The aim of this article is to demonstrate an application of Spectral Optical Coherence Tomography SOCT for visualization of the anterior segment of the human eye. A SOCT system with an axial resolution of 4-6 μm and a lateral one of 10 μm provides tomograms composed of 3000 - 5000 A-scans when a total acquisition time of 100-250 ms is used to acquire tomograms. The quality of the images is adequate for detailed evaluation of the corneal structure and contact lens fit. Erosion of the epithelium, scars and lesions may be precisely localized. The design, shape and edge position of the contact lens, as well as other fitting relationships between the lens and the ocular surface, may be accurately assessed. The information provided by SOCT may be helpful in diagnosis, evaluation and documentation of corneal pathologies and contact lens complications.

This paper gives a description of the use of Optical Coherence Tomography to localize the Ex-PRESS^TM mini implant placed in the anterior segment of the eye. An OCT scanner, central wavelength 1280 nm, bandwidth 60 nm, resolution of 12 μm, was build onto a slitlamp to scan the anterior segment of the eye. Five ex-vivo porcine eyes received an Ex-Press implant, and were used as a model to visualize the position of the implant in the anterior segment. In the ex-vivo porcine eyes the OCT images showed the anatomy of the anterior segment in great detail. The anterior segment OCT was able to visualize the whole outline, and the position of the implant. The acquisition time of 0.8 sec is short enough to allow for scanning patients, and AS-OCT is expected to aid in providing answers to the question which parameters will determine the success or failure of such a device.

In vivo retinal imaging with ~ 8 μm axial resolution at 1030 nm is demonstrated for the first time, enabling enhanced penetration into the choroid. A new high power, broad bandwidth light source based on amplified spontaneous emission (NP Photonics, λ_c = 1030 nm, Δλ= 50 nm, P_out = 25 mW) has been interfaced to a time domain ophthalmic OCT system. In vivo retinal OCT tomograms performed at 800 nm are compared to those achieved at 1030 nm. Retinal OCT at longer wavelengths, e.g. 1030 nm significantly improves the visualization of the retinal pigment epithelium/choriocapillaris/choroid interface and might therefore provide new insight into choroidal/choriocapillary changes in age-related macular degeneration and other diseases of the retinal pigment epithelium (RPE)-choroid complex. 1030 nm OCT could also become a valuable tool in monitoring treatment effects on the choroids as in Verteporfin therapy.

We have combined Fourier-domain optical coherence tomography (OCT) with a closed-loop Adaptive Optics (AO) system. The AO-OCT instrument has been used for in vivo retinal imaging. High-lateral resolution of our AO-OCT system allows visualization of the microscopic retinal structures not accessible by standard OCT instruments.

In this contribution we demonstrate comparison between two high speed Spectral OCT instruments with different axial and identical transverse resolutions used for imaging of various retinal pathologies. Cross-sectional OCT images of higher axial resolution enable improved visualization of small focal lesions in the retina, which can be missed in standard resolution OCT measurements. Optimal parameters of SOCT clinical systems are discussed. We compare cross-sectional images of selected clinical cases of advanced retinal pathologies obtained with both instrument.

The clinical feasibility of three-dimensional (3D) ultrahigh resolution (UHR) optical coherence tomography (OCT) has been investigated to visualize macular pathologies in more than 140 eyes. Three-dimensional retinal imaging was performed with high axial resolution of 3 μm employing a compact, commercially available ultrabroad bandwidth (160 nm) Titanium: sapphire laser at video-rate with up to 50 B-scans/second, each tomogram consisting of 512x1024 pixels, resulting in 25 Megavoxels/second. 3D UHR OCT allows identifying the contour of the hyaloid membrane, epiretinal membranes, inner limiting membrane, the topography of tractive forces from the retinal surface down to the level of the photoreceptor segments. Photoreceptor inner and outer segments are clearly delineated in configuration and size in micrometer with a characteristic peak in the subfoveal area. The pattern of the retinal vasculature is distinctly recognized by the hyperreflectivity of the vascular walls and the resulting reflectance shadow exhibiting a three-dimensional angiographic image of the entire vascular net without the use of fluorescent markers. 3D UHR OCT offers unprecedented, realistic threedimensional imaging of pathologies at all epi-, intra- and subretinal levels. Ultrastructural changes are identified and displayed using a dynamic video technique.

