Characterisation of coronary atherosclerotic morphology by spectral analysis of radiofrequency signal: in vitro intravascular ultrasound study with histological and radiological validation

Innovations in Intracoronary Imaging: Present Clinical Practices and Future Outlooks

Engaging intracoronary imaging (IC) techniques such as intravascular ultrasound or optical coherence tomography enables the precise description of vessel architecture. These imaging modalities have well-established roles in providing guidance and optimizing percutaneous coronary intervention (PCI) outcomes. Furthermore, IC is increasingly recognized for its diagnostic capabilities, as it has the unique capacity to reveal vessel wall characteristics that may not be apparent through angiography alone. This manuscript thoroughly reviews the contemporary landscape of IC in clinical practice. Focused on current methodologies, the review explores the utility and advancements in IC techniques. Emphasizing their role in clarifying coronary pathophysiology, guiding PCI, and optimizing patient outcomes, the manuscript critically evaluates the strengths and limitations of each modality. Additionally, the integration of IC into routine clinical workflows and its impact on decision-making processes are discussed. By synthesizing the latest evidence, this review provides valuable insights for clinicians, researchers, and healthcare professionals involved in the dynamic field of interventional cardiology.

Assessing engineered tissues and biomaterials using ultrasound imaging: In vitro and in vivo applications

Quantitative assessment of the structural, functional, and mechanical properties of engineered tissues and biomaterials is fundamental to their development for regenerative medicine applications. Ultrasound (US) imaging is a non-invasive, non-destructive, and cost-effective technique capable of longitudinal and quantitative monitoring of tissue structure and function across centimeter to sub-micron length scales. Here we present the fundamentals of US to contextualize its application for the assessment of biomaterials and engineered tissues, both in vivo and in vitro. We review key studies that demonstrate the versatility and broad capabilities of US for clinical and pre-clinical biomaterials research. Finally, we highlight emerging techniques that further extend the applications of US, including for ultrafast imaging of biomaterials and engineered tissues in vivo and functional monitoring of stem cells, organoids, and organ-on-a-chip systems in vitro.

Coronary artery properties in atherosclerosis: A deep learning predictive model

In this work an Artificial Neural Network (ANN) was developed to help in the diagnosis of plaque vulnerability by predicting the Young modulus of the core (E _core ) and the plaque (E _plaque ) of atherosclerotic coronary arteries. A representative in silico database was constructed to train the ANN using Finite Element simulations covering the ranges of mechanical properties present in the bibliography. A statistical analysis to pre-process the data and determine the most influential variables was performed to select the inputs of the ANN. The ANN was based on Multilayer Perceptron architecture and trained using the developed database, resulting in a Mean Squared Error (MSE) in the loss function under 10^-7, enabling accurate predictions on the test dataset for E _core and E _plaque . Finally, the ANN was applied to estimate the mechanical properties of 10,000 realistic plaques, resulting in relative errors lower than 3%.

Spectral analysis of ultrasound radiofrequency backscatter for the identification of epicardial adipose tissue

Purpose: The coronary arteries are embedded in a layer of fat known as epicardial adipose tissue (EAT). The EAT influences the development of coronary artery disease (CAD), and increased EAT volume can be indicative of the presence and type of CAD. Identification of EAT using echocardiography is challenging and only sometimes feasible on the free wall of the right ventricle. We investigated the use of spectral analysis of the ultrasound radiofrequency (RF) backscatter for its potential to provide a more complete characterization of the EAT. Approach: Autoregressive (AR) models facilitated analysis of the short-time signals and allowed tuning of the optimal order of the spectral estimation process. The spectra were normalized using a reference phantom and spectral features were computed from both normalized and non-normalized data. The features were used to train random forests for classification of EAT, myocardium, and blood. Results: Using an AR order of 15 with the normalized data, a Monte Carlo cross validation yielded accuracies of 87.9% for EAT, 84.8% for myocardium, and 93.3% for blood in a database of 805 regions-of-interest. Youden's index, the sum of sensitivity, and specificity minus 1 were 0.799, 0.755, and 0.933, respectively. Conclusions: We demonstrated that spectral analysis of the raw RF signals may facilitate identification of the EAT when it may not otherwise be visible in traditional B-mode images.

Atheroprotective Roles of Adiponectin via CCL2 Inhibition

Aim: Adiponectin (APN) exhibits different atheroprotective effects, and we have previously reported that APN function is modulated by its binding proteins, E-selectin ligand 1, Mac-2 binding protein, and cystatin C. In the present study, we aimed to identify a novel atheroprotective mechanism of APN via C–C motif chemokine 2 (CCL2).

