We have presented previously a novel method for the evaluation of the surface shape of an object, with immediate application to measurement of cornea shape. This method uses single shot C-scans obtained by using a multiple delay element (MDE) in the reference path of an OCT system. A calibrated MDE-OCT system can be used to measure the elevation of points on the cornea, in contrast to existing methods which are based on measurement of the cornea slope. The associated algorithm for extracting corneal topography data points from the MDE-OCT C-Scan image will be presented, data points which can then be used to calculate the Zernike coefficients for the cornea shape. The differences between the existing systems and the MDE-OCT method for keratometry and corneal topography are discussed.

We report on a new method for segmenting the retinal pigment epithelium (RPE) in polarization sensitive optical coherence tomography (PS-OCT) images of the human retina. Contrary to previous segmentation algorithms that were based on variations of backscattered intensity between individual layers, our method uses an intrinsic tissue property of the RPE: its depolarizing, or polarization scrambling effect on backscattered light. By using a state of the art spectral domain PS-OCT instrument, we demonstrate the method in healthy eyes and in eyes of patients with age related macular degeneration.

Fixed partial prostheses as integral ceramics, integral polymers, metal ceramics or metal polymers bridges, are mainly used in the frontal part of the dental arch (especially the integral bridges). They have to satisfy high stress requirements as well as esthetic. The masticatory stress may induce fractures of the bridges. These may be triggered by initial materials defects or by alterations of the technological process. The fractures of these bridges lead to functional, esthetic and phonetic disturbances which finally render the prosthetic treatment inefficient. The purpose of this study is to evaluate the capability of en-face optical coherence tomography (OCT) in detection and analysis of possible fractures in several integral fixed partial dentures. The materials used were represented by several fixed partial prostheses, integral ceramics, integral polymers, metal ceramics and metal polymers bridges. In order to discover the defects, scanning was performed from incisal, vestibular, oral and cervical directions material defects such as fractures and pores were investigated using OCT. In conclusion, en-face OCT has proven as a valuable non invasive method to investigate fixed partial prostheses before their insertion in the oral cavity.

We report an endoscopic optical coherence tomography (OCT) system based on a Fourier Domain Mode Locked (FDML) laser, a novel data acquisition (DAQ) system with optical frequency clocking, and a high-speed spiralscanning fiber probe. The system is capable of acquiring three-dimensional (3D) in vivo datasets at 100,000 axial lines/s and 50 frames/s, enabled by the high sweep rates of the FDML laser and the efficient data processing of the DAQ system. This high imaging rate allows densely-sampled 3D datasets to be acquired, giving a resolvable feature size of 9 &mgr;m x 20 &mgr;m x 7 &mgr;m (transverse x longitudinal x axial, XYZ). In vivo 3D endomicroscopy is demonstrated in the rabbit colon, where individual colonic crypts are clearly visualized and measured. With further improvements in DAQ technology, the imaging speed will be scalable to the hundreds of thousands of axial lines/s supported by FDML lasers.

An OCT system incorporating a coherent fibre imaging bundle is described. Fibres are accessed sequentially by a beam focused onto the input face of the bundle, allowing 2D or 3D images to be acquired using point detection. A Fizeau interferometer configuration is used, in which light from the distal end of a fibre in the bundle (forming the reference arm) mixes with light reflected by the sample itself (forming the sample arm). The use of coherent imaging bundles for OCT beam delivery allows mechanical scanning parts to be removed from the sample arm, resulting in a passive probe. Such a configuration can form a compact, robust and "downlead insensitive" OCT system. In the common-path configuration used, an inherent path-length difference is present in the Fizeau sample interferometer, so an additional processing interferometer is required to ensure path-length matching. The depth scanning mechanism is confined within the processing interferometer, external to the sample probe.

The measurement of ocular blood flow is important in studying the pathophysiology and treatment of several leading causes of blindness. We present a method for in vivo human retinal flow measurement using Fourier domain optical coherence tomography. A double circular scanning pattern was used to scan the blood vessels around the optic nerve head 8 times over 2 seconds. The venous flow totaled 36.13 μl/min in the right eye of a volunteer. The flow difference was observed before and after breath holding. The fast flow measurement method did not require any assumption on the flow profile over time or space.

Optical Doppler tomography (ODT) is a branch of optical coherence tomography (OCT) that can measure the speed of a blood flow by measuring the Doppler shift impinged on the probing sample light by the moving blood cells. However, the measured speed of blood flow is a function of the Doppler angle, which needs to be determined in order to calculate the absolute velocity of the blood flow inside a vessel. We developed a technique that can extract the Doppler angle from the 3D data measured with spectral-domain OCT, which needs to extract the lateral and depth coordinates of a vessel in each measured ODT and OCT image. The lateral coordinates and the diameter of a blood vessel were first extracted in each OCT structural image by using the technique of blood vessel shadowgram, a technique first developed by us for enhancing the retinal blood vessel contrast in the en face view of the 3D OCT. The depth coordinate of a vessel was then determined by using a circular averaging filter moving in the depth direction along the axis passing through the vessel center in the ODT image. The Doppler angle was then calculated from the extracted coordinates of the blood vessel. The technique was applied in blood flow measurements in retinal blood vessels, which has potential impact on the study and diagnosis of blinding diseases like glaucoma and diabetic retinopathy.

Quantification of the three-dimensional (3D) retinal vessel structure and blood flow is demonstrated. 3D blood flow distribution is obtained by Doppler optical coherence angiography (D-OCA). Vessel parameters, i.e. diameter, orientation, and position, are determined in an en face vessel image. The Doppler angle is estimated as the angle between the retinal vessel and the incident probing beam in representative cross-sectional flow image which extracted from the 3D flow distribution according to the vessel parameters. Blood flow velocity and volume rate can be quantified with these vessel parameters. The retinal blood flow velocity and volume rate are measured in the retinal vessels around the optic nerve head.

