Imaging atherosclerotic plaque inflammation with [18F]-fluorodeoxyglucose positron emission tomography

Clinical imaging of cardiovascular inflammation

Cardiovascular disease due to atherosclerosis is the number one cause of morbidity and mortality worldwide. In the past twenty years, compelling preclinical and clinical data have indicated that a maladaptive inflammatory response plays a crucial role in the development of atherosclerosis initiation and progression in the vasculature, all the way to the onset of life-threatening cardiovascular events. Furthermore, inflammation is key to heart and brain damage and healing after myocardial infarction or stroke. Recent evidence indicates that this interplay between the vasculature, organs target of ischemia and the immune system is mediated by the activation of hematopoietic organs (bone marrow and spleen). In this evolving landscape, non-invasive imaging is becoming more and more essential to support either mechanistic preclinical studies to investigate the role of inflammation in cardiovascular disease (CVD), or as a translational tool to quantify inflammation in the cardiovascular system and hematopoietic organs in patients. In this review paper, we will describe the clinical applications of non-invasive imaging to quantify inflammation in the vasculature, infarcted heart and brain, and hematopoietic organs in patients with cardiovascular disease, with specific focus on [18F]FDG PET and other novel inflammation-specific radiotracers. Furthermore, we will briefly describe the most recent clinical applications of other imaging techniques such as MRI, SPECT, CT, CEUS and OCT in this arena.

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.

Basic Science of PET Imaging for Inflammatory Diseases

FDG-PET/CT has recently emerged as a useful tool for the evaluation of inflammatory diseases too, in addition to that of malignant diseases. The imaging is based on active glucose utilization by inflammatory tissue. Autoradiography studies have demonstrated high FDG uptake in macrophages, granulocytes, fibroblasts, and granulation tissue. Especially, activated macrophages are responsible for the elevated FDG uptake in some types of inflammation. According to one study, after activation by lipopolysaccharide of cultured macrophages, the [¹⁴C]2DG uptake by the cells doubled, reaching the level seen in glioblastoma cells. In activated macrophages, increase in the expression of total GLUT1 and redistributions from the intracellular compartments toward the cell surface have been reported. In one rheumatoid arthritis model, following stimulation by hypoxia or TNF-α, the highest elevation of the [³H]FDG uptake was observed in the fibroblasts, followed by that in macrophages and neutrophils. As the fundamental mechanism of elevated glucose uptake in both cancer cells and inflammatory cells, activation of glucose metabolism as an adaptive response to a hypoxic environment has been reported, with transcription factor HIF-1α playing a key role. Inflammatory cells and cancer cells seem to share the same molecular mechanism of elevated glucose metabolism, lending support to the notion of usefulness of FDGPET/CT for the evaluation of inflammatory diseases, besides cancer.

Systemic atherosclerotic plaque vulnerability in patients with Coronary Artery Disease with a single Whole Body FDG PET-CT scan

OBJECTIVES

Cardiovascular disease is a leading cause of morbimortality with over half cardiovascular events occurring in the asymptomatic population by traditional risk stratification. This preliminary study aimed to evaluate systemic plaque vulnerability in patients with prior Coronary Artery Disease (CAD) with a single Whole Body [FDG] PET-CT scan in terms of plaque inflammation and calcifications.

METHODS

Twenty-two patients referred for oncological evaluation and with prior history of advanced CAD or age and gender matched controls without cardiovascular disease, underwent a Whole Body PET-CT scan 90 min after injection of 18F-FDG. A total of 975 transaxial PET images were retrospectively analysed to assess plaque inflammation using a standardized method of analysis with averaged Target-to-Background Ratios (TBRs) at different levels, in the thoracic and abdominal aorta, carotids, LAD, common iliac and femoral arteries, and were correlated with calcium scores from the CT images.

RESULTS

TBRs from the thoracic aorta were higher in male patients than controls (1.49±0.11, p<0.05) and a gradient was observed (ascending > descending > aortic arch), and were also higher in the carotids in female patients (1.43±0.07) versus controls (p<0.05). A tendency for higher levels of plaque inflammation in the abdominal aorta was noted in all groups, but no significant FDG uptake was found either in the iliac or femoral arteries in any group. Plaque inflammation was also higher in the LAD in males but with large variations. Higher levels of calcifications were noted in the LAD, infra-renal abdominal aorta and common iliac arteries, but without significant correlation with plaque inflammation except sporadic overlapping.

CONCLUSION

Patients with advanced CAD are at risk for vulnerable inflamed atheromas in other territories such as the thoracic aorta and carotid arteries, underpinning the systemic nature of the atherosclerotic disease. Coexistence with calcifications is rare, suggesting a different functional status of the plaques and different stages of the disease. Evaluation of subclinical systemic plaque vulnerability in CAD with a Whole Body [FDG] PET-CT scan is feasible and a potentially useful biomarker to assess subclinical vascular risk for risk stratification and treatment optimization, but further studies are needed.

Biomimetic nanoparticle technology for cardiovascular disease detection and treatment

Cardiovascular disease (CVD), which encompasses a number of conditions that can affect the heart and blood vessels, presents a major challenge for modern-day healthcare. Nearly one in three people has some form of CVD, with many suffering from multiple or intertwined conditions that can ultimately lead to traumatic events such as a heart attack or stroke. While the knowledge obtained in the past century regarding the cardiovascular system has paved the way for the development of life-prolonging drugs and treatment modalities, CVD remains one of the leading causes of death in developed countries. More recently, researchers have explored the application of nanotechnology to improve upon current clinical paradigms for the management of CVD. Nanoscale delivery systems have many advantages, including the ability to target diseased sites, improve drug bioavailability, and carry various functional payloads. In this review, we cover the different ways in which nanoparticle technology can be applied towards CVD diagnostics and treatments. The development of novel biomimetic platforms with enhanced functionalities is discussed in detail.

Antithrombotic Therapy in Carotid Artery Disease

The management of asymptomatic atherosclerotic carotid artery disease and the role of antithrombotic therapy is of increasing importance for stroke prevention. Non-invasive imaging of carotid plaques can identify high-risk plaque features that are associated with the risk of plaque rupture. Carotid plaque necrosis, hemorrhage, fibrous cap thinning, and the presence of foam cells have all been correlated with the risk of rupture and onset of neurological symptoms in patients with carotid stenosis. Antiplatelets are currently recommended for patients with a history of ischemic stroke and/or significant carotid artery stenosis, with aspirin and clopidogrel being the most widely used and studied agents. The role of dual antiplatelet therapy remains controversial. Moreover, there is scarce evidence on the role of newer anticoagulant agents in stable patients with carotid artery stenosis. In this review article, we discuss the pathophysiology of carotid atherosclerosis, the use of non-invasive imaging for detecting the vulnerable carotid plaque and summarize the existing clinical evidence on the use of antiplatelet and antithrombotic agents in carotid artery disease.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

