte-Carlo ray tracing and mapped into a normalized three-dimensional coordinate, the retinal illumination performance space (RIPS). In RIPS, the KPIs are combined into a single parameter ΔRIPS, which is the quantitative difference evaluated as the Euclidean distance between the ideal and actual design point. A compact SBFC illumination system with five design variables was presented to verify the proposed methodology. The final design values at the minimum ΔRIPS were determined using the Taguchi method and response surface methodology. Finally, a working prototype was built, and fundus images were acquired by clinical testing under institutional review board approval. The fundus image had sufficient brightness and resolution to diagnose the lesion with a viewing angle of approximately 50° in one shot.

Speckle- and interference fringes-free illumination system with a multi-retarder plate.

Our study proposes a novel method for obtaining speckle-free homogeneous illumination using a combination of a multi-retarder plate, a microlens array, a Fourier lens, and a diffraction optical element (DOE) based on pseudorandom binary sequences. The proof-of-concept multi-retarder plate is introduced to generate multiple uncorrelated laser beams, while a mathematical model was developed to explain the method's mechanism and evaluate its effectiveness. In the DOE passive (stationary) mode, the method was found to reduce speckle contrast to 0.167, 0.108, and 0.053 for red, green, and blue laser diodes, respectively. In active mode, the speckle contrast was further reduced to 0.011, 0.0147, and 0.008. The observed differences in speckle contrast in the stationary mode were attributed to variations in the coherence lengths of the RGB lasers. By implementing the proposed method, we successfully generated a square-shaped illumination spot that was free from interference artifacts. The spot obtained exhibited a slow, weak variation in intensity across the screen, attributable to the multi-retarder plate's suboptimal quality. However, this limitation can be readily addressed in future studies through the adoption of more advanced fabrication techniques.

Development of a shortwave infrared sinuscope for the detection of cerebrospinal fluid leaks.

Cerebrospinal fluid (CSF) rhinorrhea (leakage of brain fluid from the nose) can be difficult to identify and currently requires invasive procedures, such as intrathecal fluorescein, which requires a lumbar drain placement. Fluorescein is also known to have rare but significant side effects including seizures and death. As the number of endonasal skull base cases increases, the number of CSF leaks has also increased for which an alternative diagnostic method would be highly advantageous to patients. We aim to develop an instrument to identify CSF leaks based on water absorption in the shortwave infrared (SWIR) without the need of intrathecal contrast agents. This device needed to be adapted to the anatomy of the human nasal cavity while maintaining low weight and ergonomic characteristics of current surgical instruments. Absorption spectra of CSF and artificial CSF were obtained to characterize the absorption peaks that could be targeted with SWIR light. Different illumination systems were tested and refined prior to adapting them into a portable endoscope for testing in 3D-printed models and cadavers for feasibility. We identified CSF to have an identical absorption profile as water. In our testing, a narrowband laser source at 1480nm proved superior to using a broad 1450nm LED. Using a SWIR enabling endoscope set up, we tested the ability to detect artificial CSF in a cadaver model. An endoscopic system based on SWIR narrowband imaging can provide an alternative in the future to invasive methods of CSF leak detection.

Optical Engine Design for a Compact, High-Luminance DLP Projector Using Four-Channel LEDs and a Total Internal Reflection Prism

How to obtain higher brightness with a small volume projection engine for 4K resolution digital light processing (DLP) is of great significance. In this paper, we first use the fourth channel serving as a blue pump leading to a 52% gain of green brightness. Secondly, a new inline total internal reflection prism glued with a spherical mirror is constructed to notably reduce the length of the relay illumination system by more than 10 mm, resulting in a more compact optical engine with a volume of 210 × 140 × 36 mm3. Thirdly, a projection lens is optimized with a modulation transfer function higher than 0.6 at 93 lines for a distance of 2125 mm with distortion lower than 1%. As a result, the efficiencies of RGB lights are higher than 60%, and the luminance and uniformity on the screen reach 1412 lm and 94.5% measured by the prototype. Our proposed projection system is significantly helpful for designing a compact and high-luminance 4K DLP projection.

