Noise reduction in x-ray microtomographic images by anisotropic diffusion filtration of the scanner projection images

In this study, we investigated the efficacy of an anisotropic diffusion filter in reducing noise and suppressing and/or removing image artifacts with minimal degradation of image resolution in the three-dimensional (3D) reconstructed microtomography (micro-CT) images. The preprocessed projection images of the micro-CT scanner were filtered using the anisotropic affine filter(1). The tomographic images of test phantoms and of real tissue specimens were reconstructed using conebeam filter backprojection technique from the filtered projections, and compared to the images reconstructed from original projection images. The image variance in 3D reconstructed image slices was estimated by computing the spatial variance inside a selected region of interest (ROT) in the tomographic image of a plexiglass cylinder. The computed tomography (CT) image grayscale profiles of glass microspheres and of rat kidneys in 3D reconstructed image slices were compared to show the effect of the filtering on image resolution. The affine anisotropic filtering reduced the variance in the selected region of the micro-CT image. The comparison of intensity profiles across the glass spheres in the tomographic slices indicated that the filtering did not result in any significant loss of resolution. The filtering either reduced the magnitude of the streak artifacts or removed them completely while suppressing the ring artifacts substantially.