Showing papers on "Optical tomography published in 2007"

Biomedical Optics: Principles and Imaging

Abstract: Preface. 1. INTRODUCTION. 1.1.Motivation for optical imaging. 1.2.General behavior of light in biological tissue. 1.3.Basic physics of light-matter interaction. 1.4.Absorption and its biological origins. 1.5.Scattering and its biological origins. 1.6.Polarization and its biological origins. 1.7.Fluorescence and its biological origins. 1.8.Image characterization. 1.9.References. 1.10.Further readings. 1.11.Problems. 2. RAYLEIGH THEORY AND MIE THEORY FOR A SINGLE SCATTERER. 2.1.Introduction. 2.2.Summary of the Rayleigh theory. 2.3.Numerical example of the Rayleigh theory. 2.4.Summary of the Mie theory. 2.5.Numerical example of the Mie theory. 2.6.Appendix 2.A. Derivation of the Rayleigh theory. 2.7.Appendix 2.B. Derivation of the Mie theory. 2.8.References. 2.9.Further readings. 2.10.Problems. 3. MONTE CARLO MODELING OF PHOTON TRANSPORT IN BIOLOGICAL TISSUE. 3.1.Introduction. 3.2.Monte Carlo method. 3.3.Definition of problem. 3.4.Propagation of photons. 3.5.Physical quantities. 3.6.Computational examples. 3.7.Appendix 3.A. Summary of MCML. 3.8.Appendix 3.B. Probability density function. 3.9.References. 3.10.Further readings. 3.11.Problems. 4. CONVOLUTION FOR BROADBEAM RESPONSES. 4.1.Introduction. 4.2.General formulation of convolution. 4.3.Convolution over a Gaussian beam. 4.4.Convolution over a top-hat beam. 4.5.Numerical solution to convolution. 4.6.Computational examples. 4.7.Appendix 4.A. Summary of CONV. 4.8.References. 4.9.Further readings. 4.10.Problems. 5. RADIATIVE TRANSFER EQUATION AND DIFFUSION THEORY. 5.1.Introduction. 5.2.Definitions of physical quantities. 5.3.Derivation of the radiative transport equation. 5.4.Diffusion theory. 5.5.Boundary conditions. 5.6.Diffuse reflectance. 5.7.Photon propagation regimes. 5.8.References. 5.9.Further readings. 5.10.Problems. 6. HYBRID MODEL OF MONTE CARLO METHOD AND DIFFUSION THEORY. 6.1.Introduction. 6.2.Definition of problem. 6.3.Diffusion theory. 6.4.Hybrid model. 6.5.Numerical computation. 6.6.Computational examples. 6.7.References. 6.8.Further readings. 6.9.Problems. 7. SENSING OF OPTICAL PROPERTIES AND SPECTROSCOPY. 7.1.Introduction. 7.2.Collimated transmission method. 7.3.Spectrophotometry. 7.4.Oblique-incidence reflectometry. 7.5.White-light spectroscopy. 7.6.Time-resolved measurement. 7.7.Fluorescence spectroscopy. 7.8.Fluorescence modeling. 7.9.References. 7.10.Further readings. 7.11.Problems. 8. BALLISTIC IMAGING AND MICROSCOPY. 8.1.Introduction. 8.2.Characteristics of ballistic light. 8.3.Time-gated imaging. 8.4.Spatial-frequency filtered imaging. 8.5.Polarization-difference imaging. 8.6.Coherence-gated holographic imaging. 8.7.Optical heterodyne imaging. 