| Research purposeWith the improvement of living conditions and the increase in the aging population,the incidence of lower extremity arterial disease is gradually increasing.Because of the advantage of multi-slice spiral CT angiography(MSCTA)in the image display of lower extremity arterial diseases,in recent years,it plays a more and more important role in imaging diagnosis and post-operative evaluation of lower extremity arterial diseases.The CTA scan of lower extremity artery has a longer coverage,from the middle of abdomen to the tip of both feet,so the radiation dose of the X-ray was larger.In addition,in order to obtain a clear vascular image with high image quality,a large dose of high concentration iodine contrast agent was often injected in the CTA examination of the lower extremity artery,which was obviously increased.The risk of disseminated intravascular coagulation(DIC),the incidence of contrast agent nephropathy(CIN)and contrast agent allergic reaction were also significantly increased.Therefore,low tube voltage technique combined with low radiation dose of CARE Dose 4D tube current regulation technique and low iodine concentration(270 mg I/ml)contrast agent were used for lower extremity arterial CTA examination.To evaluate the application value of double low technique imaging in improving the quality of CTA images of lower extremity arteries and reducing radiation dose,and to make further diagnosis or treatment with"gold standard"DSA in some cases with positive examination results.The results of CTA diagnosis were compared with those of DSA diagnosis.To compare the coincidence rate between them in the diagnosis of lower extremity arterial stenosis.Materials and MethodsForty patients with suspected lower extremity arterial lesions undergoing CTA examination were randomly divided into group A(low tube voltage and low dose group:110k V CARE Dose 4D,injected with the routine iodine concentration contrast agent350mg I/ml iohexol)and group B(ultra-low tube voltage low dose group:80k V CARE Dose 4D,injected with low iodine concentration contrast agent 270mg I/ml iodixanol)were examined by CTA,respectively.Positive cases were supposed to be further diagnosed or treated by DSA within two weeks.Each patient’s age,height(cm),weight(kg)and body mass index(BMI)were measured and recorded before examination.After the examination,these CT radiation dose parameters,such as the volume CT dose index(CTDIvol),the dose length product(DLP),were recorded in detail.Afterwards the effective dose(ED)was estimated according to the formula.The CT values at the end of the abdominal aorta,the origin of the popliteal artery and the end of the posterior tibial artery were measured by CTA of the lower extremity artery in two groups,and the signal-to-noise ratio(SNR)and the contrast-to-noise ratio(CNR)of the images were calculated according to the formula.Statistical analysisIn this study,statistical analysis was performed with SPSS 23.0 software.All the measurement data were expressed as mean±SD,and all qualitative data were expressed as the frequency or rate.DSA images were considered to be the"golden standard".The degr-ee of vascular stenosis of lower extremity arteries in CTA and DSA images was compared and measured one by one.Diagnostic tests were utilized to calculate the classification of the degree of vascular stenosis,and the diagnostic coincidence rate of CTA and DSA in two groups of patients with CTA and DSA was compared respectively.χ~2 test was used to compare the diagnostic coincidence rate between the two groups.The data of normal distribution and homogeneity of variance were tested for sex composition ratio,age,BMI,CTDIvol,DLP,ED,SNR,CNR and so on in group A and B,respectively.The parameter data which do not accord with normal distribution and variance were transformed into satisfy the condition.The difference of above parameters between two groups of patients was tested by independent sample t-test.A difference with a p-value of<0.05 was considered statistically significant.Results1the results of comparison of CTA and DSA stenosis degree in patients with arteriopathy of lower extremity in group A and B:CTA examination was successfully completed in both groups,39 of them were diagnosed as having moderate stenosis and above grade lesions in any of the lower extremity arteries.In group A,total 