The authors report the construction of a dual channel OCT/indocyanine green (ICG) fluorescence system with the optical source common to both the OCT and fluorescence channels based on our previously described ophthalmic Optical Coherence Tomography (OCT)/confocal imaging system. The confocal channel is tuned to the fluorescence wavelength range of ICG dye. The system is compact and assembled on a chin rest and it enables the clinician to visualise the same area of the eye fundus in terms of both en face OCT slices and ICG angiograms, displayed side by side. The images are collected by fast en-face scanning (C-scan) followed by slower scanning along a transverse direction and depth scanning. We demonstrate the first such dual OCT/ICG-fluorescence images from healthy eyes. The system is still capable of providing chosen OCT B-scans at selected points from the ICG confocal image, in the same way the OCT/confocal configuration was used.

Most of the presently used OCT systems are based on A-scans, i.e., the fast scanning direction is the z-direction. We have developed a new OCT technique for retinal imaging that is based on a transversal scanning scheme and combines the imaging modes of a scanning laser ophthalmoscope with the depth sectioning capability of OCT. A stable high-frequency carrier is generated by use of an acousto optic modulator, and high frame rate is obtained by using a resonant scanning mirror for the priority scan (x-direction). Our prototype instrument records 64 transverse images consisting of 256x128 pixels in 1.2 seconds, thus providing the fastest retinal 3D OCT time domain scanning system reported so far. We demonstrate the capabilities of our system by measuring and imaging the fovea and the optic nerve head region of healthy human volunteers in vivo.

Recently we reported measurements of the corneal in-depth light backscattering distribution (CDLBD) by optical coherence tomography (OCT) as a possible tool for investigation of the corneal hydration and estimation of water gradients inside the cornea. In this paper, we present additional results demonstrating a strong correlation (R = 0.99) between the amplitude of light backscattering as measured by OCT and the corneal thickness. In contrary to the well-known effect of the immediate increase observed in corneal opacity during corneal swelling, we observed an initial decrease of the amplitude of light backscattering as measured by OCT in the anterior part of the stroma during the swelling process. The possible explanation for this observation is discussed. Also methodological improvements for accurate measurements of the CDLBD in vivo are outlined.

Using an advanced prototype of en-face OCT/cSLO instrument, an extensive array of clinic pathologies were studied including macular degeneration, central serous retinopathy (CSR), macular hole, macular pucker, cystoid macular edema (CME), diabetic maculopathy, and macular trauma. We report observation of reoccurring patterns in the en-face OCT images which could be identified with different diseases. Uniquely specific and reoccurring patterns could be characterized for macular hole ("Chrysanthemum flower"), CME ("Swiss cheese wheel"), Macular Pucker ("Star"), CSR ("Target") and RPE Detachment ("Ring of Light"). Other entities such as polypoidal choroidopathy and diabetic edema residues had easily recognizable features but were variable enough to defy specific descriptive comparison. To facilitate the interpretation of the en-face OCT images, a three dimensional interactive simulation was designed which allows the demonstration of characteristic features and artifacts encountered in the acquisition of transverse images.

We performed blind recognition of optical coherence tomography (OCT) images of human urinary bladder for diagnostics of carcinoma and premalignant conditions. OCT images of 63 patients were acquired in vivo during cystoscopic examination. The malignant/premalignant conditions were differentiated from benign/reactive with 98% sensitivity and 72% specificity. OCT was also used for intraoperative monitoring of zones around the tumor for adequate resection (31 patients). OCT - guided planning of the resection margin and examination of the postoperative resection line after transurethral resection (TUR) was performed.

Barrett's esophagus (BE) has become a major health care burden because of its association with adenocarcinoma of the esophagus. We have shown that endoscopic optical coherence tomography (EOCT) has a 70% accuracy in the diagnosis of dysplasia (Gastrointest Endosc 2003; 57:AB77). To demonstrate the feasiblity of computer aided diagnosis (CAD) of dysplasia in BE using EOCT digital images, to quantitate/standardize the diagnosis of dysplasia, and to develop algorithms suitable for EOCT surveillance of large areas of Barrett’s mucosa, 106 EOCT images were selected (13 patients from 28 cases) from the clinical study including 68 of non-dysplastic and 38 of dysplastic mucosa. From the digital image stream, the 3 frames immediately preceding impact of the forceps on the tissue were selected to insure close correlation between histology/EOCT image pairs. Computer aided diagnosis by center symmetric autocorrelation (CENS) and principal component analysis (PCA) were used for feature parameter extraction and analysis based on the segmented ROI. Leave-one-out cross-validation was used for classification and finally receiver operating characteristic (ROC) curve was used to evaluate the performance of CAD and the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy were calculated. The result shows that CAD is able to achieve a higher accuracy than humans for identification of dysplasia in EOCT images. CAD may be of assistance in the EOCT surveillance of large surface areas of Barrett’s mucosa for dysplasia.

The goal of our study was to conduct a statistical evaluation of the ability of optical coherence tomography (OCT) to detect neoplasia in vivo in oral cavity. The study enrolled 97 patients (35 volunteers with healthy mucosa of the oral cavity-group I, 41 patients with benign conditions-group II, 21 patients with dysplasia or carcinoma-group III). The diagnosis was established by a histopathology examination of biopsy material. Each biopsy site was imaged by OCT beforehand. Sensitivity of 83% and specificity of 98% were observed as a result of OCT image recognition of dysplastic/malignant versus benign/reactive conditions in the oral cavity. The interobserver agreement kappa was 0.76. Such sensitivity and specificity makes OCT a promising tool for non-invasive evaluation of tissue sites suspicious for high-grade dysplasia and cancer.

We suggest that Optical coherence tomography (OCT) is a potential imaging modality capable of assisting diagnosis in pulmonary medicines. OCT can provide extremely high resolution imaging and be performed with flexible fiber-optic bronchoscopy with small diameter endoscopic probes. In this study, animal models of trachea, and lung surface were to investigate utility of OCT in pulmonary. Normal, malignant, and infectious disease animal model samples measured by OCT were compared to standard histologic H&E light microscopic imaging of the same sites.

