Study On Optimization Of Dual Energy CT Scanning In Portal Phase Of Liver

Background and purpose:Enhanced CT scan of the liver can be divided into three phases of arterial phase,portal phase and delayed phase.In arterial phase,bolus-tracking technique is mostly applied in clinical practice to obtain better enhancement effect of main abdominal arteries.However,due to the impact of individual circulation,the enhancement effect of portal vein system is difficult to achieve the expected results in portal phase.Clear display of portal vein system can provide precise intrahepatic segment for clinicians,and exhibits important clinical significance for preoperative surgical planning^[1,2].With the rapid development of X-ray computed tomography,dual-energy CT?DECT?has been widely used in clinic.Owing to its matrix function,DECT has been widely used in gout diagnosis,stone analysis and enhanced examination.Besides,DECT is also characterized by retrospective reconstruction,which can contribute to realizing the effect of reducing kilovolts peak?kVp?,thus greatly improving the quality of image enhancement.Prior studies have documented that the dosage of contrast agent can be reduced by 40%^[3]while the image quality remains unchanged,which is especially suitable for liver imaging in portal phase with unexpected outcome of enhancement due to the feature of double blood supply.However,there are still many problems,as described below:1.Selection of the combination of kVp in DECT scanning;2.Image reconstruction,such as the comparison of composite-energy and monoenergetic image quality;3.Scanning timing of portal phase in DECT;4.Dosage estimation of contrast agents.Indices of body habitus such as net weight,body surface area,total weight and body mass index have been proposed as the basis for estimation.Majority of related studies support that BSA is the optimum,which can significantly improve aortic and liver enhancement,as well as consistency of enhancement among patients.However,the above conclusion was based on a retrospective analysis.Whether it conforms to the body habitus of Asians and is suitable for clinical application remains to be solved in future,which will be of great significance to solve the above problems.Specifically,a set of optimization schemes for scanning parameters,post-processing mode,scanning delay time and contrast agent dosage in DECT examination of the liver can be established,so as to improve the quality of image enhancement,reduce the contrast dosage and radiation dosage,thereby achieving the purpose of improving the quality of diagnosis.Materials and methods:?1?factors affecting liver CT enhancementA retrospective analysis was made of 87 patients who underwent abdominal enhancement from January to March,2013,excluding incomplete records of height and weight,age less than 16 years and portal vein tumor thrombus.The contrast-enhanced CT values of portal vein hepatic parenchyma and the contrast between portal vein and liver parenchyma were measured by conventional single-energy CT,with fixed-dose contrast medium and injection rate.The differences between various groups?sex,age,body mass index?were compared.?2?optimization of contrast agent application planRegressive clinical trial:Acquire the image data of cases with epigastric enhanced CT examination in Southwest Hospital in January 2014,the selection criteria:adults whose basic information records are complete,such as gender,age,height,weight and so on;furthermore,the lesion size have to be so small that can not affect the image analysis of liver parenchyma and portal vein;exclude those suffering from portal system diseases,such as cirrhosis,Budd-Chiari syndrome and portal hypertension.72 cases were enrolled,including 49 males and 23 females,aged 29-84 years with an average age of?52.8+12.7?years,an average weight of?60.2+12.8?kg and an average height of?163.3+7.4?cm.CT scan was performed with fixed dose and injection rate.Linear regression analysis was used to analyze the relationship between portal-hepatic parenchymal contrast and liver parenchymal enhancement with body weight,body surface area?BSA?and body mass index?BMI?in portal phase images,and to calculate the amount of iodine?EU?required for each 1 HU increase in contrast medium dose estimated according to different body shape index.?3?timing of portal venous phaseA retrospective analysis was made on the image data of 120 cases with epigastric enhanced CT scan in January 2013.87 cases were enrolled,excluding incomplete information of height and weight,large range of lesions affecting image analysis and age less than 18 years old.BTT was used to scan the arterial phase and delayed 30s.The blood circulation velocity was analyzed by comparing the CT values of the three layers of the hepatic apex,hepatic portal and hepatic fundus in the arterial phase sequence images.?4?the application of DECT to enhance inspection performance?1?Phantom experiment:The prototype was made with different concentrations of iodine contrast solution.On the Siemens SOMATOM Definition Flash scanner,the routine120 kVp scan and 100/Sn 140 kVp dual-energy scan were performed successively with the epigastric recommendation protocol.The linear fusion image?M₀.5?,the optimal nonlinear fusion image?OCM?and the single-energy image?Mono?optimized by contrast-to-noise ratio?CNR?spectrum curve are reconstructed from the image data collected by the latter.Calculate the contrast,CNR and quality factor?FOM?to compare image quality.?2?Prospective clinical trial:30 cases with epigastric DECT scan in Southwest Hospital in January 2015 were collected.all scan were performed with 100-Sn140 kVp,and the enhancement amplitudes of liver parenchyma and portal vein trunk were calculated.The maximum density projection?MIP?images were subjectively evaluated by 6-subscale method.?5?optimization of contrast agent application planProspective clinical trial:Acquire the image data of cases with epigastric enhanced CT examination in Southwest Hospital from October 2016 to November 2016.the selection criteria were as follows:the lesions were small in size and did not affect the image analysis of liver parenchyma and portal vein;portal system diseases such as fatty liver,cirrhosis and portal hypertension were excluded.Sixty patients were divided into two groups:the