Time-dependent speckle holograms from inside tumor spheroids using short-coherence near-infrared light provide quantitative measures of the state of health of the tumor tissue. Holographic optical coherence imaging (OCI) records full-frame en face images from successive depths inside a tumor in a so-called “flythrough”. When the flythrough is stopped at a specified depth, the holographic features can be classified as variable (relating to cell motility and Brownian motion) or persistent (arising from specific structure such as necrosis inside the tumor) depending on their temporal variations. A strong trend is observed in the ratio of variable-to-persistent features in tumors that are healthy, metabolically poisoned, or chemically cross-linked. Autocorrelation times also reflect this trend. Depth-gated speckle holography provides a means to sample biologically significant areas without the need for cellular-scale spatial resolution, with possible relevance for intraoperative applications.

In this paper we are investigating the possibility of a frequency compounding method for speckle reduction in optical coherence tomography. The method is based on incoherent summation of the magnitudes of two independent interferometric signals, which were recorded at two different center wavelengths simultaneously. We derive the corresponding speckle statistics for amplitude based OCT signals recorded with single and dual frequency sources and compare the theoretical results with measurements obtained in a uniformly scattering sample. Finally we demonstrate our method by comparing images of human skin recorded in vivo with and without frequency compounding. The compounding method results in an increased contrast and improved image quality without loss of resolution.

Background: Coronary artery disease (CAD) is the leading cause of mortality and morbidity in the industrialized world. Optical coherence tomography (OCT) is a high-resolution intravascular imaging technology with a potential for in vivo plaque characterization. Although structural remodeling of the arterial vessel wall during plaque development can change tissue optical scattering properties, very limited evidence is available on the exact optical scattering properties of plaques. The scattering coefficient, μs, and the anisotropy factor, g, can be derived from OCT images by fitting a theoretical model to individual depth-scans. The aim of the current study was to use this method to examine by OCT the scattering properties of human arteries with different stages of atherosclerotic lesion development. Methods: Normal (n=4), lipid-rich (n=4), and fibrous (n=3) aortic blocks as classified by parallel histopathologic examination were obtained within 24 hours of death and imaged by OCT. The intima was located in the OCT images, and then further split into 115 blocks (41 normal, 40 lipid-rich, and 34 fibrous) of adjacent OCT depth-scans transversely spanning ~200-300 μm. Scattering signals from each block were averaged and fit to the theoretical model. From these fittings, μs and g were extracted. Results and Discussion: The optical scattering properties of normal aortic intima were quite different from lipid-rich and fibrous lesions, respectively. We discovered that the normal intima was generally highly forward scattering, i.e., with 0.917-1, whereas lipid-rich blocks had μs<15mm^-1. Fibrous blocks displayed large variations in μs, reflecting a histopathology with varying amounts of collagen, lipids, and elastin. Based on our findings, we defined a criteria of μs and g for normal intimas, using the above values of μs and g as cutoffs. Our "normal" criteria demonstrated high sensitivity (92.4%) and specificity (82.4%). We conclude, that a detailed analysis of the tissue optical scattering properties can enhance the capacity of OCT to provide information about vascular pathology.

We built an optical coherence tomography (OCT) system with a rapid scanning optical delay (RSOD) line, which allows probing full axial eye length. The system produces Three-dimensional (3D) data sets that are used to generate 3D tomograms of the model eye. The raw tomographic data were processed by an algorithm, which is based on Snell’s law to correct the interface positions. The Zernike polynomials representation of the interfaces allows quantitative wave aberration measurements. 3D images of our results are presented to illustrate the capabilities of the system and the algorithm performance. The system allows us to measure intra-ocular distances.

Complex Spectral Optical Tomography (SOCT) in comparison to ordinary SOCT produces images free of parasitic terms with extended measurement range. This technique requires stability of the object during at least three consecutive measurements. With a new fast SOCT instrument it was possible to make measurements regardless of involuntary eye movements. The first measurements of human eye in vivo based on Complex SOCT are presented.