Methods: We conducted iMAP ^® -intravascular ultrasound (IVUS) in 111 Japanese male patients with stable angina. The plaque characteristics were determined where “plaque burden” [(EEM CSA − lumen CSA)/(EEM CSA)×100 (%)] ＞50%, and their correlation with serum CCL2 and APN levels was analyzed. Using western blot analysis, the effects of APN on the biological effects of CCL2 were examined in their mutual binding by co-immunoprecipitation assay, the monocyte migration, and the phosphorylation of MAP kinases.

Results: In a clinical study, we found that the percentage of plaque in the culprit lesion was correlated positively with serum CCL2 and negatively with serum APN levels, with significance. We identified CCL2 as a novel APN-binding serum protein using immunoprecipitation and western blot analysis. CCL2-induced phosphorylation of MAP kinases and monocyte migration was significantly attenuated by APN in vitro .

Conclusion: The opposite association of APN and CCL2 on the percentage of coronary plaque might be caused by their direct interaction and competitive functions on monocyte migration.

Multimodal intravascular imaging technology for characterization of atherosclerosis

Early detection of vulnerable plaques is the critical step in the prevention of acute coronary events. Morphology, composition, and mechanical property of a coronary artery have been demonstrated to be the key characteristics for the identification of vulnerable plaques. Several intravascular multimodal imaging technologies providing co-registered simultaneous images have been developed and applied in clinical studies to improve the characterization of atherosclerosis. In this paper, the authors review the present system and probe designs of representative intravascular multimodal techniques. In addition, the scientific innovations, potential limitations, and future directions of these technologies are also discussed.

Microstructure-based biomechanics of coronary arteries in health and disease

Coronary atherosclerosis is the major cause of mortality and disability in developed nations. A deeper understanding of mechanical properties of coronary arteries and hence their mechanical response to stress is significant for clinical prevention and treatment. Microstructure-based models of blood vessels can provide predictions of arterial mechanical response at the macro- and micro-mechanical level for each constituent structure. Such models must be based on quantitative data of structural parameters (constituent content, orientation angle and dimension) and mechanical properties of individual adventitia and media layers of normal arteries as well as change of structural and mechanical properties of atherosclerotic arteries. The microstructural constitutive models of healthy coronary arteries consist of three major mechanical components: collagen, elastin, and smooth muscle cells, while the models of atherosclerotic arteries should account for additional constituents including intima, fibrous plaque, lipid, calcification, etc. This review surveys the literature on morphology, mechanical properties, and microstructural constitutive models of normal and atherosclerotic coronary arteries. It also provides an overview of current gaps in knowledge that must be filed in order to advance this important area of research for understanding initiation, progression and clinical treatment of vascular disease. Patient-specific structural models are highlighted to provide diagnosis, virtual planning of therapy and prognosis when realistic patient-specific geometries and material properties of diseased vessels can be acquired by advanced imaging techniques.

Effect of daily glucose fluctuation on coronary plaque vulnerability in patients pre-treated with lipid-lowering therapy: a prospective observational study

OBJECTIVES

This study sought to investigate the effect of daily glucose fluctuation on coronary plaque properties in patients with coronary artery disease (CAD) pre-treated with lipid-lowering therapy.

BACKGROUND

There is growing evidence that glucose fluctuation, as a residual risk apart from dyslipidemia, is an important factor contributing to the development of CAD.

METHODS

This prospective study enrolled 70 consecutive CAD patients who were referred for percutaneous coronary intervention and whose low-density lipoprotein cholesterol level was <120 mg/dl under statin treatment or <100 mg/dl without statins. Daily glucose fluctuation was analyzed by measuring the mean amplitude of glycemic excursion (MAGE). The plaque properties in the culprit and nonculprit lesions were assessed by virtual histology intravascular ultrasound, and the volume percentage of necrotic core within the plaque (%NC) and the presence of thin-cap fibroatheroma were evaluated.

RESULTS

In total, 165 lesions were evaluated in 70 patients (40 diabetic and 30 nondiabetic patients). %NC was well correlated with MAGE (r = 0.490, p <0.001). A linear mixed effect model showed that MAGE had the strongest effect on %NC (coefficient β = 0.080 ± 0.020 [standard error], p < 0.001). The generalized linear mixed effect model revealed that MAGE was the only independent predictor of the presence of thin-cap fibroatheroma (odds ratio: 1.037; 95% confidence interval: 1.010 to 1.065; p = 0.007).

CONCLUSIONS

Daily glucose fluctuation may have an effect on coronary plaque vulnerability in patients with CAD pre-treated with lipid-lowering therapy. Further investigations should address the rationale for the early detection and control of glucose fluctuation in the era of universal statin use for CAD patients.

