Showing papers on "Optical coherence tomography published in 2014"

Optical Coherence Tomography Angiography of Optic Disc Perfusion in Glaucoma

Abstract: Purpose To compare optic disc perfusion between normal subjects and subjects with glaucoma using optical coherence tomography (OCT) angiography and to detect optic disc perfusion changes in glaucoma. Design Observational, cross-sectional study. Participants Twenty-four normal subjects and 11 patients with glaucoma were included. Methods One eye of each subject was scanned by a high-speed 1050-nm–wavelength swept-source OCT instrument. The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to compute 3-dimensional optic disc angiography. A disc flow index was computed from 4 registered scans. Confocal scanning laser ophthalmoscopy (cSLO) was used to measure disc rim area, and stereo photography was used to evaluate cup/disc (C/D) ratios. Wide-field OCT scans over the discs were used to measure retinal nerve fiber layer (NFL) thickness. Main Outcome Measures Variability was assessed by coefficient of variation (CV). Diagnostic accuracy was assessed by sensitivity and specificity. Comparisons between glaucoma and normal groups were analyzed by Wilcoxon rank-sum test. Correlations among disc flow index, structural assessments, and visual field (VF) parameters were assessed by linear regression. Results In normal discs, a dense microvascular network was visible on OCT angiography. This network was visibly attenuated in subjects with glaucoma. The intra-visit repeatability, inter-visit reproducibility, and normal population variability of the optic disc flow index were 1.2%, 4.2%, and 5.0% CV, respectively. The disc flow index was reduced by 25% in the glaucoma group ( P = 0.003). Sensitivity and specificity were both 100% using an optimized cutoff. The flow index was highly correlated with VF pattern standard deviation ( R 2 = 0.752, P = 0.001). These correlations were significant even after accounting for age, C/D area ratio, NFL, and rim area. Conclusions Optical coherence tomography angiography, generated by the new SSADA, repeatably measures optic disc perfusion and may be useful in the evaluation of glaucoma and glaucoma progression.

Graphene-based carbon-layered electrode array technology for neural imaging and optogenetic applications

Abstract: Neural micro-electrode arrays that are transparent over a broad wavelength spectrum from ultraviolet to infrared could allow for simultaneous electrophysiology and optical imaging, as well as optogenetic modulation of the underlying brain tissue. The long-term biocompatibility and reliability of neural micro-electrodes also require their mechanical flexibility and compliance with soft tissues. Here we present a graphene-based, carbon-layered electrode array (CLEAR) device, which can be implanted on the brain surface in rodents for high-resolution neurophysiological recording. We characterize optical transparency of the device at >90% transmission over the ultraviolet to infrared spectrum and demonstrate its utility through optical interface experiments that use this broad spectrum transparency. These include optogenetic activation of focal cortical areas directly beneath electrodes, in vivo imaging of the cortical vasculature via fluorescence microscopy and 3D optical coherence tomography. This study demonstrates an array of interfacing abilities of the CLEAR device and its utility for neural applications.

Optical coherence tomography today: speed, contrast, and multimodality.

Abstract: In the last 25 years, optical coherence tomography (OCT) has advanced to be one of the most innovative and most successful translational optical imaging techniques, achieving substantial economic impact as well as clinical acceptance. This is largely owing to the resolution improvements by a factor of 10 to the submicron regime and to the imaging speed increase by more than half a million times to more than 5 million A-scans per second, with the latter one accomplished by the state-of-the-art swept source laser technologies that are reviewed in this article. In addition, parallelization of OCT detection, such as line-field and full-field OCT, has shortened the acquisition time even further by establishing quasi-akinetic scanning. Besides the technical improvements, several functional and contrast-enhancing OCT applications have been investigated, among which the label-free angiography shows great potential for future studies. Finally, various multimodal imaging modalities with OCT incorporated are reviewed, in that these multimodal implementations can synergistically compensate for the fundamental limitations of OCT when it is used alone.

