Imaging of atherosclerosis

CACSNet for automatic robust classification and segmentation of carotid artery calcification on panoramic radiographs using a cascaded deep learning network

Stroke is one of the major causes of death worldwide, and is closely associated with atherosclerosis of the carotid artery. Panoramic radiographs (PRs) are routinely used in dental practice, and can be used to visualize carotid artery calcification (CAC). The purpose of this study was to automatically and robustly classify and segment CACs with large variations in size, shape, and location, and those overlapping with anatomical structures based on deep learning analysis of PRs. We developed a cascaded deep learning network (CACSNet) consisting of classification and segmentation networks for CACs on PRs. This network was trained on ground truth data accurately determined with reference to CT images using the Tversky loss function with optimized weights by balancing between precision and recall. CACSNet with EfficientNet-B4 achieved an AUC of 0.996, accuracy of 0.985, sensitivity of 0.980, and specificity of 0.988 in classification for normal or abnormal PRs. Segmentation performances for CAC lesions were 0.595 for the Jaccard index, 0.722 for the Dice similarity coefficient, 0.749 for precision, and 0.756 for recall. Our network demonstrated superior classification performance to previous methods based on PRs, and had comparable segmentation performance to studies based on other imaging modalities. Therefore, CACSNet can be used for robust classification and segmentation of CAC lesions that are morphologically variable and overlap with surrounding structures over the entire posterior inferior region of the mandibular angle on PRs.

Sex-related differences in coronary and carotid vessel geometry, plaque composition and shear stress obtained from imaging

Atherosclerosis manifests itself differently in men and women with respect to plaque initiation, progression and plaque composition. The observed delay in plaque progression in women is thought to be related to the hormonal status of women. Also features associated with the vulnerability of plaques to rupture seem to be less frequently present in women compared to men. Current invasive and non-invasive imaging modalities allow for visualization of plaque size, composition and high risk vulnerable plaque features. Moreover, image based modeling gives access to local shear stress and shear stress-related plaque growth. In this review, current knowledge on sex-related differences in plaque size, composition, high risk plaque features and shear stress related plaque growth in carotid and coronary arteries obtained from imaging are summarized.

Potential Role of Somatostatin Receptor Scintigraphy for In Vivo Imaging of Vulnerable Atherosclerotic Plaques and Its Association with Myocardial Perfusion Imaging Finding: A Preliminary Study

Objectives

This study was conducted to detect atherosclerotic plaques with somatostatin receptor scintigraphy (SRS) using Tc-99m-octreotide that binds to somatostatin receptor-2.

Methods

Of the 783 patients referred for myocardial perfusion imaging (MPI), 52 underwent additional chest single-photon emission computed tomography (SPECT) with Tc-99m-octreotide and participated in this study. In addition, 43 patients who underwent Tc-99m-octreotide scan for neuroendocrine tumor (NET) also received cardiac SPECT. Angiography was performed within 1 month after SRS for 19 patients who showed intensive uptake in SRS and had cardiac risk factors.

Results

Of 52 patients who underwent MPI and SRS, 15 showed intensive cardiac uptake in SRS. Moreover, of 43 patients who were referred for NET, 4 patients had marked cardiac uptake in SRS in the heart. Nineteen patients including 12 women and 7 men aged 28 to 84 (58±8.04) years underwent coronary angiography. SRS and angiography in the left anterior descending territory were concordant in 15/19 (79%) patients, whereas only 7/15 (46%) cases had concordant MPI and angiography results. In the right coronary artery territory, SRS and angiography were concordant in 16/19 (84%) cases, while MPI and angiography were concordant in 11/15 (73%) cases. In the left circumflex artery territory, SRS and angiography were concordant in 15/19 (79%) cases, whereas MPI and angiography were concordant in 6/15 (40%) cases. In the remaining 76 patients who did not undergo coronary angiography based on cardiovascular profile and SRS, no cardiac events occurred in a follow-up of 2-11 months (7.52±2.71).

Conclusion

Tc-99m-octreotide uptake was more concordant with coronary plaques relative to MPI findings, suggesting a potential role for Tc-99m-octreotide in the evaluation of atherosclerosis.

Non-calcified active atherosclerosis plaque detection with 18F-NaF and 18F-FDG PET/CT dynamic imaging

Arterial inflammation is an indicator of atheromatous plaque vulnerability to detach and to obstruct blood vessels in the heart or in the brain thus causing heart attack or stroke. To date, it is difficult to predict the plaque vulnerability. This study was aimed to assess the behavior of 18F-sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG) uptake in the aorta and iliac arteries as a function of plaque density on CT images. We report metabolically active artery plaques associated to inflammation in the absence of calcification. 18 elderly volunteers were recruited and imaged with computed tomography (CT) and positron emission tomography (PET) with 18F-NaF and 18F-FDG. A total of 1338 arterial segments were analyzed, 766 were non-calcified and 572 had calcifications. For both 18F-NaF and 18F-FDG, the mean SUV values were found statistically significantly different between non-calcified and calcified artery segments. Clustering CT non-calcified segments, excluding blood, resulted in two clusters C1 and C2 with a mean density of 30.63 ± 5.06 HU in C1 and 43.06 ± 4.71 HU in C2 (P < 0.05), and their respective SUV were found statistically different in 18F-NaF and 18F-FDG. The 18F-NaF images showed plaques not detected on CT images, where the 18F-FDG SUV values were high in comparison to artery walls without plaques. The density on CT images alone corresponding to these plaques could be further investigated to see whether it can be an indicator of the active plaques.

Selective Imaging of Matrix Metalloproteinase-13 to Detect Extracellular Matrix Remodeling in Atherosclerotic Lesions

PURPOSE

Overexpression and activation of matrix metalloproteinase-13 (MMP-13) within atheroma increases susceptibility to plaque rupture, a major cause of severe cardiovascular complications. In comparison to pan-MMP targeting [¹⁸F]BR-351, we evaluated the potential for [¹⁸F]FMBP, a selective PET radiotracer for MMP-13, to detect extracellular matrix (ECM) remodeling in vascular plaques possessing markers of inflammation.

PROCEDURES

[¹⁸F]FMBP and [¹⁸F]BR-351 were initially assessed in vitro by incubation with en face aortae from 8 month-old atherogenic ApoE^-/- mice. Ex vivo biodistributions, plasma metabolite analyses, and ex vivo autoradiography were analogously performed 30 min after intravenous radiotracer administration in age-matched C57Bl/6 and ApoE^-/- mice under baseline or homologous blocking conditions. En face aortae were subsequently stained with Oil Red O (ORO), sectioned, and subject to immunofluorescence staining for Mac-2 and MMP-13.