Coronary atherosclerosis is already ongoing in pre-diabetic status: Insight from intravascular imaging modalities

Diabetes mellitus is a powerful risk factor of coronary artery disease (CAD), leading to death and disability. In recent years, given the accumulating evidence that prediabetes is also related to increasing risk of CAD including cardiovascular events, a new guideline has been proposed for the treatment of blood cholesterol for primary prevention of cardiovascular events. This guideline recommends aggressive lipid-lowering statin therapy for primary prevention in diabetes and other patients. The ultimate goal of patient management is to inhibit progression of systemic atherosclerosis and prevent fatal cardiovascular events such as acute coronary syndrome (ACS). Because disruption of atherosclerotic coronary plaques is a trigger of ACS, the high-risk atheroma is called a vulnerable plaque. Several types of novel diagnostic imaging technologies have been developed for identifying the characteristics of coronary atherosclerosis before the onset of ACS, especially vulnerable plaques. According to coronary angioscopic evaluation, atherosclerosis severity and plaque vulnerability were more advanced in prediabetic than in nondiabetic patients and comparable to that in diabetic patients. In addition, pharmacological intervention by statin therapy changed plaque color and complexity, and the dynamic changes in plaque features are considered plaque stabilization. In this article, we review the findings of atherosclerosis in prediabetes, detected by intravascular imaging modalities, and the therapeutic implications.

Biological imaging of atherosclerosis: moving beyond anatomy

Biological or molecular imaging is now providing exciting new strategies to study atherosclerosis in both animals and humans. These technologies hold the promise to provide disease-specific, molecular information within the context of a systemic or organ-specific disease beyond traditional anatomical-based imaging. By integration of biological, chemical, and anatomical imaging knowledge into diagnostic strategies, a more comprehensive and predictive picture of atherosclerosis is likely to emerge. As such, biological imaging is well positioned to study different stages of atherosclerosis and its treatment, including the sequence of atheroma initiation, progression, and plaque rupture. In this review, we describe the evolving concepts in atherosclerosis imaging with a focus on coronary artery disease, and we provide an overview of recent exciting translational developments in biological imaging. The illuminated examples and discussions will highlight how biological imaging is providing new clinical approaches to identify high-risk plaques, and to streamline the development process of new atherosclerosis therapies.

Intravascular ultrasound area strain imaging used to characterize tissue components and assess vulnerability of atherosclerotic plaques in a rabbit model

The purpose of this study was to investigate the association of area strain and tissue components and vulnerability of atherosclerotic plaques in a rabbit model. Forty purebred New Zealand rabbits underwent balloon-induced abdominal aorta endothelium injury, then a high-cholesterol diet for 24 weeks. Intravascular ultrasound (IVUS) images of abdominal aortas were acquired in situ and two consecutive frames near the end-diastole were used to construct an IVUS elastogram. Histologic slices matched with corresponding IVUS images were stained for fatty and collagen components, smooth muscle cells (SMCs) and macrophages. Regions-of-interest (ROIs) in plaques were classified as fibrous, fibro-fatty or fatty according to histologic study. Vulnerability indexes of ROIs were calculated as (fat + macrophage)/(collagen + SMCs). The area strain of these ROIs was calculated by use of an in-house-designed software system with a block-matching-based algorithm. Area strain was significantly higher in fatty ROIs (0.056 ± 0.003) than in fibrous (0.019 ± 0.002, p < 0.001) or fibro-fatty ROIs (0.033 ± 0.003, p < 0.001). The sensitivity and specificity of area strain for fatty ROIs characterization was 75.0% and 80.2% (area under the curve [AUC] 0.858, 95% confidence interval [CI] = 0.800-0.916, p < 0.001) and 75.0% and 75.3% (AUC 0.859, 95% CI = 0.801-0.917, p < 0.001) for fibrous ROIs, as demonstrated by receiver operating characteristic curve analysis. Area strain was positively correlated with vulnerability index (r(2) = 0.495, p < 0.001), fatty components (r(2) = 0.332, p < 0.001) and macrophage infiltration (r(2) = 0.406, p < 0.001); and negatively correlated with collagen and SMC composition (r(2) = 0.115 and r(2) = 0.169, p < 0.001, respectively). Area strain calculation with IVUS elastography based on digital B-mode analysis is feasible and can be useful for tissue characterization and plaque vulnerability assessment.

