| Objects: To assess the feasibility of applying low dose contrast media(CM)combined with virtual monoenergetic images(VMI)and explore the optimal VMI in run-off CT angiography(CTA)on dual-layer spectral detector CT among patients with lower extremity arteriosclerosis obliterans.Methods: Patients who were clinically suspected of lower extremity arteriosclerosis obliterans and presented for further treatment were enrolled in the study and randomly assigned into a control group using routine volume CM(group A)and experimental group using half volume CM(group B).In group A and B,120 k Vp polychromatic conventional images(CI)were routinely generated via a hybrid iterative reconstruction algorithm(i Dose 4,level 3),defined as A1 and B1,respectively.Additionally,in group B,VMIs(range,40–120 ke V)at 10 ke V intervals were reconstructed via a spectral reconstruction algorithm(Spectral B,level 3),defined as B2–B10.The vascular attenuation,noise,the signal to noise ratio(SNR),contrast to noise ratio(CNR)and radiation dose of both group were evaluated.Quantitative data are expressed as mean ±SD,and qualitative data are expressed with frequencies.Variables of age,sex,body weight,height,body mass index(BMI),and CT dose index volume,dose length product,and effective dose of groups A and B were compared by independent samples t-test or Chi-square test.Analysis of variance was applied in the analysis of the vascular attenuation,noise,SNR,and CNR of A1 and B1–B10.Furthermore,the Fisher’s least significant difference test or Dunnett’s T3 test was used in post-hoc tests between pairwise comparisons.Image quality scores are expressed as medians with interquartile ranges,and the Kruskal-Wallis test was used in the analysis of image quality scores.A P value <0.05 was deemed statistically significant.Cohen’s kappa test was used to assess interobserver agreement.Results: Forty-two patients were included in the present study,with 21 each in group A and group B(group A: 15 males and 6 females;group B: 16 males and 5 females).The average age was 67.67±6.77 and 70.00±10.32,ranging from 56 to 81 years and 45 to85 years in groups A and B,respectively.Differences in age,sex,height,weight,and BMI between groups A and B were not significant.The radiation dose demonstrated no significant difference between groups A and B(dose length product: 1804.71±516.76 vs1986.19±460.30 m Gy·cm,P=0.237;volume CT dose index: 14.73±3.43 vs 16.05±2.94 m Gy,P=0.190;the effective dose: 10.65±3.05 vs 11.72±2.72 m Sv,P=0.237).The results of objective image quality: the mean vascular attenuation was higher in group B2(40ke V)and was lower in group B3(50 ke V)in comparison with that in group A1(492.09±152.06 vs 415.03±69.91 HU,333.11±98.82 vs 415.03±69.91 HU,P>0.05).The mean noise was similar in group B2(40 ke V)and was lower in group B1 as well as B3-B10(50-120 ke V)compared with that in group A1(15.18±5.70 vs 17.12±4.65 HU,P>0.05;6.79±1.21～11.49±3.47 vs 17.12± 4.65 HU,P<0.05).The mean SNR and CNR in group B2(40 ke V),as well as the mean SNR in group B3(50 ke V),were significantly higher(39.20±7.24 vs 29.33±7.21,33.54±7.58 vs 25.49±6.56,33.45±6.85 vs 29.33±7.21,P<0.05)and the mean CNR in group B3(50 ke V)was similar to that in group A1(27.17±7.10 vs 25.49±6.56,P>0.05).The results of subjective image quality: scores of subjective image quality in group B2(40 ke V)and B3(50 ke V)were similar to those in group A1 [5(4.5,5)vs 5(4,5),5(5,5)vs 5(4,5),P>0.05 ] and showed a declining trend in group B4(60 ke V)[4(4,5)vs 5(4,5),P>0.05].Scores of group B1 and groups B5-B10 were significantly inferior to those of group A1(P<0.05).The interobserver agreement was good to excellent(Kappa values≥0.691).Conclusions: It is feasible to perform run-off CTA using low dose CM with VMI on dual-layer spectral detector CT and VMIs at 40-50 ke V were the recommended choice without compromising image quality. |
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