This PDF file contains the front matter associated with SPIE-OSA Proceedings Volume 6627, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Performance characteristics of recently developed superluminescent diodes (SLDs) based on double quantum-well (InGa)As heterostructure and InAs/AlGaAs/GaAs quantum-dot heterostructure are presented. Emission spectra of these SLDs cover spectral bands 960-1080 nm and 1100-1230 nm respectively. Owing to their usage, combined light sources of BroadLighter series cover now the entire NIR-range of 770-1230 nm. New prototypes of swept-wavelength light sources in the range of 820-1080 nm based on quantum-well broadband SOAs and tunable acousto-optic filters are described.

An off-the-shelf turn-key supercontinuum light source based on a passively mode-locked fiber laser, a fiber amplifier and a highly nonlinear fiber is evaluated for its application in ultrahigh resolution optical coherence tomography (OCT). Two spectral bands - one red shifted and one blue shifted in reference to the wavelength of the fiber laser - are employed as low coherence sources in OCT. Usable spectral bandwidths exceed 300 nm centered either at 790 or 1340 nm, with corresponding coherence lengths of 1.2 and 2.6 μm, respectively. Optimization of the spectrum for simultaneous imaging at both spectral bands results in spectral bandwidths exceeding 200 nm for each band after filtering. A free-space OCT setup supporting the full spectral bandwidth is introduced which allows for ultrahigh resolution OCT imaging using both spectral bands simultaneously. Axial free space resolutions were measured to be less than 2 and 4 μm at 840 and 1230 nm, respectively. This approach combines ultrahigh resolution obtained at 840 nm with large penetration depths at 1230 nm. Frequency compounding of the OCT images can be used for speckle reduction while extracting spatially resolved spectroscopic features facilitates enhanced image contrast.

This paper reports on a high-speed, wavelength-swept laser operating at 1310nm for optical coherence tomography (OCT) applications. The simple and reliable laser comprises a pigtailed semiconductor optical amplifier (SOA) and a wavelength-scanning filter in a fiber ring cavity configuration. The tunable filter consists of a diffraction grating and polygon mirror scanner in Littrow configuration. A photodiode is used to generate a start trigger signal synchronized to the start of each frequency sweep. Intracavity prisms plays important role to provide constant and narrow laser linewidth and linear frequency sweep at the same time. The laser exhibits a peak power of over 20mW. The tuning range of the laser is as wide as 120nm maximum, and 100nm FWHM at a scanning frequency of 20kHz. Coherence length was measured to be 4mm. By utilizing a novel double pass configuration in the scanning filter an improvement in coherence length to 7mm is also achieved. OCT system configured with the light source exhibits 106dB sensitivity and 12μm axial resolution in imaging.

This paper reports on a wide-range, high-speed, wavelength-swept laser operating at 1310nm for optical coherence tomography (OCT) applications. The laser comprises a pigtailed wideband, high-gain semiconductor optical amplifier (SOA) and a wavelength-scanning filter in a fiber ring cavity configuration. The tunable filter consists of a diffraction grating and polygon mirror scanner in Littrow configuration. A photodiode is used to generate a start trigger signal synchronized to start of each frequency sweep. Intracavity prisms are aligned to provide constant and narrow laser linewidth and linear frequency sweep. This arrangement also generates a wide tuning range for a given beam deflection angle by the polygon scanner while maintaining narrow laser linewidth. The laser exhibits a peak power of 20mW. The measured tuning range of the laser is 170nm maximum, with 160nm FWHM at a scanning frequency of 20kHz using a single custom engineered SOA device. Laser output is coupled via HI1060 fiber with a cut-off wavelength of 980nm ensuring single-mode propagation over the 1230nm to 1400 nm tuning range.

Fourier domain optical coherence tomography (FD-OCT) was used to acquire three-dimensional image stacks of isolated and perfused rabbit lungs (n = 4) at different constant pulmonary airway pressures (CPAP) and during vascular fixation. After despeckling and applying a threshold, the images were segmented into air and tissue, and registered to each other to compensate for movement between CPAP steps. The air-filled cross-sectional areas were quantified using a semi-automatic algorithm. The cross-sectional area of alveolar structures taken at all three perpendicular planes increased with increasing CPAP. Between the minimal CPAP of 3 mbar and the maximum of 25 mbar the areas increased to about 140% of their initial value. There was no systematic dependency of inflation rate on initial size of the alveolar structure. During the perfusion fixation of the lungs with glutaraldehyde morphometric changes of the alveolar geometry measured with FD-OCT were negligible.

