High Resolution Vessel Wall Magnetic Resonance Imaging In Evaluation Of Middle Cerebral Arterial Atherosclerotic Plaques

Background and PurposeIschemic stroke is an important public health problem worldwide,characterized by high morbidity,high mortality,high disability and high recurrence rate.Most of intracranial atherosclerotic disease（ICAD）is directly related to arterial stenosis,The middle cerebral artery（MCA）is the most common site of stenosis.Atherosclerotic plaques can show different results due to differences in the distribution or composition.Some plaques are prone to cause ischemic stroke,while others are stable plaques with no obvious clinical symptoms.It brings two major challenges:（1）Identifying the nature and composition of culprit lesions in symptomatic patients;（2）Identifying the nature of plaques in asymptomatic patients,and detecting high-risk vulnerable plaques that cause ischemic stroke.Common cerebrovascular imaging techniques include computed tomography angiography,magnetic resonance angiography,transcranial Doppler ultrasound and digital subtraction angiography.However,these vascular imaging methods can only show the degree of lumen stenosis and cannot provide information about the underlying pathology of the vessel wall.High-resolusion magnetic resonance imaging（HRMRI）can not only show the degree of lumen stenosis,but also provide information about structure,composition of plaque and characteristics of the arterial wall.HRMRI is non-invasive,non-radiation,high resolution,and high repeatability.Previous studies have found that the morphological and compositional characteristics of plaques are more helpful than lumen stenosis when determining culprit lesions in the coronary and carotid arteries and subsequent cardiovascular ischemic events.Some studies have also found that the degree of MCA stenosis between patients with symptomatic and asymptomatic stenosis is similar.A number of studies have shown that plaque location,morphology,and signal characteristics such as plaque enhancement,plaque burden,remodeling index,and plaque distribution are better than simple lumen stenosis for stroke risk stratification in ICAD patients.In this study,HRMRI vascular wall imaging technology was used to analyze the morphology of culprit MCA and plaque characteristics in patients with asymptomatic and symptomatic stenosis,to investigate the difference in the location,morphology,and enhancement characteristics of the culprit plaques between patients with symptomatic and asymptomatic stenosis,and to explore the value of comprehensive evaluation in distinguishing high-risk plaques in the middle cerebral artery on HRMRI.Materials and Methods:In this study,all measurements were carried out by German Siemens MAGNETOM Prisma 3.0T magnetic resonance scanner with 64-channel head-neck combined coil.All of the subjects underwent DWI,3D TOF MRA and 2D-TSE high-resolution magnetic resonance imaging sequences（including precontrast T1WI,T2WI and gadolinium-enhanced T1WI）.A total of 146 patients with unilateral MCA stenosis（64 cases of asymptomatic stenosis and 82 cases of symptomatic stenosis）admitted to the First Affiliated Hospital of Zhengzhou University from September2017 to December 2019 were collected,all of the patients are right-handed.According to DWI or clinical manifestations,symptomatic patients were considered for inclusion if there was a diffusion-restrictive lesion seen on DWI in the territory of the stenotic MCA within 2 weeks of onset of symptoms.Asymptomatic patients were considered for inclusion if there was no history of cerebrovascular events or if an ischemic event occurred in a vascular territory outside the affected MCA.The distribution（superior,inferior,ventral,dorsal wall）of plaques on maximal lumen narrowing（MLN）of the affected MCA in patients with symptomatic and asymptomatic stenosis was counted.For quantitative ananlysis,we measured the vessel area of maximal lumen narrowing(VA_MLN),lumen area of maximal lumen narrowing(LA_MLN)and the vessel area of referential lumen(VA_RL),lumen area of referential lumen(LA_RL)and the signal intensity of the plaque before and after contrast of two groups,and then calculated the wall area of maximal lumen narrowing(WA_MLN),degree of stenosis,remodeling index,plaque area（PA）,percentage of plaque burden,and plaque enhancement rate.Each parameter was compared for analysis.Statistical software SPSS 21.0 was used for data analysis.The chi-square test or rank sum test was used to compare the differences between qualitative data.The normality of the data is verified by the Shapiro-Wilk normality test.Quantitative data accorded with the normal distribution were expressed as the mean±standard deviation（（?）s）,while the data accorded with the non-normal distribution were expressed as the median（interquartile range）.If the quantitative data accorded with the normal distribution and the variance is homogeneous,independent sample t test is used for comparison between two groups;if the quantitative data accorded with the non-normal distribution,the Wilcoxon rank sum test is used for comparison between the two groups.The test level was set toα=0.05,and P<0.05 considered the difference to be statistically significant.The Med Clac software was used to analyze the receiver operating characteristic curve（ROC）.Result1.There were statistically significant differences in the distribution of plaques on the superior walls（4 cases in asymptomatic stenosis group/19 cases in symptomatic stenosis group）and inferior walls（28 cases in asymptomatic stenosis group/15 cases in symptomatic stenosis group）of MCA between the two groups（P<0.05）,while there were no statistically significant differences in the distribution of plaques on the other walls between the groups（P>0.05）.2.VA_MLN,WA_MLN,and VA_RLin the asymptomatic group were 7.26（2.18）mm²,5.57（1.88）mm²,8.02（3.23）mm²,respectively,and in the symptomatic group VA_MLN,WA_MLN,and VA_RLwere 8.59（4.34）mm²,7.17（3.65）mm²,8.73（3.68）mm²,respectively.The differences between the two groups of VA_MLN,WA_MLN,and VA_RLwere statistically significant（P<0.05）.The differences between the two groups of LA_MLNand LA_RLwere not statistically significant（P>0.05）.3.The degree of stenosis,remodeling index,PA,percentage of plaque burden and plaque enhancement rate in the asymptomatic group were 61.90%（22.62%）,0.88（0.31）,1.38（2.38）mm²,17.46%（29.96%）,0.94（1.11）,respectively.The degree of stenosis,remodeling index,PA,percentage of plaque burden and plaque enhancement rate in the symptomatic group were 67.74%（22.62%）,1.05（0.34）,2.94（2.81）mm²,33.07%（21.88%）,1.15（0.93）,respectively.The differences in the degree of stenosis,remodeling index,PA,percentage of plaque burden and plaque enhancement rate between the two groups were statistically significant（P<0.05）.4.The degree of stenosis,VA_MLN,WA_MLN,VA_RL,PA,percentage of plaque burden,remodeling index,plaque enhancement rate were all capable of diagnosing symptomatic stenosis.Among them,WA_MLNhad the best diagnostic capability,and the area under the curve was 0.762（95%confidence interval was[0.684,0.828]）,optimal cut-off value was 6.34 mm²and the corresponding sensitivity and specificity were 73.2%and 75.0%,respectively.ConclusionIt is of importance in clinical value that high-resolution MRI can comprehensively evaluate middle cerebral artery atherosclerotic plaques in plaque location,shape and enhancement,etc.Symptomatic stenosis is more significant in the degree of stenosis,remodeling method,plaque burden,plaque enhancement,which is helpful for early identification and determination of high-risk plaques.