Quantification of inflammation within rabbit atherosclerotic plaques using the macrophage-specific CT contrast agent N1177: a comparison with 18F-FDG PET/CT and histology

Vulnerable atherosclerotic carotid plaque evaluation by ultrasound, computed tomography angiography, and magnetic resonance imaging: an overview

Ischemic syndromes associated with carotid atherosclerotic disease are often related to plaque rupture. The benefit of endarterectomy for high-grade carotid stenosis in symptomatic patients has been established. However, in asymptomatic patients, the benefit of endarterectomy remains equivocal. Current research seeks to risk stratify asymptomatic patients by characterizing vulnerable, rupture-prone atherosclerotic plaques. Plaque composition, biology, and biomechanics are studied by noninvasive imaging techniques such as magnetic resonance imaging, computed tomography, ultrasound, and ultrasound elastography. These techniques are at a developmental stage and have yet to be used in clinical practice. This review will describe noninvasive techniques in ultrasound, magnetic resonance imaging, and computed tomography imaging modalities used to characterize atherosclerotic plaque, and will discuss their potential clinical applications, benefits, and drawbacks.

Focal arterial inflammation precedes subsequent calcification in the same location: a longitudinal FDG-PET/CT study

BACKGROUND

Arterial calcium (Ca) deposition has been identified as an active inflammatory process. We sought to test the hypothesis that local vascular inflammation predisposes to subsequent arterial calcium deposition in humans.

METHODS AND RESULTS

From a hospital database, we identified 137 patients (age, 61 ± 13 years; 48.1% men) who underwent serial positron-emission tomography/computed tomography (1-5 years apart). Focal arterial inflammation was prospectively determined by measuring 18F-flourodeoxyglucose uptake (using baseline positron-emission tomography) within predetermined locations of the thoracic aortic wall and was reported as a standardized uptake value. A separate, blinded investigator evaluated calcium deposition (on the baseline and follow-up computed tomographic scans) along the same standardized sections of the aorta. New calcification was prospectively defined using square root-transformed difference of calcium volume score, with a cutoff value of 2.5. Accordingly, vascular segment was classified as either with or without subsequent calcification. Overall, 67 (9%) of aortic segments demonstrated subsequent calcification. Baseline median (interquartile range) standardized uptake value was higher in segments with versus without subsequent calcification (2.09 [1.84-2.44] versus 1.92 [1.72-2.20], P=0.002). This was also true in the subset of segments with Ca present at baseline (2.08 [1.81-2.40] versus 1.86 [1.66-2.09], P=0.02), as well as those without (2.17 [1.87-2.51] versus 1.93 [1.73-2.20], P=0.04). Furthermore, across all patients, subsequent Ca deposition was associated with the underlying 18F-flourodeoxyglucose uptake (inflammatory signal), measured as standardized uptake value (odds ratio [95% confidence interval]=2.94 [1.27-6.89], P=0.01) or target-to-background ratio (2.59 [1.18-5.70], =0.02), after adjusting for traditional cardiovascular risk factors.

CONCLUSIONS

Here, we provide first-in-man evidence that arterial inflammation precedes subsequent Ca deposition, a marker of plaque progression, within the underlying location in the artery wall.

The vulnerable coronary plaque: update on imaging technologies

Several studies have been carried out on vulnerable plaque as the main culprit for ischaemic cardiac events. Historically, the most important diagnostic technique for studying coronary atherosclerotic disease was to determine the residual luminal diameter by angiographic measurement of the stenosis. However, it has become clear that vulnerable plaque rupture as well as thrombosis, rather than stenosis, triggers most acute ischaemic events and that the quantification of risk based merely on severity of the arterial stenosis is not sufficient. In the last decades, substantial progresses have been made on optimisation of techniques detecting the arterial wall morphology, plaque composition and inflammation. To date, the use of a single technique is not recommended to precisely identify the progression of the atherosclerotic process in human beings. In contrast, the integration of data that can be derived from multiple methods might improve our knowledge about plaque destabilisation. The aim of this narrative review is to update evidence on the accuracy of the currently available non-invasive and invasive imaging techniques in identifying components and morphologic characteristics associated with coronary plaque vulnerability.

Early detection and invasive passivation of future culprit lesions: a future potential or an unrealistic pursuit of chimeras?

