This PDF file contains the front matter associated with SPIE Proceedings Volume 6429, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

A swept laser source at center wavelength of 1060 nm for Fourier domain optical coherence tomography (FDOCT) was demonstrated. The laser is composed of a fiber-coupled SOA gain module, a fiber Fabry-Perot tunable filter, fiber isolators and couplers to form a ring laser. The laser is capable of a scanning range of 64 nm and coherence length of 9.8 mm at 2 KHz sweep rate. With the built swept source, a FDOCT system was developed which can achieve 12 &mgr;m axial resolution in tissue. Imaging of pig retina was demonstrated with the FDOCT system.

The 1020-1080 nm spectral region appears as a viable alternative to the 700-900 nm spectral band for in vivo eye fundus OCT imaging due to a local absorption minimum of water (main constituent of the eye aqueous and vitreous). Light at these wavelengths also experiences less attenuation due to lower scattering and absorption by melanin in the retinal pigment epithelium and choroid, which results in deeper penetration of the probe beam in the choroid. T-scan based en face OCT is a modification of the OCT technique that has the unique capability of acquiring both longitudinal (B-scans) and tranversal (C-scans) OCT images of the eye fundus in real time and allows the addition of a confocal scanning ophthalmoscope channel to the OCT instrument. We report for the first time a combined T-scan based en face OCT and confocal scanning opthalmoscopy system for imaging the human eye fundus in vivo in the 1050 nm region. The instrument allows the visualization of choroidal blood vessels in both the confocal and OCT channels without the use of contrast agents such as indocyanine green (ICG) dye and could prove an alternative tool for diagnosing eye conditions like age related macular degeneration that are preceded by choroidal neovascularisation.

Phase-insensitive optical coherence angiography also denoted as scattering optical coherence angiography (S-OCA), which uses optical coherence tomography (OCT) as an imaging engine and a software segmentation algorithm as a contrast engine, is a non-invasive alternative to indocyanine green angiography (ICGA). Three-dimensional in vivo vasculature of the human retina and choroid is visualized by S-OCA. A three-dimensional swept-source OCT with 1.05 um probe is built as the imaging engine of the S-OCT. The side lobes in the point spread function due to ripple peaks in the light source spectrum are eliminated by a software adaptive spectral shaping. Because of the deeper penetration of the 1.05 um probe to a scattering tissue, the in vivo human choroid and the scleral ring (scleral canal wall) are clearly visualized. The chromatic dispersion of the eye is automatically canceled in the manner of minimization of the information entropy of an OCT image. An intensity based levelset segmentation algorithm was developed for the enhanced visualization of the three-dimensional structure of the retinal and choroidal vascular network. This algorithm successfully visualizes the vascular networks of the in vivo human macula and optic nerve head.

Retinal imaging ranks amongst the most important clinical applications for optical coherence tomography (OCT) [1, 2]. The recent demonstration of increased sensitivity [3-6] in Fourier Domain detection [7, 8] has opened the way for dramatically higher imaging speeds, up to axial scan rates of several tens of kilohertz. However, these imaging speeds are still not sufficient for high density 3D datasets and a further increase to several hundreds of kilohertz is necessary. In this paper we demonstrate a swept laser source at 1050 nm with a sweep rate of 202 kHz. The laser source provides ~10 mW average output power, up to 60 nm total sweep range and a sensitivity roll off of less than 10 dB over 4 mm. In vivo 2D and 3D imaging of the human retina at a record axial scan rate of 101 kHz is demonstrated. These results suggest that swept source OCT has the potential to significantly outperform spectral/Fourier domain OCT for ophthalmic imaging applications in the future.

Ultrahigh axial resolution in adaptive optics - optical coherence tomography (AO-OCT) is fundamentally limited by the intrinsic chromatic aberrations of the human eye. Variation in refractive index of the ocular media with wavelength causes the spectral content of broadband light sources to focus at different depths in the retina for light entering the eye and at the imaging detector for light exiting. This effect has not been previously reported for ultrahigh-resolution OCT (without AO) likely because the effect is masked by the relatively long depth of focus dictated by the small pupils used in these systems. With AO, the pupil size is much larger and depth of focus substantially narrower. As such the chromatic aberrations of the eye can counteract the lateral resolution benefit of AO when used with broadband light sources. To more fully tap the potential of AO-OCT, compensation of the eye's chromatic and monochromatic aberrations must occur concurrently. One solution is to insert an achromatizing lens in front of the eye whose chromatic aberrations are equal but opposite in sign to that of the eye. In this paper we evaluate the efficacy of a novel design that uses a custom achromatizing lens placed near the fiber collimating optic. AO-OCT images are acquired on several subjects with and without the achromatizing lens and in combination with two light sources of different spectral width. The combination of the achromatizing lens and broadband light source yielded the sharpest images of the retina and the smallest speckle.

Noninvasive angiography is demonstrated for the in vivo human eye. Three-dimensional flow imaging has been performed with high-speed spectral-domain optical coherence tomography. Three-dimensional vasculature of ocular vessels has been visualized. By integrating volume sets of flow images, two-dimensional images of blood vessels are obtained. Retinal and choroidal blood vessel images are simultaneously obtained by separating the volume set into retinal part and choroidal part.

Measurement of retinal blood vessel parameters like the blood blow in the vessels may have significant impact on the study and diagnosis of glaucoma, a leading blinding disease worldwide. Optical coherence tomography (OCT) is a noninvasive imaging technique that can provide not only microscopic structural imaging of the retina but also functional information like the blood flow velocity in the retina. The aim of this study is to automatically extract the parameters of retinal blood vessels like the 3D orientation, the vessel diameters, as well as the corresponding absolute blood flow velocity in the vessel. The parameters were extracted from circular OCT scans around the optic disc. By removing the surface reflection through simple segmentation of the circular OCT scans a blood vessel shadowgram can be generated. The lateral coordinates and the diameter of each blood vessel are extracted from the shadowgram through a series of signal processing. Upon determination of the lateral position and the vessel diameter, the coordinate in the depth direction of each blood vessel is calculated in combination with the Doppler information for the vessel. The extraction of the vessel coordinates and diameter makes it possible to calculate the orientation of the vessel in reference to the direction of the incident sample light, which in turn can be used to calculate the absolute blood flow velocity and the flow rate.

