1. 1-24 of 625 1 2 3 4 ... 24 25 26 »
    1. Generation and characterization of mid-infrared supercontinuum in polarization maintained ZBLAN fibers

      Generation and characterization of mid-infrared supercontinuum in polarization maintained ZBLAN fibers

      We present mid-infrared (MIR) supercontinuum generation in polarization-maintained ZBLAN fibers pumped by 2 µm femtosecond pulses from a Tm:YAP regenerative amplifier. A stable supercontinuum that spreads from 380 nm to 4 µm was generated by coupling only 0.5 µJ pulse energy into an elliptical core ZBLAN fiber. The supercontinuum was characterized using cross-correlation frequency-resolved optical gating (XFROG). The complex structure of the XFROG trace due to the pulse-to-pulse spectrum instability have been fixed by reducing the length of the applied fibers or improving the quality of the incident pulse spectrum

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    2. Polarization-sensitive imaging with simultaneous bright- and dark-field optical coherence tomography

      Polarization-sensitive imaging with simultaneous bright- and dark-field optical coherence tomography

      We present a polarization-sensitive (PS) extension for bright- and dark-field (BRAD) optical coherence tomography imaging. Using a few-mode fiber detection scheme, the light backscattered at different angles is separated, and the BRAD images of tissue scattering are generated. A calibration method to correct for the fiber birefringence is proposed. Since particle scattering profiles are polarization dependent, a PS detection extends the capabilities for investigating the scattering properties of biological tissues. Both phantoms consisting of different-sized microparticles and a brain tissue specimen were imaged to validate the system performance and demonstrate the complementary image contrast.

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    3. Metre-per-second microfluidic flow velocimetry with dual beam optical coherence tomography

      Metre-per-second microfluidic flow velocimetry with dual beam optical coherence tomography

      A novel dual beam Optical Coherence Tomography (OCT) instrument has been developed for high velocity flow measurement, principally in microfluidics applications. The scanned dual beam approach creates a pair of image-frames separated by a small spatiotemporal offset. Metre-per-second flow measurement is achieved by rapid re-imaging by the second beam allowing for particle tracking between each image-frame of the pair. Flow at 1.06 m/s using a single optical access port has been measured, more than two orders of magnitude larger than previously reported OCT systems, at centimetre depth and with millimetre scale depth of field within a microfluidic chip ...

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    4. Synchronized, concurrent optical coherence tomography and videostroboscopy for monitoring vocal fold morphology and kinematics

      Synchronized, concurrent optical coherence tomography and videostroboscopy for monitoring vocal fold morphology and kinematics

      Voice disorders affect a large number of adults in the United States, and their clinical evaluation heavily relies on laryngeal videostroboscopy, which captures the medial-lateral and anterior-posterior motion of the vocal folds using stroboscopic sampling. However, videostroboscopy does not provide direct visualization of the superior-inferior movement of the vocal folds, which yields important clinical insight. In this paper, we present a novel technology that complements videostroboscopic findings by adding the ability to image the coronal plane and visualize the superior-inferior movement of the vocal folds. The technology is based on optical coherence tomography, which is combined with videostroboscopy within the ...

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    5. Optic axis uniformity as a metric to improve the contrast of birefringent structures and analyze the retinal nerve fiber layer in polarization-sensitive optical coherence tomography

      Optic axis uniformity as a metric to improve the contrast of birefringent structures and analyze the retinal nerve fiber layer in polarization-sensitive optical coherence tomography

      A new metric is used to improve the contrast of birefringent structures in biological tissue using polarization-sensitive optical coherence tomography. This metric, optic axis uniformity (OAxU), is based on the optic axis of birefringence and quantifies the uniformity of the optic axis direction. OAxU provides surprisingly strong contrast for fibrous structures such as muscle and the retinal nerve fiber layer (RNFL). We used OAxU for automatic segmentation of the RNFL in human eyes. From the segmentation, en face images of RNFL thickness and RNFL birefringence were created. The measured birefringence values are consistent with earlier reports.

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    6. Computational adaptive optics for optical coherence tomography using multiple randomized subaperture correlations

      Computational adaptive optics for optical coherence tomography using multiple randomized subaperture correlations

      Computational adaptive optics (CAO) is emerging as a viable alternative to hardware-based adaptive optics—in particular when applied to optical coherence tomography of the retina. For this technique, algorithms are required that detect wavefront errors precisely and quickly. Here we propose an extension of the frequently used subaperture image correlation. By applying this algorithm iteratively and, more importantly, comparing each subaperture not to the central subaperture but to several randomly selected apertures, we improved aberration correction. Since these modifications only slightly increase the run time of the correction, we believe this method can become the algorithm of choice for many ...

