Cone-beam CT rotation center calibration method based on the L0 norm minimization of reconstructed image gradient

Abstract

The invention relates to a cone-beam CT rotation center calibration method based on the L0 norm minimization of reconstructed image gradient. The method comprises the following steps: S1) placing even metal round balls on a rotation station; arranging the ray source and the detector on the circular track around the rotation center; initiating the cone-beam CT system; and scanning to obtain the projection data of the metal round balls; S2) according to the projection data of the metal round balls and the initial rotation center position of the cone-beam CT, using the FDK reconstruction algorithm and reconstruction software to obtain the reconstruction images of the metal round balls; and calculating the L0 norm of the reconstructed image gradient; S3) adjusting the offset parameters of the rotation center in the reconstruction software and reconstructing again to obtain the updated reconstruction images and calculating the L0 norm of the reconstructed image gradient; and S4) circularly adjusting the offset parameters of step 3 until the L0 norm of the reconstructed image gradient becomes the smallest within a certain error scope; and calibrating the offset parameters of the rotation center at this time as the desired calibration ones. The mode that the method uses can be manufactured simply. With only one time of cone-beam CT scanning, the imaging quality of the cone-beam CT system is increased.

Description

technical field [0001] The invention belongs to the technical field of biomedical imaging and non-destructive testing, and relates to a cone beam CT (Computed Tomography) rotation center calibration method based on the minimization of the L0 norm of the reconstructed image gradient. Background technique [0002] CT technology has been successfully applied in the field of non-destructive testing and has achieved great development. The cone-beam CT system with circular trajectory is mainly composed of three parts: X-ray source, rotating table and detector. The ideal imaging relationship of cone-beam CT system requires that the line connecting the ray source and the center of the detector (central ray) be perpendicular to the plane where the detector is located. , and perpendicular to the rotation axis of the turntable, the intersection point is the center of rotation. In the three-dimensional image reconstruction that requires high reconstruction image quality, the projection...

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Problems solved by technology

[0003] In order to compensate the influence of the offset of the rotation center on the quality of the reconstructed image, Stephen et al. proposed a method of correcting the projection center by using the projected sinogram in the Journal of Nuclear Science in 1990 to calculate the offset of the rotation center, but this The correction effect of the method is not obvious when the system noise is large; Fu Jian et al. proposed in the Journal of Military Engineering in 2003 that the deviation of the focus is equivalent to the deviation of the rotation center, and different offsets are given to the ray source. The image is reconstructed and the offset corresponding to the reconstructed image with the highest signal-to-noise ratio and contrast is used to calculate the real offset of the rotation center. This method selects the signal-to-noise ratio and contrast to describe the accuracy of the rotation center, although there is a certain degree of effect but the calibration accuracy is limited

In 2006, Tong Liu et al. fixed a thin steel wire on the rotating platform at a certain distance from the rotation center in the Journal of Optical Engineering, and used the geometric relationship of the steel wire projection image to find the offset of the rotation center. This method The projected image of the steel wire on the detector is idealized as a point, which is far from the actual situation; Li Baolei et al. proposed a sinogram-based calibration method for the rotation center of an industrial CT system in the Journal of Aeronautical Sciences in 2009, using the center The rotation position of projection rays is invariant, and the position of the rotation center is determined by calculating the minimum value of the difference between the projection data separated by 180° before and after; this method requires that the dose of the radiation source is very stable, otherwise a larger error will be introduced, making the position of the rotation center inaccurate

According to the symmetry principle of the projection image about the rotation center in the Journal of Medical and Health Equipment in 2009, Zhang Wei et al. first binarized the projection image, then calculated the centroid of the projection image, and finally averaged the coordinates of the centroid obtained from multiple angles. The position of the center of rotation is obtained. This method reduces the influence of noise on the position of the center of mass, but the error caused by binarization and the center of mass will seriously affect the determination of the position of the center of rotation.

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