We describe a high-speed Fourier domain optical coherence tomography (OCT) using optical de-multiplexers for spectral dispersion of interferograms. The optical de-multiplexer enables to separate 256 narrow spectral bands from a broadband incident light in 25.0 GHz frequency interval centered at 192.2 THz (1559.8 nm) and allows simultaneous detection of all the bands at the speed of DAQ. Using the optical de-multiplexers into a Fourier domain OCT system as spectral analyzers, OCT imaging of 60,000,000 axial scans per second has been achieved. Using a resonant scanner for lateral scan, 16 kHz frame rate, 1400 A-lines per frame, 3 mm depth range, 23 micron meter resolution OCT imaging has been demonstrated.

The linear wave-number spectrometer for spectral domain optical coherence tomography (SD-OCT) is proposed. Compensation by optical glass prism is used to make optical frequency readouts equidistant in diffraction grating based spectrometer. We demonstrate that selection of only two optical prism parameters almost completely eliminates non-equidistance of optical frequency readouts. Proposed optically linearized spectrometer allows reconstructing OCT image without any numerical resampling.

The lateral resolution of Fourier domain optical coherence tomography (FD-OCT) systems is limited by the depth of focus that can be achieved over the desired imaging depth at the chosen wavelength. Various solutions have been proposed such as Bessel beams and computational methods; however these suffer from various practical drawbacks. We present a novel optical set-up involving multiple optical channels that does not suffer from these drawbacks and delivers at least double the resolution of a single beam system. The theory of this approach is discussed, also the realisation in a practical laboratory system, measurement results and initial application in assessing oesophageal cancers and pre-cancers.

We demonstrate a novel implementation of spectral domain OCT by using a proposed sweeping detector at 1320 nm wavelength range. A fiber pigtailed Fabry-Perot tunable filter is newly adapted to receive spectral interferometer information using a photo-receiver instead of using charged couple detector arrays. In order to show a possibility of the scheme in other view point, we have changed the position of the Fabry-Perot tunable filter of the interferometer. The combination of a super luminescent LED and a semiconductor optical amplifier was used as an optical source. Its output power is about 10 mW and the spectral bandwidth is about 60 nm. The filtered light after passing thorough the Fabry- Perot tunable filter has 0.15 nm instantaneous spectral linewidth with 1.3 mW average output power. The system with an axial resolution of 12 μm performed OCT imaging of a cornea of a rat eye proving potential about the application of the proposed sweeping detector OCT.

Optical Coherence Tomography (OCT) is a promising medical imaging technique. It has found applications in many fields of medicine and has a large potential for the optical biopsy of tumours. One of the technological challenges impairing faster adoption of OCT is the relative complexity of the optical instrumentation required, which translates into expensive and bulky setups. In this paper we report an implementation of Time Domain OCT (TD-OCT) based on a silicon photonic platform. The devices are fabricated using Silicon-On-Insulator (SOI) wafers, on which rib waveguides are defined. While most of the components needed are well-known in this technology, a fast delay line with sufficient scanning range is a specific requirement of TD-OCT. In the system reported, this was obtained making use of the thermo-optical effect of silicon. By modulating the thermal resistance of the waveguide to the substrate, it is possible to establish a trade-off between maximum working frequency and power dissipation. Within this trade-off, the systems obtained can be operated in the kHz range, and they achieve temperature shifts corresponding to scanning ranges of over 2mm. Though the current implementation still requires external sources and detectors to be coupled to the Planar Lightwave Circuit (PLC), future work will include three-dimensional integration of these components onto the substrate. With the potential to include the read-out and driving electronics on the same die, the reported approach can yield extremely compact and low-cost TD-OCT systems, enabling a wealth of new applications, including gastrointestinal pills with optical biopsy capabilities.

The authors report investigations into the suitability of a broadband supercontinuum fiber laser (SCFL) for use in Optical Coherence Tomography (OCT). The supercontinuum of light extending from 400 nm to 1800 nm can be used selectively in several spectral wavebands from 600 nm to 1700 nm in order to characterize the performance of single mode (SM) fiber OCT systems through spectral and auto-correlation measurements, dispersion measurements and image acquisition. Spectral selection and tailoring is made possible through a combination of bandpass optical filters. In addition, for the first time, given the optical bandwidth available, we perform evaluation of effective noise bandwidths which take into consideration the spectral behavior of the optical splitter in the balanced detection receiver.

We demonstrate the feasibility of OCT imaging for the investigation of samples, which are processed by the short pulse laser. The use of short pulse lasers in various material processing have provided the advantages such as a high peak power and a small heat affected zone over conventional methods based on mechanical treatment. However, due to the improper application of the lasers, the unwanted surface or structural deformation of materials and the thermal damages around an irradiation spot can be caused. Thus, the real-time monitoring/evaluation of laser processing performance in-situ is needed to prevent the excessive deformation of the material and to determine optimal processing conditions. As a standard method to investigation of the material processing by using the lasers, the scanning electron microscopy (SEM) or the transmission electron microscopy (TEM) observation of a physically cleaved surface is used although sample damages are given during the cleaving and polishing process. In this paper, we utilized the OCT advantages such as high resolution and non-invasive investigation to evaluate the laser processing performance. OCT images for the deformation monitoring of the ABS plastic present correlation with images obtained from conventional investigation methods. OCT images of the maxillary bone clearly show the difference in the pit formation of the biological sample at different irradiation conditions. We prove the potential of OCT for the evaluation of laser-processed various samples. Integrating OCT system into a laser processing system, we can visualize the effect of laser-based treatments in clinical and industrial fields.

