Optical coherence tomography (OCT) is a noninvasive imaging technology, which provides subsurface imaging of biological tissue with a resolution in the micrometer range. OCT sensors either work in the time or Fourier domain. We present a new interferometer setup based on a fiber double pinhole arrangement. Two fibers are placed in parallel similar to Young’s two-pinhole interference experiment with spatial coherent and temporal incoherent light. The interference pattern is observed on a linear CCD-array. A complete A-scan can be derived from a single readout of the CCD-array. The experimental setup is described in detail. The main parameters of the setup are derived theoretically and compared with experiments. First images of technical and biological samples are presented.

In optical coherence tomography (OCT), axial and lateral resolutions are determined by the source coherence length and numerical aperture of the sampling lens, respectively. While axial resolution can be improved using a broadband light source, there is a trade-off between lateral resolution and focus depth when conventional optical elements are used. In this paper, we report on the incorporation of an axicon lens into the sample arm of the interferometer to overcome this limitation. Using an axicon lens with a top angle of 160 degrees, 10 micrometers or better lateral resolution is maintained over a focus depth of at least 6 mm. In addition to high lateral resolution, the focusing spot intensity is approximately constant over the whole focus depth.

A method to measure the longitudinal flow velocity component based on phase resolved frequency domain optical coherence tomography (FDOCT) is introduced. At a center wavelength of 800nm the accessible velocity components ranges from 2 micrometers /s up to 2 mm/s. The upper limit is set by half the maximum frame rate of the CCD detector array. The lower limit is determined by the minimum resolvable phase change in the system, which is set by the system phase noise of 1 deg. First tests of the method include the velocity measurement of a mirror mounted on an oscillating piezo translator, and the flow of 8 micrometers latex spheres dispersed in water through a glass capillary.

The high scattering nature of non-transparent human tissue limits the imaging depth of optical coherence tomography (OCT) to 1-2 millimeters. By using the longer wavelength of the light source, the penetration depth is improved; the imaging contrast is however decreased largely due to the reduced backscattering in microscopic scale and the reduced refractive heterogeneity in macroscopic scale. For more effective diagnosis using OCT, a concurrent improvement of penetration depth and imaging contrast are often needed. We report in this paper that the OCT imaging depth and contrast can be enhanced concurrently by the use of osmotic agents. We demonstrate experimentally, by examples, that the topical applications of glycerol and propylene glycol, two common biocompatible and osmotically active solutions, onto the tissue surfaces could significantly improve the OCT imaging contrast and depth capability. The biotissues demonstrated include the rat skin, human oesophageal and gastric tissues.

We introduce a novel high speed no moving parts optical coherence tomography (OCT) system that acquires sample data at less than a microsecond/data point sampling rate. The basic principle of the proposed OCT system relies on using an acousto-optic deflector (AOD). This OCT system has the attractive features of an acousto-optic scanning heterodyne interferometer coupled with an acousto-optic variable optical delay line (ODL) operating in a reflective mode. Fundamentally, OCT systems use a broadband light source for high axial resolution inside the sample or living tissue under examination. Inherently, acousto-optic (AO) devices are Bragg-mode wavelength sensitive elements. In this paper, we identify that Bragg cell generated two beams naturally have an unbalanced and orthogonal spectrum with respect to each other. This mismatch in spectrums in turn violates the ideal auto-correlation condition for a high signal-to-noise ratio broadband interferometric sensor such as OCT. We solve this fundamental limitation of Bragg cell use for OCT by deploying a new interferometric architecture where the two interfering beams have the same power spectral profile over the bandwidth of the broadband source. With the proposed acousto-optic based system, high (e.g., MHz) intermediate frequency can be generated for low 1/f noise heterodyne detection. System issues such as resolution, number of axial scans, and delay-path selection time are addressed. Experiments described demonstrate our high speed acousto-optically tuned OCT system where optical delay lines can be selected at sub-microsecond speeds.

We present the concept of a so-called true-reflection OCT imaging algorithm. The algorithm is based on a recently developed analytical model of the optical coherence tomography technique, which is valid in both the single and multiple scattering regimes simultaneously. The model is based on the extended Huygens-Fresnel principle and takes into account the so-called shower curtain effect. With this new algorithm, it is possible to reduce the effects of scattering from conventional OCT images and create so-called true-reflection OCT images. This type of postprocessing is similar to the correction for attenuation often used in ultrasonic imaging. The principle of the algorithm is demonstrated experimentally by measurements on a solid phantom. Finally, the reduction of the dynamic range of the data when using the algorithm is an additional advantage of this post processing technique.

