MR Vessel Wall Imaging Of Carotid Atherosclerotic Vulnerable Plaque Characteristics

Part ICharacteristics of Symptomatic Carotid Atherosclerotic Plaque in Cerebral Ischemic Patients Using MR Vessel Wall ImagingObjective:To investigate the characteristics of carotid plaque between symptomatic and asymptomatic sides in cerebral ischemic patients and between patients with first-time and recurrent stroke using 3.0T high-resolution MR vessel wall imaging(MR-VWI).Materials and Methods:Patients with recent(<1 week)internal carotid artery territorial ischemic stroke were recruited in our study.Each patient was suffered from unilateral limb symptoms(the symptomatic carotid arteries defined as the arteries responsible for the ipsilateral stroke)and received multi-contrast MR-VWI of bilateral carotid arteries.The carotid atherosclerotic luminal stenosis,plaque burden(wall thickness/area/volume),plaque components(intraplaque hemorrhage[IPH],lipid-rich necrotic core[LRNC],calcification and fibrous cap rupture)and AHA classification were analyzed quantitatively and qualitatively,and based on which to compare:(1)the remodeling of carotid artery;(2)the differences of carotid atherosclerotic plaque between symptomatic and asymptomatic sides;(3)and the difference of carotid plaque in symptomatic sides of patients with first-time and recurrent acute ischemic stroke.Results:One hundred and fourteen patients were recruited with carotid stenosis of20.3±16.5%.The main findings were as follows:(1)A substantial number of high-risk plaques exist in carotid arteries with lower grade stenosis(in carotid arteries with 30%-49%stenosis,86.7%and 26.7%were found to have LRNC and IPH,respectively);(2)Compared with asymptomatic plaques,symptomatic plaques had a higher incidence of lumen stenosis,plaque burden and CA(P<0.05).Symptomatic plaques also had larger LRNC and IPH(P<0.05)and more high stroke risk Type VI lesions(OR=13.87);(3)The plaque burden were greater in patients with recurrent stroke than in patients with first-time stroke(P<0.05).Patients with recurrent stroke showed significantly higher prevalence of calcification(68.4%vs.39.4%,P<0.05),a larger volume of LRNC(179.14±254.81 mm~2 versus 71.65±111.15 mm~2,P<0.05)as well as Type VI lesions(21.1%vs.10.5%).Conclusions:Among ischemic patients with unilateral limb symptoms,the vulnerability of carotid atherosclerotic plaques in symptomatic sides are obviously higher than the asymptomatic sides.Carotid plaques in patients with recurrent ischemic stroke are significantly aggravated compared with those in patients with first-time stroke.Monitoring carotid plaques in patients with initial stroke by MR-VWI may be helpful for secondary stroke prevention.Part II Association of Carotid Atherosclerotic Plaque Features with Acute Ischemic Stroke Using MR Vessel Wall ImagingObjective: To determine the associations of carotid plaque characteristics by MR vessel wall imaging(MR-VWI)with NIH Stroke Scale(NIHSS)and acute cerebral infarct(ACI)lesions on diffusion weighted imaging(DWI).Materials and Methods: Patients suffered from unilateral limb symptoms(internal carotid artery territorial)with acute ischemic stroke were recruited in our study.Each patient received NIHSS in 48 h,carotid MR-VWI and brain DWI+MRA in 1 week after onset of symptoms.The carotid atherosclerotic lesion variables(luminal stenosis,plaque burden and components)and corresponding ACI lesion patterns and size were analyzed to evaluate:(1)the associations of carotid plaque characteristics with NIHSS scores;(2)the correlation between symptomatic carotid plaque features and intracranial artery stenosis as well as the ACI lesion patterns;(3)the associations of carotid plaque characteristics with ACI presence and volume.Results: One hundred and fourteen patients were recruited.The main findings were as follows:(1)Carotid plaque features were insignificantly associated with NIHSS scores after adjustment for stenosis(P>0.05);(2)The prevalence of carotid plaque in symptomatic side was 66.7%.The patients with carotid plaque and MCA<50% stenosis more frequently presented with concomitant perforator and multiple lesions;(3)Carotid morphological measurements,such