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    7. Attenuation of stripe artifacts in optical coherence tomography images through wavelet-FFT filtering

      Attenuation of stripe artifacts in optical coherence tomography images through wavelet-FFT filtering

      The use of polarization-maintaining (PM) fibers for polarization-sensitive optical coherence tomography (PS-OCT) can result in numerous image artifacts which degrade the reliability of birefringence measurements. Similar artifacts can also arise in conventional OCT, due to stray reflections from optical surfaces, a problem which is increasing in tandem with the steady rise in source coherence lengths. Here, a recently presented wavelet-FFT filter[Opt. Express 17 (10), 8567 (2009). [ PubMed ] ] is combined with surface flattening displacement fields in order to suppress ghost artifacts following either a duplicate or inverse profile to that of the sample surface. In addition, horizontal coherence stripes originating ...

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    8. Analysis of low-scattering regions in optical coherence tomography: applications to neurography and lymphangiography

      Analysis of low-scattering regions in optical coherence tomography: applications to neurography and lymphangiography

      Analysis of semi-transparent low scattering biological structures in optical coherence tomography (OCT) has been actively pursued in the context of lymphatic imaging, with most approaches relying on the relative absence of signal as a means of detection. Here we present an alternate methodology based on spatial speckle statistics, utilizing the similarity of a distribution of given voxel intensities to the power distribution function of pure noise, to visualize the low-scattering biological structures of interest. In a human tumor xenograft murine model, we show that these correspond to lymphatic vessels and nerves; extensive histopathologic validation studies are reported to unequivocally establish ...

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    9. Polarization-sensitive optical coherence tomography with a conical beam scan for the investigation of birefringence and collagen alignment in the human cervix

      Polarization-sensitive optical coherence tomography with a conical beam scan for the investigation of birefringence and collagen alignment in the human cervix

      By measuring the phase retardance of a cervical extracellular matrix, our in-house polarization-sensitive optical coherence tomography (PS-OCT) was shown to be capable of (1) mapping the distribution of collagen fibers in the non-gravid cervix, (2) accurately determining birefringence, and (3) measuring the distinctive depolarization of the cervical tissue. A conical beam scan strategy was also employed to explore the 3D orientation of the collagen fibers in the cervix by interrogating the samples with an incident light at 45° and successive azimuthal rotations of 0-360°. Our results confirmed previous observations by X-ray diffraction, suggesting that in the non-gravid human cervix collagen ...

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    10. Optical properties of human milk

      Optical properties of human milk

      With human milk being the most important source of infant nutrition, the protection and support of breastfeeding are essential from a global health perspective. Nevertheless, relatively few objective methods are available to investigate human milk composition and lactation physiology when a mother experiences breastfeeding problems. We argue that optics and photonics offer promising opportunities for this purpose. Any research activity within this new application field starts with a thorough understanding on how light interacts with human milk. Therefore, the aim of this study was to investigate the full set of optical properties for human milk and the biological variability therein ...

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    11. Handheld probe for quantitative micro-elastography

      Handheld probe for quantitative micro-elastography

      Optical coherence elastography (OCE) has been proposed for a range of clinical applications. However, the majority of these studies have been performed using bulky, lab-based imaging systems. A compact, handheld imaging probe would accelerate clinical translation, however, to date, this had been inhibited by the slow scan rates of compact devices and the motion artifact induced by the user’s hand. In this paper, we present a proof-of-concept, handheld quantitative micro-elastography (QME) probe capable of scanning a 6 × 6 × 1 mm volume of tissue in 3.4 seconds. This handheld probe is enabled by a novel QME acquisition protocol that ...

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    12. Motorized capsule for shadow-free OCT imaging and synchronous beam control

      Motorized capsule for shadow-free OCT imaging and synchronous beam control

      We demonstrate a tethered motorized capsule for unobstructed optical coherence tomography (OCT) imaging of the esophagus. By using a distal reflector design, we avoided the common shadow artifact induced by the motor wires. A synchronous driving technique features three types of beam-scanning modes of the capsule, i.e., circumferential beam scanning, localized beam scanning, and accurate beam positioning. We characterized these three modes and carried out ex vivo imaging experiments using the capsule. The results show that the capsule can potentially be a useful tool for diagnostic OCT imaging and OCT-guided biopsy and therapy of the esophagus.

