FDG-PET can distinguish inflamed from non-inflamed plaque in an animal model of atherosclerosis. Int J Cardiovasc Imaging. 2010;26:41-48. [PMID: 19784796 DOI: 10.1007/s10554-009-9506-6]

Advanced Imaging Techniques for Atherosclerosis and Cardiovascular Calcification in Animal Models

The detection and assessment of atherosclerosis and cardiovascular calcification can inform risk stratification and therapies to reduce cardiovascular morbidity and mortality. In this review, we provide an overview of current and emerging imaging techniques for assessing atherosclerosis and cardiovascular calcification in animal models. Traditional imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), offer non-invasive approaches of visualizing atherosclerotic calcification in vivo; integration of these techniques with positron emission tomography (PET) imaging adds molecular imaging capabilities, such as detection of metabolically active microcalcifications with 18F-sodium fluoride. Photoacoustic imaging provides high contrast that enables in vivo evaluation of plaque composition, yet this method is limited by optical penetration depth. Light-sheet fluorescence microscopy provides high-resolution, three-dimensional imaging of cardiovascular structures and has been used for ex vivo assessment of atherosclerotic calcification, but its limited tissue penetration and requisite complex sample preparation preclude its use in vivo to evaluate cardiac tissue. Overall, with these evolving imaging tools, our understanding of cardiovascular calcification development in animal models is improving, and the combination of traditional imaging techniques with emerging molecular imaging modalities will enhance our ability to investigate therapeutic strategies for atherosclerotic calcification.

Asymptomatic Penetrating Atherosclerotic Ulcer Findings on 18 F-FDG PET/CT

ABSTRACT

We present a case of an 84-year-old man with a history of smoking, hypertension, and coronary artery disease with an incidental spiculated left apical pulmonary nodule, suspicious for a stage I non-small cell lung cancer. 18 F-FDG PET/CT performed for staging, which confirmed a small metabolically active pulmonary nodule. As an incidental finding, there was focal FDG uptake in the proximal descending aorta corresponding to a partially thrombosed outpouching of the aortic wall, in keeping with a penetrating atherosclerotic ulcer.

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.

Imaging High-Risk Atherothrombosis Using a Novel Fibrin-Binding Positron Emission Tomography Probe

BACKGROUND AND PURPOSE

High-risk atherosclerosis is an underlying cause of cardiovascular events, yet identifying the specific patient population at immediate risk is still challenging. Here, we used a rabbit model of atherosclerotic plaque rupture and human carotid endarterectomy specimens to describe the potential of molecular fibrin imaging as a tool to identify thrombotic plaques.

METHODS

Atherosclerotic plaques in rabbits were induced using a high-cholesterol diet and aortic balloon injury (N=13). Pharmacological triggering was used in a group of rabbits (n=9) to induce plaque disruption. Animals were grouped into thrombotic and nonthrombotic plaque groups based on gross pathology (gold standard). All animals were injected with a novel fibrin-specific probe ⁶⁸Ga-CM246 followed by positron emission tomography (PET)/magnetic resonance imaging 90 minutes later. ⁶⁸Ga-CM246 was quantified on the PET images using tissue-to-background (back muscle) ratios and standardized uptake value.

RESULTS

Both tissue-to-background (back muscle) ratios and standardized uptake value were significantly higher in the thrombotic versus nonthrombotic group (P<0.05). Ex vivo PET and autoradiography of the abdominal aorta correlated positively with in vivo PET measurements. Plaque disruption identified by ⁶⁸Ga-CM246 PET agreed with gross pathology assessment (85%). In ex vivo surgical specimens obtained from patients undergoing elective carotid endarterectomy (N=12), ⁶⁸Ga-CM246 showed significantly higher binding to carotid plaques compared to a D-cysteine nonbinding control probe.

CONCLUSIONS

We demonstrated that molecular fibrin PET imaging using ⁶⁸Ga-CM246 could be a useful tool to diagnose experimental and clinical atherothrombosis. Based on our initial results using human carotid plaque specimens, in vivo molecular imaging studies are warranted to test ⁶⁸Ga-CM246 PET as a tool to stratify risk in atherosclerotic patients.

Cardiac Imaging in Dialysis Patients

There is a well-established yet unexplained high prevalence of cardiovascular morbidity and mortality in individuals with end-stage kidney disease receiving dialysis. Potential causes include changes in cardiac structure and function, with increased left ventricular mass index as the best established cardiac structural change associated with this increase in mortality. However, in recent years, new echocardiographic and cardiac magnetic resonance imaging techniques have emerged that may provide novel markers that may better explain the mechanisms underlying the cardiovascular morbidity and mortality observed in end-stage kidney disease. This review outlines advances in cardiac imaging and the current status of imaging modalities, including echocardiography, cardiac magnetic resonance imaging, and cardiac positron emission tomography, to identify dialysis patients at high risk for cardiovascular mortality.

Molecular Imaging of Inflammation in a Mouse Model of Atherosclerosis Using a Zirconium-89-Labeled Probe

Background

Beyond clinical atherosclerosis imaging of vessel stenosis and plaque morphology, early detection of inflamed atherosclerotic lesions by molecular imaging could improve risk assessment and clinical management in high-risk patients. To identify inflamed atherosclerotic lesions by molecular imaging in vivo, we studied the specificity of our radiotracer based on maleylated (Mal) human serum albumin (HSA), which targets key features of unstable atherosclerotic lesions.

Materials and Methods

Mal-HSA was radiolabeled with a positron-emitting metal ion, zirconium-89 (⁸⁹Zr⁴⁺). The targeting potential of this probe was compared with unspecific ⁸⁹Zr-HSA and ¹⁸F-FDG in an experimental model of atherosclerosis (Apoe^–/– mice, n=22), and compared with wild-type (WT) mice (C57BL/6J, n=21) as controls.

