This PDF file contains the front matter associated with SPIE Proceedings Volume 10053, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Two-photon excited fluorescence (TPEF) for in-vivo retinal imaging is an emerging tool for vision science. TPEF has multiple benefits in comparison to conventional confocal fluorescence scanning laser ophthalmoscopy for retinal imaging, including better axial resolution and the ability to use infrared excitation light for imaging the highly photosensitive tissue in the retina. TPEF is very sensitive to the focused spot size, which is enlarged by aberrations induced by the refractive elements of the mouse eye when imaging with a large numerical aperture. Our system begins with a femtosecond pulsed laser for two-photon excitation, which is also sufficiently spectrally broadband to allow for an optical coherence tomography (OCT) sub-system to guide aberration correction. The OCT system operated at 1 volumes/second with our custom GPU accelerated real-time processing. Our lens-based optical design features two deformable elements, one with large stroke for focus control on the retina and the other with multiple actuators for aberration correction. Our wavefront-sensorless adaptive optics (SAO) is driven by a modal search with a sharpness quality metric on the en-face OCT image of the selected retinal layer. After optimization, the speed was increased to 10 fps for TPEF imaging to allow for streaming and averaging ~200 frames per image. To demonstrate the system capabilities, we performed in-vivo retinal fluorescein angiography using TPEF. Our results demonstrate depth-resolved aberration correction with the SAO-OCT to increase the TPEF signal intensity. We also present TPEF at multiple vascular layers in the mouse retina alongside the volumetric OCT to localize the vessels.

Handheld optical coherence tomography (OCT) systems facilitate imaging of young children, bedridden subjects, and those with less stable fixation. Smaller and lighter OCT probes allow for more efficient imaging and reduced operator fatigue, which is critical for prolonged use in either the operating room or neonatal intensive care unit. In addition to size and weight, the imaging speed, image quality, field of view, resolution, and focus correction capability are critical parameters that determine the clinical utility of a handheld probe. Here, we describe an ultra-compact swept source (SS) OCT handheld probe weighing only 211 g (half the weight of the next lightest handheld SSOCT probe in the literature) with 20.1 µm lateral resolution, 7 µm axial resolution, 102 dB peak sensitivity, a 27° x 23° field of view, and motorized focus adjustment for refraction correction between -10 to +16 D. A 2D microelectromechanical systems (MEMS) scanner, a converging beam-at-scanner telescope configuration, and an optical design employing 6 different custom optics were used to minimize device size and weight while achieving diffraction limited performance throughout the system’s field of view. Custom graphics processing unit (GPU)-accelerated software was used to provide real-time display of OCT B-scans and volumes. Retinal images were acquired from adult volunteers to demonstrate imaging performance.

Multimodal imaging systems that combine scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) have demonstrated the utility of concurrent en face and volumetric imaging for aiming, eye tracking, bulk motion compensation, mosaicking, and contrast enhancement. However, this additional functionality trades off with increased system complexity and cost because both SLO and OCT generally require dedicated light sources, galvanometer scanners, relay and imaging optics, detectors, and control and digitization electronics. We previously demonstrated multimodal ophthalmic imaging using swept-source spectrally encoded SLO and OCT (SS-SESLO-OCT). Here, we present system enhancements and a new optical design that increase our SS-SESLO-OCT data throughput by >7x and field-of-view (FOV) by >4x. A 200 kHz 1060 nm Axsun swept-source was optically buffered to 400 kHz sweep-rate, and SESLO and OCT were simultaneously digitized on dual input channels of a 4 GS/s digitizer at 1.2 GS/s per channel using a custom k-clock. We show in vivo human imaging of the anterior segment out to the limbus and retinal fundus over a >40° FOV. In addition, nine overlapping volumetric SS-SESLO-OCT volumes were acquired under video-rate SESLO preview and guidance. In post-processing, all nine SESLO images and en face projections of the corresponding OCT volumes were mosaicked to show widefield multimodal fundus imaging with a >80° FOV. Concurrent multimodal SS-SESLO-OCT may have applications in clinical diagnostic imaging by enabling aiming, image registration, and multi-field mosaicking and benefit intraoperative imaging by allowing for real-time surgical feedback, instrument tracking, and overlays of computationally extracted image-based surrogate biomarkers of disease.

High quality visualization of the retinal microvasculature can improve our understanding of the onset and development of retinal vascular diseases, which are a major cause of visual morbidity and are increasing in prevalence. Optical Coherence Tomography Angiography (OCT-A) images are acquired over multiple seconds and are particularly susceptible to motion artifacts, which are more prevalent when imaging patients with pathology whose ability to fixate is limited. The acquisition of multiple OCT-A images sequentially can be performed for the purpose of removing motion artifact and increasing the contrast of the vascular network through averaging. Due to the motion artifacts, a robust registration pipeline is needed before feature preserving image averaging can be performed. In this report, we present a novel method for a GPU-accelerated pipeline for acquisition, processing, segmentation, and registration of multiple, sequentially acquired OCT-A images to correct for the motion artifacts in individual images for the purpose of averaging. High performance computing, blending CPU and GPU, was introduced to accelerate processing in order to provide high quality visualization of the retinal microvasculature and to enable a more accurate quantitative analysis in a clinically useful time frame. Specifically, image discontinuities caused by rapid micro-saccadic movements and image warping due to smoother reflex movements were corrected by strip-wise affine registration estimated using Scale Invariant Feature Transform (SIFT) keypoints and subsequent local similarity-based non-rigid registration. These techniques improve the image quality, increasing the value for clinical diagnosis and increasing the range of patients for whom high quality OCT-A images can be acquired.

Local statistics are widely utilized for quantification and image processing of OCT. For example, local mean is used to reduce speckle, local variation of polarization state (degree-of-polarization-uniformity (DOPU)) is used to visualize melanin. Conventionally, these statistics are calculated in a rectangle kernel whose size is uniform over the image. However, the fixed size and shape of the kernel result in a tradeoff between image sharpness and statistical accuracy. Superpixel is a cluster of pixels which is generated by grouping image pixels based on the spatial proximity and similarity of signal values. Superpixels have variant size and flexible shapes which preserve the tissue structure. Here we demonstrate a new superpixel method which is tailored for multifunctional Jones matrix OCT (JM-OCT). This new method forms the superpixels by clustering image pixels in a 6-dimensional (6-D) feature space (spatial two dimensions and four dimensions of optical features). All image pixels were clustered based on their spatial proximity and optical feature similarity. The optical features are scattering, OCT-A, birefringence and DOPU. The method is applied to retinal OCT. Generated superpixels preserve the tissue structures such as retinal layers, sclera, vessels, and retinal pigment epithelium. Hence, superpixel can be utilized as a local statistics kernel which would be more suitable than a uniform rectangle kernel. Superpixelized image also can be used for further image processing and analysis. Since it reduces the number of pixels to be analyzed, it reduce the computational cost of such image processing.

Publisher’s Note: This conference presentation, originally published on 19 April 2017, was withdrawn per author request.

The mechanical forces that living cells experience represent an important framework in the determination of a range of intricate cellular functions and processes. Current insight into cell mechanics is typically provided by in vitro measurement systems; for example, atomic force microscopy (AFM) measurements are performed on cells in culture or, at best, on freshly excised tissue. Optical techniques, such as Brillouin microscopy and optical elastography, have been used for ex vivo and in situ imaging, recently achieving cellular-scale resolution. The utility of these techniques in cell mechanics lies in quick, three-dimensional and label-free mechanical imaging. Translation of these techniques toward minimally invasive in vivo imaging would provide unprecedented capabilities in tissue characterization. Here, we take the first steps along this path by incorporating a gradient-index micro-endoscope into an ultrahigh resolution optical elastography system. Using this endoscope, a lateral resolution of 2 µm is preserved over an extended depth-of-field of 80 µm, achieved by Bessel beam illumination. We demonstrate this combined system by imaging stiffness of a silicone phantom containing stiff inclusions and a freshly excised murine liver tissue. Additionally, we test this system on murine ribs in situ. We show that our approach can provide high quality extended depth-of-field images through an endoscope and has the potential to measure cell mechanics deep in tissue. Eventually, we believe this tool will be capable of studying biological processes and disease progression in vivo.

A highly-integrated MEMS-based bimodal probe design with integrated piezoelectric fiber scanner for simul- taneous endomicroscopy and optical coherence tomography (OCT) is presented. The two modalities rely on spectrally-separated optical paths that run partially in parallel through a micro-optical bench system, which has dimensions of only 13 x 2 x 3mm³ (l x w x h). An integrated tubular piezoelectric fiber scanner is used to perform en face scanning required for three dimensional OCT measurements. This scanning engine has an outer diameter of 0.9mm and a length of 9mm, and features custom fabricated 10 μm thick polyimide flexible interconnect lines to address the four piezoelectric electrodes. As a platform combining a full-field and a scanning imaging modality, the developed probe design constitutes a blue print for a wide range of multi-modal endoscopic imaging probes.

Publisher’s Note: This conference presentation, originally published on 19 April 2017, was withdrawn per author request.

The en face operating stereomicroscope offers limited depth perception and ophthalmic surgeons must often rely on stereopsis and instrument shadowing to estimate motion in the axial dimension. Recent research and commercial microscope-integrated optical coherence tomography (MIOCT) systems have allowed OCT of live surgery, but these were restricted to real-time cross-sectional (B-scan) imaging which captures limited information about maneuvers that extend over 3D space. We recently reported on a four dimensional (4D: 3D imaging over time) MIOCT and HUD system with real-time volumetric rendering for human ophthalmic surgery, but this 100 kHz OCT system was restricted to 3.3 volumes/sec to achieve sufficient lateral sampling over a 5x5 mm field of view (FOV). In this work, we present a high-speed 4D MIOCT (HS 4D MIOCT) system for volumetric imaging at 800 kHz A-scan rate. The proposed system employs a temporal spectral splitting (TSS) technique in which the spectrum of a buffered 400 kHz OCT system is windowed into sub-spectra to yield A-scans with reduced axial resolution but at a doubled A-scan rate of 800 kHz. The trade-offs of TSS for B-scan and volumetric retinal imaging were characterized in healthy adult volunteers. In addition, porcine eye surgical manipulations were imaged with HS 4D MIOCT imaging at 10.85 volumes/sec with 400x96x340 (X,Y,Z) usable voxels over a 5x5 mm lateral FOV. HS 4D MIOCT was capable of imaging subtle volumetric tissue manipulations with high temporal and spatial resolution using ANSI-limited optical power and is readily translatable to the human operating suite.

OCT angiography (OCTA) has recently garnered immense interest in clinical ophthalmology, permitting ocular vasculature to be viewed in exquisite detail, in vivo, and without the injection of exogenous dyes. However, commercial OCTA systems provide little information about actual erythrocyte speeds; instead, OCTA is typically used to visualize the presence and/or absence of vasculature. This is an important limitation because in many ocular diseases, including diabetic retinopathy (DR) and age-related macular degeneration (AMD), alterations in blood flow, but not necessarily only the presence or absence of vasculature, are thought to be important in understanding pathogenesis. To address this limitation, we have developed an algorithm, variable interscan time analysis (VISTA), which is capable of resolving different erythrocyte speeds. VISTA works by acquiring >2 repeated B-scans, and then computing multiple OCTA signals corresponding to different effective interscan times. The OCTA signals corresponding to different effective interscan times contain independent information about erythrocyte speed. In this study we provide a theoretical overview of VISTA, and investigate the utility of VISTA in studying blood flow alterations in ocular disease. OCTA-VISTA images of eyes with choroidal neovascularization, geographic atrophy, and diabetic retinopathy are presented.