18F-Sodium Fluoride Positron Emission Tomography/Computed Tomography in Ex Vivo Human Coronary Arteries With Histological Correlation

OBJECTIVE

¹⁸F-sodium fluoride (NaF) position emission tomography (PET) activity correlates with high-risk plaque. We examined the correlation between ¹⁸F-NaF PET activity and extent of calcification (microcalcification and macrocalcification) in coronary arteries. Approach and Results: Eighteen ex vivo human coronary arteries were imaged with ¹⁸F-NaF PET/CT, and target to background ratios were analyzed from 101 plaques. Histopathologic analysis evaluated for microcalcification and macrocalcification, plaque morphology, and inflammation. Plaques with microcalcification demonstrated higher ¹⁸F-NaF PET activity (n=84; mean target to background ratio±SD, 9.0±9.7,) than plaques without microcalcification (n=17, 2.9±3.8; P<0.0001). Higher ¹⁸F-NaF PET activity was associated with advanced plaques characterized by fibroatheroma (n=54, 10.7±10.3) compared with plaques with intimal thickening (n=22, 3.5±3.9) or pathological intimal thickening (n=25, 6.1±8.4; P=0.004). No significant association was found between ¹⁸F-NaF PET activity and inflammation (P=0.08).

CONCLUSIONS

In ex vivo human coronary arteries, higher ¹⁸F-NaF PET activity was associated with microcalcification and advanced plaque morphology. Since microcalcification and fibroatheromas are high-risk plaque features, ¹⁸F-NaF PET/CT may improve risk-stratification.

Nanoparticle-Aided Characterization of Arterial Endothelial Architecture during Atherosclerosis Progression and Metabolic Therapy

Atherosclerosis is associated with a compromised endothelial barrier, facilitating the accumulation of immune cells and macromolecules in atherosclerotic lesions. In this study, we investigate endothelial barrier integrity and the enhanced permeability and retention (EPR) effect during atherosclerosis progression and therapy in Apoe-/- mice using hyaluronan nanoparticles (HA-NPs). Utilizing ultrastructural and en face plaque imaging, we uncover a significantly decreased junction continuity in the atherosclerotic plaque-covering endothelium compared to the normal vessel wall, indicative of disrupted endothelial barrier. Intriguingly, the plaque advancement had a positive effect on junction stabilization, which correlated with a 3-fold lower accumulation of in vivo administrated HA-NPs in advanced plaques compared to early counterparts. Furthermore, by using super-resolution and correlative light and electron microscopy, we trace nanoparticles in the plaque microenvironment. We find nanoparticle-enriched endothelial junctions, containing 75% of detected HA-NPs, and a high HA-NP accumulation in the endothelium-underlying extracellular matrix, which suggest an endothelial junctional traffic of HA-NPs to the plague. Finally, we probe the EPR effect by HA-NPs in the context of metabolic therapy with a glycolysis inhibitor, 3PO, proposed as a vascular normalizing strategy. The observed trend of attenuated HA-NP uptake in aortas of 3PO-treated mice coincides with the endothelial silencing activity of 3PO, demonstrated in vitro. Interestingly, the therapy also reduced the plaque inflammatory burden, while activating macrophage metabolism. Our findings shed light on natural limitations of nanoparticle accumulation in atherosclerotic plaques and provide mechanistic insight into nanoparticle trafficking across the atherosclerotic endothelium. Furthermore, our data contribute to the rising field of endothelial barrier modulation in atherosclerosis.

Application of Non-invasive Imaging in Inflammatory Disease Conditions to Evaluate Subclinical Coronary Artery Disease

PURPOSE OF REVIEW

Traditional risk models, such as the Framingham risk score, fail to capture the increased cardiovascular disease risk seen in patients with chronic inflammatory diseases. This review will cover imaging modalities and their emerging applications in assessing subclinical cardiovascular disease for both research and clinical care in patients with chronic inflammatory diseases.

RECENT FINDINGS

Multiple imaging modalities have been studied to assess for subclinical cardiovascular disease via functional/physiologic, inflammatory, and anatomic assessment in patients with chronic inflammatory diseases. The use of imaging to evaluate subclinical cardiovascular disease in patients with chronic inflammatory diseases has the potential to capture early sub-clinical atherosclerosis, to improve risk stratification of future cardiovascular events, and to guide effective disease management.

Disease Activity in Mitral Annular Calcification

BACKGROUND

Mitral annular calcification (MAC) is associated with cardiovascular events and mitral valve dysfunction. However, the underlying pathophysiology remains incompletely understood. In this prospective longitudinal study, we used a multimodality approach including positron emission tomography, computed tomography, and echocardiography to investigate the pathophysiology of MAC and assess factors associated with disease activity and progression.

METHODS

A total of 104 patients (age 72±8 years, 30% women) with calcific aortic valve disease, therefore predisposed to MAC, underwent ¹⁸F-sodium fluoride (calcification activity) and ¹⁸F-Fluorodeoxyglucose (inflammation activity) positron emission tomography, computed tomography calcium scoring, and echocardiography. Sixty patients underwent repeat computed tomography and echocardiography after 2 years.

RESULTS

MAC (mitral annular calcium score >0) was present in 35 (33.7%) patients who had increased ¹⁸F-fluoride (tissue-to-background ratio, 2.32 [95% CI, 1.81-3.27] versus 1.30 [1.22-1.49]; P<0.001) and ¹⁸F-Fluorodeoxyglucose activity (tissue-to-background ratio, 1.44 [1.37-1.58] versus 1.17 [1.12-1.24]; P<0.001) compared with patients without MAC. MAC activity (¹⁸F-fluoride uptake) was closely associated with the local calcium score and ¹⁸F-Fluorodeoxyglucose uptake, as well as female sex and renal function. Similarly, MAC progression was closely associated with local factors, in particular, baseline MAC. Traditional cardiovascular risk factors and calcification activity in bone or remote atherosclerotic areas were not associated with disease activity nor progression.

CONCLUSIONS

MAC is characterized by increased local calcification activity and inflammation. Baseline MAC burden was associated with disease activity and the rate of subsequent progression. This suggests a self-perpetuating cycle of calcification and inflammation that may be the target of future therapeutic interventions.

Frontiers in positron emission tomography imaging of the vulnerable atherosclerotic plaque

Rupture of vulnerable atherosclerotic plaques leading to an atherothrombotic event is the primary driver of myocardial infarction and stroke. The ability to detect non-invasively the presence and evolution of vulnerable plaques could have a huge impact on the future identification and management of atherosclerotic cardiovascular disease. Positron emission tomography (PET) imaging with an appropriate radiotracer has the potential to achieve this goal. This review will discuss the biological hallmarks of plaque vulnerability before going on to evaluate and to present PET imaging approaches which target these processes. The focus of this review will be on techniques beyond [18F]FDG imaging, some of which are clinically advanced, and others which are on the horizon. As inflammation is the primary driving force behind atherosclerotic plaque development, we will predominantly focus on approaches which either directly, or indirectly, target this process.

