Showing papers on "Optical tomography published in 1994"

Tomographic Time-of-Flight Optical Imaging Device

Abstract: Time-resolved optical imaging has been used to image phantoms, animals, and humans, and offers the potential for the production of functional images of human tissues, such as the oxygenation of brain during stroke. We had previously reported a transmission scanner, and now give an early report on conversion to a rotational tomographic scanner with a non-parallel ray geometry similar to early CAT scanners. Initial scans show that 1) spatial imaging in turbid media using time-of-flight measurements, non-recursive algorithms, and standard tomographic geometry is possible, 2) separation of absorbance and scattering as an image is attainable, a key step in performing spatially-resolved chemometric analysis, 3) imaging of multiple objects buried within scattering material is feasible, demonstrating that equations derived for homogeneous media can be applied in at least some cases to inhomogeneous media such as tissue-like phantoms, and 4) imaging of brain pathology produces recognizable images with sufficient resolution for diagnostic decisions. We conclude that optical tomography is feasible for clinical use and that conversion of the present mechanically scanning device to a clinical scanner should be possible with retention of the current processing algorithms. Such a clinical scanner should ultimately be able to generate images in a few minutes with centimeter resolution at the center of living human brain.

Fast optical absorption tomography apparatus and method

Abstract: A design for a fast absorption optical tomography instrument is disclosed. The subject invention is capable of generating 100 projections of 100 elements each in less than 200 ns. It comprises and optical pulse generator, a tomography ring with temporally multiplexed fiber-optic fan-beam sources and fast detectors, and data acquisition electronics. A single short pulse (<10 ns) of radiation tuned to an absorption transition of the chemical species of interest produces a cross sectional image of concentration. Supplying two such pulses to the instrument can yield simultaneous quantitative images of temperature and absolute concentration in fields with temperature inhomogeneities. Additional pulses lead to concentration images of additional species.

Biomedical imaging using optical coherent tomography

Abstract: Optical Coherence Tomography (OCT) is a new optical technique for performing non-contact, micron resolution, cross sectional tomography imaging in biological systems. The authors discuss applications of OCT to ophthalmology, general medicine, and microscopy.

Improved optical tomography device

Abstract: We report the development of an improved optical tomography diagnostic which measures the velocity‐space distribution of a laboratory plasma in two dimensions The new device is capable of imaging plasma distributions over a wider range of magnetic fields and plasma column diameters than the previous design, while minimizing the risk of misdiagnosis due to perturbations caused by inserting the device in the plasma Computer‐aided control of the diagnostic allows a greater number of single‐dimensional scans to be collected in a shorter amount of time, resulting in increased resolution of the reconstructed image while freeing up more time for the user to perform the experiment Recent data using the new device are presented to show improvement of resolution gained by doubling the number of total scans Finally, we present a method to identify velocity‐space nonuniformities without the need to reconstruct a complete image

Optical tomography of tensor fields: the general case

Abstract: A general solution of the tomographic problem for weakly refracting inhomogeneous birefringent media is presented. The solution requires an unusual tomographic experiment in which the considered medium is probed with three series of standard tomographic sets of light rays, when the light is polarized. Data for the tomographic reconstruction are produced by recording the interferometric data and measuring birefringent parameters in the standard way.

Optical Tomography for Three-Dimensional Spectroscopy

Abstract: Fundamental to the development of many scientific fields is the need for quantitative observation of a specimen in three dimensions. Examples include the nondestructive inspection of materials to locate defects, measurement of atmospheric pollutants, determination of the distribution of a dye in a cell, or in vivo measurements of metabolic activity in tissue. For these type of analyses, optical measurements to determine concentration of the probe molecule are commonly employed.

Three-dimensional temperature measurements in enclosures by using multiview interferometric tomography

Abstract: Optical tomography using interferometric data is applied in this study to measure three-dimensional flow and heat transfer phenomena in a differentially heated cubic enclosure. The interferometric recording and reconstruction system, associated fringe readout and tomographic reconstruction procedures, and the results from this analysis are described, highlighting the specific challenges facing application of the technique to enclosure flows. The features unique to the investigation of enclosure flows using interferometric tomography include limited view angle, refraction effects and the lack of a visible reference fringe. The experimental results are verified by comparison with independent temperature measurements. The comparisons indicate that this experimental technique can yield three-dimensional perspectives of complex flows having sufficient spatial resolution to verify detailed three-dimensional direct numerical simulations.