Interferometers with a low-coherent illumination allow non-contact evaluating random tissues by locating the visibility maxima of interference fringes. The problem is the light scattering by a tissue, it is why interference fringe parameters are randomly varied. Other problem consists in the need to process large amount of data obtained in optical coherence tomography (OCT) systems. We propose to use a stochastic fringe model and Kalman filtering method for noisy low-coherence fringe processing. A fringe signal value is predicted at a next discretization step using full information available before this step and a prediction error is used for dynamic correction of fringe envelope, frequency and phase. The advantages of Kalman filtering method consist in its noise-immunity, high-speed data processing and optimal evaluation of fringe parameters. Specially fabricated random tissues have been measured with a low-coherence interferometer. The obtained data from the tissue internal structure are evaluated using a dynamic stochastic fringe processing algorithm applied to fringe signal samples series. Nonlinear Kalman filtering method was applied to measure scattering liquid velocity profile in the Doppler OCT. The measurement results are in good agreement with the results obtained by the Fourier transform method.

We present a white-light interference microscope designed to produce high-resolution three-dimensional images of biological media. This technique is an alternative to conventional optical coherence tomography (OCT). The experimental setup is based on a Linnik interferometer illuminated with 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 a high-resolution CCD camera. The short coherence length of the source and the compensation of dispersion mismatch in the interferometer arms yield an optical sectioning ability with 0.8 μm resolution in water. Transverse resolution of 1.0 μm is achieved by using high numerical aperture microscope objectives. A shot-noise limited detection sensitivity of 86 dB can be reached with 2 s acquisition time. High-resolution images of the Xenopus Laevis tadpole are shown.

Ultrahigh axial resolution OCT is demonstrated in human cells and other human biopsies for two fiber broadened femtosecond light sources, achieving 0.5μm axial resolution in the visible and 1.4μm in the in the 1300nm wavelength region.

We report on the use of two matched linearly chirped fiber Bragg grating (FBG) in the reference arm of a Michelson interferometer as a means to achieve variable optical delay. We demonstrate that the properties of a linearly chirped FBG can be exploited to achieve millimeters of optical delay with physical stretches of the FBG on the order of tens of microns; this allows for optical delay line configurations that are easily driven by piezo-electric actuators.

A stationary low coherence interferometer for optical coherence tomography (linear OCT, LOCT) based on Young's two-pinhole experiment is characterized theoretically. All OCT sensors either work in the time (TDOCT) or Fourier domain (FDOCT). In contrast to these setups, the interferometer described in this paper employs no moving parts in the reference arm and no spectrometers for depth profiling. Depth profiling is achieved by detecting the interference signal on a linear CCD-array. Different positions of the interference signal on the CCD-array correspond to different depths inside the sample. The interference signal of the setup and the sensitivity in the case of shot noise limited detection are derived theoretically and compared to sensors in the time domain. In-vitro images of porcine cornea demonstrate the clinical potential of the setup.

A novel concept for video-rate parallel acquisition of optical coherence tomography imaging is presented based on in-pixel demodulation. The main restrictions for parallel detection such as data rate, power consumption, circuit size and poor sensitivity are overcome with a smart pixel architecture incorporating an offset compensation circuit, a synchronous sampling stage, programmable time averaging and random pixel accessing, allowing envelope and phase detection in large 1D and 2D arrays.

Optical intrinsic signal imaging (OISI) provides the surface activation map of brain and has provided many insights. In this study, we show that the optical coherence tomography (OCT) can indeed provide depth resolved functional map of cat visual cortex. Activation profile obtained by integrating OCT signal across depth correlates well with that determined by the OISI. Functional OCT (fOCT) promises to be a valid technique for revealing unexplored organization inside the brain at a micro system level.

A state of the art TiAl₂O₃ laser (λ = 780 nm, Δλ = 170 nm, P_out = 350 mW), interfaced to a free space OCT system was used to quantitatively extract spatially resolved absorption profiles from non-scattering phantoms. The sources of error related to instrument performance and measurement procedure were investigated. Absorption as small as 0.2 mm^-1 was measured in phantoms as thin as 180 μm with precision better than 5% over 70 nm wavelength range.

