Dual-energy CT quantitative imaging: a comparison study between twin-beam and dual-source CT scanners

To assess image quality and to quantify the accuracy of relative electron densities (ρ_e ) and effective atomic numbers (Z_eff ) for three dual-energy computed tomography (DECT) scanners: a novel single-source split-filter (i.e., twin-beam) and two dual-source scanners.

Measurements were made with a second generation dual-source scanner at 80/140Sn kVp, a third-generation twin-beam single-source scanner at 120 kVp with gold (Au) and tin (Sn) filters, and a third-generation dual-source scanner at 90/150Sn kVp. Three phantoms with tissue inserts were scanned and used for calibration and validation of parameterized methods to extract ρ_e and Z_eff , whereas iodine and calcium inserts were used to quantify Contrast-to-Noise-Ratio (CNR). Spatial resolution in tomographic images was also tested.

The third-generation scanners have an image resolution of 6.2, ~0.5 lp/cm higher than the second generation scanner. The twin-beam scanner has low imaging contrast for iodine materials due to its limited spectral separation. The parameterization methods resulted in calibrations with low fit residuals for the dual-source scanners, yielding values of ρ_e and Z_eff close to the reference values (errors within 1.2% for ρ_e and 6.2% for Z_eff for a dose of 20 mGy, excluding lung substitute tissues). The twin-beam scanner presented overall higher errors (within 3.2% for ρ_e and 28% for Z_eff , also excluding lung inserts) and also larger variations for uniform inserts.

Spatial resolution is similar for the three scanners. The twin-beam is able to derive ρ_e and Z_eff , but with inferior accuracy compared to both dual-source scanners.