This PDF file contains the front matter associated with SPIE Proceedings Volume 7168, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

A computational model for an "ideal" light source for in-vivo UHROCT imaging of human and animal retina is presented. The model considers parameters such as the wavelength dependent absorption of water, the length of the human or animal eye, the power limitations for the imaging beam as defined in the ANSI standard, etc., to determinethe broadest possible spectral bandwidth that can result in the best axial OCT resolution in the 1060nm wavelength region. A custom light source with a re-shaped spectrum was used to verify experimentally the results from the computational model. 4.3µm axial OCT resolution was achieved experimentally in free space, corresponding to 3µm resolution in retinal tissue. A custom imaging probe was developed and optimized with ZEMAX to result in 5 µm transverse resolution in the rat retina. 2D and 3D OCT tomograms acquired in-vivo from rat retinas show visualization of tiny capillaries imbedded in the inner and outer plexiform layers of the rat retinas.

Blood flow imaging of deep posterior eye has been demonstrated by using 1-μm spectral-domain optical coherence tomography. The high contrast imaging of deep posterior eye, such as the choroid and the sclera, enables blood flow imaging of choroidal vessels and short posterior ciliary arteries. Optical coherence angiography (OCA) images of outer part from the retinal pigment epithelium (RPE) reveal the vasculature of the choroid and the particular vasculature of short posterior ciliary arteries so-called the circle of Zinn-Haller. To the best of our knowledge, this is the first demonstration for flow imaging the circle of Zinn-Haller with optical coherence tomography.

Advances in Doppler spectral domain optical coherence tomography (SDOCT) have demonstrated several image acquisition schemes that enable real-time, high-resolution, volumetric display of blood flow maps. Current generation Doppler SDOCT systems use phase differences between sequential A-scans acquired at a single spatial position to calculate the velocity of moving scatterers. Recently, several methods for optical angiography have been developed which resolve moving scatterers by imposing a spatial frequency modulation across a lateral scan dimension. The carrier frequency is generated by adding a reference phase delay using a moving reference arm or an off-pivot scanning beam. The resulting data is spatial frequency windowed such that all moving scatterers (flow) modulating the carrier frequency can be separated from non-moving scatterers (structure). However, spatial frequency modulation requires precise synchronization of the reference arm delay with B-scan acquisition and multiple B-scans are required to image bidirectional flow into and out-of the A-scan axis. Here we demonstrate single-pass volumetric bidirectional blood flow imaging (SPFI) SDOCT using a modified Hilbert transform without the use of spatial frequency modulation. By windowing low-spatial frequency scatterers across a B-scan, bidirectionally moving scatterers centered at Doppler frequencies outside of the frequency window are resolved. Additionally, 3D velocimetry maps can be constructed by setting the spatial frequency window to a corresponding velocity range and shifting it across all spatial frequencies to image scatterers moving within a particular velocity range. We show that SPFI SDOCT allows for 3D imaging of in vivo human retinal microvasculature down to 20μm, thus providing information about vessel morphology and dynamics.

Doppler OCT systems allow nowadays to visualize quantitative and qualitative angiographic maps of retinal tissue. We equipped the instrument with a pulse oximeter and recorded the pulse synchronously with the resonant Doppler flow data. Recombination of tomograms according to the heart beat cycles yields full volumes for each cycle instant. We believe such multi-dimensional functional information and the ability to monitor dynamic processes over time to open exciting perspectives that ultimately contribute to a better understanding of retinal physiology and patho-physiology in-vivo.

We present in vivo human retinal blood flow investigation using Fourier domain optical coherence tomography. A pilot study was performed to evaluate the total retinal blood flow in glaucoma patients and normal subjects. For normal people, the measured total retinal flow was between 40.8 and 52.9 μl/minute. The measured venous flow for glaucoma patients was from 23.6 to 43.11 μl/minute. The retinal flow of glaucoma patients was lower than that of normal subjects. Retinal blood flow was highly correlated with visual field parameters in glaucoma patients.

We propose a modified method of acquisition and analysis of Spectral Optical Coherence Tomography (SOCT) data to provide information about flow velocities in three dimensions. Joint Spectral and Time domain Optical Coherence Tomography (joint STdOCT) enables flow velocity assessment and segmentation of flows. STdOCT method is based on direct detection of Doppler shift that arises in time during the measurement. New scanning protocols and analysis tools are proposed to create velocity distribution maps of the retina and to segment and visualize 3D flows. STdOCT segmentation is more sensitive than methods based on phase measurements and calculations are more straightforward than other techniques, which require more complex experimental setup and more sophisticated numerical tools. We also discuss parameters, which improve the flow based segmentation procedure with special attention paid to the problem of broadening of flow velocity distribution.

Congenital cardiovascular defects are very common, occurring in 1% of live births, and cardiovascular failures are the leading cause of birth defect-related deaths in infants. To improve diagnostics, prevention and treatment of cardiovascular abnormalities, we need to understand not only how cells form the heart and vessels but also how physical factors such as heart contraction and blood flow influence heart development and changes in the circulatory network. Mouse models are an excellent resource for studying cardiovascular development and disease because of the resemblance to humans, rapid generation time, and availability of mutants with cardiovascular defects linked to human diseases. In this work, we present results on development and application of Doppler Swept Source Optical Coherence Tomography (DSS-OCT) for imaging of cardiovascular dynamics and blood flow in the mouse embryonic heart and vessels. Our studies demonstrated that the spatial and temporal resolution of the DSS-OCT makes it possible to perform sensitive measurements of heart and vessel wall movements and to investigate how contractile waves facilitate the movement of blood through the circulatory system.