This paper summarizes the engineering development of our lab for endoscopic optical coherence tomography toward the ultimate goal to image bladder micro architecture and to diagnose bladder cancers. To test the utility and potential limitations of OCT setups for bladder tumor diagnosis, we used a rat bladder cancer model to track the morphological changes following tumor growth. Image results are presented, suggesting that OCT is able to differentiate cancerous lesions from inflammatory lesions based on OCT characterizations of epithelial thickness and backscattering changes of bladder tissue.

Using Optical Coherence Tomography (OCT), an emerging imaging modality, we have produced both 3D and 4D images of cardiac architecture. We captured 3D images of rabbit Purkinje fiber networks and we also created a 4D representation of a beating stage 28 chicken embryo heart. For the 4D reconstruction, we generated a movie by employing a gated reconstruction technique.

This study is focused on the assessment of refractive index of whole blood and hemoglobin solution at different concentrations of glucose using optical coherence tomography (OCT). It is shown that the OCT refractive index measurements of blood can be potentially applied as a simple and sensitive method for the evaluation of glycated hemoglobin amount.

We report on the scattering properties of oxygenated and de-oxygenated whole blood from 250-1000 nm. We determined the complex refractive index of oxygenated and de-oxygenated hemoglobin using Kramers Kronig analysis and Optical Coherence Tomography measurements. Combining these data with Mie theory, the scattering properties of oxygenated and deoxygenated whole blood were calculated. The results show strong oxygen saturation dependent scattering effects, which should be taken into account in data analysis of optical oxymetry.

We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) which uses optically switchable protein based chromophores. Photosensitive proteins, such as bacteriorhodopsin and phytochrome, are promising OCT molecular contrast agents by reason of their remarkably low transition activation intensities compatible with in vivo imaging, and their potential for use as genetically expressible markers for molecular imaging. This study details the use of a novel optical switch suppression scheme which uses the absorption change between the two state groups of phytochrome to extract concentration and distribution information of the contrast agent within a target sample.

The magneto-mechanical effect is exploited as a means of producing background-free contrast in optical coherence tomography (OCT). Contrast agents consisting of iron-oxide particles and protein microspheres encapsulating colloidal iron-oxide have a sufficiently high magnetic susceptibility to be detected by modulation of a magnetic field gradient using a small solenoid coil. The externally-applied magnetic field mechanically rotates or translates these highly scattering contrast agents within the sample at the modulation frequency, which is subsequently detected as amplitude modulation of the OCT signal. Pairs of sequential axial scans (A-lines) are acquired with the magnetic field on and off, allowing one to build up a pair of images corresponding to the "on" and "off" states of the magnetic field. These image pairs are differenced to look for magnetic-specific effects, allowing one to distinguish the magnetic contrast agents from non-magnetic structures within the sample with a signal-to-background ratio of ~23dB. This technique has the potential to be very powerful when coupled with targeting for in vivo molecular imaging. To evaluate this potential we demonstrate in vitro imaging of magnetically-labeled macrophage cells embedded in a 3D tissue phantom, in vitro tissue doped with contrast agents, and in vivo imaging of Xenopus laevis (African frog) tadpoles.

Nanoshells are a layered dielectric core/metal shell composite nanostructure with an optical resonance geometrically tunable through the visible and near infrared. Due to their small size, ability to generate a strong backscattering signal, and potential for surface modification, they may be an ideal in vivo optical coherence tomography contrast agent. We performed a pilot study to assess their capabilities. Images of a cuvette filled with dilute nanoshells, 2 μm polystyrene microspheres, or a combination were obtained. When compared to microspheres, images of the nanoshells where much brighter and attenuation of the bottom cuvette interface less. Injection of micropheres into the tail vein of mice and hamsters caused a noticeable brightening of OCT images of the dorsal skin. These pilot studies indicate that nanoshells may be an excellent OCT contrast agent; work is continuing to determine optimum nanoshell parameters and applications.

We demonstrate the use of functional optical coherence tomography (fOCT) for observing action potential propagation by detecting scattering changes in neural tissue. FOCT images of nerve fibers from the abdominal ganglion of the sea slug Aplysia californica were obtained before, during, and after electrical stimulation with monophasic as well as biphasic voltage pulses. A reversible localized increase in optical scattering was noted in the images obtained during stimulation compared to the images obtained before stimulation. In addition, M (motion)-mode images showed transient optical changes due to spontaneous electrical activity. To exclude local laser-induced temperature changes as a source for stimulation, we monitored the temperature effects of prolonged laser exposure with a thermistor and found that there was no substantial temperature increase. We conclude that OCT is sensitive to the optical changes induced in electrically stimulated nerve fibers, and that there is minimal tissue heating and no detectable damage caused by exposure to the laser.

Corneal hydration plays an essential role in maintaining optimal vision. During laser ablation surgery, corneal hydration varies greatly and is likely to affect the outcome. Quantitative measurements of this interaction may help improve the results of vision correction surgery. In addition, prescreening of corneal hydration could be used to correct the laser surgery procedure for hydration variation in the patient population. We present a functional extension of Optical Coherence Tomography (OCT) to measure cornea hydration in vitro using two light sources simultaneously, one at 1294 nm (negligible water absorption loss) and another at 1410 nm (large water absorption loss). Measuring the ratio of the intensity profile at these two wavelengths allows us to separate the effect of absorptive attenuation from the reflectivity structure of the sample. We first measured the differential absorption coefficient of a calibration target: a 1 mm cuvette containing controlled mixtures of water (H2O) and heavy water (D2O). The optical properties of heavy water are almost identical with those of water, except that it has negligible absorption near 1410 nm. Next, we scanned in vitro fresh cornea bathed in Optisol. We then scraped off the epithelium and immersed the cornea into Balanced Salt Solution in order to increase the hydration through swelling. Then, the cornea was immersed in a 15% Dextran solution to reverse the swelling. After the OCT scans, the cornea hydration level was evaluated by standard weight measurement. The result of the calibration experiment showed that a strong correlation exists between measured differential water absorption coefficient and actual water content within the cuvette. We derived the hydration level profile over corneal depth from a least squares fit of the log-intensity ratio. Average hydration from the OCT data agreed with the hydration determined by weight measurement.