The non-invasive measurement of cellular physiological responses to photostimulation in living retina may have significant clinical value and give new insight into the vision process. Optical coherence tomography (OCT) has been reported to detect suitable intrinsic optical signals (IOS) in retinal photoreceptor layers upon their stimulation. Commonly, changes in backscattering intensity were observed ex vivo and immobilized animals in vivo. However, in humans measurements were time-consuming and cumbersome. Promising results were achieved when observing phase signals to detect intrinsic optical signals. But to achieve sufficient phase stability to image an entire area of photoreceptors turned out to be challenging. Here, we report full-field swept-source OCT to be sufficiently stable to detect the phase signals after projecting a stimulation image onto the living human retina. We extracted time-courses and signal dependencies from the measured datasets. For long stimuli, we were even able to assign responses to single cones. This functional imaging of photoreceptor activity could potentially be used to detect loss of photoreceptor function prior to visible morphological changes, which is associated with numerous retinal diseases.

Visible light is absorbed by intrinsic chromophores such as photopigment, melanin, and hemoglobin, and scattered by subcellular structures, all of which are potential retinal disease biomarkers. Recently, high-resolution quantitative measurement and mapping of hemoglobin concentrations was demonstrated using visible light Optical Coherence Tomography (OCT). Yet, most high-resolution visible light OCT systems adopt free-space, or bulk, optical setups, which could limit clinical applications. Here, the construction of a multi-functional fiber-optic OCT system for human retinal imaging with <2.5 micron axial resolution is described. A detailed noise characterization of two supercontinuum light sources with differing pulse repetition rates is presented. The higher repetition rate, lower noise, source is found to enable a sensitivity of 87 dB with 0.1 mW incident power at the cornea and a 98 microsecond exposure time. Using a broadband, asymmetric, fused single-mode fiber coupler designed for visible wavelengths, the sample arm is integrated into an ophthalmoscope platform, rendering it portable and suitable for clinical use. In vivo anatomical, Doppler, and spectroscopic imaging of the human retina is further demonstrated using a single oversampled B-scan. For spectroscopic fitting of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) content in the retinal vessels, a noise bias-corrected absorbance spectrum is estimated using a sliding short-time Fourier transform of the complex OCT signal and fit using a model of light absorption and scattering. This yielded path length (L) times molar concentration, LCHbO2 and LCHb. Based on these results, we conclude that high-resolution visible light OCT has potential for depth-resolved functional imaging of the eye.

Surgical interventions for ocular diseases involve manipulations of semi-transparent structures in the eye, but limited visualization of these tissue layers remains a critical barrier to developing novel surgical techniques and improving clinical outcomes. We addressed limitations in image-guided ophthalmic microsurgery by using microscope-integrated multimodal intraoperative swept-source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography (iSS-SESLO-OCT). We previously demonstrated in vivo human ophthalmic imaging using SS-SESLO-OCT, which enabled simultaneous acquisition of en face SESLO images with every OCT cross-section. Here, we integrated our new 400 kHz iSS-SESLO-OCT, which used a buffered Axsun 1060 nm swept-source, with a surgical microscope and TrueVision stereoscopic viewing system to provide image-based feedback. In vivo human imaging performance was demonstrated on a healthy volunteer, and simulated surgical maneuvers were performed in ex vivo porcine eyes. Denselysampled static volumes and volumes subsampled at 10 volumes-per-second were used to visualize tissue deformations and surgical dynamics during corneal sweeps, compressions, and dissections, and retinal sweeps, compressions, and elevations. En face SESLO images enabled orientation and co-registration with the widefield surgical microscope view while OCT imaging enabled depth-resolved visualization of surgical instrument positions relative to anatomic structures-of-interest. TrueVision heads-up display allowed for side-by-side viewing of the surgical field with SESLO and OCT previews for real-time feedback, and we demonstrated novel integrated segmentation overlays for augmented-reality surgical guidance. Integration of these complementary imaging modalities may benefit surgical outcomes by enabling real-time intraoperative visualization of surgical plans, instrument positions, tissue deformations, and image-based surrogate biomarkers correlated with completion of surgical goals.

In this work we investigate the benefits of using optical coherence tomography angiography (OCTA) in combination with adaptive optics (AO) technology. It has been demonstrated that the contrast of vessels and small capillaries can be greatly enhanced by the use of OCTA. Moreover, small capillaries that are below the transverse resolution of the ophthalmic instrument can be detected. This opens unique opportunities for diagnosing retinal diseases. However, there are some limitations of this technology such as shadowing artifacts caused by overlying vasculature or the inability to determine the true extension of a vessel. Thus, the evaluation of the vascular structure and density can be misleading. To overcome these limitations we applied the OCT angiography technique to images recorded with AO-OCT. Due to the higher collection efficiency of AO-OCT in comparison with standard OCT an increased intensity contrast of vasculature can be seen. Using AO-OCTA the contrast of the vasculature to the surrounding static tissue is further increased. The improved transverse resolution and the reduced depth of focus of the AO-OCT greatly reduce shadowing artifacts allowing for a correct differentiation and segmentation of different vascular layers of the inner retina. The method is investigated in healthy volunteers and in patients with diabetic retinopathy.

Adaptive optics full-filed OCT (FFOCT) with a transmissive liquid crystal spatial light modulator (LCSLM) as wavefront corrector is used without strict plane conjugation for low order aberrations corrections. We validated experimentally that FFOCT resolution is independent of aberrations and only reduce the signal level. A signal based sensorless algorithm was thus applied for wavefront distortion compensation. Image quality improvements by the wavefront sensorless control of the LCSLM were evaluated on in vitro samples. By replacing the FFOCT sample arm objective with an artificial eye used to train ophthalmologists, adaptive optics retinal imaging was achieved. In vivo experiments using a liquid lens to correct focus and astigmatism are underway.

A severe traumatic injury to a peripheral nerve often requires surgical graft repair. However, functional recovery after these surgical repairs is often unsatisfactory. To improve interventional procedures, it is important to understand the regeneration of the nerve grafts. The rodent sciatic nerve is commonly used to investigate these parameters. However, the ability to longitudinally assess the reinnervation of injured nerves are limited, and to our knowledge, no methods currently exist to investigate the timing of the revascularization in functional recovery. In this work, we describe the development and use of angiographic and polarization-sensitive (PS) optical coherence tomography (OCT) to visualize the vascularization, demyelination and remyelination of peripheral nerve healing after crush and transection injuries, and across a variety of graft repair methods. A microscope was customized to provide 3.6 cm fields of view along the nerve axis with a capability to track the nerve height to maintain the nerve within the focal plane. Motion artifact rejection was implemented in the angiography algorithm to reduce degradation by bulk respiratory motion in the hindlimb site. Vectorial birefringence imaging methods were developed to significantly enhance the accuracy of myelination measurements and to discriminate birefringent contributions from the myelin and epineurium. These results demonstrate that the OCT platform has the potential to reveal new insights in preclinical studies and may ultimately provide a means for clinical intra-surgical assessment of peripheral nerve function.

Monitoring cortical hemodynamic response after ischemic stroke (IS) is essential for understanding the pathophysiological mechanisms behind IS-induced neuron loss. Functional optical coherence tomography (OCT) is an emerging technology that can fulfill the requirement, providing label-free, high-resolution 3D images of cerebral hemodynamics. Unfortunately, strong tissue scattering pose a significant challenge for existing OCT oximetry techniques, as they either ignore the effect or compensate it numerically. Here we developed a novel dual-depth sampling and normalization strategy using visible-light OCT (vis-OCT) angiograms that can provide robust and precise sO2 estimations within cerebral circulation. The related theoretical formulation were established, and its implication and limitations were discussed. We monitored mouse cortical hemodynamics using the newly-developed method. Focal ischemic stroke was induced through photothrombosis. The analysis on pre- and post-IS vis-OCT images revealed both vascular morphology and oxygenation altered substantially after the occlusion. First, the ischemic core could be clearly identified as angiographic intensity fell below the detection limit. In addition, vessel dilation presented universally in the penumbra region. Notably for pial arteriles, the percentage of increase demonstrated inverse relationship with their pre-occlusion, pre-dilation dimeter. Vis-OCT oxygenation maps on intact cortex revealed spatial sO2 variations within pial vessels. Specifically, sO2 in arterioles decreased as it bifurcated and plunged into deeper tissue. Similarly, venous sO2 was higher in the larger, more superficial pial brunches. However, such difference was no longer appreciable after photothrombosis. Averaged arteriole sO2 dropped to 64% – 67% in the penumbra region.

Electrophysiology has remained the gold standard of neural activity detection but its resolution and high susceptibility to noise and motion artifact limit its efficiency. Imaging techniques, including fMRI, intrinsic optical imaging, and diffuse optical imaging, have been used to detect neural activity, but rely on indirect measurements such as changes in blood flow. Fluorescence-based techniques, including genetically encoded indicators, are powerful techniques, but require introduction of an exogenous fluorophore. A more direct optical imaging technique is optical coherence tomography (OCT), a label-free, high resolution, and minimally invasive imaging technique that can produce depth-resolved cross-sectional and 3D images. In this study, we sought to examine non-vascular depth-dependent optical changes directly related to neural activity. We used an OCT system centered at 1310 nm to search for changes in an ex vivo brain slice preparation and an in vivo model during 4-AP induced seizure onset and propagation with respect to electrical recording. By utilizing Doppler OCT and the depth-dependency of the attenuation coefficient, we demonstrate the ability to locate and remove the optical effects of vasculature within the upper regions of the cortex from in vivo attenuation calculations. The results of this study show a non-vascular decrease in intensity and attenuation in ex vivo and in vivo seizure models, respectively. Regions exhibiting decreased optical changes show significant temporal correlation to regions of increased electrical activity during seizure. This study allows for a thorough and biologically relevant analysis of the optical signature of seizure activity both ex vivo and in vivo using OCT.

Abnormal coronary development causes various health problems. However, coronary development remains one of the highly neglected areas in developmental cardiology due to limited technology. Currently, there is not a robust method available to map the microvasculature throughout the entire embryonic heart in 3D. This is a challenging task because it requires both micron level resolution over a large field of view and sufficient imaging depth. Speckle-variance optical coherence tomography (OCT) has reasonable resolution for coronary vessel mapping, but limited penetration depth and sensitivity to bulk motion made it impossible to apply this method to late-stage beating hearts. Some success has been achieved with coronary dye perfusion, but smaller vessels are not efficiently stained and penetration depth is still an issue. To address this problem, we present an OCT imaging procedure using optical clearing and a contrast agent (titanium dioxide) that enables 3D mapping of the coronary microvasculature in developing embryonic hearts. In brief, the hearts of stage 36 quail embryos were perfused with a low viscosity mixture of polyvinyl acetate (PVA) and titanium dioxide through the aorta using micropipette injection. After perfusion, the viscosity of the solution was increased by crosslinking the PVA polymer chains with borate ions. The tissue was then optically cleared. The titanium dioxide particles remaining in the coronaries provided a strong OCT signal, while the rest of the cardiac structures became relatively transparent. Using this technique, we are able to investigate coronary morphologies in different disease models.

