This PDF file contains the front matter associated with SPIE Proceedings Volume 8934, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Since the first demonstration of swept source optical coherence tomography (SS-OCT) imaging using widely tunable micro-electromechanical systems vertical cavity surface-emitting lasers (MEMS-VCSELs) in 2011, VCSEL-based SSOCT has advanced in both device and system performance. These advances include extension of MEMS-VCSEL center wavelength to both 1060nm and 1300nm, improved tuning range and tuning speed, new SS-OCT imaging modes, and demonstration of the first electrically pumped devices. Optically pumped devices have demonstrated continuous singlemode tuning range of 150nm at 1300nm and 122nm at 1060nm, representing a fractional tuning range of 11.5%, which is nearly a factor of 3 greater than the best reported MEMS-VCSEL tuning ranges prior to 2011. These tuning ranges have also been achieved with wavelength modulation rates of >500kHz, enabling >1 MHz axial scan rates. In addition, recent electrically pumped devices have exhibited 48.5nm continuous tuning range around 1060nm with 890kHz axial scan rate, representing a factor of two increase in tuning over previously reported electrically pumped MEMS-VCSELs in this wavelength range. New imaging modes enabled by optically pumped devices at 1060nm and 1300nm include full eye length imaging, pulsatile Doppler blood flow imaging, high-speed endoscopic imaging, and hand-held wide-field retinal imaging.

Tornado Spectral Systems has developed a new spectrometer called OCTANE, the Optical Coherence Tomography Advanced Nanophotonic Engine, consisting of chip-based spectrometers for spectral domain optical coherence tomography (SD-OCT) systems. These devices include planar lightwave circuits with integrated waveguides fabricated on a planar silicon substrate. Our commercial prototypes include a NIR system centered at a wavelength of 860 nm, a spectral bandwidth of 70 nm, and 2048 output channels to record TE and TM polarizations independently at an 80 kHz line scan rate. Intended to support low-cost, high-volume applications, these spectrometers are well-suited to SD-OCT for both biological and industrial non-destructive testing applications.

We have developed and demonstrated a 2-D transverse motion tracking method that provides quantitative assessment of both direction and magnitude of motion using optical coherence tomography (OCT). This motion tracking method involves scanning the OCT beam circularly and processing the obtained three-dimensional data with novel algorithms.

We present a novel swept source optical coherence tomography configuration, equipped with acousto-optic deflectors that can be used to simultaneously acquire multiple B-scans OCT images originating from different depths. The sensitivity range of the configuration is evaluated while acquiring five simultaneous B-scans. Then the configuration is employed to demonstrate long range B-scan imaging by combining two simultaneous B-scans from a mouse head sample.

We demonstrate Adaptive optics - Optical Coherence Tomography (OCT) with modal sensorless Adaptive Optics correction with the use of novel Adaptive Lens (AL) applied for in-vivo imaging of mouse retinas. The AL can generate low order aberrations: defocus, astigmatism, coma and spherical aberration that were used in an adaptive search algorithm. Accelerated processing of the OCT data with a Graphic Processing Unit (GPU) permitted real time extraction of image projection total intensity for arbitrarily selected retinal depth plane to be optimized. Wavefront sensorless control is a viable option for imaging biological structures for which AOOCT cannot establish a reliable wavefront that could be corrected by wavefront corrector. Image quality improvements offered by adaptive lens with sensorless AO-OCT was evaluated on in vitro samples followed by mouse retina data acquired in vivo.

In vascular plexuses perpendicular to the optical axis, traditional Doppler OCT (DOCT) is highly sensitive to the Doppler angle, limiting its reproducibility and accuracy in clinical practice. A more stable approach is the dual-beam bidirectional technique that probes the sample from two distinct illumination directions allowing reconstruction of the true flow velocity and later the blood flow with knowledge of the vessel diameter. However the absolute velocity calculation still requires the evaluation of the flow angle in the en face plane. Based on dual beam bidirectional DOCT we suggest calculating the flow directly from an adequately chosen Doppler cross section and demonstrate that this method is independent of the vessel angle. The principle is implemented with Swept Source OCT at 1060nm with 100,000 A-Scans/s. We confirm, with in vitro measurements of a perfused capillary and with a selected human retinal artery, that this method employing two beams only is completely independent of any vessel orientation.

We present a method capable of measuring the total retinal blood flow in arteries and veins based on dual beam Fourierdomain Doppler optical coherence tomography (OCT) in combination with a fundus camera based Dynamic Vessel Analyzer. Incorporating a Dynamic vessel analyzer into the system not only gives a live image of the fundus – it also allows determining the vessels’ diameter precisely during the OCT measurement, which is necessary for the determination of the blood flow. While dual beam systems with fixed detection plane allow only vessels with certain orientations to be measured, the detection plane of our system can be rotated by 90°. This ensures that the blood’s velocity can be measured in all vessels around the optic nerve head. The results of the total blood flow measurements are in the same range as previously published data. Additionally, the high degree of conformity between the measured venous and arterial flow corroborated the system’s validity. For larger vessels, the logarithmic values of vessel diameter and blood flow were found to be related linearly with a regression coefficient of around 3, which is in accordance with Murray’s law. For smaller vessels (diameter below 60 μm), the values diverge from the linear dependence. The high sensitivity and the good agreement with published data suggest a high potential for examining the retinal blood flow in patients with ocular diseases.