Fully automated detection of diabetic macular edema and dry age-related macular degeneration from optical coherence tomography images

Abstract: We present a novel fully automated algorithm for the detection of retinal diseases via optical coherence tomography (OCT) imaging. Our algorithm utilizes multiscale histograms of oriented gradient descriptors as feature vectors of a support vector machine based classifier. The spectral domain OCT data sets used for cross-validation consisted of volumetric scans acquired from 45 subjects: 15 normal subjects, 15 patients with dry age-related macular degeneration (AMD), and 15 patients with diabetic macular edema (DME). Our classifier correctly identified 100% of cases with AMD, 100% cases with DME, and 86.67% cases of normal subjects. This algorithm is a potentially impactful tool for the remote diagnosis of ophthalmic diseases.

OCT for glaucoma diagnosis, screening and detection of glaucoma progression

Abstract: Optical coherence tomography (OCT) is a commonly used imaging modality in the evaluation of glaucomatous damage. The commercially available spectral domain (SD)-OCT offers benefits in glaucoma assessment over the earlier generation of time domain-OCT due to increased axial resolution, faster scanning speeds and has been reported to have improved reproducibility but similar diagnostic accuracy. The capabilities of SD-OCT are rapidly advancing with 3D imaging, reproducible registration, and advanced segmentation algorithms of macular and optic nerve head regions. A review of the evidence to date suggests that retinal nerve fibre layer remains the dominant parameter for glaucoma diagnosis and detection of progression while initial studies of macular and optic nerve head parameters have shown promising results. SD-OCT still currently lacks the diagnostic performance for glaucoma screening.

Depth-resolved model-based reconstruction of attenuation coefficients in optical coherence tomography

Abstract: We present a method, based on a single scattering model, to calculate the attenuation coefficient of each pixel in optical coherence tomography (OCT) depth profiles. Numerical simulations were used to determine the model’s response to different depths and attenuation coefficients. Experiments were performed on uniform and layered phantoms with varying attenuation coefficients. They were measured by a 1300 nm OCT system and their attenuation coefficients were evaluated by our proposed method and by fitting the OCT slope as the gold standard. Both methods showed largely consistent results for the uniform phantoms. On the layered phantom, only our proposed method accurately estimated the attenuation coefficients. For all phantoms, the proposed method largely reduced the variability of the estimated attenuation coefficients. The method was illustrated on an in-vivo retinal OCT scan, effectively removing common imaging artifacts such as shadowing. By providing localized, per-pixel attenuation coefficients, this method enables tissue characterization based on attenuation coefficient estimates from OCT data.

A Review of Optical Coherence Elastography: Fundamentals, Techniques and Prospects

Abstract: In optical coherence elastography, images are formed by mapping a mechanical property of tissue. Such images, known as elastograms, are formed on the microscale, intermediate between that of cells and whole organs. Optical coherence elastography holds great promise for detecting and monitoring the altered mechanical properties that accompany many clinical conditions and pathologies, particularly in cancer, cardiovascular disease and eye disease. In this review, we first consider how the mechanical properties of tissue are linked with tissue function and pathology. We then describe currently prominent optical coherence elastography techniques, with emphasis on the methods of mechanical loading and displacement estimation. We highlight the sensitivity to microstrain deformations at tens of micrometer resolution. Throughout, optical coherence elastography is considered in the context of other elastography methods, mainly ultrasound elastography and magnetic resonance elastography. This context serves to highlight its advantages, early stage of development of applications, and strong prospects for future impact.

Handheld probe integrating laser diode and ultrasound transducer array for ultrasound/photoacoustic dual modality imaging

Abstract: Ultrasound and photoacoustics can be utilized as complementary imaging techniques to improve clinical diagnoses. Photoacoustics provides optical contrast and functional information while ultrasound provides structural and anatomical information. As of yet, photoacoustic imaging uses large and expensive systems, which limits their clinical application and makes the combination costly and impracticable. In this work we present and evaluate a compact and ergonomically designed handheld probe, connected to a portable ultrasound system for inexpensive, real-time dual-modality ultrasound/photoacoustic imaging. The probe integrates an ultrasound transducer array and a highly efficient diode stack laser emitting 130 ns pulses at 805 nm wavelength and a pulse energy of 0.56 mJ, with a high pulse repetition frequency of up to 10 kHz. The diodes are driven by a customized laser driver, which can be triggered externally with a high temporal stability necessary to synchronize the ultrasound detection and laser pulsing. The emitted beam is collimated with cylindrical micro-lenses and shaped using a diffractive optical element, delivering a homogenized rectangular light intensity distribution. The system performance was tested in vitro and in vivo by imaging a human finger joint.

