Comparison of 64-slice multidetector computed tomography with spectral analysis of intravascular ultrasound backscatter signals for characterizations of noncalcified coronary arterial plaques

Computed Tomography Angiography Identified High-Risk Coronary Plaques: From Diagnosis to Prognosis and Future Management

CT angiography has become, in recent years, a main evaluating modality for patients with coronary artery disease (CAD). Recent advancements in the field have allowed us to identity not only the presence of obstructive disease but also the characteristics of identified lesions. High-risk coronary atherosclerotic plaques are identified in CT angiographies via a number of specific characteristics and may provide prognostic and therapeutic implications, aiming to prevent future ischemic events via optimizing medical treatment or providing coronary interventions. In light of new evidence evaluating the safety and efficacy of intervening in high-risk plaques, even in non-flow-limiting disease, we aim to provide a comprehensive review of the diagnostic algorithms and implications of plaque vulnerability in CT angiography, identify any differences with invasive imaging, analyze prognostic factors and potential future therapeutic options in such patients, as well as discuss new frontiers, including intervening in non-flow-limiting stenoses and the role of CT angiography in patient stratification.

Computed Tomography Angiography Characteristics of Thin-Cap Fibroatheroma in Patients With Diabetes

BACKGROUND

It was recently reported that thin-cap fibroatheroma (TCFA) detected by optical coherence tomography was an independent predictor of future cardiac events in patients with diabetes. However, the clinical usefulness of this finding is limited by the invasive nature of optical coherence tomography. Computed tomography angiography (CTA) characteristics of TCFA have not been systematically studied. The aim of this study was to investigate CTA characteristics of TCFA in patients with diabetes.

METHODS AND RESULTS

Patients with diabetes who underwent preintervention CTA and optical coherence tomography were included. Qualitative and quantitative analyses were performed for plaques on CTA. TCFA was assessed by optical coherence tomography. Among 366 plaques in 145 patients with diabetes, 111 plaques had TCFA. The prevalence of positive remodeling (74.8% versus 50.6%, P<0.001), low attenuation plaque (63.1% versus 33.7%, P<0.001), napkin-ring sign (32.4% versus 11.0%, P<0.001), and spotty calcification (55.0% versus 34.9%, P<0.001) was significantly higher in TCFA than in non-TCFA. Low-density noncalcified plaque volume (25.4 versus 15.7 mm3, P<0.001) and remodeling index (1.30 versus 1.20, P=0.002) were higher in TCFA than in non-TCFA. The presence of napkin-ring sign, spotty calcification, high low-density noncalcified plaque volume, and high remodeling index were independent predictors of TCFA. When all 4 predictors were present, the probability of TCFA increased to 82.4%.

CONCLUSIONS

The combined qualitative and quantitative plaque analysis of CTA may be helpful in identifying TCFA in patients with diabetes.

REGISTRATION INFORMATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04523194.

Association between high-sensitivity C-reactive protein and coronary atherosclerosis in a general middle-aged population

Despite abundant knowledge about the relationship between inflammation and coronary atherosclerosis, it is still unknown whether systemic inflammation measured as high-sensitivity C-reactive protein (hsCRP) is associated with coronary atherosclerosis in a general population. This study aimed to examine the association between hsCRP and coronary computed tomography angiography (CCTA)-detected coronary atherosclerosis in a population-based cohort. Out of 30,154 randomly invited men and women aged 50 to 64 years in the Swedish Cardiopulmonary Bioimage Study (SCAPIS), 25,408 had a technically acceptable CCTA and analysed hsCRP. Coronary atherosclerosis was defined as presence of plaque of any degree in any of 18 coronary segments. HsCRP values were categorised in four groups. Compared with hsCRP below the detection limit, elevated hsCRP (≥ 2.3 mg/L) was weakly associated with any coronary atherosclerosis (OR 1.15, 95% CI 1.07-1.24), coronary diameter stenosis ≥ 50% (OR 1.27, 95% CI 1.09-1.47), ≥ 4 segments involved (OR 1.13, 95% CI 1.01-1.26 ) and severe atherosclerosis (OR 1.33, 95% CI 1.05-1.69) after adjustment for age, sex and traditional risk factors. The associations were attenuated after further adjustment for body mass index (BMI), although elevated hsCRP still associated with noncalcified plaques (OR 1.16, 95% CI 1.02-1.32), proposed to be more vulnerable. In conclusion, the additional value of hsCRP to traditional risk factors in detection of coronary atherosclerosis is low. The association to high-risk noncalcified plaques, although unlikely through a causal pathway, could explain the relationship between hsCRP and clinical coronary events in numerous studies.

