Optimization of Dual-energy Spectral Lower-extremity Computed Tomography Venography Scanning Protocol:Phantom Study

WANG Shigeng; PU Renwang; LIU Yijun; FANG Xin; WEI Wei; LI Beibei

doi:10.15953/j.ctta.2024.117

Abstract：Objective:To optimize a scanning protocol for dual-energy spectral lower-extremity computed tomography venography(CTV)based on a phantom study.Methods:Test plugs were placed in the cavities of an energy CT quality-control phantom to simulate clinical scenarios.A 4 mgI/mL iodine rod was used to mimic venous enhancement in the lower extremities,and duck blood clots of various sizes were placed in test tubes containing 4 mgI/mL of iodine solution to simulate thrombi of different sizes in the lower-extremity veins.Revolution CT was used to perform standard CT imaging(Group A)and spectral imaging(Group B)on phantoms containing iodine rods and test tubes.The imaging parameters for Group A were as follows:tube voltage of 120 kVp,auto tube-current technology(100～600 mA),noise index(NI)of 10,and image reconstruction using 40%posterior multimodel adaptive statistical iterative reconstruction(ASIR-V).The imaging parameters for Group B were spectral imaging(GSI)mode,instantaneous dual tube voltage of 80/140 kVp,tube current with GSI Assist technology,and three scan groups based on NI values of 10,11,and 12.For each scan group,monoenergetic images at 40～70 keV with 10 keV intervals were reconstructed,each combined with 40%,60%,and 80%posterior ASIR-V,which resulted in 36 image sets.Other imaging parameters for Groups A and B were consistent.The effective radiation doses(ED)for Groups A and B were recorded after scanning,and the contrast-to-noise ratio(CNR)of the iodine rods was calculated.Subjective image quality and true-and false-positive rates for thrombus identification were assessed.Results:The EDs for Group B,with NI values of 11 and 12,were 21.5%and 32.2%lower than those for Group A,respectively.In Group B,for the scan groups with NI values of 10 and 11,except for the images at 70 keV combined with 40%ASIR-V and at 60 keV combined with 40%ASIR-V,the CNR of the iodine rods was higher than that in Group A.The highest edge-sharpness scores for the iodine rods in Group B were observed in the scan group with an NI value of 10 for images at 50 keV combined with 40%and 60%ASIR-V,and in the scan group with an NI value of 11 for images at 50 keV combined with 60%ASIR-V.These three image sets scored 5(4,5)compared with Group A's score of 3(3,4).The true-and false-positive rates for large-thrombus identification in Group A were 65.0%and 30.0%,respectively,whereas those for small-thrombus identification were 55.0%and 50.0%,respectively.In Group B,the best thrombus-identification efficacy was observed in the scan groups,with NI values of 10 and 11 for images at 50 keV combined with 60%ASIR-V.The true-and false-positive rates for large-thrombus identification were 90.0%and 5.0%,respectively,whereas those for small-thrombus identification were 80.0%and 5.0%,respectively.Conclusions:Setting the NI to 11 and reconstructing monoener-getic images at 50 keV combined with 60%ASIR-V is the optimal imaging strategy for dual-energy spectral lower-extremity CTV,which balances between image quality and radiation dose in the current phantom study.