In this communication a new manner to do away with classical optical delay line problems is proposed. According to Young's holes experiment and thanks to integrated optics, we have been able to realize a device producing spatially distributed fringes in the air. The acquisition time and the dynamic are governed by the CCD linear detector reading speed and size. The theoretical optical delay path is around 1.5 mm and the interferogram acquisition speed approaches 3 kHz. Moreover, this new approach offers all the advantages of the integrated optic technology: mechanical and thermal stability, no more alignment problem, low cost technology (ion-exchange) and small size chip. The study, the fabrication and the characterization of the first optical chip are described. First OCT measurements are also presented.

We present phase resolved digital signal processing techniques for Optical Coherence Tomography to correct for the non Gaussian shape of source spectra and for Group Delay Dispersion (GDD). A broadband source centered at 820 nm was synthesized by combining the spectra of two superluminescent diodes to improve axial image resolution in an optical coherence tomography (OCT) system. Spectral shaping was used to reduce the side lobes (ringing) in the axial point spread function due to the non-Gaussian shape of the spectra. Images of onion cells taken with each individual source and the combined sources, respectively, show the improved resolution and quality enhancement in a turbid biological sample. An OCT system operating at 1310 nm was used to demonstrate that the broadening effect of group delay dispersion (GDD) on the coherence function could be eliminated completely by introducing a quadratic phase shift in the Fourier domain of the interferometric signal. The technique is demonstrated by images of human skin grafts with group delay dispersion mismatch between sample and reference arm before and after digital processing.

Optical coherence tomography (OCT) is a relatively new developed technique to image tissue microstructure in vivo with a resolution of about 10 micrometers . So far, the research has focused on increasing the resolution, increasing the acquisition rate, developing new sample arm scanning techniques, or functional imaging like color Doppler OCT. But one of the main advantages of OCT compared to ultrasound, non-contact imaging, also results in a mayor image distortion: refraction at the air-tissue interface. Also, applied scanning configurations can lead to deformed images. Both errors prevent accurate distance and angle measurements on OCT images, necessary e.g. for Glaucoma diagnosis in the anterior segment of the eye. We describe a methodology for quantitative image correction in OCT which includes procedures for correction of arbitrary spatial warping caused by non-uniform axial reference and lateral sample scan patterns, as well as a novel approach for refraction correction in layered media based on Fermat's principle. The de-warping corrections are implemented in real-time by use of pointer (mapping) arrays, while the refraction correction algorithm is more computationally intensive and is performed off-line.

Most identification of tissues in OCT images has relied on the presence or absence of features and layers. However, in some pathologies as well as some normal tissues OCT images appear homogeneous. Examination of these images reveals that they display a characteristic repetitive structure due to speckle. Since speckle is influenced by the local index of refraction mismatches, it may be possible to differentiate between different types of tissues based on analysis of the speckle pattern. The determination of tissue type may be supported as well by local contrast distribution analysis or speckle decorrelation degree, which are widely used in measurement and characterization of surface roughness. In this study we examined three areas: 1) the application of speckle theory based on surface roughness to a three- dimensional media and a short coherence length light source, 2) the effect that the optical system design has on the received speckle distribution, and the optimum optical system geometry for speckle analysis, and 3) the speckle properties of OCT images of tissue phantoms and various tissues such as fat and muscle. Results obtained from two methods of speckle analysis (texture analysis and speckle contrast) were compared for their ability to differentiate between tissue types.

We report results of measurements by low coherence Doppler interferometry of the path length distribution of photons undergoing multiple scattering in a highly turbid medium. We use a Mach-Zehnder interferometer with multimode graded index fibers and a superluminescent diode as light source. The path length distribution is obtained by recording the heterodyne fluctuations arising due to the Brownian motion of particles in an Intralipid suspension as a function of the optical path length. The experimental path length distribution is in good agreement with predictions of Monte Carlo simulations. In the heterodyne spectrum an increase of the mean Doppler frequency with the path length is observed. The path length resolution of the setup was directly evaluated by replacing the turbid medium with randomly moving scatterers by a mirror attached to a harmonically oscillating piezo-element. The maximum (peak-to-peak) mirror displacement was 10% of the optical wavelength. We observed a narrow and strong (signal/noise ratio ~300) interference peak with the full width at the half maximum ~50 microns equal to the coherence length of the superluminescent diode. However, additional weaker satellite peaks are also observed, which may be caused by the intermodal dispersion in our multimode fibers. We demonstrate that our setup allows achieving high path length resolution for biological tissues where the width of the path length distribution is several millimeters.