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.

Feasibility of Assessing Inflammation in Asymptomatic Abdominal Aortic Aneurysms With Integrated 18F-Fluorodeoxyglucose Positron Emission Tomography/Magnetic Resonance Imaging

OBJECTIVE

This study aimed to evaluate the feasibility of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) combined with contrast enhanced magnetic resonance imaging (MRI) to identify inflammation in asymptomatic abdominal aortic aneurysms (AAA).

METHODS

FDG PET/MRI was performed on 15 patients with asymptomatic infrarenal AAAs >45 mm diameter. Prevalence of FDG uptake and MRI findings of inflammatory changes (oedema, wall thickening, and late gadolinium enhancement [LGE]) in the aortic wall were investigated at three levels: suprarenal aorta; non-aneurysmal aortic neck; and AAA.

RESULTS

The median diameter of the AAAs was 54 mm (range 47-65 mm) and the median expansion rate in the last 12 months was 3 mm (range 1-13 mm). The standard uptake value (SUV) of FDG in the aneurysmal wall (SUVmax 2.5) was higher than the blood pool (SUVmax 1.0; p < .001). The maximum target to background ratio was higher in the suprarenal aorta (mean ± SD; 3.1 ± 0.6) and aortic neck (2.7 ± 0.5) than in the aneurysmal aorta (2.5 ± 0.5; p < .001). Thirty-six FDG hotspots were observed in the aneurysmal wall of 13 patients. Wall thickening and LGE were identified in eight patients. The number of FDG hotspots correlated with recent AAA growth (r = 0.62, p = .01). The recent aneurysm expansion rate was higher in aneurysms with LGE than in those without (7 mm vs. 2 mm; p = .03). MRI inflammatory changes were observed in nine of 36 hot spots (25%) and in three of 13 patients with focal FDG uptake.

CONCLUSION

Fully integrated FDG PET/MRI can be used to study inflammation in asymptomatic AAAs. Heterogenous uptake of FDG in the aneurysmal wall indicates increased glucose metabolism, suggesting an ongoing inflammation. However, these FDG hotspots rarely correspond to MRI findings of inflammation, raising the question of which type of cellular activity is present in these areas. The presence of LGE and FDG hotspots both correlated to recent aneurysm growth, and their usefulness as clinical markers of aneurysm growth warrant additional investigation.

Triple-gated motion and blood pool clearance corrections improve reproducibility of coronary 18F-NaF PET

PURPOSE

To improve the test-retest reproducibility of coronary plaque 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) uptake measurements.

METHODS

We recruited 20 patients with coronary artery disease who underwent repeated hybrid PET/CT angiography (CTA) imaging within 3 weeks. All patients had 30-min PET acquisition and CTA during a single imaging session. Five PET image-sets with progressive motion correction were reconstructed: (i) a static dataset (no-MC), (ii) end-diastolic PET (standard), (iii) cardiac motion corrected (MC), (iv) combined cardiac and gross patient motion corrected (2 × MC) and, (v) cardiorespiratory and gross patient motion corrected (3 × MC). In addition to motion correction, all datasets were corrected for variations in the background activities which are introduced by variations in the injection-to-scan delays (background blood pool clearance correction, BC). Test-retest reproducibility of PET target-to-background ratio (TBR) was assessed by Bland-Altman analysis and coefficient of reproducibility.

RESULTS

A total of 47 unique coronary lesions were identified on CTA. Motion correction in combination with BC improved the PET TBR test-retest reproducibility for all lesions (coefficient of reproducibility: standard = 0.437, no-MC = 0.345 (27% improvement), standard + BC = 0.365 (20% improvement), no-MC + BC = 0.341 (27% improvement), MC + BC = 0.288 (52% improvement), 2 × MC + BC = 0.278 (57% improvement) and 3 × C + BC = 0.254 (72% improvement), all p < 0.001). Importantly, in a sub-analysis of 18F-NaF-avid lesions with gross patient motion > 10 mm following corrections, reproducibility was improved by 133% (coefficient of reproducibility: standard = 0.745, 3 × MC = 0.320).

CONCLUSION

Joint corrections for cardiac, respiratory, and gross patient motion in combination with background blood pool corrections markedly improve test-retest reproducibility of coronary 18F-NaF PET.

Association between carotid 18F-NaF and 18F-FDG uptake on PET/CT with ischemic vascular brain disease on MRI in patients with carotid artery disease

OBJECTIVE

Atherosclerosis is a dynamic and complex process characterized by the formation and progression of plaque mediated by various pathophysiologic steps including inflammation and calcification. The present study aimed to evaluate the association between carotid ¹⁸F-sodium fluoride (NaF) and ¹⁸F-fluorodeoxyglucose (FDG) uptake with the severity of ischemic vascular brain disease on MRI in patients with carotid artery disease.

METHODS

A total of 28 patients who were scheduled to undergo clinically indicated carotid endarterectomy or stenting for carotid artery disease were examined with ¹⁸F-NaF and ¹⁸F-FDG PET/CT and brain MRI. The PET/CT images were evaluated by qualitative and semiquantitative analyses. The maximum standardized uptake value (SUV) for the plaque and the average of mean SUV within the lumen of both internal jugular veins was calculated, and the target-to-blood pool ratio (TBR) was determined. The ischemic vascular brain disease on MRI was graded separately in the bilateral hemisphere as 0, 1, 2, and 3, with 0 being absent and 3 being the most severe.

RESULTS

In two patients, only a unilateral carotid artery was analyzed because of previous indwelling stent. ¹⁸F-NaF focal uptake was observed in 50 carotid arteries. ¹⁸F-FDG focal uptake was observed in 47 carotid arteries. The mean (± SD) ¹⁸F-NaF TBR (2.93 ± 0.89) was significantly higher than the mean (± SD) ¹⁸F-FDG TBR (2.41 ± 0.84) (p < 0.001). The mean (± SD) values of ¹⁸F-NaF TBR were 2.63 ± 0.76 in grade 1, 2.90 ± 0.91 in grade 2, and 3.81 ± 0.60 in grade 3. Significant differences in ¹⁸F-NaF TBR were observed between grades 1 and 3 (p < 0.001) and grades 2 and 3 (p = 0.02). The mean (± SD) values of ¹⁸F-FDG TBR were 2.35 ± 0.77 in grade 1, 2.23 ± 0.48 in grade 2, and 2.87 ± 1.32 in grade 3. No significant differences in ¹⁸F-FDG TBR were noted between any of the ischemic vascular brain disease grades.

CONCLUSIONS

These preliminary results suggest that carotid ¹⁸F-NaF uptake in patients with carotid artery disease may be associated with the severity of the ischemic vascular brain disease observed on MRI.

