Published for the American Association of Physicists in Medicine by the American Institute of Physics
Medical Physics vol:38 pages:S36-S49
Purpose. To reduce beam hardening artifacts in CT in case of an unknown X-ray
spectrum and unknown material properties.
Methods. We assume that the object can be segmented into a few materials with
different attenuation coefficients, and parameterize the spectrum using a small number
of energy bins. The corresponding unknown spectrum parameters and material
attenuation values are estimated by minimizing the difference between the measured
sinogram data and a simulated polychromatic sinogram. Three iterative algorithms
are derived from this approach: two reconstruction algorithms IGR and IFR, and
one sinogram precorrection method ISP.
Results. The methods are applied on real X-ray data of a high and a low-contrast
phantom. All three methods successfully reduce the cupping artifacts caused by the
beam polychromaticity in such a way that the reconstruction of each homogeneous
region is to good accuracy homogeneous, even in case the segmentation of the preliminary
reconstruction image is poor. In addition, the results show that the three
methods tolerate relatively large variations in uniformity within the segments.
Conclusions. We show that even without prior knowledge about materials or spectrum,
effective beam hardening correction can be obtained.