  Photon counting CT (PCCT) has been a research focus in the last two decades.
Recent studies and advancements have demonstrated that systems using
semiconductor-based photon counting detectors (PCDs) have the potential to
provide better contrast, noise and spatial resolution performance compared to
conventional scintillator-based systems. With multi-energy threshold detection,
PCD can simultaneously provide the photon energy measurement and enable
material decomposition for spectral imaging. In this work, we report a
performance evaluation of our first CdZnTe-based prototype full-size photon
counting CT system through various phantom imaging studies. This prototype
system supports a 500 mm scan field-of-view (FOV) and 10 mm cone coverage at
isocenter. Phantom scans were acquired using 120 kVp from 50 to 400 mAs to
assess the imaging performance on: CT number accuracy, uniformity, noise,
spatial resolution, material differentiation and quantification. Both
qualitative and quantitative evaluations show that PCCT has superior imaging
performance with lower noise and improved spatial resolution compared to
conventional energy integrating detector (EID)-CT. Using projection domain
material decomposition approach with multiple energy bin measurements, PCCT
virtual monoenergetic images (VMIs) have lower noise, and superior performance
in quantifying iodine and calcium concentrations. These improvements lead to
increased contrast-to-noise ratio (CNR) for both high and low contrast study
objects compared to EID-CT. PCCT can also generate super-high resolution (SHR)
images using much smaller detector pixel size than EID-CT and dramatically
improve image spatial resolution.