We report the existence of polarization memory effect in the polarization-sensitive optical coherence tomography (PS-OCT). Linear and circular polarized light was used in the sample arm and two spherical micro-sphere solutions were used as scattering phantoms. We further showed that this polarization effect can be clinically useful for the characterization of some real tissue properties such as tooth dentin.

A novel cross-polarized optical coherence tomography (CP-OCT) system based on standard isotropic single-mode fiber has been developed. We exploit the property of an arbitrary pair of orthogonal waves propagating in a single-mode fiber to maintain their orthogonality in the absence of anisotropy losses, regardless of the induced phase anisotropy. The well-known isotropic fiber based OCT scheme that commonly comprises an optical probe with a Fizeau interferometer and a compensating Michelson interferometer with Faraday mirrors is modified. We introduce an additional optical element to form the initial radiation as two mutually time-delayed and strictly orthogonal polarized waves. The suggested scheme allows reaching very low level of cross talk in co and cross-polarized images.

We present a simplified spectral-domain polarization-sensitive optical coherence tomography (SD-PS-OCT) setup with a spectrometer that employs only a single line scan camera. Unlike SD-PS-OCT systems reported so far, just one readout of a single line scan camera is necessary to gather information on sample reflectivity, retardation, and optic axis orientation for one A-line. Furthermore, spectrometer alignment and data acquisition synchronization are alleviated by the novel spectrometer design. First in-vivo PS-OCT images of human ocular tissue have been recorded to demonstrate the function of our setup.

A variation to the analysis of phase data achieved with spectral domain optical coherence tomography (SDOCT) is presented. By using the variance of the phase changes observed in the OCT images, scatterer motion has been imaged which is not readily observable with conventional Doppler OCT techniques. Dynamic motion contrast has been demonstrated for imaging Brownian motion of a sample system as well as imaging vasculature of in vivo 3dpf zebrafish.

The onset of congenital heart disease (CHD) is believed to occur at very early stages of development. Investigations in the initiation and development of CHD has been hampered by the inability to image early stage heart structure and function, in vivo. Imaging small animals using optical coherence tomography (OCT) has filled a niche between the limited penetration depth of confocal microscopy and insufficient resolution from ultrasound. Previous demonstrations of chick heart imaging using OCT have entailed excision of, or arresting the heart to prevent motion artifacts. In this summary, we introduce SDOCT Doppler velocimetry as an enhancement of Doppler OCT for in vivo measurement of localized temporal blood flow dynamics. With this technique, dynamic velocity waveforms were measured in the outflow tract of the heart tube. These flow dynamics correlate to a finite element model of pulsatile flow and may lead to a further understanding of morphological influences on early heart development.

The purpose of this study is to demonstrate the application of ultrahigh-resolution Spectral Domain Optical Coherence Tomography (SD-OCT) for non contact in vivo imaging of the retina of small animals and quantitative retinal information extraction using 3D segmentation of the OCT images. An ultrahigh-resolution SD-OCT system was specifically designed for in vivo retinal imaging of small animal. En face fundus image was constructed from the measured OCT data, which enables precise registration of the OCT images on the fundus. 3D segmentation algorithms were developed for the calculation of retinal thickness map. High quality OCT images of the retina of mice (B6/SJLF2 for normal retina, Rho^-/- for photoreceptor degeneration and LH_BETAT_AG for retinoblastoma) and rats (Wistar for normal retina) were acquired, where all the retinal layers can be clearly recognized. The calculated retinal thickness map makes successful quantitative comparison of the retinal thickness distribution between normal and degenerative mouse retina. The capabilities of the OCT system provide a valuable tool for longitudinal studies of small animal models of ocular diseases.

The application of polarization sensitive optical coherence tomography (PS-OCT) for imaging the human retina and the cone mosaic is presented. The system is based on a time domain technique which uses the fast (or priority) scan direction orthogonal to the incoming beam (parallel to the retinal surface). Using a resonant scanner operating at 4kHz, the system is capable to record 8000 transversal lines per second or 40 images per second (500(x)x200(y) pixels). There are some benefits of the transverse scanning technique for high transverse resolution imaging compared to fast A-scan based OCT systems (e.g. Fourier domain OCT). First, the possibility of dynamic focusing (to maintain high transverse resolution throughout imaging depth) and second the option of simultaneous recording of scanning laser ophthalmoscope (SLO) images. Since en-face images can be recorded with high speed, small structures in transverse direction (as the cone mosaic) can be recorded with greatly reduced motion artifacts. The instrument simultaneously retrieves backscattered intensity (standard OCT), retardation and fast axis orientation for each measurement location. Images with high isotropic resolution of the human retina including images of the cone mosaic are presented.

The complex conjugate artifact intrinsic to spectral domain optical coherence tomography (SDOCT) complicates retinal image acquisition in patients with poor fixation or head control, imaging of vitreal and choroidal structures, and imaging of extended retinal pathologies. We demonstrate high speed complex conjugate artifact-resolved imaging of human retina using simple and inexpensive sinusoidal reference mirror modulation in combination with 4-step integrating-bucket acquisition and a quadrature projection reconstruction algorithm. The method uses a sinusoidal PZT driving signal to modulate the reference delay continuously during N integration buckets per modulation. The spectral interferometric signal measured by the CCD is phase shifted as a function of the amplitude and phase offset of the driving signal. We show that the amplitude and phase can be optimized for DC and complex conjugate artifact removal and minimal fringe washout. This method is illustrated experimentally using a four bucket phase modulating signal and quadrature projection algorithm for complex conjugate suppression. DC suppression of 53dB and complex conjugate suppression of 30dB is demonstrated for sets of four Ascans, each acquired at 17kHz. Densely sampled (3000 A-scans/image, acquired at 1.46 images/sec) in vivo complex conjugate artifact-resolved images of fovea and optic nerve-head acquired show complex conjugate artifact suppression for most image reflections to the noise floor.

A novel method is presented for the evaluation of object shapes. The method has applicability in the measurement of the cornea curvature. An en-face OCT system using a multiple delay element in the reference path of the interferometer is proposed. This method allows detection of the polar variations of the cornea curvature from a single en-face OCT image. Inspection of multiple contours in the en-face OCT image can also be used to estimate the instantaneous axial position of the eye.

