1. 1-24 of 510 1 2 3 4 ... 20 21 22 »
    1. Measurement of optic axis orientation with single-mode fiber-based polarization-sensitive optical coherence tomography

      Measurement of optic axis orientation with single-mode fiber-based polarization-sensitive optical coherence tomography

      An algorithm is presented that can be used to obtain accurate optic axis orientation of birefringent tissue samples. A single-mode fiber (SMF)-based polarization-sensitive optical coherence tomography with a single linearly polarized incident light was used in the measurements in which the light reflected from the sample and detected by the spectrometer is linearly polarized light at 45 deg with respect to the experimental horizontal axis. By employing polarization controllers to completely specify the parameters of the fiber system, the absolute optic axis orientation could then be estimated accurately by analyzing the Mueller matrices of the fiber system and sample ...

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    2. Intracardiac radiofrequency ablation in living swine guided by polarization-sensitive optical coherence tomography

      Intracardiac radiofrequency ablation in living swine guided by polarization-sensitive optical coherence tomography

      Significance: Pulmonary vein isolation with catheter-based radiofrequency ablation (RFA) is carried out frequently to treat atrial fibrillation. However, RFA lesion creation is only guided by indirect information (e.g., temperature, impedance, and contact force), which may result in poor lesion quality (e.g., nontransmural) and can lead to reoccurrence or complications. Aim: The feasibility of guiding intracardiac RFA with an integrated polarization-sensitive optical coherence tomography (PSOCT)-RFA catheter in the right atria (RA) of living swine is demonstrated. Approach : In total, 12 sparse lesions were created in the RA of three living swine using an integrated PSOCT-RFA catheter with standard ...

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    3. Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography

      Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography

      Significance: It is generally agreed that the corneal mechanical properties are strongly linked to many eye diseases and could be used to assess disease progression and response to therapies. Elastography is the most notable method of assessing corneal mechanical properties, but it generally requires some type of external excitation to induce a measurable displacement in the tissue. Aim: We present Heartbeat Optical Coherence Elastography (Hb-OCE), a truly passive method that can measure the elasticity of the cornea based on intrinsic corneal displacements induced by the heartbeat. Approach: Hb-OCE measurements were performed in untreated and UV-A/riboflavin cross-linked porcine corneas ex ...

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    4. Low-cost, ultracompact handheld optical coherence tomography probe for in vivo oral maxillofacial tissue imaging

      Low-cost, ultracompact handheld optical coherence tomography probe for in vivo oral maxillofacial tissue imaging

      Significance: Optical coherence tomography (OCT) has proven useful for detecting various oral maxillofacial abnormalities. To apply it to clinical applications including biopsy guidance and routine screening, a handheld imaging probe is indispensable. OCT probes reported for oral maxillofacial imaging were either based on a bulky galvanometric mirror pair (not compact or long enough) or a distal-end microelectromechanical systems (MEMS) scanner (raised safety concerns), or adapted from fiber-optic catheters (ill-suited for oral cavity geometry). Aim: To develop a handheld probe featuring great compactness and excellent maneuverability for oral maxillofacial tissue imaging. Approach: A dual-axis MEMS scanner was deployed at the proximal ...

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    5. Parametric imaging of attenuation by optical coherence tomography: review of models, methods, and clinical translation

      Parametric imaging of attenuation by optical coherence tomography: review of models, methods, and clinical translation

      Significance: Optical coherence tomography (OCT) provides cross-sectional and volumetric images of backscattering from biological tissue that reveal the tissue morphology. The strength of the scattering, characterized by an attenuation coefficient, represents an alternative and complementary tissue optical property, which can be characterized by parametric imaging of the OCT attenuation coefficient. Over the last 15 years, a multitude of studies have been reported seeking to advance methods to determine the OCT attenuation coefficient and developing them toward clinical applications. Aim: Our review provides an overview of the main models and methods, their assumptions and applicability, together with a survey of preclinical ...

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    6. Longitudinal optical coherence tomography imaging of tissue repair and microvasculature regeneration and function after targeted cerebral ischemia

      Longitudinal optical coherence tomography imaging of tissue repair and microvasculature regeneration and function after targeted cerebral ischemia

      Significance: Understanding how the brain recovers from cerebral tissue and vascular damage after an ischemic event can help develop new therapeutic strategies for the treatment of stroke. Aim: We investigated cerebral tissue repair and microvasculature regeneration and function after a targeted ischemic stroke. Approach: Following photothrombosis occlusion of microvasculature, chronic optical coherence tomography (OCT)-based angiography was used to track ischemic tissue repair and microvasculature regeneration at three different cortical depths and up to 28 days in awake animals. Capillary network orientation analysis was performed to study the structural pattern of newly formed microvasculature. Based on the time-resolved OCT-angiography, we ...

