Visualization of Local Changes in Vessel Wall Morphology and Plaque Progression in Serial Carotid Artery Magnetic Resonance Imaging

Carotid atherosclerosis is an important cause of ischemic stroke. Assessment of plaque composition in addition to degree of luminal stenosis can be used to identify patients with increased risk of stroke and assess disease progression. Magnetic resonance imaging (MRI) is an excellent noninvasive imaging technique to assess vessel wall morphology and plaque composition, with good accuracy and reproducibility.1 Serial MRI of the carotid artery is used in several studies which focus on measuring the natural history of carotid artery plaques in symptomatic1 and asymptomatic2 patients and effects of lipid-lowering therapy using statins.3,4 The current standard to analyze serial MRI scans is to compare volume measurements based on manual segmentations of the vessel wall and plaque components. Before comparing the scans, the scans have to be aligned to each other on a slice level. Different approaches exist to align scans from different time points. One study aligns the scans by centering the image stack at each time point over the plaque,1 and another study uses the baseline scan as a reference at the follow-up session to ensure targeting the same arterial segment.4 Alternatively, postprocessing can be used to match the axial images from different time points according to their distance to the carotid bifurcation.2,3 Furthermore, comparison between time points is hindered by inconsistent repositioning of the artery from scan to scan in conjunction with thick image slices. Balu et al5 studied the influence of subject repositioning on measurement precision in serial MRI and identified orientation variability as the most important factor that affected reproducibility. Besides repositioning variability, the current comparison of time points is primarily based on volume measurements, which is a limited representation of the available image data, and no attention is given to local changes or visual …