Distribution of Inflammation Within Carotid Atherosclerotic Plaques With High-Risk Morphological Features

In Vivo Classification and Characterization of Carotid Atherosclerotic Lesions with Integrated 18F-FDG PET/MRI

BACKGROUND

The aim of this study was to exploit integrated PET/MRI to simultaneously evaluate the morphological, component, and metabolic features of advanced atherosclerotic plaques and explore their incremental value.

METHODS

In this observational prospective cohort study, patients with advanced plaque in the carotid artery underwent 18F-FDG PET/MRI. Plaque morphological features were measured, and plaque component features were determined via MRI according to AHA lesion-types. Maximum standardized uptake values (SUVmax) and tissue to background ratio (TBR) on PET were calculated. Area under the receiver-operating characteristic curve (AUC) and net reclassification improvement (NRI) were used to compare the incremental contribution of FDG uptake when added to AHA lesion-types for symptomatic plaque classification.

RESULTS

A total of 280 patients with advanced plaque in the carotid artery were recruited. A total of 402 plaques were confirmed, and 87 of 402 (21.6%) were symptomatic plaques. 18F-FDG PET/MRI was performed a mean of 38 days (range 1-90) after the symptom. Increased stenosis degree (61.5% vs. 50.0%, p < 0.001) and TBR (2.96 vs. 2.32, p < 0.001) were observed in symptomatic plaques compared with asymptomatic plaques. The performance of the combined model (AHA lesion type VI + stenosis degree + TBR) for predicting symptomatic plaques was the best among all models (AUC = 0.789). The improvement of the combined model (AHA lesion type VII + stenosis degree + TBR) over AHA lesion type VII model for predicting symptomatic plaques was the highest (AUC = 0.757/0.454, combined model/AHA lesion type VII model), and the NRI was 50.7%.

CONCLUSIONS

Integrated PET/MRI could simultaneously evaluate the morphological component and inflammation features of advanced atherosclerotic plaques and provide supplementary optimization information over AHA lesion-types for identifying vulnerable plaques in atherosclerosis subjects to achieve further stratification of stroke risk.

Simultaneous 18-FDG PET and MR imaging in lower extremity arterial disease

Background

Simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) is a novel hybrid imaging method integrating the advances of morphological tissue characterization of MRI with the pathophysiological insights of PET applications.

Aim

This study evaluated the use of simultaneous 18-FDG PET/MR imaging for characterizing atherosclerotic lesions in lower extremity arterial disease (LEAD).

Methods

Eight patients with symptomatic stenoses of the superficial femoral artery (SFA) under simultaneous acquisition of 18-FDG PET and contrast-enhanced MRI using an integrated whole-body PET/MRI scanner. Invasive plaque characterization of the SFA was performed by intravascular imaging using optical coherence tomography. Histological analysis of plaque specimens was performed after directional atherectomy.

Results

MRI showed contrast enhancement at the site of arterial stenosis, as assessed on T2-w and T1-w images, compared to a control area of the contralateral SFA (0.38 ± 0.15 cm vs. 0.23 ± 0.11 cm; 1.77 ± 0.19 vs. 1.57 ± 0.15; p-value <0.05). On PET imaging, uptake of 18F-FDG (target-to-background ratio TBR > 1) at the level of symptomatic stenosis was observed in all but one patient. Contrast medium-induced MR signal enhancement was detected in all plaques, whereas FDG uptake in PET imaging was increased in lesions with active fibroatheroma and reduced in fibrocalcified lesions.

Conclusion

In this multimodal imaging study, we report the feasibility and challenges of simultaneous PET/MR imaging of LEAD, which might offer new perspectives for risk estimation.

Imaging Carotid Plaque Inflammation Using Positron Emission Tomography: Emerging Role in Clinical Stroke Care, Research Applications, and Future Directions

Atherosclerosis is a chronic systemic inflammatory condition of the vasculature and a leading cause of stroke. Luminal stenosis severity is an important factor in determining vascular risk. Conventional imaging modalities, such as angiography or duplex ultrasonography, are used to quantify stenosis severity and inform clinical care but provide limited information on plaque biology. Inflammatory processes are central to atherosclerotic plaque progression and destabilization. 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is a validated technique for quantifying plaque inflammation. In this review, we discuss the evolution of FDG-PET as an imaging modality to quantify plaque vulnerability, challenges in standardization of image acquisition and analysis, its potential application to routine clinical care after stroke, and the possible role it will play in future drug discovery.

Effects of Lipid Lowering Therapies on Vulnerable Plaque Features: An Updated Narrative Review of the Literature

The clinical evidence on the efficacy of lipid lowering therapy in patients with coronary artery disease (CAD) is unequivocally established. However, the effects of these therapies on plaque composition and stability are less clear. The use of intracoronary imaging (ICI) technologies has emerged as a complement to conventional angiography to further characterize plaque morphology and detect high-risk plaque features related to cardiovascular events. Along with clinical outcomes studies, parallel imaging trials employing serial evaluations with intravascular ultrasound (IVUS) have shown that pharmacological treatment has the capacity to either slow disease progression or promote plaque regression, depending on the degree of lipid lowering achieved. Subsequently, the introduction of high-intensity lipid lowering therapy led to much lower levels of low-density lipoprotein cholesterol (LDL-C) levels than achieved in the past, resulting in greater clinical benefit. However, the degree of atheroma regression showed in concomitant imaging trials appeared more modest as compared to the magnitude of clinical benefit accrued from high-intensity statin therapy. Recently, new randomized trials have investigated the additional effects of achieving very low levels of LDL-C on high-risk plaque features-such as fibrous cap thickness and large lipid accumulation-beyond its size. This paper provides an overview of the currently available evidence of the effects of moderate to high-intensity lipid lowering therapy on high-risk plaque features as assessed by different ICI modalities, reviews data supporting the use of these trials, and analyse the future perspectives in this field.

PET-MRI of Coronary Artery Disease

Simultaneous positron emission tomography and magnetic resonance imaging (PET-MRI) combines the anatomical detail and tissue characterization of MRI with the functional information from PET. Within the coronary arteries, this hybrid technique can be used to identify biological activity combined with anatomically high-risk plaque features to better understand the processes underlying coronary atherosclerosis. Furthermore, the downstream effects of coronary artery disease on the myocardium can be characterized by providing information on myocardial perfusion, viability, and function. This review will describe the current capabilities of PET-MRI in coronary artery disease and discuss the limitations and future directions of this emerging technique. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 3.

