Applied Research Of Low Tube Voltage Combined With Low Dose Contrast Medium In Head And Neck CT Angiography

Purpose To explore the feasibility of low tube voltage and low dose contrast medium in head and neck CT angiography(CTA)by reducing the tube voltage and contrast medium dose during head and neck CT angiography,which is of great significance to reduce the radiation dose and the amount of contrast medium.Materials and methods A total of 120 patients who underwent head and neck CTA examination in Qingdao Municipal Hospital from June 2020 to October 2021 were collected.Inclusion criteria:(1)no serious heart,liver and kidney dysfunction;(2)no previous history of hypersensitivity to iodine contrast agents;(3)no obvious hyperthyroidism;(4)mental and cognitive clarity can cooperate with CTA examination;(5)body mass index(BMI)≤25kg/m~2.Exclusion criteria:(1)patients whose injection rate could not reach 5ml/s,(2)patients with severe vascular stenosis in head and neck.According to the method of random number table,the patients were randomly divided into three groups with 40 cases in each group.Group A was the routine group,the tube voltage was 140k V,test contrast agent dose was 20ml and scanning contrast agent dose was 50ml;group B:the tube voltage was 100k V,test contrast agent dose was 20ml,scan contrast agent dose was 20ml;in group C,the tube voltage was 80k V,and the dose of contrast medium for test and scan was 20ml.After each injection of contrast agent,the three groups were injected with 20ml normal saline,and the injection speed of contrast agent and normal saline was 5ml/s.After scanning,some data processing was carried out through the post-processing workstation AW4.6,such as multi planar reformatting(MPR),volume rendering(VR),maximum density projection(MIP)and curved surface reconstruction(CPR).The CT values of aortic arch,bilateral common carotid arteries,bilateral internal carotid arteries and bilateral middle cerebral arteries were measured.Meanwhile,the background noise(SD),signal-noise ratio(SNR)and contrast-noise ratio(CNR)of aortic arch,bifurcation section of right common carotid artery and initial segment of middle cerebral artery were compared.The radiation dose index:dose length product(DLP)and CT volume dose index(CTDIvol)were recorded at the end of each scan,and the effective radiation dose(ED)was calculated according to the formula.Then the two attending physicians were asked to use the double-blind method to subjectively evaluate the scanned images and reconstructed images.The statistical software was SPSS26.0,Kruskal-Wallis H test was used to compare the subjective score of images,Kappa test was used to evaluate the consistency of the subjective scores of the two doctors,and one-way ANOVA was used to compare the vascular CT value,SNR,CNR and radiation dose.LSD-t test was used for pairwise comparison between groups.Results In sex,age,height,weight,BMI and scan length,there was no significant difference among the three groups(P>0.05).The difference among the three groups was not statistically significant in image subjective score(P>0.05).The average CT value of left internal carotid artery was(363.70±50.64)HU in group A,(318.95±52.32)HU in group B and(381.81±58.53)HU in group C,and there was statistically significant difference among the three groups(F=14.395,P<0.05).In pairwise comparison,group B was 12.30%lower than group A,and there was significant difference between group A and B(t=3.71,P<0.05);group C was 5.00%higher than group A,but there was no statistical meaning exists between the two groups;group C was 19.71%higher than group B and there was significant difference between group C and B(t=5.21,P<0.05).the CT value of bilateral common carotid artery and bilateral internal carotid artery in group B and C were higher than 300HU,which could meet the diagnostic requirements.The SNR and CNR of aortic arch section and right common carotid artery bifurcation section in group A were significantly higher than those in group B and C,with significant statistical differences(P<0.05);while those in group C were slightly lower than group B,but no statistical meaning existed between the two groups(P>0.05).In CNR at the beginning of right middle cerebral artery among the three groups,there existed significant statistical differences(F=75.022,P<0.05),but there was no significant statistical difference in SNR(F=1.156,P>0.05).The average CT values of superior vena cava and venous sinus in group B and C were obviously lower than those in group A(P<0.05).No significant statistical difference was found in CTDIvol and DLP among the three groups(P<0.05).The effective doses(ED)of the three groups were(2.32±0.07)m Sv,(1.63±0.14)m Sv and(0.88±0.06)m Sv,respectively.Group B was 29.74%lower than that of group A,group C was 46.01%lower than that of group B and 62.07%lower than that of group A.At the same time,the total contrast agent dosage in group B and C was lower than that in group A by 30ml.Iodine intake in group B and C was 42.90%lower than that in group A.Conclusion In head and neck CTA imaging,using 100k V or 80k V tube voltage,20ml testing contrast agent and 20ml scanning contrast medium can meet the needs of diagnosis,and at the same time reduce the radiation dose and the total amount of contrast medium,which is feasible in clinical examination.