Study of the Photon-Counting Computed Tomography

Abstract

Purpose: To compare image quality at low- and routine-doses between a photon-counting (PCCT) and an energy integrating (EICT) CT system at different patient sizes and to evaluate the effect of pulse pileup on PCCT. Methods: For the comparison between PCCT and EICT, a size-variant phantom was used to characterize image quality as a function of patient size. The phantom contained five cylinders of different diameters attached by slanted tapered sections, and each cylinder contained two sections: one uniform and the other with air, water, bone, polystyrene, and iodine inserts. The phantom was scanned on Siemens SOMATOM Definition Flash and NAEOTOM Alpha at two dose levels - 1.18 mGy (low) and 7.51 mGy (routine) without tube current modulation. All other acquisition settings were not changed. Several FBP reconstructions were performed with different Br kernels. NPS, TTF, CNR, and detectability index (d’) were acquired using imQuest, an open-source software package. For the pileup evaluation, an ACR CT accreditation phantom was used to characterize image quality as a function of tube current. The phantom was scanned on Siemens NAEOTOM Alpha at five different tube currents. Tube current modulation was turned off. All other acquisition settings were not changed. Images were reconstructed using FBP algorithm and Br44 convolution kernel. NPS, TTF, CNR, and CT number were acquired using imQuest, an open-source software package.