Shear wave imaging optical coherence tomography (SWI-OCT) for ocular tissue biomechanics.

Abstract: We report on a noncontact low-coherence optical phase-based imaging method, termed shear wave imaging optical coherence tomography (SWI-OCT), which enables 2D depth-resolved visualization of the low-amplitude elastic wave propagation in tissue with ultrahigh frame rate. SWI-OCT is based on 1D transverse scanning of the M-mode OCT imaging that is precisely synchronized with a low-pressure short-duration air-puff loading system. This approach of scanning and data recording allows visualization of the induced tissue deformation at high frame rate. The applied phase-resolved interferometric technique, with sensitivity on the nanometer scale, makes the low-amplitude tissue displacement detectable. For the demonstration of this method, and to study its application for tissue biomechanics, we performed pilot experiments on agar phantoms and ex vivo rabbit corneas. Samples with different elastic properties can be differentiated based on the velocity of the elastic wave propagation that is directly visualized with a 25 kHz frame rate. Our results indicate that SWI-OCT has the potential to be further developed as a major technique for depth-resolved high-resolution tissue elastography in vivo.

Handheld ultrahigh speed swept source optical coherence tomography instrument using a MEMS scanning mirror

Abstract: We developed an ultrahigh speed, handheld swept source optical coherence tomography (SS-OCT) ophthalmic instrument using a 2D MEMS mirror. A vertical cavity surface-emitting laser (VCSEL) operating at 1060 nm center wavelength yielded a 350 kHz axial scan rate and 10 µm axial resolution in tissue. The long coherence length of the VCSEL enabled a 3.08 mm imaging range with minimal sensitivity roll-off in tissue. Two different designs with identical optical components were tested to evaluate handheld OCT ergonomics. An iris camera aided in alignment of the OCT beam through the pupil and a manual fixation light selected the imaging region on the retina. Volumetric and high definition scans were obtained from 5 undilated normal subjects. Volumetric OCT data was acquired by scanning the 2.4 mm diameter 2D MEMS mirror sinusoidally in the fast direction and linearly in the orthogonal slow direction. A second volumetric sinusoidal scan was obtained in the orthogonal direction and the two volumes were processed with a software algorithm to generate a merged motion-corrected volume. Motion-corrected standard 6 x 6 mm2 and wide field 10 x 10 mm2 volumetric OCT data were generated using two volumetric scans, each obtained in 1.4 seconds. High definition 10 mm and 6 mm B-scans were obtained by averaging and registering 25 B-scans obtained over the same position in 0.57 seconds. One of the advantages of volumetric OCT data is the generation of en face OCT images with arbitrary cross sectional B-scans registered to fundus features. This technology should enable screening applications to identify early retinal disease, before irreversible vision impairment or loss occurs. Handheld OCT technology also promises to enable applications in a wide range of settings outside of the traditional ophthalmology or optometry clinics including pediatrics, intraoperative, primary care, developing countries, and military medicine.

Swept-source OCT angiography of the retinal vasculature using intensity differentiation-based optical microangiography algorithms.

Abstract: Background and objective To demonstrate the feasibility of using a 1,050-nm swept-source optical coherence tomography (SS-OCT) system to achieve noninvasive retinal vasculature imaging in human eyes. Materials and methods Volumetric data sets were acquired using a 1-µm SS-OCT prototype that operated at a 100-kHz A-line rate. A scanning protocol designed to allow for motion contrast processing, referred to as OCT angiography or optical microangiography (OMAG), was used to scan an approximately 3 × 3–mm area in the central macular region of the retina within approximately 4.5 seconds. An intensity differentiation-based OMAG algorithm was used to extract three-dimensional retinal functional microvasculature information. Results Intensity signal differentiation generated capillary-level resolution en face OMAG images of the retina. The parafoveal capillaries were clearly visible, thereby allowing visualization of the foveal avascular zone in healthy subjects. Conclusion The capability of OMAG to produce retinal vascular images was demonstrated using the 1-µm SS-OCT prototype. This technique has potential clinical value for studying retinal vasculature abnormalities.