We propose and demonstrate two new techniques based on the hybrid-interferometer, composed of optical low-coherence interferometer and confocal optics to simultaneously measure the phase index (n_p), group index (n_g) and geometrical thickness (t) of optically transparent materials. In the first method, we utilize the interference signal measured with several laser sources having different center wavelength and calculate the square of dispersion parameter τ_c²) of a glass plate from the interference signals. By analyzing the dispersion effect of interference signals, we can successfully separate the three parameters. In the second method, we approximate the derivative term of phase index in the definition of group index, by using the confocal signals measured with the laser sources having different center wavelength. From this approximation, we can also separate the parameters. The average measurement errors of first and second method are ~0.123 %, ~0.061 % in geometrical thickness, ~0.133 %, ~0.066 % in phase index, and ~0.106 %, ~0.057 % in group index, respectively, for eight different samples which are B270, CaF2, two of BK7, two of fused silica, cover glass and cigarette cover film. We are currently attempting to improve the accuracy and this technique will be extended to index measurement for biomedical tissues.

We propose and demonstrate a programmable high-speed, frequency-swept laser for swept-source optical coherence tomography (SS-OCT). This new technique is based on Vernier effect of two pieces of Fabry-Perot electro-optic modulators. This technique offers a non-mechanical optical filter with high resolution and wide tuning range. By applying it to a Fourier domain mode-locked laser, such sweeps are generated. The Vernier effect filter can be modulated by arbitrary wave forms, thus this laser source can eliminate the rescaling process which is the main bottle-neck of the operation time in SS-OCT by applying frequency sweep to equidistant spacing in frequency. Effective repetition frequencies of 100kHz~1MHz are demonstrated with a tuning range of 17THz (140nm) at 1550nm center wavelength. OCT imaging of in vivo human sweat duct with A-line rate of 100kHz and 300kHz are also demonstrated. The resolution of 12μm~ is realized without rescaling process. We present an analysis which suggests design approaches for optimization performance.

Balanced detection is required to suppress relative intensity noise (RIN) in optical frequency domain imaging (OFDI). Because a 50/50 fiber coupler does not provide a 50% splitting ratio over the full sweeping wavelength, balanced detection by the coupler's differential output with a balanced receiver is not perfect. We have designed a new balancing scheme that detects two outputs of 50/50 coupler separately and corrects the spectral deviation in the digital domain. A better balanced detection scheme has been designed in this work. In stead of detecting the hardware balanced signal from the 50/50 fiber coupler, we digitize the two channel fringe signal independently and perform the signal balancing in the poset process. The new software based balancing significantly improves the RIN suppression. Afterward, a systematic noise analysis has been performed on the 1050nm OFDI system. The results demonstrate a RIN suppression of 33dB by spectrally corrected balanced detection, which is 11dB more that regular balanced detection.

We demonstrate a sensitivity improvement in an optical frequency domain reflectometry-optical coherence tomography (OFDR-OCT) system with a discretely swept light source by incorporating a semiconductor optical amplifier (SOA) in a sample arm. With the system, we achieve a high sensitivity of -134.4 dB when we measure the reflective mirror with an A-line rate of 0.25 kHz. This improves the sensitivity (-125.2 dB) by 9.2 dB compared with a system without the SOA. The OCT system without the SOA shows a signal-to-noise ratio (SNR) of 56 dB when the signal light power is attenuated by about 66 dB, and the SNRs of less than 56 dB are obtained at higher attenuation levels. However, an SOA-incorporated OCT system provides the SNR of 56 dB at the much higher attenuation level of 86 dB. This means that using the SOA offers the large signal light power margin of 20 dB needed to obtain SNR of 56 dB. It is shown that the power margin is qualitatively dependent on the optical gain of the SOA. From an experimental analysis of the noises in the SOA-incorporated system, we found that the sensitivity enhancement is mainly limited by the beat noise between the reference light and the amplified spontaneous emission (ASE) of the SOA. We obtained images that show clear cluster structures of enamel crystals near the dentin-enamel junction of an extracted human tooth with our SOA-incorporated discretely swept OFDR-OCT imaging, revealing the potential to achieve a high-speed OCT system with high sensitivity.

A high-speed, broadband Fourier domain mode-locked (FDML) wavelength swept source at center wavelength of 1300 nm for high-resolution and high-speed Fourier domain optical coherence tomography was demonstrated. With two semiconductor optical amplifiers as gain media, the laser is capable of FWHM tuning range of more than 135 nm and the edge-to-edge scanning range of more than 160 nm at 45.6 kHz sweeping rate. The peak power is 11.4 mW for both the forward and backward scans. With the built swept source, a FDOCT system was developed which can achieve 6.6 μm axial resolution in air.

We demonstrate a single-mode and fast wavelength swept light source by using Superestrucuture grating distributed Bragg reflector (SSG-DBR) lasers for use in optical frequency-domain reflectometry optical coherence tomography. The SSG-DBR lasers provide single-mode operation resulting in high coherency. Response of the wavelength tuning is very fast; several nanoseconds, but there was an unintentional wavelength drift resulting from a thermal drift due to injecting tuning current. The dri¹ft unfortunately requires long time to converge; more than a few milliseconds. For suppressing the wavelength drift, we introduced Thermal Drift Compensation mesa (TDC) parallel to the laser mesa with the spacing of 20 μm. By controlling TDC current to satisfy the total electric power injected into both the laser mesa and the TDC mesa, the thermal drift can be suppressed. In the present work, we fabricated 4 wavelength's kinds of SSG-DBR laser, which covers respective wavelength band; S-band (1496-1529 nm), C-band (1529-1564 nm), L^--band (1564-1601 nm), and L⁺-band (1601-1639). We set the frequency channel of each laser with the spacing 6.25 GHz and 700 channels. The total frequency channel number is 2800 channels (700 ch × 4 lasers). We simultaneously operated the 4 lasers with a time interval of 500 ns/channel. A wavelength tuning range of more than 140 nm was achieved within 350 μs. The output power was controlled to be 10 mW for all channels. A single-mode, accurate, wide, and fast wavelength sweep was demonstrated with the SSG-DBR lasers having TDC mesa structure for the first time.

