Correction algorithm for bone-induced spectral artifacts in computed tomograph imaging
First Claim
1. A method for correcting an image having dense object-induced spectral artifacts generated using data collected in a computed tomography system, said method comprising the steps of:
- (a) reconstructing an image BWEQ of a calibration object;
(b) reconstructing an image WEQ of a water equivalent cylinder having about a same diameter as the calibration object;
(c) generating a ratio of images BWEQ and WEQ;
(d) extracting a region of interest by multiplying the generated ratio by a function II(r) to obtain a calibration pattern CP;
(e) averaging the calibration pattern in azimuth to obtain a calibration vector;
(f) removing low frequency components from the vector;
(g) multiplying the result of step (f) by a CT number scale factor (ctscale) and an apodizing window Aw(r) to generate a calibration error vector CEV representative of an image error introduced by the non-corrected dense object-induced artifact.
1 Assignment
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Accused Products
Abstract
A spectral correction algorithm for correcting dense object-induced spectral artifacts is described. In one embodiment, a calibration object, representative of typical head scanning conditions is scanned and the data reconstructed to provide an image. A water or water-equivalent cylinder of about the same diameter also is scanned and reconstructed, on the same display field of view (DFOV). These two images are designated respectively by BWEQ and WEQ. The ratio of images BWEQ and WEQ is then evaluated, and a region of interest extracted by multiplying the ratio by a function II(r), to obtain a calibration pattern CP. The calibration pattern is then averaged in azimuth to obtain a calibration vector. This calibration vector is fitted with low--order polynomial, and then divided by the fitting polynomial, to take out from the vector the low frequency components that, for instance, would be introduced on an "ideal" scanner. By subtracting 1.0 from the ratio, and multiplying by a CT number scale factor (ctscale) and an apodizing window Aw(r), a calibration error vector CEV is obtained that is representative of the circularly symmetric image error introduced by the non-corrected bone-induced artifact. The corresponding error calibration vector can be expanded into a circularly symmetric image error pattern I[CEV(r)], and subtracted from the calibration image, to provide a substantially artifact free image. The method can be extended to extract and correlate error vectors on an image segment basis such that the resulting error image pattern is not circularly symmetric.
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Citations
20 Claims
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1. A method for correcting an image having dense object-induced spectral artifacts generated using data collected in a computed tomography system, said method comprising the steps of:
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(a) reconstructing an image BWEQ of a calibration object; (b) reconstructing an image WEQ of a water equivalent cylinder having about a same diameter as the calibration object; (c) generating a ratio of images BWEQ and WEQ; (d) extracting a region of interest by multiplying the generated ratio by a function II(r) to obtain a calibration pattern CP; (e) averaging the calibration pattern in azimuth to obtain a calibration vector; (f) removing low frequency components from the vector; (g) multiplying the result of step (f) by a CT number scale factor (ctscale) and an apodizing window Aw(r) to generate a calibration error vector CEV representative of an image error introduced by the non-corrected dense object-induced artifact. - View Dependent Claims (2, 3, 4, 5)
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6. A method for correcting an image of a head having dense object-induced spectral artifacts generated using data collected in a computed tomography system, said method comprising the steps of:
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(a) reconstructing a scan image SCANI of the head; (b) reconstructing an image WEQ1 of a water equivalent cylinder having about a same diameter as the head; (c) generating a ratio of images SCANI and WEQ1; (d) extracting a region of interest by multiplying the generated ratio of SCANI and WEQ1 by a function II(r) to obtain a scan pattern SP; (e) averaging the scan pattern in azimuth to obtain a scan vector; (f) removing low frequency components from the scan vector; and (g) multiplying the result of said step of removing low frequency components from the scan vector by a CT number scale factor (ctscale) and an apodizing window Aw(r) to generate a scan error vector SEV representative of an image error introduced by non-corrected bone-induced artifact. - View Dependent Claims (7, 8, 9, 10, 11, 12)
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13. An apparatus for correcting an image having dense object-induced spectral artifacts generated using data collected in a computed tomography system, said apparatus configured to:
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(a) reconstruct an image BWEQ of a calibration object; (b) reconstruct an image WEQ of a water equivalent cylinder having about a same diameter as the calibration object; (c) generate a ratio of images BWEQ and WEQ; (d) extract a region of interest by multiplying the generated ratio by a function II(r) to obtain a calibration pattern CP; (e) average the calibration pattern in azimuth to obtain a calibration vector; (f) remove low frequency components from the vector; (g) multiply the result of step (f) by a CT number scale factor (ctscale) and an apodizing window Aw(r) to generate a calibration error vector CEV representative of an image error introduced by the non-corrected dense object-induced artifact. - View Dependent Claims (14, 15)
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16. An apparatus for correcting an image of a head having dense object-induced spectral artifacts generated using data collected in a computed tomography system, said apparatus configured to:
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(a) reconstruct a scan image SCANI of the head; (b) reconstruct an image WEQ1 of a water equivalent cylinder having about the same diameter as the head; (c) generate a ratio of images SCANI and WEQ1; (d) extract a region of interest by multiplying the generated ratio of SCANI and WEQ1 by a function II(r) to obtain a scan pattern SP; (e) average the scan pattern in azimuth to obtain a scan vector; (f) remove low frequency components from the scan vector; and (g) multiply the result of said step of removing low frequency components from the scan vector by a CT number scale factor (ctscale) and an apodizing window Aw(r) to generate a scan error vector SEV representative of an image error introduced by non-corrected bone-induced artifact. - View Dependent Claims (17, 18, 19, 20)
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Specification