Congenital heart defects (CHDs) are the most common birth defect, affecting between 4 and 75 per 1,000 live births depending on the inclusion criteria. Many of these defects can be traced to defects of cardiac cushions, critical structures during development that serve as precursors to many structures in the mature heart, including the atrial and ventricular septa, and all four sets of cardiac valves. Epithelial-mesenchymal transition (EMT) is the process through which cardiac cushions become populated with cells. Altered cushion size or altered cushion cell density has been linked to many forms of CHDs, however, quantitation of cell density in the complex 3D cushion structure poses a significant challenge to conventional histology. Optical coherence tomography (OCT) is a technique capable of 3D imaging of the developing heart, but typically lacks the resolution to differentiate individual cells. Our goal is to develop an algorithm to quantitatively characterize the density of cells in the developing cushion using 3D OCT imaging. First, in a heart volume, the atrioventricular (AV) cushions were manually segmented. Next, all voxel values in the region of interest were pooled together to generate a histogram. Finally, two populations of voxels were classified using either K-means classification, or a Gaussian mixture model (GMM). The voxel population with higher values represents cells in the cushion. To test the algorithm, we imaged and evaluated avian embryonic hearts at looping stages. As expected, our result suggested that the cell density increases with developmental stages. We validated the technique against scoring by expert readers.

Cardiac pacing could be a powerful tool for investigating mammalian cardiac electrical conduction systems as well as for treatment of certain cardiac pathologies. However, traditional electrical pacing using pacemaker requires an invasive surgical procedure. Electrical currents from the implanted electrodes can also cause damage to heart tissue, further restricting its utility. Optogenetic pacing has been developed as a promising, non-invasive alternative to electrical stimulation for controlling animal heart rhythms. It induces heart contractions by shining pulsed light on transgene-generated microbial opsins, which in turn activate the light gated ion channels in animal hearts. However, commonly used opsins in optogenetic pacing, such as channelrhodopsin-2 (ChR2), require short light wavelength stimulation (475 nm), which is strongly absorbed and scattered by tissue. Here, we performed optogenetic pacing by expression of recently engineered red-shifted microbial opsins, ReaChR and CsChrimson, in a well-established animal model, Drosophila melanogaster, using the 617 nm stimulation light pulses. The OCM technique enables non-invasive optical imaging of animal hearts with high speed and ultrahigh axial and transverse resolutions. We integrated a customized OCM system with the optical stimulation system to monitor the optogenetic pacing noninvasively. The use of red-sifted opsins enabled deeper penetration of simulating light at lower power, which is promising for applications of optogenetic pacing in mammalian cardiac pathology studies or clinical treatments in the future.

Nearly 2 million women in the United States alone are at risk for an alcohol-exposed pregnancy, including more than 600,000 who binge drink. Even low levels of prenatal alcohol exposure (PAE) can lead to a variety of birth defects, including craniofacial and neurodevelopmental defects, as well as increased risk of miscarriages and stillbirths. Studies have also shown an interaction between drinking while pregnant and an increase in congenital heart defects (CHD), including atrioventricular septal defects and other malformations. We have previously established a quail model of PAE, modeling a single binge drinking episode in the third week of a woman’s pregnancy. Using optical coherence tomography (OCT), we quantified intraventricular septum thickness, great vessel diameters, and atrioventricular valve volumes. Early-stage ethanol-exposed embryos had smaller cardiac cushions (valve precursors) and increased retrograde flow, while late-stage embryos presented with gross head/body defects, and exhibited smaller atrio-ventricular (AV) valves, interventricular septum, and aortic vessels. We previously showed that supplementation with the methyl donor betaine reduced gross defects, improved survival rates, and prevented cardiac defects. Here we show that these preventative effects are also observed with folate (another methyl donor) supplementation. Folate also appears to normalize retrograde flow levels which are elevated by ethanol exposure. Finally, preliminary findings have shown that glutathione, a crucial antioxidant, is noticeably effective at improving survival rates and minimizing gross defects in ethanol-exposed embryos. Current investigations will examine the impact of glutathione supplementation on PAE-related CHDs.

There is strong evidence that the morphological parameters of multicellular tumor spheroids (MCTS), particularly size, sphericity, and growth pattern, play a role in their cytochemical responses. Because tumor spheroids accurately represent the three-dimensional (3D) structure of in vivo tumors, they may also mimic in vivo cytochemical responses, thus lending them relevance to cancer research. Knowledge of MCTS attributes, including oxygen and nutrient gradients, hypoxia resistance, and drug response, assist specialists seeking the most efficient ways to treat cancer. Structural information on tumor spheroids can provide insight into these attributes, and become a valuable asset for treatment in vivo. Currently, high-resolution bioimaging modalities, most notably bright field imaging, phase contrast imaging, fluorescent microscopy, and confocal imaging, are being employed for this purpose. However, these modalities lack sufficient penetration depth to resolve the entire geometry of large spheroids (>200um). In response to this deficiency, we propose a potential high-throughput imaging platform using optical coherence tomography (OCT) to quantify MCTS morphology. OCT’s high resolution and depth penetration allow us to obtain complete, high-detailed, 3D tumor reconstructions with accurate diameter measurements. Furthermore, a computer-based voxel counting method is used to quantify tumor volume, which is significantly more accurate than the estimations required by 2D-projection modalities. Thus, this imaging platform provides one of the most complete and robust evaluations of tumor spheroid morphology, and shows great potential for contribution to the study of cancer treatment and drug discovery.

Aberrations in an optical system cause a reduction in imaging resolution and poor image contrast, and limit the imaging depth when imaging biological samples. Computational adaptive optics (CAO) provides an inexpensive and simpler alternative to the traditionally used hardware-based adaptive optics (HAO) techniques. In this paper, we present an automated computational aberration correction method for broadband interferometric imaging techniques, e.g. optical coherence tomography (OCT) and optical coherence microscopy (OCM). In the proposed method, the process of aberration correction is modeled as a filtering operation on the aberrant image using a phase filter in the Fourier domain. The phase filter is expressed as a linear combination of Zernike polynomials with unknown coefficients, which are estimated through an iterative optimization scheme based on maximizing an image sharpness metric. The Resilient backpropagation (Rprop) algorithm, which was originally proposed as an alternative to the gradient-descent-based backpropagation algorithm for training the weights in a multilayer feedforward neural network, is employed to optimize the Zernike polynomial coefficients because of its simplicity and the robust performance to the choice of various parameters. Stochastic selection of the number and type of Zernike modes is introduced at each optimization step to explore different trajectories to enable search for multiple optima in the multivariate search space. The method was validated on various tissue samples and shows robust performance for samples with different scattering properties, e.g. a phantom with subresolution particles, an ex vivo rabbit adipose tissue, and an in vivo photoreceptor layer of the human retina.

Optical coherence tomography (OCT) enables non-invasive, high-resolution, tomographic imaging of biological tissues by leveraging principles of low coherence interferometry; however, OCT lacks molecular specificity. Spectroscopic OCT (SOCT) overcomes this limitation by providing depth-resolved spectroscopic signatures of chromophores, but SOCT has been limited to a couple of endogenous molecules, namely hemoglobin and melanin. Stimulated Raman scattering, on the other hand, can provide highly specific molecular information of many endogenous species, but lacks the spatial and spectral multiplexing capabilities of SOCT. In this work we integrate the two methods, SRS and SOCT, to enable simultaneously multiplexed spatial and spectral imaging with sensitivity to many endogenous biochemical species that play an important role in biology and medicine. The method, termed SRS-SOCT, has the potential to achieve fast, volumetric, and highly sensitive label-free molecular imaging, which would be valuable for many applications. We demonstrate the approach by imaging excised human adipose tissue and detecting the lipids’ Raman signatures in the high-wavenumber region. Details of this method along with validations and results will be presented.

Real-time volumetric high-definition wide-field-of-view in-vivo cellular imaging requires micron-scale resolution in 3D. Compactness of the handheld device and distortion-free images with cellular resolution are also critically required for onsite use in clinical applications. By integrating a custom liquid lens-based microscope and a dual-axis MEMS scanner in a compact handheld probe, Gabor-domain optical coherence microscopy (GD-OCM) breaks the lateral resolution limit of optical coherence tomography through depth, overcoming the tradeoff between numerical aperture and depth of focus, enabling advances in biotechnology. Furthermore, distortion-free imaging with no post-processing is achieved with a compact, lightweight handheld MEMS scanner that obtained a 12-fold reduction in volume and 17-fold reduction in weight over a previous dual-mirror galvanometer-based scanner. Approaching the holy grail of medical imaging – noninvasive real-time imaging with histologic resolution – GD-OCM demonstrates invariant resolution of 2 μm throughout a volume of 1 x 1 x 0.6 mm³, acquired and visualized in less than 2 minutes with parallel processing on graphics processing units. Results on the metrology of manufactured materials and imaging of human tissue with GD-OCM are presented.

We have developed a highly realistic, Maxwell-based, model of an existing experimental optical coherence tomography based approach for characterizing blood cells flowing through a microfluidic channel. The characterization technique is indirect as it relies upon the perturbation, by blood cells, of light back-scattered by specially designed highly scattering substrate. This is in contrast with characterization techniques which directly sense light back-scattered by the cells. Up until now, our hypothesis for distinguishing between different blood cell types has been based upon experimental measurements and knowledge of cell morphology. The absence of a mathematical model capable of modelling image formation, when the wave nature of light is integral, has impeded our ability to validate and optimize the characterization method. Recently, such a model has been developed and we have adapted it to simulate our experimental system and blood cells. The model has the following features: the field back scattered by the sample, for broadband and arbitrary profile beams, is calculated according to Maxwell’s equations; the sample is a deterministic refractive index distribution; the scattered and reference electric fields are explicitly interfered; single and multiple scattering are implicitly modeled; most system parameters of practical significance (e.g. numerical aperture or wavefront aberration) are included the model. This model has been highly successful in replicating and allowing for interpretation of experimental results. We will present the key elements of the three-dimensional computational model, based upon Maxwell’s equations, as well as the key findings of the computational study. We shall also provide comparison with experimental results.

Incorporating different data processing methods, Optical coherence tomography (OCT) has the ability for high-resolution micro-angiography and quantitative flow velocity measurement. However, OCT micro-angiography cannot provide quantitative measurement of flow velocity, and the velocity measurement based on Doppler OCT requires the determination of Doppler angles, which are difficult for whole vascular network. In this study, we report a relative standard deviation OCT (RSD-OCT) for the mapping of the flow velocity in a vascular network without the calculation of Doppler angle. From the theoretical analysis and experimental validation, the RSD-OCT is angle-independent and can quantify the flow velocity conveniently after a calibration.

Optical coherence tomography angiography (OCTA) is a promising imaging modality that enables a label-free, high-resolution and high-contrast image of biological tissue microvasculature. Typically, the blood flow contrast is implemented by mathematically analyzing the temporal dynamics of light scattering, and setting a threshold to distinguish the dynamic blood flow from the static tissue bed. However, high flow contrast is degraded by the residual overlap that results in misclassification errors between dynamic and static signals. Our study has demonstrated that flow contrast can be enhanced using a single-shot angular compounded OCTA (AC-OCTA). Because a continuous modulation is induced by the offset that the probing beam is away from the beam center in the typical OCT sample arm, different incidence angles in the probing beam are encoded in B-scan modulation frequencies. The complex-valued spectral interferogram is reconstructed by removing the conjugate terms in the depth space and its Fourier transform along the transversal fast-scan direction generates a wide conjugate-free B-scan modulation spectrum in the full space of the spatial domain. By splitting the modulation spectrum, angle-resolved independent sub-angiograms are generated and then compounded to enhance the flow contrast. Both flow phantom and in vivo animal cerebral vascular imaging demonstrated that the proposed angular compounded OCTA can offer a ~50% decrease of misclassification errors and an improved flow contrast and vessel connectivity. This AC-OCTA is beneficial to facilitating the interpretation of OCT angiograms in clinical applications.