Introduction: Non-melanoma skin cancer (NMSC) is the most prevalent cancer in the Western World. OCT has proved potential in assisting clinical diagnosis and perhaps reducing the need for biopsies in NMSC. As non-invasive treatment is increasingly used for NMSC patients with superficial lesions, the development of non-invasive diagnostic technologies is highly relevant. Methods: The aim of this cross-sectional clinical study, enrolling 100 NMSC patients and 20 healthy volunteers, is to investigate the diagnostic accuracy and applicability of OCT in NMSC diagnosis. Our OCT-system has been developed at Risoe National Laboratory, Denmark and offers ppolarization sensitive-OCT (PS-OCT) that may have additional advantaged as NMSC differ in content of birefringent collagens from normal skin. Results: Basal cell carcinomas (BCC) can in some cases be distinguished from normal skin in OCT-images, as normal skin exhibits a layered structure this layering is not present in BCC and sometimes not in actinic keratosis (AK). BCC lesions seem to be clearly less reflective than normal tissue. The predictive value of OCT in NMSC will be presented from a clinical point of view. Discussion: The earlier a skin cancer is diagnosed, the better the prognosis. Estimation of diagnostic accuracy and abilities of OCT in clinical studies of skin cancer patients is essential to establish the role and future set-ups for diagnostic OCT-systems.

One of the most critical but poorly understood processes during cardiovascular development is the establishment of a functioning coronary artery (CA) system. Due to the lack of suitable imaging technologies, it is currently impossible to visualize this complex dynamic process on living human embryos. Furthermore, due to methodological limitations, this intriguing process has not been unveiled in living animal embryos, too. We present here, to the best of our knowledge, the first in vivo images of developing CAs obtained from the hearts of chick embryos grown in shell-less cultures. The in vivo images were generated by optical coherence tomography (OCT). The OCT system used in this study is a mobile fiber-based time-domain real-time OCT system operating with a center wavelength of 1330 nm, an A-scan rate of 4 kHz, and a typical frame rate of 8 frames/s. The axial resolution is 17 &mgr;m (in tissue), and the lateral resolution is 30 &mgr;m. The OCT system is optimized for in vivo chick heart visualization and enables OCT movie recording with 8 frames/s, full-automatic 3D OCT scanning, and blood flow visualization, i.e., Doppler OCT imaging. Using this OCT system, we generated in vivo OCT recordings of chick embryo hearts to study the process of connection of the future right coronary artery (RCA) to the aorta. Recordings were made at three critical stages during development: day 8 (no clear connection yet), day 9 (established connection of RCA with the aorta with clear blood flow) and day 10 (further remodeling of the established RCA).

For chemical burns a considerable lack of methods exists for defining penetration kinetics and effects of decontamination within biological structures. We demonstrate that time-resolved high-resolution optical coherence tomography can close this gap by monitoring changes in scattering properties and thicknesses of rabbit cornea ex vivo after topical application of different corrosives. Modifications in the corneal microstructure due to direct chemical interaction or changes in the hydration state as a result of osmotic imbalance compromise the corneal transparency. The associated increase in light scattering intensity within the cornea is observed with high spatial and temporal resolution. Parameters affecting the severity of pathophysiological damage like diffusion velocity, depth of penetration, resistance of barriers, and effectiveness of emergency treatment procedures are obtained. This study demonstrates the potential of high-resolution OCT for the visualization and direct non-invasive measurement of specific interaction of chemicals with the eye, exemplified on hydrofluoric acid burn.

In vivo imaging of blood vessels obtain useful insights in characterizing the dynamics of vasoconstriction and vasodilation. Fourier domain optical Coherence Tomography (FD-OCT) imaging technique permits in vivo investigation of blood vessels in their anatomical context without preparation traumata by temporal resolved image stacks. OCT is an optical, contact less imaging technique based on Michelson interferometry of short coherent near infrared light. Particularly by the possibility of a contact-less measurement and the high axial resolution up to 10 microns OCT is superior to an investigation by ultra sound measurement. Furthermore we obtain a high time resolution of vessel dynamic measurements with the used Fourier domain OCT-system by a high A-scan rate [1,22kHz]. In this study the model of saphenous artery was chosen for analyzing function and dynamics. The arteria saphena in the mouse is a suitable blood vessel due to the small inner diameter, a sensitive response to vasoactive stimuli and an advantageous anatomically position. Male wild type mice (C57BL/6) at the age of 8 weeks were fed control or high-fat diet for 10 weeks before analyzing the vasodynamics. The blood vessel was stimulated by dermal application of potassium to induce vasoconstriction or Sodium-Nitroprusside (SNP) to induce vasodilation. The morphology of the a. saphena and vein was determined by 3D image stacks. Time series (72 seconds, 300x512 pixel per frame) of cross-sectional images were analysed using semi automatic image processing software. Time course of dynamic parameters of the vessel was measured.

