Beam hardening correction using a conical water-equivalent phantom for preclinical micro-CT

Beam hardening artifacts are a common occurrence in x-ray CT images. X-ray sources typically produce polychromatic photons and their relative absorption is a strong function of their energy. Despite this fact, most reconstruction algorithms assume the attenuation coefficient of the subject being scanned is invariant with the energy of the incident photons, and the quality of the reconstructed images is reduced. A practical method of correction for those artifacts is to calibrate the acquired data to the expected projections of a known geometry. Generally this method requires scans of multiple phantoms varying in size to calculate the parameters of the calibration function. The selection of the phantom data for determining the parameters can also affect the performance of the method. This work proposes a beam hardening correction (BHC) scheme using a specially designed, conical phantom for preclinical micro-CT. The conical shape simplifies both the data acquisition and the calculation of the calibration function for different object sizes. A 3 rd degree polynomial is chosen as the calibration function used to correct the CT projection data. Experiments conducted with the Siemens Inveon™ micro CT showed that the artifacts were greatly suppressed.