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Heinrich Muller was a nineteenth-century German retinal anatomist who, during his short career, was one of the discoverers of the rod photopigment rhodopsin and neuroglia in the retina, now known as Muller cells. He also described the ocular muscles and double foveae of some birds. An important, but largely neglected, insight by Muller was to combine careful psychophysical measurements and geometrical optics to find the location of the photosensitive layer of the retina in the living eye. Here, we provide translated passages from Muller's (1855) publication and compare his entoptic observations with retinal imaging using optical coherence tomography. Muller correctly deduced from his careful experiments that vision is initiated in the photoreceptors located in the back of the retina.

The retinal volumetric flow rate contains useful information not only for ophthalmo-logy but also for the diagnosis of common civilization diseases such as diabetes, Alzheimer's disease, or cerebrovascular diseases. Non-invasive optical methods for quantitative flow assessment, such as Doppler optical coherence tomography (OCT), have certain limitations. One is the phase wrapping that makes simultaneous calculations of the flow in all human retinal vessels impossible due to a very large span of flow velocities. We demonstrate that three-dimensional Doppler OCT combined with three-dimensional four Fourier transform fast phase unwrapping (3D 4FT FPU) allows for the calculation of the volumetric blood flow rate in real-time by the implementation of the algorithms in a graphics processing unit (GPU). The additive character of the flow at the furcations is proven using a microfluidic device with controlled flow rates as well as in the retinal veins bifurcations imaged in the optic disc area of five healthy volunteers. We show values of blood flow rates calculated for retinal capillaries and vessels with diameters in the range of 12–150 µm. The potential of quantitative measurement of retinal blood flow volume includes noninvasive detection of carotid artery stenosis or occlusion, measuring vascular reactivity and evaluation of vessel wall stiffness.

Ocular blood flow measurement may have a number of potential applications that explore the relationship between blood flow in the eye and diseases such as: diabetic retinopathy, ocular artery obstruction, hypertensive retinopathy and Alzheimer's disease. Reliable and quantitative method for retinal blood flow estimation is still to be created. Doppler OCT is one of candidates for such a method, but suffers from a number of limitations. Recently we proposed a solution to one of the most prominent artefacts in Doppler OCT, which is the phase wrapping problem. This allows for precise recovery of velocity profile the Doppler OCT technique remains sensitive to temporal dependence of the result on the blood flow velocity changing with the pulse during the OCT measurement. In this report we explore this problem and show that the synchronization of the OCT measurement with heart beats only partially gives control over the acquired blood flows.

We present a modified Fast Phase Unwrapping (FPU) algorithm and its application for calculation of the axial flow velocity and volumetric flow rate in Doppler optical coherence tomography (DOCT). We outline the FPU method and show that it can be implemented in Fourier-domain optical coherence tomography using Fourier transformations (4FT). We present two-dimensional (2D) and three-dimensional (3D) realizations of the algorithm to reconstruct unwrapped phase in numerical simulations, as well as in data collected from phantom. We demonstrate that the phase unwrapping outcomes of the 2D and 3D 4FT FPU algorithms depend on the phase noise in the input data. For low phase noise data both algorithms generate reliable results. With increasing noise, the 2D algorithm starts generating phase unwrapping errors earlier than the 3D version. With the phase noise larger than a limiting value, none of the algorithms provides error-free results. We demonstrate that within their phase noise applicability limits, the phase unwrapping methods enable calculation of volumetric flow rates in the flow phantom even in the presence of phase wraps. We demonstrate that application of phase unwrapping methods enables extension of the measurable flow velocities beyond the phase range limitation of the Doppler OCT data.

Angiographic imaging of the human eye with optical coherence tomography (OCT) is becoming an increasingly important tool in the scientific investigation and clinical management of several blinding diseases, including age-related macular degeneration and diabetic retinopathy. We have observed that OCT angiography (OCTA) of the human choriocapillaris and choroid with a 1.64 MHz A-scan rate swept-source laser yields higher contrast images as compared to a slower rate system operating at 100 kHz. This result is unexpected because signal sensitivity is reduced when acquisition rates are increased, and the incident illumination power is kept constant. The contrast of angiography images generated by acquiring multiple sequential frames and calculating the variation caused by blood flow, however, appears to be improved significantly when lower-contrast images are taken more rapidly. To demonstrate that the acquisition rate plays a role in the quality improvement, we have imaged five healthy subjects with a narrow field of view (1.2 mm) OCTA imaging system using two separate swept-source lasers of different A-line rates and compared the results quantitatively using the radially-averaged power spectrum. The average improvement in the contrast is 23.0% (+/-7.6%). Although the underlying cause of this enhancement is not explicitly determined here, we speculate that the higher-speed system suppresses the noise contribution from eye motion in subjects and operates with an inter-scan time that better discriminates the flow velocities present in the choroid and choriocapillaris. Our result informs OCT system developers on the merits of ultrahigh-speed acquisition in functional imaging applications.

