Showing papers on "Optical tomography published in 2003"

Optical coherence tomography - principles and applications

Abstract: There have been three basic approaches to optical tomography since the early 1980s: diffraction tomography, diffuse optical tomography and optical coherence tomography (OCT). Optical techniques are of particular importance in the medical field, because these techniques promise to be safe and cheap and, in addition, offer a therapeutic potential. Advances in OCT technology have made it possible to apply OCT in a wide variety of applications but medical applications are still dominating. Specific advantages of OCT are its high depth and transversal resolution, the fact, that its depth resolution is decoupled from transverse resolution, high probing depth in scattering media, contact-free and non-invasive operation, and the possibility to create various function dependent image contrasting methods. This report presents the principles of OCT and the state of important OCT applications. OCT synthesises cross-sectional images from a series of laterally adjacent depth-scans. At present OCT is used in three different fields of optical imaging, in macroscopic imaging of structures which can be seen by the naked eye or using weak magnifications, in microscopic imaging using magnifications up to the classical limit of microscopic resolution and in endoscopic imaging, using low and medium magnification. First, OCT techniques, like the reflectometry technique and the dual beam technique were based on time-domain low coherence interferometry depth-scans. Later, Fourier-domain techniques have been developed and led to new imaging schemes. Recently developed parallel OCT schemes eliminate the need for lateral scanning and, therefore, dramatically increase the imaging rate. These schemes use CCD cameras and CMOS detector arrays as photodetectors. Video-rate three-dimensional OCT pictures have been obtained. Modifying interference microscopy techniques has led to high-resolution optical coherence microscopy that achieved sub-micrometre resolution. This report is concluded with a short presentation of important OCT applications. Ophthalmology is, due to the transparent ocular structures, still the main field of OCT application. The first commercial instrument too has been introduced for ophthalmic diagnostics (Carl Zeiss Meditec AG). Advances in using near-infrared light, however, opened the path for OCT imaging in strongly scattering tissues. Today, optical in vivo biopsy is one of the most challenging fields of OCT application. High resolution, high penetration depth, and its potential for functional imaging attribute to OCT an optical biopsy quality, which can be used to assess tissue and cell function and morphology in situ. OCT can already clarify the relevant architectural tissue morphology. For many diseases, however, including cancer in its early stages, higher resolution is necessary. New broad-bandwidth light sources, like photonic crystal fibres and superfluorescent fibre sources, and new contrasting techniques, give access to new sample properties and unmatched sensitivity and resolution.

Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography

Abstract: A signal-to-noise ratio (SNR) analysis is presented for optical coherence tomography (OCT) signals in which time-domain performance is compared with that of the spectral domain. A significant SNR gain of several hundredfold is found for acquisition in the spectral domain. The SNR benefit is demonstrated experimentally in a hybrid time-domain-spectral-domain OCT system.

High-resolution multiphoton tomography of human skin with subcellular spatial resolution and picosecond time resolution

Abstract: High-resolution four-dimensional (4-D) optical tomography of human skin based on multiphoton autofluorescence imaging and second harmonic generation (SHG) was performed with the compact femtosecond laser imaging system DermaInspect as well as a modified multiphoton microscope. Femtosecond laser pulses of 80 MHz in the spectral range of 750 to 850 nm, fast galvoscan mirrors, and a time-correlated single-photon counting module have been used to image human skin in vitro and in vivo with subcellular spatial and 250-ps temporal resolution. The nonlinear induced autofluorescence originates from naturally endogenous fluorophores and protein structures such as reduced nicotinamide adenine dinucleotide phosphate, flavins, collagen, elastin, porphyrins, and melanin. Second harmonic generation was used to detect collagen structures. Tissues of patients with dermatological disorders such as psoriasis, fungal infections, nevi, and melanomas have been investigated. Individual intratissue cells and skin structures could be clearly visualized. Intracellular components and connective tissue structures could be further characterized by fluorescence excitation spectra, by determination of the fluorescence decay per pixel, and by fluorescence lifetime imaging. The novel noninvasive multiphoton autofluorescence-SHG imaging technique provides 4-D (x,y,z,tau) optical biopsies with subcellular resolution and offers the possibility of introducing a high-resolution optical diagnostic method in dermatology.

A submillimeter resolution fluorescence molecular imaging system for small animal imaging.