High strain spots in the vessel wall indicate the presence of vulnerable plaques. The majority of acute cardiovascular events are preceded by rupture of such a plaque in a coronary artery. Intracoronary optical coherence tomography (OCT) can be extended, in principle, to an elastography technique, mapping the strain in the vascular wall. However, the susceptibility of OCT to frame-to-frame decorrelation, caused by tissue and catheter motion, inhibits reliable tissue displacement tracking and has to date obstructed the development of OCT-based intravascular elastography. We introduce a new technique for intravascular optical coherence elastography, which is robust against motion artifacts. Using acoustic radiation force, we apply a pressure to deform the tissue synchronously with the line scan rate of the OCT instrument. Radial tissue displacement can be tracked based on the correlation between adjacent lines, instead of subsequent frames in conventional elastography. The viability of the method is demonstrated with a simulation study. The root mean square (rms) error of the displacement estimate is 0.55 &mgr;m, and the rms error of the strain is 0.6%. It is shown that high-strain spots in the vessel wall, such as observed at the sites of vulnerable atherosclerotic lesions, can be detected with the technique. Experiments to realize this new elastographic method are presented. Simultaneous optical and ultrasonic pulse-echo tracking demonstrate that the material can be put in a high-frequency oscillatory motion with an amplitude of several micrometers, more than sufficient for accurate tracking with OCT. The resulting data are used to optimize the acoustic pushing sequence and geometry.

The keyword for management of cervical cancer is prevention. The present program within the UK, the 'National Health Service (NHS) cervical screening programme' (NHSCSP), is based on cytology. Although the program has reduced the incidence of cervical cancer, this program requires patient follow ups and relies on diagnostic biopsying. There is potential for reducing costs and workload within the NHS, and relieving anxiety of patients. In this study, Optical Coherence Tomography (OCT) was investigated for its capability to improve this situation. Our time domain bench top system used a superluminescent diode (Superlum), centre wave length ~1.3 &mgr;m, resolution (air) ~15 &mgr;m. Tissue samples were obtained according to the ethics approval by Gloucestershire LREC, Nr. 05/Q2005/123. 1387 images of 199 participants have been compared with histopathology results and categorized accordingly. Our OCT images do not reach the clarity and resolution of histopathology. Further, establishing and recognizing features of diagnostic significance seems difficult. Automated classification would allow one to take decision-making to move from the subjective appraisal of a physician to an objective assessment. Hence we investigated a classification algorithm for its ability in recognizing pre-cancerous stages from OCT images. The initial results show promise.

Phase retardation of retinal nerve fiber layer (RNFL) is measured by polarization-sensitive spectral domain optical coherence tomography (PS-SD-OCT) and scanning laser polarimetry (SLP). In PS-SD-OCT, birefringence of the optical fiber and the cornea is compensated by Jones matrix based analysis. Three-dimensional phase retardation map around the optic nerve head and en face phase retardation map of the RNFL are shown. It is shown that the phase retardation curves around the optic nerve head measured by PS-SD-OCT and SLP have similar values. PS-SD-OCT can measure the cumulative phase retardation of RNFL as well as SLP and has a possibility to evaluate RNFL for glaucomatous eyes.

Resonant Doppler Fourier Domain Optical Coherence Tomography is a functional imaging modality for quantifying fast tissue flow. The method profits from the effect of interference fringe blurring in spectrometer-based FDOCT in the presence of sample motion. If the reference path length is changed in resonance with the Doppler frequency of the sample flow the signals of resting structures will be suppressed whereas the signals of blood flow are enhanced. This allows for an easy extraction of vascularization structure. 3D images of blood vessels at the human optic nerve head are obtained with high axial resolution of 8 μm in air and an imaging speed of 17.400 depth profiles per second. An electro-optic modulator allows controlled reference phase shifting during camera integration. A differential approach is presented for the quantification of fast flows that are un-accessible via standard phase sensitive Doppler analysis. Flow velocity analysis extracts only the axial component which is dependent on the orientation of the vessel with respect to the optical axis. 3D information of the segmented vessel structure is readily used to obtain the flow velocity vectors along the individual vessels and to calculate the true angle-corrected flow speed.

A novel technique for analyzing Optical Coherence Tomography (OCT) signals is presented. Spectral analysis of the interferometric OCT signal reveals scatterer size-depended changes which can offer diagnostic information and be used to segment OCT images.

A novel dual angle optical coherence tomography (OCT) method is developed that has been termed stereoscopic OCT, highlighting the similarities between this technique and stereoscopic ranging. OCT images are obtained at two angles of incidence with respect to the surface of a layered phantom. From these measurements, optical path lengths are determined for each layer that are used to calculate the refractive index and physical thickness of each layer directly from Snell's law. This method may prove to be useful for characterising the bulk optical properties of biological material in vivo, that are presently not well known or understood.

