Research On Artifact In Rock X-Ray CT Image

From X-ray computerized tomography (CT), the interior information of an object can be picked up in a non-destructive way, and CT is quantified and dynamic, so it used widely from medicine field to industry non-destructive test and rock engineering. The purpose of rock material CT test is that monitoring the internal fracturing process of rock, analyzing the relation between rock characteristic and CT data, searching the laws of rock fracturing process. Because of apparatus definition, test method, image reconstruction and so on, rock material CT image has some artifact, the research of the artifact administers to exactly image judge, CT image information apply and deeply analysis of test result.Based on study of CT working principle and image reconstruction, the CT test is done with two type of rock sample ,one is homogeneous without crack and the other with crack founded in advance, the CT data with different stress are gained, which are changed to CT images. Compared with rock sample, four types of artifact are discovered in CT image: boundary artifact, arc artifact, offset artifact and crack artifact. A set of method that contains image reconstruction, CT data statistic, wavelet transform, Fourier transform, filter optimization, curve fitting and so on is applied to research the mechanism of CT artifact, the method of removing artifact and picking up sample information.The research shows that boundary artifact is related to the filter in reconstruction algorithm, the quality of CT image can be improved with filter optimization, although the artifact can not be removed completely, it contains some boundary information of the rock sample, from which the geometrical scale of sample can be picked up. The reason of arc artifact is that the X-ray beam becomes hard, and it can be removed with Fourier transform or wavelet decomposition. The reason of offset artifact is that the rock sample place changed when X-ray scan at different times, the artifact can be removed with image registration. Crack artifact is related to the resolving power of CT machine, because of the scan spacingand the width of X-ray beam, if the crack in rock is smaller than the resolving power, the crack in CT image would become distortional, based on the minimum of CT data in crack artifact, the width of crack can be measured . All the research is based on rock material, and it is useful for brittle and homogeneous material CT test.