| Objective:To explore the application of spectral CT optimal monochromatic imaging combined with adaptive iterative reconstruction(ASIR)and adaptive iterative reconstruction-V(ASIR-V)to optimize the image quality in the arterial phase of chest enhanced CT scan.Methods:From October 2017 to June 2018,A total of 62 patients who underwent contrastenhanced chest CT examination using spectral CT were included(38 men and 24women).The age ranged from 33 to 72 years old,with the mean of 54±7.2 years.Exclusion criteria were as follows:(I)there were other beam-hardening artifacts caused by metal material in Mediastinal region;(II)Mediastinal struction with obvious mass were not clear enough to assess the image quality.All examinations were carried out on a 64-row multi-detector CT system(Discovery CT 750 HD;GE Healthcare,Milwaukee,WI,USA).Detailed GSI parameters were set by the manufacture and were as follows: tube voltage,fast k Vp switching between 80 and 140 k Vp(0.5 ms);tube current,260 m As;thickness,5.00mm;pitch,1.375:1;rotation time,0.8s/rot;scanning field of view(FOV),apex to the bottom of the lung at the end of inspiration;and displayed FOV,36×36cm.The nonionic contrast media(Omnipaque 300 g I/100 m L,GE Healthcare,USA)at the dose of 1.2m L/kg was injected into the right(n =49)or left antecubital vein(n =13)using a power injector at a rate of 3.0m L/s.This was followed by 20 m L saline flushing at a rate of 3.0 m L/s.The arterial and venous phases were obtained at 25 to 30 seconds and 60 to 75 seconds after the injection of the contrast medium.12 sets of the arterial phase Images were acquired using gemstone spectral imaging(GSI)mode in 62 adult patients who underwent chest enhanced CT scan.They included 1set of 140 k Vp polychromatic images(QC)and 11 sets of monochromatic images in 40-140 ke V.The contrast-to-noise ratio(CNR)、beam-hardening artifact(BHA)of 12 sets of images were statistically analyzed with ANOVA and subjective scores were statistically analyzed with Rank Sum Test.Then the optimal monochromatic images with smaller artifacts and higher image quality were obtained.The optimal monochromatic images were acquired by reconstructed with ASIR and ASIR-V at 30%,50% and 70% levels respectively.6 sets of images were obtained and compared with QC and that monochromatic image under traditional reconstructed modes(FBP)with the same statistical methods as before.Results:In FBP mode,The CNR of 80 ke V images was 7.7±2.0,and it had no significant difference with QC images(P>0.05).The BHA in blood vessels was 44.4±22.0,which was lower than QC images(P<0.05).The subjective image quality score of 80 ke V images was 4.50±0.621.There was no significant difference with QC images(P>0.05),and subjective score of artifact was 2.45±0.619,which was lower than QC images(P<0.05).80 ke V group had lower artifact level and higher image quality.So 80 ke V was choosed as the optimal monochromatic energy to be reconstructed with ASIR and ASIR-V.The CNR of 80 ke V +50% ASIR-V group was 13.9±4.3,which was higher than those of140 k Vp and 80 ke V images in FBP(P < 0.05).And their BHA in soft tissue and blood vessels had no significant differences with QC images(P>0.05).The subjective score was4.90±0.298,which was higher than that of other groups(P < 0.05).Conclusions:Comparing with conventional chest contrast-enhanced CT images in arterial phase,80 ke V+50% ASIR-V images can effectively eliminate the beam-hardening artifact and improve image quality.This mode can be used in routine enhanced CT examination. |
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