Application Of Dual-source CT Dual-energy Pulmonary Angiography With Low-dose Contrast Agent And Low Radiation Dose

With high scanning speed and accurate diagnostic results,multi-slice spiral CT is important for emergency patients.Multi-slice spiral CT pulmonary angiography has become the first-line imaging diagnostic method for pulmonary embolism.With the application of CT examination technology,it has become the main source of iatrogenic radiation,and contrast nephropathy is the third major cause of hospital acquired nephropathy.ALARA(as low as reasonably achievable)principle,that is,radiation protection optimization,has been treated as the main principle of radiation protection in CT examination.Considering the economic and social factors,the individual dose,the number of people exposed and the possibility of exposure are kept as low as reasonably possible.Therefore,in order to maintain the image quality for diagnosis,we should try to reduce the dose of radiation and iodine contrast agent.In recent years,dual source CT has been widely used in clinic.We can not only obtain low kVp,high kVp,linear blending,Non-linear blending images,but also obtain keV images at different levels with dual energy CT imaging.With the advent of third generation of Siemens dual source CT,the performance of hardware was further improved.More mature dual energy CT imaging technology can be applied to more inspections with lower radiation dosage.The purpose of this paper is to evaluate the quality of images in the third generation dual energy CT pulmonary angiography with low-dose contrast agent and low radiation dose,and to explore different scanning parameters and post-processing methods.Part Ⅰ Evaluation of Advanced Virtual Monoenergetic Technique in Dual-source Dual-energy Pulmonary CT AngiographyObjective:Compare the CT value,SD value,signal to noise ratio(SNR)and contrast to noise ratio(CNR)of 40+ keV,50+keV,60+keV images of DE-CTPA.To evaluate the ability of advanced virtual monoenergetic technique(VMI+)to improve the display of pulmonary arteries.Methods:Thirty cases whose CT values in pulmonary artery and its branches lower than 300 HU in linear blending images while image quality was poor in distal branches were included in this study.All patients underwent dual-source dual-energy(100 kV/Sn140 kV)CT pulmonary angiography(CTPA)with small amount of contrast medium(30 ml)from February 2017 to May 2018.Non-linear blending images were classified in group 1,100 kVp images from one tube were group 2,and low VMI+images(40+keV,50+keV,60+keV)were group 3,4 and 5 respectively.CT and SD values of segmental,subsegmental and distal branches were measured and SNR,CNR were calculated.Two readers evaluated the quality of images.The inter-reader agreement was performed by Kappa test.Results:Among all the 5 groups,CT values of pulmonary artery of group 3,4,5 were higher than group 1 and 2(P<0.05).SD values of pulmonary artery of group 3 were higher than other 4 groups(P<0.05).SNR of segmental artery in group 3 were higher than group 1(P<0.05).SNR of subsegmental artery in group 3 and 4 were higher than group 1(P<0.05).SNR of segmental and subsegmental pulmonary artery in group 3,4 and 5 were higher than group 2(P<0.05).Compared with group 1,the difference of SNR of distal branches among group 3,4 and 5 was not significant(P>0.05);SNR in group 3,4,5 were higher than group 2(P<0.05).CNR were not significantly different between group 3,4,5 and group 1(P>0.05),and higher than group 2(P<0.05).The effective dose was 3.09 mSv.The two readers had good consistency in evaluating image quality(Kappa value>0.75,P<0.05).Conclusion:Low VMI+ images can effectively improve CT values of pulmonary arteries and display the distal branches better with DE-CTPA,image quality of low VMI+ images is comparable with non-linear blending images,better than low tube voltage(100 kVp)images.SNR and CNR values of 40+keV are better than 50+keV,60+keV and may be first-chosen.Part Ⅱ Application of Dual-energy CT(70 kV/sn150 kV)Pulmonary Angiography Combined with Advanced Modeled Iterative Reconstruction in Normal BMIsObjective:To evaluate the quality of ADMIRE combined with 70kVp,non-linear blending,40+keV,50+keV,60+keV images in dual-energy CT(70 kV/sn150 kV)pulmonary angiography with low contrast agent dosage in normal BMIs(18.5kg/m2≤BMI<24kg/m2).Methods:Totally 74 cases with normal BMI(18.5kg/m2≤BMI<24kg/m2)underwent DE-CTPA with small amount of contrast medium(30 ml)from June 2017 to October 2019.37 were assigned to protocol Ⅰ(100 kV/sn140 kV),the other half were assigned