Noninvasive Imaging to Assess Atherosclerotic Plaque Composition and Disease Activity: Coronary and Carotid Applications

Abstract

Cardiovascular disease is one of the leading causes of mortality and morbidity worldwide. Atherosclerosis imaging has traditionally focused on detection of obstructive luminal stenoses or measurements of plaque burden. However, with advances in imaging technology it has now become possible to noninvasively interrogate plaque composition and disease activity, thereby differentiating stable from unstable patterns of disease and potentially improving risk stratification. This manuscript reviews multimodality imaging in this field, focusing on carotid and coronary atherosclerosis and how these novel techniques have the potential to complement current imaging assessments and improve clinical decision making.

Keywords: atherosclerosis; plaque burden; positron emission tomography; vulnerable plaque.

CENTRAL ILLUSTRATION

Multimodality Assessment of Atherosclerotic Plaque Characteristics and Disease Activity Multimodality noninvasive imaging allows comprehensive analysis of atherosclerotic plaque in the coronary and vascular bed. Beyond the standard assessment of luminal stenosis and disease burden, emerging techniques enable clinical assessment of plaque characteristics and disease activity. Computed tomography (A) and magnetic resonance (B to D) provide the registered anatomic background information relating to plaque morphology, which can be combined with positron emission tomography data ¹⁸F-sodium fluoride (E, G), ⁶⁸Ga-DOTATATE (F), and ¹⁸F-fluorodeoxyglucose (H), which has potential to examine multiple markers of plaque biology. F reproduced with permission from Tarkin et al. (53).

FIGURE 1

Pathological Features Associated With Culprit Atherosclerotic Plaque Typical adverse plaque characteristics include macrophage accumulation, a large lipid core, positive remodeling, a thin fibrous cap, and microcalcification. Intraplaque microvessels result from angiogenesis driven by hypoxia and inflammatory stimuli within the necrotic core. These vessels can result in intraplaque hemorrhage, which increases the risk of plaque destabilization. Each of these represents a potential noninvasive imaging target.

FIGURE 2

Multiparametric Assessments of the Carotid Arteries in a Patient Post–Transient Ischemic Attack (A) Magnetic resonance angiogram of a patient with transient ischemic attack with time of flight image demonstrating a complex culprit lesion in the right internal carotid artery (green arrow). (B) T1-weighted magnetic resonance images of the same patient with a high T1 signal (red arrow) associated with methemoglobin within areas of fresh thrombus. (C) Positron emission tomography/magnetic resonance imaging with ¹⁸F-sodium fluoride showing increased signal intensity (blue arrow) in the right internal carotid artery corresponding with stenosis and symptoms.

FIGURE 3

Assessment of Coronary Plaque Characteristics on Coronary Computed Tomography Angiography (A) Low-attenuation plaque (red arrow) in the proximal left anterior descending artery with spotty calcification and associated vessel stenosis. (B) Nonobstructive plaque in proximal left anterior descending artery with spotty calcification (green arrow). (C) An atherosclerotic plaque with positive remodeling (blue arrow) and low-attenuation plaque in the left anterior descending artery. (D) Williams et al. (68) demonstrated that patients with obstructive disease and 1 or more high-risk plaque had a 10-fold increased risk of subsequent myocardial infarctions than patients with normal coronaries. Figure 3D reproduced with permission from Williams et al. (68).

FIGURE 4

Assessment of Coronary Plaque Characteristics on Magnetic Resonance (A) High-intensity plaque in the proximal left anterior descending artery (yellow arrow) on noncontrast T1-weighted magnetic resonance. (B) T1-weighted images coregistered with magnetic resonance coronary angiogram, increased signal at site of high-intensity plaque (yellow arrow). (C) Kaplan-Meier curves comparing the probability of coronary events in patients with and without high-intensity plaque on noncontrast T1-weighted imaging. Adverse plaque characteristic conferred a higher incidence of adverse clinical events. Reproduced with permission from Noguchi et al. (86). CAD = coronary artery disease; PMR = plaque-to-myocardium signal intensity ratio.

FIGURE 5

Assessment of Disease Activity in the Coronary Arteries Positron emission tomography/computed tomography imaging of the coronaries with ¹⁸F-sodium fluoride. (A) Invasive coronary angiography showing a culprit lesion in right coronary artery (red arrow). (B) Intense focal ¹⁸F-sodium fluoride uptake is observed at the site of the culprit plaque on positron emission tomography/computed tomography. (C) Invasive coronary angiography showing culprit plaque in the left circumflex artery (red arrow). (D) Intense focal ¹⁸F-sodium fluoride uptake is observed at the site of the culprit plaque on positron emission tomography/computed tomography.