Spectral material characterization with dual-energy CT: comparison of commercial and investigative technologies in phantoms

Background: Dual-energy computed tomography (DECT) enables tissue discrimination based on the X-ray attenuations at different photon energies emitted by the tube. The spectral dependencies of net X-ray attenuation can be analyzed and used to characterize specific materials. Purpose: To evaluate the capability of DECT to characterize and differentiate high-density materials, using spectral analysis. Material and Methods: Images of phantoms containing iodine, barium, gadolinium, and calcium solutions in five concentrations were obtained from three DECT scanners and with sequential scanning at different kV values from three conventional MDCT devices. DECT studies were performed with commercial dual-source and rapid kV-switching systems, and a spectral-detector CT (SDCT) prototype based on dual-layer detector technology. Spectral maps describing Hounsfield Units (HU) in low-versus high-energy images were calculated and characterizing curves for all materials were compared. Results: Spectral low-to-high energy maps yielded linear curves (R-2 = 0.98-0.999) with increasing slopes for calcium, gadolinium, barium, and iodine, respectively. Slope differences between all material pairs were highest (reaching 45%) for DECT with dual-source (140/80 kV) and rapid kV-switching (60/80 keV), reaching statistical significance (P < 0.05) with most techniques. Slope differences between all material pairs for sequential scanning were lower (reaching 32%). Slope differences lacked statistical significance for iodine-barium with two sequential-acquisition techniques and the dual-source DECT scanner, and the calcium-gadolium pair with the dual-source scanner. Conclusion: All designated techniques for dual-energy scanning provide robust and material-specific spectral characterization and differentiation of barium, iodine, calcium, and gadolinium, though to varying degrees.