Non-invasive detection of vulnerable coronary plaque

Critical coronary stenoses have been shown to contribute to only a minority of acute coronary syndromes and sudden cardiac death. Autopsy studies have identified a subgroup of high-risk patients with disrupted vulnerable plaque and modest stenosis. Consequently, a clinical need exists to develop methods to identify these plaques prospectively before disruption and clinical expression of disease. Recent advances in invasive and non-invasive imaging techniques have shown the potential to identify these high-risk plaques. Non-invasive imaging with magnetic resonance imaging, computed tomography and positron emission tomography holds the potential to differentiate between low- and high-risk plaques. There have been significant technological advances in non-invasive imaging modalities, and the aim is to achieve a diagnostic sensitivity for these technologies similar to that of the invasive modalities. Molecular imaging with the use of novel targeted nanoparticles may help in detecting high-risk plaques that will ultimately cause acute myocardial infarction. Moreover, nanoparticle-based imaging may even provide non-invasive treatments for these plaques. However, at present none of these imaging modalities are able to detect vulnerable plaque nor have they been shown to definitively predict outcome. Further trials are needed to provide more information regarding the natural history of high-risk but non-flow-limiting plaque to establish patient specific targeted therapy and to refine plaque stabilizing strategies in the future.

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.

Relationship between tissue characterization with 40 MHz intravascular ultrasound imaging and 64-slice computed tomography

BACKGROUND

Identification of coronary plaque composition is important for selecting the treatment strategy, and 64-slice computed tomography (CT) is a noninvasive method of characterizing atherosclerotic plaques. However, the correlation between plaque characteristics detected by CT and intravascular ultrasound (IVUS) is not clear. A 40 MHz IVUS imaging system (iMap-IVUS) has recently been developed to evaluate plaque composition. The aim of this study was to compare iMap-IVUS with 64-slice CT angiography for the characterization of non-calcified coronary plaques.

METHODS AND RESULTS

Both 64-slice CT angiography and iMap-IVUS were performed in 19 patients (38 plaques). CT values were measured as Hounsfield units (HU) in circular regions of interest (ROI) drawn on the plaques. The iMap-IVUS system analyzed coronary plaques as fibrotic, lipidic, necrotic, or calcified tissue based on the radiofrequency spectrum. A positive correlation was found between CT values and the percentage of fibrotic plaque (r=0.34, p=0.036) or calcified plaque (r=0.40, p=0.011). Conversely, a negative correlation was found between CT values and the percentage of lipidic plaque (r=-0.41, p=0.01), or necrotic plaque (r=-0.41, p=0.01).

CONCLUSIONS

Good correlations were observed between the characteristics of non-calcified plaque determined by iMap-IVUS and the CT values of plaque detected by 64-slice CT scanning.

Numerical modeling of stress in stenotic arteries with microcalcifications: a micromechanical approximation

Most finite element models of atherosclerotic arteries do not account for the heterogeneity of the plaque constituents at the microscale. Failure of plaque lesions has been shown to be a local event, linked to stress concentrations caused by cap thinning, inflammation, macroscopic heterogeneity, and recently, the presence of microcalcifications. There is growing evidence that microcalcifications exist in the fibrous cap of plaque lesions. However, their role is not yet fully understood. The goal of the present work is to investigate the effects of localized regions of microcalcifications on the stress field of atherosclerotic plaque caps in a section of carotid artery. This is achieved by performing finite element simulations of three-dimensional fluid-structure interaction models. The material response in the region of microcalcification is modeled using a combination of finite elements, homogenization theory, and a stress concentration function that approximates the average local stresses in the fibrous tissue and microcalcification phases. The results indicate that the circumferential stress in the fibrous tissue phase increases as the volume fraction of microcalcifications is increased, and that the stress exceeds a critical threshold when the fibrous cap thickness is decreased. Furthermore, the presence of the microcalcifications significantly influences the distribution of stress by shifting the maximum circumferential stress away from the cap shoulders, where failure is most common when the effective region of microcalcification is located at the center of the cap. This is a possible explanation of why 40% of plaque ruptures occur away from the shoulder region of the cap.

