Comparative Multi-modality Study Of Real-time Tissue Elastography,contrast-enhanced Ultrssound,with The CT Spectral Imaging To Assess The Stability Of Carotid Plaques

Objective:This study established New Zealand rabbits animal models of atherosclerotic plaque to validate the diagnosis of atherosclerotic plaque which diagnosticed by real-time tissue elastography technology,contrast-enhanced ultrasound and energy spectrum ct.Through the clinical study of patients who undergoing carotid endarterectomy,and compared with the pathological results,the study compared the diagnostic values of three methods and different diagnosis efficiency,and provided diagnostic evidence for the prevention and further treatment of cerebral ischemia.Methods:Animal experiment:1.Six healthy male New Zealand rabbits were selected,3 months old,after confirmed with no atherosclerotic plaque on abdominal aorta by ultrasound,then werereared with high fat feed（1%cholesterol+8%egg yolk+8%lard）.Two months later the ultrasound examination were performed once every two weeks.When finding the plaque obvious,they were evaluated by elastography technology,contrast-enhanced ultrasound and energy spectrum CT in one week.2.Ultrasound:observe the size and echogenicity of the plaque,start Real-time elastography（RTE）technology,and give scores to the RTE imges by Itoh 5 points method.If the plaq;if the plaque was scored4 or 5,it would be fibrous.Select the plaque which was observed asthe region of interest A（ROI A）,the blood area on the same level was ROI B.Calculate the B/A Ratio,if B/A≤5,it would be lipid;if B/A>5 and B/A<20,it would be mixed;if B/A≥20,it would be fibrous.And initiate the built-in data processing system to analyze the ROI,to get the blue area area ratio（AREA%）and the elasticity index.3.Contrast-enhanced ultrasound:Select the plaque of interested,after the administration of contrast agent SonoVuethrough elbow vein,choose contrast enhancement mode to obtain the images.Observe if there is any enhancement in the plaque.Enhancement within the plaque was categorized as grade 0 to grade 4 by visual interpretation and was evaluated by quantitative analysis.The enhanced intensity（EI）of the plaque and the ratio of EI within the plaque to that in the lumen of the carotid artery were calculated by Qlab analysis software.4.Energy spectrum CT:CTA examination was performed on rabbits with contrast agent iohexol,then turn on GSI scan modes.All images were reconstructed with single energy（MONO）and mixed energy（QC）.The parameters were same as the scan settings.The mixed energy was calculated graphically using the image analysis software,and analyze the ratio of lumen area（LA）and total vascular area（TVA）5.After the contrast experiment of the three methods was over,the air embolization method euthanasia was performed on the New Zealand rabbits,and then the abdominal aorta was immediately dissected and separated,and then embedded,sliced and stained.Observe the plaques by light microscope and compare the above three methods,and distinguish the plaques into lipid（IV type）,mixed（V type,VI type）and fibrous（VII type）plaques referring to American Heart Association（AHA）classification（revised edition）.Clinical study:1.Between October 2014 to June 2017,45 patients diagnosed with carotid atherosclerotic disease in our hospital and performed with carotid endarterectomy were included in our study,male 29 cases,female 16 cases,the age of patients ranged from 42to 77 years old,the median age was 62 years.They were all performed with above three methods to evaluate the carotid plaques,with pathology as the reference standard.2.Ultrasound:observe the size and echogenicity of the plaque,start Real-time elastography（RTE）technology,and give scores to the RTE imges by Itoh 5 points method.If the plaq;if the plaque was scored4 or 5,it would be fibrous.Select the plaque which was observed asthe region of interest A（ROI A）,the blood area on the same level was ROI B.Calculate the B/A Ratio,if B/A≤5,it would be lipid;if B/A>5 and B/A<20,it would be mixed;if B/A≥20,it would be fibrous.And initiate the built-in data processing system to analyze the ROI,to get the blue area area ratio（AREA%）and the elasticity index.3.Contrast-enhanced ultrasound:Select the plaque of interested,after the administration of contrast agent SonoVuethrough elbow vein,choose contrast enhancement mode to obtain the images.Observe if there is any enhancement in the plaque.Enhancement within the plaque was categorized as grade 0 to grade 4 by visual interpretation and was evaluated by quantitative analysis.If the the plaque was graded 0-1,it would be judged as stable plaque in advance;If the the plaque was graded 2-4,it would be judged as vulnerable plaque in advance.The enhanced intensity（EI）of the plaque and the ratio of EI within the plaque to that in the lumen of the carotid artery were calculated by Qlab analysis software.4.Energy spectrum CT:CTA examination was performed on rabbits with contrast agent iohexol,then turn on GSI scan modes.All the images received by CT were transferred to GE energy spectrum CT workstation,spectrum curve,the iodine concentration and effective atomic number image were calculated by reconstructing the images.5.Pathology:The plaques were distinguished into lipid（IV type）,mixed（V type,VI type）and fibrous（VII type）plaques referring to American Heart Association（AHA）classification（revised edition）.6.The