Patent ID: 7570734

Claim:
A method for correcting an X-ray image in an X-ray computerized tomography scanner having a rotary arm and a scan mechanism, the rotary arm having an X-ray source generating cone beam X-rays and a two-dimensional X-ray detector opposing to the X-ray source, the scan mechanism supporting and rotating the rotary arm on a non-vertical rotary axis, wherein two-dimensional X-ray image data from the X-ray detector are acquired and processed while the scan mechanism rotates the rotary arm, the method comprising the steps of: putting a correction phantom around the rotary axis or substantially on the rotary axis between the X-ray source and the two-dimensional X-ray detector, the correction phantom being made of an X-ray transmitting material and embedding an object which absorbs X-rays; acquiring the image data of the object by generating X-rays by the X-ray source and receiving the X-rays transmitting the object by the X-ray detector while rotating the rotary arm, the image data extending in a direction of the rotary axis of the rotary arm and in another direction perpendicular to the rotary axis; determining a locus of the object in the two-dimensional image; estimating an ideal locus of the object in the direction of the rotary axis based on the determined locus in the two-dimensional image data; determining a difference between the calculated position of the ideal locus and a counterpart position of the determined locus in the direction of the rotary axis; and reconstructing an X-ray CT image of the object based on the two dimensional image data of the object wherein a position of the X-ray CT image in the direction of the rotary axis is corrected based on the determined difference between the calculated position and the counterpart position in the direction of the rotary axis; wherein the step of determining the ideal locus comprises the steps of: determining a width 2R of deviation in a direction perpendicularly to the rotary axis in the determined locus of the object in the two-dimensional image; determining a distance r of the object from the rotary axis based on the width 2R of the deviation in the two-dimensional image; determining an average position in the direction of the rotary axis of the determined locus in the two-dimensional image; determining a position z B of the object in z axis based on the average position; determining a rotation angle θ of the rotary arm based on the determined locus in the two-dimensional image; and calculating a position z P of the locus of the object in the direction of the rotary axis according to a following relationship: Z P = FS _ * Z B OF _ + r · sin ⁢ ⁢ θ , wherein FS is distance from focal point F of the X-ray source to the imaging plane, OF is distance from the rotary axis to the focal point, and θ is rotation angle of the rotary arm, to determine the position z P as the ideal locus of the object in the direction of the rotary axis.