Abstract: Most current imagingsystems developed for tomographic investigations of intact tissues using diffuse photons suffer from a limited number of sources and detectors. In this paper we describe the construction and evaluation of a large dataset, low noise tomographic system for fluorescenceimaging in small animals. The system consists of a parallel plate-imaging chamber and a lens coupled CCD camera, which enables conventional planar imaging as well as fluorescencetomography. The planar imaging data are used to guide the acquisition of a Fluorescence Molecular Tomography (FMT) dataset containing more than 10 6 measurements, and to superimpose anatomical features with tomographic results for improved visual representation. Experimental measurements exhibited good agreement with the diffusion theory models used to predict light propagation within the chamber. Tests of the instrument’s capacity to quantitatively reconstruct fluorochrome distributions in three dimensions showed less than 5% errors between actual fluorochrome concentrations and FMT findings, and suggested a detection threshold of approximately 100 femptomoles for small localized objects. Experiments to assess the instrument’s spatial resolution demonstrated the ability of the system to resolve objects placed at clear distances of less than 1 mm. This is a significant resolution increase over previously developed systems for animal imaging, and is primarily due to the large dataset employed and the use of inversion methods. Finally, the in vivoimaging capacity is showcased. It is expected that the large dataset collected can enable superior imaging of molecular probes in vivo and improve quantification of fluorescence signatures.

Real-time in vivo imaging by high-speed spectral optical coherence tomography

Abstract: An improved spectral optical coherence tomography technique is used to obtain cross-sectional ophthalmic images at an exposure time of 64μs per A-scan. This method allows real-time images as well as static tomograms to be recorded in vivo.

Common-path interferometer for frequency-domain optical coherence tomography.

Abstract: A Michelson-type spectral interferometer that uses a common beam path for the reference and the sample arms is described. This optical arrangement is more compact and stable than the more commonly used dual-arm interferometer and is well suited for frequency-domain optical coherence tomography of biological samples. With a 16-bit CCD camera, the instrument has sufficient dynamic range and resolution for imaging to depths of 2 mm in scattering biological materials. Images obtained with this spectral interferometer are presented, including cross-sectional images in a Xenopus laevis tadpole.

Three-dimensional diffuse optical tomography in the parallel plane transmission geometry: evaluation of a hybrid frequency domain/continuous wave clinical system for breast imaging.

Abstract: Three-dimensional diffuse optical tomography (DOT) of breast requires large data sets for even modest resolution (1 cm). We present a hybrid DOT system that combines a limited number of frequency domain (FD) measurements with a large set of continuous wave (cw) measurements. The FD measurements are used to quantitatively determine tissue averaged absorption and scattering coefficients. The larger cw data sets (10(5) measurements) collected with a lens coupled CCD, permit 3D DOT reconstructions of a 1-liter tissue volume. To address the computational complexity of large data sets and 3D volumes we employ finite difference based reconstructions computed in parallel. Tissue phantom measurements evaluate imaging performance. The tests include the following: point spread function measures of resolution, characterization of the size and contrast of single objects, field of view measurements and spectral characterization of constituent concentrations. We also report in vivo measurements. Average tissue optical properties of a healthy breast are used to deduce oxy- and deoxy-hemoglobin concentrations. Differential imaging with a tumor simulating target adhered to the surface of a healthy breast evaluates the influence of physiologic fluctuations on image noise. This tomography system provides robust, quantitative, full 3D image reconstructions with the advantages of high data throughput, single detector-tissue coupling path, and large (1L) imaging domains. In addition, we find that point spread function measurements provide a useful and comprehensive representation of system performance.

Multiwavelength three-dimensional near-infrared tomography of the breast: initial simulation, phantom, and clinical results

Abstract: Three-dimensional (3D), multiwavelength near-infrared tomography has the potential to provide new physiological information about biological tissue function and pathological transformation. Fast and reliable measurements of multiwavelength data from multiple planes over a region of interest, together with adequate model-based nonlinear image reconstruction, form the major components of successful estimation of internal optical properties of the region. These images can then be used to examine the concentration of chromophores such as hemoglobin, deoxyhemoglobin, water, and lipids that in turn can serve to identify and characterize abnormalities located deep within the domain. We introduce and discuss a 3D modeling method and image reconstruction algorithm that is currently in place. Reconstructed images of optical properties are presented from simulated data, measured phantoms, and clinical data acquired from a breast cancer patient. It is shown that, with a relatively fast 3D inversion algorithm, useful images of optical absorption and scatter can be calculated with good separation and localization in all cases. It is also shown that, by use of the calculated optical absorption over a range of wavelengths, the oxygen saturation distribution of a tissue under investigation can be deduced from oxygenated and deoxygenated hemoglobin maps. With this method the reconstructed tumor from the breast cancer patient was found to have a higher oxy-deoxy hemoglobin concentration and also a higher oxygen saturation level than the background, indicating a ductal carcinoma that corresponds well to histology findings.