There are two events happening simultaneously after the impregnation of tissue with the hyperosmotic agents. The diffusion of the agents into tissue reduces the refractive index mismatch between the scattering centres and background medium. And in the meantime, the hyperosmotic characteristics of agents cause tissue dehydration. Both processes are believed to have the effects on reducing light scattering of biological tissue. In order to investigate the role of dehydration in optical clearing effect on the tissue with the application of hyperosmotic agents, the skin tissues with the application of glycerol are dynamically imaged with optical coherence tomography (OCT). We demonstrate experimentally that both the depth and the contrast of OCT imaging of tissue can be enhanced by the application of agents. Higher concentration of agents causes more water loss of skin tissue and a stronger optical clearing effect. We suggest that the dehydration induced by the agents contributes to the enhancement of both OCT imaging depth and contrast. OCT imaging movies of optical clearing effect of hyperosmotic agents on the skin tissues in vitro are provided.

Previously we have demonstrated by an integrating-sphere technique a useful correlation between bone mineral density (BMD) and the optical scattering coefficient (μs). We have used OCT to study this relationship, with a view to assessing its viability as an in vivo measure of BMD. We used an OCT system operating at 1.3 microns to image various bone samples and to make images in different directions. To investigate the accuracy of OCT measurements we collected averaged images taken at different sites along the shaft of a bone sample. A small (about 3%) variation in measured coefficients, justifies the possibility of using the OCT technique for this kind of measurement. Measurements of bone both with and without periosteum, showed essentially the same optical properties. Applying the incident light beam perpendicular and parallel to the main direction of the collagen fibers gave differences in scattering coefficient of about 40% that confirms our previous suggestion about anisotropy of bone matter. Images of bone samples for different demineralisation time were collected. They allowed following changes in calcium distribution in cortical part of bone with the increasing time of acid activity.

We describe a technique that uses the Doppler optical coherence tomography to estimate accurately the scattering fluid-flow velocity without a priori knowledge of the Doppler angle. It is based on the combined use of the Doppler shift on interference signal and the Doppler spectrum broadening due to the moving particles across probe beam. It is shown that the estimated values of Doppler angle and average fluid velocity from the experiments agree well with the preset ones

We realized an in vivo Fourier domain optical coherence tomography (FD OCT) setup that allows acquiring retinal depth scans at a rate of 25.000 per second. We demonstrate the possibility to measure Doppler flow depth profile in specific regions of interest. The method to extract the flow profiles is based on a local phase analysis of the backscattered signal and allows for bidirectional Doppler flow imaging. The velocity resolution in tissue is 200μm/s. We verified the method by measuring pump controlled in vitro flow through a glass capillary. The system allows for a real-time colour encoded Doppler tomogram rate of 2-4 per second. We recorded the pulsatility of different vessels close to optic nerve head.

Doppler optical coherence tomography (DOCT) is a powerful tool for providing not only subsurface microstructural, but also functional information. Our group's system is able to image blood vessels as small as ~ 30 μm in diameter, with blood flows as slow as ~ 20 μm/s. Photodynamic therapy (PDT), once a "novel" cancer treatment, is now a major research field in biophotonics and is gaining clinical popularity. The highly sensitive DOCT system was used to image microcirculation in normal rat colon and a rat prostate cancer model before, during, and after PDT. The results demonstrate that DOCT can monitor the vascular changes during PDT and that DOCT can highlight the differences in tissue response with different treatment protocols. Furthermore, DOCT demonstrated differences in response between normal and cancerous tissues.

We demonstrate tomographic imaging of the refractive index of turbid media using bifocal optical coherence refractometry (BOCR). The technique, which is a variant of optical coherence tomography, is based on measurement of the optical pathlength difference between two foci simultaneously present in the medium of interest. We describe a new method to axially shift the bifocal optical pathlength, thus, avoiding the need to physically relocate the objective lens or the sample during an axial scan, and present an experimental realization based on an adaptive liquid-crystal lens. We present experimental results, which demonstrate refractive index tomography of a range of turbid liquid samples, and also in situ living tissue. BOCR has potential for in vivo refractive index tomography of biological tissue.

We describe a methodology to record spatial variation of refractive index of porcine renal artery using differential phase optical coherence tomography (DP-OCT). DP-OCT provides a quantitative measure of thin specimen phase retardation and refractive index with phase resolution of 5 nm and lateral resolution of 3 mm. DP-OCT instrumentation is an all-fiber, dual channel Michelson interferometer constructed using polarization maintaining fiber. Two orthogonal polarization modes of light are spatially separated using a Wollaston prism and directed into separate photoreceivers. Because phase noise in the environment is equally present in both channels, computation of phase difference between the two signal channels is attributed exclusively to variation in the specimen's composite refractive index. Porcine renal artery is freshly harvested from a local slaughter house. The lumen is cut open and sliced at 5 mm thickness. Microscopic slide for the tissue section is processed by standard histology method with mounting media. Two dimensional en face dual-channel phase images are taken over 150 mm x 200 mm region on the microscopic slide and the images are reconstructed by plotting relative phase variation as the OCT beam is moved across the artery cross section.

Combining endoscopy with optical coherence tomography (OCT) can improve the diagnosis in minimal invasive procedures. Up to now OCT probes were constructed using rotating or moving single-mode fibers or micro scanners at the tip of the probe. We describe an endoscopic OCT system which uses a specially designed rigid endoscope with an extracorporal scanner to create OCT images with 15 μm resolution. The OCT endoscope was constructed using a 270 mm gradient index lens with a diameter of 3 mm. Dispersion of the endoscope was compensated in the OCT interferometer by an all fiber approach. The system is now being tested for detecting malignancies in the urinary bladder.

We report on work to construct a dispersion control system using a spatial light modulator (SLM) in conjunction with optical coherence tomography. To test feasibility of the dispersion control system, we simulate the group delay by water, analyze phase of coherence function, and compute the dispersion compensating function for the SLM. In addition, a unique interferometer configuration utilizing the SLM is described. We verify that dispersion information in optical coherence imaging can be measured by phase analysis of coherence function in optical frequency domain and modified for a variety of applications using the control system.