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    7. INS-fOCT: a label-free, all-optical method for simultaneously manipulating and mapping brain function

      INS-fOCT: a label-free, all-optical method for simultaneously manipulating and mapping brain function

      Significance: Current approaches to stimulating and recording from the brain have combined electrical or optogenetic stimulation with recording approaches, such as two-photon, electrophysiology (EP), and optical intrinsic signal imaging (OISI). However, we lack a label-free, all-optical approach with high spatial and temporal resolution. Aim: To develop a label-free, all-optical method that simultaneously manipulates and images brain function using pulsed near-infrared light (INS) and functional optical coherence tomography (fOCT), respectively. Approach: We built a coregistered INS, fOCT, and OISI system. OISI and EP recordings were employed to validate the fOCT signals. Results: The fOCT signal was reliable and regional, and the ...

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    8. Laser-induced elastic wave classification: thermoelastic versus ablative regimes for all-optical elastography applications

      Laser-induced elastic wave classification: thermoelastic versus ablative regimes for all-optical elastography applications

      Significance : Shear wave optical coherence elastography is an emerging technique for characterizing tissue biomechanics that relies on the generation of elastic waves to obtain the mechanical contrast. Various techniques, such as contact, acoustic, and pneumatic methods, have been used to induce elastic waves. However, the lack of higher-frequency components within the elastic wave restricts their use in thin samples. The methods also require moving parts and/or tubing, which therefore limits the extent to which they can be miniaturized. Aim : To overcome these limitations, we propose an all-optical approach using photothermal excitation. Depending on the absorption coefficient of the sample ...

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    9. Achieving the ideal point spread in swept source OCT

      Achieving the ideal point spread in swept source OCT

      Side lobe artifacts on point spread functions can be traced back to (1) fringe visibility variation across the spectrum, (2) errors in sampling instances, and (3) window functions. We demonstrate signal processing methods for correcting for all three of these issues. These methods require a system calibration step. If the systems slowly age, the recalibration step could be performed in the field with a fixtured target.

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    10. Selective retina therapy monitoring by speckle variance optical coherence tomography for dosimetry control

      Selective retina therapy monitoring by speckle variance optical coherence tomography for dosimetry control

      Significance: Selective retina therapy (SRT) selectively targets the retinal pigment epithelium (RPE) and reduces negative side effects by avoiding thermal damages of the adjacent photoreceptors, the neural retina, and the choroid. However, the selection of proper laser energy for the SRT is challenging because of ophthalmoscopically invisible lesions in the RPE and different melanin concentrations among patients or even regions within an eye. Aim: We propose and demonstrate SRT monitoring based on speckle variance optical coherence tomography (svOCT) for dosimetry control. Approach: M-scans, time-resolved sequence of A-scans, of ex vivo bovine retina irradiated by 1.7-μs duration laser pulses ...

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    11. Dimensional characterization of large opaque samples and microdeformations by low coherence interferometry

      Dimensional characterization of large opaque samples and microdeformations by low coherence interferometry

      We report on the application of an interferometric system based on the low-coherence interferometry technique to the dimensional characterization of large opaque mechanical parts as well as microdeformations experienced by them. The implemented scheme is capable of simultaneously measuring very small deformations and relatively large dimensions or thicknesses (several centimeters) of the sample. By applying the chirp Fourier transform algorithm, it was possible to measure changes in thickness with an uncertainty of 0.35  μm when a 7-cm-thick sample was measured. The measurement scheme was implemented in optical fiber, which makes it highly adaptable to industrial conditions. It employs a ...

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    12. In vivo brain imaging with multimodal optical coherence microscopy in a mouse model of thromboembolic photochemical stroke

      In vivo brain imaging with multimodal optical coherence microscopy in a mouse model of thromboembolic photochemical stroke

      We used a new multimodal imaging system that combines optical coherence microscopy and brightfield microscopy. Using this in vivo brain monitoring approach and cranial window implantation, we three-dimensionally visualized the vascular network during thrombosis, with high temporal (18 s) and spatial (axial, 2.5  μm; lateral, 2.2  μm) resolution. We used a modified mouse model of photochemical thromboembolic stroke in order to more accurately parallel human stroke. Specifically, we applied green laser illumination to focally occlude a branch of the middle cerebral artery. Despite the recanalization of the superficial arteries at 24 h after stroke, no blood flow was ...