Optical coherence tomography (OCT) provides high spatial resolution and sensitivity that are ideal for imaging the cornea and lens. Quantifying the biomechanical properties of these tissues could add clinically valuable information. Thus, we propose a dynamic elastography method combining OCT detection and a mechanical actuator to map the shear modulus of soft tissues. We used a piezoelectric actuator driven in the kHz range and we used phase-sensitive OCT (PhS-OCT) to track the resulting shear waves at an equivalent frame rate of 47 kHz. We mapped the shear wave speed of anesthetized mice cornea using monochromatic excitations. We found a significant difference between a group of knock-out (3.92 ± 0.35 m/s, N=4) and wild-type mice (5.04 ± 0.51 m/s, N=3). These preliminary results demonstrate the feasibility of using PhS-OCT to perform in vivo shear wave elastography of the cornea. We then implemented a shear pulse compression approach on ex vivo human cornea. For that purpose, frequency- modulated excitations were used and the resulting displacement field was digitally compressed in a short broadband pulse with a 7 dB gain in signal-to-noise ratio (SNR).

There are several applications of quantitative micro-displacement measurement of a biological specimen, including characterization of mechanical property and monitoring a laser-induced photothermal expansion. In this study, we proposed a quantitative micro-displacement measurement method using optical coherence tomography (OCT). Specifically, the axial displacement is measured by Doppler OCT and magnitude of displacement is measured by correlation coefficient. By using this method, we measured the local and microdisplacement of the chicken muscles during laser irradiation. The proposed method successfully visualizes thermal changes of chicken muscle due to the laser irradiation. The measured displacement and deformation are useful information for the further understanding of the thermal changes.

Noninvasively probing the biomechanical properties of crystalline lens has been challenging due to its unique features such as location inside the eye and being optically and ultrasonically transparent. Here we introduce a method of relying on the spectral analysis of the lens surface response to a mechanical stimulation for the depthdependent assessment of lens biomechanical properties. In this method, acoustic radiation force (ARF) is used to remotely induce the deformation on the surface of the crystalline lens, and a phase-sensitive optical coherence tomography (PhS-OCT) system, co-focused with ARF, utilized to monitor the localized temporal response of ARFinduced deformations on the lens surface. The dominant frequency from the amplitude spectra of the surface response is obtained as the indicator of the depthwise elasticity distribution. Pilot experiments were performed on tissue-mimicking layered phantoms and ex vivo porcine crystalline lens. Results indicate that the frequency response of the sample surface is contributed by the mechanical properties of layers located at different depths and the depthdependent elastic properties can be revealed from the amplitude spectrum. Further study will be focused on combining the experimental measurements with theoretical model and inverse numerical method for depth-resolved elastography of the crystalline lens.

Nowadays optical coherence tomography (OCT) is a rapidly developing technique with various applications, including biomedical imaging and diagnosis. One of the main shortcomings of current OCT techniques is low resolution and sensitivity to structural changes (typically about 10 microns). The best ultra-high resolution OCT techniques demonstrate sensitivity to structural changes and depth resolution of about 1 micron. Since many applications of interest (such as cancer) depend on structural changes at the nanoscale, OCT would definitely benefit from improved structural resolution and sensitivity. A new spectral encoding of spatial frequency (SESF) approach for quantitative characterization of the structure with nanoscale sensitivity has been developed recently. Ability to map axial structural information into each pixel of a 2D image with nanoscale sensitivity has been demonstrated and application of this approach to 3D microscopic imaging has been discussed. Here we present a novel technique, nano-sensitive OCT (nsOCT), to dramatically increase sensitivity of the OCT to structural changes. We propose to directly translate information about particular structure from Fourier domain to the image domain and map this information into the corresponding location within the 3D OCT image. As a result, submicron axial structure can be visualized and nanoscale structural alterations for each volume of interest within the 3D OCT image can be detected. Preliminary results show that using nsSOCT, based on conventional spectral domain OCT system with resolution 30 x 30 x 12 μm, it is possible to detect structural changes within scattering sample as small as 30 nm.

We report the use of conventional Optical Coherence Tomography (OCT) for visualization of propagation of low frequency electric field in soft biological tissues ex vivo. To increase the overall quality of the experimental images an adaptive Wiener filtering technique has been employed. Fourier domain correlation has been subsequently applied to enhance spatial resolution of images of biological tissues influenced by low frequency electric field. Image processing has been performed on Graphics Processing Units (GPUs) utilizing Compute Unified Device Architecture (CUDA) framework in the frequencydomain. The results show that variation in voltage and frequency of the applied electric field relates exponentially to the magnitude of its influence on biological tissue. The magnitude of influence is about twice more for fresh tissue samples in comparison to non-fresh ones. The obtained results suggest that OCT can be used for observation and quantitative evaluation of the electro-kinetic changes in biological tissues under different physiological conditions, functional electrical stimulation, and potentially can be used non-invasively for food quality control.

