Low Tube Voltage,contrast Medium Volume And Flow Rate Protocol In 3^rd Generation Dual-source CT Coronary Angiography: Initial Exploration

Background and Objective: CT coronary angiography(CTCA)has been used as an irreplaceable noninvasive imaging modality in detecting and excluding coronary artery disease.However,the ionizing radiation injury and iodine-induced nephrosis resulting from CTCA are not negligible.How to decrease radiation dose and volume of contrast medium(CM)required has become a focus of study.With increasingly improvement in CT technology,various high-end CT equipments have been introduced clinically,especially with the birth of the 3rd dual source CT(DSCT),which achieving substantial reduction in radiation exposure and CM volume while maintaining diagnostic image quality.The aim of the current study was to assess the feasibility and clinical value of prospectively ECG-triggered high-pitch CTCA using a 3rd generation DSCT with 20 mL low CM and 3.0mL/s low flow rate at 70 kVp.Methods and Materials:(1)Sixty-eight patients with body mass index(BMI)?30.0 kg/m2,heart rate(HR)?75 beats per minute(bpm)underwent high pitch CTCA on a 3rd generation DSCT at 70 kVp.The CM injection protocol was set as 20 mL of 370 mg I/m L iodinated contrast material with a flow rate of 3.0 m L/s.Automated tube current modulation(CAREDose4D,Siemens)was applied to the study.All the original imaging data were reconstructed with advanced modeled iterative reconstruction(ADMIRE).Image quality was objectively evaluated by CT parameters of CT attenuation,noise,SNR and CNR as well as subjectively evaluated using a four-point scale(1=excellent to 4=non-diagnostic).Radiation dose was recorded and compared for each patient.Image quality parameters of the overweight group(BMI<25 kg/m2)and non-overweight group(BMI?25 kg/m2)were compared by using One-Way ANOVA.(2)One-hundred and fourteen patients with BMI?30.0 kg/m2 and HR?75bpm underwent prospectively ECG-triggered high-pitch CTCA on a 3rd generation DSCT.All patients were divided into 2 groups according to tube voltage and CM injection protocol: Group A(80 kVp,n=48),the volume of CM was 40 ml and the flow rate of CM was 4.0 mL/s;Group B(70 kVp,n=66),the volume of CM was 20 ml and the flow rate of CM was 3.0 mL/s.Group A and group B were further diveided into 2 subgroups respectively according to BMI:non-overweight subgroup with BMI<25kg/m2 and overweight subgroup with BMI?25kg/m2.Image quality was evaluated and compared between the two groups.Effective dose(ED)and size-specifc dose estimate(SSDE)were calculated and compared.Differences in subjective and objective parameters and radiation dose were tested between the two groups by using the t-test for independent samples and Mann-Whitney U test.Interobserver variability between the two readers with regard to subjective image quality assessment was evaluated with ? statistics.Image quality parameters of the four subgroups(Aoverweight group?Anon-overweight group?Boverweight group and Bnon-overweight group)were compared by using One-Way ANOVA and LSD pair comparison.P<0.05 was considered statistically significant.Results:(1)Among the total 68 patients,66 patients(97.1 %)had diagnostic quality images and two patients(2.9 %)had one vessel graded as “unevaluable” resulting in overall poor image quality because of motion artifacts.All coronary artery CT values in CTCA images of these patients reached diagnostically sufficient attenuation threshold value of 325HU(461±92 HU).Significant effect of BMI(BMI<25kg/m2 and BMI?25kg/m2)on CTCA objective image quality with regard to SNR and CNR were observed(P<0.05),and moderate correlation between BMI and noise was showed(r2=0.403,P<0.001).ED was 0.33±0.04 mSv and the SSDE was 2.46±0.36 mGy.(2)Image noise was significantly higher in B group than A group.However,the intraluminal CT attenuation was significantly higher in B group than A group(both P <0.05).There was no significant difference in SNRs and CNRs between the two groups(both P>0.05).Subjective image quality evaluation showed no significant difference between the two groups(P > 0.05).Within the two goups,the overweight subgroup had significantly higher noise than non-overweight subgroup(both P<0.05)and there was no significant difference in intraluminal CT attenuation between the two subgroups(all P > 0.05)while SNRs and CNRs were significantly lower in the overweight subgroup than non-overweight subgroup(all P <0.05).Additionally,Boverweight group had significantly higher noise than Aoverweight group(P=0.002)and the two subgroups of B group showed significantly higher intraluminal CT value in aorta,LM and LAD(all P<0.05).There was no significant difference in SNRs and CNRs between Aoverweight subgroup and Boverweight subgroup(all P>0.05).Compared with the A group,the ED of the B group was reduced by 40%.Conclusion:With 3rd generation DSCT,prospectively ECG-triggered high-pitch CTCA 70 kVp acquisition mode with 20 mL low CM volume and 3.0mL/s low CM flow rate results in robust image quality,and the reduction of radiation dose,CM volume and flow rate was significant compared to the 80 kVp protocol.