This article demonstrates two modalities to acquire information on cardiac function in larval Drosophila Melanogaster: in-vivo imaging and heartbeat monitoring. To achieve these goals a dedicated imaging instrument able to provide simultaneous en-face Optical Coherence Tomography (OCT) and Laser Scanning Confocal Microscopy (LSCM) images has been developed. With this dual imaging system, the heart can easily be located and visualised within the specimen and the change of the heart shape in a cardiac cycle monitored. The system can easily be switched to a stethoscopic regime, simply by interrupting the scanning of the light beam across the sample, after selecting the point of interest in the imaging regime. Here we have used targeted gene expression to knockdown the myospheroid (mys) gene in the larval heart using a specific RNAi construct. By knocking down a β integrin subunit encoded by mys we have recorded an enlarged heart chamber in both diastolic and systolic states. Also, the fraction of reduction of the chamber diameter was smaller in the knockdown heart. These phenotypic differences indicate that impaired cardiac contractility occurs in the heart where the integrin gene express level is reduced. As far as we are aware, this is for the first time when it is shown in Drosophila that integrins have a direct relationship to a dilated heart defect, and conseqThis article demonstrates two modalities to acquire information on cardiac function in larval Drosophila Melanogaster: in-vivo imaging and heartbeat monitoring. To achieve these goals a dedicated imaging instrument able to provide simultaneous en-face Optical Coherence Tomography (OCT) and Laser Scanning Confocal Microscopy (LSCM) images has been developed. With this dual imaging system, the heart can easily be located and visualised within the specimen and the change of the heart shape in a cardiac cycle monitored. The system can easily be switched to a stethoscopic regime, simply by interrupting the scanning of the light beam across the sample, after selecting the point of interest in the imaging regime. Here we have used targeted gene expression to knockdown the myospheroid (mys) gene in the larval heart using a specific RNAi construct. By knocking down a β integrin subunit encoded by mys we have recorded an enlarged heart chamber in both diastolic and systolic states. Also, the fraction of reduction of the chamber diameter was smaller in the knockdown heart. These phenotypic differences indicate that impaired cardiac contractility occurs in the heart where the integrin gene express level is reduced. As far as we are aware, this is for the first time when it is shown in Drosophila that integrins have a direct relationship to a dilated heart defect, and consequently we demonstrate the utility of Drosophila as model for the study of vertebrate heart disease. By monitoring the heartbeat we also demonstrated a reduction of the heart rate in Tropomyosin mutant compared to the wild type larva.uently we demonstrate the utility of Drosophila as model for the study of vertebrate heart disease. By monitoring the heartbeat we also demonstrated a reduction of the heart rate in Tropomyosin mutant compared to the wild type larva.

The early stages of ocular diseases such as Diabetic Retinopathy are manifested by morphological changes in retinal tissue occurring on cellular level. Therefore, a number of ophthalmic diseases can be diagnosed at an early stage by detecting spatial and temporal variations in the scattering profile of retinal tissue. It was recently demonstrated that, OCT can be used to probe the functional response of retinal photoreceptors to external light stimulation [1]-[3]. fUHROCT measures localized differential changes in the retina reflectivity over time resulting from external light stimulation of the retina. Currently the origins of the observed reflectivity changes are not well understood. However, due to the complex nature of retinal physiology using purely experimental approaches in this case is problematic. For example fUHROCT is sensitive to small changes in the refractive index of biological tissue which as demonstrated previously, can result from a number of processes such as membrane hyperpolarization, osmotic swelling, metabolic changes, etc. In this paper, we present a computational model of interaction between photoreceptor cells and optical plane wave based on the Finite Integration Technique (FIT).

We report an imaging study using integrated 3D-OCT and OCM for the assessment of various human thyroid and breast pathologies. The 3D-OCT data sets enable en face projection imaging, which provides large field of view with uniform focus and signal level, while OCM provides high magnification that enables cellular resolution imaging. We have demonstrated that the integrated 3D-OCT and OCM technology provide a substantial improvement over standard OCT for the visualization of tissue pathology and can serve as a useful imaging tool in the clinical settings.

Molecular imaging is a powerful tool for investigating disease processes and potential therapies in both in vivo and in vitro systems. However, high resolution molecular imaging has been limited to relatively shallow penetration depths that can be accessed with microscopy. Optical coherence tomography (OCT) is an optical analogue to ultrasound with relatively good penetration depth (1-2 mm) and resolution (~1-10 μm). We have developed and characterized photothermal OCT as a molecular contrast mechanism that allows for high resolution molecular imaging at deeper penetration depths than microscopy. Our photothermal system consists of an amplitude-modulated heating beam that spatially overlaps with the focused spot of the sample arm of a spectral-domain OCT microscope. Validation experiments in tissue-like phantoms containing gold nanospheres that absorb at 532 nm revealed a sensitivity of 14 parts per million nanospheres (weight/weight) in a tissue-like environment. The nanospheres were then conjugated to anti-EGFR, and molecular targeting was confirmed in cells that over-express EGFR (MDA-MB-468) and cells that express low levels of EGFR (MDA-MB-435). Molecular imaging in three-dimensional tissue constructs was confirmed with a significantly lower photothermal signal (p<0.0001) from the constructs composed of cells that express low levels of EGFR compared to the over-expressing cell constructs (300% signal increase). This technique could potentially augment confocal and multiphoton microscopy as a method for deep-tissue, depth-resolved molecular imaging with relatively high resolution and target sensitivity, without photobleaching or cytotoxicity.

