Concurrent Carotid Inflammation in Acute Coronary Syndrome as Assessed by 18F-FDG PET/CT: A Possible Mechanistic Link for Ischemic Stroke

Novel Targets for Molecular Imaging of Inflammatory Processes of Carotid Atherosclerosis: A Systematic Review

Computed tomography angiography (CTA), magnetic resonance angiography (MRA) and 18F-FDG-PET have proven clinical value when evaluating patients with carotid atherosclerosis. In this systematic review, we will focus on the role of novel molecular imaging tracers in that assessment and their potential strengths to stratify stroke risk. We systematically searched PubMed, Embase, the Web of Science Core Collection, and Cochrane Library for articles reporting on molecular imaging to noninvasively detect or characterize inflammation in carotid atherosclerosis. As our focus was on nonclassical novel targets, we omitted reports solely on 18F-FDG and 18F-NaF. We summarized and mapped the selected studies to provide an overview of the current clinical development in molecular imaging in relation to risk factors, imaging and histological findings, diagnostic and prognostic performance. We identified 20 articles in which the utilized tracers to visualize carotid wall inflammation were somatostatin subtype-2- (SST2-) (n = 5), CXC-motif chemokine receptor 4- (CXCR4-) (n = 3), translocator protein- (TSPO-) (n = 2) and aVβ3 integrin-ligands (n = 2) and choline-tracers (n = 2). Tracer uptake correlated with traditional cardiovascular risk factors, that is, age, gender, diabetes, hypercholesterolemia, and hypertension as well as prior cardiovascular disease. We identified discrepancies between tracer uptake and grade of stenosis, plaque calcification, and 18F-FDG uptake, suggesting the importance of alternative characterization of atherosclerosis beyond classical neuroimaging features. Immunohistochemical analysis linked tracer uptake to markers of macrophage infiltration and neovascularization. Symptomatic carotid arteries showed higher uptake compared to asymptomatic (including contralateral, nonculprit) arteries. Some studies demonstrated a potential role of these novel molecular imaging as a specific intermediary (bio)marker for outcome. Several novel tracers show promise for identification of high-risk plaque inflammation. Based on the current evidence we cautiously propose the SST2-ligands and the choline radiotracers as viable candidates for larger prospective longitudinal outcome studies to evaluate their predictive use in clinical practice.

Stress-associated neurobiological activity is linked with acute plaque instability via enhanced macrophage activity: a prospective serial 18F-FDG-PET/CT imaging assessment

AIMS

Emotional stress is associated with future cardiovascular events. However, the mechanistic linkage of brain emotional neural activity with acute plaque instability is not fully elucidated. We aimed to prospectively estimate the relationship between brain amygdalar activity (AmygA), arterial inflammation (AI), and macrophage haematopoiesis (HEMA) in acute myocardial infarction (AMI) as compared with controls.

METHODS AND RESULTS

18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) imaging was performed within 45 days of the index episode in 62 patients (45 with AMI, mean 60.0 years, 84.4% male; 17 controls, mean 59.6 years, 76.4% male). In 10 patients of the AMI group, serial 18F-FDG-PET/CT imaging was performed after 6 months to estimate the temporal changes. The signals were compared using a customized 3D-rendered PET reconstruction. AmygA [target-to-background ratio (TBR), mean ± standard deviation: 0.65 ± 0.05 vs. 0.60 ± 0.05; P = 0.004], carotid AI (TBR: 2.04 ± 0.39 vs. 1.81 ± 0.25; P = 0.026), and HEMA (TBR: 2.60 ± 0.38 vs. 2.22 ± 0.28; P < 0.001) were significantly higher in AMI patients compared with controls. AmygA correlated significantly with those of the carotid artery (r = 0.350; P = 0.005), aorta (r = 0.471; P < 0.001), and bone marrow (r = 0.356; P = 0.005). Psychological stress scales (PHQ-9 and PSS-10) and AmygA assessed by PET/CT imaging correlated well (P < 0.001). Six-month after AMI, AmygA, carotid AI, and HEMA decreased to a level comparable with the controls.