A range of compounding techniques have been suggested for dealing with the signal degrading speckle noise in optical coherence tomography (OCT). Recent implementations of angular compounding have shown great promise, but some of the implementations require substantial modifications of the OCT system. Here, we consider a method that in principle can be fitted to most OCT systems without major modifications. Specifically, we address a spatial diversity technique for suppressing speckle noise in OCT images of human skin. The method is a variant of changing the position of the sample relative to the measuring probe. Instead of physically moving the sample, which is often not feasible for in vivo imaging, the position of the focal plane of the probe beam is shifted. If the numerical aperture is sufficiently high this spatial diversity scheme incorporates a variant of angular compounding. We have tested the scheme with a mobile fiber-based time-domain real-time OCT system. Essential enhancement was obtained in image contrast when performing in vivo imaging of normal skin and lesions. Resulting images show improved delineation of structure in correspondence with the observed improvements in contrast-to-noise ratios.

Simulated OCT images of skin were obtained implementing Monte Carlo simulations. The multilayer skin model used in simulations was based on the experimental OCT images obtained at the wavelength of 910 nm. The following skin layers were considered in the model: stratum corneum, epidermis prickle layer, epidermis basal layer, dermis with upper plexus, dermis, and dermis with lower plexus. The images were obtained both with and without speckle accounting. The latter case is calculated from the envelopes of calculated interference signals while the former accounts for the interference fringe patterns. The contributions of least and multiple scattering, diffusive and non-diffusive components of the backscattered light to the resulting OCT image were separated and analyzed. It was shown that least scattering contribution represents the imaging of the upper skin layers, while multiple scattering contribution can be characterized as blurred image with reduced contrast preserving, however, essential details. The least scattering component contributes to the image for optical depth up to 1 mm. From the analysis of the contribution of non-diffusive and diffusive components it follows that the diffusive component contributes to imaging the object starting from the epidermis basal layer and is more blurred compared to the multiple scattering contribution. The non-diffusive component contributes to the image for optical depth up to 1.3 mm. The effect of coherence length on the contributions of least and multiple scattering was also studied. It was shown, that contribution of multiple scattering increases with a decrease of the coherence length.

Speckle is inherent to any Optical Coherence Tomography (OCT) imaging of biological tissue. It is often seen as degrading the signal, but it also carries information about the tissue microstructure. One parameter of interest is the speckle size. We study the variations in speckle size on optical phantoms with different density of scatterers. Phantoms are fabricated with a new approach by introducing silica microspheres in a curing silicon matrix, providing phantoms with a controlled density of scatterers. These phantoms are also solid, deformable, and conservable. Experimental results are obtained with Time-Domain OCT (TD-OCT). Modeling is performed by simulating a phantom as a random distribution with of discrete scatterers. Both experimental results and modeling show that the speckle size varies when there are few scatterers contained within the probed volume, the latter being defined by the coherence length and the spot size of the focusing optics. As a criterion to differentiate tissues, the speckle size has the same sensitivity as the contrast parameter that is studied in Ref. 1. This work also contributes to a better understanding of speckle in OCT.

We use a random process model for the photocurrent in time-domain optical coherence tomography (TD-OCT) to obtain a maximum likelihood estimate of the reflectance at different depths of an object. This statistical image restoration approach is generally more effective than the previously reported deterministic methods, as it accounts for the statistics of the noise. We also present an expression for the Fisher information matrix in TD-OCT, which could be used to optimize TD-OCT setups. We present theoretical results which we apply to a simulated TD-OCT imaging example.

The theory of optical coherence tomography (OCT) was conventionally considered as the light beams propagating in the system to be in the forms of planar waves. However, the actual behaviors of the light beams in an OCT system are more likely to be Gaussian beams. With the consideration of the light beam passing through the focal lens in the sample arm to be a Gaussian beam, we deduced the theory of OCT in an analytic form. We also simulated and analyzed the interference signals with different positions of the photodetector and the interface in the sample as well as their transverse patterns spectrally. The results were demonstrated by experiments with a Fourier-domain OCT system.

Estimation of the tissue optical characteristics using optical coherence tomography (OCT) requires good modeling. Present modeling of the system includes effects such as scattering of light in tissues. However, absorption effects were often neglected in the model. They may be significant depending on the tissue type and the wavelength of the light source. We present a study where the effects of absorption in light propagation in biological tissue were examined in the theoretical modeling of OCT based on the single-scattering model. OCT M-scans were performed on liquid tissue phantoms at 1% concentration. In order to mimic the effects of absorption, India ink was added to the solution. Different concentrations of Indian ink were used to vary the absorption coefficient in the tissue phantoms. Estimation of the absorption, scattering coefficients from the OCT signal were obtained. Substantial reduction in the slope of the logarithmic OCT signal was observed when India ink was introduced to the liquid tissue phantoms. The results suggest that the effects of the absorption clearly affected the estimation of the overall extinction coefficient. In order to improve the accuracy of estimation of these characteristics, absorption effects should be taken into account.