Monocyte and Macrophage Dynamics in the Cardiovascular System: JACC Macrophage in CVD Series (Part 3)

It has long been recognized that the bone marrow is the primary site of origin for circulating monocytes that may later become macrophages in atherosclerotic lesions. However, only in recent times has the complex relationship among the bone marrow, monocytes/macrophages, and atherosclerotic plaques begun to be understood. Moreover, the systemic nature of these interactions, which also involves additional compartments such as extramedullary hematopoietic sites (i.e., spleen), is only just becoming apparent. In parallel, progressive advances in imaging and cell labeling techniques have opened new opportunities for in vivo imaging of monocyte/macrophage trafficking in atherosclerotic lesions and at the systemic level. In this Part 3 of a 4-part review series covering the macrophage in cardiovascular disease, the authors intersect systemic biology with advanced imaging techniques to explore monocyte and macrophage dynamics in the cardiovascular system, with an emphasis on how events at the systemic level might affect local atherosclerotic plaque biology.

PET/MRI in large-vessel vasculitis: clinical value for diagnosis and assessment of disease activity

Diagnosis of large vessel vasculitis (LVV) and evaluation of its inflammatory activity can be challenging. Our aim was to investigate the value of hybrid positron-emission tomography/magnetic resonance imaging (PET/MRI) in LVV. All consecutive patients with LVV from the Department of Internal Medicine who underwent PET/MRI were included. Three PET/MRI patterns were defined: (i) "inflammatory," with positive PET (>liver uptake) and abnormal MRI (stenosis and/or wall thickening); (ii) "fibrous", negative PET (≤liver uptake) and abnormal MRI; and (iii) "normal". Thirteen patients (10 female; median age: 67-years [range: 23-87]) underwent 18 PET/MRI scans. PET/MRI was performed at diagnosis (n = 4), at relapse (n = 7), or during remission (n = 7). Among the 18 scans, eight (44%) showed an inflammatory pattern and three (17%) a fibrous pattern; the other seven were normal. The distribution of the three patterns did not differ between patients with Takayasu arteritis (TA, n = 10 scans) and those with giant cell arteritis (GCA, n = 8 scans). PET/MRI findings were normal in 2/10 (20%) TA scans vs. 5/8 (62%) GCA scans (p = 0.3). Median SUVmax was 4.7 [2.1-8.6] vs. 2 [1.8-2.6] in patients with active disease vs. remission, respectively (p = 0.003). PET/MRI is a new hybrid imaging modality allowing comprehensive and multimodal analysis of vascular wall inflammation and the vascular lumen. This technique offers promising perspectives for the diagnosis and monitoring of LVV.

Screening for Atherosclerotic Cardiovascular Disease in Patients With Type 2 Diabetes Mellitus: Controversies and Guidelines

If a disease state is highly prevalent and its consequences are severe, it may be appropriate to seek methods to identify it early to forestall its development and complications. Diabetes mellitus is a proven risk factor for the development of atherosclerosis, although its face and outcome are changing, as shown in contemporary clinical trials. In fact, decompensated heart failure seems to drive the hospitalization rate in patients with diabetes, and mortality from heart failure is reduced with modern hypoglycemic treatments. Nonetheless, atherosclerotic complications continue to be a major health concern in this segment of the population and cardiovascular imaging has been employed in an attempt to achieve a more accurate risk stratification. Although imaging for detection of obstructive coronary artery disease failed to reach such a goal, imaging for preclinical atherosclerosis may be more successful. In this review, we discuss the use of computed tomography and positron emission tomography to detect preclinical coronary atherosclerosis in asymptomatic patients with diabetes. Despite recent advances in the field, several questions remain to be answered as to the ultimate benefit of imaging for prevention in diabetes mellitus.

Development, synthesis, and 68Ga-Labeling of a Lipophilic complexing agent for atherosclerosis PET imaging

Cardiovascular disease is the leading cause of mortality and morbidity worldwide. Atherosclerosis accounts for 50% of deaths in western countries. This multifactorial pathology is characterized by the accumulation of lipids and inflammatory cells within the vascular wall, leading to plaque formation. We describe herein the synthesis of a PCTA-based ⁶⁸Ga³⁺ chelator coupled to a phospholipid biovector 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), which is the main constituent of the phospholipid moiety of High-Density Lipoprotein (HDL) phospholipid moiety. The resulting ⁶⁸Ga-PCTA-DSPE inserted into HDL particles was compared to ¹⁸F-FDG as a PET agent to visualize atherosclerotic plaques. Our agent markedly accumulated within mouse atheromatous aortas and more interestingly in human endarterectomy carotid samples. These results support the potential use of ⁶⁸Ga-PCTA-DSPE-HDL for atherosclerosis PET imaging.

Association of aortic vascular uptake of 18FDG by PET/CT and aortic wall thickness by MRI in psoriasis: a prospective observational study

BACKGROUND

The contribution of inflammation to the incidence of cardiovascular disease (CVD) has been increasingly recognized in recent years. We investigated the relationship of aortic vascular uptake of 18F-FDG by PET/CT and aortic wall thickness (AWT) by MRI in psoriasis, a chronic inflammatory disease with increased incidence of CVD. One hundred sixty-five patients with plaque psoriasis participated in an ongoing longitudinal cohort study. Subclinical atherosclerosis was assessed as aortic uptake of 18F-FDG by PET/CT reported as target-to-background ratio (TBR) and AWT by MRI reported as maximal thickness.

RESULTS

Patients with psoriasis were middle aged, predominantly male, and had mild CV risk by traditional risk factors. Psoriasis severity as measured by PASI score was a notable determinant of AWT (ρ = 0.20, p = 0.01). Moreover, aortic vascular uptake of 18F-FDG associated with AWT by MRI at baseline in unadjusted analysis (β = 0.27 p = 0.001) and following adjustment for traditional cardiovascular risk factors, waist-to-hip ratio, and statin use (β = 0.21 p = 0.01). Finally, following 1 year of psoriasis treatment, a decrease in aortic vascular uptake of 18F-FDG was associated with a reduction in AWT in fully adjusted models (β = 0.33, p = 0.02).

CONCLUSION

In conclusion, we demonstrate that psoriasis severity and aortic vascular uptake of 18F-FDG in the aorta were associated with AWT. Following treatment of psoriasis, a decrease in aortic vascular uptake of 18F-FDG was associated with a reduction in AWT at 1 year. These findings suggest that aortic vascular uptake of 18F-FDG is associated with early evidence of vascular disease assessed by aortic wall thickness. Prospective studies in larger populations including other inflammatory diseases are warranted.

Development of an inflammation imaging tracer, 111In-DOTA-DAPTA, targeting chemokine receptor CCR5 and preliminary evaluation in an ApoE-/- atherosclerosis mouse model

BACKGROUND

Chemokine receptor 5 (CCR5) plays an important role in atherosclerosis. Our objective was to develop a SPECT tracer targeting CCR5 for imaging plaque inflammation by radiolabeling D-Ala-peptide T-amide (DAPTA), a CCR5 antagonist, with 111In.

