Abstract
The ring artifacts introduced by the defective pixels with non-linear responses in the high-resolution detector, have a great impact on subsequent processing and quantitative analysis of the reconstructed images. In this paper, a multistep method is proposed to suppress the ring artifacts of micro CT images, which firstly locates the positions of the defective pixels in the sinogram, and then corrects the corresponding value in the projections. Since the defective pixels always appear as vertical stripes in the sinogram, a horizontal curve is derived by summing the pixel values along vertical direction, thus the abrupt segments related to the defective stripes are enhanced notably, and a proportion coefficient based on the second derivative of the curve is taken as the indicator for the position and the severity of the defective pixels. Then, the detected defective pixels in the sinogram are transferred and relocated in the projections, an improved 3D block matching filtering (BM3D) algorithm is applied to restore the defective pixels in corresponding projection images. In the end, the tomographic images are reconstructed from the corrected projections. In the experiment, a small piece of the motherwort’s rhizome and a part of a mouse’s lung are imaged by micro-CT, and the result shows that, compared with the other four state-of-art methods, the proposed method has a great reduction on the ring artifacts of the reconstructed images, and makes less impact in spatial resolution and contrast in the same time.
Highlights
Micro-CT is a non-destructive 3D imaging technique for small objects, which plays an important role in basic medical research, such as bone structure observation [1], advanced material exploring etc
The defective pixels are the intrinsic characteristics of the detector [2], which always result in some ring artifacts in the reconstructed images
In contrast with the hardware based ones, the software based approaches are easier in practice, which often transform the reconstructed images into polar coordinates to remove ring artifacts [7,8]
Summary
Micro-CT is a non-destructive 3D imaging technique for small objects, which plays an important role in basic medical research, such as bone structure observation [1], advanced material exploring etc. In contrast with the hardware based ones, the software based approaches are easier in practice, which often transform the reconstructed images into polar coordinates to remove ring artifacts [7,8] It is hard for keeping same resolution due to interpolation during the transformation via different coordinate systems. Podgorsak et al proposed a median filtering-based method [19] based on the assumption that the values measured by the same defective pixel have same attenuation against the ideal values These methods have achieved some effects in ring artifacts removal, but some detailed features of the images may be lost during the filtering process [15]. The specific procedures including algorithm details, data experiments will be elucidated in the following chapters
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