Photodisruption of femtosecond laser at 1700nm wavelength has been demonstrated as a potential subsurface surgical method that can be used in trabeculectomy for glaucoma treatment without causing failure due to scarring at the level of conjunctiva and underlying tissue [1, 2]. In this study, Fourier domain optical coherence tomography (FD-OCT) technology is used to demonstrate high speed non-invasive imaging of high precision photodisruption in human sclera. Photodisruption cavities of different size in human sclera can reveal itself in its 3D FDOCT image. Transclera channel cut from back to surface and partial transclera channel are easily identified in 3D OCT image. The whole 3D data set acquired with high speed frequency domain OCT system permits further quantitative analysis of subsurface phtodisruption incisions. The preliminary results indicate that high speed frequency domain OCT system is a good candidate for imaging subsurface photodisruption with femtosecond laser and its 3D image may provide good guidance during surgical procedures when it is integrated with laser ablation system.

Vitrectomy (removal of the vitreous humor) is an ophthalmic surgery required as a precursor to several posterior chamber procedures. Vitrectomy is commonly performed using an endoscopic vitreous cutter and fiber based light delivery for observation through a surgical microscope. Cross-sectional visualization of the retina and remnant vitreous layers during surgery using an external optical coherence tomography (OCT) scanner is impractical due to deformation in the shape of the eye and the cornea. We present a forward imaging probe with 820 &mgr;m outer diameter (21 gauge needle) for cross-sectional endoscopic OCT imaging during ophthalmic surgeries. The Paired-Angle-Rotating Scanner (PARS) OCT probe is based on angle polished gradient index (GRIN) lenses which are rotated about the optical axis. The scan pattern is determined by the angle between the GRIN lenses and the relative angular velocity. Endoscopic placement of the PARS-OCT probe tip near the retinal surface permits use of a longer wavelength light, in particular 1310 nm, which would otherwise suffer significant attenuation traversing the vitreous humor. The prototype endoscopic PARS-OCT probe is coupled to a commercially available 1310 nm swept laser source, and uses commercial software for data acquisition, processing, and display of retinal images in real time at an A-scan rate of 16 kHz. We present an analysis of aberrations due to off axis use of GRIN lenses and measure the scan pattern of the PARS probe. Images acquired on an ex vivo porcine retina are presented, motivating development of the endoscopic PARS-OCT probe for clinical evaluation.

We present pulsed illumination spectral-domain optical coherence tomography (SD-OCT) for in vivo human retinal imaging. We analyze the signal-to-noise (SNR) for continuous wave (CW) and pulsed illumination SD-OCT. The lateral beam scan motion is responsible for a SNR drop due to lateral scanning induced interference fringe washout. Pulsed illumination can reduce the SNR drop by shorter sample illumination time during the integration time of a camera. First, we demonstrate the SNR benefit of pulsed illumination over CW as function of lateral scan speed for a paper sample. For in-vivo human retinal imaging with pulsed illumination, the maximum permissible exposure (MPE) according to pulse repetition rate is presented based on ANSI standard. Finally, we show better SNR in retinal images of a normal subject with pulsed illumination SD-OCT over CW at high lateral scanning speed.

Spectral domain optical coherence tomography (SDOCT) is a relatively new imaging technique that allows high-speed cross-sectional scanning of retinal structures with little motion artifact. However, instrumentation for these systems is not yet fast enough to collect high-density three-dimensional retinal maps free of the adverse effects of lateral eye movements. Low coherence interferometry instruments must also contend with axial motion primarily from head movements that shift the target tissue out of the coherence detection range. Traditional SDOCT instruments suffer from inherent deficiencies that exacerbate the effect of depth motion, including limited range, depth-dependent signal attenuation, and complex conjugate overlap. We present initial results on extension of our transverse retinal tracking system to three-dimensions especially for SDOCT imagers. The design and principle of operation of two depth tracking techniques, adaptive ranging (AR) and Doppler velocity (DV) tracking, are presented. We have integrated the threedimensional tracking hardware into a hybrid line scanning laser ophthalmoscope (LSLO)/SDOCT imaging system. Imaging and tracking performance was characterized by tests involving a limited number of human subjects. The hybrid imager could switch between wide-field en-face confocal LSLO images, high-resolution cross-sectional OCT images, and an interleaved mode of sequential LSLO and OCT images. With 3-D tracking, the RMS error for axial motion decreased to <50 µm and for lateral motion decreased to <10 µm. The development of real-time tracking and SDOCT image processing hardware is also discussed. Future implementation of 3-D tracking should increase the yield of usable images and decrease the patient measurement time for clinical SDOCT systems.

Time domain optical coherence tomography (OCT) traditionally uses scanning optical delay lines with moving parts and a point detectors. OCT systems build with a linear detector array (linear OCT or L-OCT) are simple and robust, but a detector with approx. 10,000 elements is needed for an imaging depth of 2 millimeter, which is necessary for most biomedical applications. We present a new optical setup for L-OCT with increased measurement range. An additional grating performs a reduction of the spatial frequencies of the fringe pattern on the detector without loss of SNR, so the signal can be sampled with a minimal number of pixels. The theory for this approach is addressed and first measurements are presented.

Optical coherence tomography (OCT) is a noninvasive imaging technique with high in-depth resolution. We employed OCT technique for monitoring and quantification of analyte and drug diffusion in cornea and sclera of rabbit eyes in vitro. Different analytes and drugs such as metronidazole, dexamethasone, ciprofloxacin, mannitol, and glucose solution were studied and whose permeability coefficients were calculated. Drug diffusion monitoring was performed as a function of time and as a function of depth. Obtained results suggest that OCT technique might be used for analyte diffusion studies in connective and epithelial tissues.

The two-harmonic FD-OCT method, where the quadrature components of the spectral interferogram are obtained by simultaneous acquisition of the first and second harmonics of the phase-modulated interferogram, is used for complex-conjugate- resolved imaging of biological samples. The method is implemented using sampling of the phase modulated interferogram with an integrating detector array followed by digital demodulation at the first and second harmonics. A complex conjugate rejection ratio as high as 70 dB is achieved.

Depth dependent broadening of the axial point spread function due to dispersion in the imaged media, and algorithms for postprocess correction have been previously described for both time domain and frequency domain optical coherence tomography. Homogeneous media dispersion artifacts disappear when frequency domain samples are uniformly spaced in circular wavenumber, as opposed to uniform sampling in optical frequency. In this paper, we explicate the source of this point spread broadening and simulate its magnitude in aqueous media. We conclude with a suggestion for interferometric k-triggering which accounts for dispersion in the media.