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    13. Chip-based frequency comb sources for optical coherence tomography

      Chip-based frequency comb sources for optical coherence tomography

      Optical coherence tomography (OCT) is a powerful interferometric imaging technique widely used in medical fields such as ophthalmology, cardiology and dermatology. Superluminescent diodes (SLDs) are widely used as light sources in OCT. Recently integrated chip-based frequency combs have been demonstrated in numerous platforms and the possibility of using these broadband chip-scale combs for OCT has been raised extensively over the past few years. However, the use of these chip-based frequency combs as light sources for OCT requires bandwidth and power compatibility with current OCT systems and have not been shown to date. Here we generate frequency combs based on chip-scale ...

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    14. High dynamic range optical coherence tomography angiography (HDR-OCTA)

      High dynamic range optical coherence tomography angiography (HDR-OCTA)

      The dynamic range of current optical coherence tomography (OCT) angiography (OCTA) images is limited by the fixed scanning intervals. High speed OCT devices introduce the possibility of extending the flow signal dynamic range. In this study, we created a novel scanning pattern for achieving high dynamic range (HDR)-OCTA with a superior scanning efficiency. We implemented a bidirectional, interleaved scanning pattern that is sensitive to different flow speeds by adjustable adjacent inter-scan time intervals. We found that an improved flow dynamic range can be achieved by generating 3 different B-scan time intervals using 3 repetitions.

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    15. Off-axis optical coherence tomography imaging of the crystalline lens to reconstruct the gradient refractive index using optical methods

      Off-axis optical coherence tomography imaging of the crystalline lens to reconstruct the gradient refractive index using optical methods

      Earlier studies have shown that the gradient index of refraction (GRIN) of the crystalline lens can be reconstructed in vitro using Optical Coherence Tomography (OCT) images. However, the methodology cannot be extended in vivo because it requires accurate measurements of the external geometry of the lens. Specifically, the posterior surface is measured by flipping the lens so that the posterior lens surface faces the OCT beam, a method that cannot be implemented in vivo . When the posterior surface is imaged through the lens in its natural position, it appears distorted by the unknown GRIN. In this study, we demonstrate a ...

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    16. Segmentation of mouse skin layers in optical coherence tomography image data using deep convolutional neural networks

      Segmentation of mouse skin layers in optical coherence tomography image data using deep convolutional neural networks

      Optical coherence tomography (OCT) enables the non-invasive acquisition of high-resolution three-dimensional cross-sectional images at micrometer scale and is mainly used in the field of ophthalmology for diagnosis as well as monitoring of eye diseases. Also in other areas, such as dermatology, OCT is already well established. Due to its non-invasive nature, OCT is also employed for research studies involving animal models. Manual evaluation of OCT images of animal models is a challenging task due to the lack of imaging standards and the varying anatomy between models. In this paper, we present a deep learning algorithm for the automatic segmentation of ...

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    17. Microfabrication of axicons by glass blowing at a wafer-level

      Microfabrication of axicons by glass blowing at a wafer-level

      This Letter reports on the generation of glass-based axicons realized at the wafer level by means of microfabrication. The technique is based on micro glass blowing allowing parallel fabrication of numerous components at a time. Blowing is achieved due to cavities containing a gas that expands when the wafer stack is introduced in a furnace. Such cavities, generated in a silicon wafer and sealed by a bonded glass wafer, act as pistons pushing locally the other side of the glass wafer where the micro-optical component profile emerges. After cavities’ removal by polishing, it is shown that such a component produces ...

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    18. In vivo tomographic visualization of intracochlear vibration using a supercontinuum multifrequency-swept optical coherence microscope

      In vivo tomographic visualization of intracochlear vibration using a supercontinuum multifrequency-swept optical coherence microscope

      This study combined a previously developed optical system with two additional key elements: a supercontinuum light source characterized by high output power and an analytical technique that effectively extracts interference signals required for improving the detection limit of vibration amplitude. Our system visualized 3D tomographic images and nanometer scale vibrations in the cochlear sensory epithelium of a live guinea pig. The transverse- and axial-depth resolution was 3.6 and 2.7 µm, respectively. After exposure to acoustic stimuli of 21–25 kHz at a sound pressure level of 70–85 dB, spatial amplitude and phase distributions were quantified on a ...