This work is dedicated to development of the OCT system with angiography for everyday clinical use. Two major problems were solved during the development: compensation of specific tissue displacements, induced by contact scanning mode and physiological motion of patients (e.g. respiratory and cardiac motions) and on-line visualization of vessel net, to provide the feedback for system operator. The performance of the resulting OCT-based microangiography device with hand-held probe was evaluated by visualization of vessels nets of volunteers oral mucosa and skin on different locations (hands, face, abdomen etc.). Success-rate more than 90% was demonstrated during the experiments.

Oxygen saturation (sO2) of RBCs in capillaries can indirectly assess local tissue oxygenation and metabolic function. For example, the altered retinal oxygenation in diabetic retinopathy and local hypoxia during tumor development in cancer are reflected by abnormal sO2 of local capillary networks. However, it is far from clear whether accurate label-free optical oximetry (i.e. measuring hemoglobin sO2) is feasible from dispersed red blood cells (RBCs) at the single-capillary level. The sO2-dependent hemoglobin absorption contrast present in optical scattering signal is complicated by geometry-dependent scattering from RBCs. Here we provide a theoretical model to calculate the backscattering spectra of single RBCs based on the first-order Born approximation, considering the orientation, size variation, and deformation of RBCs. We show that the oscillatory spectral behavior of RBC geometries is smoothed by variations in cell size and orientation, resulting in clear sO2-dependent spectral contrast. In addition, this spectral contrast persists with different deformations of RBCs, allowing the sO2 of individual RBCs in capillaries to be characterized. The theoretical model is verified by Mie theory and experiments using visible light optical coherence tomography (vis-OCT). Thus, this study shows for the first time the feasibility of, and provides a theoretical model for, label-free optical oximetry at the single-capillary level by backscattering-based imaging modalities, challenging the popular view that such measurements are impossible at the single-capillary level. This is promising for in vivo backscattering-based optical oximetry at the single-capillary level, to measure local capillary sO2 for early diagnosis, progression monitoring, and treatment evaluation of diabetic retinopathy and cancer.

A customized 1310-nm Jones-matrix optical coherence tomography (JM-OCT) for dermatological investigation was constructed and used for in vivo normal human skin tissue imaging. This system can simultaneously measure the threedimensional depth-resolved local birefringence, complex-correlation based OCT angiography (OCT-A), degree-ofpolarization- uniformity (DOPU) and scattering OCT intensity. By obtaining these optical properties of tissue, the morphology, vasculature, and collagen content of skin can be deduced and visualized. Structures in the deep layers of the epithelium were observed with depth-resolved local birefringence and polarization uniformity images. These results suggest high diagnostic and investigative potential of JM-OCT for dermatology.

Uterine cervical collagen fiber network is vital to the normal cervical function in pregnancy. Previously, we presented an orientation estimation method to enable dispersion analysis on a single axial slice of human cervical tissue obtained from the upper half of cervix using optical coherence tomography (OCT). How the collagen fiber network structure changes from the internal os (top of the cervix which meets the uterus) to external os (bottom of cervix which extends into the vagina), remains unknown due to depth penetration limitations of OCT. To establish a collagen fiber directionality “map” of the entire cervix, we imaged serial axial slices of human NP (n=11) and PG (n=2) cervical tissue obtained from the internal to external os using Institutional Review Board approved protocols at Columbia University Medical Center. Each slice was divided into four quadrants. In each quadrant, we stitched multiple overlapped OCT volumes and analyzed the en face images that were parallel to the surface. A pixel-wise directionality map was generated. We analyzed fiber trend by measuring the mean angles and quantified dispersion by calculating the standard deviation of the fiber direction over a region of 400 μm × 400 μm. For the initial four samples, our analysis confirms a circumferential fiber pattern in the outer region of slices at all depths. We found that the standard deviation close to internal os showed no significance to the standard deviation close to external os (p>0.05), indicating comparable dispersion.

Polarization-sensitive optical coherence tomography (PS-OCT) and second harmonic generation (SHG) microscopy are two imaging modalities with different resolutions, field-of-views (FOV), and contrasts, while they both have the capability of imaging collagen fibers in biological tissues. PS-OCT can measure the tissue birefringence which is induced by highly organized fibers while SHG can image the collagen fiber organization with high resolution. Articular cartilage, with abundant structural collagen fibers, is a suitable sample to study the correlation between PS-OCT and SHG microscopy. Qualitative conjecture has been made that the phase retardation measured by PS-OCT is affected by the relationship between the collagen fiber orientation and the illumination direction. Anatomical studies show that the multilayered architecture of articular cartilage can be divided into four zones from its natural surface to the subchondral bone: the superficial zone, the middle zone, the deep zone, and the calcified zone. The different zones have different collagen fiber orientations, which can be studied by the different slopes in the cumulative phase retardation in PS-OCT. An algorithm is developed based on the quantitative analysis of PS-OCT phase retardation images to analyze the microstructural features in swine articular cartilage tissues. This algorithm utilizes the depth-dependent slope changing of phase retardation A-lines to segment structural layers. The results show good consistency with the knowledge of cartilage morphology and correlation with the SHG images measured at selected depth locations. The correlation between PS-OCT and SHG microscopy shows that PS-OCT has the potential to analyze both the macro and micro characteristics of biological tissues with abundant collagen fibers and other materials that may cause birefringence.

In this manuscript we communicate a theoretical study on a plug-in optical module to be used within a Fourier-domain optical coherence tomography system (FD-OCT). The module can be inserted between the object under investigation and any single-mode fiber based FD-OCT imaging instrument, enabling the latter to carry out polarization measurements on the former. Similarly to our previous communication1 this is an active module which requires two sequential steps to perform a polarization measurement. Alternating between the two steps is achieved by changing the value of the retardance produced by two electro-optic polarization modulators, which together behave as a polarization state rotator. By combining the rotation of the polarization state with a projection against a linear polarizer it is possible to ensure that the polarization measurements are free from any undesirable polarization effects caused by the birefringence in the collecting fiber and diattenuation in the fiber-based couplers employed in the system. Unlike our previous work, though, this module adopts an in-line configuration, employing a Faraday rotator to ensure a non-reciprocal behavior between the forward and backward propagation paths. The module design also allows higher imaging rates due to the use of fast electro-optic modulators. Simulations have been carried out accounting for the chromatic effects of the polarization components, in order to evaluate the theoretical performance of the module.

Polarization sensitive optical coherence tomography (PS-OCT) is increasingly used in a range of applications, both in bench-top and catheter-based imaging configurations. Reconstruction of tissue birefringence is subject to many system and processing-dependent artifacts. However, methods for the calibration and validation of PS-OCT are missing. Here, we report on a method to fabricate tissue-like imaging phantoms exhibiting clearly defined regions with controllable amounts of birefringence. We employed the photoelastic effect to enable the generation of controllable amounts of stress-induced birefringence in rubber samples, verified with polarized light microscopy. Pigmented ink was added to liquid latex solution to mold and cure rubber bands with controlled backscattering and transparency. Differently stretched segments were embedded in a stress-free background matrix to generate clearly defined areas with high birefringence contrast in an area of homogenous backscatter intensity. Arranged in planar geometry or on the outside of a glass capillary, the stretched rubber bands defined phantoms for bench-top and catheter-based imaging, respectively. Segmentation of the defined regions of interest in the reconstructed volumetric birefringence tomograms enabled assessing measurement consistency, between repeated imaging with a single system, or between independent imaging systems. Consistent and durable imaging phantoms are crucial for advancing PS-OCT imaging technology. Our tissue-like imaging phantoms exhibit clearly defined regions with controlled amounts of birefringence and facilitate testing, calibration, and validation of imaging systems and reconstruction strategies.

In this study, we developed and applied highly-scattering large gold nanorods (LGNRs) and custom spectral detection algorithms for high sensitivity contrast-enhanced optical coherence tomography (OCT). We were able to detect LGNRs at a concentration as low as 50 pM in blood. We used this approach for noninvasive 3D imaging of blood vessels deep in solid tumors in living mice. Additionally, we demonstrated multiplexed imaging of spectrally-distinct LGNRs that enabled observations of functional drainage in lymphatic networks. This method, which we call MOZART, provides a platform for molecular imaging and characterization of tissue noninvasively at cellular resolution.

Breast cancer has the second highest mortality rate of all cancers in females. Surgical excision of malignant tissue forms a central component of breast-conserving surgery (BCS) procedures. Incomplete excision of malignant tissue is a major issue in BCS with typically 20 – 30% cases requiring a second surgical procedure due to postoperative detection of tumor in the margin. A major challenge for surgeons during BCS is the lack of effective tools to assess the surgical margin intraoperatively. Such tools would enable the surgeon to more effectively remove all tumor during the initial surgery, hence reducing re-excision rates. We report advances in the development of a new tool, optical coherence micro-elastography, which forms images, known as elastograms, based on mechanical contrast within the tissue. We demonstrate the potential of this technique to increase contrast between malignant tumor and healthy stroma in elastograms over OCT images. We demonstrate a key advance toward clinical translation by conducting wide-field imaging in intraoperative time frames with a wide-field scanning system, acquiring mosaicked elastograms with overall dimensions of ~50 × 50 mm, large enough to image an entire face of most lumpectomy specimens. We describe this wide-field imaging system, and demonstrate its operation by presenting wide-field optical coherence tomography images and elastograms of a tissue mimicking silicone phantom and a number of representative freshly excised human breast specimens. Our results demonstrate the feasibility of scanning large areas of lumpectomies, which is an important step towards practical intraoperative margin assessment.

For a large number of cancer surgeries, the lack of reliable intraoperative diagnosis leads to reoperations or bad outcomes for the patients. To deliver better diagnosis, we developed Dynamic Full Field OCT (D-FFOCT) as a complement to FFOCT. FFOCT already presents interesting results for cancer diagnosis e.g. Mohs surgery and reaching 96% accuracy on prostate cancer. D-FFOCT accesses the dynamic processes of metabolism and gives new tools to diagnose the state of a tissue at the cellular level to complement FFOCT contrast. We developed a processing framework that intends to maximize the information provided by the FFOCT technology as well as D-FFOCT and synthetize this as a meaningful image. We use different time processing to generate metrics (standard deviation of time signals, decorrelation times and more) and spatial processing to sort out structures and the corresponding imaging modality, which is the most appropriate. Sorting was achieved through quadratic discriminant analysis in a N-dimension parametric space corresponding to our metrics. Combining the best imaging modalities for each structure leads to a rich morphology image. This image displaying the morphology is then colored to represent the dynamic behavior of these structures (slow or fast) and to be quickly analyzed by doctors. Therefore, we achieved a micron resolved image, rich of both FFOCT ability of imaging fixed and highly backscattering structures as well as D-FFOCT ability of imaging low level scattering cellular level details. We believe that this morphological contrast close to histology and the dynamic behavior contrast will push forward the limits of intraoperative diagnosis further on.

We have been developing an automated method to image lymphatic vessels both ex vivo and in vivo with optical coherence tomography (OCT), using their optical transparency. Our method compensates for the OCT signal attenuation for each A-scan in combination with the correction of the confocal function and sensitivity fall-off, enabling reliable thresholding of lymphatic vessels from the OCT scans. Morphological image processing with a segment-joining algorithm is also incorporated into the method to mitigate partial-volume artifacts, which are particularly evident with small lymphatic vessels. Our method is demonstrated for two different clinical application goals: the monitoring of conjunctival lymphatics for surgical guidance and assessment of glaucoma treatment; and the longitudinal monitoring of human burn scars undergoing laser ablation treatment. We present examples of OCT lymphangiography ex vivo on porcine conjunctivas and in vivo on human burn scars, showing the visualization of the lymphatic vessel network and their longitudinal changes due to treatment.