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    13. Utility of endoscopic anatomical optical coherence tomography in functional rhinoplasty

      Utility of endoscopic anatomical optical coherence tomography in functional rhinoplasty

      Objective measurement of the nasal valve region is valuable for the assessment of functional rhinoplasty surgical outcomes. Anatomical optical coherence tomography (aOCT) is an imaging modality that may be used to obtain real-time, quantitative, and volumetric scans of the nasal airway. We aim to evaluate if volumetric aOCT imaging is useful for the examination of the nasal valve region before and after functional rhinoplasty procedures. aOCT scans of the nasal valves were performed on four cadaveric heads before and after spreader graft and butterfly graft procedures. The resulting aOCT images were compared against video endoscopy images, and the segmented volumes ...

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      Mentions: Amy L. Oldenburg
    14. Spatiotemporal dynamics of pial collateral blood flow following permanent middle cerebral artery occlusion in a rat model of sensory-based protection: a Doppler optical coherence tomography study

      Spatiotemporal dynamics of pial collateral blood flow following permanent middle cerebral artery occlusion in a rat model of sensory-based protection: a Doppler optical coherence tomography study

      There is a growing recognition regarding the importance of pial collateral flow in the protection from impending ischemic stroke both in preclinical and clinical studies. Collateral flow is also a major player in sensory stimulation-based protection from impending ischemic stroke. Doppler optical coherence tomography has been employed to image spatiotemporal patterns of collateral flow within the dorsal branches of the middle cerebral artery (MCA) as it provides a powerful tool for quantitative in vivo flow parameters imaging (velocity, flux, direction of flow, and radius of imaged branches). It was employed prior to and following dorsal permanent MCA occlusion (pMCAo) in ...

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    15. Special Section Guest Editorial: Advances in Retinal Imaging

      Special Section Guest Editorial: Advances in Retinal Imaging

      The guest editorial provides an introduction to the Special Section on Advanced Retinal Imaging: Instrumentation, Methods, and Applications. The retina is a peripheral part of the central nerve system (CNS) and shares many similarities with the cerebral cortex. They both have layered anatomy, the same types of functional elements and neurotransmitters, and similar vascular organization and blood-tissue barriers. With far fewer neuronal cell types and simpler anatomical structures, the retina is an excellent target for studying neural circuitry and neurovascular coupling. Meanwhile, approximately 80 percent of information from the outside world is processed as visual perception, 1 and retina-related blindness ...

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    16. Computed optical coherence microscopy of mouse brain ex vivo

      Computed optical coherence microscopy of mouse brain ex vivo

      The compromise between lateral resolution and usable imaging depth range is a bottleneck for optical coherence tomography (OCT). Existing solutions for optical coherence microscopy (OCM) suffer from either large data size and long acquisition time or a nonideal point spread function. We present volumetric OCM of mouse brain ex vivo with a large depth coverage by leveraging computational adaptive optics (CAO) to significantly reduce the number of OCM volumes that need to be acquired with a Gaussian beam focused at different depths. We demonstrate volumetric reconstruction of ex-vivo mouse brain with lateral resolution of 2.2  μm, axial resolution of ...

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    17. Coregistered optical coherence tomography and frequency-encoded multispectral imaging for spectrally sparse color imagingv

      Coregistered optical coherence tomography and frequency-encoded multispectral imaging for spectrally sparse color imagingv

      We present a system combining optical coherence tomography (OCT) and multispectral imaging (MSI) for coregistered structural imaging and surface color imaging. We first describe and numerically validate an optimization model to guide the selection of the MSI wavelengths and their relative intensities. We then demonstrate the integration of this model into an all-fiber bench-top system. We implement frequency-domain multiplexing for the MSI to enable concurrent acquisition of both OCT and MSI at OCT acquisition rates. Such a system could be implemented in endoscopic practices to provide multimodal, high-resolution imaging of deep organ structures that are currently inaccessible to standard video ...

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    18. Etching-enabled extreme miniaturization of graded-index fiber-based optical coherence tomography probes

      Etching-enabled extreme miniaturization of graded-index fiber-based optical coherence tomography probes

      We introduced and validated a method to miniaturize graded-index (GRIN) fiber-based optical coherence tomography (OCT) probes down to 70  μm in diameter. The probes consist in an assembly of single-mode (SM), coreless (CL), and graded-index (GRIN) fibers. We opted for a probe design enabling controlled size reduction by hydrogen fluoride etching. The fabrication approach prevents nonuniform etching for both the GRIN and SM fiber components, while it requires no probe polishing postetching. We found that the miniaturized probes present insignificant loss of sensitivity (∼1  dB) compared to their thicker (125  μm) counterparts. We also showed that their focusing capabilities remain ...