Microvascular imaging: techniques and opportunities for clinical physiological measurements

Abstract: The microvasculature presents a particular challenge in physiological measurement because the vessel structure is spatially inhomogeneous and perfusion can exhibit high variability over time This review describes, with a clinical focus, the wide variety of methods now available for imaging of the microvasculature and their key applications Laser Doppler perfusion imaging and laser speckle contrast imaging are established, commercially-available techniques for determining microvascular perfusion, with proven clinical utility for applications such as burn-depth assessment Nailfold capillaroscopy is also commercially available, with significant published literature that supports its use for detecting microangiopathy secondary to specific connective tissue diseases in patients with Raynaud's phenomenon Infrared thermography measures skin temperature and not perfusion directly, and it has only gained acceptance for some surgical and peripheral microvascular applications Other emerging technologies including imaging photoplethysmography, optical coherence tomography, photoacoustic tomography, hyperspectral imaging, and tissue viability imaging are also described to show their potential as techniques that could become established tools for clinical microvascular assessment Growing interest in the microcirculation has helped drive the rapid development in perfusion imaging of the microvessels, bringing exciting opportunities in microvascular research

Retinal Nerve Fiber Layer Thickness Changes in Parkinson Disease: A Meta-Analysis

Abstract: Background Parkinson disease (PD) is a neurodegenerative process that leads to a selective loss of dopaminergic neurons, mainly in the basal ganglia of the brain. Numerous studies have analyzed the ability of optical coherence tomography (OCT) to detect retinal nerve fiber layer (RNFL) thickness abnormalities and changes in PD, but the results have not always been consistent. Therefore, we carried out a meta-analysis to evaluate the RNFL thickness measured with OCT in PD.

Noncontact depth-resolved micro-scale optical coherence elastography of the cornea.

Abstract: High-resolution elastographic assessment of the cornea can greatly assist clinical diagnosis and treatment of various ocular diseases Here, we report on the first noncontact depth-resolved micro-scale optical coherence elastography of the cornea achieved using shear wave imaging optical coherence tomography (SWI-OCT) combined with the spectral analysis of the corneal Lamb wave propagation This imaging method relies on a focused air-puff device to load the cornea with highly-localized low-pressure short-duration air stream and applies phase-resolved OCT detection to capture the low-amplitude deformation with nano-scale sensitivity The SWI-OCT system is used here to image the corneal Lamb wave propagation with the frame rate the same as the OCT A-line acquisition speed Based on the spectral analysis of the corneal temporal deformation profiles, the phase velocity of the Lamb wave is obtained at different depths for the major frequency components, which shows the depthwise distribution of the corneal stiffness related to its structural features Our pilot experiments on ex vivo rabbit eyes demonstrate the feasibility of this method in depth-resolved micro-scale elastography of the cornea The assessment of the Lamb wave dispersion is also presented, suggesting the potential for the quantitative measurement of corneal viscoelasticity

Spectral domain optical coherence tomography findings in patients with acute syphilitic posterior placoid chorioretinopathy

Abstract: Purpose:To describe the appearance of acute syphilitic posterior placoid chorioretinitis, a rare ocular manifestation of syphilis, on spectral domain optical coherence tomography (SD OCT) both before and after treatment.Methods:Ophthalmic examination and imaging studies of 30 eyes of 19 confirmed ca

Optical coherence micro-elastography: mechanical-contrast imaging of tissue microstructure

Abstract: We present optical coherence micro-elastography, an improved form of compression optical coherence elastography. We demonstrate the capacity of this technique to produce en face images, closely corresponding with histology, that reveal micro-scale mechanical contrast in human breast and lymph node tissues. We use phase-sensitive, three-dimensional optical coherence tomography (OCT) to probe the nanometer-to-micrometer-scale axial displacements in tissues induced by compressive loading. Optical coherence micro-elastography incorporates common-path interferometry, weighted averaging of the complex OCT signal and weighted least-squares regression. Using three-dimensional phase unwrapping, we have increased the maximum detectable strain eleven-fold over no unwrapping and the minimum detectable strain is 2.6 μe. We demonstrate the potential of mechanical over optical contrast for visualizing micro-scale tissue structures in human breast cancer pathology and lymph node morphology.

Diagnosing glaucoma progression with optical coherence tomography.