We analyse polarisation effects in spectroscopic optical coherence tomography. Birefringence induced changes in polarisation are wavelength dependent and the spectrum of the interference signal will therefore depend on the polarisation properties of the sample. We have avoided this problem by realising a combination of dual wavelength spectroscopic OCT system and polarisation sensitive detection

We describe two novel techniques for contrast enhancement in optical coherence tomography (OCT) which enables molecular specific imaging. The first, a pump-probe technique, is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample arm light acting as probe light. Preliminary results exhibiting contrast enhancement in cross-sectional OCT images using methylene blue dye are presented. The second method is an optical switch suppression technique based on the use of a transmembrane protein called bacteriorhodopsin. Initial experiments indicate that biochemical optical switches, such as bacteriorhodopsin, are excellent contrast agent candidates for molecular contrast OCT.

En-face OCT relies on scanning fast along a direction perpendicular to the optical axis. C-scan images (en-face slices at constant depth) can be obtained at different depths. The quality of the image and what part of a particular layer is visible depends on the properties of the sampling function. In this paper we examine how the scanning configuration, the interface optics, the coherence length of the source used, and the object itself influence the shape of the sampling function.

We demonstrate methods for achieving high resolution imaging using alternate scanning techniques in optical coherence tomography and optical coherence microscopy. These techniques enable high transverse resolutions and overcome depth of field limitations. Cellular level resolutions in human tissue may be achieved.

We report the first (to the best of out knowledge) en face polarization sensitive optical coherence tomography (PS-OCT) system. The transverse raster scanning of the target is achieved using a pair of galvo-scanner mirrors. The set-up is based on incoherent detection in two optical and electronic channels and employs balanced detection to reduce the excess photon noise generated by the low coherence source (superluminescent diode). The outputs of the two channels are processed using software to provide a polarisation insensitive (pure reflectivity) image and a birefringence retardation map. Images from ex vivo (human tooth) and in vivo targets (human retina) have been acquired. Particulars of en face optical coherence tomography imaging of birefringent tissue are discussed.

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of optical coherence tomography (OCT). We used phase resolved PS-OCT to measure and image three dimensional birefringent properties of pathologic and non pathologic human corneas and compare the results. Knowing the retardation and optic axis distribution might be useful information for early detection of different corneal diseases.

The hemoglobin solution with different concentrations of glucose and, therefore, different levels of glycated hemoglobin was studied by optical coherence tomography (OCT). Obtained images of OCT were used for the measurements of refractive index of samples. Our results showed that the refractive index can be potentially applied as simple and sensitive method for the evaluation of glycated hemoglobin amount.

A compact, low cost prismless Titanium:sapphire laser with 154nm bandwidth and 20mW output power was developed and ultrahigh resolution OCT ex vivo imaging in an animal model with sub-2μm and in vivo imaging in patients with 3μm axial resolution is demonstrated. This light source not only significantly reduces costs for broadband OCT light sources, but has also great potential for clinical OCT applications due to its small footprint (500x200mm including pump laser), user-friendliness and power stability.

Ultrahigh resolution ophthalmic OCT has been performed in more than 250 eyes of 160 patients, demonstrating unprecedented visualization of intraretinal morphology of several retinal pathologies. and therefore the potential to enhance sensitivity and specificity for early ophthalmic diagnosis as well as to monitor the efficacy of therapy. In addition, it might contribute to a better understanding of ocular pathogenesis. This is demonstrated by investigating both normal retinal morphology in an animal model and the impairment of the photoreceptor layer in different macular pathologies.

Diagnostic value of standard OCT for recognizing cervical neoplasia has been evaluated: sensitivity is 82%, specificity is 78%, and diagnostics accuracy is 81%. To increase it several approaches have been suggested: application of hyperosmotic agents, cross-polarization tomography, complementary use of fluorescence spectroscopy and OCT, additional computer processing of the OCT-images and optical coherence microscipy.

In this paper we demonstrate real-time in vivo and in vitro OCT images of human dental tissue obtained in a clinical setting. For the first time we have used a compact, commercial prototype OCT system with a surgical microscope as a beam delivery system for investigations of dental tissue. We have imaged demineralised tissue, caries lesions and restored teeth and demonstrate the detection of changes in tissue microstructure. We discuss the details of this system and its potential and limitations with respect to dental applications.

Ultrahigh resolution OCT is used to visualize experimentally induced osteoarthritis in a rat knee model. Using a Cr⁴⁺:Forsterite laser, ultrahigh image resolutions of 5um are achieved. Progression of osteoarthritic remodeling and cartilage degeneration are quantified. The utility of OCT for the assessment of cartilage integrity is demonstrated.