Conventional OCT images, obtained using a focused Gaussian beam have a lateral resolution of approximately 30 μm and a depth of focus (DOF) of 2-3 mm, defined as the confocal parameter (twice of Gaussian beam Rayleigh range). Improvement of lateral resolution without sacrificing imaging range requires techniques that can extend the DOF. Previously, we described a self-imaging wavefront division optical system that provided an estimated one order of magnitude DOF extension. In this study, we further investigate the properties of the coaxially focused multi-mode (CAFM) beam created by this self-imaging wavefront division optical system and demonstrate its feasibility for real-time biological tissue imaging. Gaussian beam and CAFM beam fiber optic probes with similar numerical apertures (objective NA≈0.5) were fabricated, providing lateral resolutions of approximately 2 μm. Rigorous lateral resolution characterization over depth was performed for both probes. The CAFM beam probe was found to be able to provide a DOF that was approximately one order of magnitude greater than that of Gaussian beam probe. By incorporating the CAFM beam fiber optic probe into a μOCT system with ~1.5 μm axial resolution, we were able to acquire cross-sectional images of swine small intestine ex vivo, enabling the visualization of subcellular structures, providing high quality OCT images over more than a 300 μm depth range.

Optical coherence tomography (OCT) retinal imaging contributes to understanding central nervous system (CNS) diseases because the eye is an anatomical “window to the brain” with direct optical access to nonmylenated retinal ganglion cells. However, many CNS diseases are associated with neuronal changes beyond the resolution of standard OCT retinal imaging systems. Though studies have shown the utility of scattering angle resolved (SAR) OCT for particle sizing and detecting disease states ex vivo, a compact SAR-OCT system for in vivo rodent retinal imaging has not previously been reported. We report a fiber-based SAR-OCT system (swept source at 1310 nm ± 65 nm, 100 kHz scan rate) for mouse retinal imaging with a partial glass window (center aperture) for angular discrimination of backscattered light. This design incorporates a dual-axis MEMS mirror conjugate to the ocular pupil plane and a high collection efficiency objective. A muring retina is imaged during euthanasia, and the proposed SAR-index is examined versus time. Results show a positive correlation between the SAR-index and the sub-cellular hypoxic response of neurons to isoflurane overdose during euthanasia. The proposed SAR-OCT design and image process technique offer a contrast mechanism able to detect sub-resolution neuronal changes for murine retinal imaging.

Time domain OCT measures the interference between sample and reference radiation as a function of the reference arm length. In full-field-OCT (FF-OCT) a camera is used instead of a scanned beam for a parallel detection of the interference pattern and thus acquiring a complete en face image. Because multiple images have to be acquired to resolve the phase ambiguity, this method is prone to motion artifacts. We present a novel motion-insensitive approach to FF-OCT. Spatially coherent illumination and an off-axis reference beam is used to introduce path-length differences between reference and sample light in neighboring pixels. This spatial carrier frequency replaces the temporal carrier frequency in scanned TD-OCT. The setup is based on a Mach-Zehnder interferometer with a super-luminescent diode and a CMOS area camera. The Sensitivity of the system was determined to be 75 dB. The field of view was 1.42 x 1.42 mm. Each frame had 237x237 lateral channels at an axial resolution of 9 µm in tissue. By step-wise changing the length of the reference arm between the en face scans, volumetric in vivo FF-OCT measurements of the human retina have been acquired within 1.3 s. OCT with a spatially coherent off-axis reference beam is suitable for in vivo imaging of human retina. The quality of the images is sufficient to discriminate the different tissue layers.

In this communication, we present the utility of the Master/Slave (MS) method in combination with the coherence revival technique to obtain full axial range Optical Coherence Tomography (OCT) cross-section images. The MS method eliminates two major drawbacks of the conventional Fourier Transformed (FT) based OCT technology when applied to the coherence revival technique: the need of data re-sampling as well as the need to compensate for unbalanced dispersion in the interferometer.

While traditional, flying-spot, spectral domain OCT systems can achieve MHz linerates, they are limited by the need for mechanical scanning to produce a B-mode image. Line-field OCT (LF OCT) removes the need for mechanical scanning by simultaneously recording all A-lines on a 2D CMOS sensor. Our LF OCT system operates at the highest A-line rate of any spectral domain (SD) LF OCT system reported to date (1,024,000 A-lines/s). This is comparable with the fastest flying-spot SDOCT system reported. Additionally, all OCT systems face a tradeoff between imaging speed and sensitivity. Long exposure times improve sensitivity but can lead to undesirable motion artifacts. LF OCT has the potential to relax this tradeoff between sensitivity and imaging speed because all A-lines are exposed during the entire frame acquisition time. However, this advantage has not yet been realized due to the loss of power-per-A-line by spreading the illumination light across all A-lines on the sample. Here we use a supercontinuum source to illuminate the sample with 500mW of light in the 605-950 nm wavelength band, effectively providing 480 µW of power-per-A-line, with axial and lateral resolutions of 1.8 µm and 14 µm, respectively. With this system we achieve the highest reported sensitivity (113 dB) of any LF OCT system. We then demonstrate the capability of this system by capturing the rapidly beating cilia of human bronchial-epithelial cells in vitro. The combination of high speed and high sensitivity offered by supercontinuum-based LF SD OCT offers new opportunities for studying cell and tissue dynamics.

FDML lasers provide sweep rates in the MHz range at wide optical bandwidths, making them ideal sources for high speed OCT. Recently, at lower speed, ultralong-range swept-source OCT has been demonstrated using a tunable vertical cavity surface emitting laser (VCSEL) and also using a Vernier-tunable laser. These sources provide relatively high sweep rates and meter range coherence lengths. In order to achieve similar coherence, we developed an extremely well dispersion compensated Fourier Domain Mode Locked (FDML) laser, running at 3.2 MHz sweep rate and 120 nm spectral bandwidth. We demonstrate that this laser offers meter range coherence and enables volumetric long range OCT of moving objects.

The limited dynamic range of optical coherence tomography (OCT) Doppler velocity measurements makes it difficult to conduct experiments on samples requiring a large dynamic range without phase wrapping at high velocities or loss of sensitivity at slow velocities. Hemodynamics and wall motion undergo significant increases in velocity as the embryonic heart develops. Experimental studies indicate that altered hemodynamics in early-stage embryonic hearts can lead to congenital heart diseases (CHDs), motivating close monitoring of blood flow over several stages of development. We have built a high-speed OCT system using an FDML laser (Optores GmbH, Germany) at a sweep rate of 1.68 MHz (axial resolution - 12 μm, sensitivity - 105 dB, phase stability - 17 mrad). The speed of this OCT system allows us to acquire high-density B-scans to obtain an extended velocity dynamic range without sacrificing the frame rate (100 Hz). The extended dynamic range within a frame is achieved by varying the A-scan interval at which the phase difference is found, enabling detection of velocities ranging from tens of microns per second to hundreds of millimeters per second. The extra lines in a frame can also be utilized to improve the structural and Doppler images via complex averaging. In structural images where the presence of blood causes additional scattering, complex averaging helps retrieve features located deeper in the tissue. Moreover, high-density frames can be registered to 4D volumes to determine the orthogonal direction of flow for calculating shear stress as well as estimating the cardiac output. In conclusion, high density B-scans acquired by our high-speed OCT system enable image enhancement and direct measurement of biological parameters in cohort studies.

We developed full-range, ultrahigh-resolution (UHR) spectral-domain optical coherence tomography (SD-OCT) in 1.7 um wavelength region for high-resolution and deep-penetration OCT imaging of turbid tissues. To realize an ultrahigh axial resolution, the ultra-broadband supercontinuum source at 1.7 um wavelength with a spectral width of 0.4 um at FWHM and home-built spectrometer with a detection range from 1.4 to 2.0 um were employed. Consequently, we achieved the axial resolution of 3.6 um in tissue (a refractive index n = 1.38). To observe deep regions of turbid tissues while keeping the ultrahigh axial resolution, a full-range OCT method to eliminate a coherent ghost image was utilized for our UHR-SD-OCT. Because the full-range method allows us to avoid the formation of a coherent ghost image when the zero delay position is in the inside of specimens, we set the zero delay position to the laser focus position in this study, and then, a region of interest in specimens was moved to the laser focus position where the highest signal intensity is achieved, resulting in the improvement of the observation depth. Thanks to the deep-penetration property of the 1.7 um light and elimination of a ghost image, we successfully demonstrated the visualization of the mouse brain structures at a depth over 1.5 mm from the surface with the 1.7 um UHR-SD-OCT. In this experiment, we confirmed that the brain specific structures, such as corpus callosum, pyramidal cell layer, and hippocampus, were clearly observed.

Most of current OCT-based angiography suffers from small FOV with short imaging range. Here we implement an ultralong-range OCT system for vascular imaging based on an akinetic swept source. This swept-source OCT (SS-OCT) system enables us to achieve up to 46 mm long imaging range with unprecedented roll-off performance. To compare with traditional spectral domain OCT (SD-OCT) system, we demonstrated the vascular imaging of the entire mice brain with wide FOV by this ultralong-range SS-OCT system and captured the blood flow images at different depth position, which shows the great advantages and bright future of this ultralong-range SS-OCT in vascular imaging.

Optical coherence microscopy (OCM) is a high-resolution imaging technique based on optical coherence tomography and confocal microscopy. The recent studies on OCM operating at 800-1300 nm spectral region have shown that OCM enables to visualize micrometer- or sub-micrometer-scale structures of animal tissues. Although OCMs offers such high-resolution label-free imaging capability of animal tissues, the imaging depth was restricted by multiple light scattering and light absorption of water in samples. Here, for high-resolution deep-tissue imaging, we developed an OCM in the 1700-nm spectral band by using a supercontinuum (SC) source with a Gaussian-like spectral shape in the wavelength region. Recently, it has been reported that the 1700-nm spectral band is a promising choice for enhancing the imaging depth in the observation of turbid scattering tissues because of the low attenuation coefficient of light. In this study, to clarify that the 1700-nm OCM has a potential to realize the enhanced imaging depth, we compared the attenuation of the signal-to-noise ratio between the 1700-nm and 1300-nm OCM imaging of a mouse brain under the same signal detection sensitivity condition. The result shows that the 1700-nm OCM enables us to achieve the enhanced imaging depth. In this 1700-nm OCM, we also confirmed that the lateral resolution of 1.3 µm and axial resolution of 2.8 µm in tissue were achieved.

Shear wave OCE (SW-OCE) uses an OCT system to track propagating mechanical waves, providing the information needed to map the elasticity of the target sample. In this study we demonstrate high speed, 4D imaging to capture transient mechanical wave propagation. Using a high-speed Fourier domain mode-locked (FDML) swept-source OCT (SS-OCT) system operating at ~1.62 MHz A-line rate, the equivalent volume rate of mechanical wave imaging is 16 kvps (kilo-volumes per second), and total imaging time for a 6 x 6 x 3 mm volume is only 0.32 s. With a displacement sensitivity of ~10 nanometers, the proposed 4D imaging technique provides sufficient temporal and spatial resolution for real-time optical coherence elastography (OCE). Combined with a new air-coupled, high-frequency focused ultrasound stimulator requiring no contact or coupling media, this near real-time system can provide quantitative information on localized viscoelastic properties. SW-OCE measurements are demonstrated on tissue-mimicking phantoms and porcine cornea under various intra-ocular pressures. In addition, elasticity anisotropy in the cornea is observed. Images of the mechanical wave group velocity, which correlates with tissue elasticity, show velocities ranging from 4-20 m/s depending on pressure and propagation direction. These initial results strong suggest that 4D imaging for real-time OCE may enable high-resolution quantitative mapping of tissue biomechanical properties in clinical applications.