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    19. Ocular anterior chamber blood cell population differentiation using spectroscopic optical coherence tomography

      Ocular anterior chamber blood cell population differentiation using spectroscopic optical coherence tomography

      There is potential clinical significance in identifying cellular responses in the anterior chamber (AC) of the eye, which can indicate hyphema (an accumulation of red blood cells [RBCs]) or aberrant intraocular inflammation (an accumulation of white blood cells [WBCs]). In this work, we developed a spectroscopic OCT analysis method to differentiate between populations of RBCs and subtypes of WBCs, including granulocytes, lymphocytes and monocytes, both in vitro and in ACs of porcine eyes. We developed an algorithm to track single cells within OCT data sets, and extracted the backscatter reflectance spectrum of each single cell from the detected interferograms using ...

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    20. Fiber-based polarization-sensitive optical coherence tomography of a minimalistic system configuration

      Fiber-based polarization-sensitive optical coherence tomography of a minimalistic system configuration

      We present a very simple method of constructing a polarization-sensitive optical coherence tomography (PS-OCT) system. An ordinary fiber-based swept-source OCT system was reconfigured for PS-OCT by adding a long section of polarization-maintaining fiber in the sample arm. Two polarization modes of a large group-delay difference formed spatially distinguished polarization channels. The depth-encoded information on the polarization states was retrieved by an amplitude-based analysis. We found that our method provides an economic scheme of PS-OCT. It demonstrates that an ordinary OCT system can be easily reconfigured for PS-OCT imaging if it has sufficient margins in the imaging range.

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    21. Compressed sensing spectral domain optical coherence tomography with a hardware sparse-sampled camera

      Compressed sensing spectral domain optical coherence tomography with a hardware sparse-sampled camera

      We present a sparse-sampled camera for compressed sensing spectral domain optical coherence tomography (CS SD-OCT), which is mainly composed of a novel mask with specially designed coating and a commercially available CCD camera. The sparse-sampled camera under-samples the SD-OCT spectrum in hardware, thus reduces the acquired image data and can achieve faster A-scan speed than conventional CCD camera with the same pixel number. Compared with a conventional SD-OCT system, the CS SD-OCT system equipped with the sparse-sampled camera has better fall-off and SNR performance. CS-OCT imaging of bio-tissue is also demonstrated.

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    22. Improve depth of field of optical coherence tomography using finite energy Airy beam

      Improve depth of field of optical coherence tomography using finite energy Airy beam

      We report a technique to break the depth of field (DOF) limit in optical coherence tomography (OCT) using a finite energy Airy beam. The Airy beam is generated using a phase mask in a Fourier transform schematic and provides the DOF improvement due to its low diffraction. We compare Airy beam OCT with conventional Gaussian beam OCT using lateral resolution and sensitivity. Experimental data from the polystyrene beads in water as well as lemon tissue confirm the extension of DOF up to 10 mm in Airy beam OCT, while the DOF of Gaussian beam OCT is less than 3.0 ...

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    23. Convective Nozaki-Bekki holes in a long cavity OCT laser

      Convective Nozaki-Bekki holes in a long cavity OCT laser

      We show, both experimentally and theoretically, that the loss of coherence of a long cavity optical coherence tomography (OCT) laser can be described as a transition from laminar to turbulent flows. We demonstrate that in this strongly dissipative system, the transition happens either via an absolute or a convective instability depending on the laser parameters. In the latter case, the transition occurs via formation of localised structures in the laminar regime, which trigger the formation of growing and drifting puffs of turbulence. Experimentally, we demonstrate that these turbulent bursts are seeded by appearance of Nozaki-Bekki holes, characterised by the zero ...

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    24. Depth-resolved birefringence imaging of collagen fiber organization in the human oral mucosa in vivo

      Depth-resolved birefringence imaging of collagen fiber organization in the human oral mucosa in vivo

      Stromal collagen organization has been identified as a potential prognostic indicator in a variety of cancers and other diseases accompanied by fibrosis. Changes in the connective tissue are increasingly considered for grading dysplasia and progress of oral squamous cell carcinoma, investigated mainly ex vivo by histopathology. In this study, polarization-sensitive optical coherence tomography (PS-OCT) with local phase retardation imaging is used for the first time to visualize depth-resolved (i.e., local) birefringence of healthy human oral mucosa in vivo . Depth-resolved birefringence is shown to reveal the expected local collagen organization. To demonstrate proof-of-principle, 3D image stacks were acquired at labial ...

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