Deep learning for asbestos counting

The PCM (phase contrast microscopy) method for asbestos counting needs special sample treatments, hence it is time consuming and rather expensive. As an alternative, we implemented a deep learning procedure on images directly acquired from the untreated airborne samples using standard Mixed Cellulose Ester (MCE) filters. Several samples with a mix of chrysotile and crocidolite with different concentration loads have been prepared. Using a 20x objective lens coupled with a backlight illumination system a number of 140 images were collected from these samples, which along with additional 13 highly fibre loaded artificial images constituted the database. About 7500 fibres were manually recognised and annotated following the National Institute for Occupational Safety and Health (NIOSH) fibre counting Method 7400 as input for the training and validation of the model. The best trained model provides a total precision of 0.84 with F1-Score of 0.77 at a confidence of 0.64. A further post-detection refinement to ignore detected fibres < 5 µm in length improves the final precision. This method can be considered as a reliable and competent alternative to conventional PCM.

High-irradiance illumination system for transmission extreme ultraviolet microscopy

A high-irradiance illumination system with normal-incidence multilayer mirrors is developed. The system consists of two concave Mo/Si multilayer mirrors with aspherical substrates that provide critical illumination by imaging a laser-produced plasma (LPP) light source at a wavelength of 13.6 nm with a magnification of almost unity. By effectively correcting spherical aberration, a raytracing computation indicates that the irradiance on the sample can be increased by about four times compared to that for a conventional system with spherical mirrors. We experimentally confirmed the enhancement by combining a LPP light source with aspherical mirrors fabricated by magneto rheological finishing.

Photographic Gel Artifact Simulating International Classification of Retinopathy of Prematurity Notch: Stanford University Network for Diagnosis of Retinopathy of Prematurity (SUNDROP) Report no. 16

To report a series of fundus photographs taken for retinopathy of prematurity (ROP) screening that contain artifacts with imaging characteristics mimicking a notch, a recently refined classification metric in the International Classification of Retinopathy of Prematurity, third edition. Retrospective case series. Infants requiring ROP screening in neonatal intensive care units from the Stanford University Network for Diagnosis of Retinopathy of Prematurity (SUNDROP) and TeleROP telemedicine screening programs. Preterm infants meeting ROP examination criteria were screened with 130° wide-angle imaging systems. The images were taken by a trained nurse in the neonatal intensive care unit and transferred to an ROP specialist using a Health Insurance Portability and Accountability Act-compliant picture archiving and communication system for interpretation. Presence of an artifact that appeared consistent with a notch. We identified a total of 17 cases in ROP screening with artifact findings that had imaging characteristics similar to a notch. The artifactual appearance of the pseudo-notch was created by the camera illumination system within the gel-lens interface when the lens was not well apposed to the cornea. In telemedicine screening for ROP, we present fundus images of eyes with a pseudo-notch appearance; review of overlapping images can help differentiate between notch and artifact. Pediatric retinal specialists need to be aware that artifacts play a confounding role in screening for ROP, that can be mitigated through the use of overlapping and redundant images. Proprietary or commercial disclosure may be found after the references.

Determination of Correlated Color Temperature in Ex Vivo Porcine Eyes during Intraocular Illumination.

(1) Background: In ophthalmic surgery, white light is mostly applied to illuminate the intraocular space, and ophthalmologists are comfortable working with it. Diaphanoscopic illumination changes the spectral composition of light, resulting in a change in the correlated color temperature (CCT) of the intraocular illumination. This color change makes it difficult for surgeons to recognize the structures in the eye. CCT during intraocular illumination has not yet been measured before, and it is the aim of this study to perform such measurement. (2) Methods: CCT was measured inside ex vivo porcine eyes during diaphanoscopic illumination and endoillumination using a current ophthalmic illumination system with a detection fiber inside the eye. By applying pressure on the eye with a diaphanoscopic fiber, the dependency of CCT on pressure was examined. (3) Results: The intraocular CCT values during endoillumination were 3923 K and 5407 K for the halogen and xenon lamps, respectively. During diaphanoscopic illumination, a strong unwanted red shift was observed, resulting in 2199 K and 2675 K for the xenon and the halogen lamps, respectively. Regarding different applied pressures, the CCT did not differ considerably. (4) Conclusions: This red shift should be compensated for in the development of new illumination systems since surgeons are used to white light illumination, which also simplifies the identification of retinal structures.

