Carotid plaque inflammation assessed with (18)F-FDG PET/CT is higher in symptomatic compared with asymptomatic patients

Single-nucleotide polymorphism rs2910829 in PDE4D is related to stroke susceptibility in Chinese populations: The results of a meta-analysis

Stroke is a debilitating condition that often leads to disability and death. The increasing prevalence of stroke has drawn worldwide attention. Extensive evidence indicates a crucial role of genetic determinants in the occurrence and perpetuation of stroke. An Icelandic study identified a significant correlation of the phosphodiesterase 4D (PDE4D) single-nucleotide polymorphism (SNP) rs2910829 with stroke susceptibility. However, subsequent studies reported in Chinese populations were contradictory. We implemented a meta-analysis to inspect whether SNP rs2910829 is related to stroke susceptibility in Chinese populations and subsequently performed an in silico analysis to predict its potential functions. Finally, we analysed data from 24 studies comprising 7,484 Chinese stroke patients and 7,962 control individuals. Compared with the CC genotype, the TT genotype was associated with increased susceptibility to stroke (pooled odds ratio [OR] 1.28, 95% confidence interval [CI] 1.13-1.46, P < 0.001), whereas the CT genotype was not. Correspondingly, a significant association was detected under the recessive model (TT vs CT + CC: OR 1.30, 95% CI 1.15-1.47, P < 0.001). Similar results were obtained in large artery atherosclerosis (LAA) stroke but not in small vessel stroke. Bioinformatics analysis also revealed that SNP rs2910829 and its linked SNPs might be implicated in transcriptional regulation. This meta-analysis reveals significant relationships between the PDE4D SNP rs2910829 and susceptibility to stroke and subtype-LAA stroke in Chinese individuals, and further investigations are warranted to evaluate this effect.

Proteomic analysis of the extracellular matrix of human atherosclerotic plaques shows marked changes between plaque types

Cardiovascular disease is the leading cause of death, with atherosclerosis the major underlying cause. While often asymptomatic for decades, atherosclerotic plaque destabilization and rupture can arise suddenly and cause acute arterial occlusion or peripheral embolization resulting in myocardial infarction, stroke and lower limb ischaemia. As extracellular matrix (ECM) remodelling is associated with plaque instability, we hypothesized that the ECM composition would differ between plaques. We analyzed atherosclerotic plaques obtained from 21 patients who underwent carotid surgery following recent symptomatic carotid artery stenosis. Plaques were solubilized using a new efficient, single-step approach. Solubilized proteins were digested to peptides, and analyzed by liquid chromatography-mass spectrometry using data-independent acquisition. Identification and quantification of 4498 plaque proteins was achieved, including 354 ECM proteins, with unprecedented coverage and high reproducibility. Multidimensional scaling analysis and hierarchical clustering indicate two distinct clusters, which correlate with macroscopic plaque morphology (soft/unstable versus hard/stable), ultrasound classification (echolucent versus echogenic) and the presence of hemorrhage/ulceration. We identified 714 proteins with differential abundances between these groups. Soft/unstable plaques were enriched in proteins involved in inflammation, ECM remodelling, and protein degradation (e.g. matrix metalloproteinases, cathepsins). In contrast, hard/stable plaques contained higher levels of ECM structural proteins (e.g. collagens, versican, nidogens, biglycan, lumican, proteoglycan 4, mineralization proteins). These data indicate that a single-step proteomics method can provide unique mechanistic insights into ECM remodelling and inflammatory mechanisms within plaques that correlate with clinical parameters, and help rationalize plaque destabilization. These data also provide an approach towards identifying biomarkers for individualized risk profiling of atherosclerosis.

Optoacoustic biomarkers of lipids, hemorrhage and inflammation in carotid atherosclerosis

Imaging plays a critical role in exploring the pathophysiology and enabling the diagnostics and therapy assessment in carotid artery disease. Ultrasonography, computed tomography, magnetic resonance imaging and nuclear medicine techniques have been used to extract of known characteristics of plaque vulnerability, such as inflammation, intraplaque hemorrhage and high lipid content. Despite the plethora of available techniques, there is still a need for new modalities to better characterize the plaque and provide novel biomarkers that might help to detect the vulnerable plaque early enough and before a stroke occurs. Optoacoustics, by providing a multiscale characterization of the morphology and pathophysiology of the plaque could offer such an option. By visualizing endogenous (e.g., hemoglobin, lipids) and exogenous (e.g., injected dyes) chromophores, optoacoustic technologies have shown great capability in imaging lipids, hemoglobin and inflammation in different applications and settings. Herein, we provide an overview of the main optoacoustic systems and scales of detail that enable imaging of carotid plaques in vitro, in small animals and humans. Finally, we discuss the limitations of this novel set of techniques while investigating their potential to enable a deeper understanding of carotid plaque pathophysiology and possibly improve the diagnostics in future patients with carotid artery disease.

Novel Imaging-Based Biomarkers for Identifying Carotid Plaque Vulnerability

Carotid artery disease has traditionally been assessed based on the degree of luminal narrowing. However, this approach, which solely relies on carotid stenosis, is currently being questioned with regard to modern risk stratification approaches. Recent guidelines have introduced the concept of the "vulnerable plaque," emphasizing specific features such as thin fibrous caps, large lipid cores, intraplaque hemorrhage, plaque rupture, macrophage infiltration, and neovascularization. In this context, imaging-based biomarkers have emerged as valuable tools for identifying higher-risk patients. Non-invasive imaging modalities and intravascular techniques, including ultrasound, computed tomography, magnetic resonance imaging, intravascular ultrasound, optical coherence tomography, and near-infrared spectroscopy, have played pivotal roles in characterizing and detecting unstable carotid plaques. The aim of this review is to provide an overview of the evolving understanding of carotid artery disease and highlight the significance of imaging techniques in assessing plaque vulnerability and informing clinical decision-making.

"Vascular inflammation and cardiovascular disease: review about the role of PET imaging"

Inflammation characterizes all stages of atherothrombosis and provides a critical pathophysiological link between plaque formation and its acute rupture, leading to coronary occlusion and heart attack. In the last 20 years the possibility of quantifying the degree of inflammation of atherosclerotic plaques and, therefore, also of vascular inflammation aroused much interest. ¹⁸Fluoro-deoxy-glucose photon-emissions-tomography (¹⁸F-FDG-PET) is widely used in oncology for staging and searching metastases; in cardiology, the absorption of ¹⁸F-FDG into the arterial wall was observed for the first time incidentally in the aorta of patients undergoing PET imaging for cancer staging. PET/CT imaging with ¹⁸F-FDG and ¹⁸F-sodium fluoride (¹⁸F-NaF) has been shown to assess atherosclerotic disease in its molecular phase, when the process may still be reversible. This approach has several limitations in the clinical practice, due to lack of prospective data to justify their use routinely, but it's desirable to develop further scientific evidence to confirm this technique to detect high-risk patients for cardiovascular events.

