Vessel Wall Magnetic Resonance Imaging Of Occluded And Long-segmental Stenotic Internal Cartid Artery

BackgroundAs the second leading cause of death worldwide and the most common cause of long-term disability,stroke represents a massive public health problem.Approximately 18-25%of all ischemic strokes are attributable to thromboembolism caused by carotid atherosclerotic disease.Symptomatic internal carotid artery occlusion has a risk of annual recurrent stroke of approximately 3-10%,emphasizing the importance of effective treatment and the secondary prevention of its recurrence.For acute ischemic stroke,the addition of endovascular thrombectomy of proximal large artery occlusion to intravenous alteplase increases functional independence for a further fifth of patients and protects patients from recurrent stroke.Chronic internal carotid artery occlusion may also manifest as acute ischemic symptoms due to insufficient cerebral perfusion and microembolization.However,compared with acute occlusion,the recanalization of chronic occlusion displayed a relatively low success rate and severe complications.Therefore,precise differentiation of acute and chronic occlusion and systematic evaluation of whole-segmental atherosclerotic distribution with appropriate imaging modality may be helpful for the selection of suitable surgical cases and the successful recanalization.Traditional lumenography is based on the quantification of the degree of stenosis for stratifying the severity of carotid artery atherosclerosis and,thus,for the choice of intervention strategies.However,lumenography is unable to display the vessel wall characteristics and plaque composition.And vessel stenosis is a poor indicator of plaque burden as vessels accommodate plaques by remodeling,particularly early in their natural history.Thus,the traditional idea of using the degree of luminal stenosis as the sole imaging marker for the selection of the best therapeutic approach is challenged.Vessel wall magnetic resonance imaging(VWI)enables direct visualization of both luminal change and vessel wall pathology,and has been already well established to analyze carotid atherosclerosis.Traditional 2-dimensional(2D)VWI can qualitatively and quantitatively analyze the components of atherosclerotic plaque(fibrous cap,lipid-rich necrotic core,calcification,intraplaque hemorrhage,and inflammation,etc.)using multicontrast weighting techniques.3D VWI provides large spatial coverage and can simultaneously perform wall imaging of the extracranial and intracranial ICA.And T1 SPACE allows for multiplanar and curved planar reconstructions,which are of high interest given the anatomical tortuosity of the carotid arteries.Currently,there is no research focused on the wall remodeling in the occluded internal carotid artery and systematic evaluation of plaque burden in long-segmental internal carotid artery stenosis by using VWI.In this study,we evaluated the unique vessel wall appearance of the occluded and long-segmental stenotic carotid artery and explored the potential implications for clinical management using 2D and more effective 3D VWI.This study contains two parts,as follows:Part Ⅰ Remodeling of occluded internal carotid artery in vessel wall magnetic resonance imagingObjective:The purpose of the present study was to investigate the remodeling,signal intensity(SI),and enhancement pattern of the extracranial occluded internal carotid artery(OICA)by VWI and explore the wall characteristics of acute occlusion.Methods:Patients with MRA and ultrasound confirmed OICA were prospectively enrolled in our study.Symptomatic OICAs were defined as ICAs that exhibited ipsilateral downstream cerebral ischemia or ophthalmic artery embolism within the last three months.Otherwise,asymptomatic OICAs were defined.ICAs with atherosclerosis but no stenosis in our VWI database were recruited as the atherosclerotic control group.The clinical details as age,sex,history of hypertension,diabetes mellitus,hyperlipidemia,coronary artery disease,and smoking habits were collected.All cases underwent a 3-Tesla MR examination to acquire 3D time-of-flight(TOF)MRA and 2D pre-and post-contrast T1-weighted fast spin echo sequences.Five consecutive slices from the first image showing occlusion(i.e.O1,O2,O3,O4,and 05)were chosen for imaging analysis.The outer wall area(OWA)was calculated based on the outer contour of the ICA drawn on the pre-contrast VWI.Negative remodeling was defined as a lower OWA compared to that of the atherosclerotic group.Two neuroradiologists who were blinded to the clinical characteristics evaluated the SI on T1 and the presence and pattern of enhancement on postcontrast T1.Based on those parameters,the remodeling pattern of OICA and the difference between(1)the symptomatic and asymptomatic OICA;and(2)the proximal and distal segment of occlusion were evaluated.Results:Forty-six atherosclerotic OICAs from 38 consecutive cases were recruited.Six patients were excluded from the study,of which,3 patients could not tolerate the MR examination,and 3 patients showed