Combined optical coherence tomography and intravascular ultrasound radio frequency data analysis for plaque characterization. Classification accuracy of human coronary plaques in vitro

This study was performed to characterize coronary plaque types by optical coherence tomography (OCT) and intravascular ultrasound (IVUS) radiofrequency (RF) data analysis, and to investigate the possibility of error reduction by combining these techniques. Intracoronary imaging methods have greatly enhanced the diagnostic capabilities for the detection of high-risk atherosclerotic plaques. IVUS RF data analysis and OCT are two techniques focusing on plaque morphology and composition. Regions of interest were selected and imaged with OCT and IVUS in 50 sections, from 14 human coronary arteries, sectioned post-mortem from 14 hearts of patients dying of non-cardiovascular causes. Plaques were classified based on IVUS RF data analysis (VH-IVUS^TM), OCT and the combination of those. Histology was the benchmark. Imaging with both modalities and coregistered histology was successful in 36 sections. OCT correctly classified 24; VH-IVUS 25, and VH-IVUS/OCT combined, 27 out of 36 cross-sections. Systematic misclassifications in OCT were intimal thickening classified as fibroatheroma in 8 cross-sections. Misclassifications in VH-IVUS were mainly fibroatheroma as intimal thickening in 5 cross-sections. Typical image artifacts were found to affect the interpretation of OCT data, misclassifying intimal thickening as fibroatheroma or thin-cap fibroatheroma. Adding VH-IVUS to OCT reduced the error rate in this study.

Update on Clinical Imaging of Coronary Plaque in Acute Coronary Syndrome

Current evidence suggests that understanding coronary artery disease extends beyond identifying and treating traditional risk factors. Progression of coronary plaque contributes to the development of acute coronary syndrome (ACS). In this article, we reviewed current literature for modalities to image coronary plaque as well as discussed the role of emerging techniques that can improve our understanding of the pathophysiology of ACS. Key words: Coronary disease, Myocardial infarction, Vulnerable plaque

Current status of vulnerable plaque detection

Critical coronary stenoses have been shown to contribute to only a minority of acute coronary syndromes (ACS) and sudden cardiac death. Autopsy studies have identified a subgroup of high-risk patients with disrupted vulnerable plaque and modest stenosis. Consequently, a clinical need exists to develop methods to identify these plaques prospectively before disruption and clinical expression of disease. Recent advances in invasive and noninvasive imaging techniques have shown the potential to identify these high-risk plaques. The anatomical characteristics of the vulnerable plaque such as thin cap fibroatheroma and lipid pool can be identified with angioscopy, high frequency intravascular ultrasound, intravascular MRI, and optical coherence tomography. Efforts have also been made to recognize active inflammation in high-risk plaques using intravascular thermography. Plaque chemical composition by measuring electromagnetic radiation using spectroscopy is also an emerging technology to detect vulnerable plaques. Noninvasive imaging with MRI, CT, and PET also holds the potential to differentiate between low and high-risk plaques. However, at present none of these imaging modalities are able to detect vulnerable plaque neither has been shown to definitively predict outcome. Nevertheless in contrast, there has been a parallel development in the physiological assessment of advanced atherosclerotic coronary artery disease. Thus recent trials using fractional flow reserve in patients with modest non flow-limiting stenoses have shown that deferral of PCI with optimal medical therapy in these patients is superior to coronary intervention. Further trials are needed to provide more information regarding the natural history of high-risk but non flow-limiting plaque to establish patient-specific targeted therapy and to refine plaque stabilizing strategies in the future.

Imaging and quantitative analysis of atherosclerotic lesions by CARS-based multimodal nonlinear optical microscopy

OBJECTIVE

The purpose of this study was to assess the ability of label-free multimodal nonlinear optical (NLO) microscopy to characterize, and thus enable quantitative in situ analyses of, different atherosclerotic lesion types, according to the original scheme suggested by the AHA Committee.

METHODS AND RESULTS

Iliac arteries were taken from 24 male Ossabaw pigs divided into lean control and metabolic syndrome groups and were imaged by multimodal NLO microscopy where sum-frequency generation (SFG) and 2-photon excitation fluorescence (TPEF) were integrated on a coherent anti-Stokes Raman scattering (CARS) microscope platform. Foam cells, lipid deposits, matrices, and fibrous caps were visualized with submicron 3D resolution. Starting from the adaptive intimal thickening in the initial stage to the fibrous atheroma or mineralization in the advanced stages, lesions were visualized without labels. Histological staining of each lesion confirmed the lesion stages. Lipid and collagen contents were quantitatively analyzed based on the CARS and SFG signals. Lipid accumulation in thickened intima culminated in type IV whereas the highest collagen deposition was found in Type V lesions. Luminal CARS imaging showed the capability of viewing the location of superficial foam cells that indicate relatively active locus in a lesion artery.

CONCLUSIONS

We have demonstrated the capability of CARS-based multimodal NLO microscopy to interrogate different stages of lesion development with subcellular detail to permit quantitative analysis of lipid and collagen contents.

Validation of in vivo plaque characterisation by virtual histology in a rabbit model of atherosclerosis

AIMS

Most acute coronary syndromes are caused by plaque rupture. The risk of plaque rupture is related to plaque composition. The purpose of this study was to validate VH-IVUS for in vivo plaque characterisation.