Harnessing imaging biomarkers to refine individualized cardiovascular disease risk: a case-based discussion

Traditional models of cardiovascular risk assessment rely on population-level risk factors and may not accurately capture individualized risk. Imaging biomarkers such as plaque characterization and pericoronary fat inflammation may offer refined risk prediction and allow physicians to personalize care-plans for cardiovascular disease prevention. The integration of plaque morphology and pericoronary inflammation into clinical care is highlighted using a case-based discussion. This article reviews the existing body of evidence supporting the use of novel biomarkers in an individualized comprehensive risk assessment algorithm.

High-risk coronary plaque in SLE: low-attenuation non-calcified coronary plaque and positive remodelling index

Background

Positive remodelling index and presence of low-attenuation non-calcified plaque (LANCP) are characteristic vessel changes in unstable coronary plaques. We sought to characterise these high-risk plaque features in patients with systemic lupus erythematosus (SLE) and to compare them with controls.

Methods

A total of 72 patients who satisfied the SLICC classification criteria for SLE had coronary CT angiography (CCTA) studies, 30 of which had follow-up CCTA, as screening for occult coronary atherosclerotic disease in asymptomatic individuals. A total of 100 consecutive controls with no known history of lupus, heart disease or revascularisation who had two coronary CT angiograms at least 1 year apart were included in the study. These were asymptomatic patients referred by their primary physicians for screening of coronary artery disease and the screening interval was decided by the primary physicians. The methodology for image acquisition was identical.

Results

LANCP burden at baseline was significantly greater in patients with SLE compared with controls. LANCP volume was significantly greater in patients over 60 years of age (p<0.05) and in those with current prednisone dose >10 mg/day. LANCP burden remained stable over follow-up. There were no significant differences in remodelling index compared with controls.

Conclusion

This is the first study describing high-risk CCTA features of coronary plaque in patients with SLE. Both LANCP and positive remodelling are common in SLE. These characteristic vessel changes may identify patients with SLE at increased risk of cardiovascular events and those in need for more frequent cardiac monitoring.

Vulnerable Plaques Producing an Acute Coronary Syndrome Exhibit a Different CT Phenotype than Those That Remain Silent

Background: All plaques that trigger acute coronary syndromes (ACS) present various characteristics of vulnerability. However, not all vulnerable plaques (VP) lead to an ACS. This raises the question as to which of the established CT vulnerability features hold the highest probability of developing ACS.

Aim: To identify the distinct phenotype of VP that exposes the unstable atheromatous plaque to a higher risk of rupture.

Material and Methods: In total, 20 patients in whom cardiac computed tomographic angiography (CCTA) identified the presence of a vulnerable plaque and who developed an ACS within 6 months after CCTA examination were enrolled in the study, and compared to 20 age- and gender-matched subjects with VPs who did not develop an ACS. All included patients presented VPs at baseline, defined as the presence of minimum 50% degree of stenosis and at least one CT marker of vulnerability (low attenuation plaques [LAP], napkin-ring sign [NRS], positive remodeling [PR], spotty calcifications [SCs]).