We have proposed and developed a multi-modal non-invasive biomedical optical imager. It was combined from the subsystems of optical microangiography and dual-wavelength laser speckle contrast imaging. The system was designed to maintain the performances of both subsystems. It was capable of simultaneously imaging the hemodynamic and metabolic responses in tissue environment in vivo. To achieve such requirements, we utilized unique optical setup, such as paired dichroic mirrors to compensate dispersion, additional relay lens to increase working distance and translational sample probe to freely select imaging area and focal plane. The multi-functionality of the system was demonstrated in an investigation of hemodynamic and metabolic responses on an acute wound healing model in mouse pinna in vivo. The microvasculature, blood flow and hemoglobin concentration from millimeter down to capillary level were comprehensively visualized. The captured instantaneous responses to wound onset differed greatly between localized areas; after that blood flow had a rebalance tendency, and hemoglobin concentration dynamically recovered to baseline situation.

In this paper, we propose a method to quantify red blood cell (RBC) flow through capillary loops and microvessels using optical microangiography (OMAG). Current existing methods of capillary flow quantification either require a very long scanning time (~few minutes) or a large acquisition number per location (+100 scans per location) to form a highresolution spectral estimation. We utilize a model-based super-resolution spectral estimation technique based on principle of orthogonality to quantify moving RBCs within a voxel. The scanning protocol required for our method is very similar to 3D ultrahigh sensitive OMAG that requires few scans per location (8) and can be performed in few seconds that makes it applicable for in vivo experiments. This method is analogous to power Doppler in ultrasonography and estimates the number of red blood cells passing through the beam as opposed to the velocity of the particles. The technique is tested both qualitatively and quantitatively by using OMAG to image microcirculation within mouse ear flap in vivo.

A new imaging technique is presented by introducing the concept of conical scan to the variable-incidenc-angle polarimetry (VIA) previously developed by our group. The technique would facilitate the translating of the VIA technique to the clinic by simplifying the requirements of measurements in two orthogonal planes by using a conical scan protocol. Conical scan PS-OCT images could illustrate directly the azimuthal angle of the collage fibers in birefringent tissue, which was validated by measurements on a bovine tendon. We have showed the unique technique can be used to locate the “brushing direction” of collagen fibers in articular cartilage. Measuring this direction over the cartilage surface could potentially help designing of tissue-engineering scaffolds for cartilage repair.

High-resolution tomography is of great importance to many areas of biomedical imaging, but with it comes several apparent tradeoffs such as a narrowing depth-of-field and increasing optical aberrations. Overcoming these challenges has attracted many hardware and computational solutions. Hardware solutions, though, can become bulky or expensive and computational approaches can require high computing power or large processing times. This study demonstrates memory efficient implementations of interferometric synthetic aperture microscopy (ISAM) and computational adaptive optics (CAO) – two computational approaches for overcoming the depthof- field limitation and the effect of optical aberrations in optical coherence tomography (OCT). Traditionally requiring lengthy post processing, here we report implementations of ISAM and CAO on a single GPU for real-time in vivo imaging. Real-time, camera-limited ISAM processing enabled reliable acquisition of stable data for in vivo imaging, and CAO processing on the same GPU is shown to quickly correct static aberrations. These algorithmic advances hold the promise for high-resolution volumetric imaging in time-sensitive situations as well as enabling aberrationfree cellular-level volumetric tomography.

Peripheral arterial disease (PAD) is an atherosclerotic disease of the extremities that leads to high rates of myocardial infarction and stroke, increased mortality, and reduced quality of life. PAD is especially prevalent in diabetic patients, and is commonly modeled by hind limb ischemia in mice to study collateral vessel development and test novel therapies. Current techniques used to assess recovery cannot obtain quantitative, physiological data non-invasively. Here, we have applied hyperspectral imaging and swept source optical coherence tomography (OCT) to study longitudinal changes in blood oxygenation and vascular morphology, respectively, intravitally in the diabetic mouse hind limb ischemia model. Additionally, recommended ranges for controlling physiological variability in blood oxygenation with respect to respiration rate and body core temperature were determined from a control animal experiment. In the longitudinal study with diabetic mice, hyperspectral imaging data revealed the dynamics of blood oxygenation recovery distally in the ischemic footpad. In diabetic mice, there is an early increase in oxygenation that is not sustained in the long term. Quantitative analysis of vascular morphology obtained from Hessian-filtered speckle variance OCT volumes revealed temporal dynamics in vascular density, total vessel length, and vessel diameter distribution in the adductor muscle of the ischemic limb. The combination of hyperspectral imaging and speckle variance OCT enabled acquisition of novel functional and morphological endpoints from individual animals, and provides a more robust platform for future preclinical evaluations of novel therapies for PAD.

Optical coherence tomography is an imaging modality that is broadly used in ophthalmic diagnostics. The current generation of OCT systems enables reliable acquisition of volumetric scans containing information about the thicknesses of the various retinal layers. Thus, monitoring layer thickness changes is the main quantitative analysis performed by commercial instruments. In principle, measurements of the OCT signal intensity could also provide information on the health status of the retinal tissue. Unfortunately quantitative measurements and interpretation of scattering changes in retinal OCT is very limited due to variation in overall brightness of the OCT B-scans between imaging sessions. These changes might be caused by variation in alignment or focusing, as well as variation in the quality of the eye’s optics (changes in the tear film, dilation of pupil etc.). Therefore, quantitative analysis of layer intensity requires careful normalization to minimize the effects of such variables. In this manuscript we demonstrate that changes in OCT signal intensity occur in a mouse model of light-induced photoreceptor degeneration. Normalization and quantification of light scattering changes in human patients could likewise lead to improved understanding of clinical OCT data.

