Method and apparatus for X-ray computed tomography
First Claim
1. A method for cone-beam X-ray computed tomography in which a scanner mounting an X-ray source for applying a cone-beam X ray and a two-dimensional X-ray detector for detecting an X-ray is rotated around an object to measure omnidirectional projection data around said object and a distribution of X-ray attenuation coefficients of said object is reconstructed, comprising the steps of:
- correcting an image geometric distortion of said projection data;
detecting a view field boundary of said two-dimensional X-ray detector from said projection data whose geometric distortion is corrected;
extrapolating projection data of a predetermined width from said view field boundary detected in the step of detecting a view field and boundary; and
reconstructing said distribution of X-ray attenuation coefficients of said object from said projection data extrapolated in the step of extrapolating projection data.
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Accused Products
Abstract
A method for X-ray computed tomography includes a process for rotating around an object an X-ray source for applying a cone-beam X ray and a scanner having a two-dimensional X-ray detector mounted thereon for deriving projection data and a process for preparing a geometric distortion correction table for correcting an image geometric distortion of the two-dimensional X-ray detector for the projection data, for reconstructing a distribution of X-ray attenuation coefficients of the object from said corrected projection data. The method further includes a process for calculating a function for evaluating the correction table, a process for comparing the calculated value with a threshold value, a process for correcting the correction table through the interpolation based on the compared result, a process for correcting an image geometric distortion of the projection data by using the corrected table, a process for detecting a location of a view field boundary of the detector from the distortion-corrected projection data, and a process for generating the projection data of a predetermined width from the detected location of the view field boundary through the effect of the extrapolation. The method operates to reconstruct a distribution of X-ray attenuation coefficients of the object from the extrapolated projection data.
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Citations
30 Claims
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1. A method for cone-beam X-ray computed tomography in which a scanner mounting an X-ray source for applying a cone-beam X ray and a two-dimensional X-ray detector for detecting an X-ray is rotated around an object to measure omnidirectional projection data around said object and a distribution of X-ray attenuation coefficients of said object is reconstructed, comprising the steps of:
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correcting an image geometric distortion of said projection data; detecting a view field boundary of said two-dimensional X-ray detector from said projection data whose geometric distortion is corrected; extrapolating projection data of a predetermined width from said view field boundary detected in the step of detecting a view field and boundary; and reconstructing said distribution of X-ray attenuation coefficients of said object from said projection data extrapolated in the step of extrapolating projection data. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for cone-beam X-ray computed tomography having a scanner mounting an X-ray source for applying a cone-beam X ray and a two-dimensional X-ray detector for detecting an X-ray, means for rotating said scanner around an object, and means for measuring omnidirectional projection data around said object, said apparatus serving to reconstruct a distribution of X-ray attenuation coefficients of said object based on said projection data, comprising:
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correcting means for correcting an image geometric distortion of said projection data; detecting means for detecting a location of a view field boundary of said detector of said projection data whose geometric distortion is corrected by said correcting means; extrapolating means for generating said projection data of a predetermined width from said view field boundary location detected by said detecting means; and means for reconstructing the distribution of X-ray attenuation coefficients of said object from said projection data extrapolated in said extrapolating means. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A method for cone-beam X-ray computed tomography in which a scanner mounting an X-ray source for applying a cone-beam X ray and a two-dimensional X-ray detector for detecting an X-ray is rotated around an object to measure omnidirectional projection data around said object, an image geometric distortion of said projection data is corrected by referring to a geometric distortion correction table, and a distribution of X-ray attenuation coefficients of said object is reconstructed by using said distortion-corrected projection data comprising the steps of:
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preparing said correction table and storing said table in means for saving a correction table; calculating an evaluation function for evaluating continuity of said prepared correction table between the previous and the subsequent projections of each subject projection on which said projection data is obtained; deleting said prepared correction table that is not continuously changed between said previous and subsequent projections from said means for saving a correction table, replacing said correction table that is not continuously changed with a new correction table interpolated from said prepared correction tables of the previous and the subsequent projections, and saving said new correction table in said means for saving a correction table; and reconstructing the distribution of X-ray attenuations of said object. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. An apparatus for cone-beam X-ray computed tomography having a scanner mounting an x-ray source for applying a cone-beam X ray and a two-dimensional X-ray detector for detecting an X-ray, means for rotating said scanner around an object, means for measuring omnidirectional projection data around said object, means for preparing a correction table on which an image geometric distortion of said projection data is corrected, and means for correcting an image geometric distortion of said projection data by referring to said correction table, for reconstructing a distribution of X-ray attenuation coefficients of said object on said distortion-corrected projection data, comprising:
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means for preparing said correction table having; means for preparing said correction table of each projection for obtaining said projection data in advance; evaluating means for calculating an evaluation function for evaluating continuity of said correction tables between the previous and the subsequent projections of a subject projection for obtaining said projection data, and comparing the value of the calculated evaluation function with a predetermined threshold value for evaluating said prepared correction table; interpolating means for deriving said prepared correction table that is not continuously changed between said previous and subsequent projections from said prepared correction tables for said previous and subsequent projections through the effect of the interpolation, based on the evaluated result of said evaluating means; and means for reconstructing the distribution of X-ray attenuation coefficients of said object. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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29. A method for cone-beam X-ray computed tomography in which a scanner mounting an X-ray source for applying a cone-beam X ray and a scanner having a two-dimensional X-ray detector for detecting an X-ray is rotated around an object to measure omnidirectional projection data around said object, an image geometric distortion of said projection data is corrected by referring a correction table, and a distribution of X-ray attenuation coefficients is reconstructed by using said distortion-corrected projection data, comprising the steps of:
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preparing said correction table in advance and saving said table in means for saving correction table; calculating an evaluation function for evaluating continuity of said prepared correction table between the previous and the subsequent projections of a subject projection for obtaining said projection data; deleting said prepared correction table that is not continuously changed between the previous and the subsequent projections from said means for saving correction table based on the calculated value of said evaluation function, replacing said correction table that is not continuously changed with a correction table obtained by interpolating said prepared correction tables of the previous and the subsequent projections, and saving the replaced correction table in said means for saving correction table; detecting a location of a view field boundary of said two-dimensional X-ray detector from said distortion-corrected projection data by using the correction table saved in said means for saving correction table; and extrapolating projection data of a predetermined width from said location of the view field boundary detected in the step of detecting; and reconstructing said X-ray attenuation coefficients distribution from the projection data extrapolated in the step of extrapolating.
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30. An apparatus for X-ray computed tomography having a scanner mounting an X-ray source for applying a cone-beam X ray and a two-dimensional X-ray detector for detecting an X-ray, means for rotating said scanner around an object, means for measuring omnidirectional projection data around said object, and means for measuring omnidirectional projection data around said object, for reconstructing an X-ray attenuation distribution, comprising:
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means for preparing a correction table on which an image geometric distortion of said projection data is corrected, said preparing means having means for preparing said correction table of each projection for obtaining said projection data in advance and means for saving said prepared correction table; evaluating means for calculating an evaluation function for evaluating continuity of said correction table between the previous and the subsequent projections of each subject projection for obtaining said projection data and comparing the calculate value of said evaluation function with a predetermined threshold value for evaluating said prepared correction table; interpolating means for replacing said prepared correction table that is not continuously changed between said previous and subsequent projections with a correction table interpolated from the prepared correction tables of said previous and subsequent projections, based on the evaluating result of said evaluation function; means for correcting an image geometric distortion of said projection data by referring to said correction table; means for detecting a location of a view field boundary of said two-dimensional X-ray detector about said distortion-corrected projection data; extrapolating means for generating said projection data of a predetermined width from said location of the view field boundary detected by said detecting means; and means for reconstructing said X-ray attenuation distribution of said object from said projection data extrapolated in said extrapolating means.
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Specification