Results: The two groups were not different in regards to age, gender, cardiovascular risk factors, and comorbidities. Patients who developed an ACS at six months presented higher volumes of lipid-rich (p = 0.01) and calcified plaques (p = 0.01), while subjects in the control group presented plaques with a larger fibrotic content (p = 0.0005). The most frequent vulnerability markers within VPs that had triggered ACS were LAPs (p <0.0001) and PR (p <0.0001). Multivariate analysis identified LAP as the strongest independent predictor of ACS at 6 months in our study population (OR 8.18 [1.23-95.08], p = 0.04).

Conclusions: VPs producing an ACS exhibit a different phenotype compared to VPs that remain silent. The CCTA profile of VPs producing an ACS includes the presence of low attenuation, positive remodeling, and lipid-rich atheroma. The presence of these features in VPs identifies very high-risk patients, who can benefit from adapted therapeutic strategies in order to prevent an ACS.

The Effect of Periplaque Fat on Coronary Plaque Vulnerability in Patients with Stable Coronary Artery Disease – a 128-multislice CT-based Study

Background: The role of periplaque fat (PPF), as a fragment of the total epicardial adipose tissue, measured in the vicinity of a target coronary lesion, more specifically within the close proximity of a vulnerable plaque, has yet to be evaluated.

The study aimed to evaluate the interrelation between PPF and coronary plaque vulnerability in patients with stable coronary artery disease (CAD). Secondary objective: evaluation of the relationship between the total pericardial fat and markers for plaque vulnerability.

Materials and methods: We prospectively enrolled 77 patients with stable CAD, who underwent 128-multislice computed tomography coronary angiography (CTCA), and who presented minimum one lesion with >50% stenosis. CTCA analysis included measurements of: total pericardial fat and PPF volumes, coronary plaque characteristics, markers for plaque vulnerability – positive remodeling (PR), low attenuation plaque (LAP), spotty calcifications (SC,) napkin ring sign (NRS). Study subjects were divided into two categories: Group 1 – 1 marker of plaque vulnerability (n = 36, 46.75%) and Group 2 – ≥1 marker of vulnerability (n = 41, 53.25%).

Results: The mean age of the population was 61.77 ± 11.28 years, and 41 (53.24%) were males. The analysis of plaque characteristics showed that Group 2 presented significantly longer plaques (16.26 ± 4.605 mm vs. 19.09 ± 5.227 mm, p = 0.02), remodeling index (0.96 ± 0.20 vs. 1.18 ± 0.33, p = 0.0009), and vessel volume (p = 0.027), and more voluminous plaques (147.5 ± 71.74 mm3 vs. 207.7 ± 108.9 mm3, p = 0.006) compared to Group 1. Group 2 presented larger volumes of PPF (512.2 ± 289.9 mm3 vs. 710.9 ± 361.9 mm3, p = 0.01) and of thoracic fat volume (1,616 ± 614.8 mm3 vs. 2,000 ± 850.9 mm3, p = 0.02), compared to Group 1, but no differences were found regarding the total pericardial fat (p = 0.49). Patients with 3 or 4 vulnerability markers (VM) presented significantly larges PPF volumes compared to those with 1 or 2 VM, respectively (p = 0.008). There was a significant positive correlation between PPF volume and the non-calcified (r = 0.474, 95% CI 0.2797–0.6311, p <0.0001), lipid-rich (r = 0.316, 95% CI 0.099–0.504, p = 0.005), and fibro-fatty (r = 0.452, 95% CI 0.2541–0.6142, p <0.0001) volumes. The total pericardial fat was significantly correlated only with the volume of lipid-rich plaques (p = 0.02).

Conclusions: Periplaque fat volume was associated with a higher degree of coronary plaque vulnerability. PPF was correlated with lipid-rich, fibro-fatty, and non-calcified plaque-related volumes, as markers for enhanced plaque vulnerability. PPF volume, assessed with native cardiac computed tomography, could become a novel marker for coronary plaque vulnerability.