We have demonstrated a Fourier-domain optical coherence tomography (FD-OCT) scheme with a high-speed frequency-swept light source based on a chirped supercontinuum pulse. Instead of using a swept laser, an ultra-wideband supercontinuum pulse was chirped or stretched in the time domain by using a long dispersive single-mode optical fiber by the help of the group velocity dispersion. The chirped pulse was used directly as frequency-swept light for OCT after measuring the relationship between the time delay and the wavelength. Very high acquisition speeds up to 5-MHz in A-line scan rate were achieved because there is no speed-limiting moving part in this scheme. And high resolution up to 3.6 &mgr;m in air was enabled owing to the use of wideband supercontinuum. It was shown that the scheme does not require re-calibration of the sweep characteristics because the sweeping mechanism is passive and stable.

Novel Fourier domain OCT method and instrumentation using Optical Frequency Comb (OFC) is demonstrated. This technique can overcome some limitations of Spectral OCT and Optical Frequency domain Imaging (Swept Source OCT) and enables ultrahigh resolution imaging in 800 nm range. In the novel method external OFC generator placed after the broad band light source is used. We will demonstrate preliminary data showing the general performance, advantages and limitations of the Fourier domain OCT method using Optical Frequency Comb generator based on Fabry-Perot interferometer (F-P). High quality, high resolution cross-sectional images of biological samples obtained with the presented technique are shown.

We have been developing a unique discretely swept optical frequency domain imaging (OFDI) using superstructured-grating distributed Bragg reflector (SSG-DBR) lasers. To increase resolution, four SSG-DBR lasers are being developed to obtain spectral coverage of 160 nm in total. To increase speed of D-OFDI imaging, simultaneous scanning of multiple sources with a parallel OFDI system and unique transversal scanning D-OFDI have been demonstrated. Introduction of an optical amplifier can increase sensitivity beyond the conventional shot noise limit. A deep 12 mm depth range has been demonstrated with the wavelength interval of 0.05 nm.

We propose a new method to increase the sensitivity of Optical Coherence Tomography (OCT) beyond the conventional shot noise limit using optical amplifiers. Criterion for effective use of optical amplifiers for OCT is discussed. Enhancement of OCT images is demonstrated with optical frequency domain reflectometry (OFDR) OCT.

We demonstrate a tunable laser operating in the 1-1.1 &mgr;m wavelength region with a tuning range of 43 nm (FWHM), an output power of 19 mW and coherence length of 14 mm. The source is based on a master laser consisting of a cavity tuned ring configuration with a fiber Fabry Perot filter used as a tuning element and a semiconductor amplifier as gain medium. The output of the master laser is subsequently power boosted using an Ytterbium doped fiber amplifier (YDFA). In addition to providing a power boost, we demonstrate that by tailoring the gain spectrum of the YDFA it is possible to increase the FWHM scanning range by 7 nm compared to that of the master laser.

Phase sensitive optical coherence tomography (OCT) can be used to obtain sub-nanometer displacement measurements of biological and non-biological samples. This technique has many applications, including detection of small amplitude surface motion, and high axial resolution OCT phase microscopy. Doppler OCT is another type of phase sensitive imaging, where differential phase measurements are used to detect fluid flow in biological specimens. For all types of phase sensitive OCT, a light source with low phase noise is required in order to provide good displacement sensitivity. High speed imaging is also necessary in order to minimize motion artifacts and enable the detection of fast transient events. In this manuscript, buffered Fourier Domain Mode Locked (FDML) lasers are demonstrated for ultrahigh-speed phase sensitive OCT detection. The lasers are operated at sweep speeds of 42, 117, and 370 kHz, and displacement sensitivities of 39, 52, and 102 pm are achieved, respectively. These displacement sensitivities are comparable to spectrometer-based phase sensitive OCT systems, but acquisition speeds 1.4 - 13x faster are possible using buffered FDML lasers. An additional factor of √2 improvement in noise performance is observed for differential phase measurements, which has important implications for Doppler OCT. Dynamic measurements of rapid, small-amplitude piezoelectric transducer motion are demonstrated. In general, buffered FDML lasers provide excellent displacement sensitivities at extremely high sweep speeds for phase sensitive OCT measurements.

A real-time, ultrahigh resolution full-field (FF) optical coherence tomography (OCT) system has been developed using a dual-channel detection technique. Our FF-OCT system is based on a white-light interference microscope combined with a polarization sensitive dual-channel detection technique using a pair of CCD cameras, where a pair of images with 90- degree phase difference are simultaneously captured with an achromatic phase shifter. By acquiring an additional pair of images using a conventional phase shift method, an inphase and a quadrature component of FF-OCT image are acquired by calculating the differences every two consecutive CCD frames. Sum of their squares then yields FF-OCT image. Using the ultrabroad bandwidth of halogen lamp and relatively high-NA objectives, an axial resolution of 1.2 &mgr;m and a transverse resolution of 1.7 &mgr;m have been achieved. Sub-cellular imaging results of porcine conjunctiva and esophagus recorded as fast as 40 ms are presented.

Line-field spectral domain optical coherence tomography (LF-SDOCT), which is a parallel detection OCT technique that provides single cross-sectional image without mechanical scanning, has been developed for very high-speed three-dimensional (3D) imaging of human retina in vivo. By optimizing the integration time of the camera for the sample motion, we have successfully performed the in vivo 3D retinal imaging, which is sufficiently free from the motion artifact. The achievable A-lines rate is 54.4 kHz A-lines/s with the maximum sensitivity of 89.4 dB, and it corresponds to more than 2 times higher speed than conventional flying spot SD-OCT system. The in vivo 3D retinal measurement with the 256 cross-sectional images (528 A-lines/image) was successfully performed at 2.5 seconds.