to protocol Ⅱ(70 kV/sn150 kV).100kVp+SAFIRE(group 1),70kVp+ADMIRE(group 2),non-linear blending(group 3),40+keV(group 4),50+keV(group 5),60+keV(group 6)images were 6 groups.CT and SD value and SNR,CNR of pulmonary trunk artery,left pulmonary artery and left superior pulmonary artery were compared.CT dose index volume(CTDIvol),dose-length production(DLP),effective dose(ED)were recorded.Two readers evaluated the quality of images.The inter-reader agreement was performed by Kappa test.Results:CT values of group 1 were lower than orther 5 groups(P<0.05).CT values of group 4 were higher than 5groups(P<0.05).In 6 groups,SD values of group 4 were highest(P<0.05).SD values were no significant difference between group3,6 and 1(P>0.05),that were higher than group2,5(P<0.05).SNR and CNR in group 2、3、4、5、6 were no statistical difference(P>0.05),but they were higher than group 1(P<0.05).The effective dose of protocol Ⅰ and protocol Ⅱ were 3.11 mSv,1.67 mSv respectively.EDs(effective doses)of protocol Ⅱ was 46.3%lower than protocol Ⅰ.The two readers had good consistency in evaluating image quality(Kappa value>0.75,P<0.05).Conclusion:70kVp combined with ADMIRE,non-linear blending,40+keV,50+keV,60+keV images are better than 100kVp combined with SAFIRE images in normal BMIs(18.5kg/m2≤BMI<24kg/m2),and radiation dose was reduced.70 kV/sn150 kV with small amount of contrast medium(30 ml)is a feasible scanning protocol.PartⅢ Comparative Study on Image Quality of DE-CTPA Using A 70 kV/sn150 kV Model Combined with Advanced Modeled Iterative Reconstruction Method with Low-dose Contrast Agent in Overweight and Obese PatientsObjective:To evaluate the quality of 70 kVp combined with ADMIRE and non-linear blending and 40+keV images in dual-energy CT(70 kV/sn150 kV)pulmonary angiography with low-dose contrast agent for overweight and obese patients.Methods:A total of 88 patients were identified using DE-CTPA from July 2017 to December 2019.34 patients with normal BMI(Body Mass Index)and 27 overweight patients and 27 obese patients were examined using 70kV/sn150kV with 30ml contrast agent.CT value,SD value,SNR value,CNR value of pulmonary artery trunk,left pulmonary artery trunk,left superior lobar artery,segmental artery and sub-segmental artery and the radiation dose parameters were compared among 70 kVp+ADMIRE(groups 1,4,7),non-linear blending(groups2,5,8),40+keV images(groups 3,6,9).One way ANOVA and Kruskal-Wallis test were used.Two readers evaluated the quality of images.The inter-reader agreement was performed by Kappa test.Results:CT values of groups 3,6 and 9 were higher than those of the other 6 groups(P<0.05),and there was no significant difference among three groups(P>0.05).There was no significant difference in CT values of 70kvp and non-linear images among normal BMI,overweight and obese patients(P>0.05).SD values of segmental arteries in group 3 and 9 were higher than those in group 1,2,4,5,7 and 8,those in group 6 were higher than group 4 and 5,and those in group 5 were lower than groups 1 and 7,the differences were statistically significant(P<0.05).SD values of subsegmental arteries in group 3,6 and 9 were higher than those in group 1,2,5,7 and 8(P<0.05),and there was no significant difference between group 4 and other 8 groups(P>0.05).SD values of pulmonary artery trunk,left pulmonary artery trunk and lobar artery in groups 3,6 and 9 were higher than those in the other 6 groups(P<0.05),and there was no significant difference among three groups(P>0.05).There was no significant difference in SD values of 70kvp,pulmonary artery trunk,left pulmonary artery trunk and lobar artery in normal BMI,overweight and obese patients(P>0.05).There was no significant difference in SNR and CNR values among the pulmonary artery trunk,lobar artery,segmental artery and subsegmental artery in 9 groups(P>0.05).SNR and CNR values of left pulmonary artery in group 2 were higher than those in group 7(P<0.05),and there was no significant difference among the other 8 groups(P>0.05).The EDs(effective doses)of normal BMI,overweight and obese patients were 1.51mSv,1.74mSv,2.22mSv respectively.The two readers had good consistency in evaluating image quality(Kappa value>0.75,P<0.05).Conclusion:For patients with overweight and obese patients,using ADMIRE in conjunction with 70 kV/150 kV scanning mode with small amount of contrast medium(30 ml)on the third generation dual-source CTPA results in diagnostic image quality and significantly reduced radiation dose and contrast material dose.It was initially confirmed to be suitable for patients with BMI≥24kg/m2.