Microcalcifications, Their Genesis, Growth, and Biomechanical Stability in Fibrous Cap Rupture

For many decades, cardiovascular calcification has been considered as a passive process, accompanying atheroma progression, correlated with plaque burden, and apparently without a major role on plaque vulnerability. Clinical and pathological analyses have previously focused on the total amount of calcification (calcified area in a whole atheroma cross section) and whether more calcification means higher risk of plaque rupture or not. However, this paradigm has been changing in the last decade or so. Recent research has focused on the presence of microcalcifications (μCalcs) in the atheroma and more importantly on whether clusters of μCalcs are located in the cap of the atheroma. While the vast majority of μCalcs are found in the lipid pool or necrotic core, they are inconsequential to vulnerable plaque. Nevertheless, it has been shown that μCalcs located within the fibrous cap could be numerous and that they behave as an intensifier of the background circumferential stress in the cap. It is now known that such intensifying effect depends on the size and shape of the μCalc as well as the proximity between two or more μCalcs. If μCalcs are located in caps with very low background stress, the increase in stress concentration may not be sufficient to reach the rupture threshold. However, the presence of μCalc(s) in the cap with a background stress of about one fifth to one half the rupture threshold (a stable plaque) will produce a significant increase in local stress, which may exceed the cap rupture threshold and thus transform a non-vulnerable plaque into a vulnerable one. Also, the classic view that treats cardiovascular calcification as a passive process has been challenged, and emerging data suggest that cardiovascular calcification may encompass both passive and active processes. The passive calcification process comprises biochemical factors, specifically circulating nucleating complexes, which would lead to calcification of the atheroma. The active mechanism of atherosclerotic calcification is a cell-mediated process via cell death of macrophages and smooth muscle cells (SMCs) and/or the release of matrix vesicles by SMCs.

Colchicine Therapy and Plaque Stabilization in Patients With Acute Coronary Syndrome: A CT Coronary Angiography Study

OBJECTIVES

The authors sought to evaluate the plaque-modifying effects of low-dose colchicine therapy plus optimal medical therapy (OMT) in patients post-acute coronary syndrome (ACS), as assessed by coronary computed tomography angiography (coronary CTA).

BACKGROUND

Colchicine therapy has been postulated to have beneficial anti-inflammatory effects in patients with ACS, translating into reduction in future adverse cardiovascular events. However, whether favorable plaque modification underpins this is yet unproven.

METHODS

In this prospective nonrandomized observational study of 80 patients with recent ACS (<1 month), patients received either 0.5 mg/day colchicine plus OMT or OMT alone and were followed for 1 year. Our primary outcome was change in low attenuation plaque volume (LAPV), a marker of plaque instability on coronary CTA and robust predictor of adverse cardiovascular events. Secondary outcomes were changes in other coronary CTA measures and in high-sensitivity C-reactive protein (hsCRP).

RESULTS

Mean duration of follow-up was 12.6 months; mean age was 57.4 years. Colchicine therapy significantly reduced LAPV (mean 15.9 mm³ [-40.9%] vs. 6.6 mm³ [-17.0%]; p = 0.008) and hsCRP (mean 1.10 mg/l [-37.3%] vs. 0.38 mg/l [-14.6%]; p < 0.001) versus controls. Reductions in total atheroma volume (mean 42.3 mm³ vs. 26.4 mm³; p = 0.28) and low-density lipoprotein levels (mean 0.44 mmol/l vs. 0.49 mmol/l; p = 0.21) were comparable in both groups. With multivariate linear regression, colchicine therapy remained significantly associated with greater reduction in LAPV (p = 0.039) and hsCRP (p = 0.004). There was also a significant linear association (p < 0.001) and strong positive correlation (r = 0.578) between change in LAPV and hsCRP.