METHODS AND RESULTS

Six rabbits were fed a cholesterol-supplemented diet for 12 to 18 months. Thereafter, VH-IVUS imaging of the aorta was performed. After sacrifice, the VH-IVUS images were matched to the corresponding histological cross sections. A total of 260 atherosclerotic plaques were analysed. VH-IVUS had a high sensitivity, specificity and positive predictive value for the detection of non-calcified thin cap fibroatheroma (88%, 96%, 87%, respectively) and calcified thin cap fibroatheroma (95%, 99%, 93%, respectively). These values were respectively 82%, 94%, 85% for non-calcified fibroatheroma and 78%, 98%, 84% for calcified fibroatheroma. The lowest values were obtained for pathological intimal thickening (74%, 92%, 70%, respectively). For all plaque types, VH-IVUS had a kappa-value of 0.79. Linear regression analysis and Bland-Altman plots showed a strong correlation between VH-IVUS and histology for fibrous tissue, fibrofatty tissue, necrotic calcified tissue and confluent necrotic core.

CONCLUSIONS

VH-IVUS showed a good accuracy for in vivo plaque characterisation and is a promising technique for the detection of the vulnerable plaque.

Coronary plaque dimensions and composition by intravascular ultrasound radio frequency lesion segment analysis in stable and unstable angina patients

AIMS

We hypothesized that the plaque composition and plaque type classification differs between acute coronary syndrome (ACS) and stable angina (SA) patients.

METHODS AND RESULTS

We analyzed culprit lesion (CL) and nonculprit lesion (NCL) of ACS patients compared with target lesion (TL) and nontarget lesion (NTL) of SA patients by intravascular ultrasound radio frequency analysis in 874 lesion segments of 424 patients (ACS: 193 patients/SA: 231 patients). Comparing all lesion segments in ACS and SA patients did not show significant differences in absolute or relative plaque composition. However, necrotic core area was larger in CL versus TL (0.9+/-0.7 vs. 0.7+/-0.5 mm, P=0.005) and all plaque components were significantly higher in CL compared with NCL and TL compared with NTL, respectively. A higher amount of thin cap fibroatheroma lesions (15.2 vs. 5.1%, P<0.0001) was detected in ACS compared with SA patients. Fibrocalcific lesions were lower in ACS patients (3 vs. 10.5%, P<0.0001).

CONCLUSION

The differentiation in CL/NCL of ACS and TL/NTL of SA patients revealed significant differences in plaque composition and plaque types when examined by intravascular ultrasound radiofrequency analysis. However, considerable overlap between plaque characteristics exists for ACS and SA patients.

Accuracy of dual-source CT in the characterisation of non-calcified plaque: use of a colour-coded analysis compared with virtual histology intravascular ultrasound

Non-invasive assessment of plaque volume and composition is important for risk stratification and long-term studies of plaque stabilisation. Our aim was to evaluate dual-source computed tomography (DSCT) and colour-coded analysis in the quantification and classification of coronary atheroma. DSCT and virtual histology intravascular ultrasound (IVUS-VH) were prospectively performed in 14 patients. 22 lesions were compared in terms of plaque volume, maximal per cent vessel stenosis and percentages of fatty, fibrous or calcified components. Plaque characterisation was performed with software that automatically segments luminal or outer vessel boundaries and uses CT attenuation for a colour-coded plaque analysis. Good correlation was found for per cent vessel stenosis in DSCT (53+/-13%) and IVUS (51+/-14%; r(2) = 0.70). Mean volumes for entire plaque and non-calcified atheroma were 68.5+/-33 mm(3) and 56.7+/-30 mm(3), respectively, in DSCT and 60.8+/-29 mm(3) and 55.8+/-26 mm(3), respectively, in IVUS. Mean percentages of fatty, fibrous or calcified components were 28.2+/-6%, 53.2+/-9% and 18.7+/-13%, respectively, in DSCT and 29.9+/-5%, 55.3+/-12% and 14.4+/-9%, respectively, in IVUS-VH. Significant overestimation was present for the entire plaque and the volume of calcified plaque (p = 0.03; p = 0.0004). Although good correlation with IVUS was obtained for the entire plaque (r(2) = 0.76) and non-calcified plaque volume (r(2) = 0.84), correlation proved very poor and insignificant for percentage plaque composition. Interclass correlation coefficients for non-calcified plaque volume and percentages of fatty, fibrous or calcified components were 0.99, 0.99, 0.95 and 0.98, respectively, and intraclass coefficients were 0.98, 0.93, 0.98 and 0.99, respectively. We found that using Hounsfield unit-based analysis, DSCT allows for accurate quantification of non-calcified plaque. Although percentage plaque composition proves highly reproducible, it is not correlated with IVUS-VH.