Results

PET/MRI, gamma counter measurements, and autoradiography showed the accumulation of ⁸⁹Zr-Mal-HSA in the atherosclerotic lesions of Apoe^–/– mice. The maximum standardized uptake values (SUV_max) for ⁸⁹Zr-Mal-HSA at 16 and 20 weeks were 26% and 20% higher (P<0.05) in Apoe^–/– mice than in control WT mice, whereas no difference in SUV_max was observed for ¹⁸F-FDG in the same animals. ⁸⁹Zr-Mal-HSA uptake in the aorta, as evaluated by a gamma counter 48 h postinjection, was 32% higher (P<0.01) for Apoe^–/– mice than in WT mice, and the aorta-to-blood ratio was 8-fold higher (P<0.001) for ⁸⁹Zr-Mal-HSA compared with unspecific ⁸⁹Zr-HSA. HSA-based probes were mainly distributed to the liver, spleen, kidneys, bone, and lymph nodes. The phosphor imaging autoradiography (PI-ARG) results corroborated the PET and gamma counter measurements, showing higher accumulation of ⁸⁹Zr-Mal-HSA in the aortas of Apoe^–/– mice than in WT mice (9.4±1.4 vs 0.8±0.3%; P<0.001).

Conclusion

⁸⁹Zr radiolabeling of Mal-HSA probes resulted in detectable activity in atherosclerotic lesions in aortas of Apoe^–/– mice, as demonstrated by quantitative in vivo PET/MRI. ⁸⁹Zr-Mal-HSA appears to be a promising diagnostic tool for the early identification of macrophage-rich areas of inflammation in 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.

Assessing the interactions between radiotherapy and antitumour immunity

Immunotherapy, specifically the introduction of immune checkpoint inhibitors, has transformed the treatment of cancer, enabling long-term tumour control even in individuals with advanced-stage disease. Unfortunately, only a small subset of patients show a response to currently available immunotherapies. Despite a growing consensus that combining immune checkpoint inhibitors with radiotherapy can increase response rates, this approach might be limited by the development of persistent radiation-induced immunosuppression. The ultimate goal of combining immunotherapy with radiotherapy is to induce a shift from an ineffective, pre-existing immune response to a long-lasting, therapy-induced immune response at all sites of disease. To achieve this goal and enable the adaptation and monitoring of individualized treatment approaches, assessment of the dynamic changes in the immune system at the patient level is essential. In this Review, we summarize the available clinical data, including forthcoming methods to assess the immune response to radiotherapy at the patient level, ranging from serum biomarkers to imaging techniques that enable investigation of immune cell dynamics in patients. Furthermore, we discuss modelling approaches that have been developed to predict the interaction of immunotherapy with radiotherapy, and highlight how they could be combined with biomarkers of antitumour immunity to optimize radiotherapy regimens and maximize their synergy with immunotherapy.

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.

Imaging plaque inflammation in asymptomatic cocaine addicted individuals with simultaneous positron emission tomography/magnetic resonance imaging

BACKGROUND

Chronic cocaine use is associated with stroke, coronary artery disease and myocardial infarction, resulting in severe impairments or sudden mortality. In the absence of clear cardiovascular symptoms, individuals with cocaine use disorder (iCUD) seeking addiction treatment receive mostly psychotherapy and psychiatric pharmacotherapy, with no attention to vascular disease (i.e., atherosclerosis). Little is known about the pre-clinical signs of cardiovascular risk in iCUD and early signs of vascular disease are undetected in this underserved population.

AIM

To assess inflammation, plaque burden and plaque composition in iCUD aiming to detect markers of atherosclerosis and vascular disease.

METHODS

The bilateral carotid arteries were imaged with positron emission tomography/magnetic resonance imaging (PET/MRI) in iCUD asymptomatic for cardiovascular disease, healthy controls, and individuals with cardiovascular risk. PET with 18F-fluorodeoxyglucose (¹⁸F-FDG) evaluated vascular inflammation and 3-D dark-blood MRI assessed plaque burden including wall area and thickness. Drug use and severity of addiction were assessed with standardized instruments.

RESULTS

The majority of iCUD and controls had carotid FDG-PET signal greater than 1.6 but lower than 3, indicating the presence of mild to moderate inflammation. However, the MRI measure of wall structure was thicker in iCUD as compared to the controls and cardiovascular risk group, indicating greater carotid plaque burden. iCUD had larger wall area as compared to the healthy controls but not as compared to the cardiovascular risk group, indicating structural wall similarities between the non-control study groups. In iCUD, wall area correlated with greater cocaine withdrawal and craving.

CONCLUSION

These preliminary results show markers of carotid artery disease burden in cardiovascular disease-asymptomatic iCUD. Broader trials are warranted to develop protocols for early detection of cardiovascular risk and preventive intervention in iCUD.

Imaging Intraplaque Inflammation in Carotid Atherosclerosis With 18F-Fluorocholine Positron Emission Tomography-Computed Tomography: Prospective Study on Vulnerable Atheroma With Immunohistochemical Validation

BACKGROUND

(18)F-fluorocholine ((18)F-FCH) uptake is associated with cell proliferation and activity in tumor patients. We hypothesized that (18)F-FCH could similarly be a valuable imaging tool to identify vulnerable plaques and associated intraplaque inflammation and atheroma cell proliferation.