High-power ultra-broadband sources such as a supercontinuum are very attractive in optical coherence tomography (OCT) and optical coherence-domain reflectometry (OCDR) due to their very high resolution potential. However, the large and extensive coherence-function sidelobes typical of such sources preclude their use in conventional OCDR and OCT systems. In addition, device or sample dispersion over such broad bandwidths may also significantly limit the achievable performance. Here we describe a novel experiment using a supercontinuum source with a static Michelson interferometer to perform OCDR at 1.55micrometers . Quadrature spectral detection is used to maximize the scanning range and to allow direct compensation for both the undesirable spectral shape of the source and for the dispersion in the system. Such a non-scanning-interferometer approach is an interesting possible alternative for very broadband, ultra-high resolution OCT systems. We demonstrate that an otherwise obscured small reflection next to a large reflection can be revealed by appropriately weighting the data to reshape the supercontinuum spectrum and compensate for dispersion. Significant reduction of the supercontinuum coherence function sidelobes is achieved, and a resolution in air of 7micrometers (FWHM) is obtained, or less than 5micrometers in media of refractive index 1.45.

We present a phase resolved partial coherence interferometer (PR-PCI) to measure absorption and dispersion of water and some other liquids. For that purpose we are investigating three different methods. In the first method we obtain spectral information of the sample by Fourier-transforming the interferometric signal. To correct for variations in scanning motor speed the interferometric signals are corrected by a signal obtained from an auxiliary He-Ne laser interferometer. The spectral information is used to calculate the absorption cross sections of several liquids like water, Deuterium oxide and acetone. The second method investigated is based on measurement of dispersion with an algorithm already introduced for differential phase contrast imaging to extract the phase information of the interferometric signal obtained by two short coherence light sources. Thereby we calculated the difference in the optical path lengths from the phase difference of the two light sources resulting from dispersion of the sample with high precision. This phase difference was used to calculate the sample dispersion. The third method is based on a differential absorption technique. The amplitude of two SLDs with different center wavelengths, one center wavelength within and one outside a water absorption band, were recorded. By measuring the difference of the amplitudes of the two signals we obtain the different extinction of the light beams when propagating through dense tissue.

We demonstrate for the first time optical coherence tomography (OCT) in the visible wavelength range with unprecedented sub-micrometer axial resolution, achieved by employing a photonic crystal fiber in combination with a sub-15fs Ti:sapphire laser (FEMTOLASERS). The shaped emission spectrum produced by the photonic crystal fiber ranges from 535 nm to 700 nm (centered at ~600 nm) resulting in ~0.9 micrometers axial OCT resolution in air corresponding to ~0.6 micrometers in biological tissue. Preliminary demonstration of the sub-micrometer resolution achieved with this visible light OCT setup is demonstrated on a 2.2 micrometers thick nitrocellulose membrane. The visible wavelength range not only enables extremely high axial resolution for OCT imaging, but also offers an attractive region for spectroscopic OCT.

A polarization controllable optical coherence tomography (OCT) system was built with the broadband source generated with femtosecond Ti:sapphire laser pulses in fiber. Spectral broadening in such fiber originated from self-phase modulation, four-wave mixing, Raman scattering, and other nonlinear-optics effects. Two different mode-locked Ti:sapphire lasers with 100 fsec and 12 fsec pulses were used. The generated spectral shape and width were compared in terms of the application to the OCT system. The relationship between the OCT resolution and the source spectrum shape was studied. Also, an algorithm was built for increasing the effective longitudinal resolution in data processing. The scheme of this algorithm meant to separate the contribution of the central portion from those of the tails in the interference fringe envelope. By removing the tail contribution to the scanning results, the effective longitudinal resolution was improved. Such a procedure is particularly important when the light source spectrum is not a well-defined shape. This procedure involved in the computation of a matrix inversion. The OCT system and the process algorithm were used for oral cancer study. Features of oral cancer were well identified. A probe was also fabricated for in vivo scan of oral tissues.

Low coherence photorefractive holography is a wide-field technique for 3-D imaging that offers a unique mechanism to discriminate against a background of diffuse light. This provides a wide-field method to image through scattering materials that we have demonstrated may be implemented at frame rates as high as ~ 470/second. We present our recently developed low coherence photorefractive microscope and demonstrate how it may be realized using a spatially coherent broadband c.w. diode-pumped solid-state laser. This can provide real-time sectioned images of moving 3-D objects using only a simple uncooled 8-bit CCD camera. We also demonstrate a photorefractive 3-D imaging technique that exploits structured illumination and photorefractive holography to achieve a real-time wide-field sectioning microscope that may be applied to fluorescence, as well as reflected light. We also discuss issues for improving the sensitivity and spectral coverage of photorefractive holography using semi-insulating MQW devices.

Parallel optical coherence tomography is demonstrated at video rate using a 58 by 58 smart-pixel detector array. A sample volume of 210x210x80 micrometers³ (corresponding to 58x58x58 voxels) was imaged at 25 Hz. A femtosecond mode-locked Ti:Sapphire laser in combination with a free space Michelson interferometer was employed to achieve a 3 micrometer longitudinal resolution. We used 20x microscope objectives in both sample arm and reference arm and measured a 8 micrometer transverse resolution. The sensitivity of the system was 76 dB.

