Full field-of-view, high-resolution, photon-counting detector CT: technical assessment and initial patient experience.

We report a comprehensive evaluation of a full field-of-view (FOV) photon-counting detector (PCD) CT system using phantoms, and qualitatively assess image quality in patient examples. A whole-body PCD-CT system with 50 cm FOV, 5.76 cm z-detector coverage and two acquisition modes (standard: 144 × 0.4 mm collimation and ultra-high resolution, UHR: 120 × 0.2 mm collimation) was used in this study. Phantom scans were acquired to assess image uniformity, CT number accuracy, noise power spectrum, spatial resolution, material decomposition and virtual monoenergetic imaging (VMI) performance. Four patients were scanned on the PCD-CT system with matched or lower radiation dose than their prior clinical CT scans performed using energy-integrating detector (EID) CT, and the potential clinical impact of PCD-CT was qualitatively evaluated. Phantom results showed water CT numbers within ±5 HU, and image uniformity measured between peripheral and central ROIs to be within ±5 HU. For the UHR mode using a dedicated sharp kernel, the limiting in-plane spatial resolution was 40 line-pairs/cm, which corresponds to a 125 µm spatial resolution. The full-width-at-half-maximum for the section sensitivity profile was 0.33 mm for the smallest slice thickness (0.2 mm) using the UHR mode. Material decomposition in a multi-energy CT phantom showed accurate material classification, with a root-mean-squared-error of 0.3 mg/cc for iodine concentrations (2 to 15 mg/cc) and 14.2 mg/cc for hydroxyapatite concentrations (200 and 400 mg/cc). The average percent error for CT numbers corresponding to the iodine concentrations in VMI (40-70 keV) was 2.75 %. Patient PCD-CT images demonstrated better delineation of anatomy for chest and temporal bone exams performed with the UHR mode, which allowed the use of very sharp kernels not possible with EID-CT. VMI and virtual non-contrast images generated on a patient head CT angiography exam using the standard acquisition mode demonstrated the multi-energy capability of the PCD-CT system.