Analytic calculation of CT phantom projections and its application in beam hardening correction

To develop an efficient beam hardening correction for medical diagnostic X-ray CT (computed tomography), an analytic calculation method was proposed to simulate polychromatic X-ray projections. The method combines the energy spectrum distribution of X-ray source, geometrical shapes and material compositions of sub-regions of phantoms. Firstly, CT values are mapped into material compositions under the precondition that only human being tissues are considered. And then, boundaries of sub-regions are determined by the proposed analytic method. Finally, projections are calculated according to the energy spectrum distribution of X-ray source. Compared with the linear integral projecting, the proposed method can not only generate more realistic projections, but also provide a unified projection data for beam hardening correction and CT reconstruction. Experiments of FORBILD head phantom show that the CT-value inconsistency error of bone correction in bone region is lower than the water correction around 4-5Hu, but higher than the monochromatic reconstruction around 5-6Hu.