Vascular and microvascular anastomosis are critical components of reconstructive microsurgery, vascular surgery and transplant surgery. Imaging modality that provides immediate, real-time in-depth view and 3D structure and flow information of the surgical site can be a great valuable tool for the surgeon to evaluate surgical outcome following both conventional and innovative anastomosis techniques, thus potentially increase the surgical success rate. Microvascular anastomosis for vessels with outer diameter smaller than 1.0 mm is extremely challenging and effective evaluation of the outcome is very difficult if not impossible using computed tomography (CT) angiograms, magnetic resonance (MR) angiograms and ultrasound Doppler. Optical coherence tomography (OCT) is a non-invasive high-resolution (micron level), high-speed, 3D imaging modality that has been adopted widely in biomedical and clinical applications. Phaseresolved Doppler OCT that explores the phase information of OCT signals has been shown to be capable of characterizing dynamic blood flow clinically. In this work, we explore the capability of Fourier domain Doppler OCT as an evaluation tool to detect commonly encountered post-operative complications that will cause surgical failure and to confirm positive result with surgeon’s observation. Both suture and cuff based techniques were evaluated on the femoral artery and vein in the rodent model.

We have developed a novel integrated optical coherence tomography (OCT)-intravascular ultrasound (IVUS) probe, with a 1.5 mm-long rigid-part and 0.9 mm outer diameter, for real-time intracoronary imaging of atherosclerotic plaques and guiding interventional procedures. By placing the OCT ball lens and IVUS 45MHz single element transducer back-to-back at the same axial position, this probe can provide automatically co-registered, co-axial OCT-IVUS imaging. To demonstrate its capability, 3D OCT-IVUS imaging of a pig’s coronary artery in real-time displayed in polar coordinates, as well as images of two major types of advanced plaques in human cadaver coronary segments, was obtained using this probe and our upgraded system. Histology validation is also presented.

Eric Swanson discusses the migration of optical coherence tomography (OCT) into clinical practice in, "Clinical Translation in OCT: Role of Research, Funding, and Entrepreneurism." The translation from research to successful clinical impact is challenging and often the process passes through several stages including product development, initial sales and product iteration, market growth, and, finally, the next generation products. Each step can take several years, requiring persistence and perseverance on the parts of technologists and investors alike. The first release of a reliable, manufacturable, and supportable commercial product into the hands of clinicians is a critical milestone. It allows for fine tuning of the product attributes on the road to proving clinical utility and sometimes results in discovery of unforeseen applications. Clinical translation of OCT has been impactful, scientifically, clinically, and economically. Over 20M patients per year undergo OCT diagnostic imaging and the cumulative OCT system sales over the past decade are well in excess of $1B. Many applications remain to be commercialized could potentially further benefit healthcare and improve quality of life. Startups have played, and continue to play, an important role in the translation of new applications of OCT.

SPIE member David Boas (Massachusetts General Hospital) discusses techniques for understanding oxygen delivery through the vascular network, in "Optical Spectroscopy and Tomography of Oxygen Delivery: From Macro to Micro and Back." The use of microscopy coupled with modeling techniques to study the heterogeneous and complex oxygen delivery network and blood flow pattern in the vascular network is detailed.

In regenerative medicine, the zebrafish is a prominent animal model for studying degeneration and regeneration processes, e.g. of photoreceptor cells in the retina. By means of optical coherence tomography (OCT), these studies can be conducted over weeks using the same individual and hence reducing the variability of the results. To allow an improvement of zebrafish retinal OCT imaging by suitable optics, we developed a zebrafish eye model using geometrical data obtained by in vivo dispersion encoded full range OCT as well as a dispersion comprising gradient index (GRIN) lens model based on refractive index data found in the literature. Using non-sequential ray tracing, the focal length of the spherical GRIN lens (diameter of 0.96 mm) was determined to be 1.22 mm at 800 nm wavelength giving a Matheissen’s ratio (ratio of focal length to radius of the lens) of 2.54, which fits well into the range between 2.19 and 2.82, found for various fish lenses. Additionally, a mean refractive index of 1.64 at 800 nm could be retrieved for the lens to yield the same focal position as found for the GRIN condition. With the aid of the zebrafish eye model, the optics of the OCT scanner head were adjusted to provide high-resolution retinal images with a field of view of 30° x 30°. The introduced model therefore provides the basis for improved retinal imaging with OCT and can be further used to study the image formation within the zebrafish eye.

A recent trend in optical coherence tomography (OCT) hardware has been the move towards higher A-scan rates. However, the estimation of axial blood flow velocities is affected by the presence and type of noise, as well as the estimation method. Higher acquisition rates alone do not enable the accurate quantification of axial blood velocity. Moreover, decorrelation is an unavoidable feature of OCT signals when there is motion relative to the OCT beam. For in-vivo OCT measurements of blood flow, decorrelation noise affects Doppler frequency estimation by broadening the signal spectrum. Here we derive a maximum likelihood estimator (MLE) for Doppler frequency estimation that takes into account spectral broadening due to decorrelation. We compare this estimator with existing techniques. Both theory and experiment show that this estimator is effective, and outperforms the Kasai and additive white Gaussian noise (AWGN) ML estimators. We find that maximum likelihood estimation can be useful for estimating Doppler shifts for slow axial flow and near transverse flow. Due to the inherent linear relationship between decorrelation and Doppler shift of scatterers moving relative to an OCT beam, decorrelation itself may be a measure of flow speed.