8.8.Radon transformation and computed tomography. 8.9.Confocal microscopy. 8.10.Two-photon microscopy. 8.11.Appendix 8.A. Holography. 8.12.References. 8.13.Further readings. 8.14.Problems. 9. OPTICAL COHERENCE TOMOGRAPHY. 9.1.Introduction. 9.2.Michelson interferometry. 9.3.Coherence length and coherence time. 9.4.Time-domain OCT. 9.5.Fourier-domain rapid scanning optical delay line. 9.6.Fourier-domain OCT. 9.7.Doppler OCT. 9.8.Group velocity dispersion. 9.9.Monte Carlo modeling of OCT. 9.10.References. 9.11.Further readings. 9.12.Problems. 10. MUELLER OPTICAL COHERENCE TOMOGRAPHY. 10.1.Introduction. 10.2.Mueller calculus versus Jones calculus. 10.3.Polarization state. 10.4.Stokes vector. 10.5.Mueller matrix. 10.6.Mueller matrices for a rotator, a polarizer, and a retarder. 10.7.Measurement of Mueller matrix. 10.8.Jones vector. 10.9.Jones matrix. 10.10.Jones matrices for a rotator, a polarizer, and a retarder. 10.11.Eigenvectors and eigenvalues of Jones matrix. 10.12.Conversion from Jones calculus to Mueller calculus. 10.13.Degree of polarization in OCT. 10.14.Serial Mueller OCT. 10.15.Parallel Mueller OCT. 10.16.References. 10.17.Further readings. 10.18.Problems. 11. DIFFUSE OPTICAL TOMOGRAPHY. 11.1.Introduction. 11.2.Modes of diffuse optical tomography. 11.3.Time-domain system. 11.4.Direct-current system. 11.5.Frequency-domain system. 11.6.Frequency-domain theory: basics. 11.7.Frequency-domain theory: linear image reconstruction. 11.8.Frequency-domain theory: general image reconstruction. 11.9.Appendix 11.A. ART and SIRT. 11.10.References. 11.11.Further readings. 11.12.Problems. 12. PHOTOACOUSTIC TOMOGRAPHY. 12.1.Introduction. 12.2.Motivation for photoacoustic tomography. 12.3.Initial photoacoustic pressure. 12.4.General photoacoustic equation. 12.5.General forward solution. 12.6.Delta-pulse excitation of a slab. 12.7.Delta-pulse excitation of a sphere. 12.8.Finite-duration pulse excitation of a thin slab. 12.9.Finite-duration pulse excitation of a small sphere. 12.10.Dark-field confocal photoacoustic microscopy. 12.11.Synthetic aperture image reconstruction. 12.12.General image reconstruction. 12.13.Appendix 12.A. Derivation of acoustic wave equation. 12.14.Appendix 12.B. Green's function approach. 12.15.References. 12.16.Further readings. 12.17.Problems. 13. ULTRASOUND-MODULATED OPTICAL TOMOGRAPHY. 13.1.Introduction. 13.2.Mechanisms of ultrasonic modulation of coherent light. 13.3.Time-resolved frequency-swept UOT. 13.4.Frequency-swept UOT with parallel-speckle detection. 13.5.Ultrasonically modulated virtual optical source. 13.6.Reconstruction-based UOT. 13.7.UOT with Fabry-Perot interferometry. Problems. Reading. Furhter Reading. APPENDIX A. DEFINITIONS OF OPTICAL PROPERTIES. APPENDIX B. List of Acronyms. Index.

