Separable scatter model of the detector and object contributions using continuously thickness-adapted kernels in CBCT

Due to the increased cone beam coverage and the introduction of flat panel detector, the size of X-ray illumination fields has grown dramatically in Cone Beam Computed Tomography (CBCT), causing an increase in scatter radiation. Existing reconstruction algorithms do not model the scatter radiation, so scatter artifacts appear in the reconstruction images. The contribution of scattering of photons inside the detector itself becomes prominent and challenging in case of X-ray source of high energy (over a few 100 keV) which is used in typical industrial Non Destructive Testing (NDT). In this paper, comprehensive evaluation of contribution of detector scatter is performed using continuously thickness-adapted kernels. A separation of scatter due to object and the detector is presented using a four-Gaussian model. The results obtained prove that the scatter correction only due to the object is not sufficient to obtain reconstruction image free from artifacts as the detector also scatters considerably. The obtained results are also validated experimentally using a collimator to remove the contribution of object scatter.