Emerging PET Tracers in Cardiac Molecular Imaging

¹⁸F-fluorodeoxyglucose (FDG) and ¹⁸F-sodium fluoride (NaF) represent emerging PET tracers used to assess atherosclerosis-related inflammation and molecular calcification, respectively. By localizing to sites with high glucose utilization, FDG has been used to assess myocardial viability for decades, and its role in evaluating cardiac sarcoidosis has come to represent a major application. In addition to determining late-stage changes such as loss of perfusion or viability, by targeting mechanisms present in atherosclerosis, PET-based techniques have the ability to characterize atherogenesis in the early stages to guide intervention. Although it was once thought that FDG would be a reliable indicator of ongoing plaque formation, micro-calcification as portrayed by NaF-PET/CT appears to be a superior method of monitoring disease progression. PET imaging with NaF has the additional advantage of being able to determine abnormal uptake due to coronary artery disease, which is obscured by physiologic myocardial activity on FDG-PET/CT. In this review, we discuss the evolving roles of FDG, NaF, and other PET tracers in cardiac molecular imaging.

Chemotherapy, hypothyroidism and oral dysbiosis as a novel risk factor of cardiovascular pathology development

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in the population, as well as the economic burden of the health care system. Currently, CVDs account for more than 17.6 million deaths a year and are projected to exceed 23.6 million by 2030. Unstable atheroma, and its rupture, underlies the pathology of most cardiovascular complications, particularly acute coronary syndrome, mortality from which, compared with other CV events, remains the leading one. Despite numerous efforts by WHO, national health systems, and medical authorities, the incidence and mortality from cardiovascular events remain critically high. Thus, the search for new risk factors for the development of CV pathology looks very relevant. Our working group decided to amalgamate our research data, which reflects the study of modern risk factors from the Armenian, Russian, Georgian, and Iranian medical schools. In particular, the aspects of cardiotoxic effects of chemotherapy, hypothyroidism, and oral dysbiosis are discussed.

Morphological feature and mapping inflammation in classified carotid plaques in symptomatic and asymptomatic patients: A hybrid 18F-FDG PET/MR study

Purpose

To investigate morphological and inflamed-metabolism features of carotid atherosclerotic plaques between symptomatic and asymptomatic patients with hybrid ¹⁸F-FDG PET/MR imaging.

Methods

A total of 20 symptomatic and 20 asymptomatic patients with carotid plaques underwent hybrid ¹⁸F-FDG PET/MR scans. American heart association (AHA) lesion types were classified, and plaque compositions were further determined on consecutive MRI axial sections in both carotid arteries. ¹⁸F-FDG uptake in carotid arteries was quantified using region of interest (ROI) methods based on maximum standardized uptake values (SUVmax) and target-to-background ratio (TBR) on corresponding positron emission tomography (PET) images.

Results

A total of seventy-one carotid plaques were quantified. AHA type VI was the most common (23, 32.4%), and the region of carotid bifurcation was the most common place presenting lesions (32, 45.1%). Compared with the asymptomatic group, the prevalence of high-risk features including plaque burden, lumen stenosis, maximum necrotic core area, and maximum intra-plaque hemorrhage area increased in the symptomatic group. Carotid TBR values of plaque in symptomatic group (TBR = 2.56 ± 0.34) was significantly higher than that in asymptomatic group (TBR = 1.57 ± 0.14) (P < 0.05). hs-CRP is an independent risk factor for the stability of carotid plaque. The correlation between normalized wall index (NWI) and TBR values was significantly positive in both the symptomatic and the asymptomatic groups (P < 0.01), and both NWI and TBR were significantly correlated with the level of hs-CRP (P < 0.01).

Conclusion

Integrated ¹⁸F-FDG PET/MR scans presented distinct risk features between symptomatic and asymptomatic patients. Hybrid ¹⁸F-FDG PET/MR systems combined with clinical serum hs-CRP may help distinguish vulnerable carotid plaques.

Multimodality Imaging in the Detection of Ischemic Heart Disease in Women

Women with coronary artery disease tend to have a worse short and long-term prognosis relative to men and the incidence of atherosclerotic cardiovascular disease is increasing. Women are less likely to present with classic anginal symptoms when compared with men and more likely to be misdiagnosed. Several non-invasive imaging modalities are available for diagnosing ischemic heart disease in women and many of these modalities can also assist with prognostication and help to guide management. Selection of the optimal imaging modality to evaluate women with possible ischemic heart disease is a scenario which clinicians often encounter. Earlier modalities such as exercise treadmill testing demonstrate significant performance variation in men and women, while newer modalities such as coronary CT angiography, myocardial perfusion imaging and cardiac magnetic resonance imaging are highly specific and sensitive for the detection of ischemia and coronary artery disease with greater parity between sexes. Individual factors, availability, diagnostic performance, and female-specific considerations such as pregnancy status may influence the decision to select one modality over another. Emerging techniques such as strain rate imaging, CT-myocardial perfusion imaging and cardiac magnetic resonance imaging present additional options for diagnosing ischemia and coronary microvascular dysfunction.

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.

A preliminary study of relationship among the degree of internal carotid artery stenosis, wall shear stress on MR angiography and 18F-FDG uptake on PET/CT

BACKGROUND

This preliminary study was undertaken to evaluate relationship among the degree of internal carotid artery (ICA) stenosis, wall shear stress (WSS) by computational fluid dynamics (CFD) on magnetic resonance angiography (MRA) and 18F-FDG uptake of ICA on PET/CT.

METHODS

A total of 40 carotid arteries in 20 patients with carotid atherosclerotic disease were examined with MRA and 18F-FDG PET/CT. Atherosclerotic risk factors were assessed in all patients. Degree of ICA stenosis was calculated according to NASCET method. CFD analysis was performed and maximum WSS (WSSmax) was measured. 18F-FDG uptake in ICA was quantified using maximum target-to-blood pool ratio (TBRmax).