Quantitative microscopy of phase objects by optical diffraction tomography

Abstract: Optical diffraction tomography (ODT) is a novel imaging technique in which a transparent object is illuminated from many different directions. The object's complex refractive index distribution is reconstructed digitally from the scattered field data by means of a reconstruction algorithm. Preliminary experimental results are presented for the imaging of an object whose refractive index and shape are known a priori. The results show that both the refractive index and the shape may be reconstructed accurately by the proposed ODT technique.

Optical ray deflection tomography with fan-shaped beams

Abstract: Interferometric optical tomography is a valuable method for combustion and flow diagnostics. However, it meets serious experimental difficulties when investigated objects are large (about 50 sm or greater) and/or perturbations of refractive index are greater than 0.01. In the latter case the interference fringes become too thin, while in the former case too large and expensive optical elements (lenses and holograms) are required. These difficulties can be overcome by using optical ray-deflection tomography with fan-shaped beams. In the paper a scheme of the tomographic experiment, reconstruction algorithms, and experimental results are presented.

Solution to the time-dependent photon transport equation

Abstract: Researchers in biomedical optics use either the photon diffusion model or the Monte Carlo simulation to approach the `forward problem' of image reconstruction of the optical diffusion tomography for turbid media. Solving the photon transport equation is an alternate method to solve the `forward problem,' and might be more accurate because light propagation in turbid media is supposed to be better depicted by the photon transport equation than the other two methods. A solution to the time-dependent integro-differential equation has been found, using a hybrid (finite-difference and analytic) method. When the spatial and directional distributions of the initial light beam are given, analytical solutions to the photon transport equation are obtained for following discrete instances. This new approach has potential application to the time-resolved optical diffusion tomography as a more accurate solution to the `forward problem.'© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Studies on Laser Spectroscopic Computed Tomography and Biophotonic Imaging Utilizing Coherent Detection Imaging Method

Abstract: There is currently a great deal of importance of noninvasive imaging of the interior of living bodies and organisms in biomedicine using computed tomography methods based on X-rays, nuclear magnetic resonance, ultrasound, positron emission and other specialized technologies. These methods offer images of morphological/structural information or anatomical details, but to some degree they all have drawbacks such as resolution, ionizing radiation, administration of tracing agents, portability, expense, continuous monitor and others. Optical tomography method is attractive and expected to provide an alternative technology capable of overcoming some of the above limitations and of complementing existing techniques, because optical radiation is nonionizing, and, at low intensities has no harmful effects on the tissue. Many biomolecular species, such as proteins, cytochromes, enzymes, dyes and others, are known to exhibit individual specific reactions to the light through absorption and emission. Especially, the red and near infrared regions from about 0.6 to 1.3μm are suitable for developing noninvasive and noncontact, diagnostic techniques based on quantitative, spectroscopic (wavelength-dependent) analysis in living tissues.1 Accordingly, spectroscopic computed tomography (CT) with appropriately selected wavelengths should carry biochemical/physiological information and then give images concerning the metabolic state of tissues in addition to anatomical features. However, optical imaging methods have always been stymied by the degree to which living tissues and organisms scatter and diffuse the photon, and in practice the optical radiation has been considered until now the most difficult imaging probe.

Determining underwater optical characteristics using serial section tomography

Abstract: The technique of optical serial sectioning is a method which can be used to infer the optical characteristics of a three-dimensional structure with minimal disruption of the media. The method consists of scanning a plane or stripe of light through a three dimensional object and concurrently recording the scattered radiation at a fixed angle. Under suitable circumstances, the 3-dimensional structure of the concentration of absorbers can be inferred by performing an inversion on the recorded data. The article explores both the noise propagation and also the uniqueness of the solution. A so called "low passed" inversion is shown to be unique and, by suitable approximation, it is inferred that the true, unfiltered inversion is also. >

Comparative study on computed tomography algorithms

Abstract: This study uses Computed Tomography (CT) for reconstructing images of solid propellant rocket motors during static firing tests. Implementation, verification and comparison of four CT algorithms are presented. These four algorithms are: Algebraic Reconstruction Technique, Linear Superposition with Compensation, and Fourier Convolution technique with parallel beams and fan-beam. The phantom used in the comparison between algorithms is similar in cross-section to a solid propellant rocket motor. Comparison between algorithms on the ability to detect artifacts is made. Also, a comparison is made using data obtained by optical tomography of the absorption coefficient inside a 20 mm gas gun barrel. Finally, a comparison of the running time versus number of projections, number of ray sums, and resolution is studied.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.