Optical coherence tomography (OCT) has proved to be an effective tool to study the development of mammalian embryos due to its high resolution and contrast. However, light attenuation is an important factor which constrains the imaging depth of OCT. Limitation of imaging depth will inhibit us to better study the structural characteristics of mouse embryos. Here we propose a new method, rotational imaging OCT (riOCT), to improve the imaging depth and provide full-body embryonic imaging. The experimental setup comprises the swept source OCT system and the square glass tube mounted on a rotational stage. The E10.5 mouse embryos are dissected and immersed in the glass tube using 0.9% saline solution. 3D structural imaging is performed at four different angles with the interval of 90 degrees. The OCT image records the optical distances of different components such as glass, gelatin and tissue. The position of rotation center is determined by the track of the glass tube center at different angles. The final image is acquired by rotating the images at different angles according to the rotation center. Results indicate that this method is able to improve the visualization of structural information of mouse embryo compared to conventional OCT.

Cross-correlation of Intravascular Optical Coherence Tomography (IV-OCT) images is affected by image distortion due to the non-uniform rotational velocity of the imaging catheter. It results in non-representative cross-correlation maps such that for a static scan, the coefficients fluctuate from high to low correlation values. The variation in cross-correlation at flow locations is muted, in comparison to stationary regions. In the present study, the variation of correlation values and its standard deviation (SD) is used to suppress the distortion related noise effects and to extract flow maps from static scan images. The standard deviation of the cross-correlation variation can distinguish flow locations from the surrounding tissue region. The advantage of this technique is its ability to identify slow flow, even Brownian flow, in the presence of motion artifacts. The SD mask used for generating flow maps, is optimized using tissue mimicking phantoms. Finally, the ability of this technique to suppress noise and capture flow maps is demonstrated by imaging microflow through excised porcine coronary artery wall and mucosa membrane imaging.

A MEMS-based common-path endoscopic imaging probe for 3D swept-source optical coherence tomography (SSOCT) has been developed. The common path is achieved by setting the reference plane at the rear surface of the GRIN lens inside the probe. MEMS devices have the advantages of low cost, small size and fast speed, which are suitable for miniaturizing endoscopic probes. The aperture size of the two-axis MEMS mirror employed in this endoscopic probe is 1 mm by 1 mm and the footprint of the MEMS chip is 1.55 mm by 1.7 mm. The MEMS mirror achieves large two dimensional optical scan angles up to 34° at 4.0 V. The endoscopic probe using the MEMS mirror as the scan engine is only 4.0 mm in diameter. Additionally, an optimum length of the GRIN lens is established to remove the artifacts in the SSOCT images generated from the multiple interfaces inside the endoscopic imaging probe. The MEMS based commonpath probe demonstrates real time 3D OCT images of human finger with 10.6 μm axial resolution, 17.5 μm lateral resolution and 1.0 mm depth range at a frame rate of 50 frames per second.

Recently, full-range optical coherence tomography (OCT) systems have been developed to image the human airway. These novel systems utilize a fiber-based OCT probe which acquires three-dimensional (3-D) images with micrometer resolution. Following an airway injury, mucosal edema is the first step in the body’s inflammatory response, which occasionally leads to airway stenosis, a life-threatening condition for critically ill newborns. Therefore, early detection of edema is vital for airway management and prevention of stenosis. In order to examine the potential of the full-range OCT to diagnose edema, we investigated temporal correlation of OCT images obtained from the subglottic airway of live rabbits. Temporally correlated OCT images were acquired at fixed locations in the rabbit subglottis of either artificially induced edema or normal tissues. Edematous tissue was experimentally modeled by injecting saline beneath the epithelial layer of the subglottic mucosa. The calculated cross temporal correlations between OCT images of normal airway regions show periodicity that correlates with the respiratory motion of the airway. However, the temporal correlation functions calculated from OCT images of the edematous regions show randomness without the periodic characteristic. These in-vivo experimental results of temporal correlations between OCT images show the potential of a computer-based or -aided diagnosis of edema in the human respiratory mucosa with a full-range OCT system.

Excessive nonspecific binding often occurs when labeling cells with immuno-labeled gold nanoparticles (IgG-AuNPs). We have investigated the physical properties of IgG-AuNPs assembled with three different protocols in an attempt to understand and eliminate this non-specific binding. One of these protocols involves conjugating the secondary antibody AP124F via van der Waals (vdW) and/or electrostatic forces to the AuNPs, and the other two employ a PEG-linker, OPSS-PEG-NHS (OPN). In all three protocols we follow with PEG-SH to provide protection against aggregation in saline solution. OPN and PEG-SH chains of varying molecular weights were examined in different combinations to determine the optimally protective layer. The hydrodynamic radius and surface plasmon resonance (SPR) were monitored at each stage of assembly using a dynamic light scattering (DLS) instrument and spectrophotometer, respectively. SPR measurements indicate a different physical structure near the gold surface when the PEG-linker is bound to gold first and then bound to the antibody second (AP124F-[OPN-Au]) rather than vice versa ([AP124F-OPN]- Au). These observed structural differences may lead to differences in the amount of non-specific binding observed when immuno-labeling cells. SPR measurements also yielded a half-life of 27 minutes for the binding of the PEG-linker to the surface of the AuNPs and a half-life of 133 minutes for the hydrolysis of the NHS functional groups on the OPN molecule. These different reaction rates led us to add AP124F 40 minutes after the linker began binding to the AuNPs, so that the antibody can bind covalently to the correct end of the OPN linker.

