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

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

METHODS: 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 ρe and Zeff , whereas iodine and calcium inserts were used to quantify Contrast-to-Noise-Ratio (CNR). Spatial resolution in tomographic images was also tested.

RESULTS: 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 ρe and Zeff close to the reference values (errors within 1.2% for ρe and 6.2% for Zeff for a dose of 20 mGy, excluding lung substitute tissues). The twin-beam scanner presented overall higher errors (within 3.2% for ρe and 28% for Zeff , also excluding lung inserts) and also larger variations for uniform inserts.

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