Research On Reducing Radiation Dose And Contrast Medium Volume In Coronary CT Angiography

Objective:To explore the feasibility of reducing radiation dose and dosage of contrast agent in CCTA with 70 kV tube voltage combined with iterative algorithm under prospective ECG-gated high-pitch scanning mode of dual-source CT,and explore the optimal iterative reconstruction level of image.Methods:This study is a prospective study,which is divided into two parts.The latter part is based on the former part.The first part is divided into two groups:A and B.The second part is C and D.A and C are experimental groups.B and D are control groups.All patients were scanned with second generation dual source CT.The first part:90 patients who underwent CCTA examination were divided into two groups,45 in each group(group A and group B).With body mass index(BMI)≤25 kg/m2.Both groups adopted adaptive prospective ECG trigger sequence scanning,group A(experimental group)scanning scheme:fixed tube voltage 70 kV,automatic tube current modulation,reference tube current 500 mAs;contrast medium injection flow rate and capacity were 4.0 ml/s,0.8 ml/Kg;group B(control group)scanning scheme:automatic tube voltage and tube current modulation,reference tube voltage 120 kV,reference tube current 320 mAs;The flow rate and volume of contrast medium were 5.0 ml/s and 1.0 ml/Kg,respectively.The CT value and image noise of right coronary artery(RCA),left main coronary artery(LM),left anterior descending coronary artery(LAD)and left circumflex coronary artery(LCX)were measured.The CT value of subthoracic adipose tissue at the same level was measured,and the image signal-to-noise ratio(SNR)and contrast-to-noise ratio(CNR)were calculated.The volume dose index(CTDIvol)and dose-length multiplication were recorded in both groups.The effective radiation dose(ED)was calculated by product(DLP).The age,sex,BMI,heart rate,actual tube current,image quality and radiation dose were compared between the two groups.Based on the completion of the first part,the second part was carried out.The experimental group of the second part is to change the prospective ECG-gated scanning mode of group A into the prospective ECG-gated high-pitch spiral scanning mode(Flash spiral),that is,group C;group D is the routine scanning group.Ninety patients with body mass index(BMI)less than 25 kg/m2 were examined by CCTA in Guangdong People,s Hospital.Group C:Prospective ECG-gated spiral scan mode with large pitch was adopted,fixed tube voltage 70 kV,automatic tube current modulation,reference tube current 500 mAs;contrast injection scheme was the same as group A.Group D was the same as group B.Group C images were reconstructed by filtered Back Projection(FBP)and iterative reconstruction(IR)SAFIRE 1-SAFIRE 5.Comparing the image quality of each iteration grade and FBP reconstruction in group C,the image quality,image noise,SNR,CNR and radiation dose were compared with group D after the best iteration grade image was obtained,and the general data of patients in two groups were compared.Results:There was no significant difference in age,sex,BMI,heart rate and actual tube current between groups A and B.There was no significant difference in image quality score,image noise between the two groups(P>0.05),There were statistical differences in SNR and CNR of some segments of blood vessels,but the image SNR and CNR of group A were higher than those of group B.The effective radiation dose(0.72±0.22)mSv in group A was significantly lower than that in group B(2.59±1.19)mSv,and the difference was statistically significant(P<0.05).The SAFIRE 3 subjective image quality score in group C was the highest;there was no statistical difference in general data between group C and group D,and there was no statistical difference in image quality score and image noise(P>0.05).There were statistical differences in SNR and CNR in some segments of blood vessels,but SNR and CNR in group C were higher than those in group D.CTDIvol(0.70±0.12)mGy,DLP(12.56±2.37)mGy.cm,ED(0.18±0.33)mSv in group C were significantly lower than those in group D(12.24±6.82)mGy,DLP(158.80±81.57)mGy.cm,ED(2.22± 1.14)mSv.Conclusion:For patients with low and normal body mass index(BMI<25 kg/m2),70 kV tube voltage combined with iterative CCTA under prospective ECG-gated high-pitch scanning mode of dual-source CT can significantly reduce the effective radiation dose(ED<0.3 mSv)and the dosage of contrast agent while obtaining the image quality that meets the requirements of clinical diagnosis.