Nonlinear partial volume artifacts in x‐ray computed tomography

Abstract

Dark streaks connecting the human petrous bones are often observed in cranial transverse section CT [computed tomography] reconstructions. These artifacts are usually only slightly diminished by 2-pass beam hardening corrections. Narrowing the slice thickness substantially reduces the artifacts. Axial partial volume effects can account for the presence of the artifacts. These axial partial volume effects occur when, at any point in the slice, the object has axial variations in attenuation. In such cases the log of the integrated intensity measured by the detector is not a linear function of the integrated attenuation (even for monochromatic beams). This nonlinearity causes inconsistencies in the data set which, in turn, can cause image streaks. Partial volume effect was studied using computer simulation. Algorithms are presented to correct for these effects by estimating the axial variation using neighboring slices. These correction algorithms are successful in computer simulation cases but failed with clinical data. No practical correction method is viable unless overlap scanning is employed. Thin slice scanning for sections where these artifacts are common maybe a more preferable solution.