RESULTS

Atherosclerotic risk factors did not affect imaging findings. There were significant correlations between WSSmax and degree of ICA stenosis (ρ = .81, P < .001), WSSmax and TBRmax (ρ = .64, P < .001), and TBRmax and degree of ICA stenosis (ρ = .50, P = .001).

CONCLUSIONS

These preliminary results indicate that there may be significant correlations among the degree of ICA stenosis, WSSmax and TBRmax in patients with carotid artery stenosis.

A review on advances in 18F-FDG PET/CT radiomics standardisation and application in lung disease management

Radiomics analysis quantifies the interpolation of multiple and invisible molecular features present in diagnostic and therapeutic images. Implementation of 18-fluorine-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) radiomics captures various disorders in non-invasive and high-throughput manner. ¹⁸F-FDG PET/CT accurately identifies the metabolic and anatomical changes during cancer progression. Therefore, the application of ¹⁸F-FDG PET/CT in the field of oncology is well established. Clinical application of ¹⁸F-FDG PET/CT radiomics in lung infection and inflammation is also an emerging field. Combination of bioinformatics approaches or textual analysis allows radiomics to extract additional information to predict cell biology at the micro-level. However, radiomics texture analysis is affected by several factors associated with image acquisition and processing. At present, researchers are working on mitigating these interrupters and developing standardised workflow for texture biomarker establishment. This review article focuses on the application of ¹⁸F-FDG PET/CT in detecting lung diseases specifically on cancer, infection and inflammation. An overview of different approaches and challenges encountered on standardisation of ¹⁸F-FDG PET/CT technique has also been highlighted. The review article provides insights about radiomics standardisation and application of ¹⁸F-FDG PET/CT in lung disease management.

Resveratrol treatment does not reduce arterial inflammation in males at risk of type 2 diabetes: a randomized crossover trial

PURPOSE

Resveratrol has shown promising anti-inflammatory effects in in vitro and animal studies. We aimed to investigate this effect on arterial inflammation in vivo.

METHODS

This was an additional analysis of a double-blind randomized crossover trial which included eight male subjects with decreased insulin sensitivity who underwent an ¹⁸F-fluoroxyglucose (¹⁸F-FDG) PET/CT after 34 days of placebo and resveratrol treatment (150 mg/day). ¹⁸F-FDG uptake was analyzed in the carotid arteries and the aorta, adipose tissue regions, spleen, and bone marrow as measures for arterial and systemic inflammation. Maximum target-to-background ratios (TBR_max) were compared between resveratrol and placebo treatment with the non-parametric Wilcoxon signed-rank test. Median values are shown with their interquartile range.

RESULTS

Arterial ¹⁸F-FDG uptake was non-significantly higher after resveratrol treatment (TBR_max all vessels 1.7 (1.6-1.7)) in comparison to placebo treatment (1.5 (1.4-1.6); p=0.050). Only in visceral adipose tissue, the increase in ¹⁸F-FDG uptake after resveratrol reached statistical significance (p=0.024). Furthermore, CRP-levels were not significantly affected by resveratrol treatment (p=0.091).

CONCLUSIONS

Resveratrol failed to attenuate arterial or systemic inflammation as measured with ¹⁸F-FDG PET in subjects at risk of developing type 2 diabetes. However, validation of these findings in larger human studies is needed.

Imaging inflammation in atherosclerotic plaques, targeting SST2 with [111In]In-DOTA-JR11

BACKGROUND

Imaging Somatostatin Subtype Receptor 2 (SST2) expressing macrophages by [DOTA,Tyr3]-octreotate (DOTATATE) has proven successful for plaque detection. DOTA-JR11 is a SST2 targeting ligand with a five times higher tumor uptake than DOTATATE, and holds promise to improve plaque imaging. The aim of this study was to evaluate the potential of DOTA-JR11 for plaque detection.

METHODS AND RESULTS

Atherosclerotic ApoE-/- mice (n = 22) fed an atherogenic diet were imaged by SPECT/CT two hours post injection of [111In]In-DOTA-JR11 (~ 200 pmol, ~ 50 MBq). In vivo plaque uptake of [111In]In-DOTA-JR11 was visible in all mice, with a target-to-background-ratio (TBR) of 2.23 ± 0.35. Post-mortem scans after thymectomy and ex vivo scans of the arteries after excision of the arteries confirmed plaque uptake of the radioligand with TBRs of 2.46 ± 0.52 and 3.43 ± 1.45 respectively. Oil red O lipid-staining and ex vivo autoradiography of excised arteries showed [111In]In-DOTA-JR11 uptake at plaque locations. Histological processing showed CD68 (macrophages) and SST2 expressing cells in plaques. SPECT/CT, in vitro autoradiography and immunohistochemistry performed on slices of a human carotid endarterectomy sample showed [111In]In-DOTA-JR11 uptake at plaque locations containing CD68 and SST2 expressing cells.

CONCLUSIONS

The results of this study indicate DOTA-JR11 as a promising ligand for visualization of atherosclerotic plaque inflammation.

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.

Advances in Radiopharmaceutical Sciences for Vascular Inflammation Imaging: Focus on Clinical Applications

Biomedical imaging technologies offer identification of several anatomic and molecular features of disease pathogenesis. Molecular imaging techniques to assess cellular processes in vivo have been useful in advancing our understanding of several vascular inflammatory diseases. For the non-invasive molecular imaging of vascular inflammation, nuclear medicine constitutes one of the best imaging modalities, thanks to its high sensitivity for the detection of probes in tissues. 2-[¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) is currently the most widely used radiopharmaceutical for molecular imaging of vascular inflammatory diseases such as atherosclerosis and large-vessel vasculitis. The combination of [¹⁸F]FDG and positron emission tomography (PET) imaging has become a powerful tool to identify and monitor non-invasively inflammatory activities over time but suffers from several limitations including a lack of specificity and avid background in different localizations. The use of novel radiotracers may help to better understand the underlying pathophysiological processes and overcome some limitations of [¹⁸F]FDG PET for the imaging of vascular inflammation. This review examines how [¹⁸F]FDG PET has given us deeper insight into the role of inflammation in different vascular pathologies progression and discusses perspectives for alternative radiopharmaceuticals that could provide a more specific and simple identification of pathologies where vascular inflammation is implicated. Use of these novel PET tracers could lead to a better understanding of underlying disease mechanisms and help inform the identification and stratification of patients for newly emerging immune-modulatory therapies. Future research is needed to realize the true clinical translational value of PET imaging in vascular inflammatory diseases.

