Empirical Water Precorrection for Cone-Beam Computed Tomography

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Abstract
We propose an algorithm to correct for the cupping artifact inherent in CT images due to the polychromatic nature of the spectrum. This method is empirical and does not require knowledge of the spectrum and of the attenuation coefficients. The method aims at linearizing the attenuation data using a precorrection function of polynomial form. The coefficients of the polynomial are determined from a fit of some linear combined reconstructed images of the polychromatic data with a defined template. This template is obtained from the reconstruction of the polychromatic raw data and does not make any assumptions on the phantom size or of its positioning. It is shown that the fit can be performed easily solving only a linear system, making the method very fast. An example of application is given as the water precorrection. For this particular case, practical considerations are given on the definition of the template when an attenuating object table of unknown density is within the images. The method can generally correct for any kind of cupping such as scatter as well.