Evaluation of non-stenotic carotid atherosclerotic plaques with combined FDG-PET imaging and CT angiography in patients with ischemic stroke of unknown origin

OBJECTIVES

Non-stenotic plaques are an underestimated cause of ischemic stroke. Imaging aspects of high-risk carotid plaques can be identified on CT angiography (CTA) and 18F-fluoro-deoxyglucose positron emission tomography (FDG-PET) imaging. We evaluated in patients with cryptogenic ischemic stroke the usefulness of FDG-PET-CTA.

METHODS

44 patients imaged with CTA and FDG-PET were identified retrospectively. Morphological features were identified on CTA. Intensity of FDG uptake in carotid arteries was quantified on PET.

RESULTS

Patients were imaged 7 ± 8 days after stroke. 44 non-stenotic plaques with increased 18F-FDG uptake were identified in the carotid artery ipsilateral to stroke and 7 contralateral. Most-diseased-segment TBR on FDG-PET was higher in artery ipsilateral vs. contralateral to stroke (2.24 ± 0.80 vs. 1.84 ± 0.50; p < .05). In the carotid region with high FDG uptake, prevalence of hypodense plaques and extent of hypodensity on CTA were higher in artery ipsilateral vs. contralateral to stroke (41% vs. 11%; 0.72 ± 1.2 mm2 vs. 0.13 ± 0.43 mm2; p < .05).

CONCLUSIONS

In patients with ischemic stroke of unknown origin and non-stenotic plaques, we found an increased prevalence of high-risk plaques features ipsilateral vs. contralateral to stroke on FDG-PET-CTA imaging suggesting a causal role for these plaques.

Carotid Plaque Composition and the Importance of Non-Invasive in Imaging Stroke Prevention

Luminal stenosis has been the standard feature for the current management strategies in patients with atherosclerotic carotid disease. Histological and imaging studies show considerable differences between plaques with identical degrees of stenosis. They indicate that specific plaque characteristics like Intraplaque hemorrhage, Lipid Rich Necrotic Core, Plaque Inflammation, Thickness and Ulceration are responsible for the increased risk of ischemic events. Intraplaque hemorrhage is defined by the accumulation of blood components within the plaque, Lipid Rich Necrotic Core is composed of macrophages loaded with lipid, Plaque Inflammation is defined as the process of atherosclerosis itself and Plaque thickness and Ulceration are defined as morphological features. Advances in imaging methods like Magnetic Resonance Imaging, Ultrasound, Computed Tomography and Positron Emission Tomography have enabled a more detailed characterization of the plaque, and its vulnerability is linked to these characteristics, changing the management of these patients based only on the degree of plaque stenosis. Studies like Rotterdam, ARIC, PARISK, CAPIAS and BIOVASC were essential to evaluate and prove the relevance of these characteristics with cerebrovascular symptoms. A better approach for the prevention of stroke is needed. This review summarizes the more frequent carotid plaque features and the available validation from recent studies with the latest evidence.

Association Between Carotid Artery Perivascular Fat Density and Embolic Stroke of Undetermined Source

Aim

This study aims to retrospectively evaluate the association between pericarotid inflammation and the presence of embolic stroke of undetermined source (ESUS).

Methods

In total, 126 patients with ESUS and 118 patients with ischemic stroke from large artery atherosclerosis (LAA) were enrolled. All the patients underwent brain MRI and a neck CT angiography (CTA) examination. Reviewers were blinded to infarct location and stroke cause. Paired t-tests assessed within-subjects differences in mean Hounsfield units (HUs) in carotid perivascular fat between the cerebral infarction side and contralateral side for ESUS and LAA ischemic stroke cases. The unpaired Student's t-test was used to assess between-subjects differences in mean HUs between ESUS and LAA ischemic stroke cases.

Results

In both the ESUS cases and LAA ischemic stroke cases, the pericarotid fat density around the carotid artery ipsilateral to the stroke significantly increased compared with contralateral stroke position in both the groups (ESUS cases −56.31 ± 18.70 vs. −67.31 ± 20.01, p = 0.000; LAA ischemic stroke cases −51.62 ± 19.95 vs. −64.58 ± 22.68, p = 0.000). However, there was no significant difference in ipsilateral and contralateral positions to infarct between ESUS cases and LAA ischemic stroke cases (ipsilateral to infarct −56.31 ± 18.70 vs. −51.62 ± 19.95, p = 0.059; contralateral to infarct −67.31 ± 20.01 vs. −64.58 ± 22.68, p = 0.320).

Conclusion

We found increased density in the fat surrounding carotid artery ipsilateral to stroke compared with contralateral in ESUS, suggesting the presence of an inflammatory reaction that extends beyond the vessel lumen in patients with ESUS with a risk factor profile similar to LAA strokes.

PET-Based Imaging with 18F-FDG and 18F-NaF to Assess Inflammation and Microcalcification in Atherosclerosis and Other Vascular and Thrombotic Disorders

Positron emission tomography (PET) imaging with ¹⁸F-fluorodeoxyglucose (FDG) represents a method of detecting and characterizing arterial wall inflammation, with potential applications in the early assessment of vascular disorders such as atherosclerosis. By portraying early-stage molecular changes, FDG-PET findings have previously been shown to correlate with atherosclerosis progression. In addition, recent studies have suggested that microcalcification revealed by ¹⁸F-sodium fluoride (NaF) may be more sensitive at detecting atherogenic changes compared to FDG-PET. In this review, we summarize the roles of FDG and NaF in the assessment of atherosclerosis and discuss the role of global assessment in quantification of the vascular disease burden. Furthermore, we will review the emerging applications of FDG-PET in various vascular disorders, including pulmonary embolism, as well as inflammatory and infectious vascular diseases.

Circulating Biomarkers Reflecting Destabilization Mechanisms of Coronary Artery Plaques: Are We Looking for the Impossible?