We demonstrate a compact single-shot full-field optical coherence tomography (OCT) system for obtaining real-time high-resolution depth resolved en-face OCT images from weakly scattering specimens. The experimental setup is based on a Linnik type polarization Michelson interferometer and a four-channel compact polarization phase stepper optics. The four-channel phase-stepper optics comprise of a dual channel beam splitter, a Wollaston prism and a pair of wave plate for simultaneously capturing four quadratually phase-stepped images on a single CCD. The interferometer is illuminated using a SLD source with a central wavelength of 842 nm and a bandwidth of 16.2 nm, yielding an axial resolution of 19.8 μm. Using a 10 × (0.25-NA) microscope objective and a CCD camera with 400 × 400 pixels, the system covers an area of 225 μm × 225 μm with a transverse resolution of 4.4 μm. The en-face OCT images of an onion is measured with an exposure time of 7ms and a frame rate of 28 fps.

We propose a novel focusing scheme to achieve approximately depth-invariant lateral resolution and signal to noise ratio along an extended axial scanning range for in vivo high-resolution imaging. The pupil function of the objective lens is modulated with a series of radial gratings implemented with a spatial light modulator. Each grating gives rise to a parabolic phase aberration that shifts the focal volume with a pre-defined distance along the optical axis. Dynamic focusing is readily achieved without mechanical translation of sample or focusing optics. With spatial light modulator of higher respond time, images acquired with different focal positions can be fused to retrieve a high-resolution image with depth-invariable lateral resolution and signal to noise ratio.

Magnetomotive optical coherence tomography (MMOCT) is a method for imaging the distribution of magnetic nanoparticles in tissue by applying an external dynamic magnetic field gradient during B-mode scanning. We present a new method for spectral-domain MMOCT imaging which affords increased sensitivity and frame rates compared to previous work, with a demonstrated sensitivity to <100 ppm iron oxide nanoparticles and imaging time of 5 s. Agarose phantoms embedded with iron oxide nanoparticles (~20 nm) also provide negative T₂ contrast in magnetic resonance imaging (MRI) with sensitivity <10 ppm, which is promising for multi-modality applications where MRI and MMOCT provide whole-body and microscopic imaging, respectively. To demonstrate the biomedical potential of this technique, rats are injected with the same nanoparticles as those used in MRI, and uptake into the spleen is detected and imaged post mortem by MMOCT. This illustrates a potentially powerful multi-modal platform for molecular imaging using targeted magnetic nanoparticles.

The detailed 3-D mapping of tissue microcirculation, including blood oxygen saturation and flow, would provide important biometrics needed to understand the cause and progression of numerous diseases. To that end we have started developing a two-color Fourier domain Pump-Probe Optical Coherence Tomography (PPOCT) system designed specifically to image hemoglobin with the eventual goal of measuring blood oxygen saturation. This system utilizes a two-color pump-probe scheme chosen to maximize the potential imaging depth by probing in the near IR where the tissue scattering properties are most favorable and pumping in the visible where the hemoglobin light absorption is most efficient. A sample consisting of pure hemoglobin placed between two coverslips has been used for the initial demonstration and to begin the process of optimizing the system.

In this presentation, we demonstrate a novel optical tomography technique, thermoelastic optical Doppler tomography (ODT). Short laser pulses are used to generate thermoelastic waves in biological samples. Optical phase variations in response to wave propagation are detected using ODT. It is shown that areas of different elastic property in the phantom can be clearly resolved.

We describe a visible-light spectroscopic OCT system designed to obtain localized measurements of hemoglobin oxygenation in the superficial microcirculation and also to obtain localized measurements of optical properties at visible wavelengths. The device is based on a supercontinuum source emitting in the 450-600 nm spectral range, which overlaps the visible absorption band of hemoglobin. The OCT detection system uses a spectral domain set-up using a linear CCD and home-built spectrometer and is implemented in single-mode fiber. Multi-spectral OCT images can be acquired at eight wavelengths simultaneously each with 256 axial pixels, and multi-linear regression processing can be applied at a line-rate of 1 kHz. The dynamic range of the system is characterized and found to be limited by excess noise in the supercontinuum source. The wavelength-dependence of scatter is determined for Intralipid using a single-scatter model. Coherent back-scatter from whole blood is detected in the visible spectrum and used to infer the total attenuation coefficient at 470 nm. The feasibility of obtaining oximetry data over volumes of blood as thin as 20 microns is demonstrated. The work describes first steps towards assessment of hemoglobin oxygenation in the superficial microcirculation with picoliter resolution.

High in-depth resolution imaging, such as Optical Coherence Tomography, could be the next frontier in noninvasive quantification of diffusion in epithelial tissues. In this study we employed OCT in a method that could help differentiate various forms of atherosclerosis and distinguish between normal and diseased tissue. The diffusion of glucose solution in normal and diseased pig aorta in vitro was monitored and the permeability coefficient was calculated. The results suggest that this OCT method may have high potential for early detection of tissue abnormalities while used in diffusion studies.

We present fiber-based polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) with continuous polarization modulation. The light source is a high-speed wavelength sweeping source with 1.3 um center wavelength and 20 kHz sweeping frequency. A resonant electro-optic modulator modulates the incident polarization at 100/3 MHz, one-third of the data acquisition frequency. The modulated light is coupled into a single mode fiber coupler. A linear polarizer in the reference arm makes the intensity and state of polarization of the reference light be constant. In the sample arm, the polarization-modulated beam illuminates a sample. The reference beam and back reflected light from the sample are interfered and detected by two balanced photoreceivers at 100 M samples/s for horizontally and vertically polarized components. The polarization modulation generates the 0th and 1st order signals with respect to the modulation frequency. By extracting them individually, this system can measure Jones matrices of the sample with a single A-scan. Previous fiber-based PS-OCT systems with 2 or more states of the incident polarization required a high dense transversal scan in order to keep the correlation between adjacent A-scans. However, this method does not require a high dense transversal scan, thus long transversal imaging range is possible. We show the details of the method and measurement results of a quarter waveplate and biological samples.