Frequency domain optical coherence tomography (FD-OCT) achieves high image acquisition speeds by probing all depths of a sample simultaneously. However, the tightly focused beam required for frequency domain optical coherence microscopy (FD-OCM) produces images with poor lateral resolution at depths away from the beam waist. The new technique of interferometric synthetic aperture microscopy (ISAM) can digitally focus these poorly resolved FD-OCM images, resulting in uniform lateral resolution throughout the sample volume equivalent to that in the plane of focus of the incident beam. While ISAM is computationally intensive, we demonstrate that an ISAM implementation using Nvidia’s parallel Compute Unified Device Architecture (CUDA) can achieve real-time focusing using a mid-range Nvidia GPU. The time required for digital focusing scales linearly with image size, at a rate of about 10 nanoseconds per voxel. This makes possible real-time FD-OCM. For example, a 3-D image (512 x 512 x 128 voxels) with crosssection 1.2 mm x 1.2 mm and 200 micron depth requires 17 seconds to acquire with a 100 kHz A-scan rate (and 6 repeated x-scans for motion sensitivity), but only 360 milliseconds to focus with ISAM. This example image is simulated with a numerical aperture (NA) of 0.07, so that the 200 micron depth represents four Rayleigh ranges (± 2 Rayleigh ranges from the focal plane). In addition, our simulations indicate that ISAM performs well with very noisy input data. Even with noise levels as high as 50%, ISAM produces focused images with signal-to-noise ratios of over 100. ISAM-focusing is both fast and robust.

Vernier-tuned distributed Bragg reector (VT-DBR) lasers in source swept OCT (SS-OCT) have previously been demonstrated at 1550 nm and 1600 nm.¹ Many OCT applications prefer 1310 nm operation. This work describes the first demonstration of a VT-DBR operating at 1310 nm in the O-band, ideal for use in SS-OCT. This paper addresses the device characterization of such lasers, illustrating they are capable of fast amplitude and frequency sweeps necessary for SS-OCT applications. Equivalent circuit models for each of the five ports are also created to determine their electrical parasitics. Narrow linewidths of the VT-DBR indicate coherence length of several centimeters are possible during fast wavelength sweeps.

We have developed a wavelength-swept laser source with ultrahigh phase stability. Potassium tantalate niobate (KTa_{1- x}Nb_xO₃, KTN) single crystal was employed as an electro-optic deflector for a high-speed wavelength sweep in the laser cavity. A 200-kHz sweep rate was obtained with an average output power of 20 mW and a coherence length of 8 mm at the wavelength range exceeding 100 nm. Since the electro-optic effect in KTN crystal has a fast response of more than 500 MHz, the deflection of a KTN deflector can follow the applied voltage precisely. Considering this advantage, we demonstrated a swept source with ultrahigh phase stability in the 1.3 μm wavelength range as a result of the low-jitter operation of the deflector. The standard deviation of measured timing jitters between adjacent A-lines was confirmed to be less than 78 ps, which corresponds to a phase difference of 0.017 radians at a path difference of 1.5 mm of a Michelson interferometer. The phase stability can be increased with an improved voltage source because the timing jitter is still mainly caused by the voltage applied to KTN. In addition to realizing the phase stability of neighboring A-lines, the long-term stable sweep was demonstrated by eliminating the refresh operation that was previously needed to prevent output power decay. The ultrahigh phase stability we achieved makes our swept source promising for Doppler OCT and polarization-sensitive OCT.

In this study, we polished the tip of single mode fiber to an angle that optimizes the reference power of a common-path optical coherence tomography (CP OCT) system. OCT images obtained with optimized reference show significantly improved signal to noise ratio.

A method of OCT imaging with a resolution throughout the investigated volume equal to the resolution in the best-focused region is described. It is based on summation of three-dimensional scattered field distributions at the wavelengths determined by OCT source spectral decomposition. A method of finding parameters needed for algorithmic realization of the summation is also proposed. The proposed approaches are tested on several model media, including biological ones. As the proposed algorithm is phase sensitive, and phase stability is crucial, phase equalization preprocessing which allows compensating the phase error caused by object motion during scanning was proposed.