We demonstrate a new method for simultaneous compensation of time-dependent and time-independent second- and third-order dispersion mismatches in an optical coherence tomography (OCT) system. There have been several methods for dispersion compensation in scanning interferometry by translating or tilting the diffraction grating in a rapid-scanning optical delay line (RSODL). Although these methods can provide a time-independent or time-dependent compensation of the second- or third-order dispersion, they cannot compensate the dispersion mismatch at both orders at the same time. However, the effects of both orders of dispersion mismatch caused by different lengths of fibers in the sample and reference arms in a fiber-based OCT system are significant and cannot be neglected. In this paper, we propose a new method for simultaneous compensation of time-dependent and time-independent second- and third-order dispersions by placing and adjusting a prism between the grating and the lens of the RSODL. The resulting dispersion can be calculated from the phase response of the RSODL with ray tracing analysis. The dependence of each order of dispersion on the configuration of the system is discussed with numerical analysis. The effects of the dispersion compensation are demonstrated with experiments.

We present a novel OCT (Optical Coherence Tomography) instrument which enables us to detect two orthogonal polarization states at two different wavelengths simultaneously. We have used this instrument to demonstrate, study, and compare the properties of speckle averaging using frequency compounding and polarization diversity separately and in combination. Reductions in speckle contrast obtained by measurements are compared to theoretical values and results from computer simulations of OCT signals.

The application of Optical Coherence Tomography (OCT) within ophthalmology is today relative widespread, the reason being that it is a major help in revealing details of structural damage and retinal patho-physiology that otherwise can be difficult to detect. Yet, there is still space for improvement and the OCT systems continuously improve both their speed and resolution. Besides the possibility of upgrading the hardware there is however also a possibility for "bootstrapping" the present generation of commercial devices by adequate post-processing of the acquired signals. We present evidence that with an existing commercial system it is possible to improve the signal-to-noise ratio of the recorded images by fusing multiple scans of the same retinal region. In order to achieve this improvement it is necessary to align a number of noisy signals. We have explored a number of different techniques for achieving this goal. The improvement is sufficient to reveal details that are impossible or difficult to observe from the individual OCT recordings.

A Monte Carlo model of light scattering in tissue is described and used to estimate the signal-to-noise-ratio that can be obtained with an optical coherence tomography (OCT) system. By utilizing the correspondence between the Wigner phase-space distribution and the specific intensity in the small-angle approximation, the novel Monte Carlo model is valid for light reflected both from and outside the focal plane of the system. The model is compared with experiments and an analytical model and good agreement is found. It is expected that the model can be used to examine how multiple scattering affects the axial resolution for a given source bandwidth.

A recently developed analytical optical coherence tomography (OCT) model (L. Thrane et al., J. Opt. Soc. Am. A 17, 484 (2000)) allows the extraction of optical scattering parameters therby enabling attenuation compensation in OCT images. By expanding this theoretical model, we have delevoped a new method for extracting optical scattering parameters from multi-layered tissue structures in vivo. To verify this, we have used a Monte Carlo (MC) OCT model as a numerical phantom to simulate the OCT signal for heterogeneous multi-layered tissue. Excellent agreement is obtained between the extracted values for the optical scattering properties of the different layers and the corresponding input reference values of the MC simulation, which demonstrates its feasibility for in vivo applications. This is the first time such a verification has been obtained, which holds promise of expanding the funtional imaging capabilities of OCT.

Speed improvement in the Spectral Optical Coherence Tomography (SOCT) technique allows to obtain three-dimensional images in vivo in time that does not cause discomfort to a patient. The device allows high speed imaging at 64 μs per line (15,000 A-scans/s) with less than 200 μW light power on the surface of the eye. Three alternative methods of 3-D presentations are demonstrated for images of a pupil and human skin in vivo.

Properties and applications of Spectral Domain OCT have recently been explored, demonstrating improved signal to noise ratios and the potential for high-speed acquisition. In this presentation, we demonstrate in-vivo measurements of a human retina using a Spectral Domain system with acquisition rates of 10,000, 20,000, and 30,000 A-lines per second and 580 μW incident on the eye. Images consisting of 1000 depth profiles and ranging in width from 4 to 12 mm were acquired. The dynamic ranges within an image at 104, 2x104, and 3x104 lps were 40 dB, 39 dB and 28 dB respectively. These values are comparable to that of time domain Optical Coherence tomography yet are achieved at acquisition rates over 50 times faster, demonstrating video-rate OCT imaging at up to 30 frames/sec with 1000 A-lines per image. This work is more thoroughly described in the following publications: 1) B. R. White, M. C. Pierce, N. Nassif, B. Cense, B. H. Park, G. J. Tearney, B. E. Bouma, T. C. Chen,J. F. de Boer, "In vivo dynamic human retinal blood flow imaging using ultra-high speed spectral domain optical doppler tomography," Opt. Express 11, 3490-3497 (2003). 2) N. A. Nassif, B. Cense, B. H. Park, M. C. Pierce, S. H. Yun, B. E. Bouma, G. J. Tearney, T. C. Chen, and J. F. de Boer, "In vivo high-resolution video-rate spectral-domain optical coherence tomography of the human retina and optic nerve," Opt. Express 12, 367-376 (2004). 3) N. Nassif, B. Cense, B. H. Park, S. H. Yun, T. C. Chen, B. E. Bouma, G. J. Tearney,J. F. de Boer, "In-vivo human retinal imaging by ultra high-speed spectral domain optical coherence tomography," Optics Letters 29, 480-482 (2004).

Structural changes within the anterior chamber angle of the human eye may lead to serious problems with vision. Unfortunately this part of the eye is difficult to examine and special devices have been developed to make it possible. Optical Coherence Tomography is an alternative technique for imaging of the anterior chamber angle. In this paper we show that the Fourier domain version of OCT is a promising tool in different types of imaging of the corneo-scleral junction. Cross-sectional static, dynamic and three dimensional images of the human anterior chamber angle in-vivo are presented.