METHODS

1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) conjugated DAPTA (DOTA-DAPTA) was labeled with 111In. Cell uptake studies were conducted in U87-CD4-CCR5 and U87-MG cells. Biodistribution was determined in C57BL/6 mice. Autoradiography, en face and Oil Red O (ORO) imaging studies were performed in ApoE-/- mice.

RESULTS

DOTA-DAPTA was radiolabeled with 111In with high radiochemical purity (> 98%) and specific activity (70 MBq·nmol). 111In-DOTA-DAPTA exhibited fast blood and renal clearance and high spleen uptake. The U87-CD4-CCR5 cells had significantly higher uptake in comparison to the U87-MG cells. The cell uptake was reduced by three times with DAPTA, indicating the receptor specificity of the uptake. Autoradiographic images showed significantly higher lesion uptake of 111In-DOTA-DAPTA in ApoE-/- mice than that in C57BL/6 mice. The tracer uptake in 4 month old ApoE-/- high fat diet (HFD) mice with blocking agent was twofold lower than the same mice without the blocking agent, demonstrating the specificity of the tracer for the CCR5 receptor.

CONCLUSION

111In-DOTA-DAPTA, specifically targeting chemokine receptor CCR5, is a potential SPECT agent for imaging inflammation in atherosclerosis.

Psoas muscle fluorine-18-labelled fluoro-2-deoxy-d-glucose uptake associated with the incidence of existing and incipient metabolic derangement

BACKGROUND

Skeletal muscle glucose utilization is an important component of whole-body glucose consumption in normal humans. Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) is a non-invasive molecular imaging probe for evaluating tissue glucose utilization. It remains unclear whether or not ¹⁸ F-FDG uptake by skeletal muscle has utility as a biomarker for metabolic derangement. We investigated the utility of measurement of muscle ¹⁸ F-FDG positron emission tomography/computed tomography uptake as a surrogate marker for existing and incipient metabolic abnormalities.

METHODS

Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) uptakes of insulin-sensitive organs (liver, pancreas, mesenteric visceral fat, psoas muscle, and abdominal subcutaneous fat) and their association with metabolic abnormalities were evaluated in an experimental group comprising 91 men and 66 women (mean age 49.9 ± 11.1 years). In this cross-sectional cohort, we assessed the predictive power of the optimal cut-off ¹⁸ F-FDG uptake [maximum standardized uptake value (SUV_max )]. We confirmed its feasibility and reliability for diagnosis of existing and incipient metabolic derangement in the validation group (longitudinal cohort comprising 91 men and 67 women; mean age 52.6 ± 7.9 years).

RESULTS

Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) uptake (SUV_max ) of psoas muscle was strongly correlated with clinical metabolic parameters in the experimental group. It was positively correlated with waist circumference, body mass index, fasting glucose, triglyceride, systolic and diastolic pressure, and negatively correlated with high-density lipoprotein cholesterol levels (for all, P < 0.05). SUV_max of the psoas muscle also showed the best area under the curve value (0.779) as a predictor of metabolic syndrome (MetS) in the experimental group. Using the optimal cut-off SUV_max of 1.34, the sensitivity, specificity, accuracy, positive, and negative predictive value for predicting existing MetS in the experimental group were 70.0%, 84.6%, 80.9%, 60.9%, and 89.2%, respectively. In the validation group, corresponding values were 47.6%, 92.3%, 86.1%, 50.0%, and 91.6%, respectively. Existing and incipient MetS were significantly higher in subjects with high ¹⁸ F-FDG uptake by the psoas muscle (SUV_max  > 1.34). Subjects with higher psoas muscle SUV_max had a 3.3-fold increased risk of developing MetS (P = 0.017).

CONCLUSIONS

Fluorine-18-labelled fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) uptake of psoas muscle is a promising surrogate marker for existing and incipient metabolic derangement.

Molecular Coronary Plaque Imaging Using 18F-Fluoride

BACKGROUND

Coronary 18F-fluoride positron emission tomography identifies ruptured and high-risk atherosclerotic plaque. The optimal method to identify, to quantify, and to categorize increased coronary 18F-fluoride uptake and determine its reproducibility has yet to be established. This study aimed to optimize the identification, quantification, categorization, and scan-rescan reproducibility of increased 18F-fluoride activity in coronary atherosclerotic plaque.

METHODS

In a prospective observational study, patients with multi-vessel coronary artery disease underwent serial 18F-fluoride positron emission tomography. Coronary 18F-fluoride activity was visually assessed, quantified, and categorized with reference to maximal tissue to background ratios. Levels of agreement for both visual and quantitative methods were determined between scans and observers.

RESULTS

Thirty patients (90% male, 20 patients with stable coronary artery disease, and 10 with recent type 1 myocardial infarction) underwent paired serial positron emission tomography-coronary computed tomography angiography imaging within an interval of 12±5 days. A mean of 3.7±1.8 18F-fluoride positive plaques per patient was identified after recent acute coronary syndrome, compared with 2.4±2.3 positive plaques per patient in stable coronary artery disease. The bias in agreement in maximum tissue to background ratio measurements in visually positive plaques was low between observers (mean difference, -0.01; 95% limits of agreement, -0.32 to 0.30) or between scans (mean difference, 0.06; 95% limits of agreement, -0.49 to 0.61). Good agreement in the categorization of focal 18F-fluoride uptake was achieved using visual assessment alone (κ=0.66) and further improved at higher maximum tissue to background ratio values.

CONCLUSIONS

Coronary 18F-fluoride activity is a precise and reproducible metric in the coronary vasculature. The analytical performance of 18F-fluoride is sufficient to assess the prognostic utility of this radiotracer as a noninvasive imaging biomarker of plaque vulnerability.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifiers: NCT02110303 and NCT02278211.

Imaging acquisition technique influences interpretation of positron emission tomography vascular activity in large-vessel vasculitis

OBJECTIVES

To determine the impact of imaging acquisition time on interpretation of disease activity on ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) in large-vessel vasculitis (LVV) and assess the relationship between clinical features and image acquisition time.

METHODS

Patients with giant cell arteritis (GCA) and Takayasu's arteritis (TAK) were recruited into a prospective, observational cohort. After a single injection of FDG, all patients underwent two sequential PET scans at one and two-hour time points. Images were interpreted for active vasculitis by subjective assessment, qualitative assessment, and semi-quantitative assessment. Agreement was assessed by percent agreement, Cohen's kappa, and McNemar's test. Multivariable logistic regression identified associations between PET activity and clinical variables.