Despite significant strides to mitigate the complications of acute coronary syndrome (ACS), this clinical entity still represents a major global health burden. It has so far been well-established that most of the plaques leading to ACS are not a result of gradual narrowing of the vessel lumen, but rather a result of sudden disruption of vulnerable atherosclerotic plaques. As most of the developed imaging modalities for vulnerable plaque detection are invasive, multiple biomarkers were proposed to identify their presence. Owing to the pivotal role of lipids and inflammation in the pathophysiology of atherosclerosis, most of the biomarkers originated from one of those processes, whereas recent advancements in molecular sciences shed light on the use of microRNAs. Yet, at present there are no clinically implemented biomarkers or any other method for that matter that could non-invasively, yet reliably, diagnose the vulnerable plaque. Hence, in this review we summarized the available knowledge regarding the pathophysiology of plaque instability, the current evidence on potential biomarkers associated with plaque destabilization and finally, we discussed if search for biomarkers could one day bring us to non-invasive, cost-effective, yet valid way of diagnosing the vulnerable, rupture-prone coronary artery plaques.

Multimodality molecular imaging: Gaining insights into the mechanisms linking chronic stress to cardiovascular disease

Positron emission tomography (PET) imaging can yield unique mechanistic insights into the pathophysiology of atherosclerosis. 18F-fluorodeoxyglucose (18F-FDG), a radiolabeled glucose analog, is retained by cells in proportion to their glycolytic activity. While 18F-FDG accumulates within several cell types in the arterial wall, its retention correlates with macrophage content, providing an index of arterial inflammation (ArtI) which predicts subsequent cardiovascular disease (CVD) events. Furthermore, 18F-FDG-PET imaging allows the simultaneous assessment of metabolic activity in several tissues (e.g., brain, bone marrow) and is performed in conjunction with cross-sectional imaging that enables multi-organ structural assessments. Accordingly, 18F-FDG-PET/computed tomography (CT) imaging facilitates evaluation of disease pathways that span multiple organ systems. Within this paradigm, 18F-FDG-PET/CT imaging has been implemented to study the mechanism linking chronic stress to CVD. To evaluate this, stress-associated neural activity can be quantified (as metabolic activity of the amygdala (AmygA)), while leukopoietic activity, ArtI, and coronary plaque burden are assessed concurrently. Such simultaneous quantification of tissue structures and activities enables the evaluation of multi-organ pathways with the aid of mediation analysis. Using this approach, multi-system 18F-FDG-PET/CT imaging studies have demonstrated that chronically heightened stress-associated neurobiological activity promotes leukopoietic activity and systemic inflammation. This in turn fuels more ArtI and greater non-calcified coronary plaque burden, which result in more CVD events. Subsequent studies have revealed that common stressors, such as chronic noise exposure and income disparities, drive the front end of this pathway to increase CVD risk. Hence, multi-tissue multimodality imaging serves as a powerful tool to uncover complex disease mechanisms.

Carotid plaque inflammatory activity assessed by 2-[18F]FDG-PET imaging decrease after a neurological thromboembolic event

Background

Atherosclerotic plaque vulnerability is comprised by plaque composition driven by inflammatory activity and these features can be depicted with 3D ultrasound and 2-[18F]FDG-PET, respectively. The study investigated timely changes in carotid artery plaque inflammation and morphology after a thromboembolic event with PET/CT and novel ultrasound volumetric grayscale median (GSM) readings. Patients with a single hemisphere-specific neurological symptom and the presence of an ipsilateral carotid artery atherosclerotic plaque were prospectively included to both 2-[18F]FDG PET/CT and 3D ultrasound scans of the plaque immediately after their event and again three months later. On PET/CT images the maximum standardized uptake value (SUV_max) was measured and the volumetric ultrasound acquisitions were analyzed using a semiautomated software measuring GSM values.

Results

Baseline scans were performed by a mean of 7 days (range 2–14) after the symptom and again after 98 days (range 91–176). For the entire group (n = 14), we found a decrease in average SUV_max from baseline to follow-up of − 0.18 (95% confidence interval: − 0.34 to − 0.02, P = 0.034). GSM did not increase significantly over time (mean change: + 2.21, 95% confidence interval: − 17.02 to 21.44, P = 0.808).

Conclusion

A decrease in culprit lesion 2-[18F]FDG-uptake 3 months after an event indicates a decrease in inflammatory activity, suggesting that carotid plaque stabilization over time. 3D ultrasound morphological quantitative differences in GSM were not detectable after 3 months.

Molecular Imaging of Inflammatory Disease

Inflammatory diseases include a wide variety of highly prevalent conditions with high mortality rates in severe cases ranging from cardiovascular disease, to rheumatoid arthritis, to chronic obstructive pulmonary disease, to graft vs. host disease, to a number of gastrointestinal disorders. Many diseases that are not considered inflammatory per se are associated with varying levels of inflammation. Imaging of the immune system and inflammatory response is of interest as it can give insight into disease progression and severity. Clinical imaging technologies such as computed tomography (CT) and magnetic resonance imaging (MRI) are traditionally limited to the visualization of anatomical information; then, the presence or absence of an inflammatory state must be inferred from the structural abnormalities. Improvement in available contrast agents has made it possible to obtain functional information as well as anatomical. In vivo imaging of inflammation ultimately facilitates an improved accuracy of diagnostics and monitoring of patients to allow for better patient care. Highly specific molecular imaging of inflammatory biomarkers allows for earlier diagnosis to prevent irreversible damage. Advancements in imaging instruments, targeted tracers, and contrast agents represent a rapidly growing area of preclinical research with the hopes of quick translation to the clinic.

Inter-reader agreement of 18F-FDG PET/CT for the quantification of carotid artery plaque inflammation

Introduction

A significant proportion of ischemic strokes are caused by emboli from unstable atherosclerotic carotid artery plaques. Inflammation is a key feature of plaque instability. Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-(¹⁸F)-fluoro-D-glucose (¹⁸F-FDG) is a promising technique to quantify plaque inflammation, but a consensus on the methodology has not been established. High inter-reader agreement is essential if ¹⁸F-FDG PET/CT is to be used as a clinical tool for the assessment of unstable plaques and stroke risk.

Methods

We assessed the inter-reader variability of different methods for quantification of ¹⁸F-FDG uptake in 43 patients with carotid artery stenosis ≥70%. Two independent readers delineated the plaque and collected maximum standardized uptake value (SUV_max) from all axial PET slices containing the atherosclerotic plaque.