Abstract: Purpose of reviewOptical coherence tomography (OCT) imaging of the retinal nerve fiber layer (RNFL), optic nerve head (ONH) and macula has gained popularity in recent years to detect and monitor glaucoma. With significant improvement in scan speed and scan resolution, spectral-domain OCT has become

Comprehensive overview of definitions for optical coherence tomography-based plaque and stent analyses.

Abstract: Optical coherence tomography (OCT) is the current state-of-the-art intracoronary imaging modality that allows visualization of detailed morphological characteristics of both atherosclerotic plaque and stent. So far, three expert review documents have been released for standardization of OCT image an

Acoustic Resolution Photoacoustic Microscopy

Abstract: Even if conventional optical imaging systems such as multiphoton microscopy (MPM), confocal microscopy (CM), fluorescence microscopy (FM), and optical coherence tomography (OCT) are regarded as revolutionary microscopic imaging modalities to reveal the inner information of biological tissues with very high spatial resolution, it is inherently restricted to image deep tissues due to strong optical scatting in biological tissues. Photoacoustic imaging (PAI) is a hybrid imaging modality to combine strong optical contrast and high ultrasonic resolution in deep tissues. In a microscopic imaging perspective, photoaocustic microscopy (PAM) can be implemented in two forms: optical-resolution (OR) and acoustic-resolution (AR) PAM. In OR-PAM, the lateral spatial resolution is determined by tight optical focusing, but the penetration depth is limited to one optical transport mean free path. In AR-PAM, the lateral spatial resolution is determined by loose acoustic focusing, but the penetration depth can be much enhanced and reach to several centimeters. Therefore, AR-PAM gains great attention for both preclinical and clinical applications. This review explains the principle, implementation, and applications of AR-PAM.

Utility of Intraoperative Optical Coherence Tomography During Vitrectomy Surgery for Vitreomacular Traction Syndrome

Abstract: Purpose To assess the microarchitectural changes occurring during surgery for vitreomacular traction (VMT) utilizing intraoperative optical coherence tomography (iOCT).

Subvisible retinal laser therapy: titration algorithm and tissue response.

Abstract: PURPOSE Laser therapy for diabetic macular edema and other retinal diseases has been used within a wide range of laser settings: from intense burns to nondamaging exposures. However, there has been no algorithm for laser dosimetry that could determine laser parameters yielding a predictable extent of tissue damage. This multimodal imaging and structural correlation study aimed to verify and calibrate a computational model-based titration algorithm for predictable laser dosimetry ranging from nondamaging to intense coagulative tissue effects. METHODS Endpoint Management, an algorithm based on a computational model of retinal photothermal damage, was used to set laser parameters for various levels of tissue effect. The algorithm adjusts both power and pulse duration to vary the expected level of thermal damage at different percentages of a reference titration energy dose. Experimental verification was conducted in Dutch Belted rabbits using a PASCAL Streamline 577 laser system. Titration was performed by adjusting laser power to produce a barely visible lesion at 20 ms pulse duration, which is defined as the nominal (100%) energy level. Tissue effects were then determined for energy levels of 170, 120, 100, 75, 50, and 30% of the nominal energy at 1 hour and 3, 7, 30, and 60 days after treatment. In vivo imaging included fundus autofluorescence, fluorescein angiography, and spectral-domain optical coherence tomography. Morphologic changes in tissue were analyzed using light microscopy, as well as scanning and transmission electron microscopy. RESULTS One hundred and seventy percent and 120% levels corresponded to moderate and light burns, respectively, with damage to retinal pigment epithelium, photoreceptors, and at highest settings, to the inner retina. 50% to 75% lesions were typically subvisible ophthalmoscopically but detectable with fluorescein angiography and optical coherence tomography. Histology in these lesions demonstrated some selective damage to retinal pigment epithelium and photoreceptors. The 30% to 50% lesions were invisible with in vivo multimodal imaging, and damage was limited primarily to retinal pigment epithelium, visible best with scanning electron microscopy. Over time, photoreceptors shifted into the coagulated zone, reestablishing normal retinal anatomy in lesions ≤100%, as seen in optical coherence tomography and light microscopy. Transmission electron microscopy at 2 months demonstrated restoration of synapses between shifted-in photoreceptors and bipolar cells in these lesions. Retinal pigment epithelium monolayer restored its continuity after 1 week in all lesions. No damage could be seen <30% level. CONCLUSION A retinal laser dosimetry protocol based on the Endpoint Management algorithm provides reproducible changes in retinal morphology in animals with various levels of pigmentation. This algorithm opens doors to clinical trials of well-defined subvisible and nondestructive regimes of retinal therapy, especially important for treatment of macular disorders.