New advances in image and signal processing have allowed the development of numerous invasive and noninvasive imaging modalities that have revealed details of plaque pathology and allowed us to study in vivo the atherosclerotic evolution. Recent natural history of atherosclerosis studies permitted us to evaluate changes in the compositional and morphological characteristics of the plaque and identify predictors of future events. The idea of being able to identify future culprit lesions and passivate these plaques has gradually matured, and small scale studies have provided proofs about the feasibility of this concept. This review article summarizes the recent advances in the study of atherosclerosis, cites the current evidence, highlights our limitations in understanding the evolution of the plaque and in predicting plaque destabilization, and discusses the potentiality of an early invasive sealing of future culprit lesions.

CT imaging of myocardial scars with collagen-targeting gold nanoparticles

In the setting of myocardial ischemia, recovery of myocardial function by revascularization procedures depends on the extent of coronary disease and myocardial scar burden. Currently, computed tomographic (CT) imaging offers superior evaluation of coronary lesions but lacks the capability to measure the transmural extent of myocardial scar. Our work focuses on determining if collagen-targeting gold nanoparticles (AuNPs) can effectively target myocardial scar and provide adequate contrast for CT imaging. AuNPs were coated with a collagen-homing peptide, collagen adhesin (CNA35). Myocardial scar was created in mice by occlusion/reperfusion of the left anterior descending coronary artery. Thirty days later, un-gated CT imaging was performed. Over 6h, CNA35-AuNPs provided uniform and prolonged opacification of the vascular structures (100-130 HU). In mice with larger scar burden, focal contrast enhancement was detected in the myocardium, which was not apparent within that of control mice. Histological staining confirmed myocardial scar formation and accumulation of AuNPs.

FROM THE CLINICAL EDITOR

This team of investigators presents a collagen-targeting gold nanoparticle-based approach that enables the imaging of myocardial scars via CT scans in a rodent model. This information would enable clinicians to judge the recovery potential of myocardium more accurately than the current CT-scan based approaches.

Dual-energy computed tomography imaging of atherosclerotic plaques in a mouse model using a liposomal-iodine nanoparticle contrast agent

BACKGROUND

The accumulation of macrophages in inflamed atherosclerotic plaques has long been recognized. In an attempt to develop an imaging agent for detection of vulnerable plaques, we evaluated the feasibility of a liposomal-iodine nanoparticle contrast agent for computed tomography imaging of macrophage-rich atherosclerotic plaques in a mouse model.

METHODS AND RESULTS

Liposomal-iodine formulations varying in particle size and polyethylene glycol coating were fabricated and shown to stably encapsulate the iodine compound. In vitro uptake studies using optical and computed tomography imaging in the RAW 264.7 macrophage cell line identified the formulation that promoted maximal uptake. Dual-energy computed tomography imaging using this formulation in apolipoprotein E-deficient (ApoE(-/-)) mice (n=8) and control C57BL/6 mice (n=6) followed by spectral decomposition of the dual-energy images enabled imaging of the liposomes localized in the plaque. Imaging cytometry confirmed the presence of liposomes in the plaque and their colocalization with a small fraction (≈2%) of the macrophages in the plaque.

CONCLUSIONS

The results demonstrate the feasibility of imaging macrophage-rich atherosclerotic plaques using a liposomal-iodine nanoparticle contrast agent and dual-energy computed tomography.

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.

(18)F-FDG PET imaging of murine atherosclerosis: association with gene expression of key molecular markers

Aim

To study whether ¹⁸F-FDG can be used for in vivo imaging of atherogenesis by examining the correlation between ¹⁸F-FDG uptake and gene expression of key molecular markers of atherosclerosis in apoE^−/− mice.

Methods

Nine groups of apoE^−/− mice were given normal chow or high-fat diet. At different time-points, ¹⁸F-FDG PET/contrast-enhanced CT scans were performed on dedicated animal scanners. After scans, animals were euthanized, aortas removed, gamma counted, RNA extracted from the tissue, and gene expression of chemo (C-X-C motif) ligand 1 (CXCL-1), monocyte chemoattractant protein (MCP)-1, vascular cell adhesion molecule (VCAM)-1, cluster of differentiation molecule (CD)-68, osteopontin (OPN), lectin-like oxidized LDL-receptor (LOX)-1, hypoxia-inducible factor (HIF)-1α, HIF-2α, vascular endothelial growth factor A (VEGF), and tissue factor (TF) was measured by means of qPCR.