METHODS AND RESULTS

Ten consecutive stroke patients (90% men, median age 66.5 years, range, 59.4-69.7) with ipsilateral >70% carotid artery stenosis and who underwent carotid endarterectomy were included in the study. Before carotid endarterectomy, all patients underwent positron emission tomography to assess maximum (18)F-FCH uptake in ipsilateral symptomatic carotid plaques and contralateral asymptomatic carotid arteries, which was corrected for background activity, resulting in a maximum target-to-background ratio (TBRmax). Macrophage content was assessed in all carotid endarterectomy specimens as a percentage of CD68(+)-staining per whole plaque area (plaqueCD68(+)) and as a maximum CD68(+) percentage (maxCD68(+)) in the most inflamed section/plaque. Dynamic positron emission tomography imaging demonstrated that an interval of 10 minutes between (18)F-FCH injection and positron emission tomography acquisition is appropriate for carotid plaque imaging. TBRmax in ipsilateral symptomatic carotid plaques correlated significantly with plaqueCD68(+) (Spearman's ρ=0.648, P=0.043) and maxCD68(+) (ρ=0.721, P=0.019) in the 10 corresponding carotid endarterectomy specimens. TBRmax was significantly higher (P=0.047) in ipsilateral symptomatic carotid plaques (median: 2.0; interquartile range [Q1-Q3], 1.5-2.5) compared with the contralateral asymptomatic carotid arteries (median: 1.4; Q1-Q3, 1.3-1.6). TBRmax was not significantly correlated to carotid artery stenosis (ρ=0.506, P=0.135).

CONCLUSIONS

In vivo uptake of (18)F-FCH in human carotid atherosclerotic plaques correlated strongly with degree of macrophage infiltration and recent symptoms, thus (18)F-FCH positron emission tomography is a promising tool for the evaluation of vulnerable plaques.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01899014.

Pathophysiological relevance of macrophage subsets in atherogenesis

Macrophages are highly heterogeneous and plastic cells. They were shown to play a critical role in all stages of atherogenesis, from the initiation to the necrotic core formation and plaque rupture. Lesional macrophages primarily derive from blood monocyte, but local macrophage proliferation as well as differentiation from smooth muscle cells have also been described. Within atherosclerotic plaques, macrophages rapidly respond to changes in the microenvironment, shifting between pro- (M1) or anti-inflammatory (M2) functional phenotypes. Furthermore, different stimuli have been associated with differentiation of newly discovered M2 subtypes: IL-4/IL-13 (M2a), immune-complex (M2b), IL-10/glucocorticoids (M2c), and adenosine receptor agonist (M2d). More recently, additional intraplaque macrophage phenotypes were also recognized in response to CXCL4 (M4), oxidized phospholipids (Mox), haemoglobin/haptoglobin complexes (HA-mac/M(Hb)), and heme (Mhem). Such macrophage polarization was described as a progression among multiple phenotypes, which reflect the activity of different transcriptional factors and the cross-talk between intracellular signalling. Finally, the distribution of macrophage subsets within different plaque areas was markedly associated with cardiovascular (CV) vulnerability. The aim of this review is to update the current knowledge on the role of macrophage subsets in atherogenesis. In addition, the molecular mechanisms underlying macrophage phenotypic shift will be summarised and discussed. Finally, the role of intraplaque macrophages as predictors of CV events and the therapeutic potential of these cells will be discussed.

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

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

Preclinical models of atherosclerosis. The future of Hybrid PET/MR technology for the early detection of vulnerable plaque

Cardiovascular diseases are the leading cause of death in developed countries. The aetiology is currently multifactorial, thus making them very difficult to prevent. Preclinical models of atherothrombotic diseases, including vulnerable plaque-associated complications, are now providing significant insights into pathologies like atherosclerosis, and in combination with the most recent advances in new non-invasive imaging technologies, they have become essential tools to evaluate new therapeutic strategies, with which can forecast and prevent plaque rupture. Positron emission tomography (PET)/computed tomography imaging is currently used for plaque visualisation in clinical and pre-clinical cardiovascular research, albeit with significant limitations. However, the combination of PET and magnetic resonance imaging (MRI) technologies is still the best option available today, as combined PET/MRI scans provide simultaneous data acquisition together with high quality anatomical information, sensitivity and lower radiation exposure for the patient. The coming years may represent a new era for the implementation of PET/MRI in clinical practice, but first, clinically efficient attenuation correction algorithms and research towards multimodal reagents and safety issues should be validated at the preclinical level.

Plaque Thrombosis is Reduced by Attenuating Plaque Inflammation with Pioglitazone and is Evaluated by Fluorodeoxyglucose Positron Emission Tomography

INTRODUCTION

The relationship between the beneficial effects of pioglitazone in reducing clinical events and plaque inflammatory burden remains unknown. This study aimed to determine whether pioglitazone can reduce the number of plaque thrombosis incidences and whether decreasing plaque inflammation is the mechanism by which pioglitazone reduces plaque thromboses.

METHODS AND RESULTS

therosclerotic rabbits were divided into two groups: the atherosclerosis group (n = 13) and pioglitazone group (n = 10). The rabbits underwent pharmacological triggering to induce thrombosis. Serum inflammatory markers, FDG uptake, macrophage, and neovessel staining detected arterial inflammation. PET/CT scans were performed twice (baseline and posttreatment scans). Plaque area, macrophages, and neovessels were measured and the histologic sections were matched with the PET/CT scans. Serum MMP-9 and hsCRP were lower in the pioglitazone group compared to the atherosclerosis group. The SUVmean significantly decreased in the pioglitazone group (0.62 ± 0.21 vs. 0.55 ± 0.19, P = 0.008), but increased in the atherosclerosis group (0.61 ± 0.15 vs. 0.91 ± 0.20, P < 0.000). The incidence rate of plaque rupture, plaque area, macrophage density, and neovessel density was significantly lower in rabbits with pioglitazone than without (15% vs. 38%, P < 0.001; 18.00 ± 2.30 vs. 27.00 ± 1.60; P < 0.001; 8.80 ± 3.94 vs. 28.26 ± 2.49; P < 0.001; 16.50 ± 3.09 vs. 29.00 ± 2.11; P < 0.001, respectively). Moreover, plaque area and macrophage density were positively correlated with SUV values.

