Application Research Of Low KVp And Spectral Ct Combined With ASIR And Low Contrast Dose In The Abdominal CT Angiography

Recently,with the rapid development of computed tomography(CT)technology in the field of medical imaging,computed tomography angiography(CTA)has became more and more popular in the assessment of vascular lesions in clinic.CTA is a minimally invasive and easy diagnostic procedure.However,articles indicated that the predicted cancer risks attributable to CT radiation dose had grown because of the substantial increase in the use of CT.In order to improve the image quality,we always increased the amount of contrast agent by using high-concentration contrast material in the conventional CTA imaging.However,application of high-concentration contrast material is limited in patients with borderline or impaired renal function because of the increasing risk of developing contrast induced nephropathy(CIN).Therefore,it is of great importance and significance to reduce the CT radiation dose and contrast material concentration without compromising image quality.In order to reduce the incidence of CIN,we can choose low-concentration contrast material in CTA examination.Low-concentration contrast material can also lower the CT value of intravascular,and the image quality can't meet the diagnostic requirements.Researches show that lower tube voltage is the most effective way to reduce the radiation dose.However,further reductions in radiation dose are limited due to excessively high image noise and poor image quality.Adaptive statistical iterative reconstruction(ASIR)used on CT systems has fewer assumptions regarding image noise distribution and iterative mathematical processes.Preliminary studies of abdominal CT have shown that the images with ASIR reconstruction have better image quality and less image noise than images acquired with other reconstruction algorithm.In addition,the emergence of spectral CT makes the research of medical image become a hotspot,it is different from convention CT.Spectral CT can acquire the qualitative images like conventional CT and the multi-parameter images generated from spectral imaging viewer such as:consecutive virtual monochromatic spectral image.Virtual monochromatic spectral images can optimize the image quality and contrast-to-noise ratio(CNR).Moreover,the radiation dose in spectral CT is always being studied and discussed.Low mA can optimize the radiation dose of patients in the spectral CT scanning.The purpose of the current study was to prospectively evaluate the image quality and radiation dose of low kVp and spectral CT with ASIR reconstruction technology and low contrast dose in abdominal CTA.Part 1 Application Research of Low Tube Voltage Combined with Adaptive Statistical Iterative Reconstruction and Low Contrast Dose in the Abdominal CT AngiographyObjectiveTo investigate the feasibility of low tube voltage combined with low iodine concentration contrast material and ASIR reconstruction in abdominal CTAMaterial and MethodsTotally 120 patients were enrolled in this prospective trial,and randomly divided into Groups A and B(n = 60).All examinations were performed on a 64-row multi-detector CT system(Discovery CT 750 HD,GE Healthcare,Milwaukee,WI,USA).Group A received 120kVp and filtered back projection(FBP)reconstruction,and Group B received 100kVp and ASIR 40%(ASIR40)reconstruction.The angiographic phases in groups A and B were obtained at high-concentration contrast material(370mg/ml)and low-concentration contrast material(270mg/ml),respectively.An equal amount of contrast material(1.2ml/kg)and the same iodine delivery rate(4.5ml/s)were given to all cases,followed by a 45ml saline flush at the same flow rate as contrast material.Bolus tracking was used in both groups with a trigger level of 150 HU.To analyze the CT radiation dose,the dose-length product(DLP)and CT dose index volume(CTDIvol)of the arterial phase were recorded and compared.For quantitative image analysis,the attenuation values(CT value in Hounsfield units)and standard deviation(SD)of abdominal aorta and its' main branches(celiac artery,superior mesenteric artery,left renal artery)were measured and compared,respectively.The noise(N),signal-to-noise ratio(SNR)and contrast-to-noise ratio(CNR)of the abdominal aorta were also obtained and compared,respectively.For qualitative image analysis,image quality were assessed with a 5-point scale system,based on the luminal border,image noise,and diagnostic acceptability.The branch order of renal artery and superior mesenteric artery were also visualized and assessed with a 5-point scale.SPSS 19.0 software was used for statistical analysis.Data were expressed as mean ± SD.The age,height,weight,body mass index(BMI),scan length(SL),CTDIvol,DLP,CT value,N,SNR,CNR were compared using the Student t-test for unpaired samples.Image quality scores were compared using the Mann-Whitney U test,and the inter-observer variability was estimated by the Cohen 's