Temporal Changes in Coronary 18F-Fluoride Plaque Uptake in Patients with Coronary Atherosclerosis

Advances in the application of 18F-sodium fluoride PET in the assessment of atherosclerosis

Atherosclerosis serves as the primary cause of cardiovascular diseases (CVDs), with its pathological processes encompassing lipid deposition, inflammatory responses, and calcification. Traditional imaging techniques, such as computed tomography angiography and MRI, are primarily utilized for detecting arterial stenosis and calcified plaques, yet they face challenges in accurately assessing plaque activity and instability. 18F-sodium fluoride PET (18F-NaF PET) offers a novel approach for plaque activity and stability assessment by labeling and quantifying arterial wall calcification. This article reviews the advances in the application of 18F-NaF PET in the assessment of atherosclerosis.

Effects of Evolocumab on Coronary Plaque Composition and Microcalcification Activity by Coronary PET and CT Angiography

BACKGROUND

The effects of evolocumab on the underlying coronary disease activity by positron emission tomography (PET) and coronary tree plaque composition by coronary computed tomography angiography (CTA) have not been described.

OBJECTIVES

This prospective imaging study aimed to evaluate changes in coronary plaque composition on coronary CTA and coronary microcalcification, a marker of plaque activity, on 18F-sodium fluoride (NaF) positron emission tomography (PET) after evolocumab treatment.

METHODS

This single-arm, prospective, open-label study enrolled patients with baseline extensive noncalcified plaque volume by coronary CTA (>440 µL overall coronary artery or >250 µL in any single plaque). All participants underwent baseline and 18-month follow-up coronary CTA and 18F-NaF PET. Disease activity was evaluated with 18F-NaF PET by maximum target-to-background ratios at the lesion level and by coronary microcalcification activity for the entire coronary tree.

RESULTS

A total of 47 patients (age 61.8 ± 10.1 years, 87% male) and 196 lesions were studied. Twenty-three (48.9%) patients were asymptomatic, 16 (34%) presented with chest pain, and 8 (17%) presented with dyspnea. Four (8.5%) patients had a prior coronary artery disease history. At a mean follow-up of 18 months, there was no significant change in total plaque volume (716.2 ± 431.4 µL to 710.8 ± 456.2 µL, difference: 5.4 ± 97.4 µL; P = 0.705). Changes in plaque composition were observed, with a significant reduction in noncalcified plaque (607.3 ± 346.8 µL to 562.1 ± 337.3 µL, difference: 45.2 ± 63.8 µL; P < 0.001) and low-attenuation noncalcified plaque (37.1 ± 28.9 µL to 20.4 ± 15.4 µL, difference: 16.6 ± 23.5 µL; P < 0.001). In contrast, there was an increase in calcified plaque (108.9 ± 133.7 µL to 148.7 ± 175.3 µL, difference: 39.8 ± 56.1 µL; P < 0.001). There was a significant reduction in coronary microcalcification activity (1.35 ± 1.68 to 1.08 ± 1.37; P = 0.004) and lesion target-to-background ratio (1.73 ± 0.85 to 1.62 ± 0.83; P = 0.005).

CONCLUSIONS

In stable patients with extensive noncalcified plaque volume at baseline, 18 months of evolocumab treatment was associated with a shift toward a lower risk quantitative plaque phenotype and reduction in microcalcification activity. (Effect of Evolocumab on Coronary Atherosclerosis; NCT03689946).

Inflammation in coronary atherosclerosis: diagnosis and treatment

Coronary atherosclerosis is a chronic condition characterised by the development of an atherosclerotic plaque in the inner layer of the coronary artery, mainly associated with cholesterol accumulation and favoured by endothelial dysfunction related to other cardiovascular risk factors, such as smoking, diabetes and hypertension. A key actor in this process is the systemic inflammatory response, which can make plaques either grow slowly over the course of years (like a 'mountain'), obstructing coronary flow, and causing stable coronary artery disease, or make them explode (like a 'volcano') with subsequent abrupt thrombosis causing an acute coronary syndrome. This central role of inflammation in coronary atherosclerosis has led to its consideration as a modifiable cardiovascular risk factor and a therapeutic target. Classic anti-inflammatory drugs have been tested in clinical trials with some encouraging results, and new drugs specifically designed to tackle inflammation are currently being under investigation in ongoing trials. The objectives of this review are to (1) summarise the role of inflammatory biomarkers and imaging techniques to detect inflammation at each stage of plaque progression, and (2) explore currently available and upcoming anti-inflammatory therapies.