RESULTS

High-resolution autoradiographic image analysis demonstrated target specificity and regional concordance to lipid-rich lesions. Biodistribution studies revealed hepatobiliary excretion, low accumulation of radioactivity in non-excretory organs, and few differences between strains and conditions in non-target organs. Plasma metabolite analyses uncovered that [¹⁸F]FMBP exhibited excellent in vivo stability (≥74% intact) while [¹⁸F]BR-351 was extensively metabolized (≤37% intact). Ex vivo autoradiography and histology of en face aortae revealed that [¹⁸F]FMBP, relative to [¹⁸F]BR-351, exhibited 2.9-fold greater lesion uptake, substantial specific binding (68%), and improved sensitivity to atherosclerotic tissue (2.9-fold vs 2.1-fold). Immunofluorescent staining of aortic en face cross sections demonstrated elevated Mac-2 and MMP-13-positive areas within atherosclerotic lesions identified by [¹⁸F]FMBP ex vivo autoradiography.

CONCLUSIONS

While both radiotracers successfully identified atherosclerotic plaques, [¹⁸F]FMBP showed superior specificity and sensitivity for lesions possessing features of destructive plaque remodeling. The detection of ECM remodeling by selective targeting of MMP-13 may enable characterization of high-risk atherosclerosis featuring elevated collagenase activity.

Recent advances in nanomaterials for therapy and diagnosis for atherosclerosis

Atherosclerosis is a chronic inflammatory disease driven by lipid accumulation in arteries, leading to narrowing and thrombosis. It affects the heart, brain, and peripheral vessels and is the leading cause of mortality in the United States. Researchers have strived to design nanomaterials of various functions, ranging from non-invasive imaging contrast agents, targeted therapeutic delivery systems to multifunctional nanoagents able to target, diagnose, and treat atherosclerosis. Therefore, this review aims to summarize recent progress (2017-now) in the development of nanomaterials and their applications to improve atherosclerosis diagnosis and therapy during the preclinical and clinical stages of the disease.

Advances in Multimodality Carotid Plaque Imaging: AJR Expert Panel Narrative Review

Contemporary imaging methods provide detailed visualization of carotid athero-sclerotic plaque, enabling a major evolution of in vivo carotid plaque imaging evaluation. The degree of luminal stenosis in the carotid artery bifurcation, as assessed by ultrasound, has historically served as the primary imaging feature for determining ischemic stroke risk and the potential need for surgery. However, stroke risk may be more strongly driven by the presence of specific characteristics of vulnerable plaque, as visualized on CT and MRI, than by traditional ultrasound-based assessment of luminal narrowing. This review highlights six promising imaging-based plaque characteristics that harbor unique information regarding plaque vulnerability: maximum plaque thickness and volume, calcification, ulceration, intraplaque hemorrhage, lipid-rich necrotic core, and thin or ruptured fibrous cap. Increasing evidence supports the association of these plaque characteristics with risk of ischemic stroke, although these characteristics have varying suitability for clinical implementation. Key aspects of CT and MRI protocols for carotid plaque imaging are also considered. Practical next steps and hurdles are explored for implementing routine imaging assessment of these plaque characteristics in addition to, or even as replacement for, traditional assessment of the degree of vascular stenosis on ultrasound, in the identification of individuals at high risk of ischemic stroke.

Cardiac computed tomography radiomics: an emerging tool for the non-invasive assessment of coronary atherosclerosis

In the last decades, significant advances have been made in the preventive approaches to cardiovascular disease. Even so, coronary artery disease remains one of the main causes of morbidity and mortality worldwide. Invasive imaging modalities, such as intravascular ultrasound or optical coherence tomography, have played a key role in the comprehension of the pathological processes underlying myocardial infarction and cerebrovascular disease. These imaging techniques have contributed greatly to the identification and phenotyping of the culprit lesion, the so-called vulnerable plaque. Coronary computed tomographic angiography (CCTA) has emerged in more recent years as the non-invasive modality of choice in the study of coronary atherosclerosis, showing in many studies a diagnostic yield comparable to invasive approaches. Moreover, being able to describe extra-luminal characteristics of the affected vessel, CCTA has greatly contributed towards shifting the attention of researchers from the mere quantification of luminal stenosis to the identification of adverse plaque features, which appear to have a stronger prognostic value. However, the identification of some of the hallmarks of vulnerable plaques is qualitative in nature and, therefore, subject to some degree of inter-reader variability. Moreover, CCTA is still unable to identify some fine markers of plaque vulnerability which can be detected by invasive techniques, such as neovascularization and plaque erosion, among others. Nonetheless, radiological images can be viewed as vast 3-D datasets which, via the use of recent technology, allow for the extraction of numerous quantitative features that may be used to accurately phenotype a given lesion. Radiomics is the process of extrapolating innumerable parameters from a given region of interest, with the goal of establishing correlations between quantitative variables and clinical data. These datasets can then be manipulated to create predictive models via the use of automated algorithms in a process called machine learning. As a result of these approaches, radiological images may offer information regarding the characterization of a plaque which can go much beyond the boundaries of what can be qualitatively asserted by the human eye, contributing to expanding the knowledge of the disease and ultimately assist clinical decisions. Thus far, radiomics has found its more consistent area of application in the field of oncology; to present date, the amount of clinical data regarding coronary artery disease is still relatively small, partly due to the technical difficulties associated with the implementation of such techniques to the study of a small and geometrically complex lesion such as the coronary plaque. The present review, after a summary of the imaging modalities most commonly used nowadays in the study of coronary plaques, will provide a perspective on the application of radiomic analysis to coronary artery disease.

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

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

Mechanistic Insights into the Oxidized Low-Density Lipoprotein-Induced Atherosclerosis

Dyslipidaemia has a prominent role in the onset of notorious atherosclerosis, a disease of medium to large arteries. Atherosclerosis is the prime root of cardiovascular events contributing to the most considerable number of morbidity and mortality worldwide. Factors like cellular senescence, genetics, clonal haematopoiesis, sedentary lifestyle-induced obesity, or diabetes mellitus upsurge the tendency of atherosclerosis and are foremost pioneers to definitive transience. Accumulation of oxidized low-density lipoproteins (Ox-LDLs) in the tunica intima triggers the onset of this disease. In the later period of progression, the build-up plaques rupture ensuing thrombosis (completely blocking the blood flow), causing myocardial infarction, stroke, and heart attack, all of which are common atherosclerotic cardiovascular events today. The underlying mechanism is very well elucidated in literature but the therapeutic measures remains to be unleashed. Researchers tussle to demonstrate a clear understanding of treating mechanisms. A century of research suggests that lowering LDL, statin-mediated treatment, HDL, and lipid-profile management should be of prime interest to retard atherosclerosis-induced deaths. We shall brief the Ox-LDL-induced atherogenic mechanism and the treating measures in line to impede the development and progression of atherosclerosis.

Association between periodontal disease and vulnerable plaque morphology in patients undergoing carotid endarterectomy

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Periodontal disease is associated with echolucent plaques.

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Periodontal disease is associated with increased macrophages in plaques.

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Periodontal disease is associated with decreased smooth muscle cells in plaques.