In retinal raster imaging modalities, fixational eye movements manifest as image warp, where the relative positions of the beam and retina change during the acquisition of single frames. To remove warp artifacts, strip-based registration methods-in which fast-axis strips from target images are registered to a reference frame-have been applied in adaptive optics (AO) scanning light ophthalmoscopy (SLO) and optical coherence tomography (OCT). This approach has enabled object tracking and frame averaging, and methods have been described to automatically select reference frames with minimal motion. However, inconspicuous motion artifacts may persist in reference frames and propagate themselves throughout the processes of registration, tracking, and averaging. Here we test a previously proposed method for removing movement artifacts in reference frames, using biases in stripwise cross-correlation statistics. We applied the method to synthetic retinal images with simulated eye motion artifacts as well as real AO-SLO images of the cone mosaic and volumetric AO-OCT images, both affected by eye motion. In the case of synthetic images, the method was validated by direct comparison with motion-free versions of the images. In the case of real AO images, performance was validated by comparing the correlation of uncorrected images with that of corrected images, by quantifying the effect of motion artifacts on the image power spectra, and by qualitative examination of AO-OCT B-scans and en face projections. In all cases, the proposed method reduced motion artifacts and produced more faithful images of the retina.

We demonstrate OCT angiography (OCTA) and Doppler OCT imaging of the choroid in the eyes of two healthy volunteers and in a geographic atrophy case. We show that visualization of specific choroidal layers requires selection of appropriate OCTA methods. We investigate how imaging speed, B-scan averaging and scanning density influence visualization of various choroidal vessels. We introduce spatial power spectrum analysis of OCT en face angiographic projections as a method of quantitative analysis of choroicapillaris morphology. We explore the possibility of Doppler OCT imaging to provide information about directionality of blood flow in choroidal vessels. To achieve these goals, we have developed OCT systems utilizing an FDML laser operating at 1.7 MHz sweep rate, at 1060 nm center wavelength, and with 7.5 μm axial imaging resolution. A correlation mapping OCA method was implemented for visualization of the vessels. Joint Spectral and Time domain OCT (STdOCT) technique was used for Doppler OCT imaging.

We propose a simplification for a robust and easy to implement fast phase unwrapping (FPU) algorithm that is used to solve the phase wrapping problem encountered in various fields of optical imaging and metrology. We show that the number of necessary computations using the algorithm can be reduced compared to its original version. FPU can be easily extended from two to three spatial dimensions. We demonstrate the applicability of the two- and three-dimensional FPU algorithm for Doppler optical coherence tomography (DOCT) in numerical simulations, and in the imaging of a flow phantom and blood flow in the human retina in vivo. We introduce an FPU applicability plot for use as a guide in the selection of the most suitable version of the algorithm depending on the phase noise in the acquired data. This plot uses the circular standard deviation of the wrapped phase distribution as a measure of noise and relates it to the root-mean-square error of the recovered, unwrapped phase.

We present a method of OCT angiography (OCTA) data filtering for noise suppression and improved visualization of the retinal vascular networks in en face projection images. In our approach, we use a set of filters applied in three orthogonal axes in the three-dimensional (3-D) data sets. Minimization of artifacts generated in B-scan–wise data processing is accomplished by filtering the cross-sections along the slow scanning axis. A-scans are de-noised by axial filtering. The core of the method is the application of directional filtering to the C-scans, i.e. one-pixel thick sections of the 3-D data set, perpendicular to the direction of the scanning OCT beam. The method uses a concept of structuring, directional kernels of shapes matching the geometry of the image features. We use rotating ellipses to find the most likely local orientation of the vessels and use the best matching ellipses for median filtering of the C-scans. We demonstrate our approach in the imaging of a normal human eye with laboratory-grade spectral-domain OCT setup. The “field performance” is demonstrated in imaging of diabetic retinopathy cases with a commercial OCT device. The absolute complex differences method is used for the generation of OCTA images from the data collected in the most noise-wise unfavorable OCTA scanning regime–two frame scanning.

© 2016 Optical Society of America. We compared the performance of three OCT angiography (OCTA) methods: speckle variance, amplitude decorrelation and phase variance for imaging of the human retina and choroid. Two averaging methods, split spectrum and volume averaging, were compared to assess the quality of the OCTA vascular images. All data were acquired using a swept-source OCT system at 1040 nm central wavelength, operating at 100,000 A-scans/s. We performed a quantitative comparison using a contrast-to-noise (CNR) metric to assess the capability of the three methods to visualize the choriocapillaris layer. For evaluation of the static tissue noise suppression in OCTA images we proposed to calculate CNR between the photoreceptor/RPE complex and the choriocapillaris layer. Finally, we demonstrated that implementation of intensity-based OCT imaging and OCT angiography methods allows for visualization of retinal and choroidal vascular layers known from anatomic studies in retinal preparations. OCT projection imaging of data flattened to selected retinal layers was implemented to visualize retinal and choroidal vasculature. User guided vessel tracing was applied to segment the retinal vasculature. The results were visualized in a form of a skeletonized 3D model.

Improving our understanding of brain function requires novel tools to observe multiple physiological parameters with high resolution in vivo. We have developed a multimodal imaging system for investigating multiple facets of cerebral blood flow and metabolism in small animals. The system was custom designed and features multiple optical imaging capabilities, including 2-photon and confocal lifetime microscopy, optical coherence tomography, laser speckle imaging, and optical intrinsic signal imaging. Here, we provide details of the system's design and present in vivo observations of multiple metrics of cerebral oxygen delivery and energy metabolism, including oxygen partial pressure, microvascular blood flow, and NADH autofluorescence.

