X射线断层扫描投影图像背景不一致的校准

在X射线断层扫描(X-ray CT)成像过程中,经常会出现射线源、样品和探测器三者之间的相对移动,导致采集的投影图像(Projection image)以及亮场图像(flat field image)的空间位置配准关系出现偏差。这直接影响了投影图像背景的正常扣除,以及后续的CT图像重建。本文利用互相关方法,求出各投影图像背景与探测器原始采集位置之间的不一致量。然后将投影图像和亮场图像作相应变换,最后扣除背景得到校准后的图像。由于该方法对图像灰度较为敏感,所以在对实际样品校准之前,本文先对该样品投影图像及亮场图像进行了照度归一化。实验结果表明,该方法能够有效校正由射线源、样品和探测器之间相对移动造成的CT投影图像背景不一致,获得较好的CT投影图像和重建切片。

Spatial Registration of X-ray CT Projection Images

The relative displacement among X-ray source, rotation stage, and detector in X-ray computed tomography(X-ray CT) imaging process are difficult to eliminate. This causes spatial misalignment of the projection and flat-field images, which directly affects the accuracy of flat-field subtraction and the subsequent CT reconstruction. In this paper, the quantitative spatial displacement was obtained between each projection image and the detector using a cross-correlation method. The projection images registrations were carried out according to the calculated displacement. As this method is very sensitive to image gray value, a polynomial fitting method was used to correct the non-uniform illumination in the original CT image. The numerical results based on real CT data have demonstrated that this method can effectively correct the misalignment of CT projection images, caused by relative movement among the X-ray source, the rotation stage and the detector.