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Periodontal disease is associated with plaque instability.

Background

Periodontal disease (PD) is a chronic inflammatory oral condition with potentially important systemic sequelae. We sought to determine whether the presence of PD in patients with severe carotid disease was associated with morphological features consistent with carotid plaque instability.

Methods

A total of 52 dentate patients hospitalized for carotid endarterectomy (CEA) had standardized assessments of their periodontal status, including measurements of probing pocket depth (PPD), clinical attachment level (CAL) and bleeding on probing (BoP). Carotid plaque morphology was assessed by ultrasound using the gray scale median (GSM) score and by immunohistochemistry using anti-CD68 and anti-alpha-actin antibodies, markers for macrophages and smooth muscle cells (SMCs) respectively.

Results

In total 30/52 patients (58%) had PD. Significant associations were noted between low GSM on ultrasound and each mm in PPD (p = 0.001), each mm in CAL (p = 0.002) and with a 10% increase in BoP (p = 0.009). Using the standardized PERIO definition the association remained robust (aOR = 10.4 [95% CI:2.3–46.3], p = .002). Significant associations were also observed with high macrophage accumulation and each individual PD measure (p < 0.01 for PPD, CAL and BoP) and with the PERIO definition (aOR = 15 [95% CI:1.8–127.8], p = .01). Similarly, low SMC density was also significantly associated with individual measures of PD (p < 0.05 for PPD, CAL and BoP), but not with the PERIO definition (aOR 3.4 [95% CI:0.9–12.8], p = .07).

Conclusions

The presence of PD was significantly associated with both ultrasound and immunohistochemistry features of carotid plaque instability in patients undergoing CEA.

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

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

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Intracranial arterial wall imaging: Techniques, clinical applicability, and future perspectives

Purpose

To review the current state of the art and future development of intracranial vessel wall imaging.

Methods

Recent literature review and expert opinion about intracranial arterial wall imaging.

Results

Intracranial large artery diseases represent an important cause of stroke and vascular cognitive impairment worldwide. Our traditional understanding of intracranial large artery diseases is based on the observation of luminal narrowing or occlusion with angiographic or ultrasound techniques. Recently, novel imaging techniques have made the intracranial artery wall accessible for noninvasive visualization. The main advantage of vessel-wall imaging as compared to conventional imaging techniques for visualization of intracranial arteries is the ability to detect vessel wall changes even before they get to cause any significant luminal stenosis. This diagnostic capacity is provoking a revolutionary change in the way we see the intracranial circulation. In this article, we will review the current state of magnetic resonance imaging and computed tomography-based intracranial arterial wall imaging, focusing on technical considerations and their clinical applicability. Moreover, we will provide the readers with our vision on the future development of vessel-wall imaging techniques.

Conclusion

Intracranial arterial wall imaging methods are gaining increasing potential to impact the diagnosis and treatment of patients with cerebrovascular diseases.

Translocator protein localises to CD11b+ macrophages in atherosclerosis

BACKGROUND AND AIMS

Atherosclerosis is characterized by lipid deposition, monocyte infiltration and foam cell formation in the artery wall. Translocator protein (TSPO) is abundantly expressed in lipid rich tissues. Recently, TSPO has been identified as a potential diagnostic tool in cardiovascular disease. The purpose of this study was to determine if the TSPO ligand, ¹⁸F-PBR111, can identify early atherosclerotic lesions and if TSPO expression can be used to identify distinct macrophage populations during lesion progression.

METHODS

ApoE^-/- mice were maintained on a high-fat diet for 3 or 12 weeks. C57BL/6J mice maintained on chow diet served as controls. Mice were administered ¹⁸F-PBR111 intravenously and PET/CT imaged. After euthanasia, aortas were isolated, fixed and optically cleared. Cleared aortas were immunostained with DAPI, and fluorescently labelled with antibodies to TSPO, the tissue resident macrophage marker F4/80 and the monocyte-derived macrophage marker CD11b. TSPO expression and the macrophage markers were visualised in fatty streaks and established plaques by light sheet microscopy.

RESULTS

While tissue resident F4/80 ⁺ macrophages were evident in the arteries of animals without atherosclerosis, no CD11b ⁺ macrophages were observed in these animals. In contrast, established plaques had high CD11b and low F4/80 expression. A ∼3-fold increase in the uptake of 18F-PBR111 was observed in the aortas of atherosclerotic mice relative to controls.

CONCLUSIONS

Imaging of TSPO expression is a new approach for studying atherosclerotic lesion progression and inflammatory cell infiltration. The TSPO ligand, ¹⁸F-PBR111, is a potential clinical diagnostic tool for the detection and quantification of atherosclerotic lesion progression in humans.

Assessment of artery calcification in atherosclerosis with dynamic 18F-FDG-PET/CT imaging in elderly subjects

Glucose metabolism in atherosclerotic arteries has been shown to be an indicator of inflammation, which might be a precursor of plaque rupture. In this prospective study, we assessed the correlation between artery calcification and glucose metabolism by means of 18F-FDG PET/CT imaging in elderly subjects. Nineteen elderly subjects, with age ranging from 65 to 85 years, underwent CT and dynamic 18F-FDG-PET imaging. The artery calcification was determined with a threshold of 130 Hounsfield units. Intensity of calcification and ratio of calcification area to total artery area were classified in four sequential classes from CT images. The CT artery images were also classified as having single or multi-spot calcifications. Their respective glucose metabolism was assessed with fractional uptake rate (FUR). Factor analysis was used in this study to separate blood images from tissue to extract the blood time activity curves for FUR calculations. The artery images in PET data were corrected for partial volume effect. The total arterial segments analyzed were 1332, with 1085 without calcification (81%), 247 (19%) with calcification, and 94 segments were having multi-spot of calcifications. There was a statistically significant difference in FUR values between non-calcified to calcified segments and between subjects under medication to non-medication when comparing the subjects based on calcification area. No statistically significant differences of FUR were found between single spot as a function of intensity, while in the multi-spots, there was a statistically significant difference for all artery segments. Metabolism activity varies for non-calcified to calcified segments. Based on the metabolic activity represented by FUR, calcifications in multi-spots have different effects than in single spots.

Diagnostic imaging in the management of patients with metabolic syndrome

Metabolic syndrome (MetS) is the constellation of metabolic risk factors that might foster development of type 2 diabetes and cardiovascular disease. Abdominal obesity and insulin resistance play a prominent role among all metabolic traits of MetS. Because intervention including weight loss can reduce these morbidity and mortality in MetS, early detection of the severity and complications of MetS could be useful. Recent advances in imaging modalities have provided significant insight into the development and progression of abdominal obesity and insulin resistance, as well as target organ injuries. The purpose of this review is to summarize advances in diagnostic imaging modalities in MetS that can be applied for evaluating each components and target organs. This may help in early detection, monitoring target organ injury, and in turn developing novel therapeutic target to alleviate and avert them.