Changes in the biomechanical properties of tissues are often associated with disease etiology and can provide quantitative information for clinical diagnosis. Tissue elasticity is often assessed by analyzing the speed of an elastic wave, such as in supersonic shear wave imaging and magnetic resonance elastography techniques. However, insufficient spatial resolution and large stimulation forces limit their application in small samples (dimensions on the order of millimeters or micrometers). Optical coherence elastography (OCE) is an emerging technique that provides local biomechanical properties with micrometer scale resolution. However, conventional point-by-point scanning OCE methods require long acquisition times (tens of seconds) that are unfeasible for clinical use due to motion artifacts, and repeated external excitations. Here, we demonstrate a noncontact ultrafast line-field low coherent holography system (LF-LCH) integrated with spatial phase shifting algorithm for phase retrieval based on a single interferogram. The proposed method using the Hilbert transform outperforms the Fourier transform-based technique in LF-LCH. Spatio-temporal maps of elastic wave propagation were acquired using a single air-pulse excitation and the acquisition speed can be optimized to less than 10 ms. Results on homogenous, transversely heterogeneous agar phantoms and ex vivo chicken breast agreed well with mechanical testing, demonstrating that this method can accurately detect tissue stiffness with an ultrafast line imaging rate of 200 kHz using a robust phase retrieval algorithm, which is among the highest speed for lateral imaging of elastic wave propagation with optical elastography methods.

Viscosity is often a critical characteristic of biological fluids such as blood and mucus. However, traditional rheology is often inadequate when only small quantities of sample are available. A robust method to measure viscosity of microquantities of biological samples could lead to a better understanding and diagnosis of diseases. Here, we present a method to measure viscosity by observing particle Brownian motion within a sample. M-mode optical coherence tomography (OCT) imaging, obtained with a phase-sensitive 47 kHz spectral domain system, yields a viscosity measurement from multiple 200-1000 microsecond frames. This very short period of continuous acquisition, as compared to laser speckle decorrelation, decreases sensitivity to bulk motion, thereby potentially enabling in vivo and in situ applications. The theory linking g(1) first-order image autocorrelation to viscosity is derived from first principles of Brownian motion and the Stokes-Einstein relation. To improve precision, multiple windows acquired over 500 milliseconds are analyzed and the resulting linear fit parameters are averaged. Verification experiments were performed with 200 µL samples of glycerol and water with polystyrene microbeads. Lateral bulk motion up to 2 mm/s was tolerated and accurate viscosity measurements were obtained to a depth of 400 µm or more. Additionally, the method measured a significant decrease of the apparent diffusion constant of soft tissue after formalin fixation, suggesting potential for mapping tissue stiffness over a volume.

Age-related macular degeneration and keratoconus are two ocular diseases occurring in the posterior and anterior eye, respectively. In both conditions, the mechanical elasticity of the respective tissues changes during the early onset of disease. It is necessary to detect these differences and treat the diseases in their early stages to provide proper treatment. Acoustic radiation force optical coherence elastography is a method of elasticity mapping using confocal ultrasound waves for excitation and Doppler optical coherence tomography for detection. We report on an ARF-OCE system that uses modulated compression wave based excitation signals, and detects the spatial and frequency responses of the tissue. First, all components of the system is synchronized and triggered such that the signal is consistent between frames. Next, phantom studies are performed to validate and calibrate the relationship between the resonance frequency and the Young’s modulus. Then the frequency responses of the anterior and posterior eye are detected for porcine and rabbit eyes, and the results correlated to the elasticity. Finally, spatial elastograms are obtained for a porcine retina. Layer segmentation and analysis is performed and correlated to the histology of the retina, where five distinct layers are recognized. The elasticities of the tissue layers will be quantified according to the mean thickness and displacement response for the locations on the retina. This study is a stepping stone to future in-vivo animal studies, where the elastic modulus of the ocular tissue can be quantified and mapped out accordingly.

Mechanical properties of cells and tissues play an important role in governing both normal and diseased biological processes. Recent findings in mechanobiology have demonstrated that viscosity, independent of elasticity, of extracellular matrix (ECM) can alter cellular behaviors. To obtain a comprehensive understanding of the mechanical properties of viscoelastic biological tissues for biomedical applications and mechanobiology research, both the elasticity and the viscosity must be characterized. Although optical coherence elastography (OCE) has emerged as a promising tool for probing the mechanical properties of biological tissues, quantitative OCE methods have mostly been limited to elasticity reconstruction or relied on the use of a presumed mechanical model, which may or may not adequately describe the response of a given tissue type. We present the first experimental demonstration of a mechanical model-independent reconstruction of complex shear modulus from direct measurement of surface wave propagation in viscoelastic media with dynamic acoustic radiation force (ARF)-OCE. Our results suggest that elasticity imaging based on shear wave speed alone could overlook potentially significant variations in the viscoelastic properties of biological tissues.

Mechanobiology is an emerging field which seeks to link mechanical forces and properties to the behaviors of cells and tissues in cancer, stem cell growth, and other processes. Traction force microscopy (TFM) is an imaging technique that enables the study of traction forces exerted by cells on their environment to migrate as well as sense and manipulate their surroundings. To date, TFM research has been performed using incoherent imaging modalities and, until recently, has been largely confined to the study of cell-induced tractions within two-dimensions using highly artificial and controlled environments. As the field of mechanobiology advances, and demand grows for research in physiologically relevant 3D culture and in vivo models, TFM will require imaging modalities that support such settings. Optical coherence microscopy (OCM) is an interferometric imaging modality which enables 3D cellular resolution imaging in highly scattering environments. Moreover, optical coherence elastography (OCE) enables the measurement of tissue mechanical properties. OCE relies on the principle of measuring material deformations in response to artificially applied stress. By extension, similar techniques can enable the measurement of cell-induced deformations, imaged with OCM. We propose traction force optical coherence microscopy (TF-OCM) as a natural extension and partner to existing OCM and OCE methods. We report the first use of OCM data and digital image correlation to track temporally varying displacement fields exhibited within a 3D culture setting. These results mark the first steps toward the realization of TF-OCM in 2D and 3D settings, bolstering OCM as a platform for advancing research in mechanobiology.

We developed a quantitative optical coherence elastography (qOCE) system for nonlinear mechanical characterization of biological tissues. The fiber-optic probe of the qOCE system had an integrated Fabry-Perot force sensor. To perform mechanical characterization, the tissue was compressed uniaxially by the fiber-optic probe of the qOCE system. Using the optical coherence tomography (OCT) signal detected by a spectral domain OCT engine, we were able to simultaneously quantify the force exerted to the tissue and the displacement of tissue. The quantification of the force was critical for accurate assessment of the elastic behavior of tissue, because most biological tissues have nonlinear elastic behavior. We performed qOCE characterization on tissue mimicking phantoms and biological tissues. Our results demonstrated the capability of the qOCE system for linear and nonlinear assessment of tissue elasticity.

Ophthalmic diagnostic imaging using optical coherence tomography (OCT) is limited by bulk eye motions and a fundamental trade-off between field-of-view (FOV) and sampling density. Here, we introduced a novel multi-volumetric registration and mosaicking method using our previously described multimodal swept-source spectrally encoded scanning laser ophthalmoscopy and OCT (SS-SESLO-OCT) system. Our SS-SESLO-OCT acquires an entire en face fundus SESLO image simultaneously with every OCT cross-section at 200 frames-per-second. In vivo human retinal imaging was performed in a healthy volunteer, and three volumetric datasets were acquired with the volunteer moving freely and refixating between each acquisition. In post-processing, SESLO frames were used to estimate en face rotational and translational motions by registering every frame in all three volumetric datasets to the first frame in the first volume. OCT cross-sections were contrast-normalized and registered axially and rotationally across all volumes. Rotational and translational motions calculated from SESLO frames were applied to corresponding OCT B-scans to compensate for interand intra-B-scan bulk motions, and the three registered volumes were combined into a single interpolated multi-volumetric mosaic. Using complementary information from SESLO and OCT over serially acquired volumes, we demonstrated multivolumetric registration and mosaicking to recover regions of missing data resulting from blinks, saccades, and ocular drifts. We believe our registration method can be directly applied for multi-volumetric motion compensation, averaging, widefield mosaicking, and vascular mapping with potential applications in ophthalmic clinical diagnostics, handheld imaging, and intraoperative guidance.

Adaptive optics has been successfully applied to cellular resolution imaging of the retina, enabling visualization of the characteristic mosaic patterns of the outer retina. Wavefront sensorless adaptive optics (WSAO) is a novel technique that facilitates high resolution ophthalmic imaging; it replaces the Hartmann-Shack Wavefront Sensor with an image-driven optimization algorithm and mitigates some the challenges encountered with sensor-based designs. However, WSAO generally requires longer time to perform aberrations correction than the conventional closed-loop adaptive optics. When used for in vivo retinal imaging applications, motion artifacts during the WSAO optimization process will affect the quality of the aberration correction. A faster converging optimization scheme needs to be developed to account for rapid temporal variation of the wavefront and continuously apply corrections. In this project, we investigate the Databased Online Nonlinear Extremum-seeker (DONE), a novel non-linear multivariate optimization algorithm in combination with in vivo human WSAO OCT imaging. We also report both hardware and software updates of our compact lens based WSAO 1060nm swept source OCT human retinal imaging system, including real time retinal layer segmentation and tracking (ILM and RPE), hysteresis correction for the multi-actuator adaptive lens, precise synchronization control for the 200kHz laser source, and a zoom lens unit for rapid switching of the field of view. Cross sectional images of the retinal layers and en face images of the cone photoreceptor mosaic acquired in vivo from research volunteers before and after WSAO optimization are presented.

In Optical Coherence tomography (OCT), dispersion mismatches cause degradation of the image resolution. However, dispersion is specific to the material that is causing the effect and can therefore carry useful information regarding the composition of the samples. In this summary, we propose a novel technique for estimating the dispersion in tissue which uses the image speckle to calculate the PSF degradation and is therefore applicable to any tissue and can be implemented in vivo and in situ. A Wiener-type deconvolution algorithm was used to estimate the image PSF degradation from the speckle. The proposed method was verified ex vivo resulting in comparable values of the Group Velocity Dispersion (GVD) as obtained by a standard estimation technique described in the literature. The applicability to cancer diagnosis was evaluated on a small set of gastrointestinal normal and cancer OCT images. Using the statistics of the GVD estimate, the tissue classification resulted in 93% sensitivity and 73% specificity (84% correct classification rate). The success of these preliminary results indicates the potential of the proposed method which should be further investigated to elucidate its advantages and limitations.

