Using beam-offset optical coherence tomography to reconstruct backscattered photon profiles in scattering media


Raster scanning imaging technologies capture least scattered photons (LSPs) and reject multiple scattered photons (MSPs) in backscattered photons to image the underlying structures of a scattering medium. However, MSPs can still squeeze into the images, resulting in limited imaging depth, degraded contrast, and significantly reduced lateral resolution. Great efforts have been made to understand how MSPs affect imaging performance through modeling, but the techniques for visualizing the backscattered photon profile (BSPP) in scattering media during imaging are unavailable. Here, a method of reconstructing BSPP is demonstrated using beam-offset optical coherence tomography (OCT), in which OCT images are acquired at offset positions from the illumination beam. The separation of LSPs and MSPs based on the BSPP enables quantification of imaging depth, contrast, and lateral resolution, as well as access to the depth-resolved modulated transfer function (MTF). This approach presents grea...

Automatic intraluminal scanning with a steerable endoscopic optical coherence tomography catheter for gastroenterology applications

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Significance Endoscopic optical coherence tomography (OCT) enables real-time optical biopsy of human organs. Endoscopic probes require miniaturization of optics, which in turn limits field of view. When larger imaging areas are needed such as in the gastrointestinal tract, the operator must manually scan the probe over the tissue to extend the field of view, often resulting in an imperfect scanning pattern and increased risk of missing lesions. Automatic scanning has the potential to extend the field of view of OCT, allowing the user to focus on image interpretation during real-time observations. Aim This work proposes an automatic scanning using a steerable OCT catheter integrated with a robotized interventional flexible endoscope. The aim is to extend the field of view of a low-profile OCT probe while improving scanning accuracy and maintaining a stable endoscope’s position during minimally invasive treatment of colorectal lesions. Approach A geometrical model of the steerabl...

Triple-clad W-type fiber mitigates multipath artifacts in multimodal optical coherence tomography

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Triple-clad W-type fiber mitigates multipath artifacts in multimodal optical coherence tomography Multimodal endoscopic optical coherence tomography (OCT) can be implemented with double-clad fiber by using the presumed single-mode core for OCT and the higher numerical aperture cladding for a secondary modality. However, the quality of OCT in double-clad fiber (DCF) based systems is compromised by the introduction of multipath artifacts that are nt present in single-mode fiber OCT systems. Herein, the mechanisms for multipath artifacts in DCF are linked to its modal contents using a commercial software package and experimental measurement. A triple-clad W-type fiber is proposed as a method for achieving multimodal imaging with single-mode quality OCT in an endoscopic system. Simulations of the modal contents of a W-type fiber are compared to DCF and single-mode fiber. Finally, a W-Type fiber rotary catheter is used in a DCF-based endoscopic OCT and autofluorescence imaging (AFI) system to demonstrate multipath artifact free OCT and AFI of a human fingertip.

Improved FAST algorithm for non-uniform rotational distortion correction in OCT endoscopic imaging

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Improved FAST algorithm for non-uniform rotational distortion correction in OCT endoscopic imaging Optical Coherence Tomography (OCT) is widely used for endoscopic imaging in endoluminal organs because of its high imaging accuracy and resolution. However, OCT endoscopic imaging suffers from Non-Uniform Rotational Distortion (NURD), which can be caused by many factors, such as irregular motor rotation and changes in friction between the probe and the sheath. Correcting this distortion is essential to obtaining high-quality Optical Coherence Tomography Angiography (OCTA) images. There are two main approaches for correcting NURD: hardware-based methods and algorithm-based methods. Hardware-based methods can be costly, challenging to implement, and may not eliminate NURD. Algorithm-based methods, such as image registration, can be effective for correcting NURD but can also be prone to the problem of NURD propagation. To address this issue, we process frames by coarse and fine registration, respectively. The new reference frame is generated by filtering out the A-scan that may have ...

