Relationship between sharpness and noise in CT images reconstructed with different kernels

The sharpness expressed as the full-width at half-maximum of the line spread function (LSF) was derived for different CT scanners and reconstruction kernels. The LSFs were calculated from images of a 0.28 mm tungsten bead and successfully fitted to cumulative Gaussians by means of probit plots. The corresponding image noise was measured in a homogeneous material. The investigation showed that the noise increases strongly for small improvements in sharpness. The method was reproducible and insensitive to small positional shifts of the phantom.