Phase-sensitive optical coherence elastography for mapping tissue microstrains in real time

Abstract: The authors present a phase-sensitive optical coherence elastography (PSOCE) approach to image instantaneous tissue deformations, strain rates, and strains of soft tissue in real time with sensitivity at the nanometer scale. This method exploits the phase information available in the complex optical coherence tomography images and measures the phase changes between the successive B scans to resolve the instantaneous tissue deformations. The PSOCE system described is capable of producing localized microstrain rate and strain maps of tissue subjected to a dynamic compression in real time. They show that this approach is capable of resolving deformations as small as 0.26nm.

In vivo full range complex Fourier domain optical coherence tomography

Abstract: The author presents a system and algorithm to achieve full range complex Fourier domain optical coherence tomography (OCT) capable of imaging biological tissues in vivo. The method utilizes the Hilbert transformation to obtain the analytic functions for spatial interference signals obtained from each single wavelength covered in the broadband OCT light source before performing the Fourier transformation to localize the scatters within a sample. A constant carrier frequency is introduced in the spatial OCT interference signal so that its Hilbert transformation is strictly equal to its quadrature representation. The method is experimentally validated for in vivo imaging.

The background oriented schlieren technique: sensitivity, accuracy, resolution and application to a three-dimensional density field

Abstract: Three-dimensional density information of a double free air jet was acquired using optical tomography. The projections of the density field were measured using the background oriented schlieren method (BOS). Preceding the free jet measurements, the sensitivity, accuracy and resolution of the BOS method were investigated. The sensitivity depends mostly on the focal length of the lens used, the relative position of the object between camera and background and the smallest detectable shift in the image plane. The accuracy was found to be sufficiently high to apply a tomographic reconstruction process. The resolution is determined by the transfer function of the BOS-method. It is not constant and depends on the size of the interrogation windows used for the cross-correlation-algorithm. The reconstruction of the free jet was computed, using filtered back projection. The reconstructed 3D density field shows with good resolution the typical diamond structure of the density distribution in under-expanded free jets.

Weight-matrix structured regularization provides optimal generalized least-squares estimate in diffuse optical tomography

Abstract: Diffuse optical tomography (DOT) involves estimation of tissue optical properties using noninvasive boundary measurements. The image reconstruction procedure is a nonlinear, ill-posed, and ill-determined problem, so overcoming these difficulties requires regularization of the solution. While the methods developed for solving the DOT image reconstruction procedure have a long history, there is less direct evidence on the optimal regularization methods, or exploring a common theoretical framework for techniques which uses least-squares (LS) minimization. A generalized least-squares (GLS) method is discussed here, which takes into account the variances and covariances among the individual data points and optical properties in the image into a structured weight matrix. It is shown that most of the least-squares techniques applied in DOT can be considered as special cases of this more generalized LS approach. The performance of three minimization techniques using the same implementation scheme is compared using test problems with increasing noise level and increasing complexity within the imaging field. Techniques that use spatial-prior information as constraints can be also incorporated into the GLS formalism. It is also illustrated that inclusion of spatial priors reduces the image error by at least a factor of 2. The improvement of GLS minimization is even more apparent when the noise level in the data is high (as high as 10%), indicating that the benefits of this approach are important for reconstruction of data in a routine setting where the data variance can be known based upon the signal to noise properties of the instruments.

Hybrid photoacoustic fluorescence molecular tomography using finite-element-based inversion.

Abstract: Improvements in fluorescencereconstruction when utilizing a hybrid photoacoustic(PAT)fluorescence molecular tomography (FMT) method to image optically heterogeneous media are studied and showcased. Quantitative optical absorption maps are retrieved using a normalized backprojection algorithm for PATreconstruction. Consecutively, the reconstructedabsorption distribution is employed into computing a diffusion-equation-based forward model for FMT using a finite-element solution. The potential promise of the suggested method is experimentally verified on tissue-mimicking fluorescent phantoms, where improvements in the quality of FMT reconstructions are observed when imaging at the presence of a large absorber.

Three-dimensional time-resolved optical mammography of the uncompressed breast

Abstract: Optical tomography is being developed as a means of detecting and specifying disease in the adult female breast. We present a series of clinical three-dimensional optical images obtained with a 32-channel time-resolved system and a liquid-coupled interface. Patients place their breasts in a hemispherical cup to which sources and detectors are coupled, and the remaining space is filled with a highly scattering fluid. A cohort of 38 patients has been scanned, with a variety of benign and malignant lesions. Images show that hypervascularization associated with tumors provides very high contrast due to increased absorption by hemoglobin. Only half of the fibroadenomas scanned could be observed, but of those that could be detected, all but one revealed an apparent increase in blood volume and a decrease in scatter and oxygen saturation.

Three-dimensional finite-element-based photoacoustic tomography: Reconstruction algorithm and simulations

Abstract: In this paper, a finite element reconstruction algorithm for three-dimensional photoacoustic tomography is described. The algorithm is based on rigorous iterative solution to the Helmholtz photoacoustic wave equation coupled with regularization techniques and is able to recover both the images of absorbed optical energy density and acoustic speed simultaneously. The algorithm is tested using various numerical examples that mimic cancer detection and joint imaging. The results show that the algorithm is able to reconstruct photoacoustic images quantitatively in terms of the location, size, optical and acoustic properties of the target, and background media for various examples examined.