We report a full-field, phase-shifting microscope with precise control of the optical path difference (OPD) and show topographic phase images of living cells. Our system is based on a Linnik interference microscope with Kohler illumination of a halogen lamp for the imaging lightsource. Phase-sensitive active-stabilization of the OPD is employed with an infrared laser whose optical path is the same as that of halogen light. We previously reported the results of cultured cell topography with this stabilization scheme; however the phase stability and the image quality were insufficient. We have improved the noise-cancellation system and achieved control of the OPD with stability down to 0.7 nm in the bandwidth of 500 Hz. Quarter wavelength phase-shifting was carried out with sub-nanometer accuracy, and clear topographic phase images of cultured single-layer cells were obtained. The Kohler illumination with the halogen lamp, whose coherence length is 2 &mgr;m, enables homogenous illumination and suppression of artifact signals arising from optical components not associated with the surface of interest.

In high-numerical-aperture optical coherence tomography, the depth-of-field is usually quite short and therefore the focus is scanned through the object to form a well-resolved image of the entire volume. However, this may be inconvenient for in vivo scanning when precision placement is not easily achieved between the object and the focusing objective. We show that by scanning the illumination wavelength, and using novel inverse scattering methods on the detected interferograms, features outside of the focus can be resolved and therefore the focus does not need to be scanned.

We present an experimental study of the depolarization of circularly polarized (CP) light backscattered from random media. We employ a polarization sensitive OCT, capable of producing intensity profiles for two orthogonal polarization channels simultaneously. For CP light backscattered from polystyrene solutions containing spherical particles of sizes larger than the radiation wavelength, the phenomenon of polarization memory is observed. The degree of circular polarization (DOCP) as a function of the path the light travels in the medium depends on the scatterers' size. In the case of scatterers larger than the wavelength, the DOCP exhibits a minimum indicating a helicity cross-over. The copolarized light then exceeds the intensity of cross-polarized light of backscattered radiation, a phenomenon predicted theoretically but not observed experimentally so far. The helicity cross-over is observed in the DOCP curves for large scatterers at small and large concentrations.

The early stages of malignancy, in most tissues, are characterized by unique cellular changes. Currently, these early changes are detectable only by confocal or multi-photon microscopy. Unfortunately, neither of the two imaging techniques can penetrate deep enough into the tissue to investigate the borders of thick lesions. A technique which would allow extraction of information regarding scatterer size from Optical Coherence Tomography (OCT) signals could prove a very powerful diagnostic tool and produce significant diagnostic insight. Such a procedure is proposed here. It is shown to be very effective in differentiating spectral differences which depend on scatterer size. The analysis of the OCT signal is based on spectral estimation techniques and statistical analysis. First, using autoregressive spectral estimation, it was deduced that tissues with different size scatterers exhibit marked differences in spectral content. Further, advanced analysis techniques, such as Principal Component Analysis (PCA) and Multivariate Analysis of Variance (MANOVA), provided more insight into the spectral changes. These techniques where tested on solutions of known scatterers and multilayered samples. The initial results are very encouraging and indicate that the spectral content of OCT signals can be used to extract scatterer size information. This technique can result in an extremely valuable tool for the investigation of disease tissue features which now remain below the resolution of OCT.

Digital holographic optical coherence imaging (DHOCI) is a full-frame coherence-gated imaging approach that uses a CCD camera to record and reconstruct a digital hologram from inside tissue. Our recording of digital holograms at the optical Fourier plane has advantages for diffuse targets compared with Fresnel off-axis digital holography. DHOCI is capable of performing functional imaging by using dynamic image speckle as a contrast agent to locate regions of high metabolic activity characterized by high cellular motility. We show strong dynamic speckle difference between three metabolic states of a tumor, and demonstrate that functional imaging in DHOCI can capture motility information with high contrast. We apply functional imaging to track the effect on cell motility by temperature changes or cytoskeletal drugs.

We advance the magnetomotive-optical coherence tomography (MM-OCT) technique for detecting displacements of magnetic nanoparticles embedded in tissue-like phantoms by using apmplitude and phase-resolved methods with spectral-domain optical coherence tomography (SD-OCT). The magnetomotion is triggered by the external, noninvasive application of a magnetic field. We show that both amplitude and phase data are indicative of the presence and motion of light scatterers, and could potentially be used for studying the dynamics of magnetomotion. The magnetic field modulation is synchronized with data acquisition in a controlled, integrated system that includes a console for monitoring and initiating data acquisition, scanning devices, an electromagnet power supply, and the detection system. Using Fourier analysis, we show that the amplitude and phase modulations in the samples that contain magnetic contrast agents match the frequency of the applied magnetic field, while control samples do not respond to magnetic field activity. We vary the strength of the magnetic field and show that the amplitude and phase steps between regions of zero-magnetic field and regions with non-zero magnetic field change accordingly. The phase is shown to be more sensitive.

We have undertaken an effort to further develop ground state recovery Pump-Probe Optical Coherence Tomograpy (gsrPPOCT) to specifically target and measure 3-D images of hemoglobin concentration with the goals of mapping tissue vasculature, total hemoglobin, and hemoglobin oxygen saturation. As a first step toward those goals we have measured the gsrPPOCT signal from the hemoglobin in the filament arteries of a zebra danio fish. We have further processed the resulting signal to extract a qualitative map of the hemoglobin concentration. We have also demonstrated the potential to use ground state recovery times to differentiate between two chromophores which may prove to be an effective tool for differentiating between oxy and deoxy hemoglobin.

Gold nanorods ~14 × 44nm exhibit a surface-plasmon resonance (SPR) peaked near 800nm which is dominated by absorption, not scattering. Because biological tissues in the near-infrared wavelength regime are predominantly scattering (high albedo), the addition of trace amounts of nanorods can be detected by their lowering of the albedo. Albedo is a preferred measurement parameter because it is insensitive to inhomogeneities in the density of scatterers. For optical coherence tomography (OCT) imaging applications, a related parameter called the backscattering albedo, equal to the ratio of the backscattering coefficient to the total extinction, is introduced for detecting gold nanorods. Here we use this parameter to investigate gold nanorods as contrast agents for optical coherence tomography (OCT). Measurements in 2% intralipid tissue phantoms reveal a sensitivity to ~30ppm nanorods when the density of the intralipid is randomized by 0.4% (or a fraction of 0.2). This has application toward molecular imaging using targeted nanorods within densely scattering, inhomogeneous tissues.

We used continuum generated in an 8.5 cm long fiber by a femtosecond Yb fiber laser to improve threefold the axial resolution of frequency domain SH-OCT to 12&mgr;m. The acquisition time was shortened by more than two orders of magnitude compared to time domain SH-OCT. The system was applied to image biological tissue of fish scales, pig leg tendon and rabbit eye sclera. Highly organized collagen fibrils can be visualized in the recorded images. Polarization dependence on second harmonic has been used to obtain polarization resolved images.