CONCLUSIONS

Our study suggests that pioglitazone can reduce the number of plaque thrombosis incidences by decreasing plaque inflammation. (18)F-FDG-PET/CT can detect plaque inflammation and assess the effects of antiatherosclerotic drugs.

Nuclear Molecular Imaging for Vulnerable Atherosclerotic Plaques

Atherosclerosis is an inflammatory disease as well as a lipid disorder. Atherosclerotic plaque formed in vessel walls may cause ischemia, and the rupture of vulnerable plaque may result in fatal events, like myocardial infarction or stroke. Because morphological imaging has limitations in diagnosing vulnerable plaque, molecular imaging has been developed, in particular, the use of nuclear imaging probes. Molecular imaging targets various aspects of vulnerable plaque, such as inflammatory cell accumulation, endothelial activation, proteolysis, neoangiogenesis, hypoxia, apoptosis, and calcification. Many preclinical and clinical studies have been conducted with various imaging probes and some of them have exhibited promising results. Despite some limitations in imaging technology, molecular imaging is expected to be used both in the research and clinical fields as imaging instruments become more advanced.

A pilot trial to examine the effect of high-dose niacin on arterial wall inflammation using fluorodeoxyglucose positron emission tomography

RATIONALE AND OBJECTIVES

Although studies have reported direct inhibition of inflammatory pathways with niacin, the effect of niacin on arterial wall inflammation remains unknown. We examined the effect of niacin on arterial (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT).

MATERIALS AND METHODS

Nine statin-treated patients with coronary disease were randomized to niacin 6000 mg/day or placebo. FDG-PET/CT and lipids were assessed at baseline and at 12 weeks. FDG was quantified in the aorta, right carotid artery, and left carotid artery as the target-to-background ratio (TBR) and target-to-background difference (TBD).

RESULTS

Eight patients completed the study. No significant changes in FDG measured by aortic, left carotid, or right carotid TBR or TBD were seen in either group. Compared to baseline, niacin-treated subjects exhibited a significant 29% reduction in low-density lipoprotein cholesterol (LDL-C; 95% confidence interval [CI], -50% to 8%; P = .01) and a nonsignificant 29% reduction in LDL particle number (LDL-P; 95% CI, -58% to 0.2%; P = .07). A nonsignificant 11% increase in HDL-C (95% CI, -15% to 37%; P = .30) and 8% decrease in HDL-P (95% CI, -44% to 28%; P = .51) were observed with niacin treatment. In a pooled analysis, changes in LDL-P were positively correlated with FDG uptake in the aorta (TBR r = 0.66, P = .08; TBD r = 0.75, P = .03), left carotid (TBR r = 0.65, P = .08; TBD r = 0.74, P = .03), and right carotid (TBR r = 0.54, P = .17; TBD r = 0.61, P = .11).

CONCLUSIONS

In this pilot study, adding niacin to statin therapy did not affect arterial wall inflammation measured by FDG-PET/CT. However, an association between changes in arterial FDG uptake and LDL-P was observed. Larger studies are needed to definitively examine the effect of niacin on arterial wall inflammation.

Comparison of fluorodeoxyglucose uptake in symptomatic carotid artery and stable femoral artery plaques

BACKGROUND

Fluorine-18-labelled fluoroxdeoxyglucose (FDG) positron emission tomography (PET) has been used to evaluate atherosclerotic plaque metabolic activity, and through its uptake by macrophages is believed to have the potential to identify vulnerable plaques. The aims were to compare FDG uptake in carotid plaques from patients who had sustained a recent thromboembolic cerebrovascular event with that in femoral artery plaques from patients with leg ischaemia, and to correlate FDG uptake with the proportion of M1 and M2 macrophages present.

METHODS

Consecutive patients who had carotid endarterectomy for symptomatic, significant carotid stenosis and patients with severe leg ischaemia and significant stenosis of the common femoral artery underwent FDG-PET and histological plaque analysis. The voxel with the greatest activity in the region of interest was calculated using the Patlak method over 60 min. Plaques were dual-stained for CD68, and M1 and M2 macrophage subsets.

RESULTS

There were 29 carotid and 25 femoral artery plaques for study. The maximum dynamic uptake was similar in carotid compared with femoral plaques: median (range) 9·7 (7·1-12·2) versus 10·0 (7·4-16·6) respectively (P = 0·281). CD68 macrophage counts were significantly increased in carotid compared with femoral plaques (39·5 (33·9-50·1) versus 11·5 (7·7-21·3) respectively; P < 0·001), as was the proportion of M1 proinflammatory macrophages. The degree of carotid stenosis correlated with the maximum dynamic FDG uptake (rs  = 0·48, P = 0·008).

CONCLUSION

FDG uptake was no greater in symptomatic carotid plaques than in the less inflammatory femoral plaques. In patients on statin therapy. FDG uptake occurred in areas of significant arterial stenosis, irrespective of the degree of inflammation.

Rational development of radiopharmaceuticals for HIV-1

The global battle against HIV-1 would benefit from a sensitive and specific radiopharmaceutical to localize HIV-infected cells. Ideally, this probe would be able to identify latently infected host cells containing replication competent HIV sequences. Clinical and research applications would include assessment of reservoirs, informing clinical management by facilitating assessment of burden of infection in different compartments, monitoring disease progression and monitoring response to therapy. A "rational" development approach could facilitate efficient identification of an appropriate targeted radiopharmaceutical. Rational development starts with understanding characteristics of the disease that can be effectively targeted and then engineering radiopharmaceuticals to hone in on an appropriate target, which in the case of HIV-1 (HIV) might be an HIV-specific product on or in the host cell, a differentially expressed gene product, an integrated DNA sequence specific enzymatic activity, part of the inflammatory response, or a combination of these. This is different from the current approach that starts with a radiopharmaceutical for a target associated with a disease, mostly from autopsy studies, without a strong rationale for the potential to impact patient care. At present, no targeted therapies are available for HIV latency, although a number of approaches are under study. Here we discuss requirements for a radiopharmaceutical useful in strategies targeting persistently infected cells. The radiopharmaceutical for HIV should be developed based on HIV biology, studied in an animal model and then in humans, and ultimately used in clinical and research settings.