Plaque Characteristics of Patients with Symptomatic Mild Carotid Artery Stenosis

BACKGROUND

Carotid revascularization may be considered for severe stenosis, but its use for symptomatic mild stenosis (<50%) with vulnerable plaque or ulcer remains uncertain. The characteristics of patients with symptomatic mild stenosis who underwent revascularization are reviewed.

METHODS

The subjects of this study were 18 patients with symptomatic mild stenosis (<50%) on angiography from among 175 patients who underwent revascularization in our department. The plaques were evaluated by black-blood magnetic resonance imaging (BB-MRI) and ultrasonography (US) and classified into 2 types: type 1 (n = 15), a lesion with an ulcer or mobile plaque or thrombosis on angiography or US; and type 2 (n = 3), a lesion without any of the above. Fourteen patients underwent carotid endarterectomy (CEA), and 4 patients underwent carotid artery stenting.

RESULTS

The stenosis on angiography was 27.2% ± 10.7 (5%-41%), and the area carotid artery stenosis rate on US was 69.8 ± 14.5% (44.5%-97%). The stenosis rate of these 2 methods was not at all correlated. In type 1 plaque that underwent CEA, 10 of 11 patients had vulnerable plaque by histopathology, and 1 patient had thrombus on the plaque by operative findings. In type 2 plaque that underwent CEA, all patients had vulnerable plaque by histopathology. During the follow-up period, none of the patients had restenosis or stroke.

CONCLUSIONS

The findings of US and BB-MRI in patients with symptomatic mild stenosis (<50%) on angiography are important for determining treatment. If BB-MRI or US shows the findings of vulnerable plaque in mild stenosis, surgical treatment may be considered for these patients.

Carotid atherosclerotic plaques standardised uptake values: software challenges and reproducibility

BACKGROUND

Positron emission tomography-computed tomography (PET-CT) carotid standardised uptake values (SUV) of 18F-fluorodeoxyglucose (18FDG) have been proposed as an inflammatory biomarker for determining cerebrovascular diseases such as stroke. Consideration of varying methodological approaches and software packages is critical to the calculation of accurate SUVs in cross-sectional and longitudinal patient studies. The aim of this study was to investigate whether or not carotid atherosclerotic plaque SUVs are consistent and reproducible between software packages. 18FDG-PET SUVs of carotids were taken in 101 patients using two different software packages. Quality assurance checks were performed to standardise techniques before commencing the analysis where data from five to seven anatomical sites were measured. A total of ten regions of interest were drawn on each site analysed. Statistical analyses were then performed to compare SUV measurements from the two software packages and to explore reproducibility of measurements. Lastly, the time taken to complete each analysis was measured and compared.

RESULTS

Statistically significant differences in SUV measurements, between the two software packages, ranging from 9 to 21.8% were found depending on ROI location. In 79% (n = 23) of the ROI locations, the differences between the SUV measurements from each software package were found to be statistically significant. The time taken to perform the analyses and export data from the software packages also varied considerably.

CONCLUSIONS

This study highlights the importance of standardising all aspects of methodological approaches to ensure accuracy and reproducibility. Physicians must be aware that when a PET-CT data set is analysed, subsequent follow-ups must be verified, if possible, with the same software package or cross-calibration between packages should be performed.

Characteristics and Outcomes of Vertebrobasilar Artery Dissection with Accompanied Atherosclerosis

Background

With the popularity of MRI use, vertebrobasilar artery dissection (VBD) has been found more frequently in patients with posterior circulation ischemic stroke (PCS). The relationship between VBD and atherosclerosis is unknown. The present study aimed to prove the hypothesis that PCS with pure VBD (p-VBD) and with VBD and accompanied cervical or cerebral artery atherosclerosis (a-VBD) have distinct manifestations.

Methods

Patients with VBD-related PCS who were prospectively enrolled in the Taipei Veterans General Hospital Stroke Registry between January 1, 2010 and August 31, 2014 were recruited for the present study. Patients who had (1) atherosclerotic plaques with or without stenotic flow in cervical arteries on Duplex ultrasonography or (2) focal >30% stenosis in cerebral arteries other than the dissecting region (usually in arterial bifurcations which are prone to atheroma formation) on brain MRA were defined as a-VBD.

Results

There were 91 patients (67 [73.6%] males, mean age 65.5 years [SD = 15.2, range, 21–91]) with VBD-related PCS recruited for the present study; 31 were a-VBD and 60 were p-VBD. The results showed that there were significant differences in onset age, frequency of cigarette smoking, dissecting vascular involvement, and infarct locations between the 2 groups. In addition, compared with p-VBD, the a-VBD group had poorer functional recovery at 3 months and 1 year, respectively, which was independent of age, sex, vascular risk factors, stroke severity at admission, and treatment options.

Conclusion

VBD-related PCS with and without accompanied atherosclerosis had different manifestations and should be regarded as distinct arterial diseases.

Vessel wall characterization using quantitative MRI: what's in a number?

The past decade has witnessed the rapid development of new MRI technology for vessel wall imaging. Today, with advances in MRI hardware and pulse sequences, quantitative MRI of the vessel wall represents a real alternative to conventional qualitative imaging, which is hindered by significant intra- and inter-observer variability. Quantitative MRI can measure several important morphological and functional characteristics of the vessel wall. This review provides a detailed introduction to novel quantitative MRI methods for measuring vessel wall dimensions, plaque composition and permeability, endothelial shear stress and wall stiffness. Together, these methods show the versatility of non-invasive quantitative MRI for probing vascular disease at several stages. These quantitative MRI biomarkers can play an important role in the context of both treatment response monitoring and risk prediction. Given the rapid developments in scan acceleration techniques and novel image reconstruction, we foresee the possibility of integrating the acquisition of multiple quantitative vessel wall parameters within a single scan session.

Comparison of CT and CMR for detection and quantification of carotid artery calcification: the Rotterdam Study

BACKGROUND

Carotid artery atherosclerosis is an important risk factor for stroke. As such, quantitative imaging of carotid artery calcification, as a proxy of atherosclerosis, has become a cornerstone of current stroke research. Yet, population-based data comparing the computed tomography (CT) and cardiovascular magnetic resonance (CMR) for the detection and quantification of calcification remain scarce.

METHODS

A total of 684 participants from the population-based Rotterdam Study underwent both a CT and CMR of the carotid artery bifurcation to quantify the amount of carotid artery calcification (mean interscan interval: 4.9 ± 1.2 years). We investigated the correlation between the amount of calcification measured on CT and CMR using Spearman's correlation coefficient, Bland-Altman plots, and linear regression. In addition, using logistic regression modeling, we assessed the association of CT and CMR based calcification volumes with a history of stroke.