We validate a molecular imaging technique called Nonlinear Interferometric Vibrational Imaging (NIVI) by comparing vibrational spectra with those acquired from Raman microscopy. This broadband coherent anti-Stokes Raman scattering (CARS) technique uses heterodyne detection and OCT acquisition and design principles to interfere a CARS signal generated by a sample with a local oscillator signal generated separately by a four-wave mixing process. These are mixed and demodulated by spectral interferometry. Its confocal configuration allows the acquisition of 3D images based on endogenous molecular signatures. Images from both phantom and mammary tissues have been acquired by this instrument and its spectrum is compared with its spontaneous Raman signatures.

The generation of spectroscopic optical coherence tomography (SOCT) signals suffers from an inherent trade off between spatial and spectral resolution. Here, we present a dual window (DW) method that uses two Gaussian windows to simultaneously obtain high spectral and spatial resolution. We show that the DW method probes the Winger time-frequency distribution (TFD) with two orthogonal windows set by the standard deviation of the Gaussian windows used for processing. We also show that in the limit of an infinitesimally narrow window, combined with a large window, this method is equivalent to the Kirkwood & Richaczek TFD and, if the real part is taken, it is equivalent to the Margenau & Hill (MH) TFD. We demonstrate the effectiveness of the method by simulating a signal with four components separated in depth or center frequency. Six TFD are compared: the ideal, the Wigner, the MH, narrow window short time Fourier transform (STFT), wide window STFT, and the DW. The results show that the DW method contains features of the Wigner TFD, and that it contains the highest spatial and spectral resolution that is free of artifacts. This method can enable powerful applications, including accurate acquisition of the spectral information for cancer diagnosis.

In this manuscript, we report a fast speed swept source endoscopic OCT system utilizing a 4.5mm diameter rigid GRIN lens rod probe. The rigid probe has a tunable working distance with tuning range 0~7mm. The system could take front scanning images with speed of 40frames per second (512 A line per frame). The probe can work in contact and non contact mode. Fast speed contact and non-contact imaging was demonstrated.

We present results obtained using a two-channel portable device for CP OCT based on the polarization-maintaining fiber. The device is capable of acquiring OCT images of the object in direct and orthogonal polarizations simultaneously. The OCT system has an endoscopic forward-looking probe (2.7 mm in diameter). The CP OCT imaging was done in 64 postoperative specimens, for 30 patients during cystoscopy with suspicion of urothelial neoplasia, and for 11 patients with prostatectomy due to cancer. After surgery in the tissue specimen we immediately introduced surgical suture and investigated a bladder wall by CP OCT. When comparing OCT images and histology slides we can distinguish tissue layers based on position of the suture material. CP OCT images were compared with histological data. Special staining - Sirius Red for collagen types was applied. OCT -visualization of sympathetic nerve was made during open surgery. We found, that a strong signal in orthogonal polarization is produced by structures consisting of Type I collagen. We demonstrated that endoscopic benign and early malignant pathological processes that cannot be detected by standard OCT may be differentiated by CP OCT. Sympathetic nerve of neurovascular bundle gives a strong signal in both polarizations: direct and orthogonal. Based on these CP OCT features we can visualize nerve during operation (open or endoscopic surgery) and thus preserve it.

We report on an extension of our previously presented polarization sensitive optical coherence tomography (PS-OCT) technique towards quantitative measurements and imaging of depolarization of light backscattered by the various layers of the human ocular fundus in vivo. We use a state of the art spectral domain PS-OCT instrument that measures a 3D data set within 3 seconds. For measurement of the degree of polarization uniformity, we calculate the Stokes vector of the light backscattered at each point in the imaged volume. We average the Stokes vector elements within an evaluation window that slides over an entire B-scan. From the averaged Stokes vector elements, we calculate the degree of polarization uniformity DOPU within the evaluation window and plot DOPU as a function of position. While anterior retinal layers (and layers below the retinal pigment epithelium (RPE)) show DOPU values near 1, DOPU is only ~ 0.3 - 0.5 in the RPE, with the lowest values found near the center of the fovea. The method might be useful for diagnosing the state of a tissue or for improved segmentation of the RPE.

Conjunctiva and sclera are not always discriminated in anterior eye optical coherence tomography (OCT) images, although they have distinctive tissue properties. In contrast, characteristic pattern can be observed at the sclera in a phase retardation OCT image measured by polarization sensitive OCT (PS-OCT). This is because sclera consists of collagen and it has birefringence. We developped a new algorithm which discriminates conjunctiva and sclera based on the local statistics of intensity and phase retardation OCT images. In 4 of 4 cases, conjunctiva and sclera were discriminated. This new algorithm is useful to discriminate tissues of PS-OCT images not by anatomical tissue structures but by direct tissue properties.

Polarization-sensitive optical coherence tomography (PS-OCT) for retinal imaging has been developed with time-domain or spectral-domain OCT using broadband light sources at 800-nm band. Recent studies suggested that a 1 μm band could achieve higher penetration for imaging the posterior segment of the eye. In this presentation, we demonstrate fiber-based swept-source PS-OCT at 1 μm wavelength. Birefringence of the posterior eye segment is measured with a single depth scan by using the method of continuous polarization modulation. To our knowledge, this is the first time to show the phase retardation image of the posterior eye segment at 1 μm wavelength.