18F-FDG PET and intravascular ultrasonography (IVUS) images compared with histology of atherosclerotic plaques: 18F-FDG accumulates in foamy macrophages

PURPOSE

Intravascular ultrasonography (IVUS) and (18)F-FDG PET have been used to evaluate the efficacy of antiatherosclerosis drugs. These two modalities image different characteristics of atherosclerotic plaques, and a comparison of IVUS and PET images with histology has not been performed. The aim of this study was to align IVUS and PET images using anatomic landmarks in Watanabe heritable hyperlipidaemic (WHHL) rabbits, enabling comparison of their depiction of aortic atherosclerosis. Cellular (18)F-FDG localization was evaluated by (3)H-FDG microautoradiography (micro-ARG).

METHODS

A total of 19 WHHL rabbits (7 months of age) were divided into three groups: baseline (n = 6), 3 months (n = 4), and 6 months (n = 9). PET, IVUS and histological images of the same aortic segments were analysed. Infiltration by foamy macrophages was scored from 0 to IV using haematoxylin and eosin (H&E) and antimacrophage immunohistochemical staining, and compared with (3)H-FDG micro-ARG findings in two additional WHHL rabbits.

RESULTS

IVUS images did not identify foamy macrophage deposition but revealed the area of intimal lesions (r = 0.87). (18)F-FDG PET revealed foamy macrophage distribution in the plaques. The intensity of (18)F-FDG uptake was correlated positively with the degree of foamy macrophage infiltration. Micro-ARG showed identical (3)H-FDG accumulation in the foamy macrophages surrounding the lipid core of the plaques.

CONCLUSION

F-FDG PET localized and quantified the degree of infiltration of foamy macrophages in atherosclerotic lesions. IVUS defined the size of lesions. (18)F-FDG PET is a promising imaging technique for evaluating atherosclerosis and for monitoring changes in the composition of atherosclerotic plaques affecting their stability.

Complementarity between (18)F-FDG PET/CT and Ultrasonography or Angiography in Carotid Plaque Characterization

Background and Purpose

To estimate clinical roles of 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) versus angiography and ultrasonography in carotid plaque characterization.

Methods

We characterized two groups of patients with recently (<1 month) symptomatic (n=14; age=71.8±8.6 years, mean±SD) or chronic (n=13, age=68.9±9.0 years) carotid stenosis using a battery of imaging tests: diffusion magnetic resonance (MR) imaging, MR or transfemoral angiography, duplex ultrasonography (DUS), and carotid FDG-PET/computed tomography.

Results

The degree of angiographic stenosis was greater in patients with recently symptomatic carotid plaques (67.5±21.5%) than in patients with chronic carotid plaques (32.4±26.8%, p=0.001). Despite the significant difference in the degree of stenosis, lesional maximum standardized uptake values (maxSUVs) on the carotid FDG-PET did not differ between the recently symptomatic (1.56±0.53) and chronic (1.56±0.34, p=0.65) stenosis groups. However, lesional-to-contralesional maxSUV ratios were higher in the recently symptomatic stenosis group (113±17%) than in the chronic stenosis group (98±10%, p=0.017). The grayscale median value of the lesional DUS echodensities was lower in the recently symptomatic stenosis group (28.2±10.0, n=9) than in the chronic stenosis group (53.9±14.0, n=8; p=0.001). Overall, there were no significant correlations between angiographic stenosis, DUS echodensity, and FDG-PET maxSUV. Case/subgroup analyses suggested complementarity between imaging modalities.

Conclusions

There were both correspondences and discrepancies between the carotid FDG-PET images and DUS or angiography data. Further studies are required to determine whether FDG-PET could improve the clinical management of carotid stenosis.

Small animal positron emission tomography imaging and in vivo studies of atherosclerosis

Atherosclerosis is a growing health challenge globally, and despite our knowledge of the disease has increased over the last couple of decades, many unanswered questions remain. As molecular imaging can be used to visualize, characterize and measure biological processes at the molecular and cellular levels in living systems, this technology represents an opportunity to investigate some of these questions in vivo. In addition, molecular imaging may be translated into clinical use and eventually pave the way for more personalized treatment regimes in patients. Here, we review the current knowledge obtained from in vivo positron emission tomography studies of atherosclerosis performed in small animals.

Glucose metabolic trapping in mouse arteries: nonradioactive assay of atherosclerotic plaque inflammation applicable to drug discovery

Background

¹⁸F-Fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging of atherosclerosis in the clinic is based on preferential accumulation of radioactive glucose analog in atherosclerotic plaques. FDG-PET is challenging in mouse models due to limited resolution and high cost. We aimed to quantify accumulation of nonradioactive glucose metabolite, FDG-6-phosphate, in the mouse atherosclerotic plaques as a simple alternative to PET imaging.