RESULTS

We found a strong correlation between CT and CMR based calcification volumes (Spearman's correlation coefficient:0.86, p-value ≤0.01). Bland-Altman analyses showed a good agreement, though CT based calcification volumes were systematically larger. Finally, calcification volume assessed with either imaging modality was associated with a history of stroke with similar effect estimates (odds ratio (OR) per 1-SD increase in calcification volume: 1.52 (95% CI:1.00;2.30) for CT, and 1.47 (95% CI:1.01;2.14) for CMR.

CONCLUSION

CT based and CMR based volumes of carotid artery calcification are highly correlated, but CMR based calcification is systematically smaller than those obtained with CT. Despite this difference, both provide comparable information with regard to a history of stroke.

Assessment of Coronary Plaque Vulnerability in Acute Coronary Syndromes using Optical Coherence Tomography and Intravascular Ultrasound. A Systematic Review

The aim of this systematic review was to analyze studies characterizing vulnerable coronary plaques using optical coherence tomography (OCT) and intravascular ultrasound (IVUS), in order to identify the most efficient invasive technique permitting plaque characterization in patients with acute myocardial infarction.

Method: A total number of 432 studies were identified, 420 through database searching and 12 through manual searching. Eight duplicate studies were removed, leaving a total number of 424 studies to be screened. Twenty-six studies only available in Abstract-only form were excluded, resulting in 398 studies checked for eligibility. Eleven studies fulfilled the eligibility criteria and were included in this systematic analysis. Plaque vulnerability was investigated in plaques with thin cap fibroatheroma (TCFA) versus those with thick cap fibroatheroma, in ruptured coronary plaques versus non-ruptured coronary plaques, in culprit versus non-culprit lesions and in lipid-rich versus non-lipid-rich plaques.

Results: A total of 1,568 coronary plaques in 1,225 patients with acute coronary syndromes (ACS) who underwent both IVUS and OCT for analysis of plaque features were included in the final analysis. The review identified the following IVUS-derived features as significantly correlated with plaque vulnerability: plaque burden (p <0.001), remodeling index (p <0.001), external elastic membrane cross-sectional area (p <0.001), and the amount of necrotic core (p <0.001), while OCT-derived features characterizing unstable plaque were TCFA (p <0.001), lipid arch (p <0.001), accumulation of macrophages (p = 0.03), and presence of intracoronary thrombus (p <0.001).

Conclusion: Both IVUS and OCT are invasive imaging techniques able to provide relevant information on the vulnerability of coronary atheromatous plaques, identifying, as they do, various plaque features significantly associated with unstable plaques. Information provided by the two techniques is complementary, and both methods can serve as a useful clinical diagnostic tool, especially in cases of ACS patients undergoing a revascularization procedure.

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

INTRODUCTION

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

SOURCES OF DATA

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

AREAS OF AGREEMENT

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

AREAS OF CONTROVERSY

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

GROWING POINTS

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

AREAS TIMELY FOR DEVELOPING RESEARCH

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

In Vivo Targeting and Imaging of Atherosclerosis Using Multifunctional Virus-Like Particles of Simian Virus 40

Atherosclerosis is a leading cause of death globally. Targeted imaging and therapeutics are desirable for the detection and treatment of the disease. In this study, we developed trifunctional Simian virus 40 (SV40)-based nanoparticles for in vivo targeting and imaging of atherosclerotic plaques. These novel trifunctional SV40-based nanoparticles encapsulate near-infrared quantum dots and bear a targeting element and a drug component. Using trifunctional SV40-based nanoparticles, we were able to noninvasively fluorescently image atherosclerotic plaques in live intact ApoE(-/-) mice. Near-infrared quantum dots encapsulated in the SV40 virus-like particles showed prominent optical properties for in vivo imaging. When different targeting peptides for vascular cell adhesion molecule-1, macrophages, and fibrin were used, early, developmental, and late stages of atherosclerosis could be targeted and imaged in live intact ApoE(-/-) mice, respectively. Targeted SV40 virus-like particles also delivered an increased concentration of the anticoagulant drug Hirulog to atherosclerosis plaques. Our study provides novel SV40-based nanoparticles with multivalency and multifunctionality suitable for in vivo imaging, molecular targeting, and drug delivery in atherosclerosis.

Longitudinal imaging of the ageing mouse

Several non-invasive imaging techniques are used to investigate the effect of pathologies and treatments over time in mouse models. Each preclinical in vivo technique provides longitudinal and quantitative measurements of changes in tissues and organs, which are fundamental for the evaluation of alterations in phenotype due to pathologies, interventions and treatments. However, it is still unclear how these imaging modalities can be used to study ageing with mice models. Almost all age related pathologies in mice such as osteoporosis, arthritis, diabetes, cancer, thrombi, dementia, to name a few, can be imaged in vivo by at least one longitudinal imaging modality. These measurements are the basis for quantification of treatment effects in the development phase of a novel treatment prior to its clinical testing. Furthermore, the non-invasive nature of such investigations allows the assessment of different tissue and organ phenotypes in the same animal and over time, providing the opportunity to study the dysfunction of multiple tissues associated with the ageing process. This review paper aims to provide an overview of the applications of the most commonly used in vivo imaging modalities used in mouse studies: micro-computed-tomography, preclinical magnetic-resonance-imaging, preclinical positron-emission-tomography, preclinical single photon emission computed tomography, ultrasound, intravital microscopy, and whole body optical imaging.

Optoacoustic Imaging of Human Vasculature: Feasibility by Using a Handheld Probe

Purpose To investigate whether multispectral optoacoustic tomography (MSOT) developed for deep-tissue imaging in humans could enable the clinical assessment of major blood vessels and microvasculature. Materials and Methods The study was approved by the Institutional Review Board of the University Medical Center Groningen (CCMO-NL-43587) and registered in the Dutch National Trial Registry (NTR4125). The authors designed a real-time handheld optoacoustic scanner for human use, based on a concave 8-MHz transducer array, attaining 135° angular coverage. They applied a single-pulse-frame (SPF) sequence, which enabled motion insensitive optoacoustic imaging during handheld operation. SPF optoacoustic imaging was applied to imaging arteries and microvascular landmarks in the lower extremities of 10 healthy volunteers. The diameters selected microvessels were determined by measuring the full width at half maximum through the vessels in the MSOT images. Duplex ultrasonography was performed on the same landmarks in seven of the 10 volunteers for subjective comparison to the corresponding optoacoustic images. Results Optoacoustic imaging resolved blood vessels as small as 100 µm in diameter and within 1 cm depth. Additionally, MSOT provided images reflecting hemoglobin oxygen saturation in blood vessels, clearly identifying arteries and veins, and was able to identify pulsation in arteries during imaging. Larger blood vessels, specifically the tibialis posterior and the dorsalis pedis arteries, were also visualized with MSOT. Conclusion Handheld MSOT was found to be capable of clinical vascular imaging, providing visualization of major blood vessels and microvasculature and providing images of hemoglobin oxygen saturation and pulsation. (©) RSNA, 2016.