Two novel high-brightness broadband light sources based on quantum-well superluminescent diodes for optical coherence tomography and other applications with record CW output power and spectral bandwidth are described.

Despite many efforts, some tissue changes, associated with diseases such as cancer, remain beyond the detection limit of OCT. A technique which would allow extraction of information regarding these unresolvable features from the OCT signal could prove a very powerful diagnostic tool. This manuscript presents such a procedure. It begins with the separation of the signal in resolvable and unresolvable components using wavelet decomposition. Subsequently, the power spectral density of the unresolvable part is determined with autoregressive spectral estimation. Statistical analysis is then employed to extract information regarding the uresolvable, but diagnostically significant, scatterers in tissue. These characteristics could considerably improve the clinical utility of OCT.

A method of lateral superresolution for Fourier domain optical coherence tomography is presented. This method consists of intentional defocus and its numerical compensation using a spatial frequency- phase filter. The designing process of the phase filter is described, and the superresolution effect is discussed theoretically. Experimental results of knife-edge test prove that the frequency filter enhances the lateral resolution better than a trans-form limited resolution.

Optical Doppler tomography (ODT) combines Doppler velocimetry and optical coherence tomography (OCT) to obtain high-resolution cross-sectional imaging of particle flow velocity in scattering media such as the human retina and skin. Here, we present the results of a theoretical analysis of ODT where multiple scattering effects are included. The purpose of this analysis is to determine how multiple scattering affects the estimation of the depth-resolved localized flow velocity. Depth-resolved velocity estimates are obtained directly from the corresponding mean or standard deviation of the observed Doppler frequency spectrum. Thus, in the present analysis, the dependence of the mean and standard deviation of the Doppler shift on the scattering properties of the flowing medium are obtained. Taking the multiple scattering effects into account, we are able to explain previous measurements of depth-resolved retinal flow profiles where the influence of multiple scattering was observed [Yazdanfar et al., Opt. Lett. 25, 1448 (2000)]. To the best of our knowledge, no analytical model exists that are able to explain these observations.

We investigate the effect of multiple scattering upon Doppler optical coherence tomography images of model blood vessels immersed in a fluuid with similar optical properties to those of the human dermis. Furthermore, we quantify the deviation of the acquired velocity profiles from that known to exist within the glass capillary at various depths within the scattering media. A flow phantom consisting of a glass tube containing whole blood flowing under laminar conditions submerged in a variable depth of Intralipid was used to simulate a blood vessel within the cutaneous microcirculation. Doppler optical coherence tomography images and velocity profiles of the tube acquired at various depths within the Intralipid are compared to those obtained from the same tube in a non-scattering media with the same refractive index.

Primarily, low-coherence interferometry yields the optical length, i. e. the product of sample length or sample depth data times the complementary sample refractive index. Each quantity, refractive index as well as sample depth can be obtained from the optical length if the complement is known. In a first step presented here, we use sample dispersion data for absolute depth or thickness measurement of dispersive samples. We shall discuss the physical implications and present preliminary results.

The ability to delineate structural information in medical images is important for accurate diagnoses and will often depend on how the image is presented. Various methods of signal and image processing have been explored to improve this process across a wide range of medical imaging techniques. We present the application of chromatic analysis, a measurement technique developed for colorimetry applications, for signal processing of optical coherence tomography (OCT) images in human tissue. In particular, specific characteristics in the optical signal relating to various structural features are identified using chromatic filters and this information is used to process the OCT image. The technique was developed using mathematically simulated OCT signals and the applied to experimental OCT images of human tissue biopsy samples of the oesophagus. In the processed images, reflecting surfaces are highlighted and background noise is reduced to improve image interpretation.

A new transmissive grating-based scanning delay-line for optical coherence tomography is proposed, with dispersion compensation capability. Compared to other spectral delay-lines, our implementation has less loss due to a halved number of diffraction grating reflections, and implements a walk off compensation scheme. The performance of the delay line is evaluated. The delay line transmissive geometry targets balance detection configurations.