We demonstrate compact ultrahigh resolution OCT systems for in vivo studies, with broadband light sources based on a commercially available Nd:Glass femtosecond laser and nonlinear fiber continuum generation. In vivo OCT images of hamster cheek pouch and human skin acquired at 4 frames per second and with 5.5 μm axial resolution are presented. These systems are robust, compact and portable.

Optical coherence tomography (OCT) images of basal cell carcinomas (BCCs) have been acquired using a compact handheld proble with an integrated video camera allowing the OCT images to be correlated to a skin surface image. In general the healthy tissue of the skin has an obvious stratified structure, whereas the cancerous tissue shows a more homogeneous structure. Thus it was demonstrated that it is possible to distinguish BCCs from healthy tissue by means of OCT. Furthermore different histological types of BCC were identified. Comparison of OCT images taken prior to and immediately after photodynamic theory clearly shows the tissue response to the treatment, and indicates local oedema in the treated area.

Capabilities of optical coherence tomography (OCT) as well as OCT enhanced by tissue clearing using glycerol solution for differential diagnosis of erythematoses, bullous and papulous skin diseases are demonstrated on 118 patients sample. It is shown that high-skilled dermatologists familiar with fundamentals of skin pathomorphology but without previous experience in OCT studies and interpretation of optical features are capable, when using OCT, of distinguishing optical images of various skin diseases to a high diagnostic accuracy (ranging from 76% to 94%) and with good multirater interobserver agreement between different specialists (kappa up to 0.69). Application of glycerol improves contrast and penetration depth of OCT images of skin significantly, thus reliably improving diagnostic validity of the technique and facilitating differential diagnosis of clinically similar dermatoses accompanied by papulous eruption.

Optical Coherence Tomography (OCT) provides more parameters than pure morphology does. In a recent paper we have shown that the refractive index (RI) can be evaluated in a localized manner in skin tissue under in vivo conditions. Further evaluation provides scattering parameters (scatter width) of turbid materials down to penetration depths of some 100 μm. Measurements have been done in vitro in pig skin and in vivo in human skin with our OCT scanner SkinDex 300. The parameters RI and scatter width may have a viable impact on skin research and clinical diagnoses. In addition, we demonstrate the breakdown of the ballistic light propagation in turbid material and tissue due to multiple forward scattering.

The morphology of healthy and pathological human brain tissue, as well as the brain structural organization of various animal models has been imaged in-vitro using ultrahigh resolution optical coherence tomography (UHR OCT). Micrometer-scale OCT resolution (< 2 μm axial resolution) was achieved at different central wavelengths by interfacing three state-of-the-art broad bandwidth light sources (Ti:Al₂O₃, λc = 790 nm, Δλ = 260 nm and P_out = 50 mW; PCF based laser, λc = 1150 nm, Δλ = 350 nm and P_out = 2 W; Fiber laser based light source, λc = 1350 nm, Δλ = 470 nm and P_out = 4 mW) to a modular free-space OCT system, utilizing a dynamic focusing and designed for optimal performance in the appropriate wavelength regions. Images acquired from a fixed honeybee brain demonstrated the ability of UHR OCT to image the globular structure of the brain, some fine morphological details such as the nerve fiber bundles connecting the medulla (visual center) to the honeybee eyes, and the interfaces between different tissue layers in the medulla. Tomograms of various human neuropathologies demonstrated the feasibility of UHR OCT to visualize morphological details such as small (~20 μm) calcifications typical for fibrous meningioma, and enlarged nuclei of cancer cells (~10-15 μm) characteristic for many other neuropathologies. In addition UHR OCT was used to image cellular morphology in living ganglion cells.

While endoscopic optical coherence tomography has been established successfully in vivo ,implementation of endoluminal optical coherence microscopy remains demanding,s suitable confocal probe is lacking. A miniaturized confocal laser scanning microscope is presented,which fulfills the requirements for endoluminal optical coherence microscopy. First,imaging experience gained for optical coherence microscopy of nimal gastrointestinal tissue samples is described. For this purpose,laboratory scale optical coherence microscope with an image acquisition time of 1min 30 s was employed. Cellular membranes can be identified throughout the gastrointestinal organs. Frequency domain image analysis can be used to distinguish columnar from squamous epithelium. Profilometric information on sample surfaces can be obtained directly as isophase lines. Second, the miniaturized confocal laser scanning microscope is characterized. Having an effective diameter of 25 mm, it houses single-mode optical fiber,scanning mirror and an objective lens. The micro-electro-mechanical mirror with gimballed suspension allows two dimensional scanning without introducing an optical path difference. The sinusoidal movement of both axes has to be considered to approximate cartesian image coordinates. Field geometry is illustrated s function of excitation amplitude and frequency. Acceptable image quality is chieved for frame rate of 0.5 Hz. A strategy to position the focal plane axially within the sample volume is discussed.