Quantitative Assessment of Abdominal Aortic Calcifications Using Lateral Lumbar Radiograph, Dual-Energy X-ray Absorptiometry, and Quantitative Computed Tomography of the Spine

Abdominal aortic calcifications (AACs) represent an independent determinant of cardiovascular events and are strongly associated with cardiovascular disease. To our knowledge, a comparison between lateral lumbar radiography, lateral spine dual-energy x-ray absorptiometry (DXA), and quantitative computed tomography (QCT) in the assessment of AAC has not been performed. Our objective was to compare those methods in the detection and quantification of AAC using a simplified 8-point score system (AAC-8). Three hundred twenty-three postmenopausal women underwent lateral lumbar radiography, lateral spine DXA, and QCT for osteoporosis screening and were scored for AAC using the AAC-8. Lateral lumbar radiographs, lateral spine DXA, and QCT detected AAC in 58%, 55%, and 60% of the subjects, respectively. The nonparametric intraclass correlation coefficient between lateral lumbar radiograph and lateral spine DXA and lateral lumbar radiograph and QCT were 0.699 (95% confidence interval [CI]: 0.638-0.752) and 0.829 (95% CI: 0.783-0.865). Area under operating curve (receiver operating characteristic [ROC]) for lateral spine DXA was 0.826 (95% CI: 0.764-0.888), whereas for QCT was 0.948 (95% CI: 0.922-0.974) considering lateral lumbar radiograph as gold standard. AAC has been shown to be a significant predictive marker of overall cardiovascular disease. DXA may be a screening tool among asymptomatic patients with low radiation exposure to identify an important cardiovascular disease risk factor. QCT represents a reliable technique that may be applied as a future standard to facilitate the detection of abdominal aortic calcification as well as to provide more accurate measurement of bone densitometry.

Cardiovascular imaging: what have we learned from animal models?

Cardiovascular imaging has become an indispensable tool for patient diagnosis and follow up. Probably the wide clinical applications of imaging are due to the possibility of a detailed and high quality description and quantification of cardiovascular system structure and function. Also phenomena that involve complex physiological mechanisms and biochemical pathways, such as inflammation and ischemia, can be visualized in a non-destructive way. The widespread use and evolution of imaging would not have been possible without animal studies. Animal models have allowed for instance, (i) the technical development of different imaging tools, (ii) to test hypothesis generated from human studies and finally, (iii) to evaluate the translational relevance assessment of in vitro and ex-vivo results. In this review, we will critically describe the contribution of animal models to the use of biomedical imaging in cardiovascular medicine. We will discuss the characteristics of the most frequent models used in/for imaging studies. We will cover the major findings of animal studies focused in the cardiovascular use of the repeatedly used imaging techniques in clinical practice and experimental studies. We will also describe the physiological findings and/or learning processes for imaging applications coming from models of the most common cardiovascular diseases. In these diseases, imaging research using animals has allowed the study of aspects such as: ventricular size, shape, global function, and wall thickening, local myocardial function, myocardial perfusion, metabolism and energetic assessment, infarct quantification, vascular lesion characterization, myocardial fiber structure, and myocardial calcium uptake. Finally we will discuss the limitations and future of imaging research with animal models.

Non-invasive imaging and cellular tracking of pulmonary emboli by near-infrared fluorescence and positron-emission tomography

Functional imaging of proteolytic activity is an emerging strategy to quantify disease and response to therapy at the molecular level. We present a new peptide-based imaging probe technology that advances these goals by exploiting enzymatic activity to deposit probes labelled with near-infrared (NIR) fluorophores or radioisotopes in cell membranes of disease-associated proteolysis. This strategy allows for non-invasive detection of protease activity in vivo and ex vivo by tracking deposited probes in tissues. We demonstrate non-invasive detection of thrombin generation in a murine model of pulmonary embolism using our protease-activated peptide probes in microscopic clots within the lungs with NIR fluorescence optical imaging and positron-emission tomography. Thrombin activity is imaged deep in tissue and tracked predominantly to platelets within the lumen of blood vessels. The modular design of our probes allows for facile investigation of other proteases, and their contributions to disease by tailoring the protease activation and cell-binding elements.

Functional imaging of proteolytic activity is an emerging strategy to guide patient diagnosis and monitor clinical outcome. Here the authors present a peptide-based probe to detect and localize thrombin activity ex vivo and non-invasively in mouse models of wounding and pulmonary thrombosis.

SPECT/CT Imaging of High-Risk Atherosclerotic Plaques using Integrin-Binding RGD Dimer Peptides

Vulnerable atherosclerotic plaques with unique biological signatures are responsible for most major cardiovascular events including acute myocardial infarction and stroke. However, current clinical diagnostic approaches for atherosclerosis focus on anatomical measurements such as the degree of luminal stenosis and wall thickness. An abundance of neovessels with elevated expression of integrin αvβ3 is closely associated with an increased risk of plaque rupture. Herein we evaluated the potential of an αvβ3 integrin-targeting radiotracer, (99m)Tc-IDA-D-[c(RGDfK)]2, for SPECT/CT imaging of high-risk plaque in murine atherosclerosis models. In vivo uptake of (99m)Tc-IDA-D-[c(RGDfK)]2 was significantly higher in atherosclerotic aortas than in relatively normal aortas. Comparison with the negative-control peptide, (99m)Tc-IDA-D-[c(RADfK)]2, proved specific binding of (99m)Tc-IDA-D-[c(RGDfK)]2 for plaque lesions in in vivo SPECT/CT and ex vivo autoradiographic imaging. Histopathological characterization revealed that a prominent SPECT signal of (99m)Tc-IDA-D-[c(RGDfK)]2 corresponded to the presence of high-risk plaques with a large necrotic core, a thin fibrous cap, and vibrant neoangiogenic events. Notably, the RGD dimer based (99m)Tc-IDA-D-[c(RGDfK)]2 showed better imaging performance in comparison with the common monomeric RGD peptide probe (123)I-c(RGDyV) and fluorescence tissue assay corroborated this. Our preclinical data demonstrated that (99m)Tc-IDA-D-[c(RGDfK)]2 SPECT/CT is a sensitive tool to noninvasively gauge atherosclerosis beyond vascular anatomy by assessing culprit plaque neovascularization.