Estimating inflammatory risk in atherosclerotic cardiovascular disease: plaque over plasma?

Inflammation is an important driver of disease in the context of atherosclerosis, and several landmark trials have shown that targeting inflammatory pathways can reduce cardiovascular event rates. However, the high cost and potentially serious adverse effects of anti-inflammatory therapies necessitate more precise patient selection. Traditional biomarkers of inflammation, such as high-sensitivity C-reactive protein, show an association with cardiovascular risk on a population level but do not have specificity for local plaque inflammation. Nowadays, advancements in non-invasive imaging of the vasculature enable direct assessment of vascular inflammation. Positron emission tomography (PET) tracers such as 18F-fluorodeoxyglucose enable detection of metabolic activity of inflammatory cells but are limited by low specificity and myocardial spillover effects. 18F-sodium fluoride is a tracer that identifies active micro-calcification in plaques, indicating vulnerable plaques. Gallium-68 DOTATATE targets pro-inflammatory macrophages by binding to somatostatin receptors, which enhances specificity for plaque inflammation. Coronary computed tomography angiography (CCTA) provides high-resolution images of coronary arteries, identifying high-risk plaque features. Measuring pericoronary adipose tissue attenuation on CCTA represents a novel marker of vascular inflammation. This review examines both established and emerging methods for assessing atherosclerosis-related inflammation, emphasizing the role of advanced imaging in refining risk stratification and guiding personalized therapies. Integrating these imaging modalities with measurements of systemic and molecular biomarkers could shift atherosclerotic cardiovascular disease management towards a more personalized approach.

Beyond the Lumen: Molecular Imaging to Unmask Vulnerable Coronary Plaques

Vulnerable coronary atherosclerotic plaque involves a dynamic pathophysiologic process within and surrounding an atheromatous plaque in coronary artery intima. The process drastically increases the risk of plaque rupture and is clinically responsible for most cases of acute coronary syndromes, myocardial infarctions, and sudden cardiac deaths. Early detection of vulnerable plaque is crucial for clinicians to implement appropriate risk-mitigation treatment strategies, offer timely interventions, and prevent potentially life-threatening events. There is an imperative clinical need to develop practical diagnostic pathways that utilize non-invasive means to risk-stratify symptomatic patients. Since the early 1990s, the identification of vulnerable plaque in clinical practice has primarily relied on invasive imaging techniques. In the last two decades, CT coronary angiogram (CTCA) has rapidly evolved into the prevalent non-invasive diagnostic modality for assessing coronary anatomy. There are now validated plaque appearances on CTCA correlating with plaque vulnerability. It is worth noting that in clinical practice, most CTCA reports omit mention of vulnerable plaque details because spatial resolution (0.3-0.5 mm) is often insufficient to reliably detect some crucial features of vulnerable plaques, such as thin fibrous caps. Additionally, accurately identifying vulnerable plaque features requires substantial expertise and time, which many cardiologists or radiologists may lack in routine reporting. Cardiac magnetic resonance imaging (cMRI) is also non-invasive and allows simultaneous anatomic and functional assessment of coronary plaques. Despite several decades of research and development, routine clinical application of cMRI in coronary plaque imaging remains hampered by complex imaging protocols, inconsistent image quality, and cost. Molecular imaging with radiotracers, specifically positron emission tomography (PET) with sodium fluoride (Na18F PET), have demonstrated significant potential as a sensitive and specific imaging procedure for diagnosing vulnerable coronary artery plaque. The study protocol is robust and brief, requiring minimal patient preparation. Compared to CTCA and cMRI, the diagnostic accuracy of this test is less dependent on the experience and expertise of the readers. Furthermore, validated automated quantitative algorithms complement the visual interpretation of the study, enhancing confidence in the diagnosis. This combination of factors makes Na18F PET a promising tool in cardiology for identifying high-risk coronary plaques.