Author Manuscript 2011 February 1., Purpose: The purpose of this study was to report normal macular thickness measurements and assess reproducibility of retinal thickness measurements acquired by a time-domain optical coherence tomography (OCT) (Stratus, Carl Zeiss Meditec, Inc., Dublin, CA) and three commercially available spectral/Fourier domain OCT instruments (Cirrus HD-OCT, Carl Zeiss Meditec, Inc.; RTVue-100, Optovue, Inc., Fremont, CA; 3D OCT-1000, Topcon, Inc., Paramus, NJ). Methods: Forty randomly selected eyes of 40 normal, healthy volunteers were imaged. Subjects were scanned twice during 1 visit and a subset of 25 was scanned again within 8 weeks. Retinal thickness measurements were automatically generated by OCT software and recorded after manual correction. Regression and Bland-Altman plots were used to compare agreement between instruments. Reproducibility was analyzed by using intraclass correlation coefficients, and incidence of artifacts was determined. Results: Macular thickness measurements were found to have high reproducibility across all instruments with intraclass correlation coefficients values ranging 84.8% to 94.9% for Stratus OCT, 92.6% to 97.3% for Cirrus Cube, 76.4% to 93.7% for RTVue MM5, 61.1% to 96.8% for MM6, 93.1% to 97.9% for 3D OCT-1000 radial, and 31.5% to 97.5% for 3D macular scans. Incidence of artifacts was higher in spectral/Fourier domain instruments, ranging from 28.75% to 53.16%, compared with 17.46% in Stratus OCT. No significant age or sex trends were found in the measurements. Conclusion: Commercial spectral/Fourier domain OCT instruments provide higher speed and axial resolution than the Stratus OCT, although they vary greatly in scanning protocols and are currently limited in their analysis functions. Further development of segmentation algorithms and quantitative features are needed to assist clinicians in objective use of these newer instruments to manage diseases., National Institutes of Health (U.S.) (Contract RO1-EY11289-23), National Institutes of Health (U.S.) (Contract R01-EY13178-07), National Institutes of Health (U.S.) (Contract P30-EY008098), United States. Air Force Office of Scientific Research (FA9550-07-1-0101), United States. Air Force Office of Scientific Research (FA9550-07-1-0014)

Objective To evaluate intraretinal anatomy in patients with exudative age-related macular degeneration (AMD) using high-speed ultrahigh resolution optical coherence tomography (hsUHR-OCT) before and 1 month after intravitreal injection of ranibizumab. Design Retrospective case series. Participants Twelve eyes of 12 patients. Methods A broad bandwidth superluminescent diode laser light source and spectral/Fourier domain signal detection were used to create a prototype hsUHR-OCT instrument with 3.5 μm axial image resolution and approximately 25,000 lines/second acquisition speed. Twelve eyes of 12 patients with exudative AMD were imaged with hsUHR-OCT before and 1 month after intravitreal ranibizumab injection. High pixel density and raster-scanned 3-dimensional (3D) OCT data sets were generated. Three-dimensional imaging software was used to calculate subretinal/retinal pigment epithelium fluid volume and volume of the fibrovascular lesion. Main Outcome Measures Qualitative and quantitative analysis of hsUHR-OCT images and 3D data sets. Results All eyes had some degree of normalization of macular contour after intravitreal ranibizumab. The inner/outer photoreceptor segment junction visualized on hsUHR-OCT was discontinuous, overlying the fibrovascular lesion in all 12 of 12 eyes both before and after treatment; 9 of 12 eyes had focal areas of thinning of the outer nuclear layer, which remained after treatment. Volumetric measurements were possible in 8 of 12 eyes with 3D-rendering software. Fibrovascular lesion volume did not change significantly after treatment. Conclusions hsUHR-OCT is capable of unprecedented imaging speed and resolution, making it a valuable instrument in measuring in vivo intraretinal pathology. All 12 eyes had some normalization of macular contour. Fibrovascular lesion volume did not change significantly 1 month after treatment, suggesting that ranibizumab does not cause much initial regression of preexisting neovascular tissue. Photoreceptor abnormalities remained in all patients after treatment of wet AMD, suggesting that although ranibizumab improves overall retinal architecture, some photoreceptor damage may be irreversible. Financial Disclosure(s) Proprietary or commercial disclosure may be found after the references.

Aims: To demonstrate ultrahigh-resolution, three-dimensional optical coherence tomography (3D-OCT) and projection OCT fundus imaging for enhanced visualisation of outer retinal pathology in non-exudative age-related macular degeneration (AMD). Methods: A high-speed, 3.5 μm resolution OCT prototype instrument was developed for the ophthalmic clinic. Eighty-three patients with non-exudative AMD were imaged. Projection OCT fundus images were generated from 3D-OCT data by selectively summing different retinal depth levels. Results were compared with standard ophthalmic examination, including fundus photography and fluorescein angiography, when indicated. Results: Projection OCT fundus imaging enhanced the visualisation of outer retinal pathology in non-exudative AMD. Different types of drusen exhibited distinct features in projection OCT images. Photoreceptor disruption was indicated by loss of the photoreceptor inner/outer segment (IS/OS) boundary and external limiting membrane (ELM). RPE atrophy can be assessed using choroid-level projection OCT images. Conclusions: Projection OCT fundus imaging facilities rapid interpretation of large 3D-OCT data sets. Projection OCT enhances contrast and visualises outer retinal pathology not visible with standard fundus imaging or OCT fundus imaging. Projection OCT fundus images enable registration with standard ophthalmic diagnostics and cross-sectional OCT images. Outer retinal alterations can be assessed and drusen morphology, photoreceptor impairment and pigmentary abnormalities identified.