Mid-infrared optical coherence tomography.

Abstract: A time domain optical coherence tomography (OCT) system is described that uses mid-infrared light (6–8μm). To the best of our knowledge, this is the first OCT system that operates in the mid-infrared spectral region. It has been designed to characterize bioengineered tissues in terms of their structure and biochemical composition. The system is based upon a free-space Michelson interferometer with a germanium beam splitter and a liquid nitrogen cooled HgCdTe detector. A key component of this work has been the development of a broadband quantum cascade laser source (InGaAs∕AlInAs containing 11 different active regions of the three well vertical transition type) that emits continuously over the 6–8μm wavelength range. This wavelength range corresponds to the so called “mid-infrared fingerprint region” which exhibits well-defined absorption bands that are specifically attributable to the absorbing molecules. Therefore, this technology provides an opportunity for optical coherence molecular imaging without the need for molecular contrast agents. Preliminary measurements are presented.

Measurement of absolute flow velocity vector using dual-angle, delay-encoded Doppler optical coherence tomography.

Abstract: Single-beam laser Doppler measurements of flow velocity are only sensitive to the velocity component parallel to the optical axis. We describe a simple modification to a standard Doppler optical coherence tomography (OCT) system using a single sample beam that provides velocity information from multiple angles within the beam. By introducing a glass plate midway into the OCT beam path, the sample beam is divided into several components, each with a different group delay and each providing a separate interferogram with its own effective Doppler angle. By combining the Doppler shift measured in each of these component interferograms, the flow velocity vector is fully determined.

Fingerprint detection using full-field swept-source optical coherence tomography

Abstract: We report the application of full-field swept-source optical coherence tomography for fingerprint detection. This system consists of a superluminescent diode as broadband light source and an acousto-optic tunable filter as wavelength-tuning device. The conventional optical coherence tomographic system was modified by coating aluminum oxide on one side of the beam splitter which is used as reference mirror and fingerprints on the glass slide as object. Low-coherence interferometry, nonmechanical scanning, and compactness are the main advantages of the proposed system over conventional fingerprint detection techniques. The present technique is noninvasive in nature and does not require any physical or chemical processing.

High antinoise photoacoustic tomography based on a modified filtered backprojection algorithm with combination wavelet.

Abstract: How to extract the weak photoacoustic signals from the collected signals with high noise is the key to photoacoustic signal processing. We have developed a modified filtered backprojection algorithm based on combination wavelet for high antinoise photoacoustic tomography. A Q-switched-Nd: yttrium-aluminum-garnet laser operating at 532 nm is used as light source. The laser has a pulse width of 7 ns and a repetition frequency of 20 Hz. A needle polyvinylidene fluoride hydrophone with diameter of 1 mm is used to capture photoacoustic signals. The modified algorithm is successfully applied to imaging vascular network of a chick embryo chorioallantoic membrane in situ and brain structure of a rat brain in vivo, respectively. In the reconstructed images, almost all of the capillary vessels and the vascular ramifications of the chick embryo chorioallantoic membrane are accurately resolved, and the detailed brain structures of the rat brain organization are clearly identified with the skull and scalp intact. The experimental results demonstrate that the modified algorithm has much higher antinoise capacity, and can greatly improve the reconstruction image quality. The spatial resolution of the reconstructed images can reach 204 microm. The modified filtered back-projection algorithm based on the combination wavelet has the potential in the practical high-noise signal processing for deeply penetrating photoacoustic tomography.

Depth of field extension for optical tomography

Abstract: An optical projection tomography system is illuminated with a light source. An object-containing tube, a portion of which is located within the region illuminated by the light source, contains an object of interest that has a feature of interest. A detector is located to receive emerging radiation from the object of interest. A lens, including optical field extension elements, is located in the optical path between the object region and the detector, such that light rays from multiple object planes in the object-containing tube simultaneously focus on the detector. The object-containing tube moves relatively to the detector and the lens operate to provide multiple views of the object region for producing an image of the feature of interest at each view.