Uncovering atherosclerotic cardiovascular disease by PET imaging

Assessing atherosclerosis severity is essential for precise patient stratification. Specifically, there is a need to identify patients with residual inflammation because these patients remain at high risk of cardiovascular events despite optimal management of cardiovascular risk factors. Molecular imaging techniques, such as PET, can have an essential role in this context. PET imaging can indicate tissue-based disease status, detect early molecular changes and provide whole-body information. Advances in molecular biology and bioinformatics continue to help to decipher the complex pathogenesis of atherosclerosis and inform the development of imaging tracers. Concomitant advances in tracer synthesis methods and PET imaging technology provide future possibilities for atherosclerosis imaging. In this Review, we summarize the latest developments in PET imaging techniques and technologies for assessment of atherosclerotic cardiovascular disease and discuss the relationship between imaging readouts and transcriptomics-based plaque phenotyping.

Coronary Atherosclerotic Plaque Activity and Risk of Myocardial Infarction

BACKGROUND

Total coronary atherosclerotic plaque activity across the entire coronary arterial tree is associated with patient-level clinical outcomes.

OBJECTIVES

We aimed to investigate whether vessel-level coronary atherosclerotic plaque activity is associated with vessel-level myocardial infarction.

METHODS

In this secondary analysis of an international multicenter study of patients with recent myocardial infarction and multivessel coronary artery disease, we assessed vessel-level coronary atherosclerotic plaque activity using coronary 18F-sodium fluoride positron emission tomography to identify vessel-level myocardial infarction.

RESULTS

Increased 18F-sodium fluoride uptake was found in 679 of 2,094 coronary arteries and 414 of 691 patients. Myocardial infarction occurred in 24 (4%) vessels with increased coronary atherosclerotic plaque activity and in 25 (2%) vessels without increased coronary atherosclerotic plaque activity (HR: 2.08; 95% CI: 1.16-3.72; P = 0.013). This association was not demonstrable in those treated with coronary revascularization (HR: 1.02; 95% CI: 0.47-2.25) but was notable in untreated vessels (HR: 3.86; 95% CI: 1.63-9.10; Pinteraction = 0.024). Increased coronary atherosclerotic plaque activity in multiple coronary arteries was associated with heightened patient-level risk of cardiac death or myocardial infarction (HR: 2.43; 95% CI: 1.37-4.30; P = 0.002) as well as first (HR: 2.19; 95% CI: 1.18-4.06; P = 0.013) and total (HR: 2.50; 95% CI: 1.42-4.39; P = 0.002) myocardial infarctions.

CONCLUSIONS

In patients with recent myocardial infarction and multivessel coronary artery disease, coronary atherosclerotic plaque activity prognosticates individual coronary arteries and patients at risk for myocardial infarction.

Role of 18F-sodium fluoride positron emission tomography in imaging atherosclerosis

Atherosclerosis involving vascular beds across the human body remains the leading cause of death worldwide. Coronary and peripheral artery disease, which are almost universally a result of atherosclerotic plaque, can manifest clinically as myocardial infarctions, ischemic stroke, or acute lower-limb ischemia. Beyond imaging myocardial perfusion and blood-flow, nuclear imaging has the potential to depict the activity of the processes that are directly implicated in the atherosclerotic plaque progression and rupture. Out of several tested tracers to date, the literature is most advanced for 18F-sodium fluoride positron emission tomography. In this review, we present the latest data in the field of atherosclerotic 18F-sodium fluoride positron emission tomography imaging, discuss the advantages and limitation of the techniques, and highlight the aspects that require further research in the future.