Results

Uptake values with and without background correction were calculated and intraclass correlation coefficients were highest for uncorrected uptake values (0.97–0.98) followed by those background corrected by subtraction (0.89–0.94) and lowest for those background corrected by division (0.74–0.79).

Conclusion

Quantification methods without background correction have the highest inter-reader agreement for ¹⁸F-FDG PET of carotid artery plaque inflammation. The use of the single highest uptake value (max SUV_max) from the plaque will facilitate the method’s clinical utility in stroke prevention.

Microdistribution of Magnetic Resonance Imaging Contrast Agents in Atherosclerotic Plaques Determined by LA-ICP-MS and SR-μXRF Imaging

Purpose

Contrast-enhanced magnetic resonance imaging (MRI) has the potential to replace angiographic evaluation of atherosclerosis. While studies have investigated contrast agent (CA) uptake in atherosclerotic plaques, exact CA spatial distribution on a microscale is elusive. The purpose of this study was to investigate the microdistribution of gadolinium (Gd)- and iron (Fe) oxide-based CA in atherosclerotic plaques of New Zealand White rabbits.

Procedures

The study was performed as a post hoc analysis of archived tissue specimens obtained in a previous in vivo MRI study conducted to investigate signal changes induced by very small superparamagnetic iron oxide nanoparticles (VSOP) and Gd-BOPTA. For analytical discrimination from endogenous Fe, VSOP were doped with europium (Eu) resulting in Eu-VSOP. Formalin-fixed arterial specimens were cut into 5-μm serial sections and analyzed by immunohistochemistry (IHC: Movat’s pentachrome, von Kossa, and Alcian blue (pH 1.0) staining, anti-smooth muscle cell actin (anti-SMA), and anti-rabbit macrophage (anti-RAM-11) immunostaining) and elemental microscopy with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and synchrotron radiation μX-ray fluorescence (SR-μXRF) spectroscopy. Elemental distribution maps of Fe, Eu, Gd, sulfur (S), phosphorus (P), and calcium (Ca) were investigated.

Results

IHC characterized atherosclerotic plaque pathomorphology. Elemental microscopy showed S distribution to match the anatomy of arterial vessel wall layers, while P distribution corresponded well with cellular areas. LA-ICP-MS revealed Gd and Fe with a limit of detection of ~ 0.1 nmol/g and ~ 100 nmol/g, respectively. Eu-positive signal identified VSOP presence in the vessel wall and allowed the comparison of Eu-VSOP and endogenous Fe distribution in tissue sections. Extracellular matrix material correlated with Eu signal intensity, Fe concentration, and maximum Gd concentration. Eu-VSOP were confined to endothelium in early lesions but accumulated in cellular areas in advanced plaques. Gd distribution was homogeneous in healthy arteries but inhomogeneous in early and advanced plaques. SR-μXRF scans at 0.5 μm resolution revealed Gd hotspots with increased P and Ca concentrations at the intimomedial interface, and a size distribution ranging from a few micrometers to submicrometers.

Conclusions

Eu-VSOP and Gd have distinct spatial distributions in atherosclerotic plaques. While Eu-VSOP distribution is more cell-associated and might be used to monitor atherosclerotic plaque progression, Gd distribution indicates arterial calcification and might help in characterizing plaque vulnerability.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-020-01563-z.

Search for Reliable Circulating Biomarkers to Predict Carotid Plaque Vulnerability

Atherosclerosis is responsible for 20% of ischemic strokes, and the plaques from the internal carotid artery the most frequently involved. Lipoproteins play a key role in carotid atherosclerosis since lipid accumulation contributes to plaque progression and chronic inflammation, both factors leading to plaque vulnerability. Carotid revascularization to prevent future vascular events is reasonable in some patients with high-grade carotid stenosis. However, the degree of stenosis alone is not sufficient to decide upon the best clinical management in some situations. In this context, it is essential to further characterize plaque vulnerability, according to specific characteristics (lipid-rich core, fibrous cap thinning, intraplaque hemorrhage). Although these features can be partly detected by imaging techniques, identifying carotid plaque vulnerability is still challenging. Therefore, the study of circulating biomarkers could provide adjunctive criteria to predict the risk of atherothrombotic stroke. In this regard, several molecules have been found altered, but reliable biomarkers have not been clearly established yet. The current review discusses the concept of vulnerable carotid plaque, and collects existing information about putative circulating biomarkers, being particularly focused on lipid-related and inflammatory molecules.

Carotid Plaque Inflammation Assessed by 18F-FDG PET/CT and Lp-PLA2 Is Higher in Symptomatic Patients

Carotid plaque inflammation assessed by 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) and lipoprotein-associated phospholipase A2 (Lp-PLA₂) levels are higher in symptomatic patients. The aim of this study was to assess correlations between ¹⁸F-FDG uptake on PET scan of carotid artery plaques, plasma levels of Lp-PLA₂, and cerebrovascular symptoms. The study included 45 consecutive patients (22 symptomatic, 23 asymptomatic) with >70% carotid stenosis. Patients were examined by hybrid PET/CT, and maximum standardized uptake values (SUV_max) were recorded. Blood samples were obtained, and plasma was stored at -80 °C for subsequent Lp-PLA₂ analysis. Symptomatic and asymptomatic patients showed no significant difference in classical cardiovascular risk factors. Asymptomatic carotid stenosis patients more frequently had a history of coronary artery disease (P = .025) and peripheral artery disease (P = .012). The symptomatic group had higher ¹⁸F-FDG uptake in carotid plaques (P < .001), higher plasma Lp-PLA₂ (P < .01), and higher high-sensitive C-reactive protein (P = .022). 2-Deoxy-2-[¹⁸F]fluoro-D-glucose uptake on PET/CT and plasma Lp-PLA₂ show a statistically significant association with the symptomatic status of carotid plaques.

Vasculometabolic and Inflammatory Effects of Aldosterone in Obesity

CONTEXT

Not all obese individuals develop cardiovascular disease (CVD). Hyperaldosteronism is suggested to cause inflammation and metabolic dysregulation, and might contribute to CVD development in obese individuals.

OBJECTIVE

We aimed to investigate the association of aldosterone concentrations with inflammation, metabolic disturbances, and atherosclerosis in overweight and obese individuals. Additionally, we measured renin concentrations to investigate whether the observed effects reflected general activation of the renin-angiotensin-aldosterone system (RAAS).