We employed a home-built ultrahigh resolution (UHR) OCT system at 800nm to image human breast cancer sample ex vivo. The system has an axial resolution of 2.72µm and a lateral resolution of 5.52µm with an extended imaging range of 1.78mm. Over 900 UHR OCT volumes were generated on specimens from 23 breast cancer cases. With better spatial resolution, detailed structures in the breast tissue were better defined. Different types of breast cancer as well as healthy breast tissue can be well delineated from the UHR OCT images. To quantitatively evaluate the advantages of UHR OCT imaging of breast cancer, features derived from OCT intensity images were used as inputs to a machine learning model, the relevance vector machine. A trained machine learning model was employed to evaluate the performance of tissue classification based on UHR OCT images for differentiating tissue types in the breast samples, including adipose tissue, healthy stroma and cancerous region. For adipose tissue, grid-based local features were extracted from OCT intensity data, including standard deviation, entropy, and homogeneity. We showed that it was possible to enhance the classification performance on distinguishing fat tissue from non-fat tissue by using the UHR images when compared with the results based on OCT images from a commercial 1300 nm OCT system. For invasive ductal carcinoma (IDC) and normal stroma differentiation, the classification was based on frame-based features that portray signal penetration depth and tissue reflectivity. The confusing matrix indicated a sensitivity of 97.5% and a sensitivity of 77.8%.

The extensive development of frequency-domain optical coherence tomography (OCT) for more than a decade has enabled A-scan rates in the MHz range. Furthermore, frequency-domain OCT gives access to the amplitude and phase of the OCT signal. These characteristics have opened the possibilities of doing different kinds of averaging in order to improve OCT imaging. It is well known that multiple scattering in OCT reduces image contrast and resolution especially at greater depths within the tissue. Here, we demonstrate that complex averaging can decrease the effect of multiple scattering and improve OCT imaging contrast, in addition to increasing the dynamic range due to reducing the noise floor as previously demonstrated. We take advantage of the fact that complex averaging, in contrast to conventional magnitude averaging, is sensitive to phase changes, as one averages the complex-valued Fourier-transformed spectral fringe signals before calculating the magnitude. Any motion that leads to higher phase variance will lead to lower magnitude when performing complex averaging. Also, motion preferentially increases the phase variance of multiply scattered photons when compared to singly scattered photons with each scattering event spreading the phase. This indicates that we may reduce multiple scattering by implementing complex averaging to preferentially reduce the magnitude of the multiply scattered light signal in OCT images. We have performed several experiments on liquid phantoms that give experimental evidence for this hypothesis.

A number of factors can degrade the resolution and contrast of OCT images, such as: (1) changes of the OCT pointspread function (PSF) resulting from wavelength dependent scattering and absorption of light along the imaging depth (2) speckle noise, as well as (3) motion artifacts. We propose a new Super Resolution OCT (SR OCT) imaging framework that takes advantage of a Stochastically Fully Connected Conditional Random Field (SF-CRF) model to generate a Super Resolved OCT (SR OCT) image of higher quality from a set of Low-Resolution OCT (LR OCT) images. The proposed SF-CRF SR OCT imaging is able to simultaneously compensate for all of the factors mentioned above, that degrade the OCT image quality, using a unified computational framework. The proposed SF-CRF SR OCT imaging framework was tested on a set of simulated LR human retinal OCT images generated from a high resolution, high contrast retinal image, and on a set of in-vivo, high resolution, high contrast rat retinal OCT images. The reconstructed SR OCT images show considerably higher spatial resolution, less speckle noise and higher contrast compared to other tested methods. Visual assessment of the results demonstrated the usefulness of the proposed approach in better preservation of fine details and structures of the imaged sample, retaining biological tissue boundaries while reducing speckle noise using a unified computational framework. Quantitative evaluation using both Contrast to Noise Ratio (CNR) and Edge Preservation (EP) parameter also showed superior performance of the proposed SF-CRF SR OCT approach compared to other image processing approaches.

We propose a maximum a-posteriori (MAP) intensity estimator to improve the image contrast of polarization diversity (PD)-OCT imaging to achieve high contrast polarization-artifact-free images. The MAP estimator compensates for the inevitable reduction of signal-to-noise ratio (SNR) in PD-OCT caused by the splitting of power into two polarization detection channels. It also has low noise-offset in low intensity regions such as the vitreous. This method is applied to posterior eye images, and shows high-contrast, polarization-artifact-free images. This method also enables attenuation coefficient imaging with finer differentiation of attenuation levels.

Endovascular Optical Coherence Tomography (OCT) has previously been used in both bench-top and clinical environments to produce vascular images, and can be helpful in characterizing, among other pathologies, plaque build-up and impedances to normal blood ow. The raw data produced can also be processed to yield high- resolution blood velocity information, but this computation is expensive and has previously only been available a posteriori using post-processing software. Real-time Doppler OCT (DOCT) imaging has been demonstrated before in the skin and eye, but this capability has not been available to vascular surgeons. Graphics Processing Units (GPUs) can be used to dramatically accelerate this type of distributed computation. In this paper we present a software package capable of real-time DOCT processing and circular image display using GPU acceleration designed to operate with catheter-based clinical OCT systems. This image data is overlayed onto structural images providing clinicians with live, high-resolution blood velocity information to complement anatomical data.

For bioimaging applications, commercial swept-sources currently provide enough power (tens of milliwatts) insuring good imaging condition without damaging the tissues. For industrial applications, more power is needed since the amount of light collected can be very low due to challenging measurement conditions or due to poor sample reflectivity. To address this challenge, we explore three different setups to externally amplify the output of a commercial swept-source: a booster semiconductor optical amplifier (BOA), an erbium-doped fiber amplifier (EDFA) and a combination of both. These external amplification setups allow the exploration of emerging OCT applications without the need to develop new hardware.

We developed high frame-rate en face optical coherence tomography (OCT) system using KTa_1-xNb_xO₃ (KTN) optical beam deflector. In the imaging system, the fast scanning was performed at 200 kHz by the KTN optical beam deflector, while the slow scanning was performed at 800 Hz by the galvanometer mirror. As a preliminary experiment, we succeeded in obtaining en face OCT images of human fingerprint with a frame rate of 800 fps. This is the highest frame-rate obtained using time-domain (TD) en face OCT imaging. The 3D-OCT image of sweat gland was also obtained by our imaging system.

This work reports on a compact full-field optical coherence microscopy (FF-OCM) setup specifically designed to meet the needs for in vivo imaging, illuminated by a high-brightness broadband light emitting diode (LED). Broadband LEDs have spectra potentially large enough to provide imaging spatial resolutions similar to those reached using conventional halogen lamps, but their radiance can be much higher, which leads to high speed acquisition and makes in vivo imaging possible. We introduce a FF-OCM setup using a 2.3 W broadband LED, with an interferometer designed to be as compact as possible in order to provide the basis for a portable system that will make it possible to fully benefit from the capacity for in vivo imaging by providing the ability to image any region of interest in real-time. The interferometer part of the compact FF-OCM setup weighs 210 g for a size of 11x11x5 cm³. Using this setup, a sub-micron axial resolution was reached, with a detection sensitivity of 68 dB at an imaging rate of 250 Hz. Due to the high imaging rate, the sensitivity could be improved by accumulation while maintaining an acquisition time short enough for in vivo imaging. It was possible to reach a sensitivity of 75 dB at a 50 Hz imaging rate. High resolution in vivo human skin images were obtained with this setup and compared with images of excised human skin, showing high similarity.

Optical coherence tomography (OCT) has become a useful and common diagnostic tool within the field of ophthalmology. Although presently a commercial technology, research continues in improving image quality and applying the imaging method to other tissue types. Swept-wavelength lasers based upon fiber ring cavities containing fiber Fabry-P´erot tunable filters (FFP-TF), as an intracavity element, provide swept-source optical coherence tomography (SS-OCT) systems with a robust and scalable platform. The FFP-TF can be fabricated within a large range of operating wavelengths, free spectral ranges (FSR), and finesses. To date, FFP-TFs have been fabricated at operating wavelengths from 400 nm to 2.2 µm, FSRs as large as 45 THz, and finesses as high as 30 000. The results in this paper focus on presenting the capability of the FFP-TF as an intracavity element in producing swept-wavelength lasers sources and quantifying the trade off between coherence length and sweep range. We present results within a range of feasible operating conditions. Particular focus is given to the discovery of laser configurations that result in maximization of sweep range and/or power. A novel approach to the electronic drive of the PZT-based FFP-TF is also presented, which eliminates the need for the existence of a mechanical resonance of the optical device. This approach substantially increases the range of drive frequencies with which the filter can be driven and has a positive impact for both the short all-fiber laser cavity (presented in this paper) and long cavity FDML designs as well.

This work reports on the feasibility of dynamic imaging using conventional reflectivity-based tomographic images obtained with full-field optical coherence microscopy (FF-OCM). Implementation of speckle variance for flow mapping with an imaging rate of 180 Hz is demonstrated by mapping 20% intralipid flowing into 100-μm-diameter microcapillary tubes at speeds up to ~ 50 mm/s. This constitutes a significant advance in high-resolution, real-time microvasculature mapping, using FF-OCM. The acquisition scheme in FF-OCM is particularly appropriate for en face visualization of the microvasculature, as FF-OCM directly acquires en face tomographic images unlike conventional OCT which usually requires reslicing of a three-dimensional data set to get en face images.

is vacant or filled with material having a refractive index different from the tissue, the observed structure is deformed significantly. This deformation artifact can be minimized by filling the cavity with liquid having a refractive index nearly equal to the tissue. Furthermore, by using dynamical OCT method, cavity image intensity can be significantly enhanced compared with the tissue. This image contrast improvement may allow imaging of cavity structures inside deep in tissues. In this paper, we demonstrate good contrast of speckle variance OCT imaging of phantoms. A trial of deep OCT imaging is introduced with which we can extend the OCT depth range to 27.5 mm with a commercial swept source, while the preinstalled k-clock allows only the OCT depth range of 5 mm.

The Akinetic swept-laser (Insight, Lafayette, USA) is an all-semiconductor compact and tunable laser source for optical coherence tomography (OCT). Wavelength sweeps with this source are composed of valid data sections interleaved with invalid data sections. The source provides a precise trigger for each wavelength sweep and a “data valid vector” (DVV) file which identifies the indices of the valid data points in a recorded interferogram. In order to identify valid data in real time during acquisition, a delay must be precisely adjusted between the trigger and the wavelength sweep. Optimizing this delay becomes tedious when changing the interferometer configuration in a multi-purpose OCT system. The source provides tools to do this, but they are not automated and require a sample with a single clean reflection. We developed a simple and robust algorithm, integrated in our OCT data acquisition and treatment software, for finding the optimal delay correction that must be applied to accurately identify the valid data obtained with the Akinetic swept-laser. It can perform optimization either from the laser spectrum or from an interferogram and facilitates delay readjustment when the interferometer configuration is modified.

Swept source optical coherence tomography (SSOCT) is an attractive biological imaging technology due to its advantages of simple setup and high imaging speed. As the light intensity attenuated rapidly in high scattering biological tissues, the contrast of OCT image will drop with depth. In this paper a new method was introduced to compensate the attenuation of imaging contrast in SSOCT. The interference signal was divided into two channels of analog to digital converter (ADC) with a splitting ratio of 1:5. The higher level signal in one channel was used to reconstruct deeper structure of tissue and the lower level signal in the other channel was used to reconstruct surface structure of tissue. Lowfrequency signals in one channel were filtered by a high pass filter and then combined with the signal in the other channel to obtain a high contrast image in both surface and deep area of tissue. Human finger and porcine airway imaging obtained with the system show that the contrast of SSOCT images can be improved in deeper region of tissue.