Bimodal endoscopic probe combining white-light microscopy and optical coherence tomography

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We present a novel bimodal endoscopic imaging probe that can simultaneously provide full-field white-light video microscopy and confocal optical coherence tomography (OCT) depth scans. The two modalities rely on spectrally separated optical paths that run partially in parallel through a micro-optical bench system, which has a cross-section of only 2   mm × 2.76   mm 2 mm×2.76 mm and is realized via standard silicon micromachining techniques. With a numerical aperture of 0.061, the video modality has a resolution and field of view of 9.3 and 1240   μm × 1080   μm 1240 μm×1080 μm , respectively. The resolution is limited by the pixel spacing of the coherent fiber bundle, which relays the acquired image from the distal to the proximal end. A custom-designed diffractive optical element placed within the video imaging path significantly improves the image contrast by up to 45% in the medium freque...

An optically-guided cochlear implant sheath for real-time monitoring of electrode insertion into the human cochlea

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In cochlear implant surgery, insertion of perimodiolar electrode arrays into the scala tympani can be complicated by trauma or even accidental translocation of the electrode array within the cochlea. In patients with partial hearing loss, cochlear trauma can not only negatively affect implant performance, but also reduce residual hearing function. These events have been related to suboptimal positioning of the cochlear implant electrode array with respect to critical cochlear walls of the scala tympani (modiolar wall, osseous spiral lamina and basilar membrane). Currently, the position of the electrode array in relation to these walls cannot be assessed during the insertion and the surgeon depends on tactile feedback, which is unreliable and often comes too late. This study presents an image-guided cochlear implant device with an integrated, fiber-optic imaging probe that provides real-time feedback using optical coherence tomography during insertion into the human cochlea. This nov...

Novel microendoscope design improves bio-imaging

Microendoscopes using fiber optics are becoming increasingly important imaging tools, but they have physical limitations. They are essential for applications that require a long working distance, high resolution, and a minimum probe diameter. A paper in IEEE Photonics Journal by Karol Karnowski of Poland’s International Centre for Translational Eye Research , Gavrielle Untracht of Technical University of Denmark , Michael Hackmann of University of Western Australia , Onur Cetinkaya of ICTER and David Sampson of the University of Surrey, UK, sheds new light on modern microendoscopes. The researchers show that endoscopic imaging probes, particularly those for so-called side viewing, combining fiber-optic (GRIN) and spherical lenses, “offer excellent performance over the entire range of numerical apertures and open the way to a broader range of imaging applications”. The performance of endoscopic imaging probes is comparable to commonly used single focusing element pr...

How to improve microendoscopes? New probe design brings promises to improve biomedical imaging

Microendoscopes are the cornerstone of modern medical diagnostics—they allow us to see what we could not even describe two decades ago. The technology is constantly improving, with ICTER scientists contributing to the development of the probes. Microendoscopes using fiber optics are becoming increasingly important imaging tools, but they have physical limitations. They are essential for applications that require a long working distance, high resolution, and a minimum probe diameter. A new research paper by Dr. Karol Karnowski of ICTER, Dr. Gavrielle Untracht of the Technical University of Denmark (DTU), Dr. Michael Hackmann of the University of Western Australia (UWA), Onur Cetinkaya of ICTER and Prof. David Sampson of the University of Surrey, sheds new light on modern microendoscopes. The research work started while the authors worked in the same research group at UWA. ( Read Full Article )

Superior Imaging Performance of All-Fiber, Two-Focusing-Element Microendoscopes

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All-fiber-optic imaging microendoscopes are emerging as an important tool in bioimaging studies, including those conducted with optical coherence tomography, but physical limitations constrain the achievable beam characteristics of designs using a single focusing element. These constraints are especially relevant for applications that require a long working distance, high resolution, and/or minimal probe diameter. Through detailed analysis based on ABCD matrix modelling, we show that side-viewing probes combining a graded-index (GRIN) fiber with a ball lens – GRIN-ball-lens probes (GBLPs) – offer superior performance over a range of numerical apertures and pave the way for a broader range of imaging applications. The performance of side-viewing GBLPs designed for 1300-nm optical coherence tomography imaging is compared against commonly used single-focusing-element all-fiber side-viewing probe designs, namely, ball-lens probes (BLPs) and GRIN-fiber probes (GFPs). All poss...

