Reconct

The generated hepatic model was applied to an existing XCAT phantom liver at 4 timepoints (corresponding to 4 static phantoms differing only in contrast location) during arterial perfusion. The phantom was male and belonged to the 50^th percentile for BMI with 0.25 mm voxel size. The phantom was virtually imaged using a scanner-specific CT simulator, DukeSim^{8 (link)}, based on the acquisition geometry of the Somatom Definition Flash (Siemens Healthcare) with tube voltage of 120 kV, tube current of 150 mAs, and a pitch of 1. The images were reconstructed using a commercial reconstruction software (ReconCT, Siemens Healthcare) via a weighted filtered back-projection algorithm with the B31f (standard) kernel to a slice thickness of 0.6 mm with slice spacing of 0.6 mm. The measurements were completed on multiple image slices. The value of 180 HU is an average across 30 slices with ROIs contained by the vessel. The value was obtained by manually (visually) identifying the vessel on the simulated image and segmenting it such that multiple ROIs could be drawn entirely inside it.

We used a validated and scanner-specific CT simulation platform (DukeSim) to generate projection images from the COPD-XCAT phantoms [13 (link)], [14 (link)]. DukeSim takes a computational phantom and a parameter file as its input and uses ray-tracing and Monte Carlo (MC) techniques to estimate primary and scatter photons that hit detector elements, respectively. Taking into account the physics of x-ray source and detectors, DukeSim then combines these two signals, computes projection images, and pre-processes them.
In this study, DukeSim was used to model the physical and geometrical properties of two EID commercial scanners (SOMATOM Definition Flash, SOMATOM Force, Siemens) and one PCCT commercial scanner (NAEOTOM Alpha, Siemens). Virtual acquisitions were performed at 2 dose levels (CTDIvol of 0.63 and 3.17 mGy) with scanner-specific x-ray spectra (120 kV) and bowtie filters, a pitch of 1.0, and tube current modulation (TCM) with “average” modulation strength and a reference diameter of 31.4 cm [15 (link)], [16 (link)].
The projection images were reconstructed using a vendor-specific reconstruction toolbox (ReconCT, Siemens). The simulation and reconstruction protocol settings are summarized in Table 1.

The DukeSim CT simulator was used to image the human phantoms, by generating scanner-specific CT projection images of voxelized computational phantoms that take into account the physical and geometric characteristics of the scanners [16 (link)–20 (link)]. In this study, a clinical PCCT and an energy-integrating CT (EICT) (NAEOTOM Alpha, SOMATOM Definition Flash, Siemens) were simulated by DukeSim to generate the CT projections of the phantoms. Virtual acquisitions were performed at 2 dose levels (CTDIvol of 6.3 and 12.6 mGy) using scanner-specific x-ray spectra (120kV) with a body bowtie filter at a pitch of 1.0 with “average” tube current modulation (TCM) and a reference diameter of 31.4 cm [15 (link),18 (link)]. The projection images were reconstructed using vendor-specific reconstruction software (ReconCT, Siemens) with the weighted filtered back projection (wFBP) for EICT images and prior-based noise reduction (PNR). Two kernel sharpnesses were used for each dataset (Qr32f and Qr60f for EICT and Qr36f and Qr61f for PCCT). The reconstructions were done at different matrix sizes (512 × 512 and 1024 × 1024) with a field of view of 500 mm, and the thinnest slice thicknesses available for each acquisition mode (0.75 for FLASH, 0.2 and 0.4 mm for NAEOTOM Alpha).

The virtual patient was imaged using a scanner-specific CT simulator (DukeSim). DukeSim models geometric and physics properties such as tube current modulation, image scatter (through monte carlo), beam hardening correction, and correlated noise in PCCT [5 (link)], [7 (link)]–[10 (link)].
The virtual acquisitions were done by modeling commercial PCCT (NAEOTOM Alpha, Siemens) and EICT (FORCE, Siemens) scanners at two doses (CTDI_vol of 20 and 40 mGy). The PCCT images were acquired at two spatial resolution modes: 1) ultra-high resolution with beam collimation of 120×0.2 mm (UHR-PCCT) and high resolution with beam collimation of 144×0.4 mm (HR-PCCT). The EICT acquisitions used a beam collimation of 0.96×0.6 mm. All acquisitions utilized a tube voltage of 120 kV, and the PCCT acquisitions used detector thresholds of 20 and 65 keV. The images were reconstructed using a vendor-specific reconstruction software (ReconCT, Siemens) with a FOV of 350 mm at two matrix sizes (512×512 and 1024×1024) using the smallest slice thickness available (0.2 mm for UHR-PCCT, 0.4 mm for HR-PCCT, and 0.75 mm for EICT). All acquisitions were reconstructed with three kernel sharpness levels based on matching the MTF between scanner kernels: Br40, Br48, and Br64 for the PCCT acquisitions and Br36, Br44, and Br59 for the EICT acquisitions.