We report on the use, in an Optical Coherence Tomography system, of a shaker with a frequency-modulated driving waveform to avoid non-linearities. The device permits to modulate the interferometric signal simply by the displacing the shaker and to recover the OCT signal in depth.

Two swept-wavelength light sources based on Ytterbium doped fibre amplifiers are demonstrated. The filtered output from a superfluorescent source is scanned over 20 nm, and used for topography with an axial resolution of <40 μm. Dynamic properties of a swept-wavelength YDFA based ring laser is investigated. This is the first reported results with dynamically swept sources centered in the 1 μm wavelength range, which is expected to be important for future development of optical coherence tomography systems for retinal imaging.

It is experimentally shown that a semiconductor optical amplifier (SOA) ensures a significant improvement of output characteristics of a superluminescent diode (SLD). Using SOA based on (InGa)PAs SC DH (central wavelength – 1300 nm) in MOPA system with SLD as a master oscillator a CW output power of 50 mw ex SM fiber was obtained. The same SOA used as a combiner of its own ASE and red-shifted input SLD light signal permits obtaining the output emission with linewidth near 70 nm.

Polarization-sensitive optical coherence tomography has been used to spatially map the birefringence of equine articular cartilage. Images obtained in the vicinity of visible osteoarthritic lesions display a characteristic disruption of the regular birefringence bands shown by normal cartilage. We also note that significant (e.g. ×2) variations in the apparent birefringence of samples taken from young (18 month) animals that otherwise appear visually homogeneous are found over spatial scales of a few millimeters. We suggest that whilst some of this variation may be due to changes in the intrinsic birefringence of the tissue, the 3-D orientation of the collagen fibers relative to the plane of the joint surface should also be taken into account. We propose a method based on multiple angles of illumination to determine the polar angle of the collagen fibers.

A great variety of tissues can be distinguished on the basis of its response to illumination with polarized light. In this study we used a phase resolved polarization sensitive optical coherence tomography (PS-OCT) system to investigate depolarization effects of different human tissues. The instrument which is based on a transversal scanning of the sample measures backscattered intensity, retardation and fast axis orientation, simultaneously. Skin, iris, and retina of healthy human volunteers were measured with our system. A depth resolution down to few micrometers could be achieved in skin and anterior eye segment. Different tissues could be classified into birefringent, polarization preserving and depolarizing tissue.

We developed a polarization sensitive spectral domain optical coherence tomography (PS-SD-OCT) system. To demonstrate the performance of our system we measured the distribution of retardation of a highly birefringent plastic sample. We recorded also images of intensity and retardation of the fovea region and the optic nerve head of a healthy volunteer.

A novel approach anticipates real time acquisition of spatially resolved polarization data to facilitate fast cross-sectional tracing collagen-related birefringence in skin down to reticular dermis, i.e. up to the depth of a few hundreds micrometers. It is based on a unique integration of a static-type interferometer in a time domain system intended for polarization-sensitive optical coherence tomography (PS-OCT). The design concept avoids any movable parts to evolve fringes over the traced depth, and exploits liquid crystal bistable switches to rapidly discriminate between orthogonal polarization components of the analyzable signal. The signal is transmitted through a polarization maintaining fiber and detected, by turns, in the single optical channel by the same line camera of appropriate format. The approach relies on the statements proven in the art. In particular, time-domain PS-OCT based on coherent detection of the fringe intensity in orthogonal polarization components of reflected signal allows identifying at least qualitatively collagen depletion regions in subsurface skin layers. Polarization state of light backscattered from sufficiently shallow depth in skin is defined mostly by linear birefringence of collagen fibers. Propagation of light in such linearly birefringent medium satisfies the reciprocity principle in optics.

