Extended depth of focus adaptive optics spectral domain optical coherence tomography

We present an adaptive optics spectral domain optical coherence tomography (AO-SDOCT) with a long focal range by active phase modulation of the pupil. A long focal range is achieved by introducing AO-controlled third-order spherical aberration (SA). The property of SA and its effects on focal range are investigated in detail using the Huygens-Fresnel principle, beam profile measurement and OCT imaging of a phantom. The results indicate that the focal range is extended by applying SA, and the direction of extension can be controlled by the sign of applied SA. Finally, we demonstrated in vivo human retinal imaging by altering the applied SA.OCIS codes: (170.4500) Optical coherence tomography, (110.1080) Active or adaptive optics, (170.4470) Ophthalmology     

Pupil tracking optical coherence tomography for precise control of pupil entry position

To maximize the collection efficiency of back-scattered light, and to minimize aberrations and vignetting, the lateral position of the scan pivot of an optical coherence tomography (OCT) retinal scanner should be imaged to the center of the ocular pupil. Additionally, several retinal structures including Henle’s Fiber Layer (HFL) exhibit reflectivities that depend on illumination angle, which can be controlled by varying the pupil entry position of the OCT beam. In this work, we describe an automated method for controlling the lateral pupil entry position in retinal OCT by utilizing pupil tracking in conjunction with a 2D fast steering mirror placed conjugate to the retinal plane. We demonstrate that pupil tracking prevents lateral motion artifacts from impeding desired pupil entry locations, and enables precise pupil entry positioning and therefore control of the illumination angle of incidence at the retinal plane. We use our prototype pupil tracking OCT system to directly visualize the obliquely oriented HFL.OCIS codes: (110.4500) Optical coherence tomography, (170.4460) Ophthalmic optics and devices     

Volumetric directional optical coherence tomography

Photoreceptor loss and resultant thinning of the outer nuclear layer (ONL) is an important pathological feature of retinal degenerations and may serve as a useful imaging biomarker for age-related macular degeneration. However, the demarcation between the ONL and the adjacent Henle’s fiber layer (HFL) is difficult to visualize with standard optical coherence tomography (OCT). A dedicated OCT system that can precisely control and continuously and synchronously update the imaging beam entry points during scanning has not been realized yet. In this paper, we introduce a novel imaging technology, Volumetric Directional OCT (VD-OCT), which can dynamically adjust the incident beam on the pupil without manual adjustment during a volumetric OCT scan. We also implement a customized spoke-circular scanning pattern to observe the appearance of HFL with sufficient optical contrast in continuous cross-sectional scans through the entire volume. The application of VD-OCT for retinal imaging to exploit directional reflectivity properties of tissue layers has the potential to allow for early identification of retinal diseases.     

Improved visualization of outer retinal morphology with aberration cancelling reflective optical design for adaptive optics - optical coherence tomography

We present an aberration cancelling optical design for a reflective adaptive optics - optical coherence tomography (AO-OCT) retinal imaging system. The optical performance of this instrument is compared to our previous multimodal AO-OCT/AO-SLO retinal imaging system. The feasibility of new instrumentation for improved visualization of microscopic retinal structures is discussed. Examples of images acquired with this new AO-OCT instrument are presented.OCIS codes: (110.4500) Optical coherence tomography, (010.1080) Active or adaptive optics, (220.1000) Aberration compensation, (170.0110) Imaging systems, (170.4470) Ophthalmology, (120.3890) Medical optics instrumentation     

Dermascope guided multiple reference optical coherence tomography

In this paper, we report the feasibility of integrating a novel low cost optical coherence tomography (OCT) system with a dermascope for point-of-care applications. The proposed OCT system is based on an enhanced time-domain optical coherence tomographic system, called multiple reference OCT (MR-OCT), which uses a single miniature voice coil actuator and a partial mirror for extending the axial scan range. The system can simultaneously register both the superficial dermascope image and the depth-resolved OCT sub-surface information by an interactive beam steering method. A practitioner is able to obtain the depth resolved information of the point of interest by simply using the mouse cursor. The proposed approach of combining a dermascope with a low cost OCT provides a unique powerful optical imaging modality for a range of dermatological applications. Hand-held dermascopic OCT devices would also enable point of care and remote health monitoring.OCIS codes: (110.4500) Optical coherence tomography, (170.3880) Medical and biological imaging, (100.3175) Interferometric imaging, (100.2000) Digital image processing, (130.3120) Integrated optics devices     

