| Part Ⅰ: Age and anatomic location related hemodynamic changes assessed by 4D flow MRI in carotid artery of healthy adultsObjective: To evaluate the hemodynamic changes(volume,velocity,wall shear stress,pressure gradient,energy loss)of carotid artery in healthy adults among different ages and anatomic locations using 4D flow MRI,explore their possible influences to carotid artery diseases.Materials and Methods: Sixty-two healthy volunteers aging from 20 to 70 years were enrolled in this study.4D flow MRI examinations were performed for each subject and analyzed using CVI42 platform to generate hemodynamic parameters.Hemodynamic parameters were compared among different age groups and anatomic locations(proximal CCA,distal CCA,proximal ICA and distal CCA)using one-way ANOVA.Paired t-test was used to estimate the differences between left and right vessels.The relationship between age and hemodynamic parameters was quantified by Pearson’s correlation coefficient.Results: There existed no differences between left and right carotid artery for all the hemodynamic parameters(all P values > 0.05),so we set each vessel as an independent sample.Proximal ICA showed significant lower volume,velocity,wall shear stress and pressure gradient than other locations(P < 0.05),the hemodynamic parameters showed a downward trend at first,reached the lowest point at proximal ICA and then began to rise,energy loss showed no difference in different location.At different ages,the hemodynamic parameters(except WSS distal to the internal carotid artery)in the young group were significantly higher than those in the middle-aged and old groups(P<0.05).PG and EL in the middle-aged group were higher than those in the elderly group as a whole,and the difference in dis-CCA was significant(P<0.05).The ELmax of the middle-aged group was higher than that of the old group(P<0.05).Wall shear stress(except in distal ICA),velocity,pressure gradient and energy loss decreased with age(P < 0.05).Conclusion: The multi-parameter analysis of 4D flow MRI identified age and anatomic location changes of hemodynamic parameters in carotid artery of healthy adults.The lower velocity,wall shear stress,pressure gradient in proximal ICA and reduced trend with age may be associated with disease occurrence.In addition,the hemodynamic parameters in different location may provide age matched control cohorts for carotid artery disease.Part Ⅱ: Differences in wall shear stress between high-risk and low-risk plaques in patients with moderate carotid artery stenosis: A 4D flow MRI studyObjective: To evaluate the difference in wall shear stress(WSS)(axial,circumferential and 3D)between high-risk and low-risk plaques in patients with moderate carotid artery stenosis and to identify which time points and directions play the dominant role in plaque risk.Materials and Methods: Forty carotid arteries in thirty patients were examined in this study(ten patients with bilateral carotid plaques).All patients underwent high-resolution magnetic resonance vessel wall imaging(HRMR-VWI),diffusion-weighted imaging(DWI),and 4D flow magnetic resonance imaging(MRI).Twenty-four patients had high-risk plaques,and sixteen patients had low-risk plaques.The 4D flow images were analysed using the cvi42 platform to calculate WSS.The independent sample t test was used to compare WSS between low-and high-risk plaques in the whole cardiac cycle,as well as at 20 different time points in the total cardiac cycle;P < 0.05 was considered statistically significant.Results: Patients with high-risk plaques had higher axial,circumferential and 3D WSS than low-risk plaques throughout the entire cardiac cycle(P < 0.05).The mean age was56.3±9.5 years,the max and mean 3D WSS of normal controls in the same age group were0.203±0.01 pa and 0.138±0.01 pa,in vulnerable plaques group,and the max and mean 3D WSS were 0.365±0.052 pa and 0.210±0.046 pa,in non-vulnerable plaques group,the max and mean values were 0.281±0.053 pa and 0.153±0.043 pa,respectively.both vulnerable and non-vulnerable plaques’ WSS has increased,but it increased more obvious in vulnerable plaques than that in non-vulnerable plaques.And the changes varied at 20 different time points.The number of insignificant difference(P > 0.05)was less in diastole than systole in different time points.Axial WSS values were higher than circumferential WSS values;the difference in axial WSS values between high-and low-risk plaques was more significant than circumferential WSS,whereas 3D WSS values best reflected the difference between high-risk and low-risk plaques because they showed significant differences at every time point.Conclusion: Increased WSS,especially during diastolic period and in the axial WSS direction,may be related to atherosclerotic plaque rupture and cause cerebrovascular events in patients with moderate carotid artery stenosis.Also,these can provide hemodynamic information and help clinicians make more accurate decisions for plaque patients.Part Ⅲ: Identification of culprit plaques in patients with cerebrovascular events using radiomics based on three-dimensional high-resolution vascular wall imagingObjective: To identify the culprit and nonculprit plaques in cerebrovascular events patients with middle cerebral artery plaque using radiomics based on three-dimensional high-resolution magnetic resonance vascular wall imaging(3D HRMR-VWI),and compare the efficacy of five different radiomics methods in identifying culprit plaques.Materials and Methods: A total of 117 patients with 139 plaques in the middle cerebral arteried were enrolled and divided into training and validation sets in a ratio of 7:3.Magnetic resonance examinations included 3D HRMR-VWI(before and after enhancement),magnetic resonance angiography and diffusion weighted imaging,Each identified plaque was classified as 69 culprit plaques and 70 nonculprit plaques.The radiomics model was constructed using 3D HRMR-VWI before and after enhancement.Traditional information included plaque characteristics(plaque diameter,minimum lumen area,intraplaque hemorrhage,minimum lumen diameter,stenosis rate,plaque burden,enhancement rate and remodeling index)and clinical risk factors(sex,age,hypertension,hyperlipidemia,diabetes,smoking,drinking,history of coronary heart disease and stroke history).Mann-Whitney U test and chi-square test were used for traditional factors,and factors with predictive value in univariate analysis were further analyzed by multivariate logistic regression.The radiomics models were modeled by the least absolute shrinkage selection operator(LASSO)method,the random forest(RF)method,the extreme learning machine(ELM)method,the linear discriminant analysis(LDA)method and the extreme gradient boosting(XGB)method.The Delong test was used to compare the differences of the modles’ efficacy in identifying culprit plaques.Results: In traditional information,only intraplaque hemorrhage was an independent predictor for culprit plaques;Radiomics played an important role in identifying culprit plaques,and its efficacy was much higher than traditional information;Enhanced 3D HRMR-VWI showed better efficiency than before enhanced 3D HRMR-VWI,and the performance of combing the two sequences is the best;Among different radiomics models,the XGB method shows the best performance,the final fusion prediction model was established by the XGB method based on intra-plaque hemorrhage and 3D HRMR-VWI radiomics,the area under curve(AUC)in the training set is 0.949,and in the validation set is 0.939.Conclusion: In this study,the use of radiomics in 3D HRMR-VWI can accurately identify culprit plaques in symptomatic middle cerebral artery plaques,the extreme gradient boosting method showed the best performance in radiomics models,which can provide a new method for clinical identification of culprit plaques. |
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