Correction for polychromatic X-ray distortion in CT images
First Claim
1. A computerized tomographic system for measuring characteristics of and imaging, body tissue comprising:
- scanning means which generate projections of said tissue by directing a known spectrum of radiation through said body and measuring the spatial intensity distribution of radiation traversing said tissue along a multiplicity of paths;
image generating means which calculate the attenuation of each pixel element of a raw image array, which is representative of a tranverse section of said tissue, from said projections;
means which analyze values in said raw image array and assign to each pixel element, on the basis of those values, a specific proportion of the attenuation coefficient to each of two or more constituents of said tissue;
means which combine said element proportions to generate a multiplicity of constituent projections for each of said constituents of said tissue;
means which combine said constituent projections, in accordance with a predetermined function approximating the non-linear interaction of said constituents with said spectral intensity distribution, to generate a multiplicity of error projections of said tissue;
means which combine said error projections to generate an error image array which is representative of the polychromatic aberration in said raw image array; and
means for subtracting said error image array from said raw image array to generate a compensated image array.
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Abstract
A method and apparatus which corrects the polychromatic distortion of CT images which is produced by the non-linear interaction of body constituents with a polychromatic X-ray beam. A CT image is processed to estimate the proportion of the attenuation coefficients of the constituents in each pixel element. A multiplicity of projections for each constituent are generated from the original image and are combined utilizing a multidimensional polynomial which approximates the non-linear interaction involved. An error image is then generated from the combined projections and is subtracted from the original image to correct for the poloychromatic distortion.
88 Citations
16 Claims
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1. A computerized tomographic system for measuring characteristics of and imaging, body tissue comprising:
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scanning means which generate projections of said tissue by directing a known spectrum of radiation through said body and measuring the spatial intensity distribution of radiation traversing said tissue along a multiplicity of paths; image generating means which calculate the attenuation of each pixel element of a raw image array, which is representative of a tranverse section of said tissue, from said projections; means which analyze values in said raw image array and assign to each pixel element, on the basis of those values, a specific proportion of the attenuation coefficient to each of two or more constituents of said tissue; means which combine said element proportions to generate a multiplicity of constituent projections for each of said constituents of said tissue; means which combine said constituent projections, in accordance with a predetermined function approximating the non-linear interaction of said constituents with said spectral intensity distribution, to generate a multiplicity of error projections of said tissue; means which combine said error projections to generate an error image array which is representative of the polychromatic aberration in said raw image array; and means for subtracting said error image array from said raw image array to generate a compensated image array. - View Dependent Claims (2, 3, 4, 5)
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6. A system for compensating polychromatic distortion in a computed tomographic image of body tissue comprising:
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means for generating an error image wherein the numerical value of each image element is representative of the polychromatic distortion in a corresponding element of said tomographic image which means include means for producing constituent projections of each of at least two constituents of said tissue from said tomographic image and means for combining said constituent projections to generate said error image and means for subtracting said error image, element by element, from said tomographic image. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. A method for measuring characteristics of, and imaging, body tissue comprising the steps of:
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directing a known spectrum of radiation through said tissue; measuring the spatial intensity distribution of said radiation traversing said tissue along a multiplicity of paths; generating a multiplicity of projections of said tissue from said spatial intensity distribution; calculating, from said projections, an attentuation value for each element of a raw image, said raw image being representative of a transverse section of said tissue and each element of said raw image corresponding to a distinct portion of said tissue; for each of said elements of said raw image, comparing the associated attenuation value with a threshold value and, on the basis of the result of said comparison, assigning a proportion of the associated attenuation value to each of two or more constituents of the tissue; for each of said constituents of the tissue, combining the associated proportions of the attenuation values associated with all of said elements to generate a multiplicity of constituent projections of said tissue; combining said constituent projections, in accordance with a predetermined function approximating the non-linear interaction of said constituents with said known spectrum of radiation, to generate a multiplicity of error projections of said tissue; combining said error projections to generate an error image which is representative of the polychromatic aberration in said raw image; and subtracting said error image from said raw image to generate a compensated image. - View Dependent Claims (15, 16)
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Specification