Design and Implementation of Solar-Powered Optical Fiber-Based Illumination and Communication System for Underground Coal Mines

Design and Implementation of Solar-Powered Optical Fiber-Based Illumination and Communication System for Underground Coal Mines

Compact ultraviolet light-emitting diode-based lithography illumination system with tunable coherent factor

Optimization of the illumination system of an ultraviolet light-emitting diode (UVLED)-based lithography system by reducing the system complexity and spatial volume has been a research focus. This work proposes a compact lithography illumination system that applies a specially designed embedded compound parabolic concentrator (ECPC) to replace the traditional collimation module and the zoom lenses module. The ECPC, comprised of two detachable parabolic surfaces, precisely collimates all light beams from the UVLED to a preset divergence angle of 6 deg and provides an adjustable lithography coherent factor. The final illumination system offers a square illumination field with a uniformity of up to 1.3% in the large coherent factor and a linearly adjustable numerical aperture in the range of 0.02 ∼ 0.04. The final exposure result of 0.7 μm based on the experiment setup further verifies the performance of the designed illumination system.

Pulse Oximetry Imaging System Using Spatially Uniform Dual Wavelength Illumination.

Pulse oximetry is a non-invasive method for measuring blood oxygen saturation. However, its detection scheme heavily relies on single-point measurements. If the oxygen saturation is measured at a single location, the measurements are influenced by the profile of illumination, spatial variations in blood flow, and skin pigment. To overcome these issues, imaging systems that measure the distribution of oxygen saturation have been demonstrated. However, previous imaging systems have relied on red and near-infrared illuminations with different profiles, resulting in inconsistent ratios between transmitted red and near-infrared light over space. Such inconsistent ratios can introduce fundamental errors when calculating the spatial distribution of oxygen saturation. In this study, we developed a novel illumination system specifically designed for a pulse oximetry imaging system. For the illumination system, we customized the integrating sphere by coating a mixture of barium sulfate and white paint inside it and by coupling eight red and eight near-infrared LEDs. The illumination system created identical patterns of red and near-infrared illuminations that were spatially uniform. This allowed the ratio between transmitted red and near-infrared light to be consistent over space, enabling the calculation of the spatial distribution of oxygen saturation. We believe our developed pulse oximetry imaging system can be used to obtain spatial information on blood oxygen saturation that provides insight into the oxygenation of the blood contained within the peripheral region of the tissue.

Retinal risk of endoillumination: A comparison of different ophthalmic illumination systems.

In vitreoretinal surgery, there is always a conflict between bright illumination of the field of operation and retinal safety. This study aimed to investigate different light sources and light guides for their potential retinal risk due to bright illumination. Irradiances in the fovea of ex-vivo porcine eyes resulting from different light sources (halogen lamp, xenon lamp and LED) and light guides are investigated for varying distances between the illumination tip and the fovea. The results are examined with regard to their photochemical and thermal retinal hazard and the maximal exposure time. The examination is carried out with the maximum intensity setting of each light source and with normalization to its brightness. With decreasing distance of the tip of the light source, the retinal hazard increases. The photochemical and thermal retinal hazard at maximum brightness are smallest for the halogen lamp, next for the xenon lamp and highest for the LED. Thus, the exposition time is the longest for the halogen lamp followed by the xenon lamp and the LED. Normalizing the results to the same brightness the maximum exposition time is nearly the same for xenon lamp and LED, but still higher in case of the halogen lamp. The choice of the most suitable lamp and illumination fiber depends on the intensity and spectral distribution of the illumination system. Concerning brightness, xenon and LED lamp are relatively harmless, but the surgeon should avoid the maximum device intensity.

The Influence of Multi-Storey Surrounding Development on a Daylighting of Interiors in Top-Lit Premises: An Experimental Study

To ensure a required daylight in premises with top system of outdoor illumination through roof lighting installations, it is necessary to take into account the photometrical effects of surrounding development. For the time being such a concept in lighting engineering design is adopted only for side lit premises through windows, though the dense urban development in modern megalopolises offers nearly the same problem for buildings with overhead daylighting system. This paper presents a brief description of experimental case studies, based on the scale model method, as well as on the photometric studies of a real premise with skylights. The studies were conducted in both cases under CIE standard overcast sky with changing geometrics and photometrical parameters of model elements. The results of the studies showed the great photometric influence of opposite-standing objects on the values of daylight factor (D) in premises with top lighting system and dependence of this influence on size, position, and structural type of skylights, as well as on size and finishing of the model parts and on distance between skylights and opposite-standing building.