Results

The uptake of ¹⁸F-FDG increased over time in the groups of mice receiving high-fat diet measured by PET and ex vivo gamma counting. The gene expression of all examined markers of atherosclerosis correlated significantly with ¹⁸F-FDG uptake. The strongest correlation was seen with TF and CD68 (p<0.001). A multivariate analysis showed CD68, OPN, TF, and VCAM-1 to be the most important contributors to the uptake of ¹⁸F-FDG. Together they could explain 60% of the ¹⁸F-FDG uptake.

Conclusion

We have demonstrated that ¹⁸F-FDG can be used to follow the progression of atherosclerosis in apoE^−/− mice. The gene expression of ten molecular markers representing different molecular processes important for atherosclerosis was shown to correlate with the uptake of ¹⁸F-FDG. Especially, the gene expressions of CD68, OPN, TF, and VCAM-1 were strong predictors for the uptake.

Progress in atherosclerotic plaque imaging

Cardiovascular diseases are the primary cause of mortality in the industrialized world, and arterial obstruction, triggered by rupture-prone atherosclerotic plaques, lead to myocardial infarction and cerebral stroke. Vulnerable plaques do not necessarily occur with flow-limiting stenosis, thus conventional luminographic assessment of the pathology fails to identify unstable lesions. In this review we discuss the currently available imaging modalities used to investigate morphological features and biological characteristics of the atherosclerotic plaque. The different imaging modalities such as ultrasound, magnetic resonance imaging, computed tomography, nuclear imaging and their intravascular applications are illustrated, highlighting their specific diagnostic potential. Clinically available and upcoming methodologies are also reviewed along with the related challenges in their clinical translation, concerning the specific invasiveness, accuracy and cost-effectiveness of these methods.

(18)FDG PET imaging can quantify increased cellular metabolism in pulmonary arterial hypertension: A proof-of-principle study

The past decade has seen increased application of 18-flurodeoxyglucose positron emission tomography (¹⁸FDG-PET) imaging to help diagnose and monitor disease, particularly in oncology, vasculitis and atherosclerosis. Disordered glycolytic metabolism and infiltration of plexiform lesions by inflammatory cells has been described in idiopathic pulmonary arterial hypertension (IPAH). We hypothesized that increased ¹⁸FDG uptake may be present in the lungs, large pulmonary arteries and right ventricle of patients with pulmonary hypertension, and that this uptake would be related to markers of immune activation. We imaged the thorax of 14 patients with pulmonary hypertension (idiopathic and chronic thromboembolic) and six controls by ¹⁸FDG-PET/computed tomography (CT) and measured uptake in the lung parenchyma, large pulmonary arteries and right ventricle. ¹⁸FDG uptake in the lungs and pulmonary arteries was normalized for venous blood activity to give a target-to-background ratio (TBR). Blood was contemporaneously drawn for high-sensitivity CRP - C-reactive protein (CRP) (hsCRP), N-Terminal Probrain natriuteric peptide (NT-ProBNP) and other inflammatory cytokines. IPAH patients had significantly higher lung parenchymal TBR (P=0.034) and right ventricle FDG uptake (P=0.007) than controls. Uptake in the main pulmonary arteries was similar in chronic thromboembolic pulmonary hypertension, IPAH and controls. There were no correlations between ¹⁸FDG uptake and hsCRP or inflammatory cytokine levels. NT-ProBNP correlated with RV uptake in those with pulmonary hypertension (r=0.55, P=0.04). In this pilot study, we found increased ¹⁸FDG uptake in the lung parenchyma and right ventricle of subjects with IPAH. The lung uptake might be useful as a surrogate marker of increased cellular metabolism and immune activation as underlying mechanisms in this disease. Further evaluation of the impact of targeted therapies in treatment-naïve patients and the significance of right ventricular uptake is suggested.

