Room: Room 202
Purpose: Virtual non-contrast (VNC) and iodine imaging from contrast-enhanced dual-energy (DE) CT provide potentials for dose reduction. Dose partitioning between the low- and high-kV scans affects the quality of DE images. This study aimed to investigate the optimal DE dose partitioning for VNC and iodine imaging.
Methods: Three semi-anthropomorphic phantoms (25cm, 35cm and 45cm wide) containing test objects with known iodine concentrations were scanned on a dual-source 192-slice CT scanner (Siemens SOMATOM Force), each with 3 DE kV combinations--80/150Sn, 90/150Sn and 100/150Sn (Sn: added tin filter). For each kV combination, 5 different dose partitioning ratios were used, with the dose percent for the low-energy scan being 30%, 40%, 50%, 60% and 70% of the total. The total CTDIvol for the three phantoms was 2.7, 9.2 and 19.8 mGy, respectively. Basis material decomposition was performed to generate the VNC and iodine images using a customized MATLAB program without additional noise reduction. Noise levels on 10 contiguous VNC and 10 iodine images were measured and averaged. Normalized noise levels were also calculated for the combined VNC and iodine task.
Results: Noise levels were shown for the combinations of three kV selections, five dose partitions and three phantom sizes. Using clinical kV selections for different phantom sizes, the optimal dose partitioning for VNC was 30%, 40% and 50% for 25, 35 and 45 cm object size, respectively. For iodine imaging it was 40%, 60% and 60% for the 25, 35, and 45 cm size, respectively. When both VNC and iodine imaging are of clinical interest, 40%, 40% and 50% was the optimal partitioning for the 25, 35, and 45 cm size, respectively.
Conclusion: The optimal dose partitioning for DE CT scans depends on the clinical task, i.e. VNC or iodine map or both tasks, as well as kV combinations and phantom size.
Funding Support, Disclosures, and Conflict of Interest: Cynthia McCollough receives grant support from Siemens Healthcare