A 42-year-old man with Hunter syndrome developed bilateral visual field loss. Visual field testing demonstrated bilateral ring scotomata that corresponded to areas of thinning seen on standard resolution optical coherence tomography. High-speed, ultrahigh resolution optical coherence tomography, capable of 3.5-micron axial resolution, showed a loss of photoreceptors outside the fovea and cystoid spaces within the inner nuclear, ganglion cell, and outer nuclear layers. These results were consistent with histopathologic features that have been reported previously in patients with Hunter syndrome. Optical coherence tomography could be used as a diagnostic modality to monitor patients with Hunter syndrome and to detect subclinical forms of disease. [Ophthalmic Surg Lasers Imaging 2007;38:423-428.] AUTHORS From New England Eye Center (MKY, RWC, TRH, IG, MW, JSD), Tufts-New England Medical Center, Tufts University, Boston, Massachusetts; the Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics (VJS, IG, JGF, MW), Massachusetts Institute of Technology, Cambridge, Massachusetts; and UPMC Eye Center and the Eye and Ear Institute (JSS), Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania Accepted for publication April 20, 2007. Supported in part by National Institutes of Health RO1-EY13178-06, RO1-EY11289-20, P30-EY08098, P30-EY13078, Air Force Office of Scientific Research, Medical Free Electron Laser Program contract FA9550-040- 1-0046, FA9550-040-1-0011, National Science Foundation ECS-0119452, BES-0522845, The Eye and Ear Foundation (Pittsburgh, PA), and Research to Prevent Blindness Unrestricted Grant and Medical Student Eye Research Fellowship. Drs. Fujimoto and Schuman receive royalties from intellectual property licensed by the Massachusetts Institute of Technology to Carl Zeiss Meditec, and Drs. Duker and Schuman receive research support from Optovue, Inc. Dr. Schuman also receives research support from Alcon Laboratories, Inc., Allergan, Inc., SOLX, and Clarity, and receives lecture fees from Alcon Laboratories, Inc., Allergan, Inc., Carl Zeiss Meditec, Merck U.S. Human Health, the National Eye Institute, Heidelberg Engineering, Inc., and Optovue, Inc. Dr. Schuman did not participate in the editorial review of this manuscript. Address correspondence to Thomas R. Hedges III, MD, Ophthalmology Department, Tufts-New England Medical Center, 750 Washington Street, Boston, MA 02111.

We tested and compared the capability of multiple optical coherence tomography (OCT) angiography methods: phase variance, amplitude decorrelation and speckle variance, with application of the split spectrum technique, to image the choroiretinal complex of the human eye. To test the possibility of OCT imaging stability improvement we utilized a real-time tracking scanning laser ophthalmoscopy (TSLO) system combined with a swept source OCT setup. In addition, we implemented a post- processing volume averaging method for improved angiographic image quality and reduction of motion artifacts. The OCT system operated at the central wavelength of 1040nm to enable sufficient depth penetration into the choroid. Imaging was performed in the eyes of healthy volunteers and patients diagnosed with age-related macular degeneration.

OCT angiography methods: speckle variance, amplitude decorrelation and phase variance will be compared in imaging of the human choroid. Application of split spectrum and volume averaging techniques will be demonstrated with swept source OCT data.

Purpose: Spectral optical coherence tomography (SOCT) is a new non-invasive, non-contact, high-resolution technique, which provides cross-sectional images of objects that weakly absorb and scatter light. The aim of this article is to demonstrate the application of SOCT to imaging of eyes fitted with contact lenses. Methods: Nine eyes of six different subjects fitted with various contact lenses have been examined with a slit-lamp and a prototype SOCT instrument. Results: Our SOCT system provides high-resolution (4–6 μm longitudinal, 10 μm transversal) tomograms composed of 3000–5000 A-scans with acquisition time of 100–250 ms. The quality of the images is adequate for detailed evaluation of contact lens fit. Design, shape and lens edge position were assessed, and complications of contact lens wear could be visualized. Thickness of the lens, corneal epithelium and stroma as well as the space between the lens and the eye surface have been measured. Conclusions: SOCT allows high-resolution, cross-sectional visualization of the eye fitted with a contact lens. The ability to carry out a detailed evaluation of the fitting relationship between the lens and the ocular surface might be useful in research and optometric practice. SOCT can also be helpful in diagnosis, evaluation and documentation of contact lens complications.

In this contribution we examine a methodology to avoid parasitic cross-correlation terms in spectral optical coherence tomography (SOCT) images. The optimal conditions of optical power and exposure time are found theoretically and confirmed experimentally to ensure that parasitic images are hidden under the shot noise. An upper limit on useful exposures may then be estimated. In a case of SOCT imaging of the retina this limit is below the ANSI safety limit.

Complex Spectral domain Optical Coherence Tomography (CSdOCT) increases twice the depth of imaging in comparison with SdOCT by suppressing one of the mirror images. We present a new method of data processing, which further reduces the residual mirror images in CSdOCT. The method takes into account object movements, always present in experiments in vivo, which introduce unpredictable phase shifts. The method is free of polychromatic phase error originating from the wavelength dependence of the phase shift introduced by the reference mirror translation. Tomograms of the anterior chamber of the human eye in vivo are chosen to demonstrate a potential of the technique.