Ultra-thin and flexible endoscopy probe for optical coherence tomography based on stepwise transitional core fiber

We present an ultra-thin fiber-body endoscopy probe for optical coherence tomography (OCT) which is based on a stepwise transitional core (STC) fiber. In a minimalistic design, our probe was made of spliced specialty fibers that could be directly used for beam probing optics without using a lens. In our probe, the OCT light delivered through a single-mode fiber was efficiently expanded to a large mode field of 24 μm diameter for a low beam divergence. The size of our probe was 85 μm in the probe’s diameter while operated in a 160-μm thick protective tubing. Through theoretical and experimental analyses, our probe was found to exhibit various attractive features in terms of compactness, flexibility and reliability along with its excellent fabrication simplicity.OCIS codes: (110.4500) Optical coherence tomography, (170.2150) Endoscopic imaging, (170.3890) Medical optics instrumentation, (060.2350) Fiber optics imaging     

Adaptive optics optical coherence tomography with dynamic retinal tracking

Adaptive optics optical coherence tomography (AO-OCT) is a highly sensitive and noninvasive method for three dimensional imaging of the microscopic retina. Like all in vivo retinal imaging techniques, however, it suffers the effects of involuntary eye movements that occur even under normal fixation. In this study we investigated dynamic retinal tracking to measure and correct eye motion at KHz rates for AO-OCT imaging. A customized retina tracking module was integrated into the sample arm of the 2nd-generation Indiana AO-OCT system and images were acquired on three subjects. Analyses were developed based on temporal amplitude and spatial power spectra in conjunction with strip-wise registration to independently measure AO-OCT tracking performance. After optimization of the tracker parameters, the system was found to correct eye movements up to 100 Hz and reduce residual motion to 10 µm root mean square. Between session precision was 33 µm. Performance was limited by tracker-generated noise at high temporal frequencies.OCIS codes: (110.1080) Active or adaptive optics, (170.4500) Optical coherence tomography, (120.3890) Medical optics instrumentation, (170.0110) Imaging systems, (170.4470) Ophthalmology, (330.5310) Vision - photoreceptors     

Adaptive optics scanning ophthalmoscopy with annular pupils

Annular apodization of the illumination and/or imaging pupils of an adaptive optics scanning light ophthalmoscope (AOSLO) for improving transverse resolution was evaluated using three different normalized inner radii (0.26, 0.39 and 0.52). In vivo imaging of the human photoreceptor mosaic at 0.5 and 10° from fixation indicates that the use of an annular illumination pupil and a circular imaging pupil provides the most benefit of all configurations when using a one Airy disk diameter pinhole, in agreement with the paraxial confocal microscopy theory. Annular illumination pupils with 0.26 and 0.39 normalized inner radii performed best in terms of the narrowing of the autocorrelation central lobe (between 7 and 12%), and the increase in manual and automated photoreceptor counts (8 to 20% more cones and 11 to 29% more rods). It was observed that the use of annular pupils with large inner radii can result in multi-modal cone photoreceptor intensity profiles. The effect of the annular masks on the average photoreceptor intensity is consistent with the Stiles-Crawford effect (SCE). This indicates that combinations of images of the same photoreceptors with different apodization configurations and/or annular masks can be used to distinguish cones from rods, even when the former have complex multi-modal intensity profiles. In addition to narrowing the point spread function transversally, the use of annular apodizing masks also elongates it axially, a fact that can be used for extending the depth of focus of techniques such as adaptive optics optical coherence tomography (AOOCT). Finally, the positive results from this work suggest that annular pupil apodization could be used in refractive or catadioptric adaptive optics ophthalmoscopes to mitigate undesired back-reflections.     

