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Objective@#To analyze the value of combining the virtual monochromatic spectral (VMS) image and adaptive statistical iterative reconstruction V (ASiR-V) in low tube current dual-energy spectral imaging in head CTA, and to explore the optimal VMS and ASiR-V level while reducing the radiation dose.@*Method@#(1) Phantom study: an Anthropomorphic PBU-60 angiographic head phantom was examined on a Revolution CT with spectral imaging mode at two different tube current. Images of different energy levels (at 40, 45, 50, 55, 60, 65 and 70 keV) in A group [the low tube current group (with 280 mA)] were reconstructed with the combination of filtered back projection (FBP), 20%, 40%, 60% and 80% ASiR-V. VMS images at 70 keV in B group [the routine tube current group (with 445 mA)] were reconstructed with FBP only. The standard deviation (SD), signal to noise ratio (SNR) and contrast to noise ratio (CNR) of phantom study were measured and examined by ANOVA variance analysis.(2) Clinical study: to prospectively select 40 patients (randomly divided into A and B groups with 20 patients in each group), the subjective scores of patients were assessed with a 5-point scale system and compared by the Mann-Whitney U test. The radiation dose was recorded and analyzed by t test.@*Results@#(1) Phantom study: there were significant differences in the image noise, CNR of the simulated cerebral vessels at different energy levels of VMS image (P<0.05). VMS images at 40 to 55 keV yielded a higher CNR compared with 70 keV (P<0.05). The SNR and CNR in the low tube current group with ASiR-V 60% and ASiR-V 80% were higher than that of the FBP, ASiR-V 20% and ASiR-V 40% images in the same group (P<0.05). (2) Clinical study: the subjective scores at 55 keV and 60 keV were higher than others (P<0.05). The subject scores of 40,50 and 55 keV were increased as the proportion of ASiR-V increased. (3) The SNR and CNR of the simulated cerebral vessels and subjective scores in of the 55 keV VMS images with ASiR-V 60% and ASiR-V 80% in the low tube current patient group was higher than that of the 70 keV FBP images in the routine tube current group (P<0.05). The radiation dose of A group was lower than B group (t=23.974, P<0.05).@*Conclusions@#VMS images in low tube current spectral imaging combined with ASiR-V can significantly reduce radiation dose and ensure image quality in head CTA. The 55 keV VMS images with ASiR-V60% and 80% provide higher image quality.
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Objective To investigate the value of "one-stop" scanning of coronary and head and neck CTA in patients with normal body mass index (18 kg/m2 ≤ BMI ≤ 25 kg/m2) using low tube voltage (80 kVp).Methods In a retrospective analysis 80 patients with normal body mass index who had completed "one-stop" scanning of coronary and head and neck CTA were divided into A and B groups according to different scanning method,and 40 consecutive cases were selected in each group.Scanning parameters of group A and group B were tube voltage 80 kV,coronary CTA tube current 550 mA,head and neck CTA tube current 500 mA,and tube voltage 100 kV,coronary CTA tube current 450 mA,head and neck CTA tube current 400 mA separately.Subjective evaluation and objective evaluation were performed on the image quality of the two groups.CT values of coronary artery and head and neck CTA trunk branch vessel,contrast-to-noise ratio (CNR),image noise (SD) and effective dose between the two groups were compared.Results The image quality of both groups met the diagnostic requirements,and there was no statistically significant difference in subjective scores between two groups (P＞0.05).The CT values of coronary arteries,the main branches of the head and neck (the common carotid artery,the internal carotid artery) and SD of head and neck CTA were significantly different between two groups (t=4.737,6.552,3.359,2.165,2.685,4.617,P＜0.05).There was no statistically significant difference in SD of coronary CTA,CT values and CNR between head and neck vessels (middle cerebral artery) in group A and group B (P＞0.05).The effective dose of coronary CTA in group A (1.16±0.20) mSy was reduced by 51.1％ than that in group B (2.37±0.77) mSv.The effective dose of head and neck CTA in group A (0.37±0.03) mSv was reduced by 47.9％ than that in group B (0.71 ± 0.17) mSv.Conclusions The image quality with subjective evaluation met the diagnostic requirements when using a low-tube voltage for "one-stop"scanning of coronary and head and neck CTA.The CNR values were basically consistent with the conventional scanning method,and the patient effective dose was reduced by about 50％.