We present a high-resolution spectral domain optical coherence tomography (SDOCT) device with a broad-band supercontinuum light generated in a photonic crystal fiber. The instrument we have developed has an axial resolution of 4 μm in air, a depth of image of 1 mm, and an exposure time of 128 μs per a single A-scan. We adopt and apply two methods for data analysis, which reduce the effects of a strong modulation and temporal fluctuations exhibited by the spectra of supercontinuum. To demonstrate the potential of the methods we show high-resolution SDOCT cross sectional images of the human cornea and retina in vivo.

Purpose To present a novel method for noninvasive visualization of 3D retinal microcapillary network (RMN) using optical coherence tomography (OCT) reflectivity maps and to validate its clinical usefulness in vascular retinal diseases. Methods OCT imaging was applied to 43 patients with diabetic retinopathy, CRVO, BRVO and in 13 healthy subjects. OCT maps of RMN from different retinal layers were reconstructed and compared with fluorescein angiography. Results OCT showed the RMN of 20 microns in diameter, revealed vascular nonperfusion and identified microexudates that were not visible on clinical examination and fundus photography. Conclusion OCT is capable to precisely detect the RMN and can be used for noninvasive diagnosis and monitoring of early stages of retinal vascular diseases.

We show results of a project which focuses on detection of activity in neural tissue with Optical Coherence Tomography (OCT) methods. Experiments were performed in neural cords dissected from the American cockroach (Periplaneta americana L.). Functional OCT imaging was performed with ultrahigh resolution spectral / Fourier domain OCT system (axial resolution 2.5 μm). Electrical stimulation (voltage pulses) was applied to the sensory cercal nerve of the neural cord. Optical detection of functional activation of the sample was performed in the connective between the terminal abdominal ganglion and the fifth abdominal ganglion. Functional OCT data were collected over time with the OCT beam illuminating selected single point in the connectives (i.e. OCT M-scans were acquired). Phase changes of the OCT signal were analyzed to visualize occurrence of activation in the neural cord. Electrophysiology recordings (microelectrode method) were also performed as a reference method to demonstrate electrical response of the sample to stimulation.

In this report the application of graphics processing unit (GPU) programming for real-time 3D Fourier domain Optical Coherence Tomography (FdOCT) imaging with implementation of Doppler algorithms for visualization of the flows in capillary vessels is presented. Generally, the time of the data processing of the FdOCT data on the main processor of the computer (CPU) constitute a main limitation for real-time imaging. Employing additional algorithms, such as Doppler OCT analysis, makes this processing even more time consuming. Lately developed GPUs, which offers a very high computational power, give a solution to this problem. Taking advantages of them for massively parallel data processing, allow for real-time imaging in FdOCT. The presented software for structural and Doppler OCT allow for the whole processing with visualization of 2D data consisting of 2000 A-scans generated from 2048 pixels spectra with frame rate about 120 fps. The 3D imaging in the same mode of the volume data build of 220 × 100 A-scans is performed at a rate of about 8 frames per second. In this paper a software architecture, organization of the threads and optimization applied is shown. For illustration the screen shots recorded during real time imaging of the phantom (homogeneous water solution of Intralipid in glass capillary) and the human eye in-vivo is presented.

The authors present the application of graphics processing unit (GPU) programming for real-time three-dimensional (3-D) Fourier domain optical coherence tomography (FdOCT) imaging with implementation of flow visualization algorithms. One of the limitations of FdOCT is data processing time, which is generally longer than data acquisition time. Utilizing additional algorithms, such as Doppler analysis, further increases computation time. The general purpose computing on GPU (GPGPU) has been used successfully for structural OCT imaging, but real-time 3-D imaging of flows has so far not been presented. We have developed software for structural and Doppler OCT processing capable of visualization of two-dimensional (2-D) data (2000 A-scans, 2048 pixels per spectrum) with an image refresh rate higher than 120 Hz. The 3-D imaging of 100×100 A-scans data is performed at a rate of about 9 volumes per second. We describe the software architecture, organization of threads, and optimization. Screen shots recorded during real-time imaging of a flow phantom and the human eye are presented.

We propose two independent OCT data processing methods allowing visualization and analysis of the blood flow. These methods utilize variations in the OCT intensity images caused by flowing blood. The first method calculates standard deviation of intensity to generate retinal OCT angiograms. We present algorithm of this method and results of application for visualization of the microvasculature in the macular area of the human eye in vivo. The second method calculates cross power spectra of the volumetric intensity images to assess blood flow velocity in three dimensions. Validation of this method for OCT imaging was performed in a flow phantom.

Although the Doppler Optical Coherence Tomography techniques have already enabled imaging of blood flow in large vessels in biological tissues, the generation of velocity maps of the capillary network is still a challenge. Since several important physiological and pathological phenomena occur in the microcirculation, the possibility of flow imaging and velocity assessment in microcapillaries may be important for medical diagnostics. Understanding of the origin of the Doppler signal in capillary vessels and limitations of such measurements is essential for further development of Doppler OCT methods. In the OCT flow maps of a microcapillary network randomly varying Doppler signals are observed. To answer the question how accurate is the Doppler OCT flow measurement for blood motion in small vessels, we have investigated the possibility to obtain velocity profiles of blood in vitro in well controlled experimental configuration. We have used a rectangular microchannel (100 μm wide, 40 μm deep) as a microcapillary phantom. Imaging was performed with a Fourier domain OCT setup with a CMOS camera. Data analysis was performed using joint Spectral and Time Domain OCT method (STdOCT).