Ovarian cancer is relatively rare but is the fifth leading cause of death from cancer in women. Little is known about the precursors and early stages of ovarian cancer partially due to the lack of a realistic animal model. A cohesive model that incorporates ovarian cancer induction into a menopausal rodent would be well suited for comprehensive studies of ovarian cancer, and non-destructive imaging would allow carcinogenesis to be followed. Optical Coherence Tomography (OCT) and Light-Induced Fluorescence (LIF) are minimally invasive optical modalities that allow both structural and biochemical changes to be noted. Rat ovaries were exposed to 4-vinylcyclohexene diepoxide (VCD) for 20 days in order to destroy the primordial follicles. Sutures coated with 7,12-dimethylbenz(a)anthracene (DMBA) were implanted in the right ovary, in order to produce epithelial based ovarian cancers. Rats were sacrificed at 1, 3, and 5 months and ovaries were harvested and imaged with a combined OCT/LIF system. Histology was preformed on the harvested ovaries and any pathology determined. OCT was able to visualize follicle loss and DMBA-induced abnormalities. LIF spectra were also different between cycling, follicle deplete, and DMBA-exposed ovaries. Overall this pilot study demonstrated the feasibility of both the animal model and optical imaging.

A compact common path Fourier domain optical coherence tomography (FD-OCT) system based on a broadband superluminescence diode is used for biomedical imaging. The epidermal thickening of human skin after exposure to ultraviolet radiation is measured to proof the feasibility of FD-OCT for future substitution of invasive biopsies in a long term study on natural UV skin protection. The FD-OCT system is also used for imaging lung parenchyma. FD-OCT images of a formalin fixated lung show the same alveolar structure as scanning electron microscopy images. In the ventilated and blood-free perfused isolated rabbit lung FD-OCT is used for real-time cross-sectional image capture of alveolar mechanics throughout tidal ventilation. The alveolar mechanics changing from alternating recruitment-derecruitment at zero positive end-expiratory pressure (PEEP) to persistent recruitment after applying a PEEP of 5 cm H₂O is observed in the OCT images.

Ultrahigh resolution OCT (UHR OCT) was performed on normal and pathologic human skin biopsies using an ultrabroad-bandwidth (260 nm) Titanium:sapphire laser, enabling sub-micrometer (0.9 μm) axial UHR OCT resolution. Penetration, image contrast as well as resolution capabilities achieved are analyzed for optimum UHR OCT in vivo performance. With the achieved resolution and the penetration depth, the transition between the dermis and the epidermis is clearly visible by UHR OCT, and also the anomalies of pathologies, which have been confirmed performing a comparison with histological analysis. Three dimensional UHR OCT of normal skin is demonstrated with less than 3 μm axial resolution at video-rate with up to 50 B-scans/second, each tomogram consisting of 512×1024 pixels, resulting in 25 Megavoxels/second.

We present pilot results in optical coherence tomography (OCT) visualization of normal mucosa radiation damage. 15 patients undergoing radiation treatment of head and neck cancer were enrolled. OCT was used to monitor the mucositis development during and after treatment. OCT can see stages of radiation mucositis development, including hidden ones, before any clinical manifestations.

We determined the scattering coefficient and scattering anisotropy of blood samples with varying hematocrit using optical coherence tomography measurements and a curve fitting procedure. Initial results show much lower scattering coefficient and scattering anisotropy than theoretically expected. Alternative fitting strategies will be explored.

Optical coherence tomography (OCT) has emerged as a powerful imaging tool for a variety of biomedical applications. Methods to enhance contrast in OCT images, including gold nanoshells, have been explored recently. Gold nanoshells are a novel type of nanoparticle composed of a silica core and a thin gold shell. By varying the relative dimensions of core and shell, the optical resonance of these nanoshells can be precisely and systematically varied over a broad wavelength region ranging from the near-UV to the mid-infrared. For this study, we designed and constructed nanoshells expected to have low absorption and high scattering for OCT at 1310 nm. We then conducted measurements to elucidate the effects of nanoshell core and shell size, nanoshell concentration, and tissue scattering coefficient on OCT image enhancement (i.e. intensity gain) by nanoshells. These measurements were performed with nanoshells suspended in water and in a variety of tissue phantoms. Increasing nanoshell core and shell size tends to increase the calculated backscattering coefficient, and thus increases OCT intensities by 2-7 dB in a tissue phantom with a biologically relevant scattering coefficient. Increasing nanoshell concentration also increases OCT intensities, however a minimum of 10⁹ nanoshells/mL is needed for appreciable enhancement in the tissue phantom. The intensity gain from one size of nanoshells varies between 5 and 9 dB depending on the scattering coefficient, with intensity gains decreasing as scattering increases. These results provide the first quantitative measurements of the effects of nanoshells to enhance OCT imaging at 1310 nm.

