The problem of reconstruction in imaging systems that are modeled using the Helmholtz wave equation (diffraction imaging) is addressed. A spectral analysis of the available diffraction data is presented to help develo...
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The problem of reconstruction in imaging systems that are modeled using the Helmholtz wave equation (diffraction imaging) is addressed. A spectral analysis of the available diffraction data is presented to help develop algorithms and constraints on a diffraction imaging system's parameters for accurate reconstruction of the desired image. Means of reducing the execution time of these algorithms and their relationship to currently available filtered backpropagation and unified Fourier reconstruction methods are also discussed.
A number of proposed reconstruction algorithms for electrical impedance tomography have employed the concept of a sensitivity coefficient which can be used to relate the magnitude of a voltage charge measured at the s...
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A number of proposed reconstruction algorithms for electrical impedance tomography have employed the concept of a sensitivity coefficient which can be used to relate the magnitude of a voltage charge measured at the surface of an object to the change in impedance within the object which has given rise to it. Iterative algorithms are required where the approach to the full non-linear problem involves inversion of the sensitivity coefficient matrix, but the task of matrix inversion is still not trivial even for a linearised version of the problem. An alternative approach is to use sensitivity coefficients calculated from Laplace fields for single-pass image reconstruction in a manner more closely related to back-projection methods. A reconstruction algorithm employing sensitivity coefficients in this manner is described and images of a phantom and a human chest section produced using the algorithm are displayed.
Three novel methods are used to reconstruct a simulated image from a set of incomplete data spanning a 160 degrees angular range. These methods are the squashing affine transformation of J.A. Reeds and L.A. Shepp (198...
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Three novel methods are used to reconstruct a simulated image from a set of incomplete data spanning a 160 degrees angular range. These methods are the squashing affine transformation of J.A. Reeds and L.A. Shepp (1987), the circular interpolation method derived from the theory of J.J. Clark, M.R. Plamer, and P.D. Lawrence (1985), and the geometry-free reconstruction using the theory of convex projections. These methods are briefly explained, and their reconstructions are compared for the case of limited angular views.
The authors investigate microwave imaging of metallic objects using a diversity method and interpret and predict the reconstructed image from an approach based on analysis of the scattering mechanism and a back-projec...
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The authors investigate microwave imaging of metallic objects using a diversity method and interpret and predict the reconstructed image from an approach based on analysis of the scattering mechanism and a back-projection algorithm used in image retrieval. The connection between the various scattering mechanisms and the reconstructed images is discussed, what the images represent is interpreted, and a prediction is made as to what the image will look like over given spectral and angular windows. A brief description is given of the microwave diversity imaging system and the formulation of the microwave diversity imaging based on the physical optics approximation. The scattering mechanism of a complex shaped metallic object is then briefly reviewed and an alternate approach to interpreting the reconstruction image based on the understanding of the scattering mechanism and the reconstruction algorithm is given. Several numerical and experimental examples are included to support this interpretation approach.
Tomographic radiopharmaceutical imaging, or emission computed tomography (ECT), provides in vivo three-dimensional maps of a pharmaceutical labeled with a gamma-ray-emitting radionuclide. ECT has developed in two comp...
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Tomographic radiopharmaceutical imaging, or emission computed tomography (ECT), provides in vivo three-dimensional maps of a pharmaceutical labeled with a gamma-ray-emitting radionuclide. ECT has developed in two complimentary directions based on the type of radionuclide that is used. Positron emission computed tomography (PET) detects the two coincident 511-keV annihilation photos from position emitters such as 11C, 13N, 15O, and 18F. Single-photon-emission computed tomography (SPECT) involves detection of gamma rays emitted singly, and sequentially, by the radionuclide tracer. The author presents examples of PET and SPECT imaging devices and reviews a widely used reconstruction algorithm. Current research areas that are under active investigation are also described
A digital electronic architecture for parallel processing of the expectation maximization (EM) algorithm for positron-emission-tomography (PET) image reconstruction is proposed. Rapid (0.2-s) EM iterations on high-res...
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A digital electronic architecture for parallel processing of the expectation maximization (EM) algorithm for positron-emission-tomography (PET) image reconstruction is proposed. Rapid (0.2-s) EM iterations on high-resolution (256*256) images are supported. Arrays of two VLSI chips perform forward and back projection calculations. The architecture is described, including data flow and partitioning relevant to EM and parallel processing. EM images are shown that are produced with software simulating the proposed hardware reconstruction algorithm. Projected cost of the system is estimated to be small in comparison to the cost of current PET scanners.
A CT scanner has been constructed specifically to determine the three-dimensional distribution of bone mineral in the medullary cavities of the radius, ulna and femur. A source of x-rays (153Gd) and a multiwire propor...
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A CT scanner has been constructed specifically to determine the three-dimensional distribution of bone mineral in the medullary cavities of the radius, ulna and femur. A source of x-rays (153Gd) and a multiwire proportional counter (MWPC) are mounted at opposite ends of a diameter of an annular mounting. The limb is placed on the axis of rotation of the annulus and a series of two-dimensional transmission projections are obtained at equal angular spacings over ***.. The distribution of bone mineral is reconstructed from the projections either by the method of maximum entropy (ME) or by convolution and back projection (CBP). These two methods have been evaluated by reconstructing a single slice of a phantom, representing the forearm, from projections simulated by computer. With a clinically acceptable exposure time, the mean medullary densities of the ulna and radius were determined with systematic errors of less than 3.5% (ME) and 11% (CBP), although for the latter method of reconstruction the systematic error was reduced to less than 2% by increasing the number of views. The mean medullary densities of the ulna and radius were determined with precisions better than 2.5% (ME) and 3.5% (CBP).
Preliminary studies are made in order to apply an X-ray CT scanner to the measurement of cross-sectional distributions of void fractions in steady state two-phase flows. Using air-water flows in a horizontal U-shaped ...
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Preliminary studies are made in order to apply an X-ray CT scanner to the measurement of cross-sectional distributions of void fractions in steady state two-phase flows. Using air-water flows in a horizontal U-shaped tube, results of CT scanner measurements are compared with those of the volumetric measurements with quick-closing valves and of hotfilm anemometer measurements. Studied are cross-sectionally averaged void fractions and void fraction profiles. The comparisons give good agreements. The effect of density fluctuations on the reconstruction of void fraction distributions in two-phase flows is also discussed. Consideration of the statistical fluctuation in the projection data for a stationary object gives the sufficient conditions required for the evaluation of the cross-sectional distribution of the scanning time-averaged void fraction in steady state two-phase flows.
The 2-dimensional reconstruction problem which occurs in radiography, radioastronomy, EM and many other fields is as follows. A 2-dimensional object which can be characterized by a variable density is scanned by some ...
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The 2-dimensional reconstruction problem which occurs in radiography, radioastronomy, EM and many other fields is as follows. A 2-dimensional object which can be characterized by a variable density is scanned by some means in such a way as to provide a series of measurements of the line integrals of the density along say N straight lines which intersect the object. The problem is to calculate the density at points in the object from the measurements of the line integrals. A number of algorithms is now available for performing this calculation. When these algorithms are used in practice most seem to use all of the N measures of the line integrals to calculate the density at each point in the object. In algorithms of this kind the use of all N points for each density calculation is unnecessary. Use of the unnecessary data points, while it may contribute to noise reduction, generates a noise-like error in the reconstruction at all but a few points at which reconstruction of the density is made.
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