In Vivo Middle Cerebral Artery Atherosclerotic Plaque Imaging By High-resolution Magnetic Resonance Imaging

Intracranial atherosclerosis (ICAS) represents the most common cause of ischemic stroke worldwide. Important predictors of stroke risk in these patients include the degree of stenosis and the underlying plaque morphology. Our traditional understanding of ICAS is based on the detection of hemodynamically relevant intracranial stenoses. Current imaging modalities for the assessment of MCA stenosis include transcranial Doppler ultrasound (TCD), magnetic resonance angiography (MRA), computed tomography angiography (CTA) and digital subtraction angiography (DSA). These evaluation tools are of limited utility because they are only able to demonstrate the degree of stenosis, but fail to provide information on the vessel wall structures.It is known from the studies of coronary and carotid arteries that vessel wall characteristics are closely related to clinical presentations and subsequent ischemic events. Therefore, ICAS should be evaluated with both lumen and wall imaging so ischemic risk and management can be determined. There has been a growing body of interest in the role of MRI for imaging the vessel wall or plaque. Plaque characteristics identified by high-resolution magnetic resonance imaging (HR MRI) in the carotid artery have been shown to correlate well with histologic findings. However, intracranial arterial wall imaging poses a greater challenge given the smaller size and relatively deep location of the target vessels. It has not yet been systemically applied to multiple intracranial vascular pathologies using1.5-T HR MRI.High-field MR system has higher SNR, may be beneficial in the visualization of intracranial artery walls. A3.0-T HR MRI has been increasingly used in the investigation of intracranial vascular pathologies. The goal of this study was to characterize the middle cerebral artery (MCA) atherosclerotic plaques with using3.0-T HR MRI.Part One Plaque imaging in symptomatic and asymptomatic middle cerebral artery atherosclerotic stenosis using high-resolution magnetic resonance imagingObjective:To compare the plaque properties between symptoms and asymptomatic MCA atherosclerotic stenosis using3.0-T multicontrast-weighted HR MRI. Methods: Multicontrast-weighted HR MRI were acquired in32patients with symptomatic and14patients with asymptomatic MCA atherosclerotic stenosis. The fingings of MCA plaques on HR MRI were compared between the two groups. Results:The lumen area (LA) was similar between the two groups (2.94±0.72mm2vs3.16±0.86mm2, P=0.355). Compared with the asymptomatic group, symptomatic MCA stenosis had a larger vessel area (VA)(19.30±1.14mm2vs18.09±1.41mm2, P=0.003) and wall area (WA)(16.37±1.14mm2vs14.93±1.46mm2, P=0.001), higher prevalence of plaque enhancement after gadolinium injection (84.4%vs35.7%, P=0.003). Conclusions:Different vessel wall properties on HR MRI were observed between symptomatic and asymptomatic MCA stenosis. The HR MRI technique is a potentially promising noninvasive tool that can be used in stratifying stroke risk in patients with MCA atherosclerotic disease.Part Two Positive remodeling in symptomatic middle cerebral artery stenosis:a high-resolution magnetic resonance imaging and microemboli monitoring study.Objective:To investigate the existence of an association between Positive Remodeling (PR) in symptomatic MCA atherosclerotic stenosis with HR MRI and TCD monitoring of microembolic signals (MESs). Methods:A total of36patients with symptomatic MCA atherosclerotic stenosis underwent MES monitoring by TCD and3.0-T HR MRI. Proton density-weighted (PdWI) cross-sectional images with submillimeter voxel size were obtained. The remodeling patterns and plaque morphology of the sites of maximal luminal narrowing were analyzed in terms of their association with the MES data. Results:PR was found in16lesions (44.4%). Compared with the non-PR group, the PR group had a greater vessel area (19.97±1.42mm2vs.18.23±1.23mm2) and greater wall area (16.93±1.47mm2vs.14.93±1.52mm2, both P<0.0001) at the sites of maximal luminal narrowing. MESs were observed more frequently in the PR group than in the non-PR group (62.5%vs.15.0%, P=0.003). Conclusion:In patients with symptomatic MCA atherosclerotic stenosis, MESs were observed more frequently in the PR group than in the non-PR group.Part Three Endovascular intervention of middle cerebral artery stenosis and a perioperative evaluation using high-resolution magnetic resonance imaging at3.0-TObjective:To evaluate MCA wall structures before and after endovascular intervention by3.0-T HR MRI. Methods:Five patients underwent primary percutaneous transluminal angioplasty (PTA) alone or stenting of medically refractory symptomatic MCA atherosclerotic stenosis. They underwent MCA wall HR MRI under a3.0-T MR scanner before and after the procedure. Results:Multicontrast-weighted HR MRI were acquired in2patients with primary angioplasty alone and3patients with wingspan stenting. HR MRI clearly identified the eccentric MCA atherosclerotic plaque and wall structures in all patients before and after endovascular intervention. In one patient with primary PTA alone, MCA plaque notable enhancement was observed on HR MRI after the procedure. At12-month HR MRI follow-up, the enhancement was no longer shown. Conclusion:PTA may transform a relatively stable plaque into a unstable plaque. HR MRI may be used to monitor changes in vessel wall and plaque characteristics in endovascular intervention of MCA atherosclerotic stenosis.