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     

True color scanning laser ophthalmoscopy and optical coherence tomography handheld probe

Scanning laser ophthalmoscopes (SLOs) are able to achieve superior contrast and axial sectioning capability compared to fundus photography. However, SLOs typically use monochromatic illumination and are thus unable to extract color information of the retina. Previous color SLO imaging techniques utilized multiple lasers or narrow band sources for illumination, which allowed for multiple color but not “true color” imaging as done in fundus photography. We describe the first “true color” SLO, handheld color SLO, and combined color SLO integrated with a spectral domain optical coherence tomography (OCT) system. To achieve accurate color imaging, the SLO was calibrated with a color test target and utilized an achromatizing lens when imaging the retina to correct for the eye’s longitudinal chromatic aberration. Color SLO and OCT images from volunteers were then acquired simultaneously with a combined power under the ANSI limit. Images from this system were then compared with those from commercially available SLOs featuring multiple narrow-band color imaging.OCIS codes: (170.4460) Ophthalmic optics and devices, (330.1710) Color, measurement, (170.0110) Imaging systems, (170.5755) Retina scanning, (170.4470) Ophthalmology, (110.4500) Optical coherence tomography     

Interlaced spectrally encoded confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography

Scanning laser ophthalmoscopy (SLO) and spectral domain optical coherence tomography (SDOCT) have become essential clinical diagnostic tools in ophthalmology by allowing for video-rate noninvasive en face and depth-resolved visualization of retinal structure. Current generation multimodal imaging systems that combine both SLO and OCT as a means of image tracking remain complex in their hardware implementations. Here, we combine a spectrally encoded confocal scanning laser ophthalmoscope (SECSLO) with an ophthalmic SDOCT system. This novel implementation of an interlaced SECSLO-SDOCT system allows for video-rate SLO fundus images to be acquired alternately with high-resolution SDOCT B-scans as a means of image aiming, guidance, and registration as well as motion tracking. The system shares the illumination source, detection system, and scanning optics between both SLO and OCT as a method of providing a simple multimodal ophthalmic imaging system that can readily be implemented as a table-top or hand-held device.     

Human retinal imaging using visible-light optical coherence tomography guided by scanning laser ophthalmoscopy

We achieved human retinal imaging using visible-light optical coherence tomography (vis-OCT) guided by an integrated scanning laser ophthalmoscopy (SLO). We adapted a spectral domain OCT configuration and used a supercontinuum laser as the illumating source. The center wavelength was 564 nm and the bandwidth was 115 nm, which provided a 0.97 µm axial resolution measured in air. We characterized the sensitivity to be 86 dB with 226 µW incidence power on the pupil. We also integrated an SLO that shared the same optical path of the vis-OCT sample arm for alignment purposes. We demonstrated the retinal imaging from both systems centered at the fovea and optic nerve head with 20° × 20° and 10° × 10° field of view. We observed similar anatomical structures in vis-OCT and NIR-OCT. The contrast appeared different from vis-OCT to NIR-OCT, including slightly weaker signal from intra-retinal layers, and increased visibility and contrast of anatomical layers in the outer retina.OCIS codes: (110.4190) Multiple imaging, (170.0110) Imaging systems, (170.4470) Ophthalmology, (170.4500) Optical coherence tomography     

Adaptive optics scanning laser ophthalmoscopy and optical coherence tomography (AO-SLO-OCT) system for in vivo mouse retina imaging

Optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) are imaging technologies invented in the 1980s that have revolutionized the field of in vivo retinal diagnostics and are now commonly used in ophthalmology clinics as well as in vision science research. Adaptive optics (AO) technology enables high-fidelity correction of ocular aberrations, resulting in improved resolution and sensitivity for both SLO and OCT systems. The potential of gathering multi-modal cellular-resolution information in a single instrument is of great interest to the ophthalmic imaging community. Although similar instruments have been developed for imaging the human retina, developing such a system for mice will benefit basic science research and should help with further dissemination of AO technology. Here, we present our work integrating OCT into an existing mouse retinal AO-SLO system, resulting in a multi-modal AO-enhanced imaging system of the living mouse eye. The new system allows either independent or simultaneous data acquisition of AO-SLO and AO-OCT, depending on the requirements of specific scientific experiments. The system allows a data acquisition speed of 200 kHz A-scans/pixel rate for OCT and SLO, respectively. It offers ∼6 µm axial resolution for AO-OCT and a ∼1 µm lateral resolution for AO-SLO-OCT imaging.     