CONCLUSIONS

Our findings suggest, for the first time, that low-dose colchicine therapy favorably modifies coronary plaque, independent of high-dose statin intensification therapy and substantial low-density lipoprotein reduction. The improvements in plaque morphology are likely driven by the anti-inflammatory properties of colchicine, as demonstrated by reductions in hsCRP, rather than changes in lipoproteins. Colchicine may be beneficial as an additional secondary prevention agent in patients post-ACS if validated in future studies.

Noninvasive diagnosis of vulnerable coronary plaque

Myocardial infarction and sudden cardiac death are frequently the first manifestation of coronary artery disease. For this reason, screening of asymptomatic coronary atherosclerosis has become an attractive field of research in cardiovascular medicine. Necropsy studies have described histopathological changes associated with the development of acute coronary events. In this regard, thin-cap fibroatheroma has been identified as the main vulnerable coronary plaque feature. Hence, many imaging techniques, such as coronary computed tomography, cardiac magnetic resonance or positron emission tomography, have tried to detect noninvasively these histomorphological characteristics with different approaches. In this article, we review the role of these diagnostic tools in the detection of vulnerable coronary plaque with particular interest in their advantages and limitations as well as the clinical implications of the derived findings.

Defining the non-vulnerable and vulnerable patients with computed tomography coronary angiography: evaluation of atherosclerotic plaque burden and composition

The shift from coronary plaque stability to plaque instability remains poorly understood despite enormous efforts and expenditures have been assigned to the study of the subject. On the other hand, there have been serious advances in imaging helping us to characterizenon-vulnerable patients The latter has much more value in the clinical decision-making process since it provides high certainty that the patient's probability of a future acute event is low and treatment decisions should be made accordingly. Although coronary plaque rupture is still recognized as the main source of acute thrombotic events, numerous studies have shown that the prediction of events on an individual basis is far more complex and demands a more open approach aimed at characterizing patient risk rather than assessing the risk of thrombosis of a single plaque. Computed tomography coronary angiography (CTCA) has the ability to evaluate non-invasively the extent, burden, severity, and characteristics of coronary artery disease (CAD) and has a close relationship to intravascular ultrasound. On the basis of an excellent negative predictive value with an annualized event rate of ∼0.20% assessed over more than 6000 patients, thus providing a 5-year warranty period, CTCA has been identified as the finest non-invasive tool to exclude CAD. This means that CTCA is able to reliably characterize the non-vulnerable patient. Conversely, in the past few years, several studies have attempted to establish CTCA-derived predictors of acute coronary syndromes, both from a lesion level and a patient level basis with very low positive predictive value, thus questioning the vulnerable patient/plaque concept.

Coronary CT angiography in managing atherosclerosis

Invasive coronary angiography (ICA) was the only method to image coronary arteries for a long time and is still the gold-standard. Technology of noninvasive imaging by coronary computed-tomography angiography (CCTA) has experienced remarkable progress during the last two decades. It is possible to visualize atherosclerotic lesions in the vessel wall in contrast to “lumenography” performed by ICA. Coronary artery disease can be ruled out by CCTA with excellent accuracy. The degree of stenoses is, however, often overestimated which impairs specificity. Atherosclerotic lesions can be characterized as calcified, non-calcified and partially calcified. Calcified plaques are usually quantified using the Agatston-Score. Higher scores are correlated with worse cardiovascular outcome and increased risk of cardiac events. For non-calcified or partially calcified plaques different angiographic findings like positive remodelling, a large necrotic core or spotty calcification more frequently lead to myocardial infarctions. CCTA is an important tool with increasing clinical value for ruling out coronary artery disease or relevant stenoses as well as for advanced risk stratification.

Assessment of coronary artery disease using coronary computed tomography angiography and biochemical markers

Chronic inflammatory mechanisms in the arterial wall lead to atherosclerosis, and include endothelial cell damage, inflammation, apoptosis, lipoprotein deposition, calcification and fibrosis. Cardiac computed tomography angiography (CCTA) has been shown to be a promising tool for non-invasive assessment of theses specific compositional and structural changes in coronary arteries. This review focuses on the technical background of CCTA-based quantitative plaque characterization. Furthermore, we discuss the available evidence for CCTA-based plaque characterization and the potential role of CCTA for risk stratification of patients with coronary artery disease.