Ultrasonographic analysis versus histopathologic evaluation of carotid advanced atherosclerotic stenosis in an experimental rabbit model

Advanced carotid atherosclerosis with severe stenosis (>70%) is a major clinical risk factor for ischemic stroke. Our ability to test new protocols for the treatment of atherosclerotic stenosis in humans is limited for obvious ethical reasons; therefore, a suitable animal model is required. The aim of this study was to generate an easily reproducible and inexpensive experimental rabbit carotid model of advanced atherosclerosis with morphological similarities to the human disease and the subsequent assessment of the reliability of B-mode ultrasound technology in the study of lumen area stenosis in this model. Briefly, New Zealand white rabbits underwent primary perivascular cold injury at the right common carotid artery followed by a 1.5% cholesterol-rich diet injury for eight weeks. All of the rabbits' arteries were imaged by B-mode ultrasound weekly, after which the rabbits were sacrificed, and their vessels were processed for histopathology. Ultrasound longitudinal view images from three cardiac cycles were processed by a new computerized analyzing method based on dynamic programming and maximum gradient algorithm for measurement of instantaneous changes in arterial wall thickness and lumen diameter in sequential ultrasound images. Histopathology results showed progressive changes, from the lipid-laden cells and fibrous connective tissue proliferation in neointimal layer, up to the fibro-lipid plaque formation, resulting in vessel wall thickening, remodeling and lumen stenosis. The B-mode ultrasound images and the histologic measurements showed an increase in the mean wall thickness and the lumen area stenosis within eight weeks. Quantitative and morphometric analysis of the mean wall thickness and the lumen area stenosis percentage showed a significant correlation between the B-mode ultrasound and the histological measurements at each time point (R = 0.989 and R = 0.995, p < 0.05, respectively). In conclusion, we successfully produced advanced atherosclerosis in the rabbit carotid artery that is similar to the condition seen in patients. This condition in rabbits can be properly assessed by B-mode ultrasound image processing.

Comparison of 18F-fluoro-deoxy-glucose, 18F-fluoro-methyl-choline, and 18F-DPA714 for positron-emission tomography imaging of leukocyte accumulation in the aortic wall of experimental abdominal aneurysms

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a frequent form of atherothrombotic disease, whose natural history is to enlarge and rupture. Indicators other than AAA diameter would be useful for preventive surgery decision-making, including positron-emission tomography (PET) methods permitting visualization of aortic wall leukocyte activation relevant to prognostic AAA evaluation. In this study, we compare three PET tracers of activated leukocytes, 18F-fluoro-deoxy-glucose (FDG), 18F-fluoro-methyl-choline (FCH), and 18F-DPA714 (a peripheral benzodiazepine receptor antagonist) for in vivo PET quantification of aortic wall inflammation in rat experimental AAAs, in correlation with histopathological studies of lesions.

METHODS

AAAs were induced by orthotopic implantation of decellularized guinea pig abdominal aorta in 46 Lewis rats. FDG-PET (n = 20), FCH-PET (n = 8), or both (n = 12) were performed 2 weeks to 4 months after the graft, 1 hour after tracer injection (30 MBq). Six rats (one of which had FDG-PET) underwent 18F-DPA714-PET. Rats were sacrificed after imaging; AAAs and normal thoracic aortas were cut into axial sections for quantitative autoradiography and histologic studies, including ED1 (macrophages) and CD8 T lymphocyte immunostaining. Ex vivo staining of AAAs and thoracic aortas with 18F-DPA714 and unlabeled competitors was performed.

RESULTS

AAAs developed in 35 out of 46 cases. FCH uptake in AAAs was lower than that of FDG in all cases on imaging, with lower AAA-to-background maximal standardized uptake value (SUV(max)) ratios (1.78 ± 0.40 vs 2.71 ± 0.54; P < .01 for SUV(max) ratios), and lower AAA-to-normal aorta activity ratios on autoradiography (3.52 ± 1.26 vs 8.55 ± 4.23; P < .005). FDG AAA-to-background SUV(max) ratios correlated with the intensity of CD8 + ED1 staining (r = .76; P < .03). FCH AAA-to-background SUV(max) ratios correlated with the intensity of ED1 staining (r = .80; P < .03). 18F-DPA714 uptake was similar in AAAs and in normal aortas, both in vivo and ex vivo.

CONCLUSIONS

In rat experimental AAA, characterized by an important aortic wall leukocytes activity, FDG-PET showed higher sensitivity than FCH-PET and 18F-DPA714-PET to detect activated leukocytes. This enhances potential interest of this tracer for prognostic evaluation of AAA in patients.