Three-layer skin-equivalent models (rafts) were created consisting of a collagen/fibroblast layer and an air-exposed keratinocyte layer. Rafts were imaged with a tri-modality microscope including optical coherence (OC), two-photon excited fluorescence (TPEF), and second harmonic generation (SHG) channels. Some rafts were stained with Hoechst 33343 or rhodamine 123, and some were exposed to dimethyl sulfoxide (DMSO). OC microscopy revealed signal in cell cytoplasm and nuclear membranes, and a characteristic texture in the collagen/fibroblast layer. TPEF showed signal in cell cytoplasm and from collagen, and stained specimens revealed cell nuclei or mitochondria. There was little SHG in the keratinocyte layer, but strong signal from collagen bundles. Endogenous signals were severely attenuated in DMSO treated rafts; stained samples revealed shrunken and distorted cell structure. OC, TPEF, and SHG can provide complementary and non-destructive information about raft structure and effect of chemical agents.

In a previous report¹ we presented a novel method using en-face OCT for the evaluation of the curvature of an object, with immediate application to measurement of corneal curvature. This method relies on single shot C-scans obtained from an en-face OCT system with a multiple delay element introduced in the reference arm. In the present report we show how the same methodology can be used for the measurement of the axial position of a spherical object. The theoretical basis and the accuracy of assessing the axial position using this method are presented. The potential application of this method in the measurement and tracking of the in-vivo axial position of the eye is also discussed.

Recently, first spectral domain (SD) polarization sensitive (PS) optical coherence tomography (OCT) systems have been presented, thus combining the ability to gather birefringence information and the advantages of SD-OCT which allows for high acquisition speed and increased sensitivity compared to conventional time domain (TD) OCT. These instruments employed different detection units to record the spectral information of the polarized interferometric signal. We present two approaches to SD PS-OCT systems with different detection units to record the spectral interferograms from the two orthogonal polarization channels of the PS interferometer. Whereas one employs two complete spectrometers, i.e. one for each polarization channel, only a single spectrometer is used for the other one. In the latter case the two polarization channels' beams share the same diffraction grating, imaging lens and line scan camera. We point out the constructional differences of these two setups, discuss advantages and limitations of the different methods and show results of calibration and performance measurements for both setups. Furthermore, PS-OCT images of human tissue are presented to demonstrate the performance of both system designs.

A fiber-optic-based, time-domain optical coherence tomography (OCT) system coupled with a pneumatically actuated micro-lens is demonstrated. The OCT system uses a superluminescent diode emitting at a center wavelength of &lgr; ≈ 1300 nm. Microsystem fabrication technologies employing polydimethylsiloxane (PDMS) are used to fabricate the micro-lens with an aperture of 2 mm. A B-scan is carried out while dynamically shifting the focal length of the micro-lens along the axial scan. The OCT scan results show a higher lateral resolution and higher contrast of the backscattered interference signals when using the tunable lens; hence, deeper axial scans are possible. The ability to miniaturize the dimensions of the micro-lens will allow the system to be applicable to en-face optical coherence tomography and endoscopic applications.

We address the problem of exact signal recovery in frequency-domain optical-coherence tomography (FDOCT). The standard technique for tomogram reconstruction is the inverse Fourier transform. However, the inverse Fourier transform is known to yield autocorrelation artifacts which interfere with the desired signal. We propose a new transformation for computing an artifact-free tomogram from intensity measurements. Our technique relies on the fact that, in the FDOCT measurements, the intensity of the total signal reflected from the object is smaller than that of the reference arm. Our technique is noniterative, nonlinear, and it leads to an exact solution in the absence of noise. The reconstructed signal is free from autocorrelation artifacts. We present results on synthesized data as well as on experimental FDOCT measurements of the retina of the eye.