We propose a new method of acquisition and analysis of Spectral Optical Coherence Tomography data. The method acquires a set of SOCT spectral fringes as a function of time. The Fourier analysis of such data allows for investigation of various functional aspects of analyzed tissue. We show that Doppler flow information of a sample can be easily evaluated from such data. We also compare the velocity estimates obtained with our method with these found via traditional phase-resolved procedure.

In this contribution we propose a new method of acquisition and analysis of Spectral Optical Coherence Tomography data to obtain information about depth dependent extinction in the scattering media. In joint Spectral and Time domain OCT a set of Spectral Optical Coherence Tomography fringes is acquired in time increments. An axial component of the flow velocity vector is accurately estimated from Doppler beating signal. Additional filtering and averaging of spatial-temporal data allows for effective reduction of the speckle noise and enables reconstructing the envelope of spectral fringes corresponding to the chosen depth. In this way the depth and wavelength dependent attenuation of light can be determined in scattering media. In this contribution we demonstrate the proof of concept of spectroscopic OCT analysis performed in scattering media and we discuss its potential for in-vivo functional imaging of the human retina.

Full-range complex spectral domain (SD) optical coherence tomography (OCT) enables the removal of the complex conjugate artefact by measurement of the phase of the spectral interference signal. In order to retrieve the complex signals, the phase of the OCT signal has to be modulated in a well-defined way. For this purpose, different devices, such as piezo mirrors or electro-optic modulators, have been added to the instruments reported so far. We present a SD-OCT system capable of elimination of the complex conjugate artefact without using any additional phase modulating devices. A stable phase modulation is generated by displacing the galvo scanner mirror used for 2D imaging in such a way that the probe beam hits the mirror off its axis of rotation. Only a single measurement is necessary for the reconstruction of each complex valued depth profile, thus allowing for high-speed imaging. The method is demonstrated for full-range imaging of the anterior segments of human eyes in vivo.

Full-range spectral domain optical coherence tomography (SD-OCT) with a 1-μm band light source is demonstrated. The phase of reference arm is modulated simultaneously as the probing beam laterally scans the sample (B-scan). The obtained two dimensional spectral interferogram is processed by Fourier transform method to obtain complex spectrum which leads to full-range OCT image. The measurement speed of this system was 7.96 kHz, the measured axial resolution was 9.6 μm in air and the sensitivity was 99.4 dB. To demonstrate the effect of mirror image elimination, in vivo human eye pathology was measured.

An optical coherence tomography (OCT) system was built to acquire in vivo, both images and vibration measurements of the organ of Corti of the guinea pig. The organ of Corti was viewed through a ~500-μm diameter hole in the bony wall of the scala tympani of the first cochlear turn. In imaging mode, the image was acquired as reflectance R(x,z). In vibration mode, the basilar membrane (BM) or reticular lamina (RL) was selected based on the image. Under software control, the system would move the scanning mirrors to bring the sensing volume of the measurement to the desired tissue location. To address the gain stability problem of the homodyne OCT system, arising from the system moving in and out of the quadrature point and also to resolve the 180 degree ambiguity in the phase measurement using an interferometer, a vibration calibration method is developed by adding a vibrating source to the reference arm to monitor the operating point of the interferometric system. Amplitude gain and phase of various cochlear membranes was measured for different sound pressure level (SPL) varying from 65dB SPL to 93 dB SPL.

An Optical Coherence Tomography (OCT) imaging system has been designed and constructed to acquire images of scattering biological samples. By simultaneously acquiring and displaying high resolution en-face (C-scan) OCT and Laser Scanning Confocal images of Drosophila melanogaster embryos we demonstrate the potential of the system to be used as a powerful tool for imaging in Drosophila embryonic development. The system can equally be used for non invasive visualizations and measurements of the movement of Drosophila melanogaster larval heart and can easily be switched in the OCT B-scan regime. The confocal channel adds guidance as the specimen can be quickly located and this makes the use of the system in a large scale gene screen feasible.

OCT is highly potential for dynamic analysis of eccrin sweat glands. It is found in our experiment that the spiral lumen of an active sweat gland expands drastically in response to mental stress. Mental-stress-induced sweating is analyzed quantitatively based on time-sequential OCT images.

Endoscopic optical coherence tomography (OCT), and other imaging modalities that use a mechanically rotated probe, often suffer from image degradation due to non-uniform rotation distortion (NURD). In this paper we present a new method to align a sequence of images by globally optimizing the match between individual lines in subsequent frames. It uses dynamic programming to find a continuous path through a cost matrix that measures the similarity between regions of two frames being aligned. The path represents the angular mismatch corresponding to the NURD. The prime advantage of this novel approach compared to earlier work is the line-to-line continuity, which accurately captures slow intra-frame variations in rotational velocity of the probe. The algorithm is optimized using data from a clinically available intravascular OCT instrument in a realistic vessel phantom. Sensitivity of the performance to imaging and optimization parameters is investigated using a computational phantom. Finally, the algorithm's efficacy is demonstrated on an in vivo recording inside a human coronary artery, exhibiting strong motion artifact.

