Purpose: The Dual-Energy CT (DECT) LiverVNC application class in the Siemens Syngo software has been used to perform non-iodine material decompositions. However, the LiverVNC application is designed with an optional size-specific calibration based on iodine measurements. The purpose of this work was to investigate the effects of this iodine-based size-specific calibration on non-iodine material decomposition and to benchmark alternative methods for size-specific calibrations in Syngo.
Methods: Calcium quantification was performed with TwinBeam and DualSpiral DECT techniques on the Siemens SOMATOM Definition Edge CT scanner. Images were acquired of the Gammex Multi-Energy CT abdomen and head phantom containing calcium inserts with concentrations ranging from 0â€“300 mgCa/ml. Several workflows in Syngo were explored investigating the effects of size-specific dual-energy ratios (DERs) and the Beam Hardening Correction (BHC) function in the LiverVNC application, which utilizes an iodine-specific size correction during material decomposition. Effects of image noise were also investigated by varying CTDIvol and using iterative reconstruction (ADMIRE).
Results: With the default BHC activated, Syngo underestimated the calcium concentrations, leaving residual calcium in the noncontrast images for all DERs. With the BHC inactivated, the use of a single DER led to either an under- or overestimate of calcium concentration depending on phantom size and DECT modality. Optimal results were found with BHC inactivated using size-specific DERs. The incorrect combinations of BHC activation, DERs and calibration curves led to errors in excess of 30% and 150% for DualSpiral and TwinBeam, respectively. CTDIvol levels and ADMIRE had no significant effect on results.
Conclusion: When performing non-iodine material decomposition in the LiverVNC application class in Syngo it is important to understand the implications of the BHC function and to account for patient size appropriately. Inactivating the BHC function and using size-specific DERs provided the most accurate calcium quantification. This workflow can be applied for other non-iodine materials.