Technical performance of a dual‐energy CT system with a novel deep‐learning based reconstruction process: Evaluation using an abdomen protocol
Authors: Oostveen Luuk J. , Boedeker Kirsten L. , Balta Christiana , Shin Daniel , de Lange Frank , Prokop Mathias , Sechopoulos Ioannis 
Published: December 2022

Background

A new tube voltage‐switching dual‐energy (DE) CT system using a novel deep‐learning based reconstruction process has been introduced. Characterizing the performance of this DE approach can help demonstrate its benefits and potential drawbacks.

Purpose

To evaluate the technical performance of a novel DECT system and compare it to that of standard single‐kV CT and a rotate/rotate DECT, for abdominal imaging.

Methods

DE and single‐kV images of four different phantoms were acquired on a kV‐switching DECT system, and on a rotate/rotate DECT. The dose for the acquisitions of each phantom was set to that selected for the kV‐switching DE mode by the automatic tube current modulation (ATCM) at manufacturer‐recommended settings. The dose that the ATCM would have selected in single‐kV mode was also recorded. Virtual monochromatic images (VMIs) from 40 to 130 keV, as well as iodine maps, were reconstructed from the DE data. Single‐kV images, acquired at 120 kV, were reconstructed using body hybrid iterative reconstruction. All reconstructions were made at 0.5 mm section thickness. Task transfer functions (TTFs) were determined for a Teflon and LDPE rod. Noise magnitude (SD), and noise power spectrum (NPS) were calculated using 240 and 320 mm diameter water phantoms. Iodine quantification accuracy and contrast‐to‐noise ratios (CNRs) relative to water for 2, 5, 10, and 15 mg I/ml were determined using a multi‐energy CT (MECT) phantom. Low‐contrast visibility was determined and the presence of beam‐hardening artifacts and inhomogeneities were evaluated.

Results

The TTFs of the kV‐switching DE VMIs were higher than that of the single‐kV images for Teflon (20% TTF: 6.8 lp/cm at 40 keV, 6.2 lp/cm for single‐kV), while for LDPE the DE TTFs at 70 keV and above were equivalent or higher than the single‐kV TTF. All TTFs of the kV‐switching DECT were higher than for the rotate/rotate DECT. The SD was lowest in the 70 keV VMI (12.0 HU), which was lower than that of single‐kV (18.3 HU). The average NPS frequency varied between 2.3 lp/cm and 4.2 lp/cm for the kV‐switching VMIs and was 2.2 lp/cm for single‐kV. The error in iodine quantification was at maximum 1 mg I/ml (at 5 mg I/ml). The highest CNR for all iodine concentrations was at 60 keV, 2.5 times higher than the CNR for single‐kV. At 70–90 keV, the number of visible low contrast objects was comparable to that in single‐kV, while other VMIs showed fewer objects. At manufacturer‐recommended ATCM settings, the CTDIvol for the DE acquisitions of the water and MECT phantoms were 12.6 and 15.4 mGy, respectively, and higher than that for single‐kV. The 70 keV VMI had less severe beam hardening artifacts than single‐kV images. Hyper‐ and hypo‐dense blotches may appear in VMIs when object attenuation exceeds manufacturer recommended limits.

Conclusions

At manufacturer‐recommended ATCM settings for abdominal imaging, this DE implementation results in higher CTDIvol compared to single‐kV acquisitions. However, it can create sharper, lower noise VMIs with up to 2.5 times higher iodine CNR compared to single‐kV images acquired at the same dose.