Clinical photon-counting CT increases CT number precision and reduces patient size dependence compared to single- and dual-energy CT

Objectives To study whether photon-counting computed tomography (PCCT) can improve CT number accuracy and precision and reduce patient size dependence compared to dual-energy CT (DECT) virtual monoenergetic imaging (VMI) and single-energy CT (SECT).Methods Clinical PCCT, DECT, and SECT scanners were used to image a multi-energy quality assurance phantom and tissue-equivalent inserts with/without an outer nested annulus, representing 2 object sizes (18 and 33 cm). CT numbers were converted to linear attenuation coefficients (LAC) and regions of interest applied. Theoretical monoenergetic LAC were calculated from known elemental compositions as a ground truth. Percent differences in mean LAC between phantom sizes, between mean and theoretical LAC, and its coefficient of variation (COV) were calculated.Results Mean LAC percent differences between small and larger phantoms were highest in DECT (within -3% to 9%) and SECT (within 1%-5%), particularly at higher calcium and iodine concentrations, while being relatively constant in PCCT over material concentrations and VMI energies (within +/- 2%). The COV in mean LAC was consistently lower (about 2-5 times) in PCCT relative to DECT and SECT for calcium in the large phantom. With consideration of the theoretical uncertainties of 2%, both PCCT and DECT showed comparable agreement to theoretical LAC.Conclusions PCCT VMI produces CT numbers with less dependence on patient size and increased precision in large object sizes than DECT VMI and SECT.Advances in knowledge Clinical PCCT provides less variable CT numbers than DECT and SECT with less sensitivity to the imaged object size.