Daylighting of Low-Rise Buildings with Roof System of Illumination in the Case of Dense Surrounding Urban Development

In this article, emphasis on the new principles and methods in daylighting design of interiors has been laid. This new approach is connected with the roof daylighting system in various buildings in the condition of dense urban development. It is felt that after the consideration of various kinds of planning and structural design, connected with the skylight’s sizes and position, the surroundings buildings height and coloristic finishing, and etc., the determination of some specific quotients will not present much of difficulties. In the article, a number of designs recommendations and conclusions have been made and a number of dependences of characteristics, important from scientific point of view, have been determined.

Deep learning for precise axial localization of trapped microspheres in reflective optical systems.

High-precision axial localization measurement is an important part of micro-nanometer optical measurement, but there have been issues such as low calibration efficiency, poor accuracy, and cumbersome measurement, especially in reflected light illumination systems, where the lack of clarity of imaging details leads to the low accuracy of commonly used methods. Herein, we develop a trained residual neural network coupled with a convenient data acquisition strategy to address this challenge. Our method improves the axial localization precision of microspheres in both reflective illumination systems and transmission illumination systems. Using this new localization method, the reference position of the trapped microsphere can be extracted from the identification results, namely the "positioning point" among the experimental groups. This point relies on the unique signal characteristics of each sample measurement, eliminates systematic repeatability errors when performing identification across samples, and improves the localization precision of different samples. This method has been verified on both transmission and reflected illumination optical tweezers platforms. We will bring greater convenience to measurements in solution environments and will provide higher-order guarantees for force spectroscopy measurements in scenarios such as microsphere-based super-resolution microscopy and the surface mechanical properties of adherent flexible materials and cells.

Двухпортовая витреомакулярная хирургия в лечении пациентов с эпиретинальным фиброзом

Perpose. To present a method of two-port vitrectomy in treatment of patients with epiretinal fibrosis. Material and methods. Two-port vitrectomy method was used to treat patients with idiopathic epiretinal fibrosis. The group included 25 patients (25 eyes) – 16 (64 %) women and 9 (36 %) men. The mean age of the patients was 61 ± 6.4 years. Exclusion criteria were glaucoma and concomitant retinal pathology. The mean value of best corrected visual acuity was 0.28 ± 0.07. The mean retinal thickness in the fovea was 417 ± 70 µm. Vitrectomy was performed with installation of two ports in the opposite quadrants – in the lower half for high-flow cannula (illuminator-chandelier built with infusion cannula), in the upper half for vitrectomy cutter and instruments. The High-Flow infusion cannula (Synergetics) integrated with the mercury vapor illuminator-chandelier is connected to the Photon II illumination system (Synergetics). Surgery was performed classically: central vitrectomy, separation of posterior hyaloid membrane, staining of membranes with vitral dye, membrane removal, tamponade ⅓ of vitreous cavity with sterile air. The average operation time was 18 minutes. Results. Six months after the operative treatment all patients noted reduction of visual discomfort and severity of metamorphopsies. Best corrected visual acuity was increased – 0.58 ± 0.1 (p ≤ 0,05 vs. preoperative values). Average retinal thickness in the fovea after surgical treatment decreased to 261 ± 25 µm according to macular OCT chart (p = 0.03). FCM readings were consistent with preoperative 5.1 ± 2.3 f/ms (p ≤ 0.01). Conclusion. The method of two-port vitrectomy with the use of mercury vapor chandeleur in the treatment of vitreomacular pathology allows safe and effective macular surgery. Keywords: retinophototoxicity, vitrectomy, epiretinal fibrosis

