Performance improvements of virtual monoenergetic images in photon-counting detector CT compared with dual source dual-energy CT: Fourier-based assessment

To confirm the performance improvement of virtual monoenergetic images (VMIs) for iodine contrast tasks in a clinical photon-counting detector CT (PCD CT) using Fourier-based assessment, compared with those in the latest-generation dual-source dual-energy CT (DECT). A water-filled bath with a diameter of 300 mm, which contains rod-shaped phantoms equivalent to diluted iodine (2 and 12 mg/mL), was scanned using PCD CT and DECT at 15, 7.5, and 3 mGy. VMIs were generated without any iterative reconstruction algorithm. Task transfer function (TTF), noise power spectrum (NPS), and slice sensitivity profile were evaluated for VMIs at 70 and 40 keV. The detectability index (d') and the squared system performance function (SPF²) calculated by TTF²/NPS were compared. At 40 keV, the d' values of PCD CT were higher (percentage increase of 25.7-39.9%) than those of DECT, whereas at 70 keV, the difference was rather small. The SPF² values at 40 keV of PCD CT grew notably higher than those of DECT as the spatial frequency increased. The higher SPF² values endorsed the lower image noise and the sharper edge of the rod phantom as observed. The d' and SPF² in VMIs at 40 keV of PCD CT were notably higher than those of DECT, which endorsed the clinical advantages of PCD CT that had been previously reported in various studies.