Experimental Study Of Functional Imaging Diagnosis Of Secondary Infectious Of SAP And Comparative Study With CT

Part 1 Study of CT and MRI Features of Normal Pig's Pancreas and the Optimal Protocol of Multi-phase Enhanced CTObjective:To study the CT and MRI features and the optimal protocol of multi-phase enhanced CT of normal pig's pancreas and compare them with human beings.Methods:CT plain scanning and thin-slice dynamic enhanced scanning were performed respectively in 10 healthy pigs.Six of them underwent MRI at the same time,including T1WI,T2WI,DWI and MRCP sequences.All of the pigs were paunched to observe pig pancreas' shape and position with naked eyes.The CT and MRI findings were compared with surgery.Results:(1) The pancreas of pig which liked "clover" was divided into three parts, pancreas head,left lobe and right lobe.The left lobe was the main part of pig's pancreas.It was resemble considerably to human being's pancreas,such as dissection location,general morphologic,the per- pancreatic vessels,CT density,MRI signals of T1WI,T2WI and diffusion-weighted imaging(DWI) and ADC value.(2) The images of pancreasticobiliary of normal pigs on MRCP were different from those of human being.It's bile duct and pancreatic duct converged at the duodenum respectively.The bile duct was comparatively wider with diameter of 5-6mm,while the pancreatic duct was narrow with diameter of 1-1.5mm and it was difficult to be shown by MRCP.(3) Multi-phase enhanced CT protocal:The results of enhanced CT scanning indicated that the time- density curve was similar with that of human being.The optimal scanning protocal was:15 s for arterial phase,35s for the pancreatic parenchyma,45 s for the peripancreatic portal vein phase.Conclusions:The CT and MRI features and Multi-phase enhanced CT scanning protocals of pancreas of pigs are considerable similar with that of human being.Therefor,the pig may be an ideal model of big animal in imaging research of pancreas diseases.Part 2 Establishment of Infected Necrotizing Pancreatitis(INP) Model of Big Animal and Its CT Findings[Objective]To investigate a way to develop a model of infected necrotizing pancreatitis(INP) in big animal and observe its CT features.[Methods]Thirty pigs,weighted 20 to 25 kilograms,were randomized into emperimental group(20 pigs) and controlled group(10 pigs).The first step,all were injected sodium taurocholate and trypsin into the main pancreatic duct to establish SAP models.The second step,48-72 hours after SAP operation,3-4ml active E.coli (10⁸ Entries/ml) were injected into pancreatic necrosis of experimental group,and the same dosage dead E coli were injected into pancreatic necrosis of controlled group.After 1h of SAP operation and 5 days of germ injection,two groups were performed contrast-enhanced MDCT and blood biochemical tests respectively.After above of experimental steps,two groups were sacrificed to perform pathological examination and of the pancreatic tissue.Compared histopathological findings with imaging findings.[Results](1)The successful ratio of the model of secondary infection of SAP were 80%(16/20).There were 17 infectious foci in 16 pigs.The germ cultivation of infectious foci were all positive(positive rate was 100%),and the positive rate of blood germ cultivation was 68.8%(11/16).In controlled group,6 pigs(6/10) were successfully completed emperimental steps,3 pigs died of SAP and 1 was cancelled because of infection by accident.(2) Blood biochemical tests:â‘ Amylase(AMY):1 hour after SAP operation,the serum level of AMY of two groups had no significant increase while after 24 hours,it increased significantly.The serum level of amylase of infection was higher significantly than that of no-infection(T=-68,P<0.001) by Wilcoxon rank sum test.â‘¡WBC:1～2 days and 5 days after erm injection,the serum levels of AMY of emperimental group were higher than controlled group significantly (χ=9.37,8.49 respectively,P=0.0022,0.0036 respectively,P < 0.05) by Wilcoxon rank sum test.