We present a polarization-maintaining (PM) fiber based optical coherence tomography system for polarization-sensitive and phase-sensitive measurements. Using a single detector, a single depth scan accurately yields retardance and polarization-insensitive reflectivity information along an A-line. Interference patterns on the orthogonal polarization channels are frequency multiplexed and extracted by digital band-pass filters. Images are insensitive to sample rotation in plane perpendicular to ranging. The use of PM-fibers allows direct calculation of birefringence without correcting the polarization transformations known in single-mode non-PM fibers. The system can be configured for differential phase measurements with minor modifications. In this case, a dual detector setup in the detection arm is used, and frequency multiplexing is not utilized.

Phase-sensitive adjuncts to optical coherence tomography (OCT) including Doppler and polarization-sensitive implementations allow for quantitative depth-resolved measurements of sample structure and dynamics including fluid flows and orientation of birefringent structures. The development of Fourier-domain OCT (FDOCT), particularly spectrometer-based spectral-domain systems with no moving parts (spectral-domain OCT or SDOCT), have greatly enhanced the phase stability of OCT systems particularly when implemented in a common-path geometry. The latter combination has given rise to a new class of nm-scale sensitive quantitative phase microscopies we have termed spectral domain phase microscopy. However, the phase information in all of these techniques suffers from a 2π ambiguity that limits resolvable pathlength differences to less than half the source center wavelength. This is problematic for situations such as cellular imaging, Doppler velocimetry, or polarization sensitive applications where it may be necessary to monitor sample profiles, displacements, phase differences, or refractive index variations which vary rapidly in space or time. A technique previously introduced in phase shifting interferometry uses phase information from multiple wavelengths to overcome this limitation. We show that by appropriate spectral windowing of the broadband light source already used in OCT, particularly by reshaping the source spectrum about two different center wavelengths, the resulting phase variation may be cast in terms of a much longer synthetic wavelength chosen to span the phase variation of interest. We show theoretically that the optimal choice of synthetic wavelength depends upon a tradeoff between the minimum resolvable phase and the length of unambiguous phase measurement. We demonstrate this technique using a broadband source centered at 790 nm by correctly reconstructing the phase profile from a phantom sample containing multiple 2π wrapping artifacts at the center wavelength and compare our result with atomic force microscopy.

By increasing the speed and reducing the complexity of OCT systems, the parallel OCT system presented here will reduce the cost of high performance instruments while making them more widespread and easy to use. The instrument integrates line scanning with a swept source to achieve ultrahigh image speeds in a much simpler way. The swept source speed requirements are significantly relaxed. In a traditional OCT, a focused beam is scanned for image formation, while parallel OCT images simultaneously a full B-scan or a complete 3D cube. The system achieved ultrahigh scan speeds (98 kHz line rates and 160 fps), and was initially tested on various reflective and diffuse targets. The system demonstrates the potential for 3-D volumetric mapping of tissue at several volumes per second.

We describe a novel compact real-time single-shot full-field optical coherence tomography based on a dual-channel phase-stepper optics, which employs a 2-D quaternionic analytic signal processing technique to reconstruct the en-face OCT image. The experimental setup was based on a Linnik type polarization Michelson interferometer followed by a dual-channel phase-stepper optics and a single CCD camera to capture two 180° phase stepped images simultaneously. The interferometer is illuminated using a SLD source with central wavelength of 842 nm and spectral bandwidth of 16.2 nm, yielding an axial resolution of 19.8 μm. Using a 10 X (0.25-NA) microscope objective and a single CCD camera, the system covers an area of 325μm x 300μm (325 × 300 pixels) with a transverse resolution of 4.4 μm. We demonstrate the feasibility of this system for real-time imaging of scattering specimens such as a diaptomus.

We propose an algorithm that effectively cancels complex conjugate mirror terms from single OCT A-scans by utilizing the dispersion mismatch between reference and sample arm to generate full range tomograms. This allows distinguishing between complex conjugate mirror terms and real structures and is therefore called dispersion encoded full range (DEFR). Whereas the computational complexity is higher, acquisition speed is not compromised since no additional A-scans need to be measured which makes this technique also robust against phase fluctuations. The iterative algorithm uses numeric dispersion compensation and exhibits no reduction in resolution compared to standard processing. Residual leakage of mirror terms is reduced by incorporating further knowledge such as the power spectrum of the light source. The suppression ratio of mirror signals is more than 50 dB and thus comparable to other complex FD-OCT techniques which use more than one A-scan.

We show that recently developed joint Spectral and Time Optical Coherence Tomography data analysis scheme combined with oscillatory change of optical path difference allows for simultaneous complex ambiguity removal and quantitative flow velocity estimation. Full range structural tomograms as well as velocity distributions of Intralipid solution in glass capillaries are presented.

We show that the decay of sensitivity with depth in Fourier Domain (FD)-OCT can be explained based on the superposition of wavetrain lengths after dispersion (diffraction). The more coherent the dispersed waves are, the slower the decay of sensitivity. An asymmetry in the decay curve with the optical path difference (OPD) can be introduced via an "intrinsic" delay which has the effect of shifting axially the two wavetrains relative to each other, originating from the object and reference beam of an interferometer. In this way, an equivalent Talbot Bands set-up is implemented, characterized by no mirror terms for the "extrinsic" delay introduced in the interferometer. Such configurations require that the two interfering beams use different parts of the diffraction grating in the interrogating spectrometer. Theory of Talbot Bands is presented and then how this knowledge can be transferred to the field of FD-OCT to achieve A-scans mirror terms free in one step. A theoretical rigorous model and a heuristic model are presented to quantify the Talbot bands.