DESIGN

A cross-sectional cohort study (300-OB study) was conducted. Various inflammatory parameters, traits of the metabolic syndrome, lipidome and metabolome parameters, fat distribution, and carotid atherosclerosis were associated with plasma aldosterone and renin levels.

SETTING

The setting of this study was the Radboudumc (i.o. Radboudumc), the Netherlands.

PATIENTS

A total of 302 individuals with a body mass index greater than or equal to 27 kg/m2 participated.

MAIN OUTCOME MEASURES AND RESULTS

Aldosterone was associated with various markers of inflammation and metabolic dysregulation, which partly differed from the associations observed for renin. Although both were associated with inflammatory cell numbers, only renin was associated with classical markers of systemic inflammation. Both were associated with the metabolic syndrome and hepatic steatosis. Of the traits that constitute metabolic syndrome, aldosterone, but not renin, was associated with triglyceride concentrations. Accordingly, aldosterone was associated with large very low-density lipoprotein particles; metabolomics studies further associated aldosterone with urate concentrations and derivatives of the linoleic acid metabolism pathway. Neither aldosterone nor renin was associated with atherosclerotic plaque thickness.

CONCLUSIONS

Aldosterone is not an important driver of systemic inflammation in the obese, whereas aldosterone concentrations and metabolic dysregulation are strongly intertwined in these individuals. Although prospective studies are necessary to validate these results, the independent effects of aldosterone on carotid atherosclerosis appear modest.

Role of 18F-FDG positron emission tomography in carotid atherosclerotic plaque imaging: A systematic review

Stroke and other thromboembolic events in the brain are often due to carotid artery atherosclerosis, and atherosclerotic plaques with inflammation are considered particularly vulnerable, with an increased risk of becoming symptomatic. Positron emission tomography (PET) with 2-deoxy-2-[Fluorine-18] fluoro-D-glucose (¹⁸F-FDG) provides valuable metabolic information regarding arteriosclerotic lesions and may be applied for the detection of vulnerable plaque. At present, however, patients are selected for carotid surgical intervention on the basis of the degree of stenosis alone, and not the vulnerability or inflammation of the lesion. During the past decade, research using PET with the glucose analog tracer ¹⁸F-fluor-deoxy-glucose, has been implemented for identifying increased tracer uptake in symptomatic carotid plaques, and tracer uptake has been shown to correlate with plaque inflammation and vulnerability. These findings imply that ¹⁸F-FDG PET might hold the promise for a new and better diagnostic test to identify patients eligible for carotid endarterectomy. The rationale for developing diagnostic tests based on molecular imaging with ¹⁸F-FDG PET, as well as methods for simple clinical PET approaches, are discussed. This is a systematic review, following Preferred Reporting Items for Systematic Reviews guidelines, which interrogated the PUBMED database from January 2001 to November 2019. The search combined the terms, “atherosclerosis,” “inflammation,” “FDG,” and “plaque imaging.” The search criteria included all types of studies, with a primary outcome of the degree of arterial vascular inflammation determined by ¹⁸F-FDG uptake. This review examines the role of ¹⁸F-FDG PET imaging in the characterization of atherosclerotic plaques.

[18F]ZCDD083: A PFKFB3-Targeted PET Tracer for Atherosclerotic Plaque Imaging

PFKFB3, a glycolysis-related enzyme upregulated in inflammatory conditions and angiogenesis, is an emerging target for diagnosis and therapy of atherosclerosis. The fluorinated phenoxindazole [¹⁸F]ZCDD083 was synthesized, radiolabeled in 17 ± 5% radiochemical yield and >99% radiochemical purity, and formulated for preclinical PET/CT imaging in mice. In vivo stability analysis showed no significant metabolite formation. Biodistribution studies showed high blood pool activity and slow hepatobiliary clearance. Significant activity was detected in the lung 2 h postinjection (pi) (11.0 ± 1.5%ID/g), while at 6 h pi no pulmonary background was observed. Ex vivo autoradiography at 6 h pi showed significant high uptake of [¹⁸F]ZCDD083 in the arch region and brachiocephalic artery of atherosclerotic mice, and no uptake in control mice, matching plaques distribution seen by lipid staining along with PFKFB3 expression seen by immunofluorescent staining. In vivo PET scans showed higher aortic region uptake of [¹⁸F]ZCDD083 in atherosclerotic ApoE^-/-Fbn1^C1039G+/- than in control mice (0.78 ± 0.05 vs 0.44 ± 0.09%ID/g). [¹⁸F]ZCDD083 was detected in aortic arch and brachiocephalic artery of ApoE^-/- (with moderate atherosclerosis) and ApoE^-/-Fbn1^C1039G+/- (with severe, advanced atherosclerosis) mice, suggesting this tracer may be useful for the noninvasive detection of atherosclerotic plaques in vivo.

A Clinical Role of PET in Atherosclerosis and Vulnerable Plaques?

Atherosclerosis is a chronic and most often progressive disease with a long clinically apparently silent period, and can become unstable at any time, due to a plaque rupture or erosion, leading to an acute atherothrombotic event. Atherosclerosis has a progression rate that is highly variable among patients and in the same patient. The progression of atherosclerotic plaque from asymptomatic to symptomatic phase depends on its structure and composition in which inflammation plays an essential role. Prototype of the ruptured plaque contains a large, soft, lipid-rich necrotic core with intraplaque hemorrhage that accounts for more than half of the volume of the plaque covered by a thin and inflamed fibrous cap with few smooth muscle cells, and a heavy infiltrate of inflammatory cells. Noninvasive imaging modalities might provide an assessment of the atherosclerotic disease process through the exploration of these plaque features. Computed tomography angiography and magnetic resonance imaging can characterize plaque morphology, whereas molecular imaging, owing to the high sensitivity of nuclear medicine for the detection of radiopharmaceuticals in tissues, allows to explore plaque biology. During the last 2 decades, FDG-PET imaging has also emerged as a powerful tool to explore noninvasively inflammatory activities in atherosclerotic plaques providing new insights on the evolution of metabolic activities in the vascular wall over time. This review highlights the role of PET imaging for the exploration of metabolic activities in atherosclerotic plaques. It will resume the evidence that have been gathered from clinical studies using FDG-PET and will discuss the perspectives of new radiopharmaceuticals for vulnerable plaque imaging.

