Precision of the measurement of CT numbers: comparison of dual-energy CT spectral imaging with fast kVp switching and conventional CT with phantoms.

PURPOSE: To compare dual-energy computed tomography (CT) spectral imaging and conventional CT imaging in terms of precision of the measurement of CT numbers in phantoms. MATERIALS AND METHODS: A circular phantom (CP) and an elliptical phantom (EP) were used. Capsules filled with iodine contrast media solutions at various concentration levels were placed in the phantoms. Conventional CT was performed at a tube voltage of 120 kVp. Simulated monochromatic images at 65 keV were obtained by dual-energy CT spectral imaging. The CT number of each iodine capsule was measured. A linear regression model was used to evaluate linearity, while analysis of covariance was used to investigate the degree of variability according to phantom shape for each imaging method. RESULTS: With conventional imaging, the slopes of the regression lines for CT numbers measured at the EP center and EP periphery were significantly lower than those measured for CP (P < 0.0001 for both EP center vs. CP and for EP periphery vs. CP). No significant difference in slope was found among phantom shapes in dual-energy spectral CT imaging. CONCLUSION: Computed tomography numbers varied considerably depending on the phantom shape in conventional CT, whereas dual-energy CT provided consistent CT numbers regardless of the phantom shape.