The early stages of malignant diseases, such as cancer, are characterized by cellular and microstructural changes which define both the diagnosis and the prognosis of the disease. Unfortunately, at the current resolution of Optical Coherence Tomography (OCT), such changes associated with early cancer are not clearly discernible. However, spectral analysis of OCT images has recently shown that additional information can be extracted from those signals, resulting in improved contrast which is directly related to scatterer size changes. Amplitude Modulation - Frequency Modulation (AM-FM) analysis is a fast and accurate technique which can also be applied to the OCT images for estimation of spectral information. It is based on the analytic signal of the real data, obtained using a Hilbert Transform, and provides the instantaneous amplitude, phase, and frequency of an OCT signal. The performance of this method is superior to both FFT-based and parametric (e.g. autoregressive) spectral analysis providing better accuracy and faster convergence when estimating scatterer features. Since disease tissues exhibit variations in scatterer size and thus also exhibit marked differences in spectral and phase characteristics, such advanced analysis techniques can provide more insight into the subtle changes observed in OCT images of malignancy. Therefore, they can make available a tool which could prove extremely valuable for the investigation of disease features which now remain below the resolution of OCT and improved the technology's diagnostic capabilities.

At BIOS08, the authors presented a novel multi-beam Optical Coherence Tomography (OCT) system that overcomes the problem of limited lateral resolution inherent in single-beam Fourier Domain OCT. We now present image processing algorithms for blending the images from each OCT beam, producing a seamless composite image, and show how the use of multiple beams can produce additional benefits, including speckle noise reduction, leading to improved clinical detail in the results.

A bidirectional FDOCT system capable of measuring absolute velocities of moving scatterers is described. In this setup the sample is illuminated with two differently polarized beams. These two probe beams impinging onto the sample at a known angle. The velocity estimation is independent of the exact direction of the velocity vector in the detection plane. Evaluation measurements were performed on a rotating disc driven at well defined velocities and tilted by various small angles around to π/2. Our results indicate a high correlation between pre-set and estimated velocities and the independency of these velocities from the tilting angle of the disc. Additional preliminary in vivo measurements proof the ability of this new method to measure absolute blood flow velocities in human retinal vessels.

Spectrometer-based or space encoded Fourier domain OCT is preferred because of its relatively simple design, fast measurement speed and good signal-to-noise ratio. Besides delivering structural information, it is often used to measure blood flow velocities. Commonly, the axial component of the velocity is calculated from the phase difference of consecutive A-Scans. While this result holds true for pure axial movement, a transversal component of the displacement will alter this simple relationship. We present a new model accounting for the changing intensity of the illuminating beam on the moving particles and explaining why the phase difference does not increase linearly with the velocity. Movements as small as 20 % of the beam diameter during the integration time of the line detector will alter the observed phase shifts noticeably. For small angles between transversal direction and direction of movement, the discrepancy between classically calculated and measured phase shift may be huge. At certain velocities and angles no correlation of the phase exists even so there is an OCT-signal. High velocities at small angles will result in a limit for the phase shift smaller than π. A safe region, where the deviations to the linear relationship between axial velocity and phase shift are small, is specified.

Blood flow measurement with spectrometer-based Fourier domain optical coherence tomography (FD-OCT) is limited by the motion-induced signal fading and the resulting reduction of flow sensitivity. Therefore, we have numerically simulated the signal power decrease of an obliquely moved scattering layer as a function of the absolute sample velocity composed of an axial and transverse component. In contrast to the prevalent expectance, the resulting signal damping is not only the sum of axial and transverse effect. In this study, we take advantage of the signal decay and present the feasibility to quantify high flow velocities at which the standard Doppler OCT does not work any longer. For the validation of our approach, a flow phantom model consisting of a 1%-Intralipid solution and a 320 μm glass capillary was used. With this phantom study, depth-resolved flow was visualized and the quantitative velocities were extracted from the OCT images without phase information.

Doppler Optical Coherence Tomography (DOCT) imaging of in-vivo retinal blood flow was widely studied as efforts of research community to push this technology into clinic. Spectral Doppler imaging of DOCT has been demonstrated as a quantification method of in-vivo pulsatile retinal blood flow in human eye. This technology has the all the advantages inherited from OCT comparing to Doppler ultrasound. Comparing to normal spatial-distributed color Doppler imaging of DOCT, spectral Doppler imaging can reveal more haemodynamics details on the time dimension. Although resistance index (RI) of a micro-vascular can be measured in vivo from human retina, the clinical significance of RI measurements still needs to be investigated. In vitro experiment conduced with ultrasound has demonstrated the higher vascular resistance value is associated with the higher RI measured assuming the constant compliance of vascular tube. In this study, the rodent window-chamber model (RWCM) was used as a platform to investigate the RI change as the micro-vasculature response to laser irradiation. The higher RI was measured after the occlusion of two veins (should it be arterials) that was verified with laser speckle imaging in our preliminary experiment results.

We propose a novel method for speckle reduction based on angular compounding by B-scan Doppler shift encoding (ACBD). By de-centering the beam from the pivot of a scanning mirror, the illumination angle can be encoded by Doppler shift detected by B-scan analysis. Compounding multiple images reconstructed from different Doppler-shift bands, we can suppress speckle without sacrificing image acquisition speed. Speckle reduction with ACBD is demonstrated by imaging a phantom and a living avian embryo

We have developed ultra-broadband Super-Luminescent Emitting Diodes (SLEDs) at 840 nm with a 3-dB bandwidth of 45-75 nm. The SLEDs show high robustness against back-reflections of up to 50% with little change in coherence length, sidelobe suppression ratio and secondary peak suppression over a wide range of back-reflections. First long-term measurements do not show any signs of device degradation. Hence, these SLEDs can be employed in OCT systems without costly broadband optical isolators.