We developed axial-lateral parallel time domain optical coherence tomography (OCT) with an ultrahigh-speed complementary metal oxide semiconductor (CMOS) camera. A cylindrical lens is inserted in the signal arm to illuminate the sample with a linear beam that can be moved horizontally by a galvano scanner. A reflective grating is installed in the Littrow configuration so that first-order diffracted light propagates backward along the incoming path at the reference beam to obtain a continuous delay. The backscattered light from the sample and the diffracted light from the grating are imaged onto a CMOS camera (512 × 512 pixels, 17 × 17 &mgr;m pixels, 10 bit resolution, frame rate 3000 fps) using an achromatic imaging lens. The camera obtains a depth-resolved interference image using diffracted light as the reference beam and a linear illumination beam without axial and vertical scans. We can obtain the OCT images (512 × 512 pixels) at 1,500 fps by calculating two sequential images. To create a 3-D image, the linear probe beam was scanned at 3 Hz to obtain volume data. 500 interference images per scan (corresponding to 250 OCT images through calculations from two sequential images) created a 3-D dataset of 512 × 250 × 512 pixels. The experimental sensitivity was approximately 76 dB after 2 × 2-pixel binning. The system was successfully used to image the human finger in vivo.

Optical coherence tomography relies on the coherent gating and coherent amplification from its reference light to produce high axial resolution, high sensitivity image. The signal to noise ratio of the optical coherence tomography image is proportional to the detected back-scattering photon numbers from sample beam. Thus, the gain of an optical amplifier device can be added to the weak sample beam reflected signal while preserving its coherence by the coherent amplification process when the weak back reflected signal is amplified by the optical amplifier device. However, the optical amplifier device will emit spontaneous emission in its coherent amplification process. In this study, we report some preliminary results on the investigation of the coherent amplification and the side effects caused by the spontaneous emission in a swept source OCT system.

Fourier-domain optical coherence tomography (FDOCT) has attained popularity due to its static parts, high imaging speed[1], and high sensitivity[2]. FDOCT makes use of spectral interferometry and collects data in the spectral domain, either using a spectrometer with a detector array or by a single point detector with a wavelength-swept light source[3]. The axial resolution depends on the bandwidth of the spectrum. The spectral response of the spectrometer is always desired to be flat in order to have the best axial resolution corresponding to the light source spectrum. Unfortunately, the optics consisting of the spectrometer usually shape the spectrum. The optimum optics design and alignment will minimize the spectral shaping. The frequency response simulation by advanced optical design software displays a clear picture for our design and system alignment. The axial imaging range of FDOCT according to the Fourier transform relationship is ultimately limited by a fringe visibility degrading curve with increasing imaging depth due to the spectral sampling spacing called the fall-off [4]. This limitation is significant for applications of spectrometer-based FDOCT where a long imaging range is desirable (e.g the anterior segment of the eye), especially when imaging uses 1.3 &mgr;m light because large pixel-count arrays are not currently commercially available. Although resolving complex-conjugate ambiguity[5] and Sub-pixel shifting[6] have extended the image range, the imaging range of FDOCT is still limited by the fall-off, which is a primary concern in the design of a spectrometer-based FDOCT system. A mathematical model of spectrometer-based FDOCT can aid in understanding of signal formation, including fall-off [ref OL].

We demonstrate dispersion compensation by using a dispersion shifted fiber (zero dispersion at a wavelength of 1550 nm) in an optical-frequency domain imaging (OFDI) - optical coherence tomography (OCT) system for tooth imaging. In the system, we use a tunable laser diode operating in the 1550 nm wavelength region (1533-1573 nm) as a light source, because we can expect a smaller absorption coefficient for the enamel layer of a tooth than with a 1300 nm light source. This simple and cost-effective method provides an axial resolution of 27 &mgr;m in air, which is the theoretically expected value, although the value is 36 &mgr;m without compensation. By measuring an extracted human tooth with compensation, we also confirm the realization of greatly improved contrast at the boundary between the enamel and dentin layers. This compensation technique might prove even more effective if we use a light source with a wider wavelength range.

A novel wavelength swept broadband source based on an ultrashort pulse laser and an external tunable filter was proposed for application of frequency domain-optical coherence tomography (FD-OCT). The laser beam coupled into the single mode fiber, which provided 0.5-nm instantaneous spectral linewidth with 1-mW average output power, was tuned from 740 nm to 850 at a 1 kHz repetition rate. The system with an axial resolution of 5 &mgr;m performed OCT imaging of air-gap between glass plates proving potential about the application of pulse laser source to FD-OCT system. The proposed swept source scheme could be applied for the implementation of ultra-high resolution FD-OCT system based on a supercontinuum source with an ultra-short pulse laser and a high nonlinear optical fiber.

We demonstrate a novel imaging technique for high-speed optical-frequency domain imaging (OFDI)with a discretely swept laser source. In this technique, one frame of OCT data can be acquired within a single frequency sweep. Tomographic images consisting of 1550 A-lines are obtained at 21 frames per second. The method is explained and experimental results are demonstrated.

The superstructured-grating distributed-Bragg-reflector laser is a small (shorter than 1 mm in length) and relatively cheap swept source for optical-frequency-domain- reflectometry optical coherence tomography (OFDR-OCT), which practically enables use of multiple sources in a single OCT system. Simultaneous scanning of multiple sources over different wavelength regions and at different wavelength values in the same wavelength region enable improvement of the resolution and scanning speed, respectively. Those improvements have been demonstrated using C-band and L-band SSG-DBR sources.