In this paper, we present a non-rotatory circumferential scanning optical probe integrated with a MEMS scanner for in vivo endoscopic optical coherence tomography (OCT). OCT is an emerging optical imaging technique that allows high resolution cross-sectional imaging of tissue microstructure. To extend its usage to endoscopic applications, a miniaturized optical probe based on Microelectromechanical Systems (MEMS) fabrication techniques is currently desired. A 3D electrothermally actuated micromirror realized using micromachining single crystal silicon (SCS) process highlights its very large angular deflection, about 45 degree, with low driving voltage for safety consideration. The micromirror is integrated with a GRIN lens into a waterproof package which is compatible with requirements for minimally invasive endoscopic procedures. To implement circumferential scanning substantially for diagnosis on certain pathological conditions, such as Barret's esophagus, the micromirror is mounted on 90 degree to optical axis of GRIN lens. 4 Bimorph actuators that are connected to the mirror on one end via supporting beams and springs are selected in this micromirror design. When actuators of the micromirror are driven by 4 channels of sinusoidal waveforms with 90 degree phase differences, beam focused by a GRIN is redirected out of the endoscope by 45 degree tilting mirror plate and achieve circumferential scanning pattern. This novel driving method making full use of very large angular deflection capability of our micromirror is totally different from previously developed or developing micromotor-like rotatory MEMS device for circumferential scanning.

We propose a new method of flow velocity estimation by analysis of time dependent beating signal using Spectral Optical Coherence Tomography. The oscillatory beating signal is caused by the Doppler shift of light reflected back from a mobile object measured in the interferometric set-up. This signal provides information about the velocity of the movable object. Measurements in model systems prove the method to give accurate results. Additional in vivo measurements of blood flow in the retinal vessels show potential applicability of this method in the field of biomedical imaging.

Due to nonlinear interaction with optical transparent samples the femtosecond technology is a very useful tool for high precision micro surgery on biological tissues. At the same time femtosecond lasers are ideal light sources for imaging methods such as optical coherence tomography (OCT) due to the broad spectrum of the laser, which is necessary for creating ultra short pulses. Using OCT structures within biological tissues can be imaged non invasive with a resolution within the low μm-range. The combined use of an ultra short pulse laser for cutting of biological tissues as well as imaging via OCT is a very interesting tool. It opens up a wide range of new surgery techniques and improves many existing methods due to high precision and high flexibility of the cutting process. Therefore we combined a femtosecond cutting system and a fourier domain OCT. In a first attempt the OCT is driven with an SLD and is used alternately to the cutting system. The OCT is integrated into the optical path which enables in situ imaging of the surgery area.

A technique to improve the signal-to-noise ratio (SNR) of a high speed 1300 nm swept source optical coherence tomography (SSOCT) system was demonstrated. A semiconductor optical amplifier (SOA) was employed in the sample arm to coherently amplify the weak light back-scattered from sample tissue without increasing laser power illuminated on the sample. The image quality improvement was visualized and quantified by imaging the anterior segment of a rabbit eye at imaging speed of 20,000 A-lines per second. The theory analysis of SNR gain is given followed by the discussion on the technologies that can further improve the SNR gain.

Theoretical and experimental results are presented using the common path Mirau interference microscope and using the Linnik microscope with annular masks to increase the depth of field. The competence between the spatial and temporal coherence was investigated theoretically and confirmed experimentally. Phase imaging of onion epidermis cells was presented showing the possibility of obtaining profiles of the cells. Frequency domain OCT was shown to be possible using full field setup.

We report first results in the development of a diffractive optical microtomography instrument for imaging transparent/semi-transparent biological samples without staining and sectioning. A brightfield transmission microscope was modified to form a Mach-Zehnder interferometer that was used to generate phase-shifted holograms recorded in image plane. Transparent/semi-transparent objects mixed with an index matching medium were inserted into a microcapillary and holograms of these objects were taken under different view angles by rotating the microcapillary. Precise rotation of the microcapillary was accomplished by clipping the microcapillary in a precisely machined V-groove, a system that when combined with software correction of the object centre achieved a precision of object positioning on the order of a micrometer. In this study, the observed objects were considered to be weakly diffracting and reconstructed by projection tomography of the phases of their measured scattered fields. The three-dimensional distribution of the refractive index was obtained by backprojecting the phases. Refractive index distributions are shown for a glass bead and a pollen grain. The measured difference between the refractive index of the glass bead and the microcapillary was within ±0.01. An isotropic spatial-resolution of the instrument in the micrometer range was obtained with an objective having a numerical aperture of 0.4.

A comparative analysis on the performance of different scanning regimes in time domain optical coherence tomography is presented in terms of image size. Safety thresholds due to the different continuous irradiation time per transverse pixel in different scanning regimes are also considered. We present the maximum exposure level for a variety of scanning procedures, employing either A scanning (depth priority) or T scanning (transverse priority) when generating cross section images, en-face images or collecting 3D volumes. We present a comparison between such B-scan images, and different criteria to allow the user to choose the right mode of operation. Mainly, two criteria are detailed, a scanning criterion and a safety criterion. The scanning criterion depends on the number of pixels along the lateral and axial directions. The analysis shows that en-face scanning allows wider images while the longitudinal scanning is more suitable to deep cross sections. The safety criterion refers to safety levels to be observed in each scanning mode. We show that the flying spot OCT imaging has different safety limits for T- and A- based imaging modes. The analysis leads to maximum permissible optical power levels that favors T-scan imaging of wide objects. We then apply the analysis considering as object the eye.

