Spectral performance of two split‐filter dual‐energy CT systems: A phantom study

Abstract

AbstractBackgroundRecently, a second generation of split filter dual‐energy CT (SFCT) platform has been developed. The thicknesses of the gold and tin filters used to obtain both low‐ and high‐energy spectra have been changed. These differences in filter thickness may affect the spectral separation between the two spectra and thus the quality of spectral images.PurposeTo compare the spectral performance of two Split‐Filter Dual‐Energy CT systems (SFCT‐1st and SFCT‐2nd) on virtual monoenergetic images (VMIs) and iodine map.MethodsA Multi‐Energy CT phantom was scanned on two SFCT with a tube voltage of 120 kVp for both systems (SFCT‐1st‐120 and SFCT‐2nd‐120) and 140 kVp only for the second generation (SFCT‐2nd‐140). Acquisitions were performed on the phantom with a CTDIvol close to 11 mGy. Noise power spectrum (NPS) and task‐based transfer function (TTF) were evaluated on VMIs from 40 to 70 keV. A detectability index (d’) was computed to assess the detection of two contrast‐enhanced lesions on VMIs. Hounsfield Unit (HU) accuracy was assessed on VMIs and the accuracy of iodine concentration was assessed on iodine maps.ResultsFor all keV, noise magnitude values were lower with the SFCT‐2nd‐120 than with the SFCT‐1st‐120 (on average: ‐22.5 ± 2.9%) and higher with the SFCT‐2nd‐140 than with the SFCT‐2nd‐120 (on average: 25.0 ± 6.2%). Average NPS spatial frequencies (fav) were lower with the SFCT‐1st‐120 than with the SFCT‐2nd‐120 (‐6.0 ± 0.5%) and the SFCT‐2nd‐140 (‐3.6 ± 1.6%). Similar TTF50% values were found for both systems and both kVp for blood and iodine inserts at 2 mg/mL (0.29 ± 0.01 mm−1) and at 4 mg/mL (0.31 ± 0.01 mm−1). d’ values peaked at 40 keV for the SFCT‐2nd and at 70 keV for the SFCT‐1st. Highest d’ values were found for the SFCT‐2nd‐120 for both simulated lesions. Accuracy of HU values and iodine concentration was higher with the SFCT‐2nd than with the SFCT 1st.ConclusionCompared to the SFCT‐1st, with similar spatial resolution and noise texture values, the SFCT‐2nd‐120 exhibited the lowest values for noise magnitude, the highest detectability index values, and more accurate HU values and iodine concentrations.