Background: Dual-layer spectral detector CT (SDCT) may provide several theoretical advantages over pre-existing\nDECT approaches in terms of adjustment-free sampling number and dose modulation, beam hardening correction,\nand production spectral images by post-processing. In addition, by adopting noise reduction algorithm, high\ncontrast resolution was expected even in low keV level. We surmised that this improvement would be beneficial to\nobese people. Therefore, our aim of study is to compare image quality of virtual monochromatic spectral images\n(VMI) and polychromatic images reconstructed from SDCT with different body size and radiation dose using\nanthropomorphic liver phantom.\nMethods: One small and one large size of body phantoms, each containing eight (four high- and four lowcontrast)\nsimulated focal liver lesions (FLLs) were scanned by SDCT (at 120 kVp) using different Dose Right Indexes\n(DRIs). VMI were reconstructed from spectral base images from 40 keV to 200 keV. Hybrid iterative reconstruction\n(iDose4) was used for polychromatic image reconstruction. Image noise and contrast to noise ratio (CNR) were\ncompared. Five radiologists independently rated lesion conspicuity, diagnostic acceptability and subjective noise\nlevel in every image sets, and determined optimal keV level in VMI.\nResults: Compare with conventional polychromatic images, VMI showed superior CNR at low keV level regardless\nof phantom size at every examined DRIs (Ps < 0.05). As body size increased, VMI had more gradual CNR decrease\nand noise increase than conventional polychromatic images. For low contrast FLLs in large phantom, lesion\nconspicuities at low radiation dose levels (DRI 16 and 19) were significantly increased in VMI (Ps < 0.05). Subjective\nimage noise and diagnostic acceptabilities were significantly improved at VMI in both phantom size.\nConclusions: VMI of dual-layer spectral detector CT with noise reduction algorithm provides improved CNR, noise\nreduction, and better subjective image quality in imaging of obese simulated liver phantom compared with\npolychromatic images. This may hold promise for improving detection of liver lesions and improved imaging of\nobese patients.
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