A time-domain optical coherence tomography system based on measuring the reflection matrix of back-scattered light is proposed for extended imaging depth into scattering media. A filtering operation is applied to the reflection matrix to preserve the back-scattered light with near-forward directions while discarding most of the multiple scattered light. A singular value decomposition is then carried out in the filtered matrix for principal component analysis, to remove the residual multi-scattered light. The results show the near-forward propagating single scattered light, which is mostly discarded in conventional OCT, can be separated computationally to increase the penetration depth of OCT.

Dispersion, a result of wavelength-dependent index of refraction variations, causes pulse-width broadening with detrimental effects in many pulsed-laser applications. It is also considered to be one of the major causes of resolution degradation in Optical Coherence Tomography (OCT). However, dispersion is material dependent and, in tissue, Group Velocity Dispersion (GVD) could be used, for example, to detect changes associated with early cancer and result in more accurate disease diagnosis. In this summary we compare different techniques for estimating the GVD from OCT images, in order to evaluate their accuracy and applicability in highly scattering samples such as muscle and adipose tissue. The methods investigated included estimation of the GVD from (i) the point spread function (PSF) degradation, (ii) the shift (walk-off) between images taken at different center wavelengths and (iii) the second derivative of the spectral phase. The measurements were degraded by the presence of strong Mie scattering and speckle noise with the most robust being the PSF degradation and the least robust the phase derivative method. If the GVD is to be used to provide sensitive diagnostic information from highly scattering human tissues, it would be preferable to use the resolution degradation as an estimator of GVD.

Optical coherence tomography (OCT) has become a favorable device in the dermatology discipline due to its moderate resolution and penetration depth. OCT images however contain grainy pattern, called speckle, due to the broadband source that has been used in the configuration of OCT. So far, a variety of filtering techniques is introduced to reduce speckle in OCT images. Most of these methods are generic and can be applied to OCT images of different tissues. In this paper, we present a method for speckle reduction of OCT skin images. Considering the architectural structure of skin layers, it seems that a skin image can benefit from being segmented in to differentiable clusters, and being filtered separately in each cluster by using a clustering method and filtering methods such as Wiener. The proposed algorithm was tested on an optical solid phantom with predetermined optical properties. The algorithm was also tested on healthy skin images. The results show that the cluster-based filtering method can reduce the speckle and increase the signal-to-noise ratio and contrast while preserving the edges in the image.

Optical coherence tomography (OCT), as a low-coherence interferometric imaging technique, inevitably suffers from speckle noise, which can reduce image quality and signal-to-noise (SNR). In this paper, we present a dual-beam angular compounding method to reduce speckle noise and improve SNR of OCT image. Two separated parallel light beams are created on the sample arm using a 1x2 optical fiber coupler and are focused into samples at different angles. The epi-detection scheme creates three different light path combinations of these two light beams above. The three combinations produce three images in single B-scan, which are completely separated in depth. The three images show uncorrelated speckle patterns and therefore can be averaged to create a new image with reduced speckle noise. Compared to those reported angular and spatial compounding methods, our method retains their advantages, and moreover has a faster imaging speed and keep the transverse resolution. This method was evaluated on human fingertips in vivo. The results demonstrated a good improvement in speckle contrast.

The resample of spectra which is essential for high-precision spectral-domain OCT data processing is sophisticated, and its precision is dependent on the method and equipment. In this paper, we proposed an OCT without inverse FFT. A series of reference spectra corresponding to different optical path length difference was used to convolve with spectra gotten by OCT to acquire time-domain tomography instead of inverse FFT, thus eliminating the resample of spectra. The reference spectra were calculated before imaging and corrected with correction spectrum from sample arm to compensate the influence of sample arm. Experiment was done with a mirror as sample and validated our setup.

Doppler optical coherence tomography (DOCT) is considered one of the most promising functional imaging modalities for neuro biology research and has demonstrated the ability to quantify cerebral blood flow velocity at a high accuracy. However, the measurement of total absolute blood flow velocity (BFV) of major cerebral arteries is still a difficult problem since it not only relates to the properties of the laser and the scattering particles, but also relates to the geometry of both directions of the laser beam and the flow. In this paper, focusing on the analysis of cerebral hemodynamics, we presents a method to quantify the total absolute blood flow velocity in middle cerebral artery (MCA) based on volumetric vessel reconstruction from pure DOCT images. A modified region growing segmentation method is first used to localize the MCA on successive DOCT B-scan images. Vessel skeletonization, followed by an averaging gradient angle calculation method, is then carried out to obtain Doppler angles along the entire MCA. Once the Doppler angles are determined, the absolute blood flow velocity of each position on the MCA is easily found. Given a seed point position on the MCA, our approach could achieve automatic quantification of the fully distributed absolute BFV. Based on experiments conducted using a swept-source optical coherence tomography system, our approach could achieve automatic quantification of the fully distributed absolute BFV across different vessel branches in the rodent brain.

Blood coagulation monitoring is important to diagnose hematological diseases and cardiovascular diseases and to predict the risk of bleeding and excessive clotting. In this study, we developed a system to dynamically monitor blood coagulation and quantitatively determine the coagulation function by blood elastic measurement. When blood forms a clot from a liquid, ultrasonic force induces a shear wave, which is detected by optical coherence tomography (OCT). The coagulation of porcine whole blood recalcified by calcium chloride is assessed using the metrics of reaction time, clot formation kinetics and maximum shear modulus. The OCE system can noninvasively monitor the blood coagulation and quantitatively determine the coagulation function.

Degenerative mitral regurgitation is a serious and frequent human heart valve disease. Malfunctioning of this valve brings the left-sided heart through a significant increase of pressure and volume overload. Severe degenerative mitral incompetence generally requires surgical repair or valve replacement with a bioprosthesis or mechanical heart valve. Degenerative disease affects the leaflets or/and the chordae tendineae, which link both leaflets to the papillary muscles. During mitral valve surgical repair, reconstruction of the valve leaflets, annulus and chordae are provided to prevent postoperative recurrence of valve regurgitation. The operative evaluation of the diseased and apparently normal chordae tendineae mainly depends of the surgeon´s experience, without any other objective diagnosis tool. In this work, PS-OCT (Polarization Sensitive-Optical Coherence Tomography) is applied for the first time to evaluate the pathological condition of human chordae coming from the mitral valve. It consists on a prospective study to test the viability of this technique for the evaluation of the collagen core of chords. This core presents a strong birefringence due to the longitudinal and organized arrangement of its collagen bundles. Different densities and organizations of the collagen core translate into different birefringence indicators whose measurement become an objective marker of the core structure. Ex-vivo mitral degenerative chordae tendineae have been analyzed with PS-OCT. Intensity OCT is used to obtain complementary morphological information of the chords. Birefringence results correlate with the previously reported values for human tendinous tissue.

Phase-resolved Doppler optical coherence tomography (PR-D-OCT) is a functional OCT imaging technique that can provide high-speed and high-resolution depth-resolved measurement on flow in biological materials. However, a common problem with conventional PR-D-OCT is that this technique often measures the flow motion projected onto the OCT beam path. In other words, it needs the projection angle to extract the absolute velocity from PR-D-OCT measurement. In this paper, we proposed a novel dual-beam PR-D-OCT method to measure absolute flow velocity without separate measurement on the projection angle. Two parallel light beams are created in sample arm and focused into the sample at two different incident angles. The images produced by these two beams are encoded to different depths in single B-scan. Then the Doppler signals picked up by the two beams together with the incident angle difference can be used to calculate the absolute velocity. We validated our approach in vitro on an artificial flow phantom with our home-built 1060 nm swept source OCT. Experimental results demonstrated that our method can provide an accurate measurement of absolute flow velocity with independency on the projection angle.

The main object of this research was to assess the ability to characterize the gold nanoparticles using optical modalities like optical coherence tomography. Since the nanoparticles, especially gold one, have been very attractive for medical diagnosis and treatment the amount of research activities have been growing rapidly. The nanoparticles designed for different applications like contrast agents or drugs delivery change the optical features of tissue in different way. Therefore, the expanded analysis of scattering optical signal may lead to obtain much more useful information about the tissues health and the treatment efficiency. The noninvasive measurements of the concentration and distribution of the nanoparticles, as well as their size in the media have been taken under consideration. For this purpose the polarization sensitive optical coherence tomography system with spectroscopic analysis (PS-SOCT) has been designed and used. In this contribution we are going to present the PS-SOCT measurement data obtained for the gold nanoparticles. The measurements have been taken for the liquid (gold nanoparticles in water) samples changing the particles concentrations in time.

We demonstrated FF OCM(full field optical coherence microscopy) using an ultrathin forward-imaging SMMF (short multimode fiber) probe of 50 μm core diameter, 125 μm diameter, and 7.4 mm length, which is a typical graded-index multimode fiber for optical communications. The axial resolution was measured to be 2.20 μm, which is close to the calculated axial resolution of 2.06 μm. The lateral resolution was evaluated to be 4.38 μm using a test pattern. Assuming that the FWHM of the contrast is the DOF (depth of focus), the DOF of the signal is obtained at 36 μm and that of the OCM is 66 μm. The contrast of the OCT images was 6.1 times higher than that of the signal images due to the coherence gate. After an euthanasia the rat brain was resected and cut at 2.6mm tail from Bregma. Contacting SMMF to the primary somatosensory cortex and the agranular insular cortex of ex vivo brain, OCM images of the brain were measured 100 times with 2μm step. 3D OCM images of the brain were measured, and internal structure information was obtained. The feasibility of an SMMF as an ultrathin forward-imaging probe in full-field OCM has been demonstrated.

Optical coherence tomography (OCT) is a noninvasive diagnostic method that offers a view into the superficial layers of the skin in vivo in real-time. OCT delivers morphological images of microstructures within the skin. Epidermal thickness in OCT images is of paramount importance, since dermo-epidermal junction (DEJ) location alteration is the start of several skin abnormalities. Due to the presence of speckle noise, devising an algorithm for locating DEJ in the OCT images is challenging. In this study we propose a semi-automatic DEJ detection algorithm based on graph theory that is resistant to speckle. In this novel approach we use attenuation map as a complementary feature compared to the previous methods that are mainly based on the intensity information. The method is based on converting border segmentation problem to the shortest path problem using graph theory. To smooth borders, we introduced a thinning fuzzy system enabling closer match to manual segmentation. Subsequently, an averaged A-scan analysis is performed to obtain the mean epidermal thickness. The DEJ detection method is performed on 96 B-Scan OCT skin images taken from different sites of body of healthy individuals. The results are evaluated based on several expert’s visual analysis.

The feasibility of a full-field optical coherence tomography (FFOCT) system for rapid wide field optical analysis of normal and malignant human ovarian tissue pathologies was demonstrated. Five features were extracted from the normalized image histogram from 56 FFOCT images, based on the differences in the morphology of the normal and malignant tissue samples.

Optical Coherence Tomography (OCT) offers real-time high-resolution three-dimensional images of tissue microstructures. In this study, we used OCT skin images acquired from ten volunteers, neither of whom had any skin conditions addressing the features of their anatomic location. OCT segmented images are analyzed based on their optical properties (attenuation coefficient) and textural image features e.g., contrast, correlation, homogeneity, energy, entropy, etc. Utilizing the information and referring to their clinical insight, we aim to make a comprehensive computational model for the healthy skin. The derived parameters represent the OCT microstructural morphology and might provide biological information for generating an atlas of normal skin from different anatomic sites of human skin and may allow for identification of cell microstructural changes in cancer patients. We then compared the parameters of healthy samples with those of abnormal skin and classified them using a linear Support Vector Machines (SVM) with 82% accuracy.