A sensitivity function-based conjugate gradient method for optical tomography with the frequency-domain equation of radiative transfer

Abstract: The Sensitivity Function-based Conjugate Gradient Method (SFCGM) is described. This method is used to solve the inverse problems of function estimation, such as the local maps of absorption and scattering coefficients, as applied to optical tomography for biomedical imaging. A highly scattering, absorbing, non-reflecting, non-emitting medium is considered here and simultaneous reconstructions of absorption and scattering coefficients inside the test medium are achieved with the proposed optimization technique, by using the exit intensity measured at boundary surfaces. The forward problem is solved with a discrete-ordinates finite-difference method on the framework of the frequency-domain full equation of radiative transfer. The modulation frequency is set to 600 MHz and the frequency data, obtained with the source modulation, is used as the input data. The inversion results demonstrate that the SFCGM can retrieve simultaneously the spatial distributions of optical properties inside the medium within a reasonable accuracy, by significantly reducing a cross-talk between inter-parameters. It is also observed that the closer-to-detector objects are better retrieved.

Image reconstruction in optical tomography in the presence of coupling errors

Abstract: Image reconstruction in optical tomography is a nonlinear and generally ill- posed inverse problem. Noise in the measured surface data can give rise to substantial artifacts in the recovered volume images of optical coefficients. Apart from random shot noise caused by the limited number of photons detected at the measurement site, another class of systematic noise is associated with losses specific to individual source and detector locations. A common cause for such losses in data acquisition systems based on fiber-optic light delivery is the imperfect coupling between the fiber tips and the skin of the patient because of air gaps or surface moisture. Thus the term coupling errors was coined for this type of data noise. However, source and detector specific errors can also occur in noncontact measurement systems not using fiber-optic delivery, for example, owing to local skin pigmentation, hair and hair follicles, or instrumentation calibration errors. Often it is not possible to quantify coupling effects in a way that allows us to remove them from the data or incorporate them into the light transport model. We present an alternative method of eliminating coupling errors by regarding the complex-valued coupling factors for each source and detector as unknowns in the reconstruction process and recovering them simultaneously with the images of absorption and scattering. Our method takes into account the possibility that coupling effects have an influence on both the amplitude and the phase shift of the measurements. Reconstructions from simulated and experimental phantom data are presented, which show that including the coupling coefficients in the reconstruction greatly improves the recovery of absorption and scattering images.

In Vivo Two- and Three-Dimensional Imaging of Artificial and Real Fingerprints With Optical Coherence Tomography

Abstract: Fingerprint recognition is one of the dominant methods among all biometric techniques. However, current commercial fingerprint reader systems are based on analysis of surface topography of a finger and, thus, have tremendous security vulnerability for simply made artificial fingerprint dummies. In this letter, we demonstrate that a novel optical coherence tomography-based method for depth-resolved 2-D and 3-D imaging and assessment of artificial and real fingerprints could significantly enhance spoof-proofing of fingerprint reader systems as well as provide information of both artificial and real ridge and furrow patterns (that form the fingerprint patterns) simultaneously.

Three-dimensional in vivo imaging of green fluorescent protein-expressing T cells in mice with noncontact fluorescence molecular tomography.

Abstract: Given that optical tomography is capable of quantitatively imaging the distribution of several important chromophores and fluorophores in vivo, there has been a great deal of interest in developing optical imaging systems with increased numbers of measurements under optimal experimental conditions. In this article, we present a novel system that enables three-dimensional imaging of fluorescent probes in whole animals using a noncontact setup, in parallel with a three-dimensional surface reconstruction algorithm. This approach is directed toward the in vivo imaging of fluorophore or fluorescent protein concentration in small animals. The system consists of a rotating sample holder and a lens-coupled charge-coupled device camera in combination with a fibercoupled laser scanning device. By measuring multiple projections, large data sets can be obtained, thus improving the accuracy of the inversion models used for quantitative three-dimensional reconstruction of fluorochrome distribution, as well as facilitating a higher spatial resolution. In this study, the system was applied to determining the distribution of green fluorescent protein (GFP)expressing T lymphocytes in a transgenic mouse model, thus demonstrating the potential of the system for studying immune system function. The technique was used to image and reconstruct fluorescence originating from 32 3 10 6 T cells in the thymus and 3 3 10 5 T cells in the spleen.