Speckle is always present in Optical Coherence Tomography (OCT) measurements. To a first approximation, the speckle size is determined by the OCT resolution length and the point spread function of the focusing optics in the sample arm. But the speckle size is also affected by the tissue microstructure. We demonstrate this phenomena by performing measurements on optical phantoms with a controlled density of scatterers using time-domain OCT. In the very low density limit, the scatterers are easily identified on the OCT cross-section and, in fact, one can hardly speak of a speckle pattern. The corresponding speckle size is the resolution length axially and the point spread function of the focusing optics transversally. As the number of scatterers increases, a true speckle field appears and the measured speckle size decreases. In the high density limit, the speckle size reaches an asymptotic value that is about 70% of its low-density regime values. In addition to experimental results, theoretical estimates of the limiting speckle size values are presented. Our work contributes to a better understanding of speckle in optical coherence tomography.

We describe variations in the degree of mineralisation within the subchondral bone plate of the equine metacarpophalangeal joint. A comparison of Optical Coherence Tomography, Micro CT, and SEM techniques was performed. These data are compared between sites on a healthy sample and at points on an osteoarthritically degenerated sample. No significant correlation was found between the optical scattering coefficient and the micro-CT derived BMD for comparisons between different sites on the bone surface. Also OCT demonstrated a larger regional variation in scattering coefficient than did micro CT for bone mineral density. This suggests that the optical scattering coefficient of bone is not related solely to the volume-density of calcium-phosphate. Patches of lower optical scattering coefficient were found in the bone structure that was related to the osteoarthritic lesion area on the overlying cartilage. Areas of microcracking, as revealed by both SEM and micro CT produced distinctive granularity in the OCT images. In further experiments, OCT was compared with micro CT and mechanical strength testing (3-point bending) in a small animal model of cardiovascular disease (cholesterol overload in mice). In the cardiovascular diseased mice, micro-CT of the trabecular bone did not demonstrate a significant change in trabecular bone mineral density before and after administration of the high cholesterol diet. However mechanical testing demonstrated a decrease in mechanical strength and OCT demonstrated a corresponding statistically significant decrease in optical scattering of the bone.

A Gouy phase shift is acquired each time a beam goes through a focal point. It is a common practice in optical coherence tomography (OCT) systems to focus the light on a sample to obtain a good transverse resolution in addition to the axial resolution provided by the coherence gating. In presence of chromatic aberration, the position of the focal point is wavelength dependent. This leads to an enhanced wavelength dependency of the Gouy phase shift for measurements performed in the focal region of the sample arm. This affects the positioning of the envelope of the interferogram and can thus have a strong impact on the axial position accuracy as measured by an OCT system using the maximum of the envelope. Chromatic aberration not only leads to a Gouy phase shift, but also to an additional wavelength-dependent term related to the transverse phase distribution over the aperture of the collecting optics. This last term brings a contribution that is of the same order as the Gouy phase shift. We demonstrated these effects in time-domain OCT in a previous paper [Lamouche et al., Optics Comm., Vol. 239, 297 (2005)]. This problem is revisited with Fourier-domain OCT by performing measurements with a swept-source OCT system. This allows to confirm that the effect observed is not interferometer dependent but purely optical in origin. It also provides a clear experimental confirmation that the effect is related to chromatic aberration. This work is of interest for OCT measurements that require accurate relative position measurements in the focal region.

A numerical method to compensate retinal shadows in choroid is presented. The averaged A-scans beneath retinal vessels and A-scans surrounded by them are calculated. The effect of absorption is estimated by subtracting those A-scans. By adding that offset value to A-scans beneath the retinal vessels, the shadows in the choroid are compensated. In vivo imaging of human eye was performed by 840 nm band standard resolution spectral domain optical coherence tomography and choroidal vasculature projection images were calculated. The removal of retinal shadows improves the readability of choroidal images.

This paper introduces a speckle reduction technique for Optical Coherence Tomography (OCT) images based on soft thresholding the wavelet coefficients using interval type II fuzzy system. The proposed method is an extension of a recently published method for additive noise using type I fuzzy system. It has been shown that the new method outperforms the traditional Wiener and modified Lee algorithms in terms of image metrics. Unlike the type I, interval type II fuzzy based thresholding filter considers the uncertainty in the calculated threshold and the wavelet coefficient is adjusted based on this uncertainty. Application of this novel algorithm to an optical coherence tomography image acquired in-vivo from a human finger tip shows reduction in speckle noise with little edge blurring and image SNR improvement of ~10dB.

We propose another window function used in production process of A-line by Fourier transform in optical frequency domain imaging. It is shown that cosine tapered window has an advantage over Gaussian window employed conventionally.

Progress in laser and camera technology has simplified the acquisition of laser speckle images relating to dermal blood flow. Using speckle contrast measurements over 5 decades of exposure time, we show that a temporal autocorrelation function, and hence spectral information and a perfusion index precisely equivalent to that produced in Doppler methods, can be derived from speckle measurements. The autocorrelation data are well approximated by a simple but nonexponential function which is parametric in a characteristic time τ_c. We suggest that the perfusion index could be found simply by determining τ_c from a small number of speckle measurements at appropriate exposures. This is illustrated by measurement of perfusion recovery following an induced change in perfusion.

We report on the fabrication and performance of a lensed photonic crystal fiber (PCF) designed as a compact but effective side-viewing optical imaging probe. The lensed-PCF probe was implemented in a single body without using any other fibers or additional optics. The beam expansion region and a focusing ball lens, necessary as a focuser, were simultaneously formed along a small piece of PCF by using arc discharges. The side-viewing ability was endowed by polishing the ball lens with a femto-second laser to form a TIR (total internal reflection) surface. The working distance and the transverse resolution of the fabricated single-body lensed-PCF were experimentally measured to be ~570 μm and 6.8 μm, respectively. With the proposed lensed-PCF probe, OCT images of an in vitro biological sample were successfully obtained

We describe preliminary results of high-speed 2-dimensional Doppler OCT measurement using a unique optical frequency domain imaging (OFDI) system. SSG-DBR laser is the light source from which wave number is swept discretely over predetermined absolute values in equal wave number interval with constant output intensity. Multi-sampling at each wave number enables us to reconstruct multiple images by 1 transversal scan, and the 2 dimensional flow image is reconstructed from the phase Doppler shift between 2 successive images. Maximum detectable velocity is restricted by sampling rate, which is higher than A-scan flow has been carried out with this system adopting Kasai velocity estimator. The results predict that the method is valid for stationary flow.