Optical coherence tomography has been proven in the last two decades its clinical value by providing 3D non-invasive in vivo biopsy of the biological samples. In addition to structural information given by the backscattered intensity, the optical absorption will also provide another powerful contrast. Optical absorbers in biological tissues exhibits important role such as hemoglobin and melanin. However, current methods of absorption contrast take long time and not suitable for in vivo imaging. Toward in vivo absorption contrast imaging, we developed photothermal OCT system by combining swept-source OCT system and excitation laser. A swept-source OCT system is used with a wavelength swept laser at 1310 nm with a scanning rate and range of 47 kHz and of 100 nm, respectively. Photocurrents from balanced photoreceivers are sampled by a high-speed digitizer by using k-clock from the source to sample optical spectrum in k-linear domain. The sensitivity of 107 dB for two polarization channels is achieved. At the sample arm, the OCT probe beam and an excitation laser are combined by a dielectric mirror. The fiber-coupled laser diode of 406 nm wavelength is used for excitation since the absorption of hemoglobin has peak around this wavelength. In order to evaluate the ability of this system, phase stability of the system was measured. The standard deviation of the phase shift is measured as 0.0028 radians, where the signal-to-noise-limited value is approximately 0.001. Several issues for in vivo case, motion, blood flow, thermal damage, and etc. will be addressed here.

A seven-zone pupil filter which can extend the depth of focus (DOF) and provide lateral super resolution in Optical Coherence Tomography is designed. Both amplitude and phase of the transmitted light beam are modified in each zone. The scalar diffraction theory is used to optimize the zone parameters. A broadband source spectrum and a Gaussian beam profile has been taken into account for the design of this filter. Several filters have been reported to extend the depth of focus (DOF) and improve the resolution but they take the assumption that a monochromatic and uniform light beam is used. With the proposed filter the DOF in OCT can be extended by 14 times while the lateral resolution can be improved by a factor of 1.47 and maintained constant within this DOF.

Optical vibrometery based on low coherence Fourier-domain optical coherence tomography (FD-OCT) technique are well capable for providing depth resolved vibration information in comparison with conventional laser based vibrometery. Recently, there has been growing interest in developing coherence-domain vibrometry for various clinical and pre-clinical applications. However, a major drawback of the conventional vibrometer based on Fourier-domain low coherence interferometry is the complex-conjugate ambiguity. This is because in FD-OCT, the detected real valued spectral interferogram is Fourier transformed to localize the scatter within the sample. The Fourier transform of a real valued function is Hermitian, so the reconstructed image is symmetric with respect to the zero-phase delay of the interferometer, leading to ambiguity in interpretation of the resulted OCT images. In this paper, we introduce a full range optical coherence vibrometry to utilize the whole imaging range of the spectrometer. The mirror image elimination is based on the linear phase modulation of the interferometer’s reference arm mirror and with an algorithm that exploits Hilbert transform to obtain full range complex imaging.

In this study, we present a new algorithm based on an artificial neural network (ANN) for reducing speckle noise from optical coherence tomography (OCT) images. The noise is modeled for different parts of the image using Rayleigh distribution with a noise parameter, sigma, estimated by the ANN. This is then used along with a numerical method to solve the inverse Rayleigh function to reduce the noise in the image. The algorithm is tested successfully on OCT images of retina, demonstrating a significant increase in the signal-to-noise ratio (SNR) and the contrast of the processed images.

We present the use of a prism as an imaging adjunct with a multimodal system of optical coherence tomography and confocal microscopy operating at 1320 nm and 970 nm respectively. A comparison is performed between en-face OCT images acquired using the system and cross section OCT images obtained through a prism inserted into neuronal tissue of an intact ex-vivo murine brain. The en-face images and cross section images are scans of the same area; however each method has shown different aspects, allowing for greater interpretation of the neuronal tissue.

Optical Coherence Tomography (OCT) images exhibit the effects of speckle which can make image interpretation and quantitative measurements difficult. Many approaches have been developed to reduce this speckle including both hardware implementations and post-processing techniques. However, they either suffer from a loss in resolution and blurring of the image or an increase in complexity and reduction in speed of the system. Wavelet decomposition has been shown to effectively separate the resolvable features of an image from the speckle pattern. The two components can then be processed separately. The speckle pattern can be filtered and then recombined with the resolvable component to create an image with improved signal-to-noise-ratio (SNR) and intact image details. The results of this algorithm are demonstrated on in vivo OCT images of skin taken with a swept-source based system. Such a technique, when applied, for example, to OCT images of disease, can be extremely useful in improving the clinical interpretation of the images as well as allowing more accurate quantitative measurements not affected by the presence of speckle.

In this paper we demonstrate that fast spectral domain optical coherence tomography imaging systems have the potential to monitor the evolution of pathological dental wear. On 10 caries free teeth, four levels of artificially defects similar to those observed in the clinic were created. After every level of induced defect, OCT scanning was performed. B-scans were acquired and 3D reconstructions were generated.

We demonstrate dynamic analysis of mental sweating of a few tens of eccrine sweat glands on a human fingertip by optical coherence tomography. We propose a novel method for evaluation of the amount of excess sweat in response to mental stress, where the en-face OCT images of the spiral lumen of the eccrine sweat gland are constructed by data acquisition of the 128 B-mode OCT images. The dynamic analysis of mental sweating is performed by the time-sequential piled-up en-face OCT images with the frame spacing of 3.3 sec. It is found that the amount of sweat in eccrine sweat glands is significantly increased in proportion to the strength of the sound stimulus.