Spectral and Time domain OCT (STdOCT) is a data analysis scheme proposed for sensitive Doppler imaging. In this work we show that it has an additional feature: when compared to those created using complex or amplitude averaging, tomograms prepared using STdOCT have the highest contrast to noise ratio and preserve high signal to noise ratio and image dynamic range. Images of uniformly scattering phantom as well as images of human retina in vivo prepared with three different techniques are shown.

In this pilot study we demonstrate results of structural Fourier domain OCT imaging of the nervous system of Periplaneta americana L. (American cockroach). The purpose of this research is to develop an OCT apparatus enabling structural imaging of insect neural system. Secondary purpose of the presented research is to develop methods of the sample preparation and handling during the OCT imaging experiments. We have performed imaging in the abdominal nerve cord excised from the American cockroach. For this purpose we have developed a Fourier domain / spectral OCT system operating at 820 nm wavelength range.

Recently introduced smart scanning protocols called segmented protocols offer possibility to create Spectral Optical Coherence Tomography images with strongly reduced speckle contrast. The algorithm is fast, robust and gives cross-sectional images with preserved high lateral resolution. To obtain efficient speckle reduction only slight modification to the optical setup is required. Cross-sectional images of anterior and posterior parts of the human eye with reduced speckle noise are presented.

Purpose—To report on a posterior segment coloboma manifesting unusual morphology as determined by high-speed, ultrahigh resolution optical coherence tomography imaging (hsUHROCT). Methods—A 47-year-old patient with bilateral colobomas was evaluated via fundus examination and hsUHR-OCT. Results—Imaging with hsUHR-OCT showed intact retinal pigment epithelium (RPE) within the posterior segment coloboma. Most of the retinal layers appeared to continue into the coloboma, although they exhibited slight attenuation. The external limiting membrane (ELM) was clearly visible continuing within the coloboma, suggesting that Muller cells and the inner segments of the photoreceptors were still present in this area. The junction between the inner and outer segments of the photoreceptors ended at the margin of the coloboma, which may be due to either photoreceptor disruption or a change in the orientation of the outer segments. Conclusion—hsUHR-OCT demonstrated the presence of Muller cells and photoreceptor inner segments within a posterior segment coloboma. The retinal pigment epithelium (RPE) was intact within the coloboma, representing an unusual morphology., National Institutes of Health (U.S.) (Grant R01-EY11289-21), United States. Air Force Office of Scientific Research (Contract FA9550-07-1-0101)

Measuring cerebral oxygen delivery and metabolism microscopically is important for interpreting macroscopic functional magnetic resonance imaging (fMRI) data and identifying pathological changes associated with stroke, Alzheimer's disease, and brain injury. Here, we present simultaneous, microscopic measurements of cerebral blood flow (CBF) and oxygen partial pressure (pO2) in cortical microvessels of anesthetized rats under baseline conditions and during somatosensory stimulation. Using a custom-built imaging system, we measured CBF with Fourier-domain optical coherence tomography (OCT), and vascular pO2 with confocal phosphorescence lifetime microscopy. Cerebral blood flow and pO2 measurements displayed heterogeneity over distances irresolvable with fMRI and positron emission tomography. Baseline measurements indicate O2 extraction from pial arterioles and homogeneity of ascending venule pO2 despite large variation in microvessel flows. Oxygen extraction is linearly related to flow in ascending venules, suggesting that flow in ascending venules closely matches oxygen demand of the drained territory. Oxygen partial pressure and relative CBF transients during somatosensory stimulation further indicate arteriolar O2 extraction and suggest that arterioles contribute to the fMRI blood oxygen level dependent response. Understanding O2 supply on a microscopic level will yield better insight into brain function and the underlying mechanisms of various neuropathologies.

The performance and imaging characteristics of ultrahigh speed ophthalmic optical coherence tomography (OCT)are investigated. In vivo imaging results are obtained at 850nm and 1050nm using dierent con“gurations ofspectral and swept source / Fourier domain OCT. A spectral / Fourier domain instrument using a high speedCMOS linescan camera with SLD light source centered at 850nm achieves speeds of 91,000 axial scans per secondwith 3um axial resolution in tissue. A spectral / Fourier domain instrument using an InGaAs linescan camerawith SLD light source centered at 1050nm achieves 47,000 axial scans per second with 7um resolution in tissue.A swept source instrument using a novel wavelength swept laser light source centered at 1050nm achieves 100,000axial scans per second. Retinal diseases seen in the clinical setting are imaged using the 91kHz 850nm CMOScamera and 47kHz 1050nm InGaAs camera based instruments to investigate the combined eects of varyingspeed, axial resolution, center wavelength, and ins trument sensitivity on image quality. The novel 1050nm sweptsource / Fourier domain instrument using a recently developed commercially available short cavity laser sourceimages at 100,000 axial scans per second and is demonstrated in the normal retina. The dense 3D volumetricdata sets obtained with ultrahigh speed OCT promise to improve reproducibility of quantitative measurements,enabling early diagnosis as well as more sensitive assessment of disease progression and response to therapy.Keywords: Ultrahigh Speed Optical Coherence Tomography; Spectral and Swept Source / Fourier DomainOCT; Ophthalmology; Retina, Fovea and Optic Nerve Head; Medical and biological imaging.