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.

Coronary arterial 18F-FDG uptake by fusion of PET and coronary CT angiography at sites of percutaneous stenting for acute myocardial infarction and stable coronary artery disease

Whether (18)F-FDG PET can detect inflammation in the coronary arteries remains controversial. We examined (18)F-FDG uptake at the culprit sites of acute myocardial infarction (AMI) after percutaneous coronary stenting (PCS) by coregistering PET and coronary CT angiography (CTA).

METHODS

Twenty nondiabetic patients with AMI (median age, 62 y; 16 men and 4 women) and 7 nondiabetic patients with stable coronary artery disease (CAD; median age, 67 y; 4 men and 3 women) underwent (18)F-FDG PET and coronary CTA 1-6 d after PCS of culprit stenoses. After a low-carbohydrate dietary preparation and more than 12 h of fasting, 480 MBq of (18)F-FDG were injected, and PET images were acquired 3 h later. Helical CTA was performed on a dual-source scanner. Stent position on attenuation-correction noncontrast CT and CTA was used to fuse PET and CTA. Two experienced readers masked to patient data independently quantified maximum target-to-background ratio (maxTBR) at each PCS site. A maxTBR greater than 2.0 was the criterion for significant uptake.

RESULTS

Compared with stable CAD patients, more AMI patients exhibited a PCS site maxTBR greater than 2.0 (12/20 vs. 1/7, P = 0.04). More AMI patients were active smokers (9/20 vs. 0/7 in stable CAD, P = 0.03). After adjusting for baseline demographic differences, stent-myocardium distance, and myocardial (18)F-FDG uptake, presentation of AMI was positively associated with a PCS site maxTBR greater than 2.0 (odds ratio, 31.6; P = 0.044). Prevalence of excess myocardial (18)F-FDG uptake was similar in both populations (8/20 AMI vs. 3/7 stable CAD, P = 0.89).

CONCLUSION

Systematic fusion of (18)F-FDG PET and coronary CTA demonstrated increased culprit site (18)F-FDG uptake more commonly in patients with AMI than in patients with stable CAD. However, this approach failed to detect increased signal at the culprit site in nearly half of AMI patients, highlighting the challenging nature of in vivo coronary artery plaque metabolic imaging. Nonetheless, our findings suggest that imaging of coronary artery inflammation is feasible, and further work evaluating (18)F-FDG uptake in high-risk coronary plaques prior to rupture would be of great interest.

Pioglitazone modulates vascular inflammation in atherosclerotic rabbits noninvasive assessment with FDG-PET-CT and dynamic contrast-enhanced MR imaging

OBJECTIVES

We sought to determine the antiatherosclerotic properties of pioglitazone using multimethod noninvasive imaging techniques.

BACKGROUND

Inflammation is an essential component of vulnerable or high-risk atheromas. Pioglitazone, a peroxisome proliferator-activated receptor-gamma agonist, possesses potent anti-inflammatory properties. We aimed to quantify noninvasively the anti-inflammatory effects of pioglitazone on atheroma using (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET)/computed tomography (CT) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI).

METHODS

Atherosclerotic plaques were induced in the aorta of 15 New Zealand white rabbits by a combination of a hyperlipidemic diet and 2 balloon endothelial denudations. Nine rabbits continued the same diet, whereas 6 rabbits received pioglitazone (10 mg/kg orally) in addition to the diet. Twelve animals underwent (18)F-FDG-PET/CT, and 15 animals underwent DCE-MRI at baseline, 1 month, and 3 months after treatment initiation. Concomitantly, serum metabolic parameters were monitored. After imaging was completed, aortic histologic analysis and correlation analysis were performed.

RESULTS

The (18)F-FDG-PET/CT imaging detected an increase in average standardized uptake value in the control group (p < 0.01), indicating progressive inflammation, whereas stable standardized uptake values were observed in the treatment group, indicating no progression. The DCE-MRI analysis detected a significant decrease in the area under the curve for the pioglitazone group (p < 0.01). Immunohistologic examination of the aortas demonstrated a significant decrease in macrophage and oxidized phospholipid immunoreactivity in the pioglitazone group (p = 0.04 and p = 0.01, respectively) with respect to control animals, underlining the imaging results. Serum metabolic parameters showed no difference between groups. Strong positive correlations between standardized uptake value and macrophage density and between area under the curve and neovessels were detected (r(2) = 0.86 and p < 0.0001, and r(2) = 0.66 and p = 0.004, respectively).