The Association of Paraoxonase-1 Polymorphism with Carotid Artery Stenosis among Elderly Chinese Population

Elderly population is in high risk of carotid atherosclerosis and artery stenosis (CAS). It has been proved that PON1 polymorphism is associated with low-density lipoprotein (LDL) oxidation, which plays an important role in artery atherosclerosis. CAS is an important cause of ischemic stroke. This study is aimed at investigating the association of PON1 (rs662) polymorphism with the risk of CAS among elderly Chinese population. Consecutive elderly patients with CAS were enrolled into the study. Genotyping for PON1 (rs662) polymorphism was performed on all participants. There were 310 CAS patients in this study, with 88 symptomatic CAS and 222 asymptomatic CAS. G allele had a frequency of 59.66% in symptomatic CAS (sCAS); and A allele had an incidence of 36.93% in asymptomatic CAS (aCAS) (P < 0.05). In all CAS patients with and without symptom, no associations were found in any genotype comparison. However, among aCAS subjects, based on GA phenotype, the odds ratio (OR) of the mutant GG with stenosis severity was 0.20 (P = 0.01). The OR of GG+GA mutation was 0.28 for moderate/severe severity, compared with GA type (P = 0.03). This study indicates that PON1 (rs662) polymorphism is not associated with the presence of symptom among CAS patients. Moreover, PON1 (rs662) polymorphism correlates with stenosis severity among aCAS.

Molecular and Nonmolecular Magnetic Resonance Coronary and Carotid Imaging

Atherosclerosis is the leading cause of cardiovascular morbidity and mortality. Over the past 2 decades, increasing research attention is converging on the early detection and monitoring of atherosclerotic plaque. Among several invasive and noninvasive imaging modalities, magnetic resonance imaging (MRI) is emerging as a promising option. Advantages include its versatility, excellent soft tissue contrast for plaque characterization and lack of ionizing radiation. In this review, we will explore the recent advances in multicontrast and multiparametric imaging sequences that are bringing the aspiration of simultaneous arterial lumen, vessel wall, and plaque characterization closer to clinical feasibility. We also discuss the latest advances in molecular magnetic resonance and multimodal atherosclerosis imaging.

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.

Biomechanical characteristics of isolated carotid atherosclerotic plaques assessed by ultrasonography

BACKGROUND

The aim of this study was to assess the biomechanical characteristics of carotid atherosclerotic plaques using intima-media thickness (IMT) automatic tracking combined with acoustic densitometry (AD) imaging, and to elucidate the relationship between biomechanical characteristics and inflammatory activity of corresponding plaques evaluated by 18F-Fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT).

METHODS

Sixty-one patients with isolated carotid atherosclerotic plaques underwent conventional carotid ultrasonography, IMT automatic tracking, and acoustic densitometry (AD) imaging. Following these assessments, patients received an 18F-FDG PET/CT scan within 24 hours. We quantified biomechanical and AD parameters including IMT strain rate (SR), IMT time strain rate (TR), and corrected average image intensity value (AIIc%) on the upstream, fibrous cap top, and downstream regions of the plaque and compared them to the reference area(normal intima adjacent to the upstream of the assessed plaque). Target background ratio (TBR) was acquired by 18F-FDG PET/CT for evaluating the inflammatory activity of corresponding plaques. We further divided all participants into an inflammatory group (TBR≥1.25) and non-inflammatory group (TBR<1.25) measures of SR/TR and AIIc% in the two groups were compared and analyzed.

RESULTS

SR/TR were significantly lower in the plaque group when compared to reference area. SR/TR at the cap top area (CTA) and downstream area (DA) of the plaques were lower than those in the reference area (P<0.05) while there was no statistically significant difference in SR or TR of the upstream area (UA) between the plaque and reference area. SR/TR were significantly greater for UA than CTA and DA (P<0.05 for both). AIIc% was significantly lower for UA and CTA than that for DA (P<0.05). The SR/TR of plaque regions were negatively correlated with corresponding AIIc% (r=-0.74, r=-0.75, P<0.05). TR in the inflammatory group was significantly lower than in the non-inflammatory group (P<0.05), while SR and AIIc% showed no statistically significant difference. TR demonstrated a significant negative correlation with TBR (r=-0.83, P<0.05). Receiver operating characteristic curve (ROC) analysis showed that the area under the curve (AUC) of TR was 0.87. Furthermore, TR less than 75.06‰ demonstrated a sensitivity of 88.0% and a specificity of 80.6% for the identification of inflammatory plaques.

CONCLUSIONS

IMT automatic tracking, combined with AD imaging, can be applied to identify the anisotropic biomechanical features of carotid plaques. This novel imaging modality may be used to provide an early assessment of the biomechanical characteristics of carotid plaques. Additionally, the TR parameter was associated with plaque inflammation reaction, possibly providing a new indicator for the early identification of plaque vulnerability.

Carotid Plaque Neovascularization Detected With Superb Microvascular Imaging Ultrasound Without Using Contrast Media

Background and Purpose- A significant proportion of ischemic strokes are caused by emboli from unstable carotid artery plaques with intraplaque neovascularization (IPN) as a key feature of plaque instability. IPN is not detectable with conventional Doppler ultrasound. Contrast-enhanced ultrasound (CEUS) can visualize IPN, but its use is limited in clinical practice because it requires an intravenous injection of contrast. Superb microvascular imaging (SMI) without contrast uses an algorithm to remove clutter and motion wall artifacts while preserving low-velocity blood flow signals, enabling visualization of IPN. Our aim was to assess the feasibility of SMI for the detection of IPN. Methods- Thirty-one patients with >50% carotid stenosis were included: 22 patients were symptomatic and 9 asymptomatic. All patients underwent conventional carotid ultrasound, CEUS, SMI, and blood tests. CEUS and SMI findings were compared and correlated to histological plaque assessments after endarterectomy. Results- There was significant positive correlation between an IPN visual 5-level classification of SMI and a semiquantitative analysis of CEUS (P<0.001, r=0.911). Plaques with higher SMI grades had higher numbers of neovessels quantified at histology (P=0.041, r=0.460). Hypoechoic plaques had higher grades of IPN on both CEUS and SMI (P<0.001). Higher visual IPN counts on SMI were associated with (1) increased areas of inflammation (P=0.043, r=0.457), (2) combined rank scores of granulation tissue, inflammation and lipids (P=0.02, r=0.494) at histology, and (3) higher peak-intensity values on quantitative CEUS (P=0.042, r=0.514). Conclusions- SMI ultrasound can detect neovascularization with accuracy comparable to CEUS, suggesting SMI to be a promising noninvasive alternative to CEUS for the assessment of carotid plaque stability.

