Scatter and beam hardening correction for mobile brain cone-beam CT

Abstract

Cone-beam computed tomography (CBCT) imaging system has been widely used in various applica-tions, and takes an important role for diagnosis of emergency patient. However large size of detector causes high scatter-to-primary ratios on CBCT projection data. Also, beam hardening artifacts in reconstructed CT images result from the polychromatic nature of X-ray beam. These two phenomena lead to unwanted results of reconstructed image such as cupping artifact, worsen soft tissue contrast, and lower CT grey value. This paper reports the result of our investigation on the effects of the scatter kernel superposition (SKS) method and linearization method for beam hardening correction on the soft tissue contrast. We used a head phantom for an experimental study. The implemented correction methods do not need any additional physical device and are computationally efficient. For the simulation study, a lab-made program was used for generating polynomial projections. Through simulation study, it was found that the beam hardening correction or scatter correction alone cannot reconstruct the image accurately. For the real experiment, the mobile half-fan CBCT system PHION (NanoFocusRay Co., Ltd, Jeonju, South Korea) and PH-3 angiographic CT head phantom ACS were used. The tube voltage was 120 kVp, tube current was 15 mA and the exposure time was 10 ms. The image was reconstructed using a filtered back projection algorithm. After scatter and beam hardening correction, contrast to noise ratio of reconstructed images increased by 7 times. Particularly images after scatter correction and beam hardening correction showed clear boundary between skull and soft tissues, while uncorrected case did not.