Phase-shifting algorithm to achieve high-speed long-depth-range probing by frequency-domain optical coherence tomography.

Abstract: Standard Fourier-domain optical coherence tomography (FDOCT) suffers from the presence of autocorrelation terms that obscure the object information and degrade the sensitivity and signal-to-noise ratio. By exploiting the phase information of the recorded interferograms, it is possible to remove those autocorrelation terms and to double the measurement range. However, standard phase-retrieval algorithms need three to five interferograms. We present a novel technique that shows all the features of complex FDOCT with only two recorded interferograms.

In vivo continuous-wave optical breast imaging enhanced with Indocyanine Green

Abstract: We investigate the uptake of a nontargeted contrast agent by breast tumors using a continuous wave diffuse optical tomography apparatus. The instrument operates in the near-infrared spectral window and employs 16 sources and 16 detectors to collect light in parallel on the surface of the tumor-bearing breast (coronal geometry). In our protocol an extrinsic contrast agent, Indocyanine Green (ICG), was injected by bolus. Three clinical scenarios with three different pathologies were investigated. A two-compartment model was used to analyze the pharmacokinetics of ICG and preprocess the data, and diffuse optical tomography was used for imaging. Localization and delineation of the tumor was achieved in good agreement with a priori information. Moreover, different dynamical features were observed for differing pathologies. The malignant cases exhibited slower rate constants (uptake and outflow) compared to healthy tissue. These results provide further evidence that in vivo pharmacokinetics of ICG in breast tumors may be a useful diagnostic tool for differentiation of benign and malignant pathologies.

Engineered microsphere contrast agents for optical coherence tomography.

Abstract: Contrast agents are utilized in virtually every imaging modality to enhance diagnostic capabilities. We introduce a novel class of optical contrast agent, namely, encapsulating microspheres, that are based not on f luorescence but on scattering nanoparticles within the shell or core. The agents are suitable for ref lectionor scattering-based techniques such as optical coherence tomography, light microscopy, and ref lectance confocal microscopy. We characterize the optical properties of gold-, melanin-, and carbon-shelled contrast agents and demonstrate enhancement of optical coherence tomography imaging after intravenous injection of such an agent into a mouse. © 2003 Optical Society of America OCIS codes: 170.4500, 160.4760, 170.4580. When one is imaging biological tissues, it is often desirable to enhance the signals measured from specific structures. Contrast agents that produce specific image signatures have been utilized in virtually every imaging modality, including ultrasound, 1 computed tomography, 2 magnetic resonance imaging, 3 and optical microscopy. 4 Optical coherence tomography (OCT) is an emerging imaging technology that has found application in a wide range of biological and medical applications. 5 In this Letter we characterize and demonstrate a new class of optical contrast agent suitable for ref lection- or scattering-based optical imaging techniques, namely, OCT but that also includes light and ref lectance confocal microscopy. These agents are biocompatible, 6 are suitable for in vivo use, and produce enhanced backscatter that is detectable in highly scattering tissue. These agents may be tailored to adhere to specific molecules, cells, or tissue types, and thus provide additional selectivity that can enhance the utility of OCT as an emerging diagnostic technique. OCT is capable of cellular-resolution imaging and may ultimately have a role in the early diagnosis

Full-field optical coherence tomography by two-dimensional heterodyne detection with a pair of CCD cameras.

Abstract: A two-dimensional heterodyne detection technique based on the frequency-synchronous detection method [Jpn. J. Appl. Phys. 39, 1194 (2000)] is demonstrated for full-field optical coherence tomography. This technique, which employs a pair of CCD cameras to detect the in-phase and quadrature components of the heterodyne signal simultaneously, offers the advantage of phase-drift suppression in interferometric measurement. Horizontal cross-sectional images are acquired at the rate of 100 frames/s in a single longitudinal scan, with a depth interval of 6 microm, making the rapid reconstruction of three-dimensional images possible.