Solid Rocket Propellant Photo-Polymerization with an In-House LED-UV Prototype

Composite solid propellants have used cast molding production technology for many decades, with intrinsic limitations on production flexibility, promptness, and grain geometry, as well as environmental implications on toxicity and global carbon footprint. This traditional method involves the use of toxic chemicals, has a long processing time, requires high temperature, and the products have limited geometries. To overcome those issues, different photo-curable resins have been evaluated as possible matrices. In fact, the UV-curing process is fast and has low energy consumption. The photocuring reaction parameters of six different pristine formulations were evaluated by Fourier transform infrared spectroscopy analysis. After finding the optimal curing parameters, different composites were prepared by adding 75 or 80 wt% ammonium sulfate particles used as an inert replacement for the oxidant. The thermomechanical properties and thermal resistance of the UV-cured composites were characterized via dynamic thermal-mechanical and thermogravimetric analysis. Subsequently, the mechanical properties of the inert propellants were investigated by tensile tests. The most promising resin systems for the production of solid rocket propellants were then 3D printed by an in-house developed illumination system and the obtained object micro-structure was evaluated by X-ray computed tomography.

Luminous Flux in Ex-Vivo Porcine Eyes during Endoillumination and during Transscleral Illumination Depending on the Transmission Properties of the Eyewall

(1) Background: During eye surgery, it is important that sufficient light enlightens the inside of the eye for small structures to become visible. The intraocular brightness is influenced by the luminous flux of the illumination system. However, the intraocular luminous flux during surgery has not been investigated so far. Insufficient luminous flux makes vision difficult for the surgeon, whereas excessive luminous flux can cause damage to the retina. Therefore, the luminous flux in lightly and strongly pigmented eyes is determined by endoillumination and diaphanoscopic illumination. (2) Methods: First, the luminous flux emitted from a diaphanoscopic illumination fiber is measured. For determining the intraocular luminous flux, this is multiplied with the transmission properties of the eyewall, which are determined for ex vivo porcine eyes. In order to compare the luminous flux of transscleral illumination with that of endoillumination, the luminous flux of various endoillumination fibers is examined. (3) Results: The results reveal that the total transmission of the eyewall is up to 2.5 times higher for blue/lightly pigmented eyes than for brown/strongly pigmented eyes. With this, the intraocular luminous flux in ex vivo porcine eyes is around 95% higher for less pigmented eyes than for strong pigmented eyes, considering intraocular reflections. (4) Conclusion: To obtain the same brightness in blue and brown eyes, the surgeon can reduce the intensity of the light source when illuminating blue eyes to reduce their retinal risk.

Experimental evaluation of the metal powder particle flow on the melt pool during directed energy deposition

The experimental evaluation of melt surface flow in blown laser cladding and additive manufacturing usually employs tracer particles added to the powder feed. This paper presents details of a high-speed imaging (HSI) and image processing technique, which can directly monitor the flow of standard (nontracer) particles on the surface of the melt. This technique should improve the accuracy of flow observations as no foreign bodies are added to the melt. To verify the technique, 316 Stainless steel powder was laser clad onto a substrate of the same material, and an HSI frame rate of 40 000 frames/s was employed with a specific illumination system. The images were subsequently image processed and the trajectories of the powder feed particles on the melt surface are analyzed and discussed here. As would be expected in this case, the observed melt surface flow was in agreement with what would be expected of a melt with a negative surface tension gradient as a function of temperature.

Development and optimization of LED systems for surface fungal decontamination of fresh produce

Uneven irradiation is the major challenge of light-emitting diode (LED) antimicrobial technology. This study developed different LED illumination systems with multi-directional light sources, spotlight reflector (SR), and parabolic reflector (PR) to ensure the high antifungal efficiency of LED on artificially inoculated litchi fruit. Results showed that multi-light LEDs enable multi-angle irradiation, therefore, could reach higher inactivation rates under the comparable energy output. Integrating LED with SR could gather the scattering light and improve the inactivation efficiency (LEDs < LEDs + SR). The addition of PR enhanced bottom irradiation, leading to a comparable effect with an extra light source (LED + SR + PR = dual-LEDs). Moreover, when comparing the energy consumption required for 90 % inactivation of fungi, the LED systems combined SR and/or PR required less power consumption than those of LEDs alone. The antifungal effects of developed systems were further validated by natural samples. These results suggest several feasible solutions to improve the antifungal efficiency of LED and also provide practical system designs to broaden the LED application in the food industry.