CONCLUSION

AmygA, AI, and HEMA were concordantly enhanced in patients with AMI, showing concurrent dynamic changes over time. These results raise the possibility that stress-associated neurobiological activity is linked with acute plaque instability via augmented macrophage activity and could be a potential therapeutic target for plaque inflammation in AMI.

Vascular findings on FDG PET/CT

Since its introduction into clinical practice, 2-deoxy-2-[18F]flu-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) has become firmly established in the field of oncological imaging, with a growing body of evidence demonstrating its use in infectious and inflammatory vascular pathologies. This pictorial review illustrates the utility of FDG PET/CT as a diagnostic tool in the investigation of vascular disease and highlights some of the more common incidental vascular findings that PET reporters may encounter on standard oncology FDG PET/CTs, including atherosclerosis, large vessel vasculitis, complications of vascular grafts, infectious aortitis and acute aortic syndromes.

Integrated cardiovascular assessment of atherosclerosis using PET/MRI

Atherosclerosis is a systemic inflammatory disease typified by the development of lipid-rich atheroma (plaques), the rupture of which are a major cause of myocardial infarction and stroke. Anatomical evaluation of the plaque considering only the degree of luminal stenosis overlooks features associated with vulnerable plaques, such as high-risk morphological features or pathophysiology, and hence risks missing vulnerable or ruptured non-stenotic plaques. Consequently, there has been interest in identifying these markers of vulnerability using either MRI for morphology, or positron emission tomography (PET) for physiological processes involved in atherogenesis. The advent of hybrid PET/MRI scanners offers the potential to combine the strengths of PET and MRI to allow comprehensive assessment of the atherosclerotic plaque. This review will discuss the principles and technical aspects of hybrid PET/MRI assessment of atherosclerosis, and consider how combining the complementary modalities of PET and MRI has already furthered our understanding of atherogenesis, advanced drug development, and how it may hold potential for clinical application.

Molecular imaging of carotid artery atherosclerosis with PET: a systematic review

PURPOSE

To conduct a systematic review of articles on PET imaging of carotid atherosclerosis with emphasis on clinical usefulness and comparison with other imaging modalities.

METHODS

Research articles reporting carotid artery PET imaging with different radiotracers until 30 November 2018 were systematically searched for in Medline/PubMed, Scopus, Embase, Google Scholar, and Cochrane Library. Duplicates were removed, and editorials, case studies, and investigations on feasibility or reproducibility of PET imaging and of patients with end-stage diseases or immunosuppressive medications were omitted. After quality assessment of included articles using Joanna Briggs Institute checklists, all eligible articles were reviewed.

RESULTS

Of 1718 primary hits, 53 studies comprising 4472 patients, aged 47-91 years (78.8% males), were included and grouped under the following headlines: diagnostic performance, risk factors, laboratory findings, imaging modalities, and treatment. ¹⁸F-fluorodeoxyglucose (FDG) (49/53) and ¹⁸F-sodium fluoride (NaF) (5/53) were the most utilized tracers to visualize carotid wall inflammation and microcalcification, respectively. Higher carotid FDG uptake was demonstrated in patients with than without symptomatic carotid atherosclerosis. Normal carotid arteries presented with the lowest FDG uptake. In symptomatic atherosclerosis, carotid arteries ipsilateral to a cerebrovascular event had higher FDG uptake than the contralateral carotid artery. FDG uptake was significantly associated with age, male gender, and body mass index in healthy individuals, and in addition with arterial hypertension, hypercholesterolemia, and diabetes mellitus in patients. Histological assessment indicated a strong correlation between microcalcification and NaF uptake in symptomatic patients. Histological evidence of calcification correlated inversely with FDG uptake, which was associated with increased macrophage and CD68 count, both accounting for increased local inflammatory response.

CONCLUSION

FDG-PET visualizes the inflammatory part of carotid atherosclerosis enabling risk stratification to a certain degree, whereas NaF-PET seems to indicate long-term consequences of ongoing inflammation by demonstrating microcalcification allowing discrimination of atherosclerotic from normal arteries and suggesting clinically significant carotid atherosclerosis.