impaired imaging quality because of motion artifacts.Finally,39 OICAs from 32 patients were included in the analysis(7 patients showed bilateral OICA),of which,25 ICAs were symptomatic and the remaining 14 ICAs were asymptomatic.Twenty-four ICAs from 22 patients were recruited as the atherosclerotic control group.Clinical characteristics including age,sex,and vascular risk factors showed no significant difference between the occluded and atherosclerotic groups(p>0.05).However,the OWA was lower in the occluded group than in the atherosclerotic group(e.g.O1 segment,0.63±0.31 vs.0.90±0.39 cm2,p=0.004).For all OICAs,the OWA was larger in symptomatic cases than asymptomatic cases(0.71±0.29 vs.0.49±0.30 cm2,p=0.025).Using a cutoff value of 0.45,the sensitivity and specificity of OWA for detecting symptomatic OICA were 0.88 and 0.55,respectively.Homogeneous SI and enhancement were more often observed at the O5 segment than the O1 segment of occlusion(p<0.05).The inter-observer agreement regarding the evaluation of VWI characteristics was desirable(κ=0.801-0.847).Conclusions:1.Asymptomatic OICA is more likely to manifest as negative remodeling than symptomatic OICA.2.The characteristics of plaque as homogeneous T1 SI and enhancement at the distal segment of OICA are not as significant as the proximal segment.3.By evaluating the remodeling pattern and providing the wall characteristics of the occlusion,VWI may provide a reference for screening acute occlusion cases and assessing the plaque burden of the distal occlusion before recanalization.Part Ⅱ Combination of extracranial and intracranial vessel wall magnetic resonance imaging in patients with long-segmental internal carotid artery stenosisPurpose:Long-segmental internal carotid artery stenosis(LICAS)is manifested as severe stenosis from the carotid bifurcation to the distant vessel,and the atherosclerosis of which may involve multiple vascular beds including extracranial and intracranial segments.We aimed to explore the pattern of wall change in atherosclerotic LICAS using 2D and 3D joint extracranial and intracranial vessel wall magnetic resonance imaging(VWI).Methods:Patients with LICAS confirmed by MRA or CTA were prospectively recruited in the study.Cases with atherosclerosis but no severe stenosis(<70%)were enrolled as the atherosclerotic control group.All patients underwent 2D and 3D joint extracranial and intracranial VWI on a 3T MRI scanner.Imaging sequences included:3D TOF MRA,2D axial pre-and postcontrast T1,and 3D sagittal pre-and postcontrast T1 sampling perfection with application-optimized contrast using different flip angle evolution(SPACE).The plaque burden(maximal wall thickness[MaxWT]and normalized wall area[NWA]),vessel area(VA),the pattern of wall thickening and enhancement,and image quality were analyzed quantitatively and qualitatively at the extracranial and intracranial segments,respectively.Negative remodeling was defined as a lower VA compared to that of the control group.An atherosclerotic plaque was defined as eccentric wall thickening.The remodeling pattern of LICAS,the differences of(1)plaque burden between LICAS and atherosclerotic group;(2)positive rate of plaque between the joint extracranial and intracranial VWI and extracranial/intracranial VWI alone;(3)image quality and morphological measurements between the 2D and 3D images were evaluated.Results:Twenty-nine ICAs with long-segmental stenosis from 23 patients were recruited in the study,of which 3 ICAs were excluded because of claustrophobia or motion artifacts.Twenty-seven ICAs from 24 patients with atherosclerosis were enrolled as the atherosclerotic control group.Clinical characteristics showed no significant difference between the two groups(p>0.05).The LICAS group showed larger MaxWT and NWA,but lower VA compared to the atherosclerotic group at both of the extracranial and intracranial segments(p<0.05).Eight ICAs(30.8%)with concentric wall thickening at the intracranial segment showed lower intracranial NWA(0.72 ±0.14 vs.0.86±0.09,p=0.007)and larger cervical MaxWT(6.05±1.07 vs 4.08±1.65 mm,p=0.005)when compared with those with eccentric pattern(69.2%).The positive rate of plaque in LICAS was improved using joint extracranial and intracranial VWI compared with intracranial VWI alone(p=0.008).Compared with 2D VWI,2D images reformatted from 3D T1 SPACE displayed larger VA(0.47 ±0.30 vs.0.43 ±0.25 cm2,p<0.001)and relatively poorer image quality(p<0.001).Conclusion:1.Diffuse atherosclerotic burden and negative remodeling were prevalent in LICAS.2.In LICAS,compared with those with eccentric wall thickening at the intracranial segment,cases with concentric wall thickening suffered larger cervical atherosclerotic burden.3.Joint extracranial and intracranial VWI can improve the detection of plaque in LICAS.4.Compared with the 2D images reformatted from 3D T1 SPACE,2D VWI displayed better imaging quality and outer boundary delineation.Using 3D sequence for lesion screening and 2D sequence for detailed refinement may serve as an efficient and precise VWI protocol.