Characterization Of Intracranial Atherosclerotic Stenosis Using 3D High-resolution Magnetic Resonance Vessel Wall Imaging

Intracranial atherosclerotic disease(ICAD)is a major cause of stroke worldwide and a prevelant disorder.Its slow progression provides an opportunity for diagnosis before symptoms occur.There is increasing evidence that atherosclerotic plaque components,i.e.rich lipid core.intraplaque hemorrhage and inflammatory cells infiltration,as well as the stenosis caused by plaque are important determinants of clinical events including stroke.It is crucial to evaluate objectively on the intracranial vessels and plaque characteristics to better stratify stroke risk and guide individual treatment.Traditional ICAD diagnosis has depended on stenosis as measured by angiography(i.e.DSA,CTA.MRA):however,lumen narrowing is a poor indicatior of plaque burden when vessels accommodate plaques by remodeling,particularly early in their natural history.Angiography may underestimate the preve lance of ICAD.Black blood MRI imaging(BBMRI)is an effective method to measure wall thickness and identify pathological features of extracranial vessels.BBMRI is capable of characterization of the extracranial carotid wall in vivo and to identify features that indicate risk for disruption.Compared to extracranial arteries,the size of intracranial arteries is small.Besides,the course of' intracranial arteries is tortous and deep in the brain,surrounded by blood and cerebrospinal fluid(CSF).3D BBMRI has been extended to characterize intracranial vessel wall in vivo,and it enables a global evaluation of multiple intracranial lesions contemporaneously.The 3D feature is crucial to the precise measurement of the inherently curved intracranial arteries.3D variable flip angle sequences were most popularly used,including volumetric isotropic turbo spin echo acquisition(VISTA,Philip),and sampling perfection with application-optimized contrasts by using different flip angle evolutions(SPACE.Siemens).This technique employs long echo train length and variable flip angle to achieve stable signals.3D BBMRI can identify ICAD and provide highly reliable wall measurements of intracranial vessels.It has great potential in clinical diagnosis of ischemic stroke and intracranial hemorrhage.The aim of our study was to improve and apply 3D high-resolution BBMRI technique to further understand the characteristics of-ICAD vessel wall and plaques,thereby providing referral for stroke prevention and risk estimation.This study contains two parts,as follows:Part 1.Improved Cerebrospinal Fluid Suppression using ADE-BBMRIObjective:To develop a 3D high resolution black blood MRI(BBMRI)method for evaluation of intracranial vessels with improved cerebrospinal fluid(CSF)suppression.The anti-driven-equilibrium(ADE)pulse was incorporated into a variable flip angle turbo spin echo-based 3D BBMRI to improve CSF suppression.Material and Methods:All exams were performed on a 3T MRI scanner(Achieva;Philips Healthcare,the Netherland).ADE-BBMRI was optimized in 8 healthy volunteers and compared with the corresponding BBMRI,with acquired 0.5mm isotropic resolution and scan time of 5.4 minutes.Contrast-enhanced ADE-BBMRI protocol was implemented in 9 patients with intracranial atherosclerosis.The targeted segments of vessel wall included middle cerebral artery(MCA)and basilar artery(BA).The signal(signal-to-noise and contrast-to-noise)and morphological measurements using VesselMass software(Leiden University Medical Center,the Netherlands)were compared between ADE-BBMRI and BBMRI,as well as pre-and post-contrast ADE-BBMRI images.Signal-to-noise ratio(SNR).contrast-to-noise ratio(CNR),lumen area(LA).wall area(WA).mean wall thickness(meanWT)and maximum wall thickness(maxWT)were calculated.Reliability was assessed by intraclass correlations(ICC).Results:ADE-BBMRI effectively suppressed the surrounding CSF signal of intracranial vessels,with a 36%-44%CSF signal reduction in comparison with BBMRI.ADE-BBMRI also reduced the overall wall signal by 8%-8.5%,but it provided a significant improvement