first one,22 males and 5 females,aged 29-70 years,average?48.7±13.3?years,average body weight?61.8±7.5?kg,average height?166.9±6.22?cm,and the second,under the condition of constant relative total dose of the former group,the contrast dose was calculated according to body weight.21 cases,9 females,age 27-68 years old,average?51±11.2?years old,average weight?59.2±8.8?kg,average height?162.9±8.7?cm.all the examination were performed with 100-Sn140kVp by DECT.Linear regression analysis was used to analyze the relationship between portal-hepatic parenchymal contrast and hepatic parenchymal enhancement with body weight and surface area.The amount of iodine?EU?needed for each 1 HU increase in contrast medium dose was calculated according to different body shape index.Results:?1?Analysis results of factors affecting liver CT enhancement?1?The CT value of liver parenchyma enhancement in portal venous phase was less than 50 HU,accounting for 52.9%.?2?The gender has an effect on the enhancement of portal venous phase,and the CT value of hepatic parenchyma enhancement was 20%lower in males than in females.?3?The patients were divided into three groups according to BMI,namely the underweight group,the normal group and the overweight group.The CT value of liver parenchymal enhancement on portal venous phase less than 50HU accounted for 17%,51%and 77%,respectively.The effect of the overweight group's liver parenchyma enhancement was not up to the clinical diagnosis.?2?Optimization results of contrast agent application programRegressive clinical trial:the correlation between portal vein-liver parenchyma contrast and BSA,body weight and BMI?r=-0.53,-0.50,-0.41,P<0.001,respectively?decreased successively.EU_BW and EU_BSA which means the average amount of iodide enhancement ratio of contrast dose was estimated by weight and BSA was 0.01005gI/kg/HU and0.36299gI/m²/HU,respectively.Clearly,the correlation between image enhancement and BMI was minimal.?3?Scanning timing analysis results in portal venous phaseThere was no significant difference in gender composition,age,height and weight between the groups?P>0.05?.In the second group,the liver parenchymal enhancement in portal venous phase:?54±16?HU was significantly higher than that in the first group?43±15?HU?P=0.016?,and slightly higher than that in the third group?49±11?HU.The second group‘s portal vein enhancement?59±22?HU in portal venous phase was slightly higher than that in the first group?54±26?HU and the third group?52±22?HU.?4?DECT applied to enhance the results of inspection performance?1?Phantom experiment:Compared with 120kVp image,contrast of M₀.5 image has no significantly different,but CNR was improved.Among the three reconstructed images of DECT,the contrast and CNR of OCM and Mono images were 33.3%,32.3%,16.6%and6.1%higher than those of M₀.5 image.?2?Retrospective clinical trials:The amplitude of liver parenchyma and main portal vein enhancement in OCM and Mono images in clinical cases was improved by 20.4%,19.2%,16.2%and 15.9%,respectively,compared with M₀.5 images.Among the score of MIP images,there was no difference between the OCM group and the Mono group,both of which were significantly higher than the M₀.5 group.?5?Optimization results of contrast agent application programProspective clinical trial:during portal venous phase,there was a negative correlation between liver parenchymal enhancement/contrast dose and BSA and body weight?r=-0.44,-0.58,P<0.05?.Correlation of portal vein-liver parenchyma contrast/dose with BSA and body weight?r=-0.58,0.10,P<0.05,respectively?.Therefore,both portal vein-liver parenchyma contrast and liver parenchyma enhancement have greater linear correlation with BSA.The mean value of liver parenchymal enhancement was increased by 10%in the BSA group compared with the BW group.The average iodide enhancement ratio of contrast dose was estimated by weight and BSA,EU_BW and EU_BSA,was 0.03002gI/kg/HU and0.9979gI/m²/HU,respectively.CONCLUSION:?1?By retrospectively analyzing the results of factors affecting liver enhancement over the years,it showed that gender and BMI had a great impact on liver parenchymal enhancement in the liver portal phase at fixed contrast doses and injection rates;It is suggested that in clinical applications,the dose of contrast should consider the effect of gender and BMI on the portal enhancement.Men and some else whose BMI>24 should use larger doses.?2?The regressive clinical trial:In order to improve the consistency of portal vein enhancement between patients,the contrast dose should be estimated based on BSA.?3?On the one hand,due to individual differences in blood circulation rates,the use of BTT in the arterial phase is not sufficient to ensure the accuracy of the portal phase timing.On the other hand,the law of change over time about BTT-based aortic CT value can reflect individual differences in blood circulation velocity,which can be used to optimize the portal phase delay time.?4?DECT applied to enhanced examination performance is divided into phantom experiments and prospective clinical trials.The phantom experiment results show that the CNR of DECT retrospective reconstruction OCM image and Mono image is significantly better than the conventional 120kVp image,which is beneficial to enhance the examination and greatly reduce the dose of contrast.The prospective clinical trials have shown that the OCM and Mono images of DECT can significantly enhance the effect of enhancement in liver examination.?5?The prospective clinical trial:At the portal phase,liver parenchymal enhancement was negatively correlated with BSA and body weight,and portal vein-hepatic parenchyma enhanced contrast was also negatively correlated with BSA.And to improve the consistency of the enhanced examination,the estimated dose of BSA can improve the consistency of the test better than body weight,so the liver enhanced CT examination can use BSA to estimate the contrast agent dose.In summary,this study retrospectively analyzed the insufficiency of the liver enhancement effect of individual liver CT enhancement in our hospital,combined with the dual-energy CT upper abdomen enhanced scanning protocol,image reconstruction,and contrast dose in other aspects of the study,a set of optimized dual-energy CT examinations for liver can be obtained.