RESULTS

79 patients (GCA  =  44, TAK  =  35) contributed 168 paired one and two-hour PET studies. A total of 94 out of 168 scans (56%) were interpreted as active at the one-hour time point, and 129 scans (77%) were interpreted as active at the two-hour time point (p < 0.01). Associations between clinical variables and PET activity categories (dual inactive, delayed active, dual active) were evaluated. Using multivariable nominal regression, clinically active disease was significantly more common in patients in the delayed active group (Odds Ratio 1.94, 95%CI 1.13-3.53; p  =  0.02) and the dual active group (Odds Ratio 1.71, 95%CI 1.06-2.93; p  =  0.04) compared to the dual inactive group.

CONCLUSIONS

Imaging protocol significantly influences interpretation of PET activity in LVV. A substantial proportion of patients with LVV have PET activity only detected by delayed imaging. These patients were significantly more likely to have concomitant clinically-determined active disease.

Anti-inflammatory effect of statin is continuously working throughout use: a prospective three time point 18F-FDG PET/CT imaging study

No data exist whether statins have robust anti-inflammatory effects of atherosclerotic plaques primarily during the early treatment period or continuously throughout use. This prospective three time point ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) study of the carotid artery assessed anti-inflammatory effects of statin during the early treatment period (initiation to 3 months) and late treatment period (3 months to 1 year) and their correlation with lipid and inflammatory profile changes during a year of therapy. Nine statin-naïve stable angina patients with inflammatory carotid plaques received 20 mg/day atorvastatin after undergoing initial ¹⁸F-FDG PET/CT scanning of carotid arteries and ascending thoracic aorta, and then completed serial ¹⁸F-FDG PET/CT imaging at 3 and 12 months whose data were analyzed. The primary outcome was the inter-scan percent change in target-to-background ratio (ΔTBR) within the index vessel. At 3 months of atorvastatin treatment, mean serum low-density lipoprotein cholesterol (LDL-C) level decreased by 36.4% to < 70 mg/dL (p = 0.001) and mean serum high-density lipoprotein cholesterol level increased to > 40 mg/dL (p = 0.041), with both maintained with no further reduction up to 1 year (p = 0.516 and 0.715, respectively) while mean serum high sensitivity C-reactive protein level only numerically decreased (p = 0.093). The index vessel ΔTBR showed continuous plaque inflammation reduction over 1 year, by 4.4% (p = 0.015) from the initiation to 3rd months and 6.2% (p = 0.009) from 3rd months to 1 year, respectively, without correlation with lipid profile changes. The ΔTBR of the bilateral carotid arteries and ascending aorta also continuously decreased from 3 months to 1 year. Three time point ¹⁸F-FDG PET/CT imaging demonstrates that statin's anti-inflammatory effect continues throughout its use up to 1 year, even though yielding stable below-target plasma LDL-C levels at 3 months.

The clinical utility of hybrid imaging for the identification of vulnerable plaque and vulnerable patients

Despite decades of research and major innovations in technology, cardiovascular disease remains the leading cause of death globally. Our understanding of major cardiovascular events and their prevention is centred around the atherosclerotic plaque and the processes that ultimately lead to acute plaque rupture. Recent advances in hybrid imaging technology allow the combination of high spatial resolution and anatomical detail with molecular assessments of disease activity. This provides the ability to identify vulnerable plaque characteristics and differentiate active and quiescent disease, with the potential to improve patient risk stratification. Combined positron emission tomography and computed tomography is the prototypical non-invasive hybrid imaging technique for coronary artery plaque assessment. In this review we discuss the current state of play in the field of hybrid coronary atherosclerosis imaging.

CCR2 expression on circulating monocytes is associated with arterial wall inflammation assessed by 18F-FDG PET/CT in patients at risk for cardiovascular disease

Aims

Circulating monocytes infiltrate the plaque and differentiate into macrophages, contributing to an inflammatory environment which is associated with higher risk of cardiovascular events. Although the pivotal role of circulating monocytes in plaque inflammation has been firmly established, the search continues to identify specific monocyte subsets that may be especially atherogenic. Therefore, we evaluated the relation between monocyte phenotype, particularly surface receptor expression, and arterial wall inflammation in patients at increased cardiovascular risk.

Methods and results

We performed a multivariate linear regression analysis in 79 patients at increased cardiovascular risk who had both an 18F-fluorodeoxyglucose positron emission tomography/computed tomography to assess arterial wall inflammation and extensive monocyte characterization (using flow cytometry). We found that CCR2, a monocyte chemokine receptor essential for transmigration, significantly correlates with arterial wall inflammation. This relationship was independent of traditional cardiovascular risk factors and statin use (β = 0.429, P = 0.015). We found no relation between arterial wall inflammation and monocyte count or monocyte subsets, namely CD14+CD16-, CD14+CD16+, CD14+CD16 ++, CCR5+, CD18+, CD11b+, or CD11c+ monocytes.

Conclusion

Monocyte CCR2 expression is associated with arterial wall inflammation in patients at increased cardiovascular risk. Our data warrant further studies to assess if inhibition of CCR2 may attenuate atherosclerotic plaque inflammation.

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.

Visual Overview—

An online visual overview is available for this article.

Carotid Plaque Inflammation Imaged by 18F-Fluorodeoxyglucose Positron Emission Tomography and Risk of Early Recurrent Stroke

Background and Purpose- Plaque inflammation contributes to stroke and coronary events. ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) identifies plaque inflammation-related metabolism. Almost no prospective data exist on the relationship of carotid ¹⁸F-FDG uptake and early recurrent stroke. Methods- We did a multicenter prospective cohort study BIOVASC (Biomarkers/Imaging Vulnerable Atherosclerosis in Symptomatic Carotid disease) of patients with carotid stenosis and recent stroke/transient ischemic attack with 90-day follow-up. On coregistered carotid ¹⁸F-FDG PET/computed tomography angiography, ¹⁸F-FDG uptake was expressed as maximum standardized uptake value (SUV_max) in the axial single hottest slice. We then conducted a systematic review of similar studies and pooled unpublished individual-patient data with 2 highly similar independent studies (Dublin and Barcelona). We analyzed the association of SUV_max with all recurrent nonprocedural stroke (before and after PET) and with recurrent stroke after PET only. Results- In BIOVASC (n=109, 14 recurrent strokes), after adjustment (for age, sex, stenosis severity, antiplatelets, statins, diabetes mellitus, hypertension, and smoking), the hazard ratio for recurrent stroke per 1 g/mL SUV_max was 2.2 (CI, 1.1-4.5; P=0.025). Findings were consistent in the independent Dublin (n=52, hazard ratio, 2.2; CI, 1.1-4.3) and Barcelona studies (n=35, hazard ratio, 2.8; CI, 0.98-5.5). In the pooled cohort (n=196), 37 recurrent strokes occurred (29 before and 8 after PET). Plaque SUV_max was higher in patients with all recurrence ( P<0.0001) and post-PET recurrence ( P=0.009). The fully adjusted hazard ratio of any recurrent stroke was 2.19 (CI, 1.41-3.39; P<0.001) and for post-PET recurrent stroke was 4.57 (CI, 1.5-13.96; P=0.008). Recurrent stroke risk increased across SUV_max quartiles (log-rank P=0.003). The area under receiver operating curve for all recurrence was 0.70 (CI, 0.59-0.78) and for post-PET recurrence was 0.80 (CI, 0.64-0.96). Conclusions- Plaque inflammation-related ¹⁸F-FDG uptake independently predicted future recurrent stroke post-PET. Although further studies are needed, ¹⁸F-FDG PET may improve patient selection for carotid revascularization and suggest that anti-inflammatory agents may have benefit for poststroke vascular prevention.