in wall-to-CSF contrast-to-noise ratio over BBMRI(middle cerebral artery.5.93±0.59 vs.3.95±1.67.p<0.01:basilar artery,3.81±1.76 vs.1.34±0.54,p= 0.01,respectively).No differences were noted in morphological measurements between two sequences(ADE-BBMRI vs.BBMRI:LA,6.35±2.87rmm2 vs.6.32±2.84mm2,p=0.23;WA,1.28±0.52mm2vs.1.27±0.53 mm2,p=0.47;MWT,0.93±0.30 mm vs.0.93±0.32mm.p= 0.95;MaxWT,1.27±0.33 mm vs.1.28±0.36mm.p= 0.84).Contrast enhanced ADE-BBMRI improved the plaque detection as demonstrated by the increased wall signal,wall-to-CSF and wall-to-blood contrast-to-noise ratio.Reliabilityfor all measurements(signal-based SNRlumen.SNRwall SNRCSF,and morphology-based LA,OWA,MWT)was fair to excellent(ICCs ranged from 0.54 to 0.95).Conclusion:3D ADE-BBMRI provides excellent blood and CSF suppression,and reliable measurements of intracranial vessels at 0.5mm isotropic resolution in approximately 5 minutes.Its clinical application may provide important insight into stroke risk.Part 2.Characterization of Asymptomatic Intracranial Atherosclerosis using 3D High Resolution Contrast-enhanced MRIPurpose:Approximately 77%of strokes occur abruptly in asymptomatic individuals,emphasizing the necessity of effective diagnosis before cerebrovascular events occur.The aim of this study was to characterize asymptomatic intracranial atherosclerosis(ICAD)using 3D high-resolution contrast-enhanced black-blood magnetic resonance imaging(BBMRI)and compare with symptomatic plaques from stroke patients.Materials and methods:This HIP A A-c ompliant study was approved by the institutional review board.Fifty-five subjects(mean age,71.3 ± 11.2 years)with evidence of ICAD(29 stroke-free participants from the Atherosclerosis Risk in Communities(ARIC)study:26 patients with cerebrovascular ischemic events)underwent 3D time-of-flight MRA and contrast-enhanced ADE-BBMRI examinations at 3T(Achieva;Philips Healthcare.the Netherland).High-resolution intracranial vessel wall imaging was acquired based oin a standardized protocol that included 3D time-of-flight(TOF)MRA.pre-and post-contrast 3D BBMRI imaging and 3D contrast-enhanced(CE)MRA.Each identified plaque was graded by plaque enhancement(0 grade.1 grade.2 grade).luminal stenosis(no detectable stenosis,<50%,51%-70%,71-99%.and occlusion)and its likelihood to have caused a stroke identified on MRI(culprit,probably-culprit.or non-culprit).The presence of intraplaque hemorrhage(IPH)and palque surface irregularity were recorded.Quantitative measurements were performed in 29 pairs of plaques from stroke(i.e.,culprit)and ARIC groups,respectively,and matched by plaque location.Plaque thickness,normalized wall index,and degree of contrast-enhancement(%CE)were calculated.Associations between the likelihood of being a culprit lesion with qualitative and quantitative measures were estimated using logistic regression.Results:There were 162 plaques(mean 5.8/person)identified in ARIC participants,and 101 of 162 plaques(62%)showed contrast enhancement(i.e.,grade 1,or 2).A total of 134 plaques(mean 5.2/person)were identified in stroke patients,of which,29(22%)were categorized as culprit plaques.Overall,111 of 134 plaques(83%)showed contrast enhancement(i.e.,grade 1,or grade 2)in stroke parients.Compared to asymptomatic plaques,culprit plaques more frequently demonstrated signal heterogeneity(79%vs.38%,p=0.001),surface irregularity(48%vs.7%,p<0.01),IPH presence(24%vs.3%,p=0.022).a larger plaque burden(84%vs.75%.p<0.01),higher stenosis grade(e.g.,>50%,48%vs.17%,p<0.01)and higher%CE(25.66±15.34 vs.8.02±5.85.p<0.01).The presence of IPH(OR.15.84:95%CI,1.52-165.44;p=0.021)and%CE(OR,1.24;95%CI.1.07-1.43;p=0.004)were independently associated its likelihood to have caused a stroke,after adjusting for wall thickness,normalized wall index and luminal stenosis.There was no association between categorical stenosis degree and culprit plaques or between normalized wall index and culprit plaques.Conclusions:3D contrast-enhanced BBMRI can characterize ICAD in asymptomatic and symptomatic population,which is promising for stratifying stroke risk.