Near-infrared (NIR) tomography breast image reconstruction with a priori structural information from MRI: algorithm development for reconstructing heterogeneities

Abstract: A combined magnetic resonance and near-infrared (MRI-NIR) imaging modality can potentially yield high resolution maps of optical properties from noninvasive simultaneous measurement. The main disadvantage of near-infrared (NIR) tomography lies in the low spatial resolution resulting from the highly scattering nature of tissue for these wavelengths. MRI has achieved high resolution, but suffers from low specificity. In this study, NIR image reconstruction algorithms that incorporate a priori structural information provided by MRI are investigated in an attempt to optimize recovery of a simulated optical property distribution. The effect of high levels of tissue heterogeneity are evaluated to determine the limitations of incorporating prior information into a realistic set of patient breast images. We assume absorption coefficient (/spl mu//sub a/) variations near /spl plusmn/40%, and transport scattering coefficient (/spl mu//sub s//sup //) variations near /spl plusmn/20%, in a coronal breast MRI geometry. Changes in tissue pathology due to tumor growth can be observed with NIR tompgraphy, and so the goal here is to determine how best to quantify these tumor-based contrast regions within the presence of high tissue heterogeneity. By applying knowledge of tissue's layered structure in reconstruction through various constraints in the iterative algorithm, quantitative recovery of the tumor optical properties improves from 69% to 74%, and localization improves as well. However, only when the true heterogeneity of the tissue distribution was included was accurate quantification of the tumor region possible. Using a good initial guess of /spl mu//sub a/ and /spl mu//sub s//sup //, derived from the regional structure of the model, quantification of the region reaches 99% of the true value, and spatial resolution retains a similar value to the original MRI image.

Three-dimensional optical tomography: resolution in small-object imaging.

Abstract: Near-infrared (NIR) optical tomography can provide estimates of the internal distribution of optical absorption and transport scattering from boundary measurements of light propagation within biological tissue. Although this is a truly three-dimensional (3D) imaging problem, most research to date has concentrated on two-dimensional modeling and image reconstruction. More recently, 3D imaging algorithms are demonstrating better estimation of the light propagation within the imaging region and are providing the basis of more accurate image reconstruction algorithms. As 3D methods emerge, it will become increasingly important to evaluate their resolution, contrast, and localization of optical property heterogeneity. We present a concise study of 3D reconstructed resolution of a small, low-contrast, absorbing and scattering anomaly as it is placed in different locations within a cylindrical phantom. The object is an 8-mm-diameter cylinder, which represents a typical small target that needs to be resolved in NIR mammographic imaging. The best resolution and contrast is observed when the object is located near the periphery of the imaging region (12–22 mm from the edge) and is also positioned within the multiple measurement planes, with the most accurate results seen for the scatter image when the anomaly is at 17 mm from the edge. Furthermore, the accuracy of quantitative imaging is increased to almost 100% of the target values when a priori information regarding the internal structure of imaging domain is utilized.

Optical-fiber-based Mueller optical coherence tomography.

Abstract: An optical-fiber-based multichannel polarization-sensitive Mueller optical coherence tomography (OCT) system was built to acquire the Jones or Mueller matrix of a scattering medium, such as biological tissue. For the first time to our knowledge, fiber-based polarization-sensitive OCT was dynamically calibrated to eliminate the polarization distortion caused by the single-mode optical fiber in the sample arm, thereby overcoming a key technical impediment to the application of optical fibers in this technology. The round-trip Jones matrix of the sampling fiber was acquired from the reflecting surface of the sample for each depth scan (A scan) with our OCT system. A new rigorous algorithm was then used to retrieve the calibrated polarization properties of the sample. This algorithm was validated with experimental data. The skin of a rat was imaged with this fiber-based system.

Uniqueness and wavelength optimization in continuous-wave multispectral diffuse optical tomography.

Abstract: We derive conditions for the unique and simultaneous recovery of chromophore concentrations and scattering coefficients in multispectral continuous-wave diffuse optical tomography. These conditions depend strongly on measurement wavelengths. We introduce and demonstrate a general methodology for choosing those wavelengths, which yields superior separation of scattering from absorption and superior separation of one chromophore from another. Application of these concepts should significantly improve the fidelity of continuous-wave diffuse near-infrared optical tomography in tissues.

Light absorption of (oxy-)hemoglobin assessed by spectroscopic optical coherence tomography.