Role of computed tomography for diagnosis and risk stratification of patients with suspected or known coronary artery disease

Cardiac computed tomographic angiography (CCTA) has emerged as a powerful imaging modality for the detection and prognostication of individuals with suspected coronary artery disease. Because calcification of coronary plaque occurs in proportion to the total atheroma volume, the initial diagnostic potential of CCTA focused on the identification and quantification of coronary calcium in low- to intermediate-risk individuals, a finding that tracks precisely with the risk of incident adverse clinical events. Beyond noncontrast detection of coronary calcium, CCTA using iodinated contrast yields incremental information about the degree and distribution of coronary plaques and stenosis, as well as vessel wall morphology and atherosclerotic plaque features. This additive information offers the promise of CCTA to provide a more comprehensive view of total atherosclerotic burden because it relates to myocardial ischemia and future adverse clinical events. Furthermore, emerging data suggest the prognostic and diagnostic importance of stenosis severity detection and atherosclerotic plaque features described by CCTA including positive remodeling, low-attenuation plaque, and spotty calcification, which have been associated with the vulnerability of plaque. We report a summary of the evidence supporting the role of CCTA in the detection of subclinical and clinical coronary artery disease in both asymptomatic and symptomatic patients and discuss the potential of CCTA to augment the identification of at-risk individuals. CCTA and coronary artery calcium scoring offer the ability to improve risk stratification, discrimination, and reclassification of the risk in patients with suspected coronary artery disease and to noninvasively determine the measures of stenosis severity and atherosclerotic plaque features.

Quantification of coronary artery plaque using 64-slice dual-source CT: comparison of semi-automatic and automatic computer-aided analysis based on intravascular ultrasonography as the gold standard

We evaluated the feasibility of automatic computer-aided analysis (CAA) compared with semi-automatic CAA for differentiating lipid-rich from fibrous plaques based on coronary CT angiography (CCTA) imaging. Seventy-four coronary plaques in 57 patients were evaluated by CCTA using 64-slice dual-source CT. Quantitative analysis of coronary artery plaques was performed by measuring the relative volumes (low, medium, and calcified) of plaque components using automatic CAA and by measuring mean CT density using semi-automatic CAA. We compared the two plaque measurement methods for lipid-rich and fibrous plaques using Pearson's correlation. Intravascular ultrasonography was used as the goal standard for assessment of plaques. Mean CT density of plaques tended to increase in the order of lipid [36 ± 19 Hounsfield unit (HU)], fibrous (106 ± 34 HU), and then calcified plaques (882 ± 296 HU). The mean relative volumes of 'low' components measured by automatic CAA were 13.8 ± 4.6, 7.9 ± 6.7, and 3.5 ± 3.0 % for lipid, fibrous, and calcified plaques, respectively (r = -0.348, P = 0.022). The mean relative volumes of 'medium' components on automatic CAA were 12.9 ± 4.1, 15.7 ± 9.6, and 5.6 ± 4.8 % for lipid, fibrous, and calcified plaques, respectively (r = -0.385, P = 0.011). The mean relative volumes of low and medium components within plaques significantly correlated with the types of plaques. Plaque analysis using automatic CAA has the potential to differentiate lipid from fibrous plaques based on measurement of the relative volume percentages of the low and medium components.

Quantitative analysis of coronary plaque composition by dual-source CT in patients with acute non-ST-elevation myocardial infarction compared to patients with stable coronary artery disease correlated with virtual histology intravascular ultrasound

RATIONALE AND OBJECTIVES

To quantitatively assess coronary atherosclerotic plaque composition in patients with