Swept-source optical coherence tomography (SS-OCT) has received much attention in recent years because of its higher sensitivity in high speed imaging. A fast and high powered wavelength-swept laser is important for SS-OCT since its speed and sensitivity directly rely on the sweeping rate and the output power of the swept laser. Much progress has been made on the development of high-speed swept lasers, but their output power has been limited. We present a Fourierdomain mode-locked 1300 nm wavelength-swept laser that uses a polygon-based narrowband optical scanning filter and a high-efficiency semiconductor optical amplifier. The optical filter and laser structure were designed and constructed for an optimized optical power output. Average output powers of 71 mW has been achieved without an external amplifier, while the wavelength is swept continuously from 1247 nm to 1360 nm. A unidirectional wavelength sweeping rate of 7452 nm/ms (65.95 kHz repetition rate) was achieved by using a 72 facet polygon scanner with a rotation rate of 916 revolutions per second. The instantaneous linewidth of this laser is 0.09 nm, which corresponds to a coherence length of 16 mm. This laser is most suitable for optical coherence tomography applications.

Novel wavelength-swept Raman laser is newly demonstrated to implement an arbitrary gain band for a swept-source optical coherence tomography (SS-OCT). Instead of conventional semiconductor optical amplifier, we adapt optical fiber Raman amplification, which can easily generate an instant femto-second optical gain at arbitrary wavelength region from 1.1 to 1.6 micrometer using a high-power optical pump power. We also experimentally demonstrate OCT images using the novel wavelength-swept Raman laser source.

We report on the development of an all-fiber frequency-swept laser light source in the 1050 nm range based on semiconductor optical amplifiers (SOA) with improved bandwidth due to multiple gain media. It is demonstrated that even two SOAs with nearly equal gain spectra can improve the performance of the light source when installed in series. This Serial SOA configuration (SSOA) is compared with the common MasterOscillator/Power Amplifier architecture (MOPA) where a single SOA is used as laser gain medium in the resonator and a second one outside as booster. We show that for high sweep rates (20 kHz) the SSOA configuration can maintain a significantly higher bandwidth (~50% higher) compared to the MOPA architecture. Correspondingly narrower point spread functions can be generated in a Michelson interferometer.

Fast wavelength tunable sampled grating distributed Bragg reflector (SG-DBR) lasers are used to generate fast, linear, continuous wavelength sweeps. High resolution wavelength sweeps in excess of 45 nm are demonstrated at a 100 kHz repetition rate. The front mirror, back mirror and phase segment tuning segments can be modulated at very fast rates, which allows for very fast wavelength ramp rates. This sweep is generated through three time synchronized current versus time waveforms applied to the back mirror, front mirror and phase sections of the laser. The sweep consists of fifty separate mode-hop-free tuning segments which are stitched together to form a near continuous wavelength ramp. The stitching points require a maximum of 60 ns for amplitude, wavelength, and thermal settling time to allow the laser to equilibrate. Wavelength tuning non-linearities, output power wavelength dependency, and wavelength discontinuities are defects in the wavelength sweep that result from properties of the wavelength tuning mechanism as well as limitations of the signal generators that produce the time varying bias currents. A Michelson Interferometer is used to examine the effects of these defects for optical coherence tomography (OCT). The OCT measurements demonstrate spectral broadening of the source and interference signal reduction as the penetration depth increases. However, these effects are not very severe for delay differences less than 2 mm even without correction for sweep nonlinearities.

A key component of the OCT technique is the light source with widely spectrum. Extremely broadband 1.0 μm semiconductor light sources are fabricated with two kinds of device structures of multiplexing emitting layer. The measured spectra of the fabricated device with "longitudinal bandgap modulated structure" show that the full-width at half-maximum spectral width could be as large as 156 nm. The wavelength swept sources which contain a fabricated device with "asymmetric dual emitting layers structure" have a center wavelength of 1.06 μm, wavelength range of 90 nm, scanning rate of 2kHz.

Simple and robust method for identifying the retinal pigment epithelium (RPE) from optical coherence tomography images is demonstrated. At first, the maximum intensity value of each A-scans were determined and the depth position of those pixels are identified. The obtained 2D matrix is used as first estimation for the position of RPE. The erroneous pixel from the RPE is masked out and new approximation for them is calculated based on the neighbouring pixels. Finally, the obtained RPE matrix is smoothened. The RPE identification is used for separating the retina and choroid from optical coherence tomography images obtained by 830 nm spectral domain OCT. Both normal and ARMD patient eye were investigated to demonstrate the usability of that method. The calculation time for three dimensional data set (1024x450x137 pixels) was only 16 seconds and it identifies RPE reliably.

Transplant technologies have been studied for the recovery of vision loss from retinitis pigmentosa (RP) and age-related macular degeneration (AMD). In several rodent retinal degeneration models and in patients, retinal progenitor cells transplanted as layers to the subretinal space have been shown to restore or preserve vision. The methods for evaluation of transplants are expensive considering the large amount of animals. Alternatively, time-domain Stratus OCT was previously shown to be able to image the morphological structure of transplants to some extent, but could not clearly identify laminated transplants. The efficacy of screening retinal transplants with Fourier-domain OCT was studied on 37 S334ter line 3 rats with retinal degeneration 6-67 days after transplant surgery. The transplants were morphologically categorized as no transplant, detachment, rosettes, small laminated area and larger laminated area with both Fourier-domain OCT and histology. The efficacy of Fourier-domain OCT in screening retinal transplants was evaluated by comparing the categorization results with OCT and histology. Additionally, 4 rats were randomly selected for multiple OCT examinations (1, 5, 9, 14 and 21days post surgery) in order to determine the earliest image time of OCT examination since the transplanted tissue may need some time to show its tendency of growing. Finally, we demonstrated the efficacy of Fourier-domain OCT in screening retinal transplants in early stages and determined the earliest imaging time for OCT. Fourier-domain OCT makes itself valuable in saving resource spent on animals with unsuccessful transplants.