Carotid Plaque Positron Emission Tomography Imaging and Cerebral Ischemic Disease

Background and Purpose- The clinical utility of positron emission tomography (PET) imaging in evaluating carotid artery plaque vulnerability remains unclear. Two tracers of recent interest for carotid plaque imaging are ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and ¹⁸F-sodium fluoride (¹⁸F-NaF). We performed a systematic review and meta-analysis evaluating the association between carotid artery ¹⁸F-FDG or ¹⁸F-NaF uptake and recent or future cerebral ischemic events. Methods- A systematic review of Ovid MEDLINE, Ovid EMBASE, and the Cochrane library was conducted from inception to December 2017 for articles evaluating PET tracer uptake in recently symptomatic versus asymptomatic carotid arteries, and articles evaluating carotid uptake in relation to future ischemic events. Cerebral ischemic events were defined as ipsilateral strokes, transient ischemic attacks, or amaurosis fugax. We quantitatively pooled studies by a random-effects model when 3 or more studies were amenable for analysis. We assessed the standardized mean difference between tracer uptake in the symptomatic versus asymptomatic carotid artery using Cohen's d metric. Results- After screening 4144 unique articles, 13 prospective cohort studies assessing carotid artery ¹⁸F-FDG uptake in patients with recent cerebral ischemia were eligible for review. Eleven cohorts of 290 subjects scanned with ¹⁸F-FDG were eligible for meta-analysis. We found that carotid arteries ipsilateral to recent ischemic events had significantly higher ¹⁸F-FDG uptake than asymptomatic arteries (Cohen's d =0.492; CI=0.130-0.855; P=0.008) as well as significant heterogeneity (Cochran's Q =31.5; P=0.0005; I²=68.3%). Meta-regression was not performed due to the limited number of studies in the analysis. Only 2 studies investigating ¹⁸F-NaF PET imaging, and another 2 articles investigating ischemic event recurrence were found. Conclusions- Recent ipsilateral cerebral ischemia may be associated with increased carotid ¹⁸F-FDG uptake on PET imaging regardless of degree of carotid stenosis, although significant heterogeneity was found, and these results should be interpreted with caution. Emerging evidence suggests a similar association may be present with ¹⁸F-NaF plaque uptake. More studies are warranted to provide definitive conclusions on the utility of ¹⁸F-FDG or ¹⁸F-NaF in carotid plaque evaluation before investigating carotid PET as a diagnostic tool for cerebral ischemic events.

Nuclear Imaging

Noninvasive imaging technologies offer to identify several anatomic and molecular features of high-risk plaques. For the noninvasive molecular imaging of atherosclerotic plaques, nuclear medicine constitutes one of the best imaging modalities, thanks to its high sensitivity for the detection of probes in tissues. 18F-fluorodeoxyglucose (FDG) is currently the most widely used radiopharmaceutical for molecular imaging of atherosclerotic plaques with positron emission tomography. The intensity of FDG uptake in the vascular wall correlates closely with the degree of macrophage infiltration in atherosclerotic plaques. FDG positron emission tomographic imaging has become a powerful tool to identify and monitor noninvasively inflammatory activities in atherosclerotic plaques over time. This review examines how FDG positron emission tomographic imaging has given us deeper insight into the role of inflammation in atherosclerotic plaque progression and discusses perspectives for alternative radiopharmaceuticals to FDG that could provide a more specific and simple identification of high-risk lesions and help improve risk stratification of atherosclerotic patients.

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18F-FDG PET/CT for the quantification of inflammation in large carotid artery plaques

BACKGROUND

There is currently no consensus on the methodology for quantification of 18F-FDG uptake in inflammation in atherosclerosis. In this study, we explore different methods for quantification of 18F-FDG uptake in carotid atherosclerotic plaques and correlate the uptake values to histological assessments of inflammation.

METHODS AND RESULTS

Forty-four patients with atherosclerotic stenosis ≥70% of the internal carotid artery underwent 18F-FDG PET/CT. Maximum standardized uptake values (SUVmax) from all plaque-containing slices were collected. SUVmax for the single highest and the mean of multiple slices with and without blood background correction (by subtraction (cSUV) or by division (target-to-background ratio (TBR)) were calculated. Following endarterectomy 30 plaques were assessed histologically. The length of the plaques at CT was 6-32 mm. The 18F-FDG uptake in the plaques was 1.15-2.66 for uncorrected SUVs, 1.16-3.19 for TBRs, and 0.20-1.79 for cSUVs. There were significant correlations between the different uptake values (r = 0.57-0.99, P < 0.001). Methods with and without blood background correction showed similar, moderate correlations to the amount of inflammation assessed at histology (r = 0.44-0.59, P < 0.02).

CONCLUSIONS

In large stenotic carotid plaques, 18F-FDG uptake reflects the inflammatory status as assessed at histology. Increasing number of PET slices or background correction did not change the correlation.

Molecular imaging of coronary inflammation

Coronary inflammation is related to atherosclerotic disease and, less frequently, systemic vasculitis. Regardless of the etiology, coronary inflammation is associated with adverse cardiac events. Molecular imaging with ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET/CT) allows in vivo assessment of coronary inflammation and evaluation of response to therapy. The aim of this review is to give an update on the recent development of FDG-PET/CT, discuss the potential roles of coronary inflammation imaging, review the limitations of FDG-PET/CT imaging, and give an overview of the new tracers available for PET/CT plaque imaging.

18F-FDG Uptake on PET/CT in Symptomatic versus Asymptomatic Carotid Disease: a Meta-Analysis

INTRODUCTION

The role of positron emission tomography (PET)/computed tomography (CT) in the determination of inflammation in arterial disease is not well defined. This can provide information about arterial wall inflammation in atherosclerotic disease, and may give insight into plaque stability. The aim of this review was to perform a meta-analysis of PET/CT with ¹⁸F-FDG (fluorodeoxyglucose) uptake in symptomatic and asymptomatic carotid artery disease.

METHODS

This was a systematic review, following PRISMA guidelines, which interrogated the MEDLINE database from January 2001 to May 2017. The search combined the terms, "inflammation", "FDG", and "stroke". The search criteria included all types of studies, with a primary outcome of the degree of arterial vascular inflammation determined by ¹⁸F-FDG uptake. Analysis involved an inverse weighted variance estimate of pooled data, using a random effects model.