Added value of aortic pulse wave velocity index for the detection of coronary heart disease by elective coronary angiography

Background: Non-invasive tests leading to elective coronary angiography (CAG) have low diagnostic yield for obstructive coronary heart disease (CHD). Aortic stiffness, an independent predictor of CHD events can be easily measured by pulse wave velocity (PWV). We aimed at retrospectively evaluating the diagnostic accuracy PWV index to detect CHD in consecutive patients with suspected CHD that underwent CAG.Method: In population of 86 healthy patients with available PWV data, a theoretical PWV was derived. In different population of 62 individuals who underwent CAG for suspected CHD, PWV index was calculated as index [(measured PWV - theoretical PWV)/theoretical PWV]. Logistic regression and comparisons between ROC curves were used to add value of CAG indication performance of PWV index.Results: Out of 62, seventeen patients presented obstructive CHD and 22 patients had non-obstructive CHD. PWV index and severity of CHD were positively correlated (p < 0.0001). After applying several models that included classical CHD predictor, the higher performance to detect abnormal CAG was obtained with the combined classifier PWV index/carotid plaque with 87% sensitivity, 93% specificity, 0.92 accuracy and 0.31 threshold. To detect obstructive CAG, individual classifier PWV index presents 94% sensitivity, 91% specificity, 0.95 accuracy and 0.46 threshold.Conclusion: PWV index is individualized approach that optimizes CHD diagnostic strategies and thus might be clinically useful for reducing the rate of unnecessary invasive CAG.

Impact of Plaque Composition on Risk of Coronary Artery Diseases in Patients with Carotid Artery Stenosis

OBJECT

Recent clinical studies have recently demonstrated a strong association between carotid artery stenosis and coronary artery disease (CAD). However, the clinical impact of carotid plaque composition on CAD remains unclear. This study was aimed to determine the relationship between carotid plaque composition and CAD in patients who underwent carotid endarterectomy (CEA) or carotid artery stenting (CAS).

METHODS

This prospective cohort study included a total of 97 patients who were admitted to our institution between January 2012 and April 2016. Magnetic resonance (MR) imaging was performed to semi-quantitatively analyze the components of carotid plaques by calculating the ratio of plaque intensity to muscle intensity on T1-weighted image. Diagnosis of CAD was based on patient history and clinical examinations during preoperative, postoperative and follow-up periods. Multivariate logistic analysis was performed to determine the risk factors for CAD. The relationship between contralateral plaque composition and CAD was also investigated.

RESULTS

Of 97 patients, 33 were diagnosed as having 44 episodes of CAD. Multivariate logistic analysis revealed that ASO (odds ratio [OR], 5.7; 95% confidence interval [CI], 1.8-18.9), contralateral carotid occlusive disease (OR, 6.5; 95%CI, 1.7-22.9), and plaque/muscle ratio (OR, 3.0; 95%CI, 1.4-10.1) were independent factors for predicting CAD. The patients diagnosed as having CAD during the follow-up period had significantly higher plaque/muscle ratio than those with CAD on preoperative evaluations (2.29 ± .21vs. 1.97 ± .33, P < .01).

CONCLUSIONS

This study clearly demonstrates that ASO, contralateral carotid artery stenosis, and high-intensity carotid plaque on T1-weighted MRI independently predict CAD. Contralateral carotid plaque composition was also associated with concomitant CAD. Moreover, high-intensity carotid plaque may predict the future development of CAD. Therefore, unstable carotid plaque should be considered as the clinical phenotype of systemic inflammation and a novel, robust marker for future CAD.

Ischemic stroke rates decrease with increased ticagrelor use after acute myocardial infarction in patients treated with percutaneous coronary intervention

Aims

It is unknown whether dual antiplatelet therapy with ticagrelor instead of clopidogrel reduces the risk of ischaemic stroke in acute myocardial infarction patients that undergo percutaneous coronary intervention. This study investigated whether the introduction of dual antiplatelet therapy with ticagrelor was associated with reduced ischaemic stroke risk in a real-world population.