The application of molecular imaging to advance translational research in chronic inflammation

Over the past several decades, molecular imaging techniques to assess cellular processes in vivo have been integral in advancing our understanding of disease pathogenesis. 18F-fluorodeoxyglucose (18-FDG) positron emission tomography (PET) imaging in particular has shaped the field of atherosclerosis research by highlighting the importance of underlying inflammatory processes that are responsible for driving disease progression. The ability to assess physiology using molecular imaging, combining it with anatomic delineation using cardiac coronary angiography (CCTA) and magnetic resonance imaging (MRI) and lab-based techniques, provides a powerful combination to advance both research and ultimately clinical care. In this review, we demonstrate how molecular imaging studies, specifically using 18-FDG PET, have revealed that early vascular disease is a systemic process with multiple, concurrent biological mechanisms using inflammatory diseases as a basis to understand early atherosclerotic mechanisms in humans.

Risk factors for symptomatic vascular events in giant cell arteritis: a study of 254 patients with large-vessel imaging at diagnosis

Aims

To identify factors associated with vascular events in patients with giant cell arteritis (GCA).

Methods

We performed a retrospective study of GCA patients diagnosed over a 20-year-period, who all underwent vascular imaging evaluation at diagnosis. Symptomatic vascular events were defined as the occurrence of any aortic event (aortic dissection or symptomatic aortic aneurysm), stroke, myocardial infarction, limb or mesenteric ischemia and de novo lower limbs arteritis stage 3 or 4. Patients with symptomatic vascular event (VE+) and without were compared, and risk factors were identified in a multivariable analysis.

Results

Thirty-nine (15.4%) of the 254 included patients experienced at least one symptomatic vascular event during follow-up, with a median time of 21.5 months. Arterial hypertension, diabetes, lower limbs arteritis or vascular complication at diagnosis were more frequent in VE+ patients (p < 0.05), as an abnormal computed tomography (CT)-scan at diagnosis (p = 0.04), aortitis (p = 0.01), particularly of the descending thoracic aorta (p = 0.03) and atheroma (p = 0.03). Deaths were more frequent in the VE+ group (37.1 versus 10.3%, p = 0.0003). In multivariable analysis, aortic surgery [hazard ratio (HR): 10.46 (1.41-77.80), p = 0.02], stroke [HR: 22.32 (3.69-135.05), p < 0.001], upper limb ischemia [HR: 20.27 (2.05-200.12), p = 0.01], lower limb ischemia [HR: 76.57 (2.89-2027.69), p = 0.009], aortic atheroma [HR: 3.06 (1.06-8.82), p = 0.04] and aortitis of the descending thoracic aorta on CT-scan at diagnosis [HR: 4.64 (1.56-13.75), p = 0.006] were independent predictive factors of a vascular event.

Conclusion

In this study on GCA cases with large vessels imaging at diagnosis, aortic surgery, stroke, upper or lower limb ischemia, aortic atheroma and aortitis of the descending thoracic aorta on CT-scan, at GCA diagnosis, were independent predictive factors of a vascular event.

Plain language summary

Risk factors for symptomatic vascular events in giant cell arteritisThis study was performed to identify the risk factors for developing symptomatic vascular event during giant cell arteritis (GCA) because these are poorly known.We performed a retrospective study of GCA patients diagnosed over a 20-year-period, who all underwent vascular imaging evaluation at diagnosis.Patients with symptomatic vascular event (VE+) and without (VE-) were compared, and risk factors were identified in a multivariable analysis.Thirty-nine patients experienced at least one symptomatic vascular event during follow-up, with a median time of 21.5 months.Arterial hypertension, diabetes, lower limbs arteritis or vascular complication at diagnosis were significantly more frequent in VE+ patients, as an abnormal CT-scan at diagnosis, aortitis, particularly of the descending thoracic aorta and atheroma. Deaths were more frequent in the VE+ group.Among 254 GCA patients, 39 experienced at least one vascular event during follow-up.Aortic surgery, stroke, upper and lower limb ischemia were vascular event risk factors.Aortic atheroma and descending thoracic aorta aortitis on CT-scan were vascular event risk factors.This study on GCA cases with large vessels imaging at diagnosis, showed that aortic surgery, stroke, upper or lower limb ischemia, aortic atheroma and aortitis of the descending thoracic aorta on CT-scan, at GCA diagnosis, were independent predictive factors of a vascular event.

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.

Arterial wall inflammation in rheumatoid arthritis is reduced by anti-inflammatory treatment

BACKGROUND

Rheumatoid arthritis (RA) patients have an increased risk of cardiovascular disease (CVD), partly due to an increased prevalence of cardiovascular risk factors, but also due to chronic systemic inflammation inducing atherosclerotic changes of the arterial wall. The aim of this study was to determine whether anti-inflammatory therapy for the treatment of RA has favorable effects on arterial wall inflammation in RA patients.

METHODS

Arterial wall inflammation before and after 6 months of anti-inflammatory treatment was assessed in 49 early and established RA patients using 18F-fluorodeoxyglucose-positron emission tomography with computed tomography (18F-FDG-PET/CT). Arterial 18F-FDG uptake was quantified as maximum standardized uptake value (SUVmax) in the thoracic aorta, abdominal aorta, carotid, iliac and femoral arteries. Early RA patients (n = 26) were treated with conventional synthetic disease modifying anti-rheumatic drugs with or without corticosteroids, whereas established RA patients (n = 23) were treated with adalimumab.

RESULTS

In RA patients, overall SUVmax was over time reduced by 4% (difference -0.06, 95%CI -0.12 to -0.01, p = 0.02), with largest reductions in carotid (-8%, p = 0.001) and femoral arteries (-7%, p = 0.005). There was no difference in arterial wall inflammation change between early and established RA patients (SUVmax difference 0.003, 95%CI -0.11 to 0.12, p = 0.95). Change in arterial wall inflammation significantly correlated with change in serological inflammatory markers (erythrocyte sedimentation rate and C-reactive protein).

CONCLUSION

Arterial wall inflammation in RA patients is reduced by anti-inflammatory treatment and this reduction correlates with reductions of serological inflammatory markers. These results suggest that anti-inflammatory treatment of RA has favorable effects on the risk of cardiovascular events in RA patients.