Wavefront sensorless adaptive optics optical coherence tomography for in vivo retinal imaging in mice

We present wavefront sensorless adaptive optics (WSAO) Fourier domain optical coherence tomography (FD-OCT) for in vivo small animal retinal imaging. WSAO is attractive especially for mouse retinal imaging because it simplifies optical design and eliminates the need for wavefront sensing, which is difficult in the small animal eye. GPU accelerated processing of the OCT data permitted real-time extraction of image quality metrics (intensity) for arbitrarily selected retinal layers to be optimized. Modal control of a commercially available segmented deformable mirror (IrisAO Inc.) provided rapid convergence using a sequential search algorithm. Image quality improvements with WSAO OCT are presented for both pigmented and albino mouse retinal data, acquired in vivo.OCIS codes: (170.4460) Ophthalmic optics and devices, (110.1080) Active or adaptive optics, (110.4500) Optical coherence tomography     

Computed optical interferometric tomography for high-speed volumetric cellular imaging

Three-dimensional high-resolution imaging methods are important for cellular-level research. Optical coherence microscopy (OCM) is a low-coherence-based interferometry technology for cellular imaging with both high axial and lateral resolution. Using a high-numerical-aperture objective, OCM normally has a shallow depth of field and requires scanning the focus through the entire region of interest to perform volumetric imaging. With a higher-numerical-aperture objective, the image quality of OCM is affected by and more sensitive to aberrations. Interferometric synthetic aperture microscopy (ISAM) and computational adaptive optics (CAO) are computed imaging techniques that overcome the depth-of-field limitation and the effect of optical aberrations in optical coherence tomography (OCT), respectively. In this work we combine OCM with ISAM and CAO to achieve high-speed volumetric cellular imaging. Experimental imaging results of ex vivo human breast tissue, ex vivo mouse brain tissue, in vitro fibroblast cells in 3D scaffolds, and in vivo human skin demonstrate the significant potential of this technique for high-speed volumetric cellular imaging.OCIS codes: (170.4500) Optical coherence tomography, (090.1000) Aberration compensation, (180.3170) Interference microscopy, (170.6900) Three-dimensional microscopy, (110.1758) Computational imaging, (100.3200) Inverse scattering     

Dual-modality fiber-based OCT-TPL imaging system for simultaneous microstructural and molecular analysis of atherosclerotic plaques

New optical imaging techniques that provide contrast to study both the anatomy and composition of atherosclerotic plaques can be utilized to better understand the formation, progression and clinical complications of human coronary artery disease. We present a dual-modality fiber-based optical imaging system for simultaneous microstructural and molecular analysis of atherosclerotic plaques that combines optical coherence tomography (OCT) and two-photon luminescence (TPL) imaging. Experimental results from ex vivo human coronary arteries show that OCT and TPL optical contrast in recorded OCT-TPL images is complimentary and in agreement with histological analysis. Molecular composition (e.g., lipid and oxidized-LDL) detected by TPL imaging can be overlaid onto plaque microstructure depicted by OCT, providing new opportunities for atherosclerotic plaque identification and characterization.OCIS codes: (110.4500) Optical coherence tomography, (190.1900) Diagnostic applications of nonlinear optics, (190.4370) Nonlinear optics, fibers, (170.6280) Spectroscopy, fluorescence and luminescence, (170.6935) Tissue characterization     

MEMS scanning micromirror for optical coherence tomography

This paper describes an endoscopic-inspired imaging system employing a micro-electromechanical system (MEMS) micromirror scanner to achieve beam scanning for optical coherence tomography (OCT) imaging. Miniaturization of a scanning mirror using MEMS technology can allow a fully functional imaging probe to be contained in a package sufficiently small for utilization in a working channel of a standard gastroesophageal endoscope. This work employs advanced image processing techniques to enhance the images acquired using the MEMS scanner to correct non-idealities in mirror performance. The experimental results demonstrate the effectiveness of the proposed technique.OCIS codes: (230.4685) Optical microelectromechanical devices, (230.0230) Optical devices, (170.2150) Endoscopic imaging, (100.0100) Image processing     

Towards simultaneous Talbot bands based optical coherence tomography and scanning laser ophthalmoscopy imaging