Methods and results

Patients with ischaemic stroke after acute myocardial infarction from 8 December 2009–31 December 2013 were identified using the Register for Information and Knowledge on Swedish Heart Intensive Care Admissions and the Swedish National Patient Register. The study period was divided into two similar periods using the date of the first prescription of ticagrelor as the cut-off. The risk of ischaemic stroke in percutaneous coronary intervention-treated acute myocardial infarction patients during the first period (100% clopidogrel treatment) versus the second period (60.7% ticagrelor treatment) was assessed using Kaplan-Meier analysis. Variables associated with ischaemic stroke were identified using a multivariable Cox proportional hazards model. There were 686 ischaemic stroke events (2.0%) among 34931 percutaneous coronary intervention-treated acute myocardial infarction patients within one year, 366 (2.2%) during the first period and 320 (1.8%) during the second period ( p = 0.004). The Cox model showed a 21% relative risk reduction in ischaemic stroke in the second period versus the first one (hazard ratio 0.79, 95% confidence interval, 0.68–0.92; p = 0.003). The independent predictors of increased stroke risk were older age, hypertension, diabetes mellitus, atrial fibrillation, heart failure during hospitalization, previous ischaemic stroke, and ST-segment elevation myocardial infarction.

Conclusion

The risk of ischaemic stroke in percutaneous coronary intervention-treated acute myocardial infarction patients decreased after the introduction of ticagrelor in Sweden.

PET imaging of the neurovascular interface in cerebrovascular disease

Cerebrovascular disease encompasses a range of pathologies that affect different components of the cerebral vasculature and brain parenchyma. Large artery atherosclerosis, acute cerebral ischaemia, and intracerebral small vessel disease all demonstrate altered metabolic processes that are key to their pathogenesis. Although structural imaging techniques such as MRI are the mainstay of clinical care and research in cerebrovascular disease, they have limited ability to detect these pathophysiological processes in vivo. By contrast, PET can detect and quantify metabolic processes that are relevant to each facet of cerebrovascular disease. Information obtained from PET studies has helped to shape the understanding of key concepts in cerebrovascular medicine, including vulnerable atherosclerotic plaque, salvageable ischaemic penumbra, neuroinflammation and selective neuronal loss after ischaemic insult. PET has also helped to elucidate the relationships between chronic hypoxia, neuroinflammation, and amyloid-β deposition in cerebral small vessel disease. This Review describes how PET-based imaging of metabolic processes at the neurovascular interface has contributed to our understanding of cerebrovascular disease.

Brain Vascular Imaging Techniques

Recent major improvements in a number of imaging techniques now allow for the study of the brain in ways that could not be considered previously. Researchers today have well-developed tools to specifically examine the dynamic nature of the blood vessels in the brain during development and adulthood; as well as to observe the vascular responses in disease situations in vivo. This review offers a concise summary and brief historical reference of different imaging techniques and how these tools can be applied to study the brain vasculature and the blood-brain barrier integrity in both healthy and disease states. Moreover, it offers an overview on available transgenic animal models to study vascular biology and a description of useful online brain atlases.

PET Imaging of Atherosclerotic Disease: Advancing Plaque Assessment from Anatomy to Pathophysiology

Atherosclerosis is a leading cause of morbidity and mortality. It is now widely recognized that the disease is more than simply a flow-limiting process and that the atheromatous plaque represents a nidus for inflammation with a consequent risk of plaque rupture and atherothrombosis, leading to myocardial infarction or stroke. However, widely used conventional clinical imaging techniques remain anatomically focused, assessing only the degree of arterial stenosis caused by plaques. Positron emission tomography (PET) has allowed the metabolic processes within the plaque to be detected and quantified directly. The increasing armory of radiotracers has facilitated the imaging of distinct metabolic aspects of atherogenesis and plaque destabilization, including macrophage-mediated inflammatory change, hypoxia, and microcalcification. This imaging modality has not only furthered our understanding of the disease process in vivo with new insights into mechanisms but has also been utilized as a non-invasive endpoint measure in the development of novel treatments for atherosclerotic disease. This review provides grounding in the principles of PET imaging of atherosclerosis, the radioligands in use and in development, its research and clinical applications, and future developments for the field.