We present a novel detection scheme for Fourier domain optical coherence microscopy (FDOCM). A Bessel-like interference pattern with a strong central lobe was created with an axicon lens. This pattern was then imaged by a telescopic system into the sample space to obtain a laterally highly confined illumination needle, extending over a long axial range. For increased efficiency, the detection occurs decoupled from the illumination, avoiding a double pass through the axicon. Nearly constant transverse resolution of ~1.5&mgr;m along a focal range of 200&mgr;m with a maximum sensitivity of 105dB was obtained. A broad bandwidth Ti:Sapphire laser allowed for an axial resolution of 3&mgr;m in air, providing the nearly isotropic resolution necessary to access the microstructure of biological tissues. Together with the speed- and sensitivity-advantage of FDOCT, this system can perform in vivo measurements in a minimally invasive way. Tomograms of the mouse mammary gland and the mouse follicle, recorded in vitro, revealed biologically relevant structural details. Images acquired with classical microscopy techniques, involving stained and fluorescent samples, validate these structures and emphasize the high contrast of the tomograms. It is comparable to the contrast achieved with classical techniques, but employing neither staining, labeling nor slicing of the samples, stressing the high potential of FDOCM for minimally invasive in vivo small animal imaging.

We present a new method to obtain additional spectroscopic information by analyzing conventional Fourier domain optical coherence tomography (FDOCT) data. Conventional FDOCT data are based on the analysis of backscattered light, while spectral FDOCT (SFDOCT) also evaluates the absorption characteristics of the different sample layers. This is a result of analyzing the peak shapes of the single, one dimensional depth profiles regarding their modification due to absorption characteristics of the sample layers. A concept for depth allocation of different absorption characteristics is discussed.

This paper reports the study of an Optical Fourier Domain Imaging (OFDI) setup for optical coherence tomography. One of the main drawbacks of OFDI is its inability to differentiate positive and negative depths. Some setups have already been proposed to remove this depth ambiguity by introducing a modulation by means of electro-optic or acousto-optic modulators. In our setup, we implement a piezoelectric fiber stretcher to generate a periodic phase shift between successive A-scans, thus introducing a transverse modulation. The depth ambiguity is then resolved by performing a Fourier treatment in the transverse direction before processing the data in the axial direction. It is similar to the B-M mode scanning already proposed for Spectral-Domain OCT¹ but with a more efficient experimental setup. We discuss the advantages and the drawbacks of our technique compared to the technique based on acousto-optics modulators by comparing images of an onion obtained with both techniques.

We developed a novel differential-phase optical coherence reflectometer (DP-OCR) by using a low-coherence light source and integrated with differential phase detection technique on surface profile measurement. In this setup, 2Å on detection of axial displacement was demonstrated. Thus, a localized surface profile was measured precisely by scanning an optical grating surface in this measurement. Moreover, the requirement on equal amplitude of the reference and signal beams of this novel reflectometer is discussed.

The capabilities of a novel deformable mirror to correct ocular aberrations are analyzed. The deformable mirror, (MIRAO52 Imagine Eyes) is incorporated within a complex retinal imaging system able to produce simultaneous en-face optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) images of the retina. The performances of the deformable mirror have been examined by evaluating the amount of aberrations which the deformable mirror is able to correct for, the improvement in the signal-to-noise ratio and transversal resolution in both OCT and SLO images obtained from an artificial eye. Pairs of C-scan images were obtained at a frame rate of 2 Hz, with and without wave-front correction. The correction of aberrations increased the signal-to-noise ratio in images obtained from artificial eyes by up to 6 dB in the OCT channel and up to 31 dB in the SLO channel. Also, we demonstrated the high capability of the MIRAO52 deformable mirror to correct for high amounts of wave-front aberrations.

Purpose: Quantification of outer retinal layers in humans. Method: 11 eyes in healthy subjects and 3 eyes in patients after resolution of central serous chorioretinopathy (CSCR). Multiple line scans were obtained using OCT Stratus and scans were registered and averaged to enhance contrast. The distance from the inner-outer segment junction to the posterior part of the retinal pigment epithelium (RPE-OS_complex) was calculated. In addition, the reflectance of the outer photoreceptor layer in the foveal center was compared to that peripheral to the fovea. Results: Mean thickness of the RPE-OS_complex in healthy subjects was 77.3 μm, in CSCR 52.9 μm. The thickness of the RPE-OS_complex was significantly correlated to visual acuity (r=0.95, p<0.01). The ratio of reflectance (fovea/parafovea) was 1.06 in healthy subjects, 1.18 in CSCR eyes. Conclusion: The RPE-OS_complex thickness was markedly reduced in eyes after resolution of CSCR and highly correlated to the visual acuity, the correlation to total foveal thickness was less. An increased backscatter was seen in CSCR, probably due to photoreceptor disorganization and atrophy.