Normalization and backscatter spectral analysis of human carotid arterial data acquired using a clinical linear array ultrasound imaging system

The risk of plaque rupture in carotid atherosclerotic disease is associated more closely with the composition of plaque rather than the severity of stenosis. The constituents of plaque can be determined from ultrasonic spectral parameters obtained from normalized backscatter tissue data. Calibration of the data is done using echoes off a specular reflector which removes the system response of an ultrasound transducer, Terason (Teratech Corporation), from the backscatter data. A reference spectrum study is used to compare specular reflectors based on time domain (echo) and frequency domain (power spectrum, centroid and parabola test) analysis. Nylon and a tissue-mimicking phantom (velocity = 1560 m/s, slope of attenuation = 0.7 dB/cm MHz) have an intermediate acoustic impedance with respect to water and appear good choices as specular reflectors for clinical ultrasound imaging scanners compared to Plexiglas and other higher reflecting materials. A tissue-mimicking phantom is used to correct for attenuation in plaque, diffraction and saturation of electronics of the ultrasound scanner. Autoregressive power spectrum estimation methods are used to extract spectral parameters (spectral slope, y-intercept, midband fit, maximum and minimum power with corresponding frequencies, and integrated backscatter) from calibrated tissue data and linear and quadratic discriminant rules developed for classification of carotid arterial plaque. Regions of interest (n = 64; 64 samples x 8 scan lines with 30 MHz sampling frequency) consisting of 48 fibrous-fibrofatty (Class 1), 11 thrombus-necrotic core (Class 2), and 5 dense calcium (Class 3) areas selected for analysis show that fibrosis can be differentiated from necrosis and calcification. The quadratic discriminant rule identified necrosis with a lower misclassification rate (9.1%) than the linear discriminant rule (18.2%).

Diagnosis of atherosclerosis by imaging

New and experimental imaging techniques are being developed that will permit better visualization and compositional characterization of atheromatous plaques. This review provides discussion of techniques that are currently used in clinical practice, as well as techniques that are investigational only, including coronary angiography, intravascular ultrasound, computed tomography, magnetic resonance imaging, positron emission tomography, and single-photon emission computed tomography. Types of atheromatous plaque are reviewed, and the value of examining vascular calcification in risk assessment is discussed. Experimental use of these imaging techniques in animal models and in clinical studies will enhance our understanding of the development of plaque and will determine whether these techniques would be useful and practical for predicting disease course. Early detection and identification of the type of plaque that is present may generate novel opportunities for primary prevention through changes in lifestyle or even through drug therapy, especially in patients at high cardiovascular risk.

Pioglitazone reduces the necrotic-core component in coronary plaque in association with enhanced plasma adiponectin in patients with type 2 diabetes mellitus

BACKGROUND

Pioglitazone has a preventive effect on cardiovascular disease, but its ability to stabilize coronary plaque is unknown.

METHODS AND RESULTS

A prospective, randomized trial was conducted in 54 patients with type 2 diabetes and stable angina pectoris, randomly assigned to either a pioglitazone group or control group. Non-culprit, angiographically mild-to-moderate obstructive lesions were examined with virtual histology intravascular ultrasound (VH-IVUS) at coronary intervention and 6 months later. In total, 42 lesions of 22 patients in the pioglitazone group and 44 lesions of 24 patients in the control group were analyzed. After 6 months, patients in the pioglitazone group had significantly improved blood sugar, high-sensitivity C-reactive protein, and plasma adiponectin levels. VH-IVUS analysis revealed that, although the total plaque-to-vessel volume was not changed in either group, the necrotic-core area had significantly decreased in the pioglitazone group (-4.6+/-5.9% vs 1.1+/-9.3%, P=0.001). There was a significant inverse correlation between the change in plasma adiponectin levels and the change in necrotic-core area (r=-0.46, P<0.0001).

CONCLUSIONS

Pioglitazone may stabilize coronary plaque by reducing the necrotic-core component, in association with enhanced plasma adiponectin levels.