(3) CT rusults:The Sensitivity,specificity,positive predictive value(PV⁺),negative predictive value(PV),Youden's index(YI),Kappa value were 18.8%,66.7%,60.0%,23.5%,-0.146,-1.12 respectively.The CTSIs of two groups were all more than 5 scores and the severe degrees were all moderate or severe.1h after SAP and 5 days after germ injection,CTSIs of two groups were analyzed by Wilcoxon rank sun test,andχ² values were 0.166,0.397 respectively. All P values were more than 0.05,which indicated that there was no statistically significant difference between infected and uninfected pancreatitis.[Conclusions](1) A stable and reliable model of secondary infection of SAP in big animal could be established satisfactorily by injected active E.coli into the pancreatitis necrosis tissue under CT guiding,which adapts well to clinic study,especially to imaging study.(2) CT plays important role in diagnosis of no-infected AP(NAP).However,it is inable to differentiate infectious focus from necrosis tissue.Therefor,CTSI may be exsit certain error when assesses the severity of infected necrotizing pancreatitis(INP).Part 3 Experimental Study of ⁹⁹Tc^m-ciprofloxacin Imaging In Detecting The Infectious Focus of SAP and Comparative Study with CT Objective:(1) To discuss the biodistribution of a novel inflammation tracer:⁹⁹Tc^m -Ciprofloxacin(CPF) in pigs.(2) To evaluate the value and limitation of ⁹⁹Tc^m-CPF functional imaging in detecting the infectious focus of SAP,and compare with CT.(3) To investigate the value of the combination of ⁹⁹Tc^m-CPF radionuclide imaging and CT in detecting infectious focus and calculating severe index of SAP.Methods:(1) CPF was labeled with ⁹⁹Tc^m and the radiochemical purity and labeling rate were measured.It was studied that biological distribution in normal and infected necrotizing pancreatitis(INP) pigs.(2) Made Six normal pigs as normal group,made 16 pigs with INP as experimental group and 6 pigs with no-infected SAP as controlled group.These 3 groups were performed CT and SPECT respectively.After detections, the three groups were sacrificed to perform pathological examination and germ cultivation.Compared imaging findings with histopathological findings,and analysed the sensitivity,specificity,sever index of SAP,et al.All P values in analysis less than 0.05 were considered to indicate a statistically significant difference.Results:(1) Both the radiochemical purity and labeling rate were over 90%in 6h at room temperature.After intravenous injection,rapid plasma clearance and renal excretion were observed.Kidney,liver,spleed were target organs for the accumulation of ⁹⁹Tc^m-CPF,while no significant uptake in either normal pancreas or that of SAP.In the INP models(n=16),accumulation of ⁹⁹Tc^m-cPF was found at the infective lesion.The study showed the optimal acquisition time for ⁹⁹Tc^m-cPF imaging was at 3h after injection when the infectious-to-background-site activity ratio reached to 3.36±0.33.(2) The sensitivity,specificity,PV⁺,PV,YI and KAPPA value of ⁹⁹Tc^m-CPF functional imaging were 88.2%,83.3%,93.8%,83.3%,0.715 and 0.667 respectively,whlile these items of CT were 17.6%,66.7%,60.0%,22.2%,-0.157 and-0.08 respectively.(3) The combination of two imaging:â‘ These items were 88.2%,83.3%,93.8%,83.3%,0.715 and 0.667 respectively,which were same as single ⁹⁹Tc^m-CPF imaging.â‘¡In experimental group,the combination of sever index was significantly higher than CTSI by matched t-test(t=-4.81, P<0.001),while in controlled group,there was no significant difference between them by matched t-test(t=1.00,P>0.1).Conclusions:(1) The study of biodistribution indicates that ⁹⁹Tc^m-CPF adapts well to detecting infectious focus of SAP,and the optimal acquisition time is 3h after injection. (2) ⁹⁹Tc^m-CPF is quite sensitive and specific tracker in detecting infectious focus of SAP.It's validity and consistency are significantly higher than those of CT,and could be used as an independent means in detecting secondary bacteroidal inflammation of SAP.It is difficult for CT to detect the secondary bacteroidal inflammation of SAP.However,CT can accurately measure necrosis area of SAP and calculate CTSI of early uninfected SAP.(3) Combination of the two techniques is more accurate than single CT in estimate severe index of INP.In conclusion,combination of the two techniques is favorable to accurately diagnose INP and assess it's severity.