elasticity score,strain rate ratio,the slope of the spectrum curve,the iodine concentration and effective atomic number were counted in fourfold table.Then the sensitivity and specificity to diagnose carotid plaques were calculated.Draw receiver operatingcharacteristiccurve（ROC）ofdifferentmethods anddifferent combined scoring models to diagnose thevulnerable plaques and stable plaques and compare them.Results:Animal experiment:The atherosclerotic plaque model on the 12 rabbits was established successfully,and the pathology results showed thatthere were 6 with lipid plaques,4 with mixed plaques,and 2 with fibrous plaque.Ultrasound showed there were 2 uniform hyperechoic plaque,6 nonuniform hyperechoic plaques,and 4 nonuniform hypoechoic plaques.Elasticity score ranged from 1 to 4,B/A ratio was 14.29±15.06 and ranged from 2.02 to32.65.The enhancement of contrast-enhanced ultrasound was categorized as 0 to 4.The EI was 4.39±0.91 and ranged from 2.02 to 36.23,Ratio was 0.30±0.07 and ranged from0.20-0.39.The lumen area（LA）and total vascular area（TVA）on energy spectrum CT were 1.46±0.36mm²,4.41±0.53mm²respectively and ranged from 1.01 mm² to 1.88mm²,the LA and TVA on pathology were 1.69±0.41mm²,2.19±0.51mm² respectively and ranged from 1.47 mm² to 2.99 mm².Clinical study:45 patients were performed with carotid endarterectomy,there were 13 with lipid plaques,18 with mixed plaques,and 14 with firbrous plaques.1.Ultrasound:Ultrasound showed 10 hypoechoic plaques,26 mixed echo plaques and 9 hyperechoic plaques.The thickness of the plaque ranged from 0.20cm to 0.39cm（the mean thickness was 0.28±0.07cm）.The elasticity score showed there were 12 lipid plaques,23 mixed plaques and 10 firbrous plaques.The strain rate ratio showed 14 lipid plaques,20 mixed plaques and 11 firbrous plaques.The elasticity score,strain rate ratio and the blue area area ratio（AREA%）of different plaques were different,each parameter gradually increased as the echogenicity increased.The elasticity scores,strain rate ratios,blue area area ratio s（AREA%）and elasticity indexes of the plaques with different pathological types were different,and the difference was statistically significant.The parameters of lipid plaques,mixed plaques and firbrous plaques all gradually increased,and their elasticity scores were 1.14±0.54、2.74±0.75、4.16±0.65;strain rate ratios were 3.55±0.78、9.78±3.63、30.55±19.79;AREA%were 18.43±2.81、61.32±16.70、80.64±16.54;elasticity indexes were 0.67±0.32、1.96±0.29、3.76±0.46respectively.Contrast-enhanced ultrasound showed 11 patients were stable（0-1grade）,34patients were vulnerable（2-4 grade）.The differences of contrast-enhanced ultrasound EI andRatioamongplaqueswithvariouspathologicalpatterns had statistical significanc（P<0.05）.The contrast-enhanced ultrasound EI and Ratio of lipid plaques,mixed plaques and firbrous plaques gradually decreased.Their EI were4.43±2.09、2.45±1.88、1.82±1.03,Ratio were 0.35±0.13、0.21±0.10、0.17±0.11respectively.2.Energy spectrum CT:Energy spectrum CT slope of curve showed 13 patients with lipid plaques,19 patients with mixed plaques and 13 patients with firbrous plaques,effective atomic number showed10 patients with lipid plaques,22 patients with mixed plaques and 13 patients with firbrous plaques,the iodine concentration showed10patients with lipid plaques,23 patients with mixed plaques and 12 patients with firbrous plaques.The values of Energy spectrum CT slope of curve and effective atomic number among plaques with various pathological patterns had statistical significanc weresignificantly different.The values of lipid plaques,mixed plaques and firbrous plaques gradually increased.The CT value,slope of curve and effective atomic number of lipid plaques were 40.58±12.77、-3.54±0.77、3.21±0.87;the mixed plaques were80.02±14.65、0.46±0.70、7.88±0.60;the firbrous plaques were 77.55±15.33、2.33±0.57、8.56±0.69 respectively.3.The diagnostic efficiency ofdifferent methods to carotid plaque:The results showed the elasticity score and strain rate ratio of ultrasonic elastography had relatively high sensitivity and specificity to lipid plaques,energy spectrum CT had relatively high sensitivity and specificity to firbrous plaques.The respectively diagnostic efficiency of Ultrasonic elastography,contrast-enhanced ultrasound and energy spectrum CT was higher than the combined scoring model including Ultrasonic elastography,contrast-enhanced ultrasound and energy spectrum CT.Conclusions:1.The establishment of rabbit atherosclerotic plaque model by high fat diet feeding is simple,and the success rate is high.The results of elastography technology contrast-enhancedultrasoundandenergyspectrumCTwere highly consistent with pathology,further clinical study should be launched.2.With pathology as the reference standard,the elasticity score and strain rate ratio of ultrasonic elastography had higher sensitivity and specificity in diagnosing lipid plaques,energy spectrum CT had had higher sensitivity and specificity in diagnosing firbrous plaques.The diagnostic efficiency between ultrasound and energy spectrum CT were similar in diagnosing mixed plaques,therefore ultrasound may be the first choice to diagnose carotid vulnerabl plaques.3.Real-time tissue elastography technology,contrast-enhanced ultrasound and energy spectrum CT can evaluate the plaques from different perspectives,the combined application can predict the stability of plaques more Comprehensively.