A miniature fiber Doppler imaging catheter for integrated functional and structural optical coherence tomography (OCT) imaging has been developed. The Doppler catheter can be used to map blood flow profile within a vessel as well as image vessel wall structures. The prototype Doppler catheter was demonstrated in measuring the intraluminal velocity profile in a vessel phantom (conduit). A simple mathematical model can be used to estimate the flow profile outside of normal OCT beam penetration. By extending the spatial range of the flow measurements to approximately two times the normal OCT image penetration depth, the total flow rate can then be calculated from the estimated velocity profiles. The measured total flow rate in the vessel phantom obtained from the Doppler imaging catheter correlates well with the calibrated flow values. The Doppler OCT catheter's ability to simultaneously obtain both structural and functional information makes it a potentially powerful device of cardiovascular imaging.

We have developed a novel optical Hilbert transformation for phase-resolved optical Doppler tomographic imaging. Using a resonant scanner in the reference arm of the interferometer and the axial scanning speed of 4 kHz, the frame rate can be as high as 10 Hz for both structural and Doppler blood flow imaging 400 axial scans. The system has high sensitivity for measuring the Doppler frequency shift due to moving red blood cells. Real time images of in vivo blood flow in human skin using this interferometer are presented.

We present a modified method of polarization sensitive optical coherence tomography (PS-OCT) that measures backscattered intensity, birefringence, and fast optic axis orientation with only one single A-scan per transverse measurement location. The technique employs a standard two-channel PS-OCT setup in combination with a phase sensitive recording of the interferometric signals in the two orthogonally polarized detection channels. We use a Hilbert transform based algorithm to extract amplitude and phase information contained in the interferometric signals. While the birefringence information is obtained from the signal amplitudes, as usual in PS-OCT, a careful analysis of the propagating beams by the Jones calculus reveals, that the information on the fast axis orientation is encoded entirely in the phase difference of the interferometric signals. We demonstrate our method and report on accuracy and precision of birefringence and fast axis measurements in a transparent technical object. Finally, we present PS-OCT maps of birefringence and of fast axis orientation recorded in scattering tissue.

We report the application of Optical coherence tomography (OCT) for visualizing a one dimensional depth resolved functional structure of cat brain in vivo. The OCT system is based on the known fact that neural activation induces structural changes such as capillary dilation and cellular swelling. Detecting these changes as an amplitude change of the scattered light, an OCT signal reflecting neural activity i.e., fOCT (functional OCT) could be obtained. Experiments have been done to obtain a depth resolved stimulus-specific profile of activation in cat visual cortex. Our results in one dimension indicate that indeed an orientation dependent functional signal could be obtained. Further, we show that this depth resolved fOCT signal is well correlated with the stimulus dependent column determined by OISI. Based on the results, the smallest functional unit in depth, resolved by the proposed system is around 40 micrometers . We are extending our system to perform two dimensional functional imaging.

The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved optical Doppler tomography (ODT) is used to image the velocity component transverse to the probing beam. Using a simple geometric optics model, the linear dependence of the Doppler bandwidth on flow velocity is theoretically derived and it is found that the effective numerical aperture (NA) of the optical objective determines the slope of this dependence. Above a certain threshold flow velocity, this linear relationship is in good agreement with experimental data. In the case where the angle between the probing beam and flow direction is within –15 degree to the perpendicular, the Doppler frequency shift is very sensitive to angle position while the Doppler bandwidth is insensitive to flow direction. Linear dependence of the flow velocity on the Doppler bandwidth allows accurate measurement of flow velocity without precise determination of flow direction. In addition, it also extends the dynamic range of the average frequency shift mapping method used in the phase-resolved ODT.

This study aims to investigate the sensitivity of spectroscopic optical coherence tomography (OCT) to small changes in the absorption properties of the imaged object as well as to evaluate its ability to resolve spatial variations in the object's absorption coefficient. Spectroscopic OCT would have the advantage to provide spatially resolved spectroscopic information at multiple wavelengths across the available bandwidth of the light source in a single measurement. An ultrahigh resolution OCT system based on a Ti:sapphire source emitting in the range of 700 nm to 900 nm with an optical bandwidth of up to 165 nm was used to measure optical absorption of specially designed, non-scattering phantoms. High speed and high resolution digitization in combination with a Morlet wavelet transform was utilized to derive spectroscopic information from the full interference OCT data. Using a non scattering phantom, the preliminary results of the present work reveal the challenges that have to be overcome in order to extract spatially resolved quantitative spectroscopic information by OCT.