Depolarization data is provided for several normal retinas. Mueller matrix images of normal human fovea were acquired with a custom imaging Mueller matrix retinal polarimeter (the GDx-MM) over a 9° field at 780nm and have been analyzed for depolarization index and the variation of degree of polarization with incident polarization state. The degree of polarization (DoP) was often above 50% and varied in complex ways as a function of the incident polarization states. The depolarization properties around the macula loosely correlated with the retardance image. High spatial frequency depolarizing structures were evident throughout the fovea.

Optical coherence tomography (OCT) is an evolving noninvasive imaging modality and has been used to image the human larynx during surgical endoscopy. The design of a long GRIN lens based probe capable of capturing images of the human larynx by use of a swept-source OCT during a typical office-based laryngoscopy examination is presented. An optical-ballast-based 4F optical relay system is proposed to realize variable working distance with a constant optical delay. In vivo OCT imaging of the human larynx is demonstrated with 40 fame/second. Office-based OCT is a promising imaging modality to study the larynx.

Optical coherence tomography (OCT) holds great promise as a routine research tool for 3-D analysis of mammalian embryos. However, despite the depth penetration afforded by this imaging modality, light attenuation in tissues imposes limitations. Here we studied the optical clearing effect of different concentrations of glycerol in mouse embryos. Depth- and time-resolved profiles for OCT signal enhancement are presented. We found that application of 50% glycerol resulted in 51.5±12.5% improvement of the OCT signal, while 25% glycerol enhanced the OCT signal by 25.2±7.3% at the depth of about 200 to 500 µm, and the glycerol permeability rate was estimated as 26.7±6 µm/min. These results demonstrate that embryonic imaging is improved by application of glycerol as optical clearing agent.

A novel 3-D image construction method with maximum intensity projection (MIP) of B-mode OCT images is proposed for in vivo dynamic analysis of mental sweating on human fingertips. Time-sequential MIP-OCT images with the frame spacing as short as 1.4 sec provide us quantitative analysis of the sweating dynamics to evaluate of activity of sympathetic nerve. Dynamic changes in the microstructure of eccrin sweat glands can be clearly observed in the 3-D images constructed by volume rendering.

Investigation of initial implant stability with different dental implant designs is an important task to obtain good quality dental implants. Failure of a dental implant is often related to failure to osseointegrate correctly. Optical Coherent Tomography is a competitive non-invasive method of osseointegration investigation. FD-OCT with Swept Source was used to obtain 3-D image of the peri-implant tissue (soft and hard) in the case of mandible fixed screw. 1350 nm centered laser source give better images than 850 nm laser source for hard tissue imaging. Present work suggests that Optical Coherent Tomography is a proper technique to obtain the image of the contact tissue-metal screw. OCT images are useful to evaluate optical properties of bone tissues.

Doppler optical coherence tomography (DOCT) combines the imaging capabilities of OCT with functional velocity imaging and is used routinely to study skin in-vivo. The skin provides a window to monitor diseases; it has been shown that changes in skin blood flow and structure are indicative of systemic disease change and representative of disease status. This study aims to aid understanding and interpretation of DOCT images of skin with respect to vessel diameter, depth and blood flow. We have constructed a tissue model using glass capillary tubes suspended at an angle of 20° to the horizontal in an Intralipid-filled tank. The Intralipid was diluted to levels which represented optimal tissue and blood flow scattering parameters. Intralipid was then pumped through the tubes to represent blood flow. The angled nature of the tubes allowed flow imaging at various depths. DOCT images were recorded using a swept-source OCT system with 1300 nm central wavelength and 6 μm axial resolution (OCMP1300SS, Thorlabs, Inc.). Data parameters extracted from images include velocity, penetration depth and their dependence on tube diameter, depth and flow. We have successfully demonstrated a tissue model that allows DOCT imaging of vessel diameter, depth and blood flow to be investigated.

Depth-resolved tissue contrast imaging using local polarization properties has been demonstrated in vivo with fiber-based polarization-sensitive swept-source optical coherence tomography. The local birefringence and differential optic axis orientation are calculated with an algorithm based on Jones matrix representation. To enhance the signal-to-noise ratio of images to speckle noise, polarization properties of local sites with thickness of ~ 100 μm are measured. High contrast images of local polarization properties are obtained without averaging. In vivo imaging of the human anterior eye chamber shows the potential of this method to discriminate the birefringent tissues.

We propose a fiber-based hand-held scanning probe suitable for the sample arm of spectral domain optical coherence tomography (SD-OCT). To achieve a compact and miniaturized probe, a single-body lensed-fiber, on which an iron-bead ferromagnetic material is loaded was fabricated and a solenoid actuator driven by readily available driving voltage (10 V) and current (120 mA) was utilized. A focusing lens was directly formed in a single-body onto the distal end of a fiber, which eliminated any complement optical components in front of a conventional sample probe and removes any optical alignment problem. By using the soft-iron solenoid actuator, the fiber in the probe is activated which gives the sample scanning for the OCT imaging. Moreover, the simple design of the solenoid allowed easy fabrication and a good practicality. With the implemented probe, OCT images of a pearl and a human finger tip were obtained at an imaging speed of 30 Hz and a scanning range of 4 mm.

