Long-term quantitative stability of a first-generation dual-source photon-counting CT

The introduction of the first clinical photon-counting CT (PCCT) presents an opportunity to improve and expand quantitative imaging to new applications with its high spatial resolution and stellar quantitative capabilities. Despite this potential, PCCT employs a photon-counting detector that introduces unknowns including temporal stability that is critical to separating biological changes from scanner changes and variation in longitudinal studies. For the purpose of determining the temporal stability of a first-generation dual-source PCCT, a phantom was subjected to near-weekly scans across a two-year period, in both single-source and dual-source modes. Virtual monoenergetic images (VMI) at 40, 70, 100, and 190 keV and iodine density maps were analyzed to determine changes in relative error and noise both related and unrelated to software/hardware changes. VMIs demonstrated improvements in quantification for dual-source mode associated with software and hardware updates but otherwise illustrated invariance with variation ranging from 0.03 to 0.08%. VMI noise similarly exhibited stability between and with major scanner updates with a maximum change of 4 HU. Iodine density maps also displayed stability between scanner updates with variation up to 0.1 mg/mL but significant improvements in quantification, especially in dual-source mode, that allowed relative error in single-source and dual-source modes to match at -0.04 and -0.02 mg/mL, respectively. Spectral results in PCCT showed temporal stability over time that improved quantification accuracy particularly for dual-source mode. This stability will boost confidence in quantitative metrics such as in longitudinal studies and thus facilitate more clinical applications that may change the workflow of diagnostic radiology.