Common-path optical coherence tomography with side-viewing bare fiber probe for endoscopic optical coherence tomography.

Abstract: All-fiber-optic common-path optical coherence tomography (OCT) using a side-viewing bare fiber probe has been demonstrated and analyzed. A bare single mode fiber tip is angle cleaved at approximately 49 degrees to enable side illumination due to total internal reflection. The bare fiber probe was inserted in an arterial tissue and a circumferential OCT scan was obtained. The research is aimed at realizing highly miniaturized monolithic probes for possible applications in miniature endoscopic OCT or intravascular OCT. The effects of the angle of the cleaved fiber on reference reflection and the sensitivity of the common-path OCT system have been studied theoretically. The angle cleaved fiber probe is also used in series with a microlens to analyze and optimize its performance in a common-path OCT system. Our research aims to explore the combined advantages of common-path OCT and extremely simplified miniature probe design and to discuss how it may greatly simplify the endoscopic OCT instrumentation eventually.

Reconstruction in optical tomography using the P-N approximations

Abstract: In this paper, we consider the inverse problem of reconstructing the absorption and scattering coefficients of the radiative transfer equation (RTE) from measurements of photon current transmitted through a scattering medium in the frequency domain. We consider an output least-squares formulation of this problem and derive the appropriate forward operators and their Frechet derivatives. For efficient implementation, we use the second-order form of the RTE and discuss its solution using a finite element method. The PN approximation is used to expand the radiance in spherical harmonics, which leads to a large sparse matrix system that can be efficiently solved. Examples are shown in the low-scattering case where the diffusion approximation fails.

Polychromatic cone-beam phase-contrast tomography

Abstract: A method is presented for quantitative phase-contrast tomography using unfiltered radiation from a small polychromatic source. The three-dimensional distribution of complex refractive index in a monomorphous object is reconstructed given a single projection image per view angle. The reconstruction algorithm is achromatic and stable with respect to high-spatial-frequency noise, in contrast to conventional tomography. The density distribution in a test sample was accurately reconstructed from polychromatic phase-contrast data collected with a point-projection x-ray microscope.

Optical tomography of the neonatal brain

Abstract: A new method of assessing neurological function and pathology in the newborn infant is being developed based on the transmission of near-infrared light across the brain. Absorption by blood over a range of wavelengths reveals a strong dependency on oxygenation status, and measurements of transmitted light enable the spatial variation in the concentrations of the oxygenated and de-oxygenated forms of hemoglobin to be derived. Optical tomography has so far provided static three-dimensional maps of blood volume and oxygenation as well as dynamic images revealing the brain's response to sensory stimulation and global hemodynamic changes. The imaging modality is being developed as a safe and non-invasive tool that can be utilized at the cotside in intensive care. Optical tomography of the healthy infant brain is also providing a means of studying neurophysiological processes during early development and the potential consequences of prematurity.

Transport- and diffusion-based optical tomography in small domains: a comparative study

Abstract: We compare reconstructions based on the radiative transport and diffusion equations in optical tomography for media of small sizes. While it is well known that the diffusion approximation is less accurate to describe light propagation in such media, it has not yet been shown how this inaccuracy affects the images obtained with model-based iterative image reconstructions schemes. Using synthetic nondifferential data we calculate the error in the reconstructed images of optical properties as functions of source modulation frequency, noise level in measurement, and diffusion extrapolation length. We observe that the differences between diffusion and transport reconstructions are large when high modulation frequencies and noise-free data are used in the reconstructions. When the noise in data reaches a certain level, approximately 12% in our simulations, the differences between diffusion- and transport-based reconstructions become almost indistinguishable. Given that state-of-the-art optical imaging systems operate at much lower noise levels, the benefits of transport-based reconstructions of small imaging domains can be realized with most of the currently available systems. However, transport-based reconstructions are considerably slower than diffusion-based reconstructions.