Intrasurgical dynamics of macular hole surgery: an assessment of surgery-induced ultrastructural alterations with intraoperative optical coherence tomography.

Abstract: Purpose:To evaluate the intrasurgical retinal architectural and macular hole (MH) geometric alterations that occur during surgical MH repair using intraoperative optical coherence tomography.Methods:A retrospective, multisurgeon, single-center, consecutive case series of 21 eyes undergoing surgical

Perspectives of mid-infrared optical coherence tomography for inspection and micrometrology of industrial ceramics

Abstract: Optical coherence tomography (OCT) is a promising tool for detecting micro channels, metal prints, defects and delaminations embedded in alumina and zirconia ceramic layers at hundreds of micrometers beneath surfaces. The effect of surface roughness and scattering of probing radiation within sample on OCT inspection is analyzed from the experimental and simulated OCT images of the ceramic samples with varying surface roughnesses and operating wavelengths. By Monte Carlo simulations of the OCT images in the mid-IR the optimal operating wavelength is found to be 4 µm for the alumina samples and 2 µm for the zirconia samples for achieving sufficient probing depth of about 1 mm. The effects of rough surfaces and dispersion on the detection of the embedded boundaries are discussed. Two types of image artefacts are found in OCT images due to multiple reflections between neighboring boundaries and inhomogeneity of refractive index.

Gadolinium-conjugated gold nanoshells for multimodal diagnostic imaging and photothermal cancer therapy.

Abstract: Multimodal imaging offers the potential to improve diagnosis and enhance the specificity of photothermal cancer therapy. Toward this goal, we have engineered gadolinium-conjugated gold nanoshells and demonstrated that they enhance contrast for magnetic resonance imaging, X-Ray, optical coherence tomography, reflectance confocal microscopy, and two-photon luminescence. Additionally, these particles effectively convert near-infrared light to heat, which can be used to ablate cancer cells. Ultimately, these studies demonstrate the potential of gadolinium-nanoshells for image-guided photothermal ablation.

Methodology for fully automated segmentation and plaque characterization in intracoronary optical coherence tomography images

Abstract: Optical coherence tomography (OCT) is a light-based intracoronary imaging modality that provides high-resolution cross-sectional images of the luminal and plaque morphology. Currently, the segmentation of OCT images and identification of the composition of plaque are mainly performed manually by expert observers. However, this process is laborious and time consuming and its accuracy relies on the expertise of the observer. To address these limitations, we present a methodology that is able to process the OCT data in a fully automated fashion. The proposed methodology is able to detect the lumen borders in the OCT frames, identify the plaque region, and detect four tissue types: calcium (CA), lipid tissue (LT), fibrous tissue (FT), and mixed tissue (MT). The efficiency of the developed methodology was evaluated using annotations from 27 OCT pullbacks acquired from 22 patients. High Pearson's correlation coefficients were obtained between the output of the developed methodology and the manual annotations (from 0.96 to 0.99), while no significant bias with good limits of agreement was shown in the Bland-Altman analysis. The overlapping areas ratio between experts' annotations and methodology in detecting CA, LT, FT, and MT was 0.81, 0.71, 0.87, and 0.81, respectively.

Adaptive optics SLO/OCT for 3D imaging of human photoreceptors in vivo

Abstract: We present a new instrument that is capable of imaging human photoreceptors in three dimensions. To achieve high lateral resolution, the system incorporates an adaptive optics system. The high axial resolution is achieved through the implementation of optical coherence tomography (OCT). The instrument records simultaneously both, scanning laser ophthalmoscope (SLO) and OCT en-face images, with a pixel to pixel correspondence. The information provided by the SLO is used to correct for transverse eye motion in post-processing. In order to correct for axial eye motion, the instrument is equipped with a high speed axial eye tracker. In vivo images of foveal cones as well as images recorded at an eccentricity from the fovea showing cones and rods are presented.