Coexistence of Calcification, Intraplaque Hemorrhage and Lipid Core within the Asymptomatic Atherosclerotic Carotid Plaque: The Rotterdam Study

Background: There is a growing amount of evidence suggesting that the composition of carotid atherosclerotic plaques may be of clinical relevance. Yet, little is known on the coexistence of potentially vulnerable and stabilizing components within asymptomatic plaques. Therefore, in this study we set out to investigate the coexistence of intraplaque calcification, hemorrhage and lipid core within the carotid artery using a multi-modality imaging approach. Methods: In 329 subjects from the population-based Rotterdam Study, all with ultrasound-confirmed carotid wall thickening, we performed a multi-detector CT and a high-resolution MRI of the carotid artery bifurcation at both sides. On the CT examinations, we quantified the volume of intraplaque calcification, and using the MRI examinations we rated the presence of intraplaque hemorrhage and of lipid core. In total, we investigated 611 carotid arteries with plaques. With logistic regression models we investigated the relationship of calcification volume - as a potential stabilizing component - with the presence of potential vulnerable components (intraplaque hemorrhage and lipid core) within each carotid plaque. We adjusted all analyses for age, sex and maximal plaque thickness. Next, we stratified on degree of stenosis (≤ or >30%) to evaluate effect modification by atherosclerotic burden. Results: We found that a larger calcification volume was associated with a higher prevalence of intraplaque hemorrhage, and a lower prevalence of lipid core (fully-adjusted odds ratio (OR) per standard deviation (SD) increase in calcification volume: 2.04 (95% confidence intervals (CI): 1.49; 2.78) and 0.72 (95% CI: 0.58; 0.90), respectively). Stratification on the degree of stenosis showed no difference in the association between calcification volume and hemorrhage over strata, while the relationship between a larger calcification volume and a lower prevalence of lipid seemed more pronounced in persons with a high degree of stenosis. Conclusions: In this population-based setting, we found that there is a complex relationship between calcification, intraplaque hemorrhage and lipid core within the carotid atherosclerotic plaque. Plaques with a higher load of calcification contain more often hemorrhagic components, but less often lipid core. Our results suggest that both in small and large plaques, intraplaque calcification may not be a stabilizing factor per se. These findings create an urge for conducting prospective studies investigating the interrelation of these different plaque components with regard to future cerebrovascular events.

Imaging and nanomedicine in inflammatory atherosclerosis

Bioengineering provides unique opportunities to better understand and manage atherosclerotic disease. The field is entering a new era that merges the latest biological insights into inflammatory disease processes with targeted imaging and nanomedicine. Preclinical cardiovascular molecular imaging allows the in vivo study of targeted nanotherapeutics specifically directed toward immune system components that drive atherosclerotic plaque development and complication. The first multicenter trials highlight the potential contribution of multimodality imaging to more efficient drug development. This review describes how the integration of engineering, nanotechnology, and cardiovascular immunology may yield precision diagnostics and efficient therapeutics for atherosclerosis and its ischemic complications.

Dual energy computed tomography quantification of carotid plaques calcification: comparison between monochromatic and polychromatic energies with pathology correlation

PURPOSE

We compared carotid plaque calcification detection sensitivity and apparent cross-sectional area on CT as a function of CT beam energy using conventional CT techniques and virtual mono-energetic CT images generated from dual-energy acquisitions.

METHODS & MATERIALS

Five ex-vivo carotid endarterectomy (CEA) specimens were imaged with dual-energy computed tomography. Virtual monochromatic spectrum (VMS) CT images were reconstructed at energies between 40-140 keV. The same specimens were imaged using conventional polyenergetic spectrum (PS) CT with peak beam energies 80, 100, 120, and 140 kVp. The histological calcium areas on each corresponding CEA specimen were traced manually on digitized images of Toluidine-Blue/Basic-Fuchsin stained plastic sections.

RESULTS

40 keV VMS CT images provided high detection sensitivity (97 %) similar to conventional PS CT images (~96 %). The calcification size measured on CT decreased systematically with increasing CT beam energy; the rate of change was larger for the VMS images than for PS images.

CONCLUSION

From a single dual-energy CT, multiple VMS-CT images can be generated, yielding equivalent detection sensitivity and size correlations as conventional PS-CT in CEA calcification imaging. VMS-CT at 80-100 keV provided the most accurate estimates of calcification size, as compared to histology, but detection sensitivity was reduced for smaller calcifications on these images.

KEY POINTS

• Calcifications depicted at 80-100 keV were most similar to the histology standard. • Conventional polychromatic images demonstrated excellent correlation with plaque size at pathology. • Conventional polychromatic images systematically overestimate plaque size. • Plaque calcifications can be missed on high energy monochromatic images.

Atherosclerosis: process, indicators, risk factors and new hopes

Background:

Atherosclerosis is the major cause of morbidities and mortalities worldwide. In this study we aimed to review the mechanism of atherosclerosis and its risk factors, focusing on new findings in atherosclerosis markers and its risk factors. Furthermore, the role of antioxidants and medicinal herbs in atherosclerosis and endothelial damage has been discussed and a list of important medicinal plants effective in the treatment and prevention of hyperlipidemia and atherosclerosis is presented.

Methods:

The recently published papers about atherosclerosis pathogenesis and herbal medicines effective in the treatment and prevention of hyperlipidemia and atherosclerosis were searched.

Results:

Inflammation has a crucial role in pathogenesis of atherosclerosis. The disease is accompanied by excessive fibrosis of the intima, fatty plaques formation, proliferation of smooth muscle cells, and migration of a group of cells such as monocytes, T cells, and platelets which are formed in response to inflammation. The oxidation of low density lipoprotein (LDL) to Ox-LDL indicates the first step of atherosclerosis in cardiovascular diseases. Malondialdehyde factor shows the level of lipoperoxidation and is a sign of increased oxidative pressure and cardiovascular diseases. In special pathological conditions such as severe hypercholesterolemia, peroxynitrite concentration increases and atherosclerosis and vascular damage are intensified. Medicinal plants have shown to be capable of interacting these or other pathogenesis factors to prevent atherosclerosis.

Conclusions:

The pathogenesis factors involved in atherosclerosis have recently been cleared and the discovery of these factors has brought about new hopes for better prevention and treatment of atherosclerosis.

Lifetime, untreated isolated GH deficiency due to a GH-releasing hormone receptor mutation has beneficial consequences on bone status in older individuals, and does not influence their abdominal aorta calcification

The GH/IGF-I axis has essential roles in regulating bone and vascular status. The age-related decrease in GH secretion ("somatopause") may contribute to osteoporosis and atherosclerosis, commonly observed in the elderly. Adult-onset GH deficiency (GHD) has been reported to be associated with reduced bone mineral density (BMD), increased risk of fractures, and premature atherosclerosis. We have shown the young adult individuals with isolated GHD (IGHD) due to a homozygous for the c.57+1G>A GHRH receptor gene mutation have normal volumetric BMD (vBMD), and not develop premature atherosclerosis, despite adverse risk factor profile. However, the bone and vascular impact of lifetime GHD on the aging process remains unknown. We studied a group of ten older IGHD subjects (≥60 years) homozygous for the mutation, comparing them with 20 age- and gender-matched controls (CO). Areal BMD was measured, and vBMD was calculated at the lumbar spine and total hip. Vertebral fractures and abdominal aortic calcifications (expressed as calcium score) were also assessed. Areal BMD was lower in IGHD, but vBMD was similar in the two groups. The percent of fractured individuals was similar, but the mean number of fractures per individual was lower in IGHD than CO. Calcium score was similar in the two groups. A positive correlation was found between calcium score and number of fractures. Untreated lifetime IGHD has beneficial consequences on bone status and does not have a deleterious effect on abdominal aorta calcification.