kappa test.Results1.There were no significant differences in the patients' age,height,weight,and BMI between Groups A and B(P>0.05).2.The CTDIvol and DLP in Group B were significantly less than those in Group A(P<0.05).There was no significant difference in the SL between Groups A and B(P>0.05)3.The evaluation showed higher CT value in Group B than in Group A(P<0.05).4.For the image noise,there was no significant difference between Groups A and B(P>0.05).The SNR and CNR were significantly higher in Group B than in Group A(P<0.05).5.Qualitative analysis indicated that,the subjective image quality score showed no significant difference between Groups A and B(P>0.05).ConclusionCompared with 120kVp with FBP reconstruction,the protocol of 100kVp with ASIR40 reconstruction provides high-quality abdominal CTA result,which allows for reduced iodine concentration and declined radiation dose.Part 2 Comparison of Spectral CT and Low kVp in the Abdominal CT Angiography with Low Contrast DoseObjectiveTo investigate the image quality and radiation dose of spectral CT and low tube voltage combined with ASIR reconstruction in the Abdominal CTA with low contrast dose.Material and MethodsTotally 120 patients were enrolled in this prospective trial,and randomly divided into Groups A and B(n = 60).All examinations were performed on a 64-row multi-detector CT system(Discovery CT 750 HD,GE Healthcare,Milwaukee,WI,USA).Groups A and B were obtained with 100kVp and spectral CT(375mA),respectively.The angiographic phases in groups A and B were obtained at the same low-concentration contrast material(270mg/ml).The amount of contrast material were 1.2ml/kg and 0.8ml/kg for groups A and B,respectively.An equal iodine delivery rate(4.5ml/s)was given to all cases,followed by a 45ml saline flush at the same flow rate as contrast material.Bolus tracking was used in both groups with a trigger level of 150HU.ASIR 40%reconstruction were given to all cases.The arterial phase of spectral CT acquisition was processed at workstation to generate a spectrum of virtual monochromatic imaging datasets at increments of 10keV from 40 to 70keV in each subject.To analyze the CT radiation dose,the DLP and CTDIvol of the arterial phase were recorded and compared.For quantitative image analysis,the attenuation values(CT value in Hounsfield units)and SD of abdominal aorta and its' main branches(celiac artery,superior mesenteric artery,left renal artery)were measured and compared,respectively.The SNR and CNR of the abdominal aorta were also obtained and compared,respectively.For qualitative image analysis,image quality were assessed with a 5-point scale system,based on the luminal border,image noise,and diagnostic acceptability.The branch order of renal artery and superior mesenteric artery were also visualized and assessed with a 5-point scale.SPSS 19.0 software was used for statistical analysis.Data were expressed as mean ? SD.The age,height,weight,BMI,SL,CTDIvol,DLP,CT value,SNR,CNR were compared using the Student t-test for unpaired samples.Image quality scores were compared using the Mann-Whitney U test,and the inter-observer variability was estimated by the Cohen's kappa test.Results1.There were no significant differences in the patients' age,height,weight,and BMI between Groups A and B(P>0.05).2.The CTDIvol and DLP in Group B were higher than those in Group A(P<0.05).There was no significant difference in the SL between Groups A and B(P>0.05).3.In comparison with 100kVp single-energy CTA images,virtual monochromatic imaging datasets at 40keV and 50keV had significantly higher intravascular aortic attenuation(P<0.05).No significant difference was observed in mean intravascular aortic attenuation between 100kVp and 60keV images(P>0.05).Intravascular aortic attenuation at 70keV images were less than those in 100kVpsingle-energy CTA images(P<0.05).4.In comparison with 100kVp single-energy CTA images,virtual monochromatic imaging datasets at 40keV had significantly higher CNR and SNR(P<0.05).No significant differences were observed in CNR and SNR between group A and group B at 50keV and 60keV images(P>0.05).CNR and SNR at 70keV images were less than those in 100kVp single-energy CTA images(P<0.05).5.The image quality score showed no significant difference between Group A and 40-60keV images in group B(P>0.05).Visualization of the branch orders of renal arteries and superior mesenteric artery indicated that there was no difference between Groups A and 40-60keV images in group B(P>0.05).ConclusionsRadiation dose in the abdominal spectral CTA was higher than in the 100kVp group,but all of the overall image quality of the spectral CTA at 40-60 keV and 100kVp can satisfy the requirement of diagnosis.Compared with spectral CTA,the contrast material dose in 100kVp was reduced by 33.3%.For the patients who were in poor renal function and cannot tolerate high concentration of contrast agent,spectral CTA is the best choice in the examination of abdominal CTA.