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.

Three-dimensional fat-saturated T1-weighted Cartesian volumetric interpolated breath-hold examination (VIBE) for the diagnosis of aortitis in patients with suspected large vessel vasculitis: a comparative study with 18F-FDG PET applying fully integrated PET/MRI

AIM

To evaluate the feasibility of T1-weighted (T1W) three-dimensional (3D) fat saturated Cartesian volumetric interpolated breath-hold examination (VIBE) magnetic resonance imaging (MRI) sequence for the diagnosis of aortitis in patients with suspected large vessel vasculitis (LVV) applying fully integrated 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) positron-emission tomography (PET)/MRI.

MATERIAL AND METHODS

Fourteen patients with aortitis and 14 patients with a negative study for aortitis using ¹⁸F-FDG PET as the standard of reference for the evaluation of inflammatory aortic involvement were included retrospectively. All patients were imaged at 3 T using T1W VIBE pre- and post-contrast. Four aortic segments were evaluated for image quality (IQ), diagnostic confidence (DC), and the degree of inflammatory activity (IA) using a Likert scale. Binomial and generalised estimating equation model tests were used to assess the diagnostic performance of T1W VIBE. Cohen's k was applied to test for interobserver reproducibility with respect to IA. Spearman's rank correlation coefficient was calculated to examine correlations between IQ, DC, IA, and PET results.

RESULTS

On a patient- and segment-based analysis, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 85.7% and 59.8%, 100% and 100%, 100% and 100%, 87.5% and 68%, and 92.9% and 82.1%, respectively. IQ and DC were acceptable to good in all examinations and substantial interobserver agreement was observed for IA (Cohen's k = 0.69). IQ and DC as well as IA and ¹⁸F-FDG vessel wall uptake were significantly correlated (r=0.763 and 0.679, respectively; p<0.0001).

CONCLUSION

T1W 3D fat saturated VIBE MRI allows diagnosis of aortitis and may aid in the management of patients with suspected LVV.

Recipient c-Kit Lineage Cells Repopulate Smooth Muscle Cells of Transplant Arteriosclerosis in Mouse Models

Supplemental Digital Content is available in the text.

Rationale:

Transplantation-accelerated arteriosclerosis is one of the major challenges for long-term survival of patients with solid organ transplantation. Although stem/progenitor cells have been implicated to participate in this process, the cells of origin and underlying mechanisms have not been fully defined.

Objective:

The objective of our study was to investigate the role of c-Kit lineage cells in allograft-induced neointima formation and to explore the mechanisms underlying this process.

Methods and Results:

Using an inducible lineage tracing Kit-CreER;Rosa26-tdTomato mouse model, we observed that c-Kit is expressed in multiple cell types in the blood vessels, rather than a specific stem/progenitor cell marker. We performed allograft transplantation between different donor and recipient mice, as well as bone marrow transplantation experiments, demonstrating that recipient c-Kit⁺ cells repopulate neointimal smooth muscle cells (SMCs) and leukocytes, and contribute to neointima formation in an allograft transplantation model. c-Kit–derived SMCs originate from nonbone marrow tissues, whereas bone marrow-derived c-Kit⁺ cells mainly generate CD45⁺ leukocytes. However, the exact identity of c-Kit lineage cells contributing to neointimal SMCs remains unclear. ACK2 (anti-c-Kit antibody), which specifically binds and blocks c-Kit function, ameliorates allograft-induced arteriosclerosis. Stem cell factor and TGF (transforming growth factor)-β1 levels were significantly increased in blood and neointimal lesions after allograft transplantation, by which stem cell factor facilitated c-Kit⁺ cell migration through the stem cell factor/c-Kit axis and downstream activation of small GTPases, MEK (mitogen-activated protein kinase kinase)/ERK (extracellular signal–regulated kinase)/MLC (myosin light chain), and JNK (c-Jun N-terminal kinase)/c-Jun signaling pathways, whereas TGF-β1 induces c-Kit⁺ cell differentiation into SMCs via HK (hexokinase)-1–dependent metabolic reprogramming and a possible downstream O-GlcNAcylation of myocardin and serum response factor.

Conclusions:

Our findings provide evidence that recipient c-Kit lineage cells contribute to vascular remodeling in an allograft transplantation model, in which the stem cell factor/c-Kit axis is responsible for cell migration and HK-1–dependent metabolic reprogramming for SMC differentiation.

Chemoradiotherapy-related carotid artery inflammation in head and neck cancer patients quantified by [18F]FDG PET/CT

OBJECTIVES

Radiotherapy (RT) is associated with an increased risk of cardiovascular disease (CVD), but little is known about the mechanism for vascular injury and methods for early detection.

MATERIALS AND METHODS

We conducted a prospective, pilot study of carotid artery inflammation using ¹⁸F-labeled 2-fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) PET/CT imaging pre- and 3 months post-RT in head-and-neck cancer (HNC) patients. [¹⁸F]FDG uptake by the carotid arteries was measured by the maximum and mean target to background ratio (TBR_MAX, TBR_MEAN) and the mean partial volume corrected standardized uptake value (pvcSUV_MEAN).

RESULTS

Of the 22 patients who completed both pre and post-RT scans, the majority (82%) had stage III or stage IV disease and received concurrent chemotherapy. TBR_MAX, TBR_MEAN, and pvcSUV_MEAN were all significantly higher 3 months after RT versus before RT with mean difference values (95% CI; p-value) of 0.17 (0.1-0.25; 0.0001), 0.19 (0.12-0.25; 0.0001), and 0.31 g/ml (0.12-0.5; 0.002), respectively. Fifteen patients (68%) had HPV-positive tumors, which were associated with lower pre-RT [¹⁸F]FDG signal, but a greater increase in TBR_MAX (19% vs 5%), TBR_MEAN (21% vs 11%) and pvcSUV_MEAN (20% increase vs 3% decrease), compared to HPV negativity.

CONCLUSION

There is a significant increase in carotid artery inflammation in HNC patients due to CRT that amounts to a degree that has previously been associated with higher risk for future CVD events. The subset of patients with HPV-positive tumors experienced the greatest increases in vascular inflammation due to CRT. Carotid [¹⁸F]FDG uptake may be an early biomarker of RT-related vascular injury.