Imaging of cerebrovascular pathology in animal models of Alzheimer's disease

In Alzheimer's disease (AD), vascular pathology may interact with neurodegeneration and thus aggravate cognitive decline. As the relationship between these two processes is poorly understood, research has been increasingly focused on understanding the link between cerebrovascular alterations and AD. This has at last been spurred by the engineering of transgenic animals, which display pathological features of AD and develop cerebral amyloid angiopathy to various degrees. Transgenic models are versatile for investigating the role of amyloid deposition and vascular dysfunction, and for evaluating novel therapeutic concepts. In addition, research has benefited from the development of novel imaging techniques, which are capable of characterizing vascular pathology in vivo. They provide vascular structural read-outs and have the ability to assess the functional consequences of vascular dysfunction as well as to visualize and monitor the molecular processes underlying these pathological alterations. This article focusses on recent in vivo small animal imaging studies addressing vascular aspects related to AD. With the technical advances of imaging modalities such as magnetic resonance, nuclear and microscopic imaging, molecular, functional and structural information related to vascular pathology can now be visualized in vivo in small rodents. Imaging vascular and parenchymal amyloid-β (Aβ) deposition as well as Aβ transport pathways have been shown to be useful to characterize their dynamics and to elucidate their role in the development of cerebral amyloid angiopathy and AD. Structural and functional imaging read-outs have been employed to describe the deleterious affects of Aβ on vessel morphology, hemodynamics and vascular integrity. More recent imaging studies have also addressed how inflammatory processes partake in the pathogenesis of the disease. Moreover, imaging can be pivotal in the search for novel therapies targeting the vasculature.

Plasmonic photothermal therapy for atheroregression below Glagov threshold

The advent of nanomedicine allowed for the development and design of tools that enhance detailed diagnosis and target treatment of atherosclerosis. Given the rapid progress in nanoagent synthesis and utility, clinical application of these technologies can be anticipated in the near future. This review article focuses on the development of these technologies in interventional cardiology, with the main goal of achieving atheroregression below a Glagov threshold of 40%. Special attention is given to plasmonic photothermal therapy. Vascular remodeling maintains the lumen dimension as long as the external elastic membrane can accommodate an increase in plaque burden that does not surpass a certain threshold. We propose that this threshold becomes the target for the development of strategies that reverse atherosclerosis, especially for the generation of devices and tools of nanomedicine.

(64)Cu-labeled LyP-1-dendrimer for PET-CT imaging of atherosclerotic plaque

The ability to detect and quantify macrophage accumulation can provide important diagnostic and prognostic information for atherosclerotic plaque. We have previously shown that LyP-1, a cyclic 9-amino acid peptide, binds to p32 proteins on activated macrophages, facilitating the visualization of atherosclerotic plaque with PET. Yet, the in vivo plaque accumulation of monomeric [(18)F]FBA-LyP-1 was low (0.31 ± 0.05%ID/g). To increase the avidity of LyP-1 constructs to p32, we synthesized a dendritic form of LyP-1 on solid phase using lysine as the core structural element. Imaging probes (FAM or 6-BAT) were conjugated to a lysine or cysteine on the dendrimer for optical and PET studies. The N-terminus of the dendrimer was further modified with an aminooxy group in order to conjugate LyP-1 and ARAL peptides bearing a ketone. Oxime ligation of peptides to both dendrimers resulted in (LyP-1)4- and (ARAL)4-dendrimers with optical (FAM) and PET probes (6-BAT). For PET-CT studies, (LyP-1)4- and (ARAL)4-dendrimer-6-BAT were labeled with (64)Cu (t1/2 = 12.7 h) and intravenously injected into the atherosclerotic (ApoE(-/-)) mice. After two hours of circulation, PET-CT coregistered images demonstrated greater uptake of the (LyP-1)4-dendrimer-(64)Cu than the (ARAL)4-dendrimer-(64)Cu in the aortic root and descending aorta. Ex vivo images and the biodistribution acquired at three hours after injection also demonstrated a significantly higher uptake of the (LyP-1)4-dendrimer-(64)Cu (1.1 ± 0.26%ID/g) than the (ARAL)4-dendrimer-(64)Cu (0.22 ± 0.05%ID/g) in the aorta. Similarly, subcutaneous injection of the LyP-1-dendrimeric carriers resulted in preferential accumulation in plaque-containing regions over 24 h. In the same model system, ex vivo fluorescence images within aortic plaque depict an increased accumulation and penetration of the (LyP-1)4-dendrimer-FAM as compared to the (ARAL)4-dendrimer-FAM. Taken together, the results suggest that the (LyP-1)4-dendrimer can be applied for in vivo PET imaging of plaque and that LyP-1 could be further exploited for the delivery of therapeutics with multivalent carriers or nanoparticles.

Accumulating advantages, reducing limitations: multimodal nonlinear imaging in biomedical sciences - the synergy of multiple contrast mechanisms

Multimodal nonlinear microscopy has matured during the past decades to one of the key imaging modalities in life science and biomedicine due to its unique capabilities of label-free visualization of tissue structure and chemical composition, high depth penetration, intrinsic 3D sectioning, diffraction limited resolution and low phototoxicity. This review briefly summarizes first recent advances in the field regarding the methodology, e.g., contrast mechanisms and signal characteristics used for contrast generation as well as novel image processing approaches. The second part deals with technologic developments emphasizing improvements in penetration depth, imaging speed, spatial resolution and nonlinear labeling strategies. The third part focuses on recent applications in life science fundamental research and biomedical diagnostics as well as future clinical applications.

Positron emission tomography of the vulnerable atherosclerotic plaque in man--a contemporary review

Atherosclerosis is the primary underlying cause of cardiovascular disease (CVD). It is the leading cause of morbidity and mortality in the Western world today and is set to become the prevailing disease and major cause of death worldwide by 2020. In the 1950s surgical intervention was introduced to treat symptomatic patients with high-grade carotid artery stenosis due to atherosclerosis – a procedure known as carotid endarterectomy (CEA). By removing the atherosclerotic plaque from the affected carotid artery of these patients, CEA is beneficial by preventing subsequent ipsilateral ischemic stroke. However, it is known that patients with low to intermediate artery stenosis may still experience ischemic events, leading clinicians to consider plaque composition as an important feature of atherosclerosis. Today molecular imaging can be used for characterization, visualization and quantification of cellular and subcellular physiological processes as they take place in vivo; using this technology we can obtain valuable information on atherosclerostic plaque composition. Applying molecular imaging clinically to atherosclerotic disease therefore has the potential to identify atherosclerotic plaques vulnerable to rupture. This could prove to be an important tool for the selection of patients for CEA surgery in a health system increasingly focused on individualized treatment. This review focuses on current advances and future developments of in vivo atherosclerosis PET imaging in man.