We report that the complex conjugate ambiguity in spectral domain OCT approaches (including swept source OCT and Fourier-domain OCT) may be removed by the use of novel interferometer designs based on NxN couplers. An interferometer based on a 3x3 truly fused fiber coupler with equal splitting ratios provides simultaneous access to components of the complex interferometric signal separated by 120o. These phase components may be converted to quadrature components by use of a simple trigonometric operation, and then inverse Fourier transformed to obtain A-scans and images free of complex conjugate artifact. We demonstrate instantaneous complex spectral-domain OCT using a novel Fourier-domain OCT system employing photodiode arrays, and will also report on a similar system design for instantaneous complex swept-source OCT.

Complex Spectral Optical Tomography (CSOCT) in comparison to ordinary SOCT produces images free of parasitic mirror terms which results in double extension of the measurement range. This technique, however, requires the exact knowledge about the values of the introduced phase shifts in consecutive measurements. Involuntary object movements, which shift the phase from one measurement to another are always present in in vivo experiments. This introduces residual ghosts in cross-sectional images. Here we present a new method of data analysis, which allows determining the real phase shifts introduced during the measurement, and which helps to reduce the ghost effect. Two-dimensional cross-sectional in vivo images of human eye and skin obtained with the aid of this improved complex spectral OCT technique are shown. The method is free of polychromatic phase error originating from the wavelength dependence of the phase shift introduced by the reference mirror translation.

We present a full-field optical coherence tomography system designed to produce high-resolution tomographic images in ultra-short acquisition times. The experimental setup is based on a Linnik interferometer illuminated by a tungsten halogen lamp. En face tomographic images are obtained in real-time without scanning by computing the difference of two phase-opposed interferometric images recorded by two high-resolution CCD cameras. Transverse resolution down to 1.6 μm is achieved by using high numerical aperture microscope objectives. Axial resolution, governed by the source coherence length, is 0.9 μm. 4x4 pixel binning leads to a detection sensitivity of ~ 65 dB. The rapid image capture of the cameras reduces acquisition time to 5 ms. The rapidity of our system makes it suitable for in vivo imaging of biological media, in particular the study of ultra-rapid biological phenomena.

OCT sensors traditionally use scanning optical delay lines with moving parts and a single detector. Compared to this OCT systems with a linear detector array (linear OCT or LOCT) are very simple and robust, but a detector with approximately 104 pixel is needed for a imaging depth of 2 millimeter. We present a new system for LOCT which extends the measurement range of LOCT systems by attaching a mask on the image sensor. The mask essentially performs a down conversion of the spatial frequencies by multiplication with a second spatial frequency. We use this effect to reduce the fringe frequency of the OCT signal so that sampling and calculating the modulation of the signal can be done with relatively few pixels. The theory for this approach is addressed and first measurements are presented.

The crucial role played by the source's degree of spatial coherence in wide-field optical coherence tomography is shown experimentally. Spatially coherent illumination, as obtained with a pulsed laser, generates a considerable amount of coherent optical cross-talk. The latter can be suppressed with spatially incoherent illumination as provided by a thermal or a pseudothermal light source. Demonstration is made for a US air force resolution target covered with a scattering solution made of polystyrene microspheres suspended in water. The origin and nature of cross-talk signals are discussed, as well as specific limitations of spatially incoherent sources.

This paper reviews the physical basis of holographic optical coherence imaging (OCI) applied in image-domain holography (IDH) and Fourier-domain holography (FDH). Holographic OCI is a multi-spatial-channel direct imaging approach that is closely related to short-coherence speckle interferometry and speckle holography, drawing in addition from laser-ranging concepts and techniques of optical coherence tomography (OCT). It produces a series of en face images at successive depths that can be presented in a so-called video "fly-through". Interchannel cross-talk is described as multichannel spatial heterodyne that produces image-bearing speckle. The speckle holograms are proposed to relate to specific structure in the tissue and may be useful as a clinical diagnostic. For instance, sub-cellular motility (a metric of the vitality of a cell and a means to quantify the response to inter-cellular signaling) can be detected with wide field of view without the need for cellular-scale optical resolution. This can be applied across biologically significant areas of tissue with potential for intraoperative applications to asses the state of health beneath the surface of broad areas of excised tissue.

Conventional polarization-sensitive optical coherence tomography (PS-OCT) can provide depth-resolved Stokes parameter measurements of light reflected from turbid media. A new algorithm, which takes into account changes in optical axis, is introduced to give depth-resolved birefringence and differential optical axis orientation images using fiber-based PS-OCT. Quaternion, a convenient mathematical tool, is used to represent an optical element and simplify the algorithm. Experimental results with beef tendon and rabbit tendon and muscle show that this technique has promising potential for imaging the birefringent structure of multiple-layer samples with varying optical axes.

Changes in retinal nerve fiber layer thickness and birefringence may both precede clinically detectable glaucomatous vision loss. Early detection of retinal nerve fiber layer changes may enable treatment to prevent permanent loss of vision. Polarization sensitive optical coherence tomography (PS-OCT) can provide objective information on retinal nerve fiber layer thickness and birefringence. PS-OCT scans around the optic nerve head (ONH) of two healthy young volunteers were made using 10 concentric circles of increasing radius. Both the mean retinal nerve fiber layer thickness and mean retinal nerve fiber birefringence for each of 48 sectors on a circle were determined with data analysis. Birefringence of healthy RNFL is constant as a function of scan radius but varies as a function of position around the ONH, with higher values occurring superior and inferior to the ONH. Measured double pass phase retardation per unit depth values around the ONH range between 0.10 and 0.35 °/μm, equivalent to birefringence values of 1.2•10^-4 and 4.1•10^-4 respectively, measured at a wavelength of 840 nm. Consequently, conversion of phase retardation measurements (as obtained with scanning laser polarimetry) to RNFL thickness measurements, assuming a constant birefringence value, will yield thickness values that are incorrect.