Abstract: The combination of optical coherence tomography and spectroscopy may allow for highly localized, quantitative measurements of tissue spectral properties. We present, for the first time to our knowledge, quantitative measurements of the absorption coefficients of phantoms and of hemoglobin and oxygenated hemoglobin with spectroscopic optical coherence tomography (SOCT). Our results suggest that SOCT will be able to provide localized, quantitative oxygenation measurements.

Contrast mechanisms in polarization-sensitive Mueller-matrix optical coherence tomography and application in burn imaging

Abstract: We investigate the various contrast mechanisms provided by polarization-sensitive (PS) Mueller-matrix optical coherence tomography (OCT). Our PS multichannel Mueller-matrix OCT is the first, to our knowledge, to offer simultaneously comprehensive polarization-contrast mechanisms, including the amplitude of birefringence, the orientation of birefringence, and the diattenuation in addition to the polarization-independent intensity contrast, all of which can be extracted from the measured Jones or the equivalent Mueller matrix. Theoretical analysis shows that when diattenuation is negligible, the round-trip Jones matrix represents a linear retarder, which is the foundation of conventional PS-OCT, and can be calculated with a single incident polarization state, although the one-way Jones matrix generally represents an elliptical retarder; otherwise, two incident polarization states are needed. The experimental results obtained from rat skin samples, which conform well with the histology, show that Mueller OCT provides complementary structural and functional information on biological samples and reveal that polarization contrast is more sensitive to thermal degeneration of biological tissue than amplitude-based contrast. Thus, Mueller OCT has significant potential for application in the noninvasive assessment of burn depth.

Measurement of the axial point spread function in scattering media using single-mode fiber-based optical coherence tomography

Abstract: The authors studied the axial point spread function of optical coherence tomography for Gaussian intensity profiles emitted from and coupled back into single-mode fibers for signals from a scattering medium. The determined Rayleigh length of the axial point spread function was roughly twice the one measured from the reflection of a mirror. Using the measured point spread function in combination with the single backscatter model allowed determination of the attenuation coefficient of the suspension.

In vivo photoacoustic imaging of blood vessels using an extreme-narrow aperture sensor

Abstract: We applied photoacoustics for noninvasive two-dimensional imaging of blood vessels in vivo, using near infrared light. This study was undertaken to develop photoacoustic tomography of tissue for the detection of embedded blood vessels using a newly developed piezoelectric double ring detector, featuring an extremely narrow aperture.

Free-space propagation of diffuse light: Theory and experiments

Abstract: In this Letter we present a simple and novel theoretical approach for modeling the intensity distribution from an arbitrarily shaped turbid volume in a noncontact geometry by considering diffuse light propagation in free space. This theory is validated with experiments for a diffusive volume of known geometry in a noncontact situation, both with and without the presence of an embedded absorber. The implications of this new formulation in the context of optical tomography in turbid media are discussed.

Compact, broad-bandwidth fiber laser for sub-2-microm axial resolution optical coherence tomography in the 1300-nm wavelength region.

Abstract: A novel, compact, user friendly fiber laser with a broad emission bandwidth (MenloSystems, λc=1375 nm, Δλ=470 nm, Pout=4 mW) was used to achieve unprecedented sub-2-µm axial resolution optical coherence tomography (OCT) in nontransparent biological tissue in the 1300-nm wavelength region. Fresh human skin and arterial biopsies were imaged ex vivo with ∼1.4‐µm axial and ∼3‐µm lateral resolution and 95-dB sensitivity, demonstrating the great potential for clinical OCT applications of this stable, low-cost, and turn-on-key fiber laser.

Noncontact optical tomography of turbid media

Abstract: Optical tomography of turbid media has so far been limited by systems that require fixed geometries or measurements employing fibers. We present a system that records noncontact optical measurements from diffuse media of arbitrary shapes and retrieves the three-dimensional surface information of the diffuse medium. We further present a novel method of combining this composite data set and obtain accurate fluorescence reconstructions. This approach offers significant experimental simplicity and yields high-information-content datasets. The performance of this novel tomographic approach is demonstrated with experimental reconstructions of phantoms.

Shot-noise detection of ultrasound-tagged photons in ultrasound-modulated optical imaging

Abstract: We propose a new detection method for ultrasound-modulated optical tomography that allows us to perform parallel speckle detection with optimum shot-noise sensitivity, using a CCD camera. Moreover, we show that making use of a spatial filter system allows us to fully filter out speckle decorrelation noise. This method is confirmed by a test experiment.

