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

Wereport a comprehensive evaluation of a full field-of-view (FOV) photon-counting detector (PCD) computed tomography (CT) system using phantoms, and qualitatively assess image quality in patient examples.Awhole-body PCD-CTsystemwith 50 cmFOV, 5.76 cmz-detector coverage and two acquisitionmodes (standard: 144 × 0.4mmcollimation and ultra-high resolution (UHR): 120 ×0.2mm collimation) was used in this study. Phantomswere scanned to assess image uniformity, CTnumber accuracy, noise power spectrum, spatial resolution, material decomposition and virtualmonoenergetic imaging (VMI) performance. Four patientswere scanned on thePCD-CTsystemwith matched or lower radiation dose than their prior clinicalCTscans performed using energy-integrating detector (EID) CT, and the potential clinical impact of PCD-CTwas qualitatively evaluated. Phantom results showedwater CTnumberswithin±5HU, and image uniformitymeasured between peripheral and central regions-ofinterests to bewithin±5HU. For theUHRmode using a dedicated sharp kernel, the cut-off spatial frequencywas 40 line-pairscm-1,which corresponds to a 125μmlimiting in-plane spatial resolution. The full-width-at-half-maximumfor the section sensitivity profile was 0.33mmfor the smallest slice thickness (0.2mm) using theUHRmode.Material decomposition in a multi-energyCTphantom showed accurate material classification, with a root-mean-squared-error of 0.3mg cc-1 for iodine concentrations (2-15mgcc-1) and 14.2mg cc-1 for hydroxyapatite concentrations (200 and 400mgcc-1).The average percent error forCTnumbers corresponding to the iodine concentrations inVMI(40-70 keV) was 2.75%. Patient PCD-CTimages demonstrated better delineation of anatomy for chest and temporal bone exams performedwith theUHRmode,whichallowed theuseof very sharp kernels not possible with EID-CT. VMIand virtual non-contrast images generated froma patient headCTangiography exam using the standard acquisitionmode demonstrated themulti-energy capability of thePCD-CTsystem.