We have constructed a compact set-up based on incoherent detection in two optical channels to provide real time polarisation sensitive OCT imaging. The system can display either a pair of two polarisation sensitive OCT images, corresponding to linear orthogonal polarisation directions or a pair of images, a polarisation insensitive (pure reflectivity) image and a birefringence retardation map. The images are collected by fast en-face scanning (T-scan) followed by slower scanning along a rectangular transverse direction and depth scanning. B-scan and C-scan images from in-vivo retina and optic nerve are presented.

We will present a new version of the polarization sensitive spectrally interfrometric optical coherence tomography which uses one broadband light source and two measurements to determine the Mueller images of a biomedical sample. This system uses phase information of the OCT images. The SI-OCT enables direct measurement of the phase-information of OCT images without complex signal processing method.

A PM fiber based PS OCT setup with simultaneous acquisition of signals in orthogonal polarization channels with an isolation ratio > 28 dB was created. The principles of measuring the tissue birefringence based on detecting only an envelope of OCT signal in the orthogonal polarization were described. The birefringence and depolarization degree of in vivo and ex vivo biotissues of different types were investigated.

Wideband light generation from a single mode optical fiber was investigated. Investigation showed that spectral structure of light broadened by self-phase modulation was not sensitive to fluctuations of the input pulse energy, and its intensity noise was much lower than that of contimuum light from a microstructure fiber. The spectral width of a femtosecond input laser pulse was successfully broadened by a factor of eleven, and a longitudinal resolution of OCT was improved from 35 to 3.7 μm. The system empoyed a dynamic focusing tracking method to maintain high lateral resolution over a large imaging depth.

Polarization-insensitive high power MQW superluminescent emitting diodes (SLEDs) were fabricated at 1300 nm with a very wide bandwidth of more than 60 nm and a very low spectrum modulation of 0.1 dB by combining high quality AR coating and several proprietary technologies including tilted cavity, window region and absorption region. Polarization dependence as low as 0.2 dB and more than 12 mW output power were obtained at 250 mA. The devices were evaluated for optical coherence domain reflectometer (OCDR) applications, and the coherence function data was quite good with a coherence measurement out to 10 mm with negligible artifacts. Devices with different cavity lengths were also fabricated and analyzed.

Described are three types of optical imaging systems based on source coherence agility. On axis ultrafast microsecond sub-surface imaging is achieved by use of a broadband low coherence optical source to implement fast Doppler time domain optical coherence tomography (OCT). This system is formed as a combination of a fast scan acousto-optically implemented variable optical delay line with a single acousto-optic (AO) Bragg cell optical heterodyne interferometer. A second imaging system is introduced with a no-moving parts probe design and fast microsecond speed optical spatial scanning along one dimension implemented using a fixed wavelength high coherence source with a single Bragg cell AO interferometer. The third design involves realization of a spectral domain OCT system implemented via the use of a tunable laser in the proposed single AO cell heterodyne interferometer.

A novel fiber-based Mueller-matrix optical coherence tomography system is demonstrated for acquiring polarization images of biological tissues in vivo. The system features a single broadband source, a rapid scanning optical delay line, and an electro-optical polarization modulator that modulates the polarization states of the source light continuously. A frame of a 200 by 1515 pixel 2D image can be acquired in half a second. The Jones matrix of a sample is calculated from two frequency components--the A-scan carrier frequency component and the beat frequency component between the modulation frequency and the carrier frequency. For samples having negligible diattenuation, the Jones matrix can be calculated from a single measurement of either the horizontal or the vertical interference signal. The system was first validated by imaging standard polarization elements and then applied to imaging biological samples.

We introduce a novel OCT-technique to measure backscattered intensity and birefringence properties (retardation and fast axis orientation) of human tissue. The experimental setup consists of a Mach Zehnder interferometer. A polarizing beam splitter placed after each interferometer exit allows a dual balanced polarization sensitive detection of the backscattered light intensity from the sample. Two acousto optic modulators (AOM's) placed in the reference arm introduce a frequency shift to the reference beam causing a beat frequency on the detection unit whenever light beams from the sample and reference arm are within the coherence gate. A translation stage placed in the reference arm allows a change in the reference arm length. Image acquisition is performed by transversal scanning of the sample at different reference arm mirror positions (corresponding to different depth positions in the sample). Two lock-in amplifiers set to the beat frequency are used to obtain real and imaginary part of each interferometric signal. This setup allows a phase resolved and polarization sensitive acquisition of the backscattered light from the sample. We demonstrate this method on human tissue in vivo and present, to the best of our knowledge, the first OCT images that are directly related to the fast axis orientation of human tissue in vivo.

We describe a Polarization Sensitive Optical Coherence Tomography (PS-OCT) system with de-correlated horizontal and vertical channels. Construction of PS-OCT depth-resolved images is achieved with a scanning bulk Michelson interferometer and a broadband TiAl₂O₃ femtosecond laser source. We de-correlate and delay horizontal and vertical channels using a birefringent crystal in the source path and calcite prism pairs in the sample and reference paths. Cross-correlation and phase changes between horizontal and vertical channels are measured at different reference-sample optical delays in correlated and de-correlated PS-OCT. PS-OCT with de-correlated (DPS-OCT) channels can broaden applications to include de-correlated Doppler imaging of blood flow and imaging the retinal nerve fiber layer with delayed channels. We achieve a differential delay of 0-400 microns between vertical and horizontal channels by translating the calcite prisms. DPS-OCT system design and experimental measurements are presented and discussed.

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of optical coherence tomography (OCT) which reveals the birefringent properties of a biological sample. Several reports on PS-OCT have demonstrated its ability to measure and image birefringence distribution in different tissues. We compare different methods, based on the use of one or more input polarization state. The image quality for single input state methods is better than if two input states are used, however, the latter methods are preferable if fiber interferometers are used or if measurements are to be performed trough superficial birefringent layers. The different image quality is probably due to a speckle effect.

