Advances in MRI for the evaluation of carotid atherosclerosis

Abstract

Carotid artery atherosclerosis is an important source of mortality and morbidity in the Western world with significant socioeconomic implications. The quest for the early identification of the vulnerable carotid plaque is already in its third decade and traditional measures, such as the sonographic degree of stenosis, are not selective enough to distinguish those who would really benefit from a carotid endarterectomy. MRI of the carotid plaque enables the visualization of plaque composition and specific plaque components that have been linked to a higher risk of subsequent embolic events. Blood suppressed T1 and T2 weighted and proton density-weighted fast spin echo, gradient echo and time-of-flight sequences are typically used to quantify plaque components such as lipid-rich necrotic core, intraplaque haemorrhage, calcification and surface defects including erosion, disruption and ulceration. The purpose of this article is to review the most important recent advances in MRI technology to enable better diagnostic carotid imaging.

Figure 1.

Normal volunteer: comparison of advanced blood suppression techniques. The double inversion recovery preparation commonly exhibits plaque-mimicking artefacts (arrow). Both improved motion-sensitized driven-equilibrium (iMSDE) and Delays Alternating with Nutations for Tailored Excitation (DANTE) are more time efficient and can mitigate these artefacts. DIR, double inversion recovery.

Figure 2.

T₁ weighted MRI of (a) two-dimensional (2D) fast spin echo (FSE) with 3-mm thickness, and (b) three-dimensional (3D) variable flip angle FSE with 0.6-mm thickness. The lipid core is clearly seen in 3D FSE (arrow, b), while the partial volume effect limits the resolution of 2D FSE (arrow, a).

Figure 3.

Carotid imaging pre (a) and post (b) T₁ weighted ultrasmall superparamagnetic iron oxide administration showing significant signal loss in the post-imaging phase (arrowhead).

Figure 4.

Arrows highlight the lesion of a 74-year-old patient in coronal slices of multicontrast carotid plaque MRI: (a) pre-contrast T₁ weighted three-dimensional (3D) fast spin echo (FSE); (b) post-contrast T₁ weighted 3D FSE and (c) direct thrombus imaging.

Figure 5.

Superficial calcium was found in 4–5% of ruptured plaques in the coronary, possibly the same proportion in the carotid, which could be because of the high stress concentration over the fibrous cap owing to the presence of superficial calcium. (Left: the reconstructed plaque geometry of a plaque located around carotid bifurcation from a symptomatic patient; middle: the co-registered CT and MR images showing juxtaluminal calcium; right: high stress concentration appears around the calcium; unit, kPa.) CTA, CT angiography; MRTOF, MR time of flight.