Characterization of coronary atherosclerosis by dual-source computed tomography and HU-based color mapping: a pilot study

To assess HU-based color mapping for characterization of coronary plaque, using intravascular ultrasound virtual histology (IVUS-VH) as a standard of reference. Dual-source computed tomography and IVUS-VH were prospectively performed in 13 patients. In five lesions, HU thresholds of the color-coding software were calibrated to IVUS-VH. In a 15-lesion verification cohort, volumes of vessel, lumen and plaque or percentages of lipid, fibrous and calcified components were obtained through use of pre-set HU cut-offs as well as through purely visual adjustment of color maps. Calibrated HU ranges for fatty or fibrous plaque, lumen and calcification were -10-69, 70-158, 159-436 and 437+. Using these cut-offs, HU-based analysis achieved good agreement of plaque volume with IVUS (47.0 vs. 51.0 mm(3)). Visual segmentation led to significant overestimation of atheroma (61.6 vs. 51.0 mm(3); P = 0.04) Correlation coefficients for volumes of vessel, lumen and plaque were 0.92, 0.87 and 0.83 with HU-based analysis or 0.92, 0.85 and 0.71 with visual evaluation. With both methods, correlation of percentage plaque composition was poor or insignificant. HU-based plaque analysis showed good reproducibility with intra-class correlation coefficients being 0.90 for plaque volume and 0.81, 0.94 or 0.98 for percentages of fatty, fibrous or calcified components. With use of optimized HU thresholds, color mapping allows for accurate and reproducible quantification of coronary plaque.

Distribution of ultrasonic radiofrequency signal amplitude detects lipids in atherosclerotic plaque of coronary arteries: an ex-vivo study

BACKGROUND

Accumulation of lipids within coronary plaques is an important process in disease progression. However, gray-scale intravascular ultrasound images cannot detect plaque lipids effectively. Radiofrequency signal analysis could provide more accurate information on preclinical coronary plaques.

METHODS

We analyzed 29 zones of mild atheroma in human coronary arteries acquired at autopsy. Two histologic groups, i.e., plaques with a lipid core (group L) and plaques without a lipid core (group N), were analyzed by automatic calculation of integrated backscatter. One hundred regions of interest were set on the target zone. Radiofrequency signals from a 50 MHz transducer were digitized at 240 MHz with 12-bit resolution. The intensity of integrated backscatter and its distribution within each plaque were compared between the two groups.

RESULTS

Although the mean backscatter was similar between the groups, intraplaque variation of backscatter and backscatter in the axial direction were larger in group L than in group N (p = 0.02). Conventional intravascular ultrasound showed extremely low sensitivity for lipid detection, despite a high specificity. In contrast, a cut-off value>32 for the total variance of integrated backscatter identified lipid-containing plaque with a high sensitivity (85%) and specificity (75%).

CONCLUSION

Compared with conventional imaging, assessment of the intraplaque distribution of integrated backscatter is more effective for detecting lipid. As coronary atheroma progresses, its composition becomes heterogeneous and multi-layered. This radiofrequency technique can portray complex plaque histology and can detect the early stage of plaque progression.

Low adiponectin levels are associated with atherogenic dyslipidemia and lipid-rich plaque in nondiabetic coronary arteries

OBJECTIVE

The purpose of this study was to determine whether an association exists between adiponectin and plaque composition in human coronary arteries.

RESEARCH DESIGN AND METHODS

Adiponectin is an adipocyte-derived protein with antiatherogenic and insulin-sensitizing properties. To date, the relationship between adiponectin and plaque composition is unknown. Fasting blood samples were collected from 185 patients undergoing coronary angiography and intravascular ultrasound (IVUS). Plaque composition was categorized as fibrous, fibrofatty, necrotic core, or dense calcium and further classified as IVUS-derived adaptive or pathological intimal thickening, fibroatheroma, fibrocalcific, or thin cap fibroatheroma.

RESULTS

Adiponectin correlated with normalized plaque volume (r = -0.16, P = 0.025) and atheroma lipid content as measured by normalized fibrofatty volume (r = -0.19, P = 0.009). Low adiponectin levels were associated with IVUS-derived pathological intimal thickening (r = -0.18, P = 0.01). With increasing quartiles (Q) of adiponectin, the normalized volume of fibrofatty plaque decreased (P = 0.03), which was driven by reductions in the nondiabetic cohort (Q1 44.2 mm(3); Q2 28.2 mm(3); Q3 24.7 mm(3); and Q4 23.4 mm(3); P = 0.01). No similar association was present in diabetic patients. Low adiponectin levels were also associated with IVUS-derived pathological intimal thickening in nondiabetic (r = -0.20, P = 0.03) but not diabetic patients.

CONCLUSIONS

Low adiponectin levels are associated with atherogenic lipoproteins (elevated triglycerides, small dense LDL cholesterol, and low HDL cholesterol), increased plaque volume, lipid-rich plaque, and IVUS-derived pathological intimal thickening in the total cohort that was driven by the nondiabetic population, suggesting an antiatherogenic role in the early stages of lesion development.