A unique feature of polarization-sensitive Mueller optical coherence tomography (Mueller-OCT) is that it can reveal various polarization properties of biological samples that are not observable using conventional OCT. One of the most important polarization parameters is birefringence, which can be measured in its integrated form using existing Mueller-OCT systems. We present a new method that uses the least squares algorithm to differentiate measured integrated Jones matrices so that the samples can be observed layer-by-layer. We tested the algorithm using simulated data with variable additive white Gaussian noise (AWGN) levels. We further verified the algorithm using in vitro measurements of the porcine tendon and the septum of the rat heart. This least squares-based algorithm has the potential to reveal structures previously hidden by the inherent masking properties of the integrated images and provide localized phase retardation and orientation information.

A phase-resolved polarization sensitive optical coherence tomography (PS-OCT) system was used to determine the burn depth of in vivo tissue non-invasively. The phase retardation information was obtained by processing the analytical interference fringe signals from two perpendicular polarization-detection channels. From the birefringence images for the four reference polarization states, the birefringence reduction in the rat skin due to thermal damage can be measured. The determined burn depth showed good agreement with histological result.

Polarization-sensitive optical coherence tomography (PSOCT) is an emerging optical imaging technique that is sensitive to the birefringence properties of tissues. It thus has applications in studying the large-scale ordering of collagen fibers within connective tissues. This ordering not only provides useful insights into the relationship between structure and function for various anatomical structures but also is an indicator of pathology. Intervertebral disk is an elastic tissue of the spine and possesses a 3-D collagen structure well suited to study using PSOCT. Since the outer layer of the disk has a lamellar structure with collagen fibers oriented in a trellis-like arrangement between lamellae, the birefringence fast-axis shows pronounced variations with depth, on a spatial scale of about 100 μm. The lamellar thickness varies with age and possibly with disease. We have used a polarisation-sensitive optical coherence tomography system to measure the birefringence properties of freshly excised, hydrated bovine caudal intervertebral disk and compared this with equine flexor tendon. Our results clearly demonstrate the ability of PSOCT to detect the outer three lamellae, down to a depth of at least 700 μm, via discontinuities in the depth-resolved retardance. We have applied a simple semi-empirical model based on Jones calculus to quantify the variation in the fast-axis orientation with depth. Our data and modeling is in broad agreement with previous studies using x-ray diffraction and polarization microscopy applied to histological sections of dehydrated disk. Our results imply that PSOCT may prove a useful tool to study collagen organisation within intervertebral disk in vitro and possibly in vivo and its variation with age and disease.

A novel method for reducing the appearance of speckle within a single image acquisition in optical coherence tomography is presented. Local variations in the optical path length of beamlets within the beam diameter are introduced by vibrating a thin water film placed in a collimated section of the sample arm beam path. Consequent averaging of small numbers of adjacent depth scans results in a reduced appearance of speckle with no change in the axial point spread function. Reduced speckle images of a layered agar sample and thin reflective surfaces are shown.

A vector-based analysis is presented for polarization-sensitive optical coherence tomography (PS-OCT) that yields diattenuation, birefringence, and relative optic axis orientation. Experimental confirmation is demonstrated by comparing the calculated diattenuation of chicken tendon and muscle to independent measurement. The diattenuation of the retinal nerve fiber layer of the superior region of a human retina is also calculated.

We have developed a scanning fiber-optic probe compatible with high-speed polarization-sensitive OCT imaging. The effect of sample arm fiber motion on the polarization state of light incident on a sample is demonstrated by the evolution of incident Stokes vectors during the course of acquiring a single image. By referencing the polarization state of light backscattered from within a sample to the measured surface state, effects of motion-induced birefringence can be isolated. Conventional and polarization-sensitive images of human tissues are presented.

First experimental results on OCT imaging of internal structure of plant tissues and in situ OCT monitoring of plant tissue regeneration at different water supply are reported. Experiments for evaluating OCT capabilities were performed on Tradescantia. The investigation of seeds swelling was performed on wheat seeds (Triticum L.), barley seeds (Hordeum L.), long-fibred flax seeds (Linum usitatissimum L.) and cucumber seeds (Cucumis sativus L.). These OCT images correlate with standard microscopy data from the same tissue regions. Seeds were exposed to a low-intensity physical factor-the pulsed gradient magnetic field (GMF) with pulse duration 0.1 s and maximum amplitude 5 mT (4 successive pulses during 0.4 s). OCT and OCM enable effective monitoring of fast reactions in plants and seeds at different water supply.

In conventional single mode fiber, Self Phase Modulation (SPM) and Degenerate Cross Phase Modulation (DXPM) are the main non linear effects contributing to continuum generation. By controlling the polarization state of the light pumping the fiber and by selecting the polarization state out of the fiber, the spectrum of continuum generation can be optimized for optical coherence tomography (OCT). We investigate the effects of polarization control and selection on continuum light source consisting of a femotosecond Nd:glass laser and ultra high numerical aperture (UHNA) single mode fiber. The point Spread Function (PSF) can be improved by controlling linear input polarization or by selecting one of two orthogonal polarization modes at the output.

In this contribution we propose numerical procedures improving axial resolution and reducing artefacts in Spectral Optical Coherence Tomography (SOCT). We present to the best of our knowledge the first results of numerical spectral shaping and least square iterative deconvolution techniques applied to SOCT. The methods do not require separate experiment to determine spectral shape of the light source and can be then applied even if it changes during the experiment. To demonstrate the improvement of image quality we apply these methods to cross sectional images of the human eye in vivo.

We present a phase-resolved optical Doppler tomography (ODT) sys tem at 1310 nm using frequency domain method. Frequency domain phase-resolved ODT potentially allows for an increased longitudinal imaging range, signal-to-noise ratio and imaging acquisition rates, which can dramatically increase the measurable velocity dynamic range. A detailed derivation of phase-resolved frequency domain ODT and a measurement of flow through micro channel are presented. This technique can be used to quantify flow in integrated microfluidic devices in which complex three-dimensional structures and a wide velocity range are present.

In this paper, a fiber OCT system illumined by a superluminescent diode in the 940 nm wavelength region is reported. To test the 940nm OCT system, ex-vivo rabbit bladder, porcine bladder and rat bladder with tumor were imaged and compared with 1320nm OCT. The results demonstrate that the 940nm OCT system provides higher axial resolution up to 5 μm and less speckle noise, but the experimental results showed that the image depth for bladder samples in the 940 nm OCT system is slightly lower than the 1300nm OCT due to water absorption. During experiments, it was found that the fiber caused more dispersion at the wavelength of 940 nm than 1320 nm.