as PWV and the LRNC size were significantly associated with ipsilateral ACIs volume before and after adjustment for significant demographic factors or stenosis in patients with carotid plaque(all p<0.05).Conclusions: Carotid plaque vulnerable characteristics(high plaque burden and large LRNC)identified by MR-VWI are independently associated with cerebral infarction as measured by DWI lesions.Our findings indicate that characterizing atherosclerotic plaque by MR-VWI might be useful for stratification of plaque risk and infarction severity.Part III Assessment of Carotid Atherosclerotic Disease Using 3D MR Vessel Wall Imaging: Comparison with DSAPurpose: To assess whether three-dimensional MR vessel wall imaging(3D-MR-VWI)can be used as a noninvasive alternative to digital subtraction angiography(DSA)at quantifying moderate to severe carotid atherosclerotic disease.Materials and Methods: Sixty-five carotid arteries from 52 patients with at least 50% stenosis underwent 3D-MR-VWI and DSA.Quantitative measurements including stenosis,lesion length and the presence/absence of plaque ulceration on the two modalities were independently determined.The intraclass correlation coefficient(ICC),Cohen's ?,sensitivity and specificity,and Bland-Altman analysis were used to assess the agreement compared to DSA.Results: Excellent agreement in measuring luminal stenosis was found between3D-MR-VWI and DSA(Spearman r=0.965,ICC 0.96;95% confidence interval [CI]: 0.93,0.97).3D-MR-VWI was also found to have high sensitivity(91.7%),specificity(96.2%)and agreement(Cohen's ?=0.85;95% CI: 0.66,0.99)with DSA for detection of ulcers.Good agreement was found between lesion length measured by 3D-MR-VWI and DSA(ICC 0.75;95% CI: 0.51,0.84).However,lesion length measurements by 3D-MR-VWI were on average 4.0 mm longer than those measured by DSA(P < 0.001).Conclusions: 3D-MR-VWI is a noninvasive and accurate way to quantify moderate to severe carotid atherosclerotic disease.With its fast acquisition and large coverage,3D-MR-VWI has the potential to become an alternative imaging approach in evaluating the severity of atherosclerosis.Part IV Tracking Progression of Angiotensin II Inducing Carotid Atherosclerotic Vulnerability in the Rabbit Model Using MR Vessel Wall ImagingObjective: To observe dynamically and evaluate the role of Angiotensin II(Ang II)inducing atherosclerotic vulnerability in the rabbits using MR vessel wall imaging(MR-VWI).Materials and Methods: Twenty-four New Zealand white rabbits were underwent intravascular balloon injury of the left common carotid artery and fed with cholesterol diet,and randomly assigned to receive either Ang II(Ang II group)or phosphatebuffered saline(control group).The rabbits were imaged 3 times: at baseline,8 and 12 weeks.Carotid lesions on both MRI and histology were categorized according to the American Heart Association(AHA)classification,and the results of MRI were compared with those of histology.The differences of carotid plaque features(plaque burden and components)between Ang II group and Control group were compared.Immunohistochemical analyses for Pentraxin 3(PTX3),RAM11,and CD31 were also performed.Results: Atherosclerotic plaque was identified in all remaining 21 rabbits.The Kappa value of AHA types between types between MR-VWI and histology was 0.79(95%CI:0.69-0.88,P <0.001).Typical features of vulnerable plaque(3 IPH plaques),were observed in 6 of 10 animals(60.0%)in Ang II group,no IPH plaque was identified in 11 rabbits of control group.MRI revealed that the effective size of plaque burden(mean wall area,max wall thickness and lipid necrotic core area)which was used to express the change of carotid morphology were significantly different between Ang II group and control group.In addition,immunohistochemical analysis demonstrated that PTX3,RAM11,CD31 were higher expressed in Ang II group plaques compared to control group plaques.Conclusions:Our results support a positive role of Ang II in plaque vulnerability together with intravascular balloon injury and cholesterol diet.The vulnerable feature of carotid plaque could be quantitatively monitored with MR-VWI in vivo and confirmed with histomorphology in rabbits.