| Objective:1.The purpose of this study was to determine the R-R interval phase with the best image quality of coronary artery in low and high heart rate patients scanned with 2nd generation dual-source CT(2-DSCT).2.To discuss the feasibility of decreasing radiation dose by shortening R-R interval exposure phase and combining low tube voltage and the iterative reconstruction techniques,and prospective ECG-gating on patients with normal body mass index(23kg/m2?BMI?28kg/m2).Materials and Methods:This thesis was divided into two parts.Part ?80 cases of patients who conducted CT angiography of coronary artery from June 2016 to December 2016 in our hospital were selected to be divided into 2 groups,including 40 cases with low heart rate(group1,?70 beats / min)and 40 cases with high heart rate(group2,heart rate > 70 beats / min).In the low heart rate group,there were 23 males(57%)and 17 females(43%)with an age range of 50-88 years old(mean age 66.75 ± 7.35 years old);in the high heart rate group,there were 21 males(53%)and 19 females(47%)with an age range of 48-85 years old(mean age 67.07 ± 6.58 years old).The adaptive prospective ECG-gated sequence scan mode was used in both groups.Time of exposure ranged from 20% to 80% of R-R interval.Reconstruction was performed every 5% intervals.The image quality of right coronary artery(RCA),left anterior descending(LAD),left main coronary artery(LM)and left circumflex branch(CX)at different R-R interval was scored and statistically analyzed,in order to determine the phase with the best image quality in the low and high heart rate groups,as well as the phase which had no statistically significant difference with the best phase.Part ?120 cases of patients who conducted CT angiography of coronary artery from February 2017 to August 2017 were selected(the range of heart rate fluctuation ?5 beats / min)with the body mass index range of 23 kg/m2 to 28 kg /m2.In accordance with the digital table,the patients were randomly divided into three groups of A,B,C,and 40 cases were in each group.In group A,there were 18 males(45%)and 22 females(55%),ranging in age from 53 to 83 years old with a mean age of(65.28 ± 8.22)years old.In group B,there were 20 males(50%)and 20 females(50%),ranging in age from 44 to 84 years old with a mean age of(65.48 ± 10.01)years old.In group C,there were 19 males(48%)and 21 females(52%),ranging in age from 46 to 81 years old with a mean age of(64.40 ± 8.88)years old.The adaptive prospective ECG-gated sequence scan mode was used in three groups of A,B,C.The different R-R interval exposure phase was selected in three groups.In group A,a wide R-R interval was selected for exposure(30%-75% of R-R interval)with the 120 k V tube voltage and reconstruction of conventional filtered back projection(FBP).In group B and C,a narrow R-R interval was selected for exposure(heart rate ?70 beats / min to select 35%-45% of R-R interval,heart rate> 70 beats / min to select 65%-75% of R-R interval).The tube voltage of group B was 120 k V,and group C was 100 k V.Coronary artery images were reconstructed by iteration method in both groups.The subjective and objective scores of coronary artery image quality were recorded,as well as CT dose index volume(CTDIvol),dose-length product(DLP),effective radiation dose(ED),CT value of the region of interest,image noise(SD),signal to noise ratio(SNR)and contrast to noise ratio(CNR).The image quality of coronary arteries in three groups were scored and statistically analyzed.Results:1.The phases with the best image quality of RCA,LM,LAD and CX in low heart rate group(group 1)were all located in 75% of R-R phase,and the phase without statistical difference was in the 70% of R-R phase in comparison with the best phase of RCA and LAD.The phase without statistical difference of LM was in 30%,35%,70% and 80% of R-R phase and that of CX was in 65% and 75% of R-R phase(P <0.05).The phases with the best image quality of RCA,LM,LAD and CX in high heart rate group(group 2)were in 45%,40%,45% and 45% of R-R intervals respectively.The phase without statistical difference of RCA was in 40% of R-R interval,LM was in 35% and 50% of R-R interval,LAD was in 35% and 40% of R-R interval and CX was in 40% of R-R interval(P <0.05).2.The exposure time TI of group A,B and C was(0.55 ± 0.05,0.32 ± 0.05,0.33 ± 0.06)s,respectively.The exposure time TI of group B and group C was significantly shortened.The difference of TI between group B and group A,group C and group A were statistically significant(P <0.05).CT dose index volume CTDIvol of group A,B and C was(34.14 ± 7.69,15.71 ± 2.09,12.19 ± 2.47)m Gy respectively,dose-length product DLP was(368.05 ± 78.00,177.05 ± 29.29,131.84 ± 31.89)m Gy.cm respectively,and effective radiation dose ED was(5.15 ± 1.09,2.48 ± 0.41,1.83 ± 0.44)m Sv respectively.CTDIvol,DLP and ED in group C were significantly decreased.Compared with group A,ED of group B decreased by about 51%,and group C decreased by about 64%;compared with group B,ED of group C decreased by about 25%,all of which were statistically significant(all P < 0.05).The CT value of the region of interest in group C(413.58 ± 30.22HU)was significantly higher than that in group A(333.22 ± 32.22HU)and group B(331.81 ± 34.10HU),and the difference between group C and A,group C and B was statistically significant(P <0.05).The image noise(SD)of group A,B and C was(24.36 ± 3.22,17.77 ± 2.07,22.32 ± 2.56),respectively.The difference of SD among the three groups was statistically significant(P <0.05).The signal to noise ratios(SNR)of group A,B and C were(13.69 ± 2.37,18.94 ± 2.17,18.26 ± 2.63)and the CNR were(17.49 ± 2.82,21.62 ± 3.45,22.95 ± 2.92)respectively.There was no significant difference in SNR and CNR between group B and group C.There was significant difference between group A and group B,group A and group C(P <0.05).The subjective evaluation of image quality of coronary arteries in group A,B and C was not statistically significant(P> 0.05).Conclusion:1.The best exposure phase of coronary CT images in patients with heart rate ?70 beats / min was in the range of 65%-75% of R-R interval,and that in patients with heart rate> 70 beats / min was in the range of 35%-45% of R-R interval.2.In the adaptive prospective ECG-gated sequence scan mode of the 2nd dual-source CT,shortening the R-R interval exposure phase and the combination of the low tube voltage and the iterative reconstruction can effectively reduce the radiation dose,and enable subjective and objective images quality of coronary artery to meet diagnostic requirements. |
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