Optical projection imaging system and method for automatically detecting cells having nuclear and cytoplasmic densitometric features associated with disease

Abstract: A system and method for rapidly detecting cells (1) of interest using multi-dimensional, highly quantitative, nuclear and cytoplasmic densitometric features (NDFs and CDFs) includes a flow optical tomography (FOT) instrument capable of generating various optical projection images (or shadowgrams) containing accurate density information from a cell, a computer (40) and software to analyze and reconstruct the projection images into a multi-dimensional data set, and automated feature collection and object classifiers. The system and method are particularly useful in the early detection of cancers such as lung cancer using a bronchial specimen from sputum or cheek scrapings and cervical/ovarian cancer using a cervical scraping, and the system can be used to detect rare cells in specimens including blood.

Electrostatic micromachine scanning mirror for optical coherence tomography

Abstract: Compact electrostatic micromirror structures for use in the scanning arm of an optical coherence tomography (OCT) system are described. These devices consist of millimeter-scale mirrors resting upon micrometer-scale polyimide hinges that are tilted by a linear micromachine actuator, the integrated force array (IFA). The IFA is a network of deformable capacitor cells that electrostatically contract with an applied voltage. The support structures, hinges, and actuators are fabricated by photolithography from polyimide-upon-silicon wafers. These devices were inserted into the scanning arm of an experimental OCT imaging system to produce in vitro and in vivo images at frame rates of 4 to 8 Hz.

Molecular contrast in optical coherence tomography by use of a pump–probe technique

Abstract: We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. 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. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.

Endoscopic optical coherence tomography with a modified microelectromechanical systems mirror for detection of bladder cancers.

Abstract: Experimental results of a modified micromachined microelectromechanical systems MEMS mirror for substantial enhancement of the transverse laser scanning performance of endoscopic optical coherence tomography EOCT are presented. Image distortion due to buckling of MEMS mirror in our previous designs was analyzed and found to be attributed to excessive internal stress of the transverse bimorph meshes. The modified MEMS mirror completely eliminates bimorph stress and the resultant buckling effect, which increases the wobbling-free angular optical actuation to greater than 37°, exceeding the transverse laser scanning requirements for EOCT and confocal endoscopy. The new optical coherence tomography OCT endoscope allows for two-dimensional cross-sectional imaging that covers an area of 4.2 mm 2.8 mm limited by scope size and at roughly 5 framess instead of the previous area size of 2.9 mm 2.8 mm and is highly suitable for noninvasive and high-resolution imaging diagnosis of epithelial lesions in vivo. EOCT images of normal rat bladders and rat bladder cancers are compared with the same cross sections acquired with conventional bench-top OCT. The results clearly demonstrate the potential of EOCT for in vivo imaging diagnosis and precise guidance for excisional biopsy of early bladder cancers. © 2003 Optical Society of America OCIS codes: 170.2150, 170.3880, 170.4500, 170.7230, 170.3890.

Time-series estimation of biological factors in optical diffusion tomography

Abstract: We apply state space estimation techniques to the time-varying reconstruction problem in optical tomography. We develop a stochastic model for describing the evolution of quasi-sinusoidal medical signals such as the heartbeat, assuming these are represented as a known frequency with randomly varying amplitude and phase. We use the extended Kalman filter in combination with spatial regularization techniques to reconstruct images from highly under-determined time-series data. This system also naturally segments activity belonging to different biological processes. We present reconstructions of simulated data and of real data recorded from the human motor cortex (Franceschini et al 2000 Optics Express 6 49-57). It is argued that the application of these time-series techniques improves both the fidelity and temporal resolution of reconstruction in optical tomography.

Full-field birefringence imaging by thermal-light polarization-sensitive optical coherence tomography. I. Theory

Abstract: A method for measuring birefringence by use of thermal-light polarization-sensitive optical coherence tomography is presented. The use of thermal light brings to polarization-sensitive optical coherence tomography a resolution in the micrometer range in three dimensions. The instrument is based on a Linnik interference microscope and makes use of achromatic quarter-wave plates. A mathematical representation of the instrument is presented here, and the detection scheme is described, together with a discussion of the validity domain of the equations used to evaluate the birefringence in the presence of white-light illumination.