We demonstrate axial-lateral parallel time-domain optical coherence tomography using an optical zoom lens and highorder diffracted lights at 830 nm to adjust imaging range. Our 2-D CCD camera (640 x 480 pixels, 207fps) measured a depth-resolved interference image using diffracted light as the reference beam and a linear illumination beam without any scan. The lateral range can be varied continuously from 6.4 to 1.6 mm by increasing the magnification of optical zoom lens. The axial range can be adjusted discretely from 1^st to 7^th orders because we used a diffraction grating with 300 lines/mm in a 830 nm wavelength region.

We propose an all-fiber probe for the sample arm of an optical coherence tomography (OCT) system. By forming a focusing lens directly on the tip of an optical fiber, a compact sample probe could be implemented. To achieve a long enough working distance and a high enough lateral resolution at the same time, a coreless silica fiber (CSF) having a diameter larger than that of a conventional single mode fiber was utilized. With the specially fabricated CSF having a diameter of 180 μm, a fiber-lens having a 120 μm radius of curvature could be made, which allowed the sample probe having a working distance as long as 920 μm and a lateral resolution as high as 9.4 μm. To present the performance of the OCT system equipped with the proposed sample probe, the OCT images of a rat finger skin and a pearl were taken. The system could image as deep as 1.0 mm of the rat finger skin and 3.5 mm of the pearl, and the images are compared with the ones taken by using a conventional objective lens (10x, NA0.25). Owing to the small form factor of the proposed probe, it can find good applications in the field of optical imaging based on endoscope or catheter.

We report spectral domain optical coherence tomography (SDOCT) with a supercontinuum source based on a photonic crystal fiber pumped with nanosecond laser pulses. The Q-switched Nd:YAG microchip laser produces 0.6 ns duration pulses at 1064 nm with 8 μJ of energy at a 6.6 kHz repetition rate. These pulses are sent through 3 m of photonic crystal fiber with a zero dispersion wavelength of 1040 nm. The fiber output is coupled into a fiber-based SDOCT system operating at a central wavelength of 800 nm. The A-line acquisition rate is 6.6 kHz, where each A-line is produced by a single supercontinuum pulse. Point spread function measurements show excellent resolution, but sensitivity is degraded by spectral fluctuations of individual supercontinuum pulses. Test images show less dynamic range compared to a Ti:Sapphire femtosecond laser based system. However, this supercontinuum source has potential for stroboscopic illumination in time-resolved low coherence interferometry.

We have fabricated superluminescent light-emitting devices in the 840nm wavelength range with flat top spectral shape. The novel design allows more than 50nm bandwidth and up to 34mW of optical power at the chip facet. Moreover, the 3dB bandwidth changes by less than 2nm within a driving current range between 120mA and 200mA. This corresponds to a power level change between 17mW and 34mW, without considerable shape changes, which is one of the main concerns for many applications. The stability of the spectral bandwidth is also reflected by the central wavelength that changes by less than 1nm in the same range of currents. The device shows great stability of the optical far field with respect to the driving current, allowing stable coupling of the emitted beam in optical fibers. We have also measured the coherence function of this device using an interferometric spectrum analyzer. Results show good side-lobes suppression ratio of more than 10dB, which remains almost unchanged over the whole range of driving currents.

We report on the use of phase-resolved DOCT to measure oscillatory flow in a rigid glass capillary. Experimental measurements are obtained in which a sinusoidal pressure gradient generates a sinusoidal varying flow of a scattering liquid (Intralipid-20%) in a 660 micron i.d. glass tube. Dynamic flow profiles are measured and compared with the analytical theory due to Womersley. Reasonable agreement is found for one half of the flow profile (-ve velocities) but the agreement is less good for the +ve velocities. Possible reasons for the discrepancy are discussed. The study indicates the usefulness of DOCT for studying fluid flow dynamics.

Sampled Grating Distributed Bragg Reflector (SGDBR) monolithic tunable lasers are now entering the production phase in telecommunications applications. These tunable lasers are unique in that they offer wide wavelength tuning (1525 to 1565 nm), fast wavelength tuning (5 ns) and high speed amplitude modulation all on the same monolithic chip^1,2,3,4. This work studies the applicability of SGDBR monolithic tunable laser diodes for biomedical imaging using swept-wavelength or Fourier domain optical coherence tomography. This paper will present our work involved with utilizing the strengths (table 1) of this SGDBR laser class and mitigating the weaknesses (table 2) of this device for swept-wavelength imaging applications. The strengths of the laser are its small size (portable solutions), wide wavelength range (good distance resolution), fast switching speeds (improved update rates), wide choice of center wavelengths, and lower power consumption. The weaknesses being addressed are the complicated wavelength tuning mechanism (3 wavelength control currents), wider laser linewidth (10s of MHz), moderate output power (10mW ), and the need for improved laser packaging. This paper will highlight the source characterization results and discuss an initial measurement architecture utilizing the SGDBR measurement engine.

Two significant figures of merit for optical coherence tomography (OCT) systems are the axial and transverse resolutions. Transverse resolution has been defined using the Rayleigh Criterion or from Gaussian beam optics. The axial resolution is generally defined in terms of the coherence length of a Gaussian shaped source. Whilst these definitions provide a useful mathematical reference they are somewhat abstracted from the three dimensional resolution that is encountered under practical imaging conditions. Therefore, we have developed a three-dimensional resolution target and measurement methodology that can be used to calibrate the three-dimensional resolution of OCT systems.

