Objective To explore the role of 256 CT iterative reconstruction in improving image quality and reducing radiation dose of carotid artery into cranial segment.Methods Sixty patients underwent head and neck CTA on a 256 CT scanner.Conventional dose scanning was performed in 30 patients using a filtered back projection (FBP) reconstruction (group A) and iterative iDose4 reconstruction (group B).Low dose scanning was performed in the other 30 patients using FBP reconstruction (group C) and iDose4 reconstruction (group D).The noise,SNR,CNR,score of image quality and effective radiation dose were evaluated in four groups.One-way ANOVA was used to analyze the image quality index between groups.Independent sample of Kruskal-Wallis test of ranked data was used to compare image quality score between groups.Paired t test was used to compare the effective radiation doses between the low dose group and conventional dose group.Results The image noise of four groups were 8.21 ±0.88,7.31 ± 0.33,11.17 ± 2.02 and 6.50 ± 0.49 respectively.SNR were 43.21 ± 4.49,5 1.83 ± 3.64,42.88 ± 9.19 and 53.47 ± 4.88,respectively.CNR were 37.88 ± 4.02,61.21 ± 6.31,36.63 ± 8.20 and 62.99 ±5.90,respectively.There were statistic differences (F =112.786,97.041 and 86.098,P ＜0.01).The differences of image noise between group A and B had no statistic significance,which was statistic different between group A and C (P ＜ 0.01).Except that the differences of SNR and CNR between group A and C,B and D had no statistic significance,the differences between other two groups had statistic significance (P ＜ 0.01).In case of image quality score of 1,2 and 3,there were 2,13 and 15 patients in group A; 0,7 and 23 patients in group B; 5,15 and 10 patients in group C; and 0,5 and 25 patients in group D.There was statistic differences of image quality score between each group (H =22.575,P ＜0.01).The effective radiation dose was (2.31 ±0.13) mSv in conventional dose group and (0.84 ±0.04) mSv in low dose group.There was statistic difference between the two groups (t =60.682,P ＜ 0.05).Conclusion Compared with conventional dose,iDose4 iterative reconstruction algorithms can obtain excellent images of CTA for carotid artery into the cranial segment with more than 50％ radiation dose decrease.