Method and apparatus for medical imaging using combined near-infrared optical tomography, fluorescent tomography and ultrasound

Abstract: Methods and apparatus for medical imaging using diffusive optical tomography and fluorescent diffusive optical tomography and ultrasound are disclosed. In one embodiment, the probe comprises emitters and detectors that are inclined at an angle of about 1 to about 30 degrees to a surface of the probe that contacts tissue, hi another embodiment, the scanned volume is divided into an inclusion region and a background region. Different voxel sizes are used in the inclusion region and the background region. Appropriate algorithms facilitate a reconstruction of the inclusion region to determine structural and functional features of the inclusion.

Imaging optically scattering objects with ultrasound-modulated optical tomography.

Abstract: We show the feasibility of imaging objects having different optical scattering coefficients relative to the surrounding scattering medium using ultrasound-modulated optical tomography (UOT). While the spatial resolution depends on ultrasound parameters, the image contrast depends on the difference in scattering coefficient between the object and the surrounding medium. Experimental measurements obtained with a CCD-based speckle contrast detection scheme are in agreement with Monte Carlo simulations and analytical calculations. This study complements previous UOT experiments that demonstrated optical absorption contrast.

Photorefractive detection of tissue optical and mechanical properties by ultrasound modulated optical tomography.

Abstract: Ultrasound-modulated optical tomography is a developing hybrid imaging modality that combines high optical contrast and good ultrasonic resolution for imaging soft biological tissue. We developed a photorefractive-crystal-based, time-resolved detection scheme with the use of a millisecond long ultrasound burst to image both the optical and the mechanical properties of biological tissues, with improved detection efficiency of ultrasound-tagged photons.

Fully adaptive finite element based tomography using tetrahedral dual-meshing for fluorescence enhanced optical imaging in tissue.

Abstract: We have developed fluorescence enhanced optical tomography based upon fully adaptive finite element method (FEM) using tetrahedral dual-meshing wherein one of the two meshes discretizes the forward variables and the other discretizes the unknown parameters to be estimated. We used the 8-subtetrahedron subdivision scheme to create the nested dualmesh in which each are independently refined. However, two tetrahedrons from the two different meshes pose an intersection problem that needs to be resolved in order to find the common regions that the forward variables (the fluorescent diffuse photon fluence fields) and the parameter estimates (the fluorescent absorption coefficients) can be mutually assigned. Using an efficient intersection algorithm in the nested tetrahedral environments previously developed by the authors, we demonstrate fully adaptive tomography using a posteriori error estimates. Performing the iterative reconstructions using the simulated boundary measurement data, we demonstrate that small fluorescent targets embedded in the breast simulating phantom in point illumination/detection geometry can be resolved at reasonable computational cost.

Digital-signal-processor-based dynamic imaging system for optical tomography.

Abstract: In this article, we introduce a dynamic optical tomography system that is, unlike currently available analog instrumentation, based on digital data acquisition and filtering techniques. At the core of this continuous wave instrument is a digital signal processor (DSP) that collects, collates, processes, and filters the digitized data set. The processor is also responsible for managing system timing and the imaging routines which can acquire real-time data at rates as high as 150Hz. Many of the synchronously timed processes are controlled by a complex programable logic device that is also used in conjunction with the DSP to orchestrate data flow. The operation of the system is implemented through a comprehensive graphical user interface designed with LABVIEW software which integrates automated calibration, data acquisition, data organization, and signal postprocessing. Performance analysis demonstrates very low system noise (∼1pW rms noise equivalent power), excellent signal precision (<0.04%–0.2%) and lon...

Strong tip effects in near-field scanning optical tomography

Abstract: A model for the interaction of the scanning probe in near-field scanning optical microscopy is presented. Multiple scattering of the illuminating field with the probe is taken into account. The implications of this so-called strong tip model for the solution of the associated inverse scattering problem are studied through simulations.