Vascular imaging of atherosclerosis: Strengths and weaknesses

Atherosclerosis is an inflammatory disease that can lead to several complications such as ischemic heart disease, stroke, and peripheral vascular disease. Therefore, researchers and clinicians rely heavily on the use of imaging modalities to identify, and more recently, quantify the burden of atherosclerosis in the aorta, carotid arteries, coronary arteries, and peripheral vasculature. These imaging techniques vary in invasiveness, cost, resolution, radiation exposure, and presence of artifacts. Consequently, a detailed understanding of the risks and benefits of each technique is crucial prior to their introduction into routine cardiovascular screening. Additionally, recent research in the field of microvascular imaging has proven to be important in the field of atherosclerosis. Using techniques such as contrast-enhanced ultrasound and superb microvascular imaging, researchers have been able to detect blood vessels within a plaque lesion that may contribute to vulnerability and rupture. This paper will review the strengths and weaknesses of the various imaging techniques used to measure atherosclerotic burden. Furthermore, it will discuss the future of advanced imaging modalities as potential biomarkers for atherosclerosis.

Imaging Atherosclerosis by PET, With Emphasis on the Role of FDG and NaF as Potential Biomarkers for This Disorder

Molecular imaging has emerged in the past few decades as a novel means to investigate atherosclerosis. From a pathophysiological perspective, atherosclerosis is characterized by microscopic inflammation and microcalcification that precede the characteristic plaque buildup in arterial walls detected by traditional assessment methods, including anatomic imaging modalities. These processes of inflammation and microcalcification are, therefore, prime targets for molecular detection of atherosclerotic disease burden. Imaging with positron emission tomography/computed tomography (PET/CT) using 18F-fluorodeoxyglucose (FDG) and 18F-sodium fluoride (NaF) can non-invasively assess arterial inflammation and microcalcification, respectively. FDG uptake reflects glucose metabolism, which is particularly increased in atherosclerotic plaques retaining macrophages and undergoing hypoxic stress. By contrast, NaF uptake reflects the exchange of hydroxyl groups of hydroxyapatite crystals for fluoride producing fluorapatite, a key biochemical step in calcification of atherosclerotic plaque. Here we review the existing literature on FDG and NaF imaging and their respective values in investigating the progression of atherosclerotic disease. Based on the large volume of data that have been introduced to the literature and discussed in this review, it is clear that PET imaging will have a major role to play in assessing atherosclerosis in the major and coronary arteries. However, it is difficult to draw definitive conclusions on the potential role of FDG in investigating atherosclerosis given the vast number of studies with different designs, image acquisition methods, analyses, and interpretations. Our experience in this domain of research has suggested that NaF may be the tool of choice over FDG in assessing atherosclerosis, especially in the setting of coronary artery disease (CAD). Specifically, global NaF assessment appears to be superior in detecting plaques in tissues with high background FDG activity, such as the coronary arteries.

An Update on [18F]Fluoride PET Imaging for Atherosclerotic Disease

Atherosclerosis is the leading cause of life-threatening morbidity and mortality, as the rupture of atherosclerotic plaques leads to critical atherothrombotic events such as myocardial infarction and ischemic stroke, which are the 2 most common causes of death worldwide. Vascular calcification is a complicated pathological process involved in atherosclerosis, and microcalcifications are presumed to increase the likelihood of plaque rupture. Despite many efforts to develop novel non-invasive diagnostic modalities, diagnostic techniques are still limited, especially before symptomatic presentation. From this point of view, vulnerable plaques are a direct target of atherosclerosis imaging. Anatomic imaging modalities have the limitation of only visualizing macroscopic structural changes, which occurs in later stages of disease, while molecular imaging modalities are able to detect microscopic processes and microcalcifications, which occur early in the disease process. Na[¹⁸F]-fluoride positron emission tomography/computed tomography could allow the early detection of plaque instability, which is deemed to be a primary goal in the prevention of cardiac or brain ischemic events, by quantifying the microcalcifications within vulnerable plaques and evaluating the atherosclerotic disease burden.

Rapid reduction in plaque inflammation by sonodynamic therapy inpatients with symptomatic femoropopliteal peripheral artery disease:A randomized controlled trial

BACKGROUND

Inflammation is actively involved in the clinical manifestation of peripheral artery disease (PAD). Sonodynamic therapy (SDT), a novel non-invasive, plaque-based, macrophage-targeted anti-inflammatory regimen for atherosclerosis has the potential to improve walking performance by reducing plaque inflammation.

METHODS

This phase-2, randomized, sham-controlled, double-blind clinical trial enrolled 32 participants with symptomatic femoropopliteal PAD. The primary outcome was the 30-day change in the target-to-background ratio (TBR) within the most diseased segment (MDS) of the femoropopliteal artery assessed through positron emission tomography/computed tomography (PET/CT). The secondary outcomes were changes in walking performance, limb perfusion, lesional morphology and quality of life measurements.

RESULTS

The mean age was 64.7 years and 63% were male. Thirty-one completed follow-up. SDT significantly decreased the MDS TBR by 0.53 (95% CI, -0.70 to -0.36, P < 0.001) compared with control. Furthermore, SDT increased peak walking time by 118.6 s (95% CI, 74.3 to 163.0, P < 0.001), increased ankle-brachial index by 0.11 (95% CI, 0.07 to 0.14, P < 0.001), decreased lesional diameter and area stenosis by 7.2% (95% CI, -8.6 to -4.5, P < 0.001) and 9.6% (95% CI, -24.5 to -5.3, P = 0.005), respectively, and increased the walking speed score of the Walking Impairment Questionnaire by 16.1 (95% CI, 2.6 to 29.5, P = 0.021) and the physical functioning score of the 36-item Short-Form Health Survey by 10.0 (95% CI, 5.0 to 20.0, P = 0.003) compared with control. These improvements were maintained in the SDT group up to 6-month.

CONCLUSIONS

SDT rapidly reduced plaque inflammation and improved walking performance among patients with symptomatic PAD.

TRIAL REGISTRATION

Clinical Trials NCT03457662.

