X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2001-07-10
2002-08-20
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S019000, C378S901000, C378S004000
Reexamination Certificate
active
06438197
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to correcting beam hardening in an X-ray computed tomography apparatus.
2. Description of the Prior Art
As a consequence of the spectral dependency of the beam attenuation behavior in an irradiated object, a shift of the average or mean energy of the X-radiation emerging from a transirradiated body toward higher energy values occurs given polychromatic X-radiation. This effect is referred to as beam hardening. In computed tomography, beam hardening causes gray scale deviations in the reconstructed image of the body compared to the theoretical case of linear, spectrally independent beam attenuation. These gray scale deviations—or beam hardening artifacts—in the reconstructed image interfere with the diagnostic content of the image and can lead to misinterpretations in the worst case.
Numerous approaches are proposed in the literature for correcting image artifacts caused by beam hardening. For example, one approach disclosed in U.S. Pat. No. 4,709,333 is known as polynomial correction. Using an attenuation value obtained by measurement that indicates the actual beam attenuation of a body affected by beam hardening, a corrected attenuation value that is employed as the basis of the image reconstruction is calculated by inserting this attenuation value into a suitable polynomial identified in a calibration phase.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a computed tomography apparatus which is operable to effectively correct for beam hardening.
This object is inventively achieved in an X-ray computed tomography apparatus having an X-ray radiator, a radiation filter arrangement arranged in the beam path of the X-rays emitted by the X-ray radiator, a detector arrangement that detects the X-rays that pass through a patient under examination and provides a set of measured intensity values for each slice projection, each of these measured intensity values being representative of the intensity of the detected X-rays in a respective projection sub-region of the slice projection, and has an electronic evaluation unit that determines an overall attenuation value for each of the measured intensity values that is representative of the actual overall attenuation of the X-rays in the respective projection sub-region effected by the radiation filter arrangement and the patient, and that determines a patient attenuation value corrected for beam hardening for each of the overall attenuation values that is representative of the theoretical, linear attenuation of the X-rays by the patient in the respective projection sub-region.
REFERENCES:
patent: 4709333 (1987-11-01), Crawford
patent: 5307264 (1994-04-01), Waggener et al.
patent: 6324240 (2001-11-01), Yan et al.
Bruce David V.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
LandOfFree
X-ray computed tomography apparatus with correction for beam... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray computed tomography apparatus with correction for beam..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray computed tomography apparatus with correction for beam... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2894705