CONCLUSIONS

Both (18)F-FDG-PET/CT and DCE-MRI demonstrate noninvasively the anti-inflammatory effects of pioglitazone on atheroma. Both imaging methods seem suited to monitor inflammation in atherosclerosis.

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.

Plaque Rupture and Thrombosis Are Reduced by Lowering Cholesterol Levels and Crystallization With Ezetimibe and Are Correlated With Fluorodeoxyglucose Positron Emission Tomography

Objective—

This study evaluated effects of lipid lowering with ezetimibe on plaque burden and associated cholesterol crystallization and inflammation in a rabbit model of plaque disruption and thrombosis.

Methods and Results—

Atherosclerotic rabbits (Group I, n=10 without; Group II, n=12 with ezetimibe, 1 mg/kg per day) were pharmacologically triggered for plaque disruption. Fluorodeoxyglucose positron emission tomography, RAM 11 macrophage staining, and serum inflammatory markers detected arterial inflammation. Serum and aortic wall cholesterol levels were measured, and thrombus area was planimetered. Cholesterol crystal density on aortic surface was scored (0 to +3) by scanning electron microscopy. Serum and aortic wall cholesterol, plaque area, and thrombosis area were significantly lower in Group II versus Group I (83.4±106.4 versus 608±386 mg/dL, P =0.002; 3.12±1.40 versus 9.39±5.60 mg/g, P =0.003; 10.84±1.6 versus 17.48±1.8 mm 2 , P <0.001; and 0.05±0.15 versus 0.72±0.58 mm 2 , P =0.01, respectively). There were significant correlations between crystal density and plaque area ( r =0.75, P <0.003) and between crystal density and RAM 11 ( r =0.82, P <0.001). Scanning electron microscopy demonstrated that there were fewer crystals in Group II versus Group I (+1.2±0.61 versus +2.4±0.63, P <0.001) and less inflammation detected by fluorodeoxyglucose positron emission tomography and RAM 11 ( P <0.004 and P <0.04, respectively).

Conclusion—

Lowering cholesterol levels with ezetimibe reduced plaque burden, crystallization, and inflammation, preventing plaque disruption and thrombosis.

Emerging applications of nanotechnology for the diagnosis and management of vulnerable atherosclerotic plaques

An estimated 16 million people in the United States have coronary artery disease (CAD), and approximately 325,000 people die annually from cardiac arrest. About two-thirds of unexpected cardiac deaths occur without prior recognition of cardiac disease. A vast majority of these deaths are attributable to the rupture of 'vulnerable atherosclerotic plaques'. Clinically, plaque vulnerability is typically assessed through imaging techniques, and ruptured plaques leading to acute myocardial infarction are treated through angioplasty or stenting. Despite significant advances, it is clear that current imaging methods are insufficiently capable for elucidating plaque composition--which is a key determinant of vulnerability. Further, the exciting improvement in the treatment of CAD afforded by stenting procedures has been buffered by significant undesirable host-implant effects, including restenosis and late thrombosis. Nanotechnology has led to some potential solutions to these problems by yielding constructs that interface with plaque cellular components at an unprecedented size scale. By leveraging the innate ability of macrophages to phagocytose nanoparticles, contrast agents can now be targeted to plaque inflammatory activity. Improvements in nano-patterning procedures have now led to increased ability to regenerate tissue isotropy directly on stents, enabling gradual regeneration of normal, physiologic vascular structures. Advancements in immunoassay technologies promise lower costs for biomarker measurements, and in the near future, may enable the addition of routine blood testing to the clinician's toolbox--decreasing the costs of atherosclerosis-related medical care. These are merely three examples among many stories of how nanotechnology continues to promise advances in the diagnosis and treatment of vulnerable atherosclerotic plaques.