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    19. Cerebral edema detection in vivo after middle cerebral artery occlusion using swept-source optical coherence tomography

      Cerebral edema detection in vivo after middle cerebral artery occlusion using swept-source optical coherence tomography

      Cerebral edema is a severe complication of ischemic cerebrovascular disease, which can lead to microcirculation compression resulting in additional ischemic damage. Real-time and continuous in vivo imaging techniques for edema detection are of great significance to basic research on cerebral edema. We attempted to monitor the cerebral edema status in rats with middle cerebral artery occlusion (MCAO) over time, using a wide field-of-view swept-source optical coherence tomography (SS-OCT) system. Optical attenuation coefficients (OACs) were calculated by an optimized depth-resolved estimation method, and en face OAC maps covering the whole cortex were obtained. Then, the tissue affected by edema was segmented ...

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    20. Acousto-optically tuned external-cavity laser diode for optical coherence tomography with continuous wavelet transform

      Acousto-optically tuned external-cavity laser diode for optical coherence tomography with continuous wavelet transform

      We propose an acousto-optically tuned external-cavity laser diode (ECLD) based on the Littrow configuration to expand the wavelength-scanning range and eliminate mechanical motions. The scanning range and tuning rate of our prototype were 68.85 nm and more than 100 kHz, respectively, without any mode hop. Moreover, we implemented this improved ECLD in an optical coherence tomography imaging system and conducted a measurement of the two-dimensional thickness distribution of a thin glass plate via continuous wavelet transform analysis.

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    21. Submillimeter diameter rotary-pullback fiber-optic endoscope for narrowband red-green-blue reflectance, optical coherence tomography, and autofluorescence in vivo imaging

      Submillimeter diameter rotary-pullback fiber-optic endoscope for narrowband red-green-blue reflectance, optical coherence tomography, and autofluorescence in vivo imaging

      A fiber-based endoscopic imaging system combining narrowband red-green-blue (RGB) reflectance with optical coherence tomography (OCT) and autofluorescence imaging (AFI) has been developed. The system uses a submillimeter diameter rotary-pullback double-clad fiber imaging catheter for sample illumination and detection. The imaging capabilities of each modality are presented and demonstrated with images of a multicolored card, fingerprints, and tongue mucosa. Broadband imaging, which was done to compare with narrowband sources, revealed better contrast but worse color consistency compared with narrowband RGB reflectance. The measured resolution of the endoscopic system is 25  μm in both the rotary direction and the pullback direction. OCT ...

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    22. In vivo evaluation of corneal biomechanical properties by optical coherence elastography at different cross-linking irradiances

      In vivo evaluation of corneal biomechanical properties by optical coherence elastography at different cross-linking irradiances

      Corneal collagen cross-linking (CXL) strengthens the biomechanical properties of damaged corneas. Quantifying the changes of stiffness due to different CXL protocols is difficult, especially in vivo . A noninvasive elastic wave-based optical coherence elastography system was developed to construct in vivo corneal elasticity maps by excitation of air puff. Biomechanical differences were compared for rabbit corneas given three different CXL protocols while keeping the total energy delivered constant. The Young’s modulus was weaker in corneas treated with higher irradiance levels over shorter durations, and a slight increase of Young’s modulus was present in all groups one week after the ...

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    23. Dual-angle optical coherence tomography for index of refraction estimation using rigid registration and cross-correlation

      Dual-angle optical coherence tomography for index of refraction estimation using rigid registration and cross-correlation

      The index of refraction ( n ) of materials and/or tissues depends on their physical properties and serves as a source of optical contrast in imaging. The variations of the index of refraction have also been investigated for diagnostic purposes in various fields, such as hematology, oncology, etc., since they can signify disease and cell dynamic changes. Optical coherence tomography (OCT) has been used in the past to measure the index ex vivo . However, most methodologies described in the literature are not appropriate for in vivo imaging since they require either a mirror below the sample or a complicated imaging setup ...

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    24. Automated A-line coronary plaque classification of intravascular optical coherence tomography images using handcrafted features and large datasets

      Automated A-line coronary plaque classification of intravascular optical coherence tomography images using handcrafted features and large datasets

      We developed machine learning methods to identify fibrolipidic and fibrocalcific A-lines in intravascular optical coherence tomography (IVOCT) images using a comprehensive set of handcrafted features. We incorporated features developed in previous studies (e.g., optical attenuation and A-line peaks). In addition, we included vascular lumen morphology and three-dimensional (3-D) digital edge and texture features. Classification methods were developed using expansive datasets (∼7000  images), consisting of both clinical in-vivo images and an ex-vivo dataset, which was validated using 3-D cryo-imaging/histology. Conditional random field was used to perform 3-D classification noise cleaning of classification results. We tested various multiclass approaches, classifiers ...

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    1-24 of 510 1 2 3 4 ... 20 21 22 »
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