We present an application of the Joint Spectral and Time domain OCT (STdOCT) method for detection of wide range of flows in the retinal vessels. We utilized spectral/Fourier domain OCT (SOCT) technique for development of scan protocols for Doppler signal analysis. We performed retinal imaging in normal eyes using ultrahigh speed (200 000 axial scans/s) SOCT instrument with a CMOS camera. Various raster scan protocols were implemented for investigation of blood flow in the retina. Data analysis was performed using the method of joint Spectral and Time domain OCT (STdOCT). Detection of blood flow velocities ranging from several tens of mm/s to a fraction of mm/s was possible with scanning methods allowing for appropriate selection of time intervals between data taken for Doppler OCT analysis. Axial blood flow velocity measurement was possible in retinal vessels. Doppler OCT signal can be utilized as a contrast mechanism for visualization of retinal capillaries.

Advanced Imaging Group, Thorlabs, Inc., Newton, NJ ABSTRACT We performed OCT imaging of the rat retin a at 70,000 axial scans per second with ~3 m axial resolution. Three-dimensional OCT (3D-OCT) data sets of the rat retina were acquired. The high speed and high density data sets enable improved en face visualization by reducing eye moti on artifacts and improve Doppler OCT measurements. Minimal motion artifacts were visible and the OCT fundus images offer more precise registration of individual OCT images to retinal fundus features. Projection OCT fundus images show features such as the nerve fiber layer, retinal capillary networks and choroidal vasculature. Doppler OCT images and quantitative measurements show pulsatility in retinal blood vessels. Doppler OCT provides non-invasive in vivo quantitative measurements of retinal blood flow properties and may benefit studies of diseases such as glaucoma and diabetic retinopathy. Ultrahigh speed imaging using ultrahigh resolution spectral / Fourier domain OCT promises to enable novel protocols for measuring small animal retinal structure and retinal blood flow. This non-invasive imaging technology is a promising tool for monitoring disease progression in rat and mouse models to assess ocul ar disease pathogenesis and response to treatment. Keywords: Ultrahigh resolution OCT, ultrahigh speed OCT, spectral/Fourier domain OCT, Doppler OCT, small animal imaging * liujj@mit.edu; phone 1 617 253-8140; fa x 1 617 253-9611; www.rle.mit.edu

Absolute measurements of cerebral blood flow (CBF) are an important endpoint in studies of cerebral pathophysiology. Currently no accepted method exists for in vivo longitudinal monitoring of CBF with high resolution in rats and mice. Using three-dimensional Doppler Optical Coherence Tomography and cranial window preparations, we present methods and algorithms for regional CBF measurements in the rat cortex. Towards this end, we develop and validate a quantitative statistical model to describe the effect of static tissue on velocity sensitivity. This model is used to design scanning protocols and algorithms for sensitive 3D flow measurements and angiography of the cortex. We also introduce a method of absolute flow calculation that does not require explicit knowledge of vessel angles. We show that OCT estimates of absolute CBF values in rats agree with prior measures by autoradiography, suggesting that Doppler OCT can perform absolute flow measurements in animal models., National Institutes of Health (U.S.) (Grant number R01-NS057476), National Institutes of Health (U.S.) (Grant number P01NS055104), National Institutes of Health (U.S.) (Grant number P50NS010828), ational Institutes of Health (U.S.) (Grant number K99NS067050), National Institutes of Health (U.S.) (Grant number R01-CA075289-13), United States. Air Force Office of Scientific Research (FA9550-07-1-0014), United States. Dept. of Defense. Medical Free Electron Laser Program (FA9550-07-1-0101)

We present the analysis of the accuracy of velocity measurement by means of joint Spectral and Time domain Optical Coherence Tomography (STdOCT) method. Additionally, we determine the minimum detectable velocity.

We describe depth-resolved microscopy of cortical hemodynamics with high-speed spectral/Fourier domain optical coherence tomography (OCT). Stimulus-evoked changes in blood vessel diameter, flow, and total hemoglobin were measured in the rat somatosensory cortex. The results show OCT measurements of hemodynamic changes during functional activation and represent an important step toward understanding functional hyperemia at the microscopic level., National Institutes of Health (U.S.) (R01-NS057476), National Institutes of Health (U.S.) (P01NS055104), National Institutes of Health (U.S.) (P50NS010828), National Institutes of Health (U.S.) (K99NS067050), National Institutes of Health (U.S.) (R01-CA075289-12), United States. Air Force Office of Scientific Research (FA9550-07-1-0014), United States. Dept. of Defense. Medical Free Electron Laser Program (FA9550-07-1-0101)