Analysis of the retinal edema of full-thickness macular holes by scanning laser ophthalmoscopy and optical coherence tomography

The purpose of this study was to investigate the relationship between the dark area illuminated by scanning laser ophthalmoscopy (SLO) and cystic spaces around macular holes as shown by optical coherence tomography (OCT). SLO allows for two dimensional retinal examination, using short wave length (514 nm, argon) which is useful for the vitreoretinal surface and inner retina; red helium-neon laser (633 nm), which is capable of imaging deeper tissues; and infrared diode laser (780 nm), for choroidal examination. OCT is analogous to ultrasound except that optical rather than acoustic reflectivity is measured. OCT can produce the cross-sectional view of retina. Using SLO (helium-neon laser) and OCT, we examined 8 eyes with full-thickness macular holes. Eight normal eyes served as controls. Cystic spaces were in proportion to dark areas with statistical significance as shown by correlation analysis. Evaluation of the full-thickness macular holes by using both SLO and OCT is highly useful.     

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

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.OCIS codes: (170.4460) Ophthalmic optics and devices, (170.5755) Retina scanning, (170.3880) Medical and biological imaging, (170.4500) Optical coherence tomography, (170.4470) Ophthalmology     

Integrated adaptive optics optical coherence tomography and adaptive optics scanning laser ophthalmoscope system for simultaneous cellular resolution in vivo retinal imaging

We describe an ultrahigh-resolution (UHR) retinal imaging system that combines adaptive optics Fourier-domain optical coherence tomography (AO-OCT) with an adaptive optics scanning laser ophthalmoscope (AO-SLO) to allow simultaneous data acquisition by the two modalities. The AO-SLO subsystem was integrated into the previously described AO-UHR OCT instrument with minimal changes to the latter. This was done in order to ensure optimal performance and image quality of the AO- UHR OCT. In this design both imaging modalities share most of the optical components including a common AO-subsystem and vertical scanner. One of the benefits of combining Fd-OCT with SLO includes automatic co-registration between two acquisition channels for direct comparison between retinal structures imaged by both modalities (e.g., photoreceptor mosaics or microvasculature maps). Because of differences in the detection scheme of the two systems, this dual imaging modality instrument can provide insight into retinal morphology and potentially function, that could not be accessed easily by a single system. In this paper we describe details of the components and parameters of the combined instrument, including incorporation of a novel membrane magnetic deformable mirror with increased stroke and actuator count used as a single wavefront corrector. We also discuss laser safety calculations for this multimodal system. Finally, retinal images acquired in vivo with this system are presented.     

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     

Miniaturized magnetic-driven scanning probe for endoscopic optical coherence tomography

We designed and implemented a magnetic-driven scanning (MDS) probe for endoscopic optical coherence tomography (OCT). The probe uses an externally-driven tiny magnet in the distal end to achieve unobstructed 360-degree circumferential scanning at the side of the probe. The design simplifies the scanning part inside the probe and thus allows for easy miniaturization and cost reduction. We made a prototype probe with an outer diameter of 1.4 mm and demonstrated its capability by acquiring OCT images of ex vivo trachea and artery samples from a pigeon. We used a spectrometer-based Fourier-domain OCT system and the system sensitivity with our prototype probe was measured to be 91 dB with an illumination power of 850 μW and A-scan exposure time of 1 ms. The axial and lateral resolutions of the system are 6.5 μm and 8.1 μm, respectively.OCIS codes: (170.4500) Optical coherence tomography, (170.3880) Medical and biological imaging, (170.2150) Endoscopic imaging, (120.5800) Scanners     

Ultrasmall spot size scanning laser ophthalmoscopy

An ultrasmall spot size scanning laser ophthalmoscope has been developed that employs an annular aberration-corrected incident beam to increase the effective numerical aperture of the eye thereby reducing the width of the probing light spot. Parafovea and foveal cone photoreceptor visibility determined from small area retinal image scans are discussed from the perspective of mode matching between the focused incident beam and the waveguide modes of individual cones. The cone visibility near the fovea centralis can be increased with the annular illumination scheme whereas the visibility of larger parafovea cones drops significantly as a consequence of poorer mode match. With further improvements of the implemented wavefront correction technology it holds promise for individual cone-photoreceptor imaging at the fovea centralis and for optical targeting of the retina with increased resolution.     

Enabling freehand lateral scanning of optical coherence tomography needle probes with a magnetic tracking system

We present a high-resolution three-dimensional position tracking method that allows an optical coherence tomography (OCT) needle probe to be scanned laterally by hand, providing the high degree of flexibility and freedom required in clinical usage. The method is based on a magnetic tracking system, which is augmented by cross-correlation-based resampling and a two-stage moving window average algorithm to improve upon the tracker's limited intrinsic spatial resolution, achieving 18 μm RMS position accuracy. A proof-of-principle system was developed, with successful image reconstruction demonstrated on phantoms and on ex vivo human breast tissue validated against histology. This freehand scanning method could contribute toward clinical implementation of OCT needle imaging.     