We report a Talbot bands-based optical coherence tomography (OCT) system capable of producing longitudinal B-scan OCT images and en-face scanning laser ophthalmoscopy (SLO) images of the human retina in-vivo. The OCT channel employs a broadband optical source and a spectrometer. A gap is created between the sample and reference beams while on their way towards the spectrometer’s dispersive element to create Talbot bands. The spatial separation of the two beams facilitates collection by an SLO channel of optical power originating exclusively from the retina, deprived from any contribution from the reference beam. Three different modes of operation are presented, constrained by the minimum integration time of the camera used in the spectrometer and by the galvo-scanners’ scanning rate: (i) a simultaneous acquisition mode over the two channels, useful for small size imaging, that conserves the pixel-to-pixel correspondence between them; (ii) a hybrid sequential mode, where the system switches itself between the two regimes and (iii) a sequential “on-demand” mode, where the system can be used in either OCT or SLO regimes for as long as required. The two sequential modes present varying degrees of trade-off between pixel-to-pixel correspondence and independent full control of parameters within each channel. Images of the optic nerve and fovea regions obtained in the simultaneous (i) and in the hybrid sequential mode (ii) are presented.OCIS codes: (110.4500) Optical coherence tomography, (120.3890) Medical optics instrumentation, (110.0180) Microscopy, (110.4190) Multiple imaging, (170.4460) Ophthalmic optics and devices, (170.1790) Confocal microscopy     

In vivo imaging of human photoreceptor mosaic with wavefront sensorless adaptive optics optical coherence tomography

Wavefront sensorless adaptive optics optical coherence tomography (WSAO-OCT) is a novel imaging technique for in vivo high-resolution depth-resolved imaging that mitigates some of the challenges encountered with the use of sensor-based adaptive optics designs. This technique replaces the Hartmann Shack wavefront sensor used to measure aberrations with a depth-resolved image-driven optimization algorithm, with the metric based on the OCT volumes acquired in real-time. The custom-built ultrahigh-speed GPU processing platform and fast modal optimization algorithm presented in this paper was essential in enabling real-time, in vivo imaging of human retinas with wavefront sensorless AO correction. WSAO-OCT is especially advantageous for developing a clinical high-resolution retinal imaging system as it enables the use of a compact, low-cost and robust lens-based adaptive optics design. In this report, we describe our WSAO-OCT system for imaging the human photoreceptor mosaic in vivo. We validated our system performance by imaging the retina at several eccentricities, and demonstrated the improvement in photoreceptor visibility with WSAO compensation.OCIS codes: (110.4500) Optical coherence tomography, (010.1080) Active or adaptive optics, (220.1000) Aberration compensation, (170.0110) Imaging systems, (170.4470) Ophthalmology, (120.3890) Medical optics instrumentation     

Optically buffered Jones-matrix-based multifunctional optical coherence tomography with polarization mode dispersion correction

Polarization mode dispersion (PMD) degrades the performance of Jones-matrix-based polarization-sensitive multifunctional optical coherence tomography (JM-OCT). The problem is specially acute for optically buffered JM-OCT, because the long fiber in the optical buffering module induces a large amount of PMD. This paper aims at presenting a method to correct the effect of PMD in JM-OCT. We first mathematically model the PMD in JM-OCT and then derive a method to correct the PMD. This method is a combination of simple hardware modification and subsequent software correction. The hardware modification is introduction of two polarizers which transform the PMD into global complex modulation of Jones matrix. Subsequently, the software correction demodulates the global modulation. The method is validated with an experimentally obtained point spread function with a mirror sample, as well as by in vivo measurement of a human retina.OCIS codes: (110.4500) Optical coherence tomography, (110.5405) Polarimetric imaging, (120.5410) Polarimetry, (170.4500) Optical coherence tomography, (170.4460) Ophthalmic optics and devices, (170.4470) Ophthalmology     

Motion artifact and speckle noise reduction in polarization sensitive optical coherence tomography by retinal tracking

We present a novel polarization sensitive optical coherence tomography (PS-OCT) system with an integrated retinal tracker. The tracking operates at up to 60 Hz, correcting PS-OCT scanning positions during the acquisition to avoid artifacts caused by eye motion. To demonstrate the practical performance of the system, we imaged several healthy volunteers and patients with AMD both with B-scan repetitions for frame averaging and with 3D raster scans. Under large retinal motions with up to 1 mm amplitude at 0.5 ~a few Hz frequency range, motion artifact suppression in the PS-OCT images as well as standard deviation noise reduction in the frame averaged retardation images are presented.OCIS codes: (170.0170) Medical optics and biotechnology, (170.0110) Imaging systems, (170.2655) Functional monitoring and imaging, (170.4470) Ophthalmology, (170.4500) Optical coherence tomography     