The human blood sedimentation peculiarities caused by chemical agents adding or coronary heart disease of a patient was studied by two coherent-domain optical techniques. These are OCT and spatially-modulated laser beam transillumination technique. The OCT method due to its high sensitivity was used to study the sedimentation of a whole and less diluted blood, i.e. the sedimentation of the aggregated blood. The spatially-modulated method was used to study a highly diluted blood, i.e. sedimentation of individual and weakly-interacting erythrocytes and was tested in clinical research.

Continuous noninvasive monitoring of blood glucose concentration can improve management of Diabetes Mellitus, reduce mortality, and considerably improve quality of life of diabetic patients. Recently, we proposed to use the OCT technique for noninvasive glucose monitoring. In this paper, we tested noninvasive blood glucose monitoring with the OCT technique in phantoms, animals, and human subjects. An OCT system with the wavelength of 1300 nm was used in our experiments. Phantom studies performed on aqueous suspensions of polystyrene microspheres and milk showed 3.2% decrease of exponential slope of OCT signals when glucose concentration increased from 0 to 100 mM. Theoretical calculations based on the Mie theory of scattering support the results obtained in phantoms. Bolus glucose injections and glucose clamping experiments were performed in animals (New Zealand rabbits and Yucatan micropigs). Good correlation between changes in the OCT signal slope and actual blood glucose concentration were observed in these experiments. First studies were performed in healthy human subjects (using oral glucose tolerance tests). Dependence of the slope of the OCT signals on the actual blood glucose concentration was similar to that obtained in animal studies. Our studies suggest that the OCT technique can potentially be used for noninvasive blood glucose monitoring.

Imaging of the in vivo murine myocardium using optical coherence tomography (OCT) is described. Application of conventional techniques (e.g. MRI, Ultrasound imaging) for imaging the murine myocardium is problematic because the wall thickness is less than 1.5mm (20g mouse), and the heart rate can be as high as six-hundred beats per minute. To acquire a real-time image of the murine myocardium, OCT can provide sufficient spatial resolution (10 micrometers ) and imaging speed (1000 A-Scans/s). Strong light scattering by blood in the heart causes significant light attenuation making delineation of the endocardium-chamber boundary problematic. By replacing whole blood in the mouse with an artificial blood substitute we demonstrate significant reduction of light scattering in the murine myocardium. The results indicate a significant reduction in light scattering as whole blood hematocrit is diminished below 5%. To measure thickness change of the myocardium during one cycle, a myocardium edge detection algorithm is developed and demonstrated.

Recent extensions to conventional OCT imaging include polarization-sensitive optical coherence tomography (PS-OCT) and optical Doppler tomography (ODT), enabling further information to be acquired in addition to tissue structure. We demonstrate here that structure, birefringence and blood flow measurements may be carried out simultaneously, using both techniques of polarization-sensitive OT and phase- resolved ODT. Images of in vivo human skin acquired with a high-speed fiber-based system are presented. The concurrent processing of data is performed with no penalty to signal- to-noise ratio, and without degradation of either the individual structure, birefringence or flow images.

The utility of a versatile multifunctional standalone Optical Coherence Tomography (OCT)/confocal system for imaging dental tissue was investigated. The system can collect A-scan (reflectivity versus depth graph), longitudinal (B-scan) and en-face (C-scan) OCT images, simultaneously with a confocal image. The power to the sample was 250(mu) W, wavelength (lambda) =850 nm and the depth resolution in air was 16 micrometers . The OCT images showed caries lesions as volumes of reduced reflectivity. Transversal images (C-scan) showed the en-face slices of the tooth tissue like in confocal microscopy. Longitudinal images showed the depth of the lesion into the tooth tissue as well as the different structural layers of sound tooth in the same way as seen in ultrasound images. A-scans performed in locations selected in the en-face images provided quantitative data about the reflectivity versus depth. The confocal channel was extremely useful for guidance and it has also shown the integral of the intensity over depth at transversal locations. We concluded that OCT proved capable to detect an early caries lesion, to show the depth of the lesion into the tissue, and quantitatively assess the degree of demineralization.

Early diagnosis with esophageal cancer limited to the mucosa will allow for local endoscopic treatment and improve prognosis. We compared with histology OCT images of healthy human esophageal tissue from two systems operating at 800 and 1275 nm to investigate which wavelength was best suited for detailed OCT imaging of the esophageal wall, and to localize the muscularis mucosae. Within an hour of surgical resection, an esophageal specimen was cleaned of excess blood and soaked in formalin for a minimum of 48 hours. In order to precisely localize the different layers of the esophageal wall on an OCT image, well-defined structures within the esophageal wall were sought. Following OCT imaging the specimen was prepared for routine histology. We observed that our 1275 nm system with 12 micrometers resolution was superior in terms of penetration. As compared to histology, the 4 micrometers resolution of our 800 nm system made fine details more visible. Using either system, a minimally trained eye could recognize the muscularis mucosae as a hypo-reflective layer. Although different conditions may apply in vivo, our ex vivo study paves the path to precise interpretation of OCT images of the esophageal wall.