Two-dimensional micro-displacement measurement for laser coagulation using optical coherence tomography

To improve the reproducibility of photocoagulation, the ability to quantitatively monitor the thermal change of laser-irradiated retinal tissue is required. Recently, optical coherence tomography has enabled non-invasive and non-contact monitoring of the tissue structural changes during laser irradiation. To further improve the capability of this technique, a method is proposed to measure tissue displacement by simultaneously using Doppler phase shifts and correlation coefficients. The theoretical approach for this method is described, and its performance is experimentally confirmed and evaluated. Finally, lateral and axial displacements in the laser-irradiated retinal tissues of an enucleated porcine eye are observed. The proposed method is found to be useful for further understanding the direct thermal response of laser-irradiated retinal tissue.OCIS codes: (170.4500) Optical coherence tomography, (170.4470) Ophthalmology, (120.6150) Speckle imaging, (170.3340) Laser Doppler velocimetry, (170.5755) Retina scanning     

Handheld,rapidly switchable,anterior/posterior segment swept source optical coherence tomography probe

We describe the first handheld, swept source optical coherence tomography (SSOCT) system capable of imaging both the anterior and posterior segments of the eye in rapid succession. A single 2D microelectromechanical systems (MEMS) scanner was utilized for both imaging modes, and the optical paths for each imaging mode were optimized for their respective application using a combination of commercial and custom optics. The system has a working distance of 26.1 mm and a measured axial resolution of 8 μm (in air). In posterior segment mode, the design has a lateral resolution of 9 μm, 7.4 mm imaging depth range (in air), 4.9 mm 6dB fall-off range (in air), and peak sensitivity of 103 dB over a 22° field of view (FOV). In anterior segment mode, the design has a lateral resolution of 24 μm, imaging depth range of 7.4 mm (in air), 6dB fall-off range of 4.5 mm (in air), depth-of-focus of 3.6 mm, and a peak sensitivity of 99 dB over a 17.5 mm FOV. In addition, the probe includes a wide-field iris imaging system to simplify alignment. A fold mirror assembly actuated by a bi-stable rotary solenoid was used to switch between anterior and posterior segment imaging modes, and a miniature motorized translation stage was used to adjust the objective lens position to correct for patient refraction between −12.6 and + 9.9 D. The entire probe weighs less than 630 g with a form factor of 20.3 x 9.5 x 8.8 cm. Healthy volunteers were imaged to illustrate imaging performance.OCIS codes: (110.4500) Optical coherence tomography, (170.4460) Ophthalmic optics and devices, (080.3620) Lens system design, (170.0110) Imaging systems, (170.5755) Retina scanning, (170.4470) Ophthalmology     

A dual-modality optical coherence tomography and fluorescence lifetime imaging microscopy system for simultaneous morphological and biochemical tissue characterization

Most pathological conditions elicit changes in the tissue optical response that may be interrogated by one or more optical imaging modalities. Any single modality typically only furnishes an incomplete picture of the tissue optical response, hence an approach that integrates complementary optical imaging modalities is needed for a more comprehensive non-destructive and minimally-invasive tissue characterization. We have developed a dual-modality system, incorporating optical coherence tomography (OCT) and fluorescence lifetime imaging microscopy (FLIM), that is capable of simultaneously characterizing the 3-D tissue morphology and its biochemical composition. The Fourier domain OCT subsystem, at an 830 nm center wavelength, provided high-resolution morphological volumetric tissue images with an axial and lateral resolution of 7.3 and 13.4 μm, respectively. The multispectral FLIM subsystem, based on a direct pulse-recording approach (upon 355 nm laser excitation), provided two-dimensional superficial maps of the tissue autofluorescence intensity and lifetime at three customizable emission bands with 100 μm lateral resolution. Both subsystems share the same excitation/illumination optical path and are simultaneously raster scanned on the sample to generate coregistered OCT volumes and FLIM images. The developed OCT/FLIM system was capable of a maximum A-line rate of 59 KHz for OCT and a pixel rate of up to 30 KHz for FLIM. The dual-modality system was validated with standard fluorophore solutions and subsequently applied to the characterization of two biological tissue types: postmortem human coronary atherosclerotic plaques, and in vivo normal and cancerous hamster cheek pouch epithelial tissue.     