Vascular imaging with positron emission tomography

Atherosclerosis is an inflammatory disease that causes most myocardial infarctions, strokes and acute coronary syndromes. Despite the identification of multiple risk factors and widespread use of drug therapies, it still remains a global health concern with associated costs. Although angiography is established as the gold standard means of detecting coronary artery stenosis, it does not image the vessel wall itself, reporting only on its consequences such as luminal narrowing and obstruction. MRI and computed tomography provide more information about the plaque structure, but recently positron emission tomography (PET) imaging using [(18) F]-fluorodeoxyglucose (FDG) has been advocated as a means of measuring arterial inflammation. This results from the ability of FDG-PET to highlight areas of high glucose metabolism, a feature of macrophages within atherosclerosis, particularly in high-risk plaques. It is suggested that the degree of FDG accumulation in the vessel wall reflects underlying inflammation levels and that tracking any changes in FDG uptake over time or with drug therapy might be a way of getting an early efficacy readout for novel anti-atherosclerotic drugs. Early reports also demonstrate that FDG uptake is correlated with the number of cardiovascular risk factors and possibly even the risk of future cardiovascular events. This review will outline the evidence base, shortcomings and emerging applications for FDG-PET in vascular imaging. Alternative PET tracers and other candidate imaging modalities for measuring vascular inflammation will also be discussed.

Imaging the vulnerable plaque

Cardiovascular diseases are still the primary causes of mortality in the United States and in Western Europe. Arterial thrombosis is triggered by a ruptured atherosclerotic plaque and precipitates an acute vascular event, which is responsible for the high mortality rate. These rupture-prone plaques are called "vulnerable plaques." During the past decades, much effort has been put toward accurately detecting the presence of vulnerable plaques with different imaging techniques. In this review, we provide an overview of the currently available invasive and noninvasive imaging modalities used to detect vulnerable plaques. We will discuss the upcoming challenges in translating these techniques into clinical practice and in assigning them their exact place in the decision-making process.

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.

The year in molecular imaging

Molecular imaging aims to enable personalized medicine via imaging-specific molecular and cellular targets that are relevant to the diagnosis and treatment of disease. By providing in vivo readouts of biological detail, molecular imaging complements traditional anatomical imaging modalities to allow: 1) visualization of important disease-modulating molecules and cells in vivo; 2) serial investigations to image evolutionary changes in disease attributes; and 3) evaluation of the in vivo molecular effects of biotherapeutics. The added information garnered by molecular imaging can improve risk assessment and prognosticative studies, this is of particular benefit in the management of cardiovascular disease (CVD).

Advances in imaging angiogenesis and inflammation in atherosclerosis

Advances in imaging technology have provided powerful tools for dissecting the angiogenic and inflammatory aspects of atherosclerosis. Improved technology along with multi-modal approaches has expanded the utilisation of imaging. Recent advances provide the ability to better define structure and development of angiogenic vessels, identify relationships between inflammatory mediators and the vessel wall, validate biological effects of anti-inflammatory and anti-angiogenic drugs, delivery and/or targeting specific molecules to inflammatory regions of atherosclerotic plaques.

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.

Iodinated NanoClusters as an inhaled computed tomography contrast agent for lung visualization

Improvements to contrast media formulations may be an effective way to increase the accuracy and effectiveness of thoracic computed tomography (CT) imaging in disease evaluation. To achieve contrast enhancement in the lungs, a relatively large localized concentration of contrast media must be delivered. Inhalation offers a noninvasive alternative to intrapleural injections for local lung delivery, but effective aerosolization may deter successful imaging strategies. Here, NanoCluster technology was applied to N1177, a diatrizoic acid derivative, to formulate low density nanoparticle agglomerates with aerodynamic diameters <or=5 microm. Excipient-free N1177 NanoCluster powders were delivered to rats by insufflation or inhalation and scanned using CT up to 1 h post dose. CT images after inhalation showed a approximately 120 (HU) Hounsfield units contrast increase in the lungs, which was more than sufficient contrast for thoracic CT imaging. Lung tissue histology demonstrated that N1177 NanoClusters did not damage the lungs. NanoCluster particle engineering technology offers a novel approach to safely and efficiently disseminate high concentrations of contrast agents to the lung periphery.