Polarization-sensitive optical coherence tomography (PSOCT) is a powerful new optical imaging modality that is sensitive to the birefringence properties of tissues. It thus has potential applications in studying the large-scale ordering of collagen fibers within connective tissues and changes related to pathology. As a tissue for study by PSOCT, intervertebral disk represents an interesting system as the collagen organisation is believed to show pronounced variations with depth, on a spatial scale of about 100 microns .We have used a polarisation-sensitive optical coherence tomography system to measure the birefringence properties of bovine caudal intervertebral disk and compared this with equine flexor tendon. The result for equine tendon, Δn = (4.4 ± 0.15) x 10^-3 at 1.3μm, is somewhat larger than values reported for bovine tendon. The annulus fibrosus of freshly excised intact bovine intervertebral disk displays an identical value of birefringence, Δn = (4.4 ± 0.4) x 10^-3 at 1.3μm. However the retardance does not increase uniformly with depth into the tissue but displays a pronounced discontinuity at a depth of around 300 microns. This is believed to be related to the lamellar structure of this tissue, in which the collagen fiber orientation alternates between successive lamellae as depth into the tissue increases. The nucleus pulposus displays polarization conversion equivalent to a birefringence an order of magnitude smaller than these values i.e. Delta;n = (0.278 ± 0.007) x 10^-3. Our measurement protocol cannot distinguish this from the effects of depolarization due to multiple scattering. These results imply that PSOCT could be a useful tool to study collagen organisation within intervertebral disk in vivo and its variation with applied load and disease.

Atherosclerosis is the underlying vascular pathology that initiates arterial thromboembolic occlusions (myocardial infarctions, strokes and peripheral vessel blockage). Two imaging modalities, Optical Coherence Tomography (OCT) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), were investigated for detection and compositional analysis of unstable plaque associated with plaque erosion and sudden occlusion. OCT produces high resolution images whereas mass spectrometry images provide information on the spatial distribution of chemical elements. Diseased carotid arteries taken from patients with high-risk lesions were imaged with OCT and ToF-SIMS to give molecular and metabolic information, and matched with histopathology. OCT results show clear indications of vascular remodeling by the presence of fatty acid deposits, fibrous tissue and calcifications. ToF-SIMS further characterized changes based on secondary ion topography analysis where a high ²³Na/³⁹K ratio was indicative of arterial tissue degradation and the amount of ⁴⁰Ca corresponded with late stage atherosclerosis. This pilot experiment has demonstrated that in vitro OCT imaging and ToF-SIMS of diseased carotid arteries have scientific merit for targeting clinically relevant morphology and metabolic changes to compare stable and unstable plaque. These optical techniques provide complimentary metabolic and molecular information on unstable plaque, specifically cell break-down with altered ion ratios of ²³Na, ³⁹K and ⁴⁰Ca.

The possibility of using short-pulse laser with interferometric fiber-optic for diagnostic of tissues is presented. The Cr:Forsterite laser operated at 1300 nm is proposed and the first characteristics of such laser are presented. The detection of backscattering light is obtained by using the Michelson type fiber-optic interferometer. The main aspect of signal processing based on a phase calculation as well as theoretical system description in the Jones’ matrix approach is also presented.

In this work we investigated the erythrocyte membrane viscoelastic behavior, in hypertensive and dislipidemic patients using the "Erythrodeformeter" that permit to obtain the stationary and dynamical linear parameters of erythrocyte membrane by laser diffractometry. Our results show that several erythrocyte membrane rheological parameters were statistically altered in patients if compared with the control group. Then, the analyzed hemorheological parameters could be use in order to detect and diagnostic the hypertension and dyslipidemic alterations.