Methodology/Principal Findings

Nonradioactive FDG was injected 30 minutes before euthanasia. Arteries were dissected, and lipids were extracted. The arteries were re-extracted with 50% acetonitrile-50% methanol-0.1% formic acid. A daughter ion of FDG-6-phosphate was quantified using liquid chromatography and mass spectrometry (LC/MS/MS). Thus, both traditional (cholesterol) and novel (FDG-6-phosphate) markers were assayed in the same tissue. FDG-6-phosphate was accumulated in atherosclerotic lesions associated with carotid ligation of the Western diet fed ApoE knockout mice (5.9 times increase compare to unligated carotids, p<0.001). Treatment with the liver X receptor agonist T0901317 significantly (2.1 times, p<0.01) reduced FDG-6-phosphate accumulation 2 weeks after surgery. Anti-atherosclerotic effects were independently confirmed by reduction in lesion size, macrophage number, cholesterol ester accumulation, and macrophage proteolytic activity.

Conclusions/Significance

Mass spectrometry of FDG-6-phosphate in experimental atherosclerosis is consistent with plaque inflammation and provides potential translational link to the clinical studies utilizing FDG-PET imaging.

A practical quantification of blood glucose production due to high-level chronic stress

Blood glucose (BG) is the primary metabolic fuel for, among others, cancer cell progression, cardiovascular disease and inflammation. Stress is an important contributor to the amount of BG produced especially by the liver. In this paper, we attempt to quantify the BG production due to chronic (in the order of weeks) high-level psychological stress in a manner that a lay person will understand. Three independent approaches were used. The first approach was based on a literature survey of stress hormone data from healthy individuals and its subsequent mathematical manipulation. The next approach was a deductive process where BG levels could be deduced from published stress data of large cardiovascular clinical trials. The third approach used empirical BG data and a BG simulation model. The three different methods produced an average BG increase of 2.2-fold above basal for high levels of stress over a period of more than a day. The standard deviation normalized to the average value was 4.5%.

Differentiation of septic and aseptic loosening by PET with both 11C-PK11195 and 18F-FDG in rat models

PURPOSE

This study aims to determine the value of PET with C-isoquinoline carboxamide (C-PK11195) and F-fluorodeoxyglucose (F-FDG) in assisting the differentiation of aseptic loosening (AL) from septic loosening (SL) in rat models.

PROCEDURES

Initially, the histological profiles of SL and AL (cellular infiltration and the number of CD68 macrophage and PBR cells) were compared. Subsequently, we investigated whether C-PK11195 alone and also in combination with F-FDG increases the sensitivity and specificity of PET imaging for distinguishing SL from AL.

RESULTS

There were distinguishable features between the histological profiles of the SL and AL rat groups. The number of CD68/PBR cells in AL rats was significantly higher than that seen in SL rats (P<0.05). The uptake of C-PK1195 was higher in AL and lower in SL rats. The uptake of F-FDG was higher in SL and lower in AL rats.

CONCLUSION

PET with a C-PK11195 and F-FDG imaging protocol is helpful in the clinical differential diagnosis of AL from SL.

Dynamic in vivo imaging of receptors in small animals using positron emission tomography

Positron emission tomography (PET) is a functional imaging technique with the potential to image and quantify receptors in vivo with high sensitivity. PET has been used extensively to study major neurotransmitters such as dopamine, serotonin, and benzodiazepine in humans as well as proving to be a very powerful tool to accelerate development and assessment of existing and novel drugs. With the recent development of dedicated PET scanners for small animals, such as the microPET, it is now possible to perform functional imaging in small animals such as rodents at high resolution. This will allow the study of animal models of disease and longitudinal studies in these models to monitor disease progression or effect of treatment in the same animal. Furthermore, the complete pharmacokinetics of a drug as well as pharmacodynamic information can be obtained in a single animal. Thus, small animal imaging will significantly reduce the number of animals needed for this type of experiment as well as reducing the effect of inter-animal variation. Experimental protocols in small animal imaging potentially can be very labor intensive. In this chapter, we discuss methods and practical aspects related to this type of experiment using the microPET system.

Quantification of atherosclerotic plaque activity and vascular inflammation using [18-F] fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT)

Conventional non-invasive imaging modalities of atherosclerosis such as coronary artery calcium (CAC) and carotid intimal medial thickness (C-IMT) provide information about the burden of disease. However, despite multiple validation studies of CAC, and C-IMT, these modalities do not accurately assess plaque characteristics, and the composition and inflammatory state of the plaque determine its stability and, therefore, the risk of clinical events. [(18)F]-2-fluoro-2-deoxy-D-glucose (FDG) imaging using positron-emission tomography (PET)/computed tomography (CT) has been extensively studied in oncologic metabolism. Studies using animal models and immunohistochemistry in humans show that FDG-PET/CT is exquisitely sensitive for detecting macrophage activity, an important source of cellular inflammation in vessel walls. More recently, we and others have shown that FDG-PET/CT enables highly precise, novel measurements of inflammatory activity of activity of atherosclerotic plaques in large and medium-sized arteries. FDG-PET/CT studies have many advantages over other imaging modalities: 1) high contrast resolution; 2) quantification of plaque volume and metabolic activity allowing for multi-modal atherosclerotic plaque quantification; 3) dynamic, real-time, in vivo imaging; 4) minimal operator dependence. Finally, vascular inflammation detected by FDG-PET/CT has been shown to predict cardiovascular (CV) events independent of traditional risk factors and is also highly associated with overall burden of atherosclerosis. Plaque activity by FDG-PET/CT is modulated by known beneficial CV interventions such as short term (12 week) statin therapy as well as longer term therapeutic lifestyle changes (16 months). The current methodology for quantification of FDG uptake in atherosclerotic plaque involves measurement of the standardized uptake value (SUV) of an artery of interest and of the venous blood pool in order to calculate a target to background ratio (TBR), which is calculated by dividing the arterial SUV by the venous blood pool SUV. This method has shown to represent a stable, reproducible phenotype over time, has a high sensitivity for detection of vascular inflammation, and also has high inter-and intra-reader reliability. Here we present our methodology for patient preparation, image acquisition, and quantification of atherosclerotic plaque activity and vascular inflammation using SUV, TBR, and a global parameter called the metabolic volumetric product (MVP). These approaches may be applied to assess vascular inflammation in various study samples of interest in a consistent fashion as we have shown in several prior publications.