Two noninvasive optical techniques, optical coherence tomography (OCT) and confocal laser scanning microscopy (CLSM) were used to measure the thickness of the epidermis of volunteers. It was found that due to their different resolution and penetration behavior, these two techniques are sensitive to different markers of the epidermal-dermal boundary. In CLSM, the tops of the dermal papillae are clearly and individually visible, whereas in OCT the fibrous structures immediately below the basal cell layer show up most clearly. Image segmentation algorithms were devised for automatic epidermal thickness determination. Both techniques were applied in a study into the effects of ultraviolet irradiation on the thickness of the epidermis. After exposure to a cumulative does of 15.7 (+/- 1.0) personal minimal erythema doses over three weeks, the changes were so small that only CLSM was able to discern them, due to its superior resolution. On average, it was found that the epidermis increases in thickness by 3 micrometers (p=0.011), which could be attributed entirely to a thickening of the stratum corneum.

We report the use of a highly sensitive phase based motion measurement technique to study the correlation of cellular metabolic rate with cellular motions. The technique is based on a modified Michelson interferometer with a composite laser beam of 1550 nm low coherence light and 775 nm CW light. In this system, motional artifacts from vibrations in the interferometer are completely eliminated. We demonstrate that the system is sensitive to motions as small as 3.6 nm and velocities as small as 1 nm/s. Using the system, we show that the cellular motions are strongly dependent on the ambient temperature. We observe that the dependency does not conform to Brownian motion predictions but instead appears to correlate with the optical ambient temperature that the cells have evolved to operate in.

We report the first results of optical coherence imaging (OCI) of rat tumor spheroids. OCI is a full-frame variant of optical coherence tomography (OCT). The coherent image spatially modulates a high-sensitivity dynamic holographic film composed of a photorefractive quantum well (PRQW). Full-frame readout out of the hologram is observed in real time on a video camera. This system may be considered generally as a video camera with a coherence filter on the lens. Tumor spheroids are small (100-1000 m) balls of tumor cells that are cultured in vitro. Larger spheroids have increasingly complex inner structure. Necrosis and calcification form and expand, reminiscent of structure in malignant cysts in human tumors. In addition, rafts of tumor cells become separated by fluid-filled voids. These features are within the resolution limit of the OCI system, and produce highly structured coherent images.

In our previous report, we have presented the possibility of optical coherence tomography (OCT) to monitor the redox state of mitochondria enzyme Cytochrome oxidase (CytOx) in bone tissue. The previous results showed that reduction of the enzyme in periosteal tissue leads to a change in attenuation coefficient of 1.68 +/- 0.67mm^-1 by OCT measurements. The new results from cultured cells fixed in 300 (mu) l agarose plug showed the difference in attenuation coefficient is 0.26+-0.10 mm^-1 (n = 9) for 7x10⁶ astrocytoma cells and 0.28+-0.13 mm^-1 (n = 7) for 20x10⁶ astrocytoma cells in agarose plug, respectively between cells with oxidised and reduced enzyme at 820nm. A decrease in attenuation coefficient of 0.35+-0.09 mm^-1 (n = 4) for 10 million SKMES cells in agarose was also observed with the redox shift of CytOx. The absorption coefficient of the oxidized-reduced form of CytOx is measured approximately 8.4+-1.5x10^-3/mm (n=3) and 8.2+-1.0x10^-3/mm (n=3) at 820nm for astrocytoma cells and rat periosteum respectively by means of a biochemical assay. Thereby it can be seen that the change in attenuation coefficient of cultured cells with redox shift of CytOx mainly results from the scattering change.

Quantitative, three-dimensional mapping of retinal architectural morphology was achieved using an ultrahigh resolution ophthalmic OCT system. This OCT system utilizes a broad bandwidth titanium-sapphire laser light source generating bandwidths of up to 300 nm near 800 nm center wavelength. The system enables real-time cross-sectional imaging of the retina with ~3 micrometers axial resolution. The macula and the papillomacular axis of a normal human subject were systematically mapped using a series of linear scans. Edge detection and segmentation algorithms were developed to quantify retinal and intraretinal thicknesses. Topographic mapping of the total retinal thickness and the total ganglion cell/inner plexiform layer thickness was achieved around the macula. A topographic mapping quantifying the progressive thickening of the nerve fiber layer (NFL) nasally approaching the optic disk was also demonstrated. The ability to create three-dimensional topographic mapping of retinal architectural morphology at ~3 micrometers axial resolution will be relevant for the diagnosis of many retinal diseases. The topographic quantification of these structures can serve as a powerful tool for developing algorithms and clinical scanning protocols for the screening and staging of ophthalmic diseases such as glaucoma.