In this paper we demonstrate a new algorithm for use in Doppler Optical Coherence Tomography (DOCT) to allow the detection of flow with a peak velocity of over 1.5 m/s. Previous Doppler estimation methods have utilized a transverse Kasai (TK) autocorrelation technique which computes the phase difference between points adjacent in time at the same spatial location, hereon referred to as transversely adjacent points. The maximum detectable TK velocity is low due to the small axial scanning frequency, f_a which creates aliasing. To overcome the low sampling rate, we propose using data acquired in the axial direction which has a sampling rate orders of magnitude larger. Taking an autocorrelation in the depth, or axial direction, yields a quantity that can be related to the mean backscattered frequency. We demonstrate that through subtraction of the axial autocorrelation of a moving scatterer from that of a stationary scatterer at the same spatial location, one is able to obtain the Doppler shift with a much higher non-aliased limit. We have defined this method the axial Kasai (AK) technique. Through use of the AK, we demonstrate maximum non-aliased Dopler frequency estimate on a time domain DOCT system to be increased from the TK limit of ±4 kHz to the AK limit of ±1.6 MHz. In contrast to the high detection range of the AK, the TK maintains superior velocity resolution for low flow rates. Through a combined approach with the AK we have demonstrated a dynamic frequency range of over 100 dB with a velocity detection range from 10 &mgr;m/s to over 1.5 m/s. The velocity range has been extended to span both microcirculation and cardiac blood velocities.

We propose a robust and efficient delay line using an ensemble of rotating rhombic prisms. Delay lines relying on rotating elements provide fast and stable operation. Optical systems using rhombic prisms are quite easy to align since these prisms are efficient even when slightly misaligned. Optical delay lines with a single rotating element usually have a poor duty cycle and show large nonlinearity in the variation of the optical path lengh with the angular position. Our delay line improves over existing technology by using off-centroid rotation and reinjection. Off-centroid rotation allows the use of multiple prisms and, by optimizing the conditions of operation, the duty cycle is increased and the nonlinearity is decreased. The duty cycle and repetition rate are further increased by reinjecting the incoming ray towards the delay line when it is not first intercepted by the prism ensemble. We have designed and built such a delay line using five prisms. The experimental device was tested at 2000 delay scans per second and provided a duty cycle larger than 80% with about 5% nonlinearity. Higher delay scan rates are easily achievable with this technology. The delay line was introduced in a time-domain optical coherence tomography system and example of imaging of biological tissue is provided.

Optical Coherence Tomography (OCT) shows great promise for low intrusive biomedical imaging applications. A parallel OCT system is a novel technique that replaces mechanical transverse scanning with electronic scanning. This will reduce the time required to acquire image data. In this system an array of small diameter fibers is required to obtain an image in the transverse direction. Each fiber in the array is configured in an interferometer and is used to image one pixel in the transverse direction. In this paper we describe a technique to package 15&mgr;m diameter fibers on a siliconsilica substrate to be used in a 2mm endoscopic probe tip. Single mode fibers are etched to reduce the cladding diameter from 125&mgr;m to 15&mgr;m. Etched fibers are placed into a 4mm by 150&mgr;m trench in a silicon-silica substrate and secured with UV glue. Active alignment was used to simplify the lay out of the fibers and minimize unwanted horizontal displacement of the fibers. A 10-channel fiber array was built, tested and later incorporated into a parallel optical coherence system. This paper describes the packaging, testing, and operation of the array in a parallel OCT system.

Recently, Fourier-Domain Optical Coherence Tomography (FDOCT), which is a spectral interferometer having a high speed scanning system, has been improved as 3-dimensional micro imaging technique. This has attracted the attention of medical scientists as a promising system of early cancer detection. It, however, has been difficult to quantitatively detect tumor lesion and its malignancy, because interference signals could be dependent on optical properties of biological tissue. In this study, we propose a tumor detection system based on FDOCT and oncotropic dye, namely Fourier-Domain Optical Coherence Dosimetry (FDOCD). OCT signals have the information of absorption by oncotropic dye as well as scattering from tissue, which are separately extracted by Windowed Inverse FFT corresponding to wavelength bands of interest. Therefore, FDOCD can simultaneously obtain two optical kinds of tomography, i.e. absorption profile as disease demarcation and scattering profile from morphologic distribution. In the present report, the calibration experiment was carried out to verify separate detection of scattering and absorbance. As a result, it indicated that FDOCD could determine the distribution of scatterer density, eliminating the signal degradation by optical absorption, e.g. drug concentration. It was suggested that FDOCD could separately and quantitatively monitor scatterer density and drug concentration.

We compare the detected signal in the radiometric transillumination experiment for two sources: a gas laser with high coherence, and an LED with low coherence. Detected signal is significantly improved when a low-coherent light source is utilized, allowing us to clearly separate ballistic photons from those that undergo multiple scattering. The preliminary experimental results confirm the feasibility of the concept, requiring precise matching of the source coherence with the scattering behavior of the tissue (phantom) under study.

Birefringence of retinal nerve fiber layer is measured by polarization-sensitive spectral domain optical coherence tomography using the B-scan-oriented polarization modulation method. 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 retinal nerve fiber layer are shown. Unlike scanning laser polarimetry, our system can measure the phase retardation quantitatively without using bow-tie pattern of the birefringence in the macular region, which enables diagnosis of glaucoma even if the patients have macular disease.

In this study, PS-OCT is used to image fresh bovine joints to investigate the orientation of collagen fibrils in relation to optical phase retardation to better understand the distribution of normal matrix orientation and articular cartilage birefringence in different regions of a whole joint. Understanding and mapping variations in matrix organization and orientation within the normal joint is an important issue in potential applications of PS-OCT for evaluation and diagnosis of degenerative joint disease (DJD). The experimental results demonstrate that articular cartilage is not polarization sensitive on the edge of the medial, but polarization sensitive on the lateral edge of the tibial plateau. The collagen orientation on the edge of the joint is different from the central areas of the joint. Normal articular cartilage demonstrates regional polarization sensitivity within joints that is important to understand in order to accurately assess cartilage health by PS-OCT.

Polarization-sensitive optical coherence tomography has been used to solve fast-axis fibre orientation in three dimension space. Previously we have demonstrated that the apparent variations in polar angle orientation of collagen fibers along sagittal ridge of equine third metacarpophalangeal joint exist. A quantitative method based on multiple angles of illumination has been proposed to determine the polar angle of the collagen fibers. This method however ignored the full 3-D structure by assuming that the collagen fibers long-axis lay within the plane of incidence. A new quantitative method based on the theory of light propagation in uniaxial materials is described which avoids this assumption. To test this method we have performed control experiments on a sample of equine tendon (this tissue has well defined c-axis lying along the long-axis of the tendon). Several samples of tendon were cut to achieve a planar surface inclined at -20° to the long axis. Additional 30° rotation provided non-zero azimuthal angle. The surface was then imaged using incident beam angles -40°, -20°, 0, +20°, +40° in two orthogonal planes. Values for both the polar and azimuthal angles were then derived using a numerical optimisation procedure. Results agreed qualitatively with the nominal values but suggested that the accuracy was limited by our method of determining the apparent birefringence.