Effects of age, diet, and type 2 diabetes on the development and FDG uptake of atherosclerotic plaques

OBJECTIVES

This study investigated the effects of age, duration of a high-fat diet, and type 2 diabetes on atherosclerotic plaque development and uptake of (18)F-fluorodeoxyglucose ((18)F-FDG) in 2 mouse models.

BACKGROUND

The animal's age and start time and duration of a high-fat diet have effects on plaque composition in atherosclerotic mice.

METHODS

The aortas of atherosclerotic low-density lipoprotein receptor deficient mice expressing only apolipoprotein B100 (LDLR(-/-)ApoB(100/100)) and atherosclerotic and diabetic mice overexpressing insulin-like growth factor II (IGF-II/LDLR(-/-)ApoB(100/100)) were investigated at 4, 6, and 12 months of age and older after varying durations of high-fat diet. C57BL/6N mice on normal chow served as controls. Plaque size (intima-to-media ratio), macrophage density (Mac-3 staining), and plaque uptake of (18)F-FDG were studied by means of in vivo positron emission tomography/computed tomography by ex vivo autoradiography and by histological and immunohistochemical methods.

RESULTS

From the ages of 4 to 6 months and 12 months and older, the plaque size increased and the macrophage density decreased. Compared with the controls, the in vivo imaging showed increased aortic (18)F-FDG uptake at 4 and 6 months, but not at 12 months and older. Autoradiography showed focal (18)F-FDG uptake in plaques at all time points (average plaque-to-normal vessel wall ratio: 2.4 ± 0.4, p < 0.001) with the highest uptake in plaques with high macrophage density. There were no differences in the plaque size, macrophage density, or uptake of (18)F-FDG between LDLR(-/-)ApoB(100/100) and IGF-II/LDLR(-/-)ApoB(100/100) mice at any time point.

CONCLUSIONS

The 6-month-old LDLR(-/-)ApoB(100/100) and IGF-II/LDLR(-/-)ApoB(100/100) mice demonstrated highly inflamed, large, and extensive atherosclerotic plaques after 4 months of a high-fat diet, presenting a suitable model for studying the imaging of atherosclerotic plaque inflammation with (18)F-FDG. The presence of type 2 diabetes did not confound evaluation of plaque inflammation with (18)F-FDG.

Non-invasive anatomic and functional imaging of vascular inflammation and unstable plaque

Over the last several decades, basic cardiovascular research has significantly enhanced our understanding of pathobiological processes leading to formation, progression, and complications of atherosclerotic plaques. By harnessing these advances in cardiovascular biology, imaging has advanced beyond its traditional anatomical domains to a tool that permits probing of particular molecular structures to image cellular behaviour and metabolic pathways involved in atherosclerosis. From the nascent atherosclerotic plaque to the death of inflammatory cells, several potential molecular and micro-anatomical targets for imaging with particular selective imaging probes and with a variety of imaging modalities have emerged from preclinical and animal investigations. Yet, substantive barriers stand between experimental use and wide clinical application of these novel imaging strategies. Each of the imaging modalities described herein faces hurdles-for example, sensitivity, resolution, radiation exposure, reproducibility, availability, standardization, or costs. This review summarizes the published literature reporting on functional imaging of vascular inflammation in atherosclerotic plaques emphasizing those techniques that have the greatest and/or most immediate potential for broad application in clinical practice. The prospective evaluation of these techniques and standardization of protocols by multinational networks could serve to determine their added value in clinical practice and guide their development and deployment.

Positron emission tomography in acute coronary syndromes

Several imaging techniques have been used to assess cardiac structure and function, to understand pathophysiology, and to guide clinical decision making in the setting of acute coronary syndromes (ACS). Over the last years, cardiac positron emission tomography (PET) has affirmed its role in this setting. Indeed, the combined quantitative assessment of myocardial metabolism and perfusion has allowed to better understand the functional status of infarcted and non-infarcted myocardium, thus improving our knowledge of myocardial response to necrosis. More recently, several studies, taking advantage of previous observations in patients with cancer, have shown that PET could also provide important information on the mechanisms of vascular instability through the early identification of activated inflammatory cells in the atherosclerotic plaque. These findings are opening the way to more effective forms of prevention of acute vascular syndromes in high-risk patients; furthermore, new more sensitive and specific tracers for the identification of vascular inflammation are under development. In this review, we describe the potential and limitations of PET in the assessment of ACS.

High-resolution imaging of human atherosclerotic carotid plaques with micro 18F-FDG PET scanning exploring plaque vulnerability

AIMS

FDG-PET can be used to identify vulnerable plaques in atherosclerotic disease. Clinical FDG-PET camera systems are restricted in terms of resolution for the visualization of detailed inflammation patterns in smaller vascular structures. The aim of the study is to evaluate the possible added value of a high-resolution microPET system in excised carotid plaques using FDG.

METHODS AND RESULTS

In this study, 17 patients with planned carotid endarterectomy were included. Excised plaques were incubated in FDG and subsequently imaged with microPET. Macrophage presence in plaques was evaluated semi-quantitatively by immunohistochemistry. Plaque calcification was assessed additionally with CT and correlated to FDG uptake. Finally, FDG uptake and macrophage infiltration were compared with patient symptomatology. Heterogeneous distributions and variable intensities of FDG uptake were found within the plaques. A positive correlation between the distribution of macrophages and the FDG uptake (r = 0.68, P < .01) was found. A negative correlation was found between areas of calcifications and FDG uptake (r = -0.84, P < .001). Ratio FDG(max) values as well as degree of CD68 accumulation were significantly higher in CVA patients compared with TIA or amaurosis fugax patients (P < .05) and CVA patients compared with asymptomatic patients (P < .05).