Real-time optical coherence tomography (OCT) was used to visualize and quantify structures in the anterior segment of the eye. Results obtained with hand-held and slit-lamp adapted OCT systems are presented. Preliminary data indicates strong potential for the use of real-time OCT in anterior segment biometry and in non-invasive assessment of normal and pathological anterior segment anatomy.

An improved Fourier domain Optical Coherence Tomography (FdOCT) technique is proposed as a new kind of ophthalmic OCT, which enables non-invasive imaging of the retina, the iris and the lens in vivo without an axial mechanical scan of the reference mirror. The FdOCT tomograms of various parts of human eye in vivo, to our knowledge, are the first obtained to date. The detailed images of the human eye are reconstructed from spectral data by the differential method. The tomograms are free of the parasitic autocorrelation terms.

The early identification of glaucomatous development is extremely important for treatment of glaucoma. Analysis of optic-nerve-head features may play a crucial role for early glaucoma diagnostics. Here we propose a critical parameter, viz., nerve tissue area, which may prove to be extremely useful for detection of glaucoma in early stages. We report a novel and robust algorithm for OCT-based automatic, objective extraction of critical optic-nerve-head features such as optic disc, nerve tissue area, and optic cup for the first time.

We report a system capable of collecting pairs of en-face OCT and confocal images from the anterior chamber. Pairs of such images are collected from up to 7 mm deep in the anterior chamber measured from the top of the cornea. The wavelength is 85micrometers and the power 0.3 mW. The system offers: (i) versatility, being capable of displaying both C-scan OCT images (constant depth, oriented perpendicularly on the optic axis) as well as B-scan OCT images (containing the optic axis or longitudinal); (ii) eye alignment using the Purkinje reflections in the confocal channel; (iii) overall eye guidance, on the confocal image; (iv) correction for the en-face movement in the B-scan images generated by en-face imaging using the confocal image. Animations of such pairs of images demonstrate the utility of the system for in vivo imaging of the anterior segment of the eye.

We developed a optical coherence tomographic (OCT) system that utilized broadband continuum generation from a crystal fiber for high axial resolution. Longitudinal resolution of 3 micrometers has been achieved in free space with continuum light from 780 to 1400nm as light source. The system employed a dynamic focusing tracking method to get high lateral resolution. Ultrahigh resolution imaging in onion was demonstrated.

We demonstrate for the first time optical coherence tomography (OCT) in the 900-1100 nm wavelength range. A photonic crystal fiber (PCF) in combination with a sub-15fs Ti:sapphire laser is used to produce an emission spectrum with an optical bandwidth of 35 nm centered at ~1070 nm. Coupling the light from the PCF based source to an optimized free space OCT system results in ~15 micrometers axial resolution in air, corresponding to ~10 micrometers in biological tissue. The near infrared wavelength range around 1100 nm is very attractive for high resolution ophthalmologic OCT imaging of the anterior and posterior eye segment with enhanced penetration. The emission spectrum of the PCF based light source can also be reshaped and tuned to cover the wavelength region around 950-970 nm, where water absorption has a local peak. Therefore, the OCT system described in this paper can also be used for spatially resolved water absorption measurements in non-transparent biological tissue. A preliminary qualitative spectroscopic Oct measurement in D₂O and H₂ O phantoms is described in this paper.

Fluorescence radiance loss in enamel following demineralization has been correlated to the amount of mineral lost during the demineralization. The correlation between fluorescence loss measured by Quantitative Light- induced Fluorescence (QLF) and the reflectivity loss measured by an en-face Optical Coherence Tomography (OCT) system was investigated in a demineralization process to produce artificial caries. We used an OCT system which can collect A-scans (reflectivity versus depth graph), B-scans (longitudinal images) and C-scans (en-face images). The power to the sample was 250 (mu) W, wavelength (lambda) =850 nm and the depth resolution in air 16micrometers . Transversal and longitudinal images showed the caries lesion as volumes of reduced reflectivity. A-scans, which show the profile of the reflectivity versus depth of penetration into the tooth tissue, were used for quantitative analysis of the reflectivity loss. Both the fluorescence radiance and reflectivity of the enamel decreased with increasing demineralization time. A linear correlation was observed between the percentage fluorescence loss measured by QLF and the percentage reflectivity loss measured by OCT. It was concluded that the decrease in reflectivity of the enamel during demineralization, measured by OCT, could be related to the amount of mineral lost during the demineralization process.