Purpose— To describe ocular findings for a 34-year-old man with chronic solar retinopathy usinghigh-speed ultrahigh-resolution (UHR) optical coherence tomography (OCT). Methods— Fundus photography, fluorescein angiography, and Stratus OCT (Carl Zeiss Meditec,Inc., Dublin, CA) were performed. A high-speed UHR OCT prototype developed in ourophthalmology clinic was used to obtain detailed images of the retina. Patients— Two eyes of one patient with chronic solar retinopathy were studied. Results— Both Stratus OCT and high-speed UHR OCT demonstrated foveal thinning bilaterally.In addition, high-speed UHR OCT showed distinct hyporeflective disruptions in the photoreceptorinner segment/outer segment junction and photoreceptor outer segments bilaterally. En face OCTimages from three-dimensional OCT data sets revealed hyporeflective regions of photoreceptoratrophy in the outer retina. Conclusions— High-speed UHR OCT showed more detail than standard OCT, and findings wereconsistent with histopathologic and ultrastructural features that have been reported previously. Solarretinopathy should be studied further with high-speed UHR OCT to determine the short- and long-term effects of solar radiation damage.

Ultrahigh speed Spectral/Fourier domain ophthalmic OCT imaging at 70,000–312,500 axial scans per second is demonstrated using a high speed CMOS camera at 800 nm. Comparative imaging results of the fovea illustrate the performance tradeoffs between different imaging speeds and spectrometer configurations. Dense 3D volumetric acquisitions show minimal motion artifacts when acquired at 250,000 axial scans per second. The porous structure of the lamina cribrosa is shown in en face images extracted from a dense volumetric acquisition of the optical nerve head acquired at 106, 382 axial scans per second. Rapid repeated volume imaging (4D-OCT) shows blood flow in retinal capillaries. Boundaries of the capillary network are enhanced by motion contrast. 3D volumetric data acquired at 49,000 axial scans per second using an InGaAs camera at 1050 nm is compared to volumetric data acquired at 101, 010 axial scans per second using a CMOS camera at 800nm. Averaging of adjacent cross sectional scans in the volume is shown to increase contrast in the images and reduce speckle. The enhanced penetration of the 1050 nm compared to the 800 nm OCT imaging system is shown. Dense 2D/3D data sets and 4D-OCT repeated volume imaging promise alternative methods for diagnosis and monitoring of disease.

Ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) using a CMOS line scan camera with image acquisition rates of 70,000 - 312,500 axial scans per second is investigated. Several design configurations are presented to illustrate design trade-offs between acquisition speed, sensitivity, resolution and sensitivity roll-off performance. We demonstrate: extended imaging range and improved sensitivity roll-off at 70,000 axial scans per second with 4096 camera pixels, high speed and ultrahigh resolution imaging at 106,382 axial scans per second, and ultrahigh speed imaging at 250,000-312,500 axial scans per second. Each configuration is characterized through optical testing and the trade-offs demonstrated with in vivo imaging of the fovea and optic disk in the human retina. We show dense homogeneous 3D-OCT volumetric data sets that were acquired by raster scanning at 250,000 axial scans per second, which is an order of magnitude faster than most current generation spectral / Fourier OCT instruments. OCT fundus images constructed from the 3D-OCT data have no noticeable discontinuity of retinal features and show that there are minimal motion artifacts. Using an improved sensitivity roll-off configuration at 70,000 axial scans per second, long cross sectional scans are acquired at high resolution for imaging large areas of the retina, including the fovea and optic disk. Using an ultrahigh speed configuration at 250,000 axial scans per second, the fine porous structures of the lamina cribrosa can be seen from slices extracted from a dense 3D data set. Rapid repeated imaging of a small volume (4D-OCT) enables time resolved visualization of the capillary network surrounding the INL and may show individual red blood cells. This capability could create the possibility for alternative techniques for quantifying capillary blood flow, which cannot be measured with Doppler OCT methods because of the capillary’s perpendicular orientation to the optical beam. The results of this study suggest that high speed CMOS cameras can achieve a significant improvement in performance for ophthalmic imaging. This promises to have a powerful impact in clinical applications by improving early diagnosis, reproducibility of quantitative measurements and enabling more sensitive assessment of disease progression or response to therapy.

Fourier domain mode locking (FDML) in the 1070 nm wavelength range is investigated. Problems, design rules and the performance of an FDML laser with a dispersive cavity are discussed. Retinal OCT imaging at 236 kHz is demonstrated.

Purpose To demonstrate applicability of high speed spectral optical coherence tomography (SOCT) method for imaging retinal pathologies in clinical conditions. Methods SOCT was performed in 67 eyes with different macular diseases. Examinations were carried out with the prototype SOCT instrument constructed in the Institute of Physics, Nicolaus Copernicus University, Toruń, Poland. A broadband superluminescent diode was used as a light source. Results The disturbances of retinal layer structure concerning mainly outer segments of photoreceptors were observed in case of central serous chorioretinopathy and choroidal neovascularization in age-related macular degeneration. Large drusen were often related to significant changes of outer nuclear layer thickness and reflectivity. Conclusions SOCT detects small disturbances of the retinal structure and helps to precisely determine layers involved in different pathologies. (Eur J Ophthalmol 2007; 17: 238–45)

High-speed, high-resolution optical coherence tomography (OCT) imaging of the human retina is demonstrated using a frequency-swept laser at 850 nm. A compact external cavity semiconductor laser design, optimized for swept-source ophthalmic OCT, is described. The laser enables an effective 16 kHz sweep rate with >10 mm coherence length and a tuning range of approximately 35 nm full width at half-maximum, yielding an axial resolution of