8 cases(1 case with bilateral lower limb examination and 7 cases with unilateral lower extremity exam-ination),were selected and successfully diagnosed or treated with DSA.A total of 222lesions were found in 8 patients with DSA,including 121 mild stenosis,42 moderate stenosis,34 severe stenosis and 25 complete occlusions,of which 113 were diagnosed by CTA as mild stenosis,44 with moderate stenosis,38 with severe stenosis and 27 with complete occlusion.In group B,there were 5 cases(all unilateral lower extremity exam-ination),of which DSA found 130 lesions,including 75 mild stenosis,33 moderate stenosis,12 severe stenosis and 10 complete occlusions.In these lesions,CTA diagnosed70 mild stenosis,35 moderate stenosis,14 severe stenosis and 11 complete occlusions.In group A,8 patients with DSA were performed and documented.Total 222 lesions were discovered by DSA,of which 206 lesions were in accordance with the diagnostic grade of CTA and DSA.CTA overestimated the degree of stenosis in 16 non-concomitant lesions.The diagnostic coincidence rate of CTA and DSA was 92.8%.In group B,among the 5patients who successfully completed DSA,121 of 130 lesions found by DSA were in line with the diagnostic grade of CTA and DSA,and 9 were not.The diagnostic coincidence rate between CTA and DSA was 93.1 and there was no significant difference(χ~2=0.01,P>0.05).2the radiation dose index of group A and group B was compared.Compared with the patients with low-tube voltage in group A,the 80k V ultra-low tube voltage technique was used to scan in group B,and CTDIvol decreased from 3.38 m Gy to 2.68 m Gy,with an average decrease of 0.7m Gy,a decrease of 20.71%,and DLP from 410.05m Gy·cm to304.70m Gy·cm,with an average decrease of 111.35m Gy·cm,a decrease of 26.76%.The decrease of ED was from 7.90m Sv to 5.79m Sv,with an average decrease of 2.11m Sv,and the decrease of 26.71%.The difference of each index was of statistical significance(t=4.220,t=5.361,t=5.361,P<0.05).3comparison of image quality of lower extremity arterial contrast enhanced CTA between group A and B:compared with those in group A using 110k V low-tube voltage technique combined with conventional 350mg I/ml iodine concentration contrast agent(The CT value at the end of the abdominal aorta was 392.09 Hu,SNR=23.56,CNR=20.65;That value at the beginning of the popliteal artery was 345.82 Hu,SNR=10.27,CNR=8.62;The value at the end of the posterior tibial artery was 211.08 Hu,SNR=7.98,CNR=6.03),in group B using 80k V ultra-low tube voltage technique combined with 270mg I/ml low-iodine concentration contrast agent scanning,the CT value at the end of the abdominal aorta was 434.79Hu,SNR=26.17,CNR=23.09;The CT value at the beginning of the popliteal artery was 385.67Hu,SNR=20.58,CNR=17.14;and the value at the end of the posterior tibial artery was 240.51Hu,7.49 and 5.76,respectively.In this study,the CT values of group A and group B were the highest at the end of the abdominal aorta and the lowest at the end of the posterior tibial artery.The CT values at the end of the abdominal aorta,the origin of the popliteal artery and the end of the posterior tibial artery in group B were higher than those in the group A.There was no significant difference between the two groups(t=-1.370,t=-1.343,t=-1.006,P>0.05).The SNR and CNR of group B was higher at the end of the abdominal aorta and popliteal artery than in group A,except at the end of the posterior tibial artery.There was no significant difference between the two groups(t=0.209,t=0.129,t=-0.734,t=-0.734,t=-2.075,t=-1.972,P>0.05).ConclusionsDouble-low technique CTA imaging of lower extremity artery with ultra-low tube voltage and low iodine concentration contrast agent has a high coincidence rate with DSA in the diagnosis of stenosis degree of diseased vessels,and can obtain clear lower extre-mity arterial imaging to meet the needs of clinical diagnosis.The image quality is not significantly different from that of conventional scanning technique,and the radiation dose can be greatly reduced,and the iodine content of contrast agent can be greatly reduced when the total dose of contrast agent is constant.It has important clinical application value and can be used in clinical diagnosis of lower extremity arterial lesions and evaluation of surgical efficacy. |
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