CONCLUSION

This ex vivo study demonstrates that excised carotid plaques can be visualized in detail using FDG microPET. Enhancement of clinical PET/CT resolution for similar imaging results in patients is needed.

Role of Global Disease Assessment by Combined PET-CT-MR Imaging in Examining Cardiovascular Disease

Atherosclerosis is considered a chronic inflammatory disease, and thereafter the degree of this pathologic process is considered to be a major determinant in plaque stability and in forecasting future events. Over the past decade, (18)F-fluorodeoxyglucose PET/computed tomography has become a well-established imaging modality in evaluating various inflammatory disorders, and has been shown to be very useful in evaluating plaque activity in major arteries. This emerging noninvasive imaging modality has great potential in evaluating plaque vulnerability and in predicting the risk of future rupture and consequent thrombosis.

Imaging intraplaque inflammation in carotid atherosclerosis with 11C-PK11195 positron emission tomography/computed tomography

AIMS

We sought to determine whether intraplaque inflammation could be measured with positron emission tomography/computed tomography angiography (PET/CTA) using (11)C-PK11195, a selective ligand of the translocator protein (18 kDa) (TSPO) which is highly expressed by activated macrophages.

METHODS AND RESULTS

Patients (n = 32; mean age 70 ± 9 years) with carotid stenoses (n = 36; 9 symptomatic and 27 asymptomatic) underwent (11)C-PK11195 PET/CTA imaging. (11)C-PK11195 uptake into carotid plaques was measured using target-to-background ratios (TBR). On CTA images, plaque composition was assessed by measuring CT attenuation of the carotid plaque. Eight patients underwent carotid endarterectomy and ultrathin contiguous sections were processed for TSPO and CD68 (using immunohistochemical staining, (3)H-PK11195 autoradiography, and confocal fluorescence microscopy). Carotid plaques associated with ipsilateral symptoms (stroke or transient ischaemic attack) had higher TBR (1.06 ± 0.20 vs. 0.86 ± 0.11, P = 0.001) and lower CT attenuation [(median, inter-quartile range) 37, 24-40 vs. 71, 56-125 HU, P = 0.01] than those without. On immunohistochemistry and confocal fluorescence microscopy, CD68 and PBR co-localized with (3)H-PK11195 uptake at autoradiography. There was a significant correlation between (11)C-PK11195 TBR and autoradiographic percentage-specific binding (r = 0.77, P = 0.025). Both TBR and CT plaque attenuation had high negative predictive values (91 and 92%, respectively) for detecting symptomatic patients. However, the best positive predictive value (100%) was achieved when TBR and CT attenuation were combined.

CONCLUSION

Imaging intraplaque inflammation in vivo with (11)C-PK11195 PET/CTA is feasible and can distinguish between recently symptomatic and asymptomatic plaques. Patients with a recent ischaemic event had ipsilateral plaques with lower CT attenuation and increased (11)C-PK11195 uptake.

Impact of statins on progression of atherosclerosis: rationale and design of SATURN (Study of Coronary Atheroma by InTravascular Ultrasound: effect of Rosuvastatin versus AtorvastatiN)

BACKGROUND

Previous imaging studies have demonstrated that the beneficial impact of high-dose statins on the progression of coronary atherosclerosis associates with their ability to lower levels of low-density lipoprotein cholesterol (LDL-C) and C-reactive protein (CRP) and to raise high-density lipoprotein cholesterol (HDL-C). The Study of Coronary Atheroma by InTravascular Ultrasound: Effect of Rosuvastatin versus AtorvastatiN (SATURN, NCT00620542) aims to compare the effects of high-dose atorvastatin and rosuvastatin on disease progression.

METHODS

A total of 1385 subjects with established coronary artery disease (CAD) on angiography were randomized to receive rosuvastatin 40 mg or atorvastatin 80 mg for 24 months. The primary efficacy parameter will be the nominal change in percent atheroma volume (PAV), determined by analysis of intravascular ultrasound (IVUS) images of matched coronary artery segments acquired at baseline and at 24-month follow-up. The effect of statin therapy on plasma lipids and inflammatory markers, and the incidence of clinical cardiovascular events will also be assessed. The study does not have the statistical power to directly compare the treatment groups with regard to clinical events.

CONCLUSION

Serial IVUS has emerged as a sensitive imaging modality to assess the impact of treatments on arterial structure. In this study, IVUS will be used to determine whether high-dose statins have different effects on plaque progression.

FDG PET imaging and cardiovascular inflammation

The underlying pathologic mechanism of most acute coronary syndromes is atherosclerotic plaque rupture. One cause of rupture is plaque inflammation, leading to fibrous cap destabilization. Several imaging techniques, including x-ray coronary angiography and multislice CT, can be used for the detection of coronary atherosclerosis. However, these anatomical methods cannot measure arterial inflammation. Positron emission tomography imaging of atherosclerosis using the metabolic marker fluorodeoxyglucose allows quantification of arterial inflammation across multiple vessels. This review discusses the rationale, utility, potential future applications, and limitations of this emerging biomarker of cardiovascular risk.

Noninvasive Positron Emission Tomography Imaging of Coronary Arterial Inflammation

The importance of inflammation to atherothrombosis has led to the pursuit of noninvasive imaging methods to measure inflammation within the arterial wall. There is substantial evidence supporting the use of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging for evaluation of atherosclerotic plaque inflammation. However, coronary imaging with this technique has been limited, due to several technical hurdles. Nonetheless, early experiences in coronary FDG-PET imaging have been encouraging. This review outlines the development of vascular PET imaging and its potential use for evaluation of coronary artery disease.