Current and Emerging Preclinical Approaches for Imaging-Based Characterization of Atherosclerosis

Atherosclerotic plaques can remain quiescent for years, but become life threatening upon rupture or disruption, initiating clot formation in the vessel lumen and causing acute myocardial infarction and ischemic stroke. Whether and how a plaque ruptures is determined by its macroscopic structure and microscopic composition. Rupture-prone plaques usually consist of a thin fibrous cap with few smooth muscle cells, a large lipid core, a dense infiltrate of inflammatory cells, and neovessels. Such lesions, termed high-risk plaques, can remain asymptomatic until the thrombotic event. Various imaging technologies currently allow visualization of morphological and biological characteristics of high-risk atherosclerotic plaques. Conventional protocols are often complex and lack specificity for high-risk plaque. Conversely, new imaging approaches are emerging which may overcome these limitations. Validation of these novel imaging techniques in preclinical models of atherosclerosis is essential for effective translational to clinical practice. Imaging the vessel wall, as well as its biological milieu in small animal models, is challenging because the vessel wall is a small structure that undergoes continuous movements imposed by the cardiac cycle as it is adjacent to circulating blood. The focus of this paper is to provide a state-of-the-art review on techniques currently available for preclinical imaging of atherosclerosis in small animal models and to discuss the advantages and limitations of each approach.

Radionuclide imaging of inflammation in atherosclerotic vascular disease among people living with HIV infection: current practice and future perspective

People living with human immunodeficiency virus (HIV) infection have twice the risk of atherosclerotic vascular disease compared with non-infected individuals. Inflammation plays a critical role in the development and progression of atherosclerotic vascular disease. Therapies targeting inflammation irrespective of serum lipid levels have been shown to be effective in preventing the occurrence of CVD. Radionuclide imaging is a viable method for evaluating arterial inflammation. This evaluation is useful in quantifying CVD risk and for assessing the effectiveness of anti-inflammatory treatment. The most tested radionuclide method for quantifying arterial inflammation among people living with HIV infection has been with F-18 FDG PET/CT. The level of arterial uptake of F-18 FDG correlates with vascular inflammation and with the risk of development and progression of atherosclerotic disease. Several limitations exist to the use of F-18 FDG for PET quantification of arterial inflammation. Many targets expressed on macrophage, a significant player in arterial inflammation, have the potential for use in evaluating arterial inflammation among people living with HIV infection. The review describes the clinical utility of F-18 FDG PET/CT in assessing arterial inflammation as a risk for atherosclerotic disease among people living with HIV infection. It also outlines potential newer probes that may quantify arterial inflammation in the HIV-infected population by targeting different proteins expressed on macrophages.

18F-FDG PET/MR-imaging in a Göttingen Minipig model of atherosclerosis: Correlations with histology and quantitative gene expression

BACKGROUND AND AIMS

The advantage of combining molecular and morphological imaging, e.g. positron emission tomography and magnetic resonance imaging (PET/MRI), is reflected in the increased use of these modalities as surrogate end-points in clinical trials. This study aimed at evaluating plaque inflammation using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)-PET/MRI, and gene expression in a minipig model of atherosclerosis.

METHODS

Göttingen Minipigs were fed for 60 weeks with fat/fructose/cholesterol-rich diet (FFC), chow (Control) or FFC-diet changed to chow midway (diet normalization group; DNO). In all groups, ¹⁸F-FDG-PET/MRI of the abdominal aorta was assessed midway and at study-end. The aorta was analyzed using histology and gene expression.

RESULTS

At study-end, FFC had significantly higher FDG-uptake compared to Control (target-to-background maximal uptake, TBR_Max (95% confidence interval) CI_TBRMax: 0.092; 7.32) and DNO showed significantly decreased uptake compared to FFC (CI_TBRMax: -5.94;-0.07). No difference was observed between DNO and Control (CI_TBRMax: -2.71; 4.11). FFC displayed increased atherosclerosis and gene expression of inflammatory markers, including vascular cell adhesion molecule 1 (VCAM-1), cluster of differentiation 68 (CD68), matrix metalloproteinase 9 (MMP9), cathepsin K (CTSK) and secreted phosphoprotein 1 (SPP1) compared to Control and DNO (all, p < 0.05). FDG-uptake correlated with gene expression of inflammatory markers, including CD68, ρ_s = 0.58; MMP9, ρ_s = 0.46; SPP1, ρ_s = 0.44 and CTSK, ρ_s = 0.49; (p ≤ 0.01 for all).

CONCLUSIONS

In a model of atherosclerosis, ¹⁸F-FDG-PET/MRI technology allows for detection of inflammation in atherosclerotic plaques, consistent with increased inflammatory gene expression. Our findings corroborate clinical data and are important in pre-clinical drug development targeting plaque inflammation.

Emerging Techniques for Cardiovascular PET

The application of positron emission tomography (PET) to cardiac disease has yielded tremendous developments in the evaluation of coronary artery, myocardial, and valvular heart disease over the past several decades. These advances have included development of new radiotracers, incremental technological improvements, and coupling of PET with other non-invasive cardiac imaging modalities. The current era has seen rapid, successive and wide-ranging advances in PET myocardial perfusion and metabolic imaging. This review will address emerging techniques in cardiovascular PET imaging, including the measurement of absolute myocardial blood flow (MBF), use of novel tracers, and other advances in heart failure, infection imaging, and valvular disease.

Perspectives on Small Animal Radionuclide Imaging; Considerations and Advances in Atherosclerosis

This review addresses nuclear SPECT and PET imaging in small animals in relation to the atherosclerotic disease process, one of our research topics of interest. Imaging of atherosclerosis in small animal models is challenging, as it operates at the limits of current imaging possibilities regarding sensitivity, and spatial resolution. Several topics are discussed, including technical considerations that apply to image acquisition, reconstruction, and analysis. Moreover, molecules developed for or applied in these small animal nuclear imaging studies are listed, including target-directed molecules, useful for imaging organs or tissues that have elevated expression of the target compared to other tissues, and molecules that serve as substrates for metabolic processes. Differences between animal models and human pathophysiology that should be taken into account during translation from animal to patient as well as differences in tracer behavior in animal vs. man are also described. Finally, we give a future outlook on small animal radionuclide imaging in atherosclerosis, followed by recommendations. The challenges and solutions described might be applicable to other research fields of health and disease as well.

PET-Based Imaging of Ischemic Heart Disease

PET-based cardiac nuclear imaging plays a large role in the management of ischemic heart disease. Compared with conventional single-photon emission CT myocardial perfusion imaging, PET provides superior accuracy in diagnosis of coronary artery disease and, with the incorporation of myocardial blood flow and coronary flow reserve, adds value in assessing prognosis for established coronary and microvascular disease. This review describes these and other uses of PET in ischemic heart disease, including assessing myocardial viability in ischemic cardiomyopathy. Developments in novel PET flow tracers and molecular imaging tools to assess atherosclerotic plaque vulnerability, vascular calcification, and vascular remodeling also are described.