Objective To compare the image quality and patient radiation dose of coronary computed tomography angiography (CCTA) received by prospectively-gated step-and-shoot (SAS) technique with those obtained by retrospectively-gated spiral (RGS) technique on a 256-slice CT scanner. Methods A total of 200 patients were enrolled in this study. One hundred patients underwent CCTA with SAS mode were subdivided into two groups: ( 1 ) 50 patients with an average heart rate (HR) ≤70 bpm were scanned with a data acquisition time window centered at the 75％ of the R-R cycle ( group A) and (2) 50 patients with HR ＞ 70 bpm were scanned with the data acquisition time window centered at the 45％ of the R-R cycle, including a phase tolerance of ±％ (group B). Other 100 patients underwent CCTA with RGS mode and ECG-based tube current modulation were also subdivided into two groups: (3) 50 patients with HR ≤70 bpm were scanned with cardiac dose right set to phase of 75％ (group C) and (4) 50 patients with HR ＞ 70 bpm were scanned with cardiac ose Rdight set to phases of 45％ and 75％ (group D). All patients were grouped in randomized order. The image quality of CCTA were evaluated using a rank scale from 1 to 4 ( 1 : excellent ; 4 : non-assessable ) .Radiation dose of the four groups received was also estimated. The image quality between groups was compared by Mann-Whitney U test.The radiation dose between groups was compared by t test. For the 100 patients received by prospective ECG-gated CCTA, the receiver operating characteristic curve (ROC) was used to analyze the CCTA image quality and average heart rate to determine the uppercutoff of HR for obtaining diagnostic coronary images with SAS mode. A spearman correlation analysis was also performed to analyze the correlation of HR and image quality in patients underwent CCTA with SAS mode.Results Of 2338 coronary artery segments, excellent or good image quality( score of 1 or 2) was achieved in 96. 5％ (585 of 606) in group A, 77.7％ (445 of 573 ) in B,96. 1％ (548 of 570) in C, and 85. 7％ (505/589) in D, with no significant difference for A vs C(Z ＝- 1. 351 ,P ＞0. 05) and with significant differenceS for B vs D (Z＝ -2. 236,P ＜0. 05). Linear correlation analysis indicated a significant degradation of image quality with the increase of heart rate using SAS mode (Spearman correlation, r ＝ 0. 577, P ＜0. 01 ). ROC analysis established an upper HR threshold of 78 bpm for obtaining diagnostic image quality using SAS mode( AUC ＝ 0. 827, P ＜ 0. 05 ). The average radiation dose in group A [ ( 2. 6 ± 0. 5 ) mSv]reduced 75 ％ comparing with that in group C [ ( 10. 6 ± 2. 3 ) mSy], and the average radiation dose in group B [ ( 4.0 ± 0. 7 ) mSy]reduced 69％ comparing with that in group D [ ( 13.0 ± 1. 4) mSv]. ConclusionUsing SAS mode to perform low-dose CCTA with 256-slice helical CT could keep the image quality and reduce radiation dose significantly. Our preliminary experience suggests a good promise of this technique which could be applied to a wider group of patients such as with higher heart rates.

Objective To investigate image quality and radiation dose of prospective ECG-gated coronary combined with carotid and cerebrovascular angiography and compare it with common coronary CTA and carotid-cerebrovascular CTA at a 256-slice spiral CT.Methods Fifty-seven patients were included in the study.The data was analyzed retrospectively and divided into 3 groups.Group 1 underwent coronary combined with carotid CTA ( n =17 ),which included a wide range of prospective ECG-gated coronary,carotid and cerebral vascular one-stop angiography.Group 2 underwent coronary CTA ( n =20),which was routine prospective ECG-gated coronary angiography.Group 3 underwent routine carotid and cerebrovascular CTA (n =20).Mean CT image attenuation and image noise were measured in the ascending aorta root,proximal parts of the bilateral common carotid artery and vertebral artery,and in the internal carotid artery at sellae level in the axial plane.Coronary artery image quality was rated using a four-point ordinal scale and carotid cerebral vascular image quality was rated using a three-point ordinal scale.Radiation dose were calculated.Mean CT image attenuation,image noise and radiation dose were compared among the 3 groups using t test.Using Mann-Whitney U,the coronary artery imaging quality was compared between group 1 and 2,and image quality of cerebral vessels was compared between group 1 and 3.Results Mean CT image attenuation [ (427 ±50) HU in group 1 and (426 ±86) HU in group 2] and image noise of the ascending aorta root [ (30 ± 9) HU in group 1 and (31 ± 9) HU in group 2 ] showed no statistical difference between group 1 and 2 (t =0.058,-0.325,P ＞0.05).There were no non-diagnosis coronary segments in group 1 and 2.And coronary segments with excellent or good image quality reached 98.1％ (202/206) in group 1 and 99.6％ ( 244/245 ) in group 2.It showed no significant difference between group 1 and 2 ( Z =-0.572,P ＞ 0.05 ).There were significant differences of mean CT image attenuation in the common carotid artery between group 1 [ ( 474 ± 70 ) HU ] and group 3 [ ( 348 ± 81 ) HU ],and in the vertebral artery between group 1 [(447 ±83)HU] and group 3 [(328 +66) HU] (t =5.043,4.869,P＜0.05).However,there was no significant difference of mean CT image attenuation in the internal carotid artery [ (370 ± 92) HU in group 1 and ( 367 ± 97 ) HU in group 3 ] ( t =0.111,P ＞ 0.05 ).There was a significant difference of image quality scores of carotid and cerebrovascular arteries between group 1 and 3 (Z =- 3.306,P ＜ 0.05 ).Effective radiation dose of groups 1,2,3 were ( 7.0 ± 0.8 ),( 3.1 ± 0.4 ) and (5.0 ± 0.3) mSv respectively.Conclusion The prospective ECG-gated coronary combined with carotid and cerebrovascular angiography is able to obtain diagnostic image quality of coronary,carotid and cerebral vascular at the 256-slice spiral CT.It is a simple,fast,noninvasive way to assess coronary and carotid cerebrovascular arteries,with advantages of less contrast medium and low radiation dose.