Multifunctional agents for concurrent imaging and therapy in cardiovascular disease

The development of agents for the simultaneous detection and treatment of disease has recently gained significant attention. These multifunctional theranostic agents posses a number of advantages over their monofunctional counterparts, as they potentially allow for the concomitant determination of agent localization, release, and efficacy. Whereas the development of these agents for use in cancers has received the majority of the attention, their use in cardiovascular disease is steadily increasing. As such, this review summarized some of the most poignant recent advances in the development of theranostic agents for the treatment of this class of diseases.

Assessment of lung inflammation with 18F-FDG PET during acute lung injury

OBJECTIVE

The purpose of this review is to describe the current experimental and clinical data regarding the fundamentals and applications of (18)F-FDG PET during acute lung injury (ALI) and acute respiratory distress syndrome (ARDS).

CONCLUSION

Lung inflammation is a key feature of ALI. During ALI, FDG PET can be used to monitor lung neutrophils, which are essential cells in the pathophysiologic mechanisms of ALI. Pulmonary FDG kinetics are altered during experimental and human ALI and are associated with regional lung dysfunction, histologic abnormalities, and prognosis. FDG PET may be a valuable noninvasive method for gaining comprehensive understanding of the mechanisms of ALI/ARDS and for evaluating therapeutic interventions.

Macrophages heterogeneity in atherosclerosis - implications for therapy

Atherosclerosis is a chronic inflammatory disease occurring within the artery wall and is an underlying cause of cardiovascular complications, including myocardial infarction, stroke and peripheral vascular disease. Its pathogenesis involves many immune cell types with a well accepted role for monocyte/macrophages. Cholesterol-loaded macrophages are a characteristic feature of plaques and are major players in all stages of plaque development. As well as modulating lipid metabolism, macrophages secrete inflammatory cytokines, chemokines and reactive oxygen and nitrogen species that drive pathogenesis. They also produce proteases and tissue factor that contribute to plaque rupture and thrombosis. Macrophages are however heterogeneous cells and when appropriately activated, they phagocytose cytotoxic lipoproteins, clear apoptotic bodies, secrete anti-inflammatory cytokines and synthesize matrix repair proteins that stabilize vulnerable plaques. Pharmacological modulation of macrophage activity therefore represents a potential therapeutic strategy for atherosclerosis. The aim of this review is to provide an overview of the current understanding of the different macrophage subsets and their monocyte precursors, and, the implications of these subsets for atherosclerosis. This will present a foundation for highlighting novel opportunities to exploit the heterogeneity of macrophages as important diagnostic and therapeutic targets for atherosclerosis and its associated diseases.

Imaging atherosclerotic plaque inflammation by fluorodeoxyglucose with positron emission tomography: ready for prime time?

Inflammation is a determinant of atherosclerotic plaque rupture, the event leading to most myocardial infarctions and strokes. Although conventional imaging techniques identify the site and severity of luminal stenosis, the inflammatory status of the plaque is not addressed. Positron emission tomography imaging of atherosclerosis using the metabolic marker fluorodeoxyglucose allows quantification of arterial inflammation across multiple vessels. This review sets out the background and current and potential future applications of this emerging biomarker of cardiovascular risk, along with its limitations.

Low dose CT of the heart: a quantum leap into a new era of cardiovascular imaging

In 10 years, computed tomography coronary angiography (CTCA) has shifted from an investigational tool to clinical reality. Even though CT technologies are very advanced and widely available, a large body of evidence supporting the clinical role of CTCA is missing. The reason is that the speed of technological development has outpaced the ability of the scientific community to demonstrate the clinical utility of the technique. In addition, with each new CT generation, there is a further broadening of actual and potential applications. In this review we examine the state of the art on CTCA. In particular, we focus on issues concerning technological development, radiation dose, implementation, training and organisation.

Nanomedicine and Cardiovascular Disease

Nanomedicine has become an important tool in the imaging and therapy of numerous diseases. This is due, in large part, to the ability to generate multifunctional nanoagents bearing combinations of targeting, diagnostic, and therapeutic moieties, allowing for the tailoring of the properties of the synthesized nanomaterials. With respect to cardiovascular disease and its sequelae, nanomedicine has the potential to detect and treat some of the leading causes of death and disability in the developed world, including atherosclerosis, thrombosis, and myocardial infarction. As such, this review focuses on some of the most poignant examples of the utility of nanomedicine in the detection and treatment of cardiovascular disease that have been recently reported.