Phase-resolved Doppler optical coherence tomography is a recently reported technique for simultaneously imaging tissue structure and blood with high velocity resolution. The optical set-up consists of a fibre-based Michelson interferometer with a 1300nm superluminescent diode in the source arm. The output power is 0.6mW with a bandwidth of 50nm. The reference arm contains a grating-based Fourier domain rapid-scanning delay line with an electro-optic phase modulator to provide a stable reference frequency (800kHz). Ten axial scans sampled, at 400Hz, from the same location are processed to generate structural and velocity data from the reconstructed phase information derived from a Hilbert transform. The sample arm probe focuses light from the fibre into the tissue, producing a beam spot of diameter approximately 20micrometers . The probe is mounted on a linear translation stage, which generates a lateral step of 10micrometers between groups of ten axial scans. The Doppler shift in each pixel is calculated from the average phase shift over the ten sequential scans at each location. The acquisition time for a 100x100 pixel image is approximately 5s. We demonstrate the systems ability to image in-vivo changes in skin perfusion, induced by standard non-invasive physiological techniques.

This paper presents a novel ophthamological optical coherence tomography detecting instrument that we design and introduces measuring arm emphatically. For the glaucoma is very common in the orient, this system can achieve both the eyeground detection and the canthus detection. And it combines the cranny lamp's conventional detection with optical coherence tomography. In order to gain the best resolution and the largest scanning range in the OCT detection, we find the optical system should obey these principles in the measuring arm design: (i) the parallel light from the collimator goes through the lens and focuses on the slot of the cranny lamp. The movement of the scanning point produced by the scanner is carrying on along the slot. (Ii) In the whole light route, the scanner images on the laser object lens of the OCT. The center light of the infrared goes through the center of the object lens all the time. Considering all the system, this design has a longitudinal resolution of 15micrometers , and a transverse resolution of 20micrometers at imaging velocity of 4 frames per second.

The application of polarization-sensitive optical coherence tomography (PS-OCT) creates new possibilities for biomedical imaging. In this work we present a numerical simulation of the signal from a PS-OCT interferometer. We explore the possibility to retrieve information concerning the optical birefringence properties of multiple layered tissues from the depth-resolved PS-OCT interferometric signal, in the presence of strong elastic light scattering. Our simulation is based on a Monte Carlo algorithm for the propagation of polarized light in a birefringent multiple scattering medium. Confocal and time-gated detection are also included. To describe the polarization state of light we use the Jones formalism, which reduces the calculation time compared with the full Stokes-Mueller formalism. To analyze the polarization state of the partially polarized backscattered light we applied a standard method using the Stokes vector, which is derived from the Jones vector. In this work we examined the Stokes vector variations with depth for the different tissues types. The oscillations of the Stokes vector are clearly demonstrated in the case of uniform birefringent medium. We also investigated a two-layered tissue, with a different birefringence of each layer. The Stokes vector variation with depth is compared to the uniform case and used to assess the depth-sensitivity of PS-OCT. Our simulation results are also compared with published experimental results of other groups.

The suitability of a source for OCT depends in part on its characteristics and the heterogeneity of the tissue involved. Published source and tissue optical property data has been used to quantify the performance of various sources for use in OCT on skin and liver. Absorption and scattering coefficients were used to estimate the amount of incident light returning from 20, 200 and 400micron depths and the mean free path of light at wavelengths in the range 500 to 2100nm. Conclusions were based on changes in intensity and bandwidth of light on travel through tissue. A tungsten halogen lamp gave the best resulting intensity and resolution of all sources studied, however its suitability for OCT would be dependent upon achieving enough spatially coherent power in a small area to achieve adequate transverse resolutions. Although the bandwidth of pulsed Cr:forsterite laser light decreases with travel through tissue, it can be used to obtain higher resolution images than radiation from most other sources. While they showed the second to highest resolution, pulsed Ti:sapphire lasers would be suited to acquiring shallower OCT images, as the radiation has the shortest mean free path and is strongly attenuated. For low-resolution applications, Yb fibre sources have superior powers and bandwidths than the superluminescent diode studied.

Optical Coherence Tomography (OCT) is a relatively new type of imaging system for medical diagnosis. Because most current OCT systems use a sharply focused beam in tissues, they have a short depth of field (high image resolution is near the focus only). In this paper, limited diffraction beams of different orders are used to increase depth of field and to reduce sidelobes in OCT. Results show that the proposed OCT system has a lateral resolution of about 4.4 wavelengths (the central wavelength of the source is about 940 nm with a bandwidth of about 70 nm) and lower than -60 dB sidelobes over an entire depth of field of 4.5 mm with the diameter of the objective lens of 1 mm.