Comparative evaluation of signal-to-noise ratio (SNR) is presented using a Full-field (FF)-OCT configuration, which is adapted to work in either Swept-Source (SS)-Full-field OCT or Time Domain (TD)-Full-field OCT regime. We implement the two regimes in the same set-up, using the same CCD camera and the same samples. We describe the experimental set-up and the procedure implemented to verify the theory which says that Spectral Domain (SD)-OCT is superior to TD-OCT. A simple theoretical analysis of the signal-to-noise ratio is presented to evaluate the improvement from TD-OCT to SD-OCT in FF configuration. Experimental results demonstrate that the SNR is indeed better in the SS-OCT regime, however not to the level predicted by theory. More work is required to understand why the experimental set-up does not achieve the improvement predicted by theory. We also show how to perform the measurements and imaging in the two regimes of operation. The system can deliver B-Scan OCT images in the SS-OCT regime and C-scan OCT images in the TD-OCT regime.

We built a high-speed, real-time spectral domain optical coherence tomography (SD-OCT) system at the 1.3 μm region using an InGaAs line-scan camera with 1024 pixels and 46.99 klines/s. In SD-OCT, the actual spatial resolution can be different from the theoretical one due to the large bandwidth of the light source and the finite number of detector pixels, especially for a long center wavelength. We calculated and compared the axial resolutions obtained from the point spread function and the physical pixel size of the OCT image. We found that the axial resolution of the SD-OCT system could be limited in the 1.3 μm region if the depth range becomes large.

One of the main drawbacks of Fourier-domain optical coherence tomography is its inability to differentiate positive and negative depths. A technique recently developed consists in introducing a transverse modulation between consecutive A-scans: this is the B-M mode scanning technique. This paper deals with the condition required on the transverse step to efficiently remove artifacts in a swept-source optical coherence tomography setup. This condition is illustrated by showing measurements on an onion acquired with different transverse steps and different focusing optics.

Improvements in identification, imaging, and visualization of the cavernous nerves during prostate cancer surgery, which are responsible for erectile function, may improve nerve preservation and postoperative sexual potency. In this study, we use a rat prostate, ex vivo, to evaluate the feasibility of optical coherence tomography (OCT) as a diagnostic tool for real-time imaging and identification of the cavernous nerves. A novel OCT system based on an all single-mode fiber common-path interferometer-based scanning system is used for this purpose. A wavelet shrinkage denoising technique using Stein's unbiased risk estimator (SURE) algorithm to calculate a data-adaptive threshold is implemented for speckle noise reduction in the OCT image. The signal-to-noise ratio (SNR) was improved by 9 dB and the image quality metrics of the cavernous nerves also improved significantly.

Meniscal tear is one of the most common knee injuries leading to pain and discomfort. Partial and total meniscectomies have been widely used to treat the avascular meniscal injuries in which tears do not heal spontaneously. However, the meniscectomies would cause an alteration of the tibiofemoral contact mechanics resulting in progressive osteoarthritis (OA). To mitigate the progression of OA, maximal preservation of meniscal tissue is recommended. The clinical challenge is deciding which meniscal tears are amenable to repair and which part of damaged tissues should be removed. Current diagnosis techniques such as arthroscopy and magnetic resonance imaging can provide macrostructural information of menisci, but the microstructural changes that occur prior to the observable meniscal tears cannot be identified by these techniques. Serving as a nondestructive optical biopsy, optical coherence tomography (OCT), a newly developed imaging modality, can provide high resolution, cross-sectional images of tissues and has been shown its capabilty in arthroscopic evaulation of articular cartilage. Our research was to demonstrate the potential of using OCT for nondestructive characterization of the histopathology of different types of meniscal tears from clinical cases in dogs, providing a fundamental understanding of the failure mechanism of meniscal tears. First, cross-sectional images of torn canine menisci obtained from the OCT and scanning electronic microscopy (SEM) were be compared. By studying the organization of collegan fibrils in torn menisci from the SEM images, the feasibility of using OCT to characterize the organization of collegan fibrils was elucidated. Moreover, the crack size of meniscal tears was quantatitively measured from the OCT images. Changes in the crack size of the tear may be useful for understanding the failure mechanism of meniscal tears.

Endoscopic OCT probes deliver light to the measurement region via a single optical fibre mounted in a probe head. The output beam is focused onto the sample, providing a single point measurement. The beam is translated, using mechanical scanning at the probe tip, to address a line or area of sampling points and produce an image. We are investigating a swept-source OCT system incorporating coherent fibre bundles, to allow many measurement points to be addressed, within an area of the sample, without the need for mechanical motion within the endoscope probe. Scanning components are still present at the input of our system, but are no longer required within the flexible endoscope section. This allows a small-diameter, electrically passive probe to be engineered using off-the-shelf scanning components. A common-path probe design is proposed, in which the bundle is external to the OCT interferometer. This eliminates contrast variations caused by non-controllable differences in the state of polarisation between fibres. Imaging bundle fibres are typically few-moded, which can lead to ghost features and reduced SNR in OCT images, but the common-path configuration also removes cross-mode interference problems, and reduces dispersion artefacts. OCT images of a microscope cover-slip and a sample of spring onion, acquired using the swept-source, bundle-based OCT system are presented. Features peculiar to the inclusion of the fibre bundle are discussed, and directions for future development of the system are outlined.