Optical coherence tomography (OCT) was used to determine optical properties of pelleted human fibroblasts in which necrosis or apoptosis was induced. We analyzed the OCT data including both the scattering properties of the medium and the axial point spread function of the OCT system. We measured that the optical attenuation coefficient in necrotic cells decreased from 2.2 ± 0.3 mm^-1 to 1.3 ± 0.6 mm^-1, whereas with the apoptotic cells a clear increase (up to 6.4 ± 1.7 mm^-1) in scattering was observed. The results on cultured cells a presented in this study indicate the ability of OCT to detect and differentiate between viable, apoptotic and necrotic cells based on their backscatter properties. This functional supplement to high-resolution OCT imaging can be of great clinical benefit, enabling on line monitoring of tissues, e.g. for feedback in cancer treatment.

Cell-based engineered tissue models have been increasingly useful in the field of tissue engineering, in in vitro drug screening systems, and in complex cell biology studies. While techniques for engineering tissue models have advanced, there have been few imaging technique capable of assessing the complex 3-D cell behaviors in real-time and at the depths that comprise thick tissues. Understanding cell behavior requires advanced imaging tools to progress from characterizing 2-D cell cultures to complex, highly-scattering, thick 3-D tissue constructs. In this study, we demonstrate that it is possible to use OCT to non-destructively evaluate dynamic cell behavior and function in a quantitative fashion in four dimensions (3-D space plus time). Dynamic processes including cell migration, proliferation, apoptosis, necrosis, and mechanical restructuring are observed during engineering tissue development. With high penetration depth and increased spatial and temporal resolution in 3-D space, OCT will be a useful tool for improving our understanding of cell dynamics in situ and in real-time, for elucidating the complex biological interactions, and for directing our designs toward functional and biomimetic engineered tissues.

Mouse models are increasingly important for studying human GI pathology. OCT provides minimally invasive, cross-sectional images that indicate the thickness and scattering density of underlying tissue. We have developed endoscopic ultrahigh resolution OCT (UHR-OCT) to imaging mouse colon in vivo. The reduced scale of the mouse colon makes tissue light penetration much less problematic, and high resolution acutely necessary. Higher lateral resolution requires a departure from the traditional cemented GRIN lens design. We support the need for better chromatic aberration than can be achieved by a GRIN lens using commercial raytracing software. We have designed and built a 2mm diameter endoscopic UHR-OCT system achromatized for 770-1020nm for use with a Titanium:sapphire laser with 260 nm bandwidth at full-width-half-maximum centered at 800 nm while achieving a 4.4um lateral spot dimension at focus. A pair of KZFSN5/SFPL53 doublets provides excellent primary and secondary color correction to maintain wide bandwidth through the imaging depth. A slight deviation from normal beam exit angle suppresses collection of the strong back reflection at the exit window surface. The novel design endoscope was built and characterized for through focus bandwidth, axial resolution, signal to noise, and lateral spot dimension. Performance is demonstrated on in vivo mouse colon. Ultrahigh-resolution images of mouse tissue enable the visualization of microscopic features, including crypts that have previously been observed with standard resolution OCT in humans but were too small to see in mouse tissue. Resolution near the cellular level is potentially capable of identifying abnormal crypt formation and dysplastic cellular organization.

A novel three dimensional, volumetric imaging technique based on optical frequency scanning Optical Coherence Tomography in a massively parallel (full field) fashion, called time-encoded frequency domain-OCT technique (teFD) is presented. Volumetric imaging is demonstrated on technical and biological targets.