Acute coronary syndromes, e.g. myocardial infarctions, are caused by the rupture of unstable plaques on coronary arteries. The stability of plaque, which depends on biomechanical properties of fibrous cap, should be diagnosed crucially. Recently, Optical Coherence Tomography (OCT) has been developed as a cross-sectional imaging method of microstructural biological tissue with high resolution 1~10 &mgr;m. Multi-functional OCT system has been promising, e.g. an estimator of biomechanical characteristics. It has been, however, difficult to estimate biomechanical characteristics, because OCT images have just speckle patterns by back-scattering light from tissue. In this study, presented is Optical Coherence Straingraphy (OCS) on the basis of OCT system, which can diagnose tissue strain distribution. This is basically composed of Recursive Cross-correlation technique (RC), which can provide a displacement vector distribution with high resolution. Furthermore, Adjacent Cross-correlation Multiplication (ACM) is introduced as a speckle noise reduction method. Multiplying adjacent correlation maps can eliminate anomalies from speckle noise, and then can enhance S/N in the determination of maximum correlation coefficient. Error propagation also can be further prevented by introducing to the recursive algorithm (RC). In addition, the spatial vector interpolation by local least square method is introduced to remove erroneous vectors and smooth the vector distribution. This was numerically applied to compressed elastic heterogeneous tissue samples to carry out the accuracy verifications. Consequently, it was quantitatively confirmed that its accuracy of displacement vectors and strain matrix components could be enhanced, comparing with the conventional method. Therefore, the proposed method was validated by the identification of different elastic objects with having nearly high resolution for that defined by optical system.

We demonstrate in-vivo imaging of sweat glands of human finger tip using the dynamic optical coherence tomography (OCT). Mentally-stress-induced sweating in sweat glands of human finger tip can be observed clearly in time-sequential OCT images. In the experiment, a sweat pore opened clearly on the skin surface according to a stimulus of sound.

We present 3-dimensional volume-rendered in vivo images of developing embryos of the African clawed frog Xenopus laevis taken with our new en-face-scanning, focus-tracking OCM system at 1300 nm wavelength. Compared to our older instrument which operates at 850 nm, we measure a decrease in the attenuation coefficient by 33%, leading to a substantial improvement in depth penetration. Both instruments have motion-sensitivity capability. By evaluating the fast Fourier transform of the fringe signal, we can produce simultaneously images displaying the fringe amplitude of the backscattered light and images showing the random Brownian motion of the scatterers. We present time-lapse movies of frog gastrulation, an early event during vertebrate embryonic development in which cell movements result in the formation of three distinct layers that later give rise to the major organ systems. We show that the motion-sensitive images reveal features of the different tissue types that are not discernible in the fringe amplitude images. In particular, we observe strong diffusive motion in the vegetal (bottom) part of the frog embryo which we attribute to the Brownian motion of the yolk platelets in the endoderm.

We propose the envelope detection method that is based on Hilbert transform for image restoration in full-filed optical coherence tomography (FF-OCT). The FF-OCT system presenting a high-axial resolution of 0.9 &mgr;m was implemented with a Kohler illuminator based on Linnik interferometer configuration. A 250 W customized quartz tungsten halogen lamp was used as a broadband light source and a CCD camera was used as a 2-dimentional detector array. The proposed image restoration method for FF-OCT requires only single phase-shifting. By using both the original and the phase-shifted images, we could remove the offset and the background signals from the interference fringe images. The desired coherent envelope image was obtained by applying Hilbert transform. With the proposed image restoration method, we demonstrate en-face imaging performance of the implemented FF-OCT system by presenting a tilted mirror surface, an integrated circuit chip, and a piece of onion epithelium.

Since many medical diagnostic methods are non-invasive and even non-contact, they are well suited for inspection of fragile and unique objects of art. In art conservation it is a need for convenient and non-invasive method for monitoring of removal of the varnish layer from paintings - one of the most crucial operations in their restoration. In this study we present application of the Spectral Optical Coherence Tomography (SOCT) for in-situ monitoring of the laser ablation of the varnish layer. The examination of the ablation craters made with Er:YAG laser permits for the optimization of the laser emission parameters like fluency and working regime, with respect to efficiency and safety of the ablation process. Frames from the SOCT movies obtained during real time monitoring of the burning of the ablation crater are shown for the first time.

A fiber probe that is capable of two-dimensional traversal scanning is developed and implemented to a time-domain optical coherence tomography (OCT). Due to its geometrical structure, the fiber cantilever of the probe has two intrinsic resonant frequencies. When the probe is base-excited by signal with two mixed frequencies near the resonances, traversal scanning pattern is generated with controllable area coverage through fine tuning of frequency ratio and fetching period. A position sensitive detector is introduced in the probe to record the real-time trajectory of the scanning pattern for image reconstruction. Fast OCT images of samples including rule, coin and leaf are obtained with the developed probe applied to our time-domain OCT setup. We envision obtaining rapid three-dimensional imaging with the developed probe in a Fourier domain OCT system.

Optical coherence tomography (OCT) is an emerging cross-sectional imaging technology. It uses broadband light sources to achieve axial image resolutions on the few micron scale. OCT is widely applied to medical imaging, it can get cross-sectional image of bio-tissue (transparent and turbid) with non-invasion and non-touch. In this paper, the principle of OCT is presented and the crucial parameters of the system are discussed in theory. With analysis of different methods and medical endoscopic system's feature, a design which combines the spectral domain OCT (SDOCT) technique and endoscopy is put forward. SDOCT provides direct access to the spectrum of the optical signal. It is shown to provide higher imaging speed when compared to time domain OCT. At the meantime, a novel OCT probe which uses advanced micromotor to drive reflecting prism is designed according to alimentary tract endoscopic feature. A simple optical coherence tomography system has been developed based on a fiber-based Michelson interferometer and spectrometer. An experiment which uses motor to drive prism to realize rotating imaging is done. Images obtained with this spectral interferometer are presented. The results verify the feasibility of endoscopic optical coherence tomography system with rotating scan.