Dual-source dual-energy CT with additional tin filtration: Dose and image quality evaluation in phantoms and in vivo

OBJECTIVE. The objective of this study was to investigate the effect on radiation dose and image quality of the use of additional spectral filtration for dual-energy CT using dual-source CT (DSCT). MATERIALS AND METHODS. A commercial DSCT scanner was modified by adding tin filtration to the high-kV tube, and radiation output and noise were measured in water phantoms. Dose values for equivalent image noise were compared between the dual-energy mode with and without tin filtration and the single-energy mode. To evaluate dual-energy CT material discrimination, the material-specific dual-energy ratio for calcium and that for iodine were determined using images of anthropomorphic phantoms. Data were additionally acquired from imaging a 38-kg pig and an 87-kg pig, and the noise of the linearly mixed images and virtual noncontrast images was compared between dual-energy modes. Finally, abdominal dual-energy CT images of two patients of similar sizes undergoing clinically indicated CT were compared. RESULTS. Adding tin filtration to the high-kV tube improved the dual-energy contrast between iodine and calcium as much as 290%. Data from our animal study showed that tin filtration had no effect on noise in the dual-energy CT mixed images but decreased noise by as much as 30% in the virtual noncontrast images. Virtual noncontrast images of patients acquired using 100 and 140 kV with added tin filtration had improved image quality relative to those generated using 80 and 140 kV without tin filtration. CONCLUSION. Tin filtration of the high-kV tube of a DSCT scanner increases the ability of dual-energy CT to discriminate between calcium and iodine without increasing dose relative to single-energy CT. Furthermore, the use of 100- and 140-kV tube potentials allows improved dual-energy CT imaging of large patients.