This paper is a part of research to develop convenient method for continuous monitoring of arterial blood pressure by non-invasive and non-oscillometric way. A simple optical method, using self-mixing in a diode laser, is used for detection of skin surface vibrations near the artery. These vibrations, which can reveal the pulsate propagation of blood pressure waves along the vasculature, are used for pulse wave registration. The registration of the Pulse Wave Transit Time (PWTT) is based on computing the time delay in different regions of the human body using an ECG as a reference signal. In this study, the comparison of method of optical self-mixing with other methods as photoplethysmographic (PPG) and bioimpedance (BI) for PWTT is done. Also correlation of PWTT, obtained with different methods, with arterial blood pressure is calculated. In our study, we used a group of volunteers (34 persons) who made the bicycle exercise test. The test consisted of cycling sessions of increasing workloads during which the HR changed from 60 to 180 beats per minute. In addition, a blood pressure (NIBP) was registered with standard sphygmomanometer once per minute during the test and all NIBP measurement values were synchronized to other signals to find exact time moments where the systolic blood pressure was detected (Korotkoff sounds starting point). Computer later interpolated the blood pressure signal in order to get individual value for every heart cycle. The other signals were measured continuously during all tests. At the end of every session, a recovery period was included until person's NIBP and heart rate (HR) normalized. As a result of our study it turned out that time intervals that were calculated from plethysmographic (PPG) waveforms were in the best correlation with systolic blood pressure. The diastolic pressure does not correlate with any of the parameters representing PWTT. The pulse wave signals measured by laser and piezoelectric transducer are very similar and do not have any qualitative differences. Since the detection of pulse wave by piezoelectric transducer is less complicated than laser detection, the piezo transducer should be preferred in such cases, but advantage of optical method of measurement is absent of any mechanical influence to artery.

Fiber-based high resolution OCT system was achieved using white-light source with a halogen lamp, which has advantages of wide spectrum, compact size and low cost. The axial resolution measured without using objective lens in the sample arm was about 2.5 mm. The thickness of a thin film (about 7 mm thick) was measured to evaluate the high resolution performance. The measured interferogram showed two well-distinguished peaks corresponding to two interfaces of the thin film. The implemented OCT system was composed of fiber-optic Michelson interferometer instead of that of conventional bulk optics. To adapt a white-light source to the fiber based OCT system and providing high resolution, a wideband single mode fiber with a large mode field diameter for high coupling efficiency, a wideband fiber coupler with flat coupling response, a cascaded detector scheme for broadband detection and dispersion control are required. Dispersion mismatch due to introducing an objective lens in the sample arm can be controlled effectively by employing a proper optical component in the reference arm. After dispersion control, resolution of about 3.5 mm was enhanced to about 2.5 mm, which is similar to the objective lens-free resolution, and wide sidelobes was also well suppressed.

We measure the skin wrinkle topology by means of low coherence interferometry (LCI), which forms the basis of the optical coherence tomography (OCT). The skin topology obtained using LCI and corresponding 2-D fast Fourier transform allow quantification of skin wrinkles. It took approximately 2 minutes to obtain 2.1 mm x 2.1 mm topological image with 4 um and 16 um resolutions in axial and transverse directions, respectively. Measurement examples show the particular case of skin contour change after-wrinkle cosmeceutical treatments and atopic dermatitis

We compare the dynamic range of OCT/OCM instruments configured with unbalanced interferometers, e.g., Michelson interferometers, with that of instruments utilizing balanced interferometers and balanced photodetection. We define the dynamic range (DR) as the ratio of the maximum fringe amplitude achieved with a highly reflecting surface to the root-mean-square (rms) noise. Balanced systems achieve a dynamic range 2.5 times higher than that of a Michelson interferometer, enabling an image acquisition speed roughly 6 times faster. This maximum improvement occurs at light source powers of a few milliwatts. At light source powers higher than 30 mW, the advantage in acquisition speed of balanced systems is reduced to a factor of 4. For video-rate imaging, the increased cost and complexity of a balanced system may be outweighed by the factor of 4 to 6 enhancement in image acquisition speed. We include in our analysis the "beat-noise" resulting from incoherent light backscattered from the sample, which reduces the advantage of balanced systems. We attempt to resolve confusion surrounding the origin and magnitude of "beat-noise", first described by L. Mandel in 1962. Beat-noise is present in both balanced and unbalanced OCT/OCM instruments.

Purpose: OCT is a new imaging method which produces a 3 mm wide x 2.5 mm deep 2D picture with a resolution of 15 μm. Materials and Methods: We utilised the Tomograph Sirius 713, developed at the Medical Laser Centre in cooperation with 4-Optics AG, Lubeck, Germany. This apparatus uses a special Super-Luminescence-Diode (SLD) that produces light within the near infrared wavelength, with a central wavelength of 1300 nm and spectral width of 45 nm. The coherence length is reduced to 15 μm. The light is introduced into a fibreglass optic which is a couple of meters long and is easy to handle. To measure the depth of invasion and position of urothelial bladder tumours, the fibreglass optic is attached to a regular endoscope (Wolf, Knittlingen, Germany) via a OCT adapter. That way, in parallel to the regular endoscopic view of the bladder mucosa with or without pathologic findings, an OCT picture of the superficial as well as the deeper muscle layers is visible online. OCT was used to obtaine 275 images from the bladder of 30 patients. Results: OCT of normal bladder mucosa produces an image with a cross section of up to 2.5 mm. It is possible to distinguish transitional epithelium, lamina propria, smooth muscles and capillaries. In cystitis the thickness of the mucosa is constant, but the distinction between the different layers is blurred. In squamous metaplasia there is thickening of the epithelial layer, with preservation of lamination of the lower layers. In transitional cell carcinoma there is a complete loss of the regular layered structure. Thus, the border between tumour and normal bladder tissue can be easily distinguished. Conclusions: This method can provide valuable information on tumour invasion and extension in real time and therefore influence therapeutic strategies