Advanced MRI for carotid plaque imaging

Abstract

Atherosclerosis is the ubiquitous underling pathological process that manifests in heart attack and stroke, cumulating in the death of one in three North American adults. High-resolution magnetic resonance imaging (MRI) is able to delineate atherosclerotic plaque components and total plaque burden within the carotid arteries. Using dedicated hardware, high resolution images can be obtained. Combining pre- and post-contrast T1, T2, proton-density, and magnetization-prepared rapid acquisition gradient echo weighted fat-saturation imaging, plaque components can be defined. Post-processing software allows for semi- and fully automated quantitative analysis. Imaging correlation with surgical specimens suggests that this technique accurately differentiates plaque features. Total plaque burden and specific plaque components such as a thin fibrous cap, large fatty or necrotic core and intraplaque hemorrhage are accepted markers of neuroischemic events. Given the systemic nature of atherosclerosis, emerging science suggests that the presence of carotid plaque is also an indicator of coronary artery plaque burden, although the preliminary data primarily involves patients with stable coronary disease. While the availability and cost-effectiveness of MRI will ultimately be important determinants of whether carotid MRI is adopted clinically in cardiovascular risk assessment, the high accuracy and reliability of this technique suggests that it has potential as an imaging biomarker of future risk.

Keywords: Atherosclerosis; Cardiovascular risk; Carotid; Imaging; MRI.

Fig. 1

Dedicated surface coils provide improved signal-to-noise ratio for superficial structures (a). When these coils are applied to a cylindrical water phantom, measuring 6 cm in diameter, the drop-off in signal intensity on the T1-weighted images provides a visual demonstration of the penetration depth of the coil (b)

Fig. 2

Patient positioning can significantly alter the depth of the carotid arteries relative to overlying muscle, grandular tissue and skin as demonstrated by these time-of-flight images obtained during the same imaging session with the patient’s neck flexed (a), in neutral position (b) and extended (c)

Fig. 3

MRI allows depiction of several atherosclerotic components including lipid core (asterisk). Signal hypointensity (asterisk) indicates the lipid core of an eccentric atherosclerotic plaque with luminal preservation on fat-saturation T1-weighted imaging pre- (a), and post-contrast (b). Multi-contrast images usually also include T2 fat saturation (c), time-of-flight (d), and MPRAGE (e)

Fig. 4

Coronal T1-weighted IR 3D FFE image depicting a hyperintensity in the left carotid artery indicating intraplaque hemorrhage. Hyperintense signal in the carotid wall >150 % of the adjacent sternocleidomastoid muscle on this sequence accurately and reliably depicts intraplaque hemorrhage

Fig. 5

A T1-weighted contrast-enhanced fat saturation image through the common carotid depicts the vessel morphology including the lumen area (dot-dash line), total vessel area (dashed line) and mean wall thickness (a value obtained by averaging a number of cords, represented by the solid lines). The wall area is calculated by subtracting the lumen area from the total vessel area. The lipid-rich necrotic core component is also outlined (dotted line)