Atherectomy catheters with imaging

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An atherectomy catheter includes an elongate flexible catheter body, an elongate deflectable distal tip coupled to the catheter body at a hinge point, a rotatable cutter near the distal end of the catheter body, and a drive shaft extending within the catheter body and configured to rotate the cutter. The atherectomy catheter further includes an optical fiber extending through the drive shaft substantially on-axis with the catheter body and attached to the cutter. The optical fiber is configured to rotate with the drive shaft. The atherectomy catheter further includes a wedge configured to deflect the distal tip away from the catheter body at the hinge point upon axial movement of the drive shaft.   ( Read Full Article )

3D-printed fiber-based zeroth- and high-order Bessel beam generator

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Bessel beams (BBs) have gained prominence thanks to their diffraction-free propagation and self-healing properties. These beams are conventionally generated using different approaches, namely by transforming a narrow circular beam with a lens, using axicons or holographic beam-shaping techniques. These methods involve space-consuming optics. To overcome this limitation, in the past, efforts have been made to create BBs directly from optical fibers. However, these solutions have limited capability to generate BBs with on-demand optical parameters and only focused on creating zeroth-order BBs. Here, we propose a photonic structure that uses stacked miniaturized optical elements 3D printed in a single step on the fiber facet. Our design allows for the generation of both zeroth- and high-order BBs and fully controllable tailoring of the beams’ parameters, such as their diffraction-free propagation distance or the width of their central peak or node. Remarkably, we report for the f...

Customized fiber generates Bessel beams

An all fiber-based approach to generating special optical beams, called Bessel beams, could open up new applications in imaging, optical trapping and communications. Bessel beams look quite different from the usual Gaussian light beams found in optics. In particular, they possess several interesting properties including self-healing, diffraction-free propagation and the ability to carry orbital angular momentum (OAM). This family of beams—also known as vortex beams with a characteristic ring-like shape and a dark central region—include different "orders" of beams carrying different values of OAM. ( Read Full Article )

Dual-modality fluorescence lifetime imaging-optical coherence tomography intravascular catheter system with freeform catheter optics

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Significance: Intravascular imaging is key to investigations into atherosclerotic plaque pathobiology and cardiovascular diagnostics overall. The development of multimodal imaging devices compatible with intracoronary applications has the potential to address limitations of currently available single-modality systems. Aim: We designed and characterized a robust, high performance multimodal imaging system that combines optical coherence tomography (OCT) and multispectral fluorescence lifetime imaging (FLIm) for intraluminal simultaneous assessment of structural and biochemical properties of coronary arteries. Approach: Several shortcomings of existing FLIm-OCT catheter systems are addressed by adopting key features, namely (1) a custom fiber optic rotary joint based on an air bearing, (2) a broadband catheter using a freeform reflective optics, and (3) integrated solid-state FLIm detectors. Improvements are quantified using a combination of experimental characterization and simulatio...

Flexible method for generating needle-shaped beams and its application in optical coherence tomography

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Needle-shaped beams (NBs) featuring a long depth-of-focus (DOF) can drastically improve the resolution of microscopy systems. However, thus far, the implementation of a specific NB has been onerous due to the lack of a common, flexible generation method. Here we develop a spatially multiplexed phase pattern that creates many axially closely spaced foci as a universal platform for customizing various NBs, allowing flexible manipulations of beam length and diameter, uniform axial intensity, and sub-diffraction-limit beams. NBs designed via this method successfully extended the DOF of our optical coherence tomography (OCT) system. It revealed clear individual epidermal cells of the entire human epidermis, fine structures of human dermal-epidermal junction in a large depth range, and a high-resolution dynamic heartbeat of alive Drosophila larvae. ( Read Full Article )

Flexible method for shaping laser beams extends depth-of-focus for OCT imaging

esearchers have developed a new method for flexibly creating various needle-shaped laser beams. These long, narrow beams can be used to improve optical coherence tomography (OCT), a noninvasive and versatile imaging tool that is used for scientific research and various types of clinical diagnoses. "Needle-shaped laser beams can effectively extend the depth-of-focus of an OCT system, improving the lateral resolution, signal-to-noise ratio, contrast and image quality over a long depth range," said research team leader Adam de la Zerda from Stanford University School of Medicine. "However, before now, implementing a specific needle-shaped beam has been difficult due to the lack of a common, flexible generation method." ( Read Full Article )


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