Spectral-domain optical coherence tomography (SD-OCT) is a non-contact and non-invasive method for measuring the change of biological tissues caused by pathological changes of body. CCD with huge number of pixels is usually used in SD-OCT to increase the detecting depth, thus enhancing the hardness of data transmission and storage. The usage of compressed sensing (CS) in SD-OCT is able to reduce the trouble of large data transfer and storage, thus eliminating the complexity of processing system. The traditional CS uses the same sampling model for SD-OCT images of different tissue, leading to reconstruction images with different quality. We proposed a CS with adaptive sampling model. The new model is based on uniform sampling model, and the interference spectral of SD-OCT is considered to adjust the local sampling ratio. Compared with traditional CS, adaptive CS can modify the sampling model for images of different tissue according to different interference spectral, getting reconstruction images with high quality without changing sampling model.

An efficient technique of correction of coherence gate curvature in spectral-domain OCT is proposed. A method of constructing of different shapes of single spectral component envelop is described. The control of the single spectral component envelop allows to eliminate over-depth artifacts caused by preserved partial coherence in the optical delays longer then coherence length.

A temporal filtering method based on an infinite-impulse-response filter is presented to reduce speckle in optical coherence tomography (OCT) images. This method works in a recursive way, linearly combining the current B-scan image frame with a previously filtered one to generate a newly filtered image. Thus, it performs with less computational complexity and time, compared to the finite-impulse-response filter based approach that typically averages multiple stored frames. To achieve speckle noise reduction while avoiding image blurring caused by sample motion, the filter coefficient is dynamically determined, depending on the parameters related to motion detection and image quality. We used the mean-squared error (MSE) between two successive frames as a criterion to detect sample motion and changed the filter coefficient when the MSE exceeded a certain threshold to prevent image blurring. The optimal coefficient and motion detection threshold were chosen for achieving robust and unblurred images in our testbed configuration. In this study, we analyzed the algorithm with OCT images acquired by a swept-source OCT system we built and also examined that the method operated in real-time even via CPU processing. Results in our and conventional schemes are compared by using various image quality metrics and by observing images. We found that the performance of speckle reduction was quite promising and simultaneously the fine details of sample structures were preserved even with sample motion.

Conventional Optical Coherence Tomography (OCT) probes usually require complex optics at their tips for focusing the incident light on the measured samples and for scattered light collection. Such complexity is not compatible with the common-path OCT architecture, in which the reference arm is replaced by partial reflection from the probe fiber-air interface. This necessitates close proximity between the measured sample and the fiber tip to have sufficient measurement depth inside the sample within the coherence length of the light. Indeed, separating the light injection and collection paths simplifies the design of the OCT heads and allows the easy integration of a MEMS scanner within the head. In this work, we propose a new OCT probe configuration that allows for such separation. To this end, a swept source OCT setup was built using a tunable laser connected to the single-mode fiber of the probe and the scattered light from the measured sample was collected using another Multi-Mode Fiber (MMF). The usage of the MMF in the reception enables higher power-collection efficiency and transfers the reference position to be at the first layer of the sample under test, which further extends the maximum depth analyzed by the OCT system and overcomes the restriction of the close proximity mentioned above. This simple concept is validated by experimental measurements carried out on 1 mm-thick sheets of glasses with and without an integrated MEMS scanner on-chip.

We report a study on design consideration and performance analysis of OCT-based topography by tracking of maximum intensity at each layer’s interface. We demonstrate that, for a given stabilized OCT system, a high precision and accuracy of OCT-based layers and thickness topography in the order of tens nanometer can be achieved by using a technique of maximum amplitude tracking. The submicron precision was obtained by over sampling through the FFT of the acquired spectral fringes but was eventually limited by the system stability. Furthermore, we report characterization of a precision, repeatability, and accuracy of the surfaces, sub-surfaces, and thickness topography using our optimized FD-OCT system. We verified that for a given stability of our OCT system, precision of the detected position of signal’s peak of down to 20 nm was obtained. In addition, we quantified the degradation of the precision caused by sensitivity fall-off over depth of FD-OCT. The measured precision is about 20 nm at about 0.1 mm depth, and degrades to about 80 nm at 1 mm depth, a position of about 10 dB sensitivity fall-off. The measured repeatability of thickness measurements over depth was approximately 0.04 micron. Finally, the accuracy of the system was verified by comparing with a digital micrometer gauging.

Photodynamic therapy (PDT) promotes skin improvement according to many practitioners, however the immediately in vivo assessment of its response remains clinically inaccessible. As a non-invasive modality, optical coherence tomography (OCT) has been shown a feasible optical diagnostic technique that provides images in real time, avoiding tissue biopsies. For this reason, our investigation focused on evaluates the PDT effect on a rodent model by means of OCT. Therefore, a normal hairless mouse skin has undergone a single-session PDT, which was performed with topical 5- aminolevulinic acid (ALA) cream using a red (630 nm) light emitting diode (LED) which reached the light dose of 75 J/cm². As the optical imaging tool, an OCT (930 nm) with axial resolution of 6.0 microns in air was used, generating images with contact to the mouse skin before, immediately after, 24 hours, and 2 weeks after the correspondent procedure. Our result demonstrates that, within 24 hours after ALA-PDT, the mouse skin from the PDT group has shown epidermal thickness (ET), which has substantially increased after 2 weeks from the treatment day. Moreover, the skin surface has become evener after ALA-PDT. Concluding, this investigation demonstrates that the OCT is a feasible and reliable technique that allows real-time cross-sectional imaging of skin, which can quantify an outcome and predict whether the PDT reaches its goal.