CLASSIFICATION OF ARTIFACTS IN X-RAY CT IMAGES DUE TO NON-LINEAR SHADOWS

Polychromaticity and noise artifacts in computed x-ray tomography can be traced to a nonlinear dependence of projection data and its variance upon an ideal consistent set of projection data. We describe both types of artifacts and present mathematical models. A comparison is made between artifacts in the image i(→r) of CT values and artifacts in the distribution σ2(→r) of the noise variance. Three classification schemes for these nonlinear artifacts are presented: the physical origin of the artifacts (I), the geometrical appearance of the artifact (II), and the degree of consistency of the nonlinear shadow (III). © 1979 IEEE.