Real-time video-rate imaging using harmonically detected Fourier domain OCT is demonstrated using an 800 nm light source and a silicon line scan camera. At an imaging rate of 11.7 B-scans (1024 pixels × 256 pixels) per second, the measured complex conjugate artifact suppression is 30-35 dB, the sensitivity is 121 dB, and the dynamic range is about 60 dB.

We elaborate further the partial coherence model for the trans-illumination interferometric experiment, by including a phase-locked device at detection plane. We demonstrate that the detected isolated signal, and thus the quality of the optical properties depend on the coherence characteristics of the source. We introduce a specific measure of coherence time for discrimination purposes, such that a photon arriving at a greater time will be efficiently filtered. The quantification of the coherence study is presented by computing the analytical interferograms for different radiation sources (Broadband source, SLED, LED, and Laser). We show that the use of a low-coherence source improves the detection of ballistic photons, at the coherence length of the source, by orders of magnitude. As a result of this study, we suggest the use of a low-coherence source, with reduced bandwidth (coherence lengths ranging from 1 - 100 μm) and compact spatial distribution, for tissue characterization purposes. For imaging of tissues, a low-coherence source with greater bandwidth is preferable, because such source effectively isolates pass-through and single scattered photons.

In this paper, we address the problem of spectral data sampling in Fourier domain optical coherence tomography (FD-OCT). The interferometric information in a Fourier Domain OCT system is retrieved from spectral measurements made using a linear array spectrometer. In such spectrometers, spectral data are available as an array of points equally spaced in the wavelength domain. To obtain the spatial profile, the spectral data have to be converted to the frequency domain before applying the Fourier transform. The inverse relationship between these domains causes an unequal spacing of data points after the spectral data is converted to the frequency domain, resulting in the degradation of the FD-OCT images. The current practice typically utilizes zero-padding and spline interpolation to circumvent this problem. While these algorithms do improve the FD-OCT images, our investigations showed that more can be done to enhance the images. Toward this end, we propose a signal processing algorithm based on non-uniform discrete Fourier transform (NUDFT). The results of our algorithm are compared against the current algorithms on both simulated and experimental results.

We evaluate the image penetration depth of optical-frequency domain imaging into the biomedical tissue at longer wavelengths. The light sources are fiber laser at the center wavelength of 1310 nm and at the center wavelength of 1550 nm. These sources provide frequency scan rate of up to 8 kHz over a wavelength range of 110 nm at 1310 nm with ~10 μm axial resolution and a wavelength range of 150 nm at 1550 nm with ~12 μm axial resolution. OCT tomograms of soft and hard tissues acquired at 1310 nm are compared to those obtained at 1550 nm.

We present here the implementation of a fiber-based common-path interferometer for Swept Source Optical Coherence Tomography (SS-OCT). A common path configuration is often a suitable approach for increasing the stability of the measurements. Optical fibers are sensitive to temperature and some other mechanical perturbations which compromise absolute accuracy measurements. A common-path configuration provides a mean to define a reference at the probe location and, thereby, to compensate for the optical path length perturbations. Additionally, in SS-OCT, we have to deal with autocorrelation noise and the mirror image artifact due to the computation of the Fourier transform. Thus, our common-path implementation also includes acousto-optics modulators to remove the depth degeneracy as it has already been done when using a "traditional" interferometer configuration. The efficiency of our system is validated by comparing images acquired with a "traditional" SS-OCT configuration and with our common path SS-OCT configuration.

In vivo three dimensional endoscopic imaging of rabbit and human gastrointestinal tracts was demonstrated based on an endoscopic swept source optical coherence tomography (SSOCT) system. The endoscopic SSOCT system is composed of a high speed SSOCT, a fast scanning rotational microelectromechanical system (MEMS) probe and real time data acquisition and imaging processing. The 2.2 mm rotational MEMS probe was miniature enough to be able to fit into the 2.8 mm biopsy channel of a standard endoscope. The gastrointestinal tracts of patients were imaged together with normal endoscopic examination. The epithelial, mucosal, lamina propria, and submucosal layers can be clearly seen on the OCT images.

In this paper, a GRIN lens rod based dynamic focusing spectral domain optical coherence tomography (OCT) system with 2D scanners is presented and is used to investigate a fresh bovine joint in vitro by 3D OCT with lateral and axial resolutions of 10 μm at the speed of 8 frames/s. The experimental results demonstrate the 3D image can more efficiency and accurate to evaluate articular cartilage joint disease. It shows great potential for use in extremely compact OCT endoscopes to combine with arthroscope to image articular cartilage in vivo for diagnosis of early DJDs and simultaneously perform both 3D imaging and surface imaging in the same channel.

We present a custom Fourier Domain Optical Coherence Tomography (FDOCT) system adapted to imaging the retinal structures in mice. The FDOCT system utilized spectrometer detection, and operated at a central wavelength of 826nm with a FWHM spectral bandwidth of 72nm, corresponding to an axial resolution of ~4microns (in air). A custom hand-held probe was constructed providing adjustable focusing and increased maneuverability over fixed systems to facilitate coupling of the raster scanned beam into the mouse eye. Image acquisition and display was performed in real time using custom written, multi-threaded software package which displays two dimensional B-scans. Cross sectional images of mouse retina, acquired in vivo an anesthetized animals, are presented.

Angiography is currently used to assess post-treatment human brain aneurysm healing, which can reveal vessel shape only. Optical coherence tomography (OCT) can reveal the vessel wall structure with high resolution, which has the advantage to assess vessel healing progress. An OCT endovascular catheter was designed and in vivo patients' studies were performed. Flush effect of saline and perfluorodecalin (PFC) were studies in rabbit aorta. The initial results show that OCT is a promising technology to assess post-treatment cerebrovascular diseases.