RESULTS

A total of 14 articles (539 patients) were included in the meta-analysis. Comparing carotid artery ¹⁸F-FDG uptake in symptomatic versus asymptomatic disease yielded a standard mean difference of 0.94 (95% CI 0.58-1.130; p < .0001; I² = 65%).

CONCLUSIONS

PET/CT using ¹⁸F-FDG can demonstrate carotid plaque inflammation, and is a marker of symptomatic disease. Further studies are required to understand the clinical implication of PET/CT as a risk prediction tool.

Anti-inflammatory approaches to ischaemic stroke prevention

Stroke is a major cause of neurological morbidity and mortality. Atherosclerosis is a major contributor to first and recurrent stroke. A growing evidence base indicates that inflammation is a key process in the pathogenesis of atherosclerosis, leading to thromboembolic events. In this review, we summarise the evidence linking inflammation to stroke risk and discuss clinical trials addressing the 'inflammation hypothesis' in coronary disease and stroke. Trial registration number CONVINCE trial ClinicalTrials.gov number; NCT 02898610; Pre-results.

Evaluation of ultrasmall superparamagnetic iron-oxide (USPIO) enhanced MRI with ferumoxytol to quantify arterial wall inflammation

BACKGROUND AND AIMS

Inflammation in atherosclerotic plaques is an important determinant of plaque vulnerability, and can be detected non-invasively using ultra-small superparamagnetic iron-oxide (USPIO) enhanced MRI. The aims of the current study were: 1) to determine whether ferumoxytol can be used for USPIO-MRI of atherosclerotic plaques, 2) to establish a protocol for quantitative USPIO-MRI of carotid artery plaques using ferumoxytol, and 3) to study the relation between USPIO uptake and plaque burden and ¹⁸F-fluorodeoxyglucose (FDG) uptake (measured by ¹⁸F-FDG PET/CT scan) in atherosclerotic plaques.

METHODS

In 9 patients with carotid artery stenosis >30% and 4 healthy controls, quantitative R2* MRI scans of the carotid arteries were performed before and 72 h after USPIO administration (4 mg/kg ferumoxytol). USPIO uptake was assessed by quantifying the difference in R2* (ΔR2*) between baseline and post-USPIO scans. In addition to MRI, ¹⁸F-FDG PET/CT was performed on both carotid arteries. MR and PET/CT images were co-registered, and ¹⁸F-FDG uptake was quantified in all slices containing atherosclerotic plaque.

RESULTS

Infusion of ferumoxytol resulted in higher R2* values after 72 h in atherosclerotic plaques (ΔR2* 24.6 ± 19.8 s^-1; p = 0.0003), but not in the healthy control vessel wall (ΔR2* 2.6 ± 5.6 s^-1, p = 0.23). USPIO uptake in patients was higher in atherosclerotic plaques compared to the patient non-plaque vessel wall (ΔR2* of 24.6 ± 19.8 vs. 7.5 ± 9.3 s^-1, p = 0.004). No correlation was found between USPIO uptake and ¹⁸F-FDG uptake in atherosclerotic plaques (R² = 0.03, p = 0.55).

CONCLUSIONS

Ferumoxytol is selectively taken up by atherosclerotic plaques and can thus be used for carotid USPIO-MRI. As USPIO and ¹⁸F-FDG uptake in atherosclerotic plaque do not correlate in this cohort, these agents may visualize different pathophysiological aspects of plaque inflammation.

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.

F-18 FDG PET/CT imaging of cardiac and vascular inflammation and infection

INTRODUCTION

Inflammation forms an important core of the aetiopathogenic process involved in many diseases affecting the heart and the blood vessels. These diseases include infections as well as inflammatory non-infectious cardiovascular conditions. The common feature of this is invasion of the heart or blood vessel by inflammatory cells. F-18 2-fluoro 2-deoxy-D glucose (FDG) is an analogue of glucose and like glucose it is taken up by activated inflammatory cells that accumulate at the site of infection. This has formed the basis of the use of F-18 FDG PET/CT in the non-invasive evaluation of human inflammatory diseases.

SOURCES OF DATA

This review is based on the published academic articles as well as our clinical experience.

AREAS OF AGREEMENT

F-18 FDG PET/CT is a useful imaging modality in the evaluation of cardiovascular inflammatory disorders. Accumulation and distribution of F-18 FDG at the site of inflammation/infection corresponds to severity of the inflammation/infection and extent of involvement.

AREAS OF CONTROVERSY

Most studies evaluating utility of F-18 FDG PET/CT in imaging cardiovascular inflammation are small observational studies hence are potentially prone to bias.

GROWING POINTS

Being a hybrid metabolic and morphologic imaging technique, F-18 FDG PET/CT offers combined advantage of complementary anatomic and metabolic information in disease process. This makes it a useful modality in the diagnosis, determination of extent of disease, prognostication as well as treatment monitoring.

AREAS TIMELY FOR DEVELOPING RESEARCH

Larger prospective studies are needed to validate the superiority of F-18 FDG PET/CT imaging over conventional anatomic imaging modalities.

Phosphodiesterase4D (PDE4D)--A risk factor for atrial fibrillation and stroke?

Mutations in the gene encoding phosphodiesterase 4D (PDE4D) enzyme are associated with ischemic stroke; however the functional implications of such mutations are not well understood. PDE4D is part of a complex protein family modulating intracellular signalling by cyclic nucleotides. The PDE4 family includes subtypes A-D, all of which show unique intracellular, cellular and tissue distribution. PDE4D is the major subtype expressed in human atrial myocytes and involved in the pathophysiology of arrhythmias, such as atrial fibrillation. The PDE4D enzyme hydrolyses cyclic adenosine monophosphate (cAMP). Though diverging results are reported, several population based studies describe association of various PDE4D single nucleotide polymorphisms (SNP) with cardio-embolic stroke in particular. Functionally, a down regulation of PDE4D variants has been reported in stroke patients. The anti-inflammatory and vasodilator properties of PDE4 inhibitors make them suitable for treatment of stroke and cardiovascular disease. PDE4D has recently been suggested as factor in atrial fibrillation. This review summarizes the possible function of PDE4D in the brain, heart, and vasculature. Further, association of the described SNPs, in particular, with cardioembolic stroke, is reviewed. Current findings on the PDE4D mutations suggest functionality involves an increased cardiac risk factor as well as augmented risk of atrial fibrillation.