Real-time three-dimensional optical coherence tomography image-guided core-needle biopsy system

Advances in optical imaging modalities, such as optical coherence tomography (OCT), enable us to observe tissue microstructure at high resolution and in real time. Currently, core-needle biopsies are guided by external imaging modalities such as ultrasound imaging and x-ray computed tomography (CT) for breast and lung masses, respectively. These image-guided procedures are frequently limited by spatial resolution when using ultrasound imaging, or by temporal resolution (rapid real-time feedback capabilities) when using x-ray CT. One feasible approach is to perform OCT within small gauge needles to optically image tissue microstructure. However, to date, no system or core-needle device has been developed that incorporates both three-dimensional OCT imaging and tissue biopsy within the same needle for true OCT-guided core-needle biopsy. We have developed and demonstrate an integrated core-needle biopsy system that utilizes catheter-based 3-D OCT for real-time image-guidance for target tissue localization, imaging of tissue immediately prior to physical biopsy, and subsequent OCT imaging of the biopsied specimen for immediate assessment at the point-of-care. OCT images of biopsied ex vivo tumor specimens acquired during core-needle placement are correlated with corresponding histology, and computational visualization of arbitrary planes within the 3-D OCT volumes enables feedback on specimen tissue type and biopsy quality. These results demonstrate the potential for using real-time 3-D OCT for needle biopsy guidance by imaging within the needle and tissue during biopsy procedures.     

Handheld miniature probe integrating diffuse optical tomography with photoacoustic imaging through a MEMS scanning mirror

We describe a novel dual-modality imaging approach that integrates diffuse optical tomography (DOT) and photoacoustic imaging (PAI) through a miniaturized handheld probe based on microelectromechanical systems (MEMS) scanning mirror. We validate this dual-modal DOT/PAI approach using extensive phantom experiments, and demonstrate its application for tumor imaging using tumor-bearing mice systematically injected with targeted contrast agents.OCIS codes: (110.6960) Tomography, (170.0110) Imaging systems, (170.5120) Photoacoustic imaging     

Analysis of individual cone-photoreceptor directionality using scanning laser ophthalmoscopy

Scanning laser ophthalmoscopy has been used to measure individual cone-photoreceptor directionalities in the living human eye. The directionality is determined at different retinal eccentricities where it is expected that cones have diameters ranging between 5-10μm, comparable to the spot size of the incident beam. Individual cone directionality values are compared with the predicted directionalities obtained by using the waveguide model of light coupling to and from photoreceptors for the case of a focused incident beam.     

Correlation between scanning laser polarimetry with and without enhanced corneal compensation and high-definition optical coherence tomography in normal and glaucomatous eyes

Purpose: To assess the relationship between high‐definition optical coherence tomography (HD‐OCT) and scanning laser polarimetry (SLP) with variable (VCC) and enhanced (ECC) corneal compensation in measuring peripapillary retinal nerve fibre layer (RNFL) thickness in healthy eyes and those with early‐to‐moderate glaucomatous VF loss. Methods: Healthy volunteers and patients with glaucoma who met the eligibility criteria were enrolled in this prospective, cross‐sectional, and observational study. Subjects underwent complete ophthalmologic examination, automated perimetry, SLP‐ECC, SLP‐VCC and HD‐OCT. SLP parameters were recalculated in 90 degrees segments (quadrants) in the calculation circle to be compared. Pearson correlation coefficients and Lin’s concordance correlation coefficients were calculated. The p‐values < 0.05 were considered statistically significant. Results: Fifty‐five normal volunteers (mean age 59.1 years) and 33 patients with glaucoma (mean age 63.8 years) were enrolled. In the glaucoma group, 18 patients (54.5%) had MD ≥ ?6.0 dB (early glaucoma) and 15 patients (45.4%) had MD between ?6.01 and ?12.0 dB (moderate glaucoma). The best correlation between HD‐OCT and SLP was found in the superior quadrant thickness, r = 0.74 (0.62–0.82) (p < 0.0001) with SLP‐VCC and in the average thickness, r = 0.80 (0.71–0.86) (p < 0.0001) and the superior quadrant thickness r = 0.80 (0.71–0.87) (p < 0.0001) with SLP‐ECC. Concordance correlation coefficients obtained for every parameter in our study between HD‐OCT and SLP‐VCC and between HD‐OCT and SLP‐ECC were poor. Conclusions: Our results suggest that HD‐OCT parameters of RNFL thickness are significantly higher than SLP‐VCC and SLP‐ECC parameters, and therefore those thickness values are not interchangeable. The HD‐OCT and SLP methods are well correlated but concordance is poor. The difference plots show a lack of agreement that changes as a proportion of the mean.