Retinal and choroidal imaging by using swept-source optical coherence tomography (SS-OCT) with a 1-μm band probe light, and high-contrast and three-dimensional (3D) imaging of choroidal vasculature are presented. This SS-OCT has a measurement speed of 28,000 A-lines/s, a depth resolution of 10.4 μm in tissue, and a sensitivity of 99.3 dB. A software-based algorithm for scattering optical coherence angiography (S-OCA) is developed for the high-contrast and 3D imaging of the choroidal vessels. This OCT is employed for the investigation of age related macular degeneration and visualizes structures beneath the retinal pigment epithelial detachment.

Noninvasive ophthalmic angiography is demonstrated for the in vivo human. Three-dimensional structural and flow imaging have been performed with a high-speed spectral-domain optical coherence tomography. The two methods are presented; (1) Doppler optical coherence angiography: three-dimensional vasculature of retinal and choroidal vessels are visualized by flow imaging; and, (2) scattering optical coherence angiography: the choroidal vasculature is segmented from three-dimensional OCT volume set. By integrating three-dimensional vasculature images, two-dimensional images of blood vessels are obtained. These are corresponding to fluorescein angiogram and indocyanine green angiogram.

Polarization properties of anterior segment disorders of the eyes were evaluated using a fiber-based polarization-sensitive Fourier-domain optical coherence tomography (PS-FD-OCT). The light source is a superluminescent diode with a central wavelength of 840 nm, and bandwidth of 50 nm. Synchronized two line-CCD cameras allow high-speed measurement of birefringence of retina (line rate 27.7 kHz), and the sensitivity of the system is 100.7 dB. Birefringence of the optical fiber was compensated with the surface reflection. Phase retardation and orientation of the birefringence were measured with a Jones matrix based algorithm. The phase retardation map of the anterior segment was visualized as a depth-resolved three-dimensional image in addition to the conventional cross sectional OCT image. In the polarization image of the normal eye, striking polarization change was observed at the sclera. In the eyes with necrotizing scleritis, abnormal thinning of the sclera could be confirmed. In the eyes after filtering glaucoma surgery, polarization change in the conjunctiva due to the abnormal fibrosis after surgery could be observed. PS-FD-OCT is an effective tool to understand the polarization properties of different types of pathological changes in the anterior segment of the eye.

In this work, we propose the use of the Mueller Coherency matrix of biological tissues in order to increase the information from tissue images and so their contrast. This method involves different Mueller Coherency matrix based parameters, like the eigenvalues analysis, the entropy factor calculation, polarization components crosstalks, linear and circular polarization degrees, hermiticity or the Quaternions analysis in case depolarisation properties of tissue are sufficiently low. All these parameters make information appear clearer and so increase image contrast, so pathologies like cancer could be detected in a sooner stage of development. The election will depend on the concrete pathological process under study. This Mueller Coherency matrix method can be applied to a single tissue point, or it can be combined with a tomographic technique, so as to obtain a 3D representation of polarization contrast parameters in pathological tissues. The application of this analysis to concrete diseases can lead to tissue burn depth estimation or cancer early detection.

A further insight into the prior concept of polarization sensitive optical coherence tomography system intended for non-laboratory conditions is brought forward and an experimental proof-of-concept is presented. A phenomenological model is adopted from the theory of light depolarization in crystalline polymers and modified to yield a simplified algorithm for mapping depolarization ratio in dermis. The algorithm could distinguish between dermal layers with depleted collagen content and normal dermis of normal perilesional skin. Dermis is simulated by bireringent lamellae of collagen arranged chaotically in multiple layers parallel to the skin surface. Both the design concept and the model imply the sub-millimeter tumor thickness as a proofed prognostic factor and an important criterion for complementary functional diagnostics of skin cancers at their early phase of vertical growth. Choice of the model is inspired by similarity of structural and optical properties between liquid-crystal collagen fibers in dermis and birefringent crystalline lamellae in polymer materials. The numerical computation based on the model allowing for real characteristics of dermis gives plausible interpreting of depolarization peculiarities caused by collagen depletion. Feasibility is discussed of exploiting fiber optic analogs of achromatic retarders. Fabrication of the fiber retarders is shown to be realistic by making use of the photonics technology possessed by the authors.