KEYWORDS: Optical coherence tomography, Imaging systems, Cornea, Signal processing, Retina, Cameras, Signal detection, Real time imaging, In vivo imaging, Sensors
A line-field optical coherence tomography (LFOCT) application is implemented for real-time in vivo corneal and retinal imaging. In contrast to other described systems of LFOCT that use single-shot high-speed cameras, we describe the first results utilizing a camera with continuous high-speed data transfer and display. The system is based on a previously published design using a center wavelength of 840nm and a bandwidth of 50nm. The system’s B-frame and en-face display speed reaches up to 5000 frames per second corresponding to 2,500,000 A-lines. A visible light camera is used to detect the interferometric signal to reduce costs and improve optomechanical integration. Balancing the sensitivity vs. acquisition speed allows continuous high data transfer and processing rates and simplifies the implementation as a bedside system. Higher frame rates are important for scan positioning on non-compliant subjects such as infants and children.
Corneal diseases are the fifth leading cause of visual loss globally. Current clinical imaging instruments such as In Vivo Confocal Microscopy (IVCM) offer high lateral resolution to observe cellular structures but lack large field of view and volumetric imaging capability and require high operator skill to focus and align. To overcome these limitations, we have developed blue (450 nm) and green (510 nm) light Optical Coherence Microscopy (OCM) to image cellular structures. Imaging was demonstrated in ex vivo samples including human donor eyes. The OCM systems were based on a spectral-domain optical coherence tomography engine and achieved 750 μm × 750 µm field of view, 1.2 mm imaging depth, and 1.6 μm lateral resolution. Epithelial cells, endothelial cells, and keratocytes of ex vivo rabbit cornea were visualized. Additionally, collagen fibers were observed in stromal lamellae with striated patterns. En face and cross-sectional images of trabecular meshwork and Schlemm’s canal in a donor human eye wedge were observed at various trans-meshwork pressures controlled by cannulation of the canal. Microbes such as filamentous fungi and bacteria were observed.
KEYWORDS: Signal processing, Optical coherence tomography, Beam diameter, Light sources and illumination, Imaging systems, High speed cameras, Medical device development
A real-time high-speed line-field optical coherence tomography (LFOCT) configuration at 5,000 B-frames or 2,500,000 A-lines per second for clinical applications is described. The development of the LFOCT technology has experienced increasing interest despite the challenge of achieving sufficient sensitivity and resolution due to crosstalk. Publications of research systems usually apply expensive infrared cameras to improve image quality. The costs, complexity, and lack of real-time data transfer of dedicated highspeed IR cameras make it challenging to employ LFOCT for a more comprehensive application range. We demonstrate using a comparatively low-cost, high-speed camera for real-time data transfer and image display in conjunction with a light source at a center wavelength of 840 nm and a bandwidth of 50 nm. Although the camera and available sample power limits the sensitivity (75 dB), we can demonstrate imaging on a human fingertip (in vivo) and the cornea of a rabbit eye. Further development of the system will focus on compensating for the camera's limited sensitivity and improving resolution to target clinical in vivo imaging such as ophthalmic applications.
Corneal disease is the fifth leading cause of global blindless. Optical coherence tomography (OCT) for anterior imaging is extensively used due to its non-invasive and high-resolution volumetric imaging characteristics. Optical coherence microscopy (OCM) is a technical variation of OCT that can image the cornea with cellular resolution. Here, we demonstrate a visible-light OCM as a low-cost and easily reproducible system to visualize various corneal cellular structures such as epithelial cells, endothelial cells, keratocytes, and collagen bundles within stromal lamellae. The visible-light OCM was also used to study pressure changes in anterior segment human donor eyes. The system achieved an axial resolution of 12 μm in tissue over a 1.2 mm imaging depth, and a lateral resolution of 1.6 µm over a field of view of up to 750 μm × 750 μm.
Thinning of the outer nuclear layer (ONL) is an important pathological feature and possible biomarker of age-related macular degeneration (AMD). The demarcation of the ONL and Henle’s fiber layer (HFL) is visually unattainable with standard optical coherence tomography (OCT) imaging. In this work, we built a volumetric directional OCT prototype which constitutes two optical scanners in the sample arm that synchronously scan the imaging beam on the pupil and retina. The imaging beam’s entry positions and incident angles on the pupil and retina respectively are precisely controlled and optimally maintained to generate sufficient contrast of the HFL over the entire macular volume.
We demonstrated a handheld swept-source optical coherence tomography (OCT) imaging system with a 400 kHz vertical-cavity surface-emitting laser (VCSEL) light source, a non-contact approach, and an unprecedented 105° field of view (FOV) that was capable of obtaining images from the posterior pole to peripheral retina in a single shot. A spiral scanning pattern allowing real-time visualization was also implemented here to improve the sampling efficiency. To the best of our knowledge, this is the widest FOV for a portable non-contact OCT retinal imaging system to date. Improvements to the FOV allow detection of peripheral pathology and aid better understanding of the role of peripheral pathology in retinal diseases.
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