Dual band dual focus optical coherence tomography for imaging the whole eye segment

We developed an improved dual band dual focus spectral domain optical coherence tomography (SD-OCT) for in vivo 2D/3D imaging of the whole eye segment, including the whole anterior segment and retina. The system featured two OCT channels with two different bands centered at 840 nm and 1050 nm, which were designed to image the retina and the anterior segments of the eye, respectively. By combing the two probe light beams for co-axial scanning and separating them for focusing at different segments of the eye with a combination of three dichroic mirrors, we not only minimized the loss of the backscattered light from the sample but also improved the imaging depth, scan range and resolution. The full resolved complex (FRC) method was applied to double the imaging depth for the whole anterior segment imaging, with which an imaging depth of 36.71 mm in air was achieved. We demonstrated that this system was capable of measuring the dynamic changes of ocular dimensions, including the asphericity of the cornea and lens, during accommodation.OCIS codes: (110.4500) Optical coherence tomography, (330.7322) Visual optics, accommodation, (170.3880) Medical and biological imaging, (170.4460) Ophthalmic optics and devices, (170.4470) Ophthalmology, (170.4500) Optical coherence tomography     

Molecular imaging needles: dual-modality optical coherence tomography and fluorescence imaging of labeled antibodies deep in tissue

Molecular imaging using optical techniques provides insight into disease at the cellular level. In this paper, we report on a novel dual-modality probe capable of performing molecular imaging by combining simultaneous three-dimensional optical coherence tomography (OCT) and two-dimensional fluorescence imaging in a hypodermic needle. The probe, referred to as a molecular imaging (MI) needle, may be inserted tens of millimeters into tissue. The MI needle utilizes double-clad fiber to carry both imaging modalities, and is interfaced to a 1310-nm OCT system and a fluorescence imaging subsystem using an asymmetrical double-clad fiber coupler customized to achieve high fluorescence collection efficiency. We present, to the best of our knowledge, the first dual-modality OCT and fluorescence needle probe with sufficient sensitivity to image fluorescently labeled antibodies. Such probes enable high-resolution molecular imaging deep within tissue.OCIS codes: (170.0180) Microscopy, (170.4500) Optical coherence tomography, (170.2520) Fluorescence microscopy, (110.2350) Fiber optics imaging     

Full-field transmission-type angle-deviation optical microscope with reflectivity-height transformation

This full-field transmission-type three-dimensional (3D) optical microscope is constructed based on the angle deviation method (ADM) and the algorithm of reflectivity-height transformation (RHT). The surface height is proportional to the deviation angle of light passing through the object. The angle deviation and surface height can be measured based on the reflectivity closed to the critical angle using a parallelogram prism and two CCDs.OCIS codes: (080.2730) Matrix methods in paraxial optics, (110.0180) Microscopy, (180.6900) Three-dimensional microscopy, (110.4850) Optical transfer functions, (110.4500) Optical coherence tomography     

Conical scan polarization-sensitive optical coherence tomography

We report on a new articular cartilage imaging technique with potential for clinical arthroscopic use, by supplementing the variable-incidence-angle polarization-sensitive optical coherence tomography method previously developed by us with a conical beam scan protocol. The technique is validated on bovine tendon by comparing experimental data with simulated data generated using the extended Jones matrix calculus. A unique capability of this new optical technique is that it can locate the “brushing direction” of collagen fibers in articular cartilage, which is structural information that extends beyond established methods such as split-line photography or birefringent fast-axis measurement in that it is uniquely defined over the full azimuthal-angle range of (-π, + π). The mapping of this direction over the cartilage surface may offer insights into the optimal design of tissue-engineering scaffolds for cartilage repair.OCIS codes: (170.4500) Optical coherence tomography, (170.3880) Medical and biological imaging, (170.3890) Medical optics instrumentation, (260.1440) Birefringence, (260.5430) Polarization