Imaging of in vivo and ex vivo biological samples using full-field optical coherence tomography is demonstrated. Three variations on the original full-field optical coherence tomography instrument are presented, and evaluated in terms of performance. The instruments are based on the Linnik interferometer illuminated by a white light source. Images in the en face orientation are obtained in real-time without scanning by using a two-dimensional parallel detector array. An isotropic resolution capability better than 1 μm is achieved thanks to the use of a broad spectrum source and high numerical aperture microscope objectives. Detection sensitivity up to 90 dB is demonstrated. Image acquisition times as short as 10 μs per en face image are possible. A variety of in vivo and ex vivo imaging applications is explored, particularly in the fields of embryology, ophthalmology and botany.

Although the resolution of optical coherence tomography (OCT) has increased in the last years considerably the method is not suited to resolve surface steps in the sub μm range. Based on the Fourier domain OCT principle we present a method to measure distances up to some millimeters with a resolution in the sub nm range. To achieve this resolution the phase of the spectral data is used. The standard deviation of hundred measurements at a distance of approximately 1 mm was 0.1 nm, which is a relative accuracy of 10^-7. The system might be used for measuring the attachment of bio molecules on protein chips.

Simulated OCT signals from plain blood samples of thicknesses from 0.05 to 1 mm were obtained implementing Monte Carlo technique. Contributions of least- and multiple scattering, diffusive and non-diffusive fractions to the parts of the signal before the rear border peak, to the peak and behind it were estimated. It was show that least scattering and non-diffusive component prevail in the signal at optical depths smaller than 0.2 and 0.3 mm correspondingly. At larger depths multiple scattering and diffuse component prevail in the signal what may limit localization and detection of scattering objects at these depths. The distributions of contributing to the signal photons over scattering orders were analyzed. It was shown, that these dependences exhibit two maxima related to the borders of the investigated layer due to high anisotropy of the medium.

Laser speckle instrument for real-time capillary flow velocity measurements is described. The instrument is developed for investigation of lymph flow dynamics in transillumination geometry simultaneously with microscopic examination of rat lymfangions. The use of two independent channels of laser speckle registration allows both to measure flow velocity and to localize centerline flow along the probing beam direction with several micrometers resolution.

The polarization sensitive optical coherence tomography (OCT) system provides useful informations about the biological tissues. The exact tissue parameters measurement and comparison predicts about the malignant and normal tissues. The degree of polarization changes with the depth of tissue samples. We have established the analytical modeling with Jones-Mueller matrix for imaging technique, which experimentally extract the birefringence, depolarization, absorption and scattering information of tissues. The Jones matrix of thermally treated porcine tendon showed a reduction of birefringence from thermal damage. The Jones matrices of porcine skin and bovine cartilage also revealed that the density and orientation of the collagen fibers in porcine skin and bovine cartilage are not distributed as uniformly as in porcine tendon. Birefringence is sensitive to changes in tissue because it is based on phase contrast.

A high speed, tunable laser using Fourier Domain Mode Locking is demonstrated for OCT imaging. Record sweep speeds up to 290 kHz, 3 cm coherence length and 145 nm range at 1300 nm are achieved.

We model the photocurrent of a depth-scan (A-scan) from an optical coherence tomography (OCT) system, using a linearly polarized thermal source, as an electronically filtered doubly-stochastic Poisson process, and we obtain its time-varying second-order statistics. We derive an expression for the instantaneous signal-to-noise ratio (SNR) of time-domain OCT which is more general than the previously reported time-averaged expressions. Unlike previous work, our analysis combines shot noise, due to detection of coherent light, and photon excess noise, due to fluctuations in the optical field, into a single noise source that we refer to as the photoelectron noise. Similar to previous results, our SNR is dominated by a term similar to shot-noise when the reference optical power is low and by a term similar to photon excess noise when the reference power is high.

Simultaneous optical coherence tomography (OCT) and video microscopy were performed on the rat somatosensory cortex through a thinned skull during forepaw stimulation. Fractional change measurements in OCT images reveal a functional signal timecourse similar to well understood hemodynamic signal timecourses measured with video microscopy. The precise etiology of the observed OCT functional signal is still under investigation, but these results suggest that OCT can provide high-resolution cross-sectional images of functional neuro-vascular activation.