Immunometabolism orchestrates training of innate immunity in atherosclerosis

Atherosclerosis is characterized by a persistent, low-grade inflammation of the arterial wall. Monocytes and monocyte-derived macrophages play a pivotal role in the various stages of atherosclerosis. In the past few years, metabolic reprogramming has been identified as an important controller of myeloid cell activation status. In addition, metabolic and epigenetic reprogramming are key regulatory mechanisms of trained immunity, which denotes the non-specific innate immune memory that can develop after brief stimulation of monocytes with microbial or non-microbial stimuli. In this review, we build the case that metabolic reprogramming of monocytes and macrophages, and trained immunity in particular, contribute to the pathophysiology of atherosclerosis. We discuss the specific metabolic adaptations, including changes in glycolysis, oxidative phosphorylation, and cholesterol metabolism, that have been reported in atherogenic milieus in vitro and in vivo. In addition, we will focus on the role of these metabolic pathways in the development of trained immunity.

18Fluorodeoxyglucose Accumulation in Arterial Tissues Determined by PET Signal Analysis

BACKGROUND

Arterial ¹⁸fluorodeoxyglucose (FDG) positron emission tomography (PET) is considered a measure of atherosclerotic plaque macrophages and is used for quantification of disease activity in clinical trials, but the distribution profile of FDG across macrophages and other arterial cells has not been fully clarified.

OBJECTIVES

The purpose of this study was to analyze FDG uptake in different arterial tissues and their contribution to PET signal in normal and atherosclerotic arteries.

METHODS

Wild-type and D374Y-PCSK9 transgenic Yucatan minipigs were fed a high-fat, high-cholesterol diet to induce atherosclerosis and subjected to a clinical FDG-PET and computed tomography scan protocol. Volumes of arterial media, intima/lesion, macrophage-rich, and hypoxic tissues were measured in serial histological sections. Distributions of FDG in macrophages and other arterial tissues were quantified using modeling of the in vivo PET signal. In separate transgenic minipigs, the intra-arterial localization of FDG was determined directly by autoradiography.

RESULTS

Arterial FDG-PET signal appearance and intensity were similar to human imaging. The modeling approach showed high accuracy in describing the FDG-PET signal and revealed comparable FDG accumulation in macrophages and other arterial tissues, including medial smooth muscle cells. These findings were verified directly by autoradiography of normal and atherosclerotic arteries.

CONCLUSIONS

FDG is taken up comparably in macrophage-rich and -poor arterial tissues in minipigs. This offers a mechanistic explanation to a growing number of observations in clinical imaging studies that have been difficult to reconcile with macrophage-selective FDG uptake.

Sex as a Biological Variable in Atherosclerosis

Atherosclerosis is a chronic inflammatory vascular disease and the predominant cause of heart attack and ischemic stroke. Despite the well-known sexual dimorphism in the incidence and complications of atherosclerosis, there are relatively limited data in the clinical and preclinical literature to rigorously address mechanisms underlying sex as a biological variable in atherosclerosis. In multiple histological and imaging studies, overall plaque burden and markers of inflammation appear to be greater in men than women and are predictive of cardiovascular events. However, while younger women are relatively protected from cardiovascular disease, by the seventh decade, the incidence of myocardial infarction in women ultimately surpasses that of men, suggesting an interaction between sex and age. Most preclinical studies in animal atherosclerosis models do not examine both sexes, and even in those that do, well-powered direct statistical comparisons for sex as an independent variable remain rare. This article reviews the available data. Overall, male animals appear to have more inflamed yet smaller plaques compared to female animals. Plaque inflammation is often used as a surrogate end point for plaque vulnerability in animals. The available data support the notion that rather than plaque size, plaque inflammation may be more relevant in assessing sex-specific mechanisms since the findings correlate with the sex difference in ischemic events and mortality and thus may be more reflective of the human condition. Overall, the number of preclinical studies directly comparing plaque inflammation between the sexes is extremely limited relative to the vast literature exploring atherosclerosis mechanisms. Failure to include both sexes and to address age in mechanistic atherosclerosis studies are missed opportunities to uncover underlying sex-specific mechanisms. Understanding the mechanisms driving sex as a biological variable in atherosclerotic disease is critical to future precision medicine strategies to mitigate what is still the leading cause of death of men and women worldwide.

Assessing the feasibility of NaF-PET/CT versus FDG-PET/CT to detect abdominal aortic calcification or inflammation in rheumatoid arthritis patients

OBJECTIVE

We aimed to determine whether NaF-PET/CT or FDG-PET/CT can detect abdominal aortic molecular calcification and inflammation in patients with rheumatoid arthritis (RA).

METHODS

In this study, 18 RA patients (4 women, 14 men; mean age 56.0 ± 11.7) and 18 healthy controls (4 women, 14 men; mean age 55.8 ± 11.9) were included. The controls were matched to patients by sex and age (± 4 years). All subjects of this study underwent NaF-PET/CT scanning 90 min following the administration of NaF. FDG-PET/CT imaging was performed 180 min following intravenous FDG injection. Using OsiriX software, the global mean standardized uptake value (global SUVmean) in abdominal aorta was calculated for both FDG and NaF. The NaF SUVmean and FDG SUVmean were divided by the blood pool activity providing target-to-background ratios (TBR) namely, NaF-TBRmean and FDG-TBRmean. The CT calcium volume score was obtained using a growing region algorithm based on Hounsfield units.

RESULTS

The average NaF-TBRmean score among RA patients was significantly greater than that of healthy controls (median 1.61; IQR 1.49-1.88 and median 1.40; IQR 1.23-1.52, P = 0.002). The average CT calcium volume score among RA patients was also significantly greater than that of healthy controls (median 1.96 cm³; IQR 0.57-5.48 and median 0.004 cm³; IQR 0.04-0.05, P < 0.001). There was no significant difference between the average FDG-TBRmean scores in the RA patients when compared to healthy controls (median 1.29; IQR 1.13-1.52 and median 1.29; IQR 1.13-1.52, respectively, P = 0.98).

CONCLUSION

Quantitative assessment with NaF-PET/CT identifies increased molecular calcification in the wall of the abdominal aorta among patients with RA as compared with healthy controls, while quantitative assessment with FDG-PET/CT did not identify a difference in aortic vessel wall FDG uptake between the RA and healthy control groups.

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.

PET Scan with Fludeoxyglucose/Computed Tomography in Low-Grade Vascular Inflammation

Fluorodeoxyglucose-PET/computed tomography combines the high sensitivity of PET with the excellent spatial resolution provided by computed tomography, making it a potentially powerful tool for capturing and quantifying early vascular diseases. Patients with chronic inflammatory states have an increased risk of cardiovascular events; there is also increased vascular fluorodeoxyglucose uptake seen compared with healthy controls. This review examines the use of fluorodeoxyglucose-PET/computed tomography in assessing low-grade vascular inflammation in chronic inflammation and then reviews fluorodeoxyglucose-PET/computed tomography as a tool in monitoring the efficacy of various treatments known to modulate cardiovascular disease.

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.

Dual-Tracer Positron-Emission Tomography for Identification of Culprit Carotid Plaques and Pathophysiology In Vivo

BACKGROUND

Inflammation and microcalcification are interrelated processes contributing to atherosclerotic plaque vulnerability. Positron-emission tomography can quantify these processes in vivo. This study investigates (1) ¹⁸F-fluorodeoxyglucose (FDG) and ¹⁸F-sodium fluoride (NaF) uptake in culprit versus nonculprit carotid atheroma, (2) spatial distributions of uptake, and (3) how macrocalcification affects this relationship.

METHODS

Individuals with acute ischemic stroke with ipsilateral carotid stenosis of ≥50% underwent FDG-positron-emission tomography and NaF-positron-emission tomography. Tracer uptake was quantified using maximum tissue-to-background ratios (TBR_max) and macrocalcification quantified using Agatston scoring.

RESULTS

In 26 individuals, median most diseased segment TBR_max (interquartile range) was higher in culprit than in nonculprit atheroma for both FDG (2.08 [0.52] versus 1.89 [0.40]; P<0.001) and NaF (2.68 [0.63] versus 2.39 [1.02]; P<0.001). However, whole vessel TBR_max was higher in culprit arteries for FDG (1.92 [0.41] versus 1.71 [0.31]; P<0.001) but not NaF (1.85 [0.28] versus 1.79 [0.60]; P=0.10). NaF uptake was concentrated at carotid bifurcations, while FDG was distributed evenly throughout arteries. Correlations between FDG and NaF TBR_max differed between bifurcations with low macrocalcification (r_s=0.38; P<0.001) versus high macrocalcification (r_s=0.59; P<0.001).

CONCLUSIONS

This is the first study to demonstrate increased uptake of both FDG and NaF in culprit carotid plaques, with discrete distributions of pathophysiology influencing vulnerability in vivo. These findings have implications for our understanding of the natural history of the disease and for the clinical assessment and management of carotid atherosclerosis.

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.

Should vascular wall 18F-FDG uptake be adjusted for the extent of atherosclerotic burden?

Vascular wall ¹⁸F-FDG uptake is often used as a surrogate marker of atherosclerotic plaque inflammation. A potential caveat is that vascular wall ¹⁸F-FDG uptake is higher simply because more atherosclerosis is present. To determine if the degree of inflammation is high or low relative to the extent of atherosclerosis, vascular wall ¹⁸F-FDG uptake may require statistical adjustment for a non-inflammatory marker reflecting the extent of atherosclerosis, e.g. calcification. Adjustments is probably needed if (1) vascular wall ¹⁸F-FDG uptake correlates sufficiently strongly with arterial calcification and (2) adjustment for extent of calcification affects determinants of vascular ¹⁸F-FDG uptake. This study addresses these questions. ¹⁸F-FDG PET/low-dose-CT scans of 99 patients were used. Cardiovascular risk factors were assessed and PET/CT scans were analysed for standardized ¹⁸F-FDG uptake values and calcification. ANOVA was used to establish the association between vascular ¹⁸F-FDG uptake and calcification. Multiple linear regression (with and without calcification as independent variable) was used to show whether determinants of vascular ¹⁸F-FDG uptake were affected by the degree of calcification. ¹⁸F-FDG uptake was related to increased calcification in the aortic arch, descending and abdominal aorta. However, ¹⁸F-FDG uptake showed considerable overlap between categories of calcification. Age and body mass index were main determinants of vascular ¹⁸F-FDG uptake. In multiple regression analyses, most standardized beta coefficients of these determinants were not affected by adjustment for the degree of calcification. Although vascular ¹⁸F-FDG uptake is related to total atherosclerotic burden, as reflected by vascular calcification, the association is weak and unlikely to affect the identification of determinants of atherosclerotic inflammation implicating no need for adjustment in future studies.

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.

Short-term discontinuation of vagal nerve stimulation alters 18F-FDG blood pool activity: an exploratory interventional study in epilepsy patients

Background

Vagus nerve activation impacts inflammation. Therefore, we hypothesized that vagal nerve stimulation (VNS) influenced arterial wall inflammation as measured by ¹⁸F-FDG uptake.

Results

Ten patients with left-sided VNS for refractory epilepsy were studied during stimulation (VNS-on) and in the hours after stimulation was switched off (VNS-off). In nine patients, ¹⁸F-FDG uptake was measured in the right carotid artery, aorta, bone marrow, spleen, and adipose tissue. Target-to-background ratios (TBRs) were calculated to normalize the respective standardized uptake values (SUVs) for venous blood pool activity. Median values are shown with interquartile range and compared using the Wilcoxon signed-rank test. Arterial SUVs tended to be higher during VNS-off than VNS-on [SUV_max all vessels 1.8 (1.5–2.2) vs. 1.7 (1.2–2.0), p = 0.051]. However, a larger difference was found for the venous blood pool at this time point, reaching statistical significance in the vena cava superior [_meanSUV_mean 1.3 (1.1–1.4) vs. 1.0 (0.8–1.1); p = 0.011], resulting in non-significant lower arterial TBRs during VNS-off than VNS-on. Differences in the remaining tissues were not significant. Insulin levels increased after VNS was switched off [55.0 pmol/L (45.9–96.8) vs. 48.1 pmol/L (36.9–61.8); p = 0.047]. The concurrent increase in glucose levels was not statistically significant [4.8 mmol/L (4.7–5.3) vs. 4.6 mmol/L (4.5–5.2); p = 0.075].

Conclusions

Short-term discontinuation of VNS did not show a consistent change in arterial wall ¹⁸F-FDG-uptake. However, VNS did alter insulin and ¹⁸F-FDG blood levels, possibly as a result of sympathetic activation.

Noninvasive Imaging Biomarkers of Vulnerable Coronary Plaques – a Clinical Update

Atherosclerosis is a slow, progressive disease, its most common manifestation and most severe consequence being coronary artery disease, one of the main causes of mortality and morbidity worldwide. The vast majority of cardiovascular deaths are caused by complications of atherosclerosis, most often being represented by the rupture of an unstable coronary plaque, regularly triggered by inflammation. A vulnerable plaque is characterized by a large, lipid-rich necrotic core, a thin fibrous cap with macrophage infiltration, and the presence of multiple specific biomarkers such as positive remodeling, irregular calcifications, and low attenuation visible with coronary computed tomography angiography (CCTA). Identifying biomarkers that could predict the risk of plaque rupture with high accuracy would be a significant advance in predicting acute cardiac events in asymptomatic patients, furthermore guiding treatment of patients with this disease. The main indication of noninvasive imaging is to identify patients at risk based on the presence or absence of symptoms that can be related to myocardial ischemia. The diagnostic objective is to confirm or to exclude the presence of coronary plaques. Coronary imaging in asymptomatic individuals is used to estimate the risk of future cardiac events through the identification of non-obstructive high-risk plaques. The possibility to monitor the evolution of vulnerable plaques via noninvasive imaging techniques, prior to the occurrence of an acute clinical event, is the main goal in plaque imaging. This manuscript will be focusing on recent advances of noninvasive imaging of vulnerable coronary plaques.

Association Between Aortic Vascular Inflammation and Coronary Artery Plaque Characteristics in Psoriasis

Importance

Inflammation is critical to atherosclerosis. Psoriasis, a chronic inflammatory disease associated with early cardiovascular events and increased aortic vascular inflammation (VI), provides a model to study the process of early atherogenesis. Fludeoxyglucose F 18 positron emission tomography/computed tomography (18F-FDG PET/CT) helps quantify aortic VI, and coronary computed tomography angiography provides coronary artery disease (CAD) assessment through evaluation of total plaque burden (TB) and noncalcified coronary plaque burden (NCB), luminal stenosis, and high-risk plaques (HRP). To our knowledge, association between aortic VI and broad CAD indices has not yet been assessed in a chronic inflammatory disease state. Such a study may provide information regarding the utility of aortic VI in capturing early CAD.

Objective

To assess the association between aortic VI and CAD indices, including TB, NCB, luminal stenosis, and HRP prevalence, in psoriasis.

Design, Setting, and Participants

In a cross-sectional cohort study at the National Institutes of Health, 215 consecutive patients with psoriasis were recruited from surrounding outpatient dermatology practices. All patients underwent 18F-FDG PET/CT for aortic VI assessment, and 190 of 215 patients underwent coronary computed tomography angiography to characterize CAD. The study was conducted between January 1, 2013, and May 31, 2017. Data were analyzed in March 2018.

Exposures

Aortic VI assessed by 18F-FDG PET/CT.

Main Outcomes and Measures

Primary outcome: TB and NCB. Secondary outcomes: luminal stenosis and HRP.

Results

Among 215 patients with psoriasis (mean [SD] age, 50.4 [12.6] years; 126 men [59%]), patients with increased aortic VI had increased TB (standardized β = 0.48; P < .001), and higher prevalence of luminal stenosis (OR, 3.63; 95% CI, 1.71-7.70; P = .001) and HRP (OR, 3.05; 95% CI, 1.42-6.47; P = .004). The aortic VI and TB association was primarily driven by NCB (β = 0.49; P < .001), whereas the aortic VI and HRP association was driven by low-attenuation plaque (OR, 5.63; 95% CI, 1.96-16.19; P = .001). All associations of aortic VI remained significant after adjustment for cardiovascular risk factors: aortic VI and TB (β = 0.23; P < .001), NCB (β = 0.24; P < .001), luminal stenosis (OR, 3.40; 95% CI, 1.40-8.24; P = .007), and HRP (OR, 2.72; 95% CI, 1.08-6.83; P = .03). No association was found between aortic VI and dense-calcified coronary plaque burden.

Conclusions and Relevance

Aortic VI is associated with broad CAD indices, suggesting that aortic VI may be a surrogate for early CAD. Larger prospective studies need to assess these associations longitudinally and examine treatment effects on these outcomes.

Imaging of atherosclerosis, targeting LFA-1 on inflammatory cells with 111In-DANBIRT

BACKGROUND

111In-DOTA-butylamino-NorBIRT (DANBIRT) is a novel radioligand which binds to Leukocyte Function-associated Antigen-1 (LFA-1), expressed on inflammatory cells. This study evaluated 111In-DANBIRT for the visualization of atherosclerotic plaque inflammation in mice.

METHODS AND RESULTS

ApoE-/- mice, fed an atherogenic diet up to 20 weeks (n = 10), were imaged by SPECT/CT 3 hours post injection of 111In-DANBIRT (~ 200 pmol, ~ 40 MBq). Focal spots of 111In-DANBIRT were visible in the aortic arch of all animals, with an average Target-to-Background Ratio (TBR) of 1.7 ± 0.5. In vivo imaging results were validated by ex vivo SPECT/CT imaging, with a TBR up to 11.5 (range 2.6 to 11.5). Plaques, identified by Oil Red O lipid-staining on excised arteries, co-localized with 111In-DANBIRT uptake as determined by ex vivo autoradiography. Subsequent histological processing and in vitro autoradiography confirmed 111In-DANBIRT uptake at plaque areas containing CD68 expressing macrophages and LFA-1 expressing inflammatory cells. Ex vivo incubation of a human carotid endarterectomy specimen with 111In-DANBIRT (~ 950 nmol, ~ 190 MBq) for 2 hours showed heterogeneous plaque uptake on SPECT/CT, after which immunohistochemical analysis demonstrated co-localization of 111In-DANBIRT uptake and CD68 and LFA-1 expressing cells.

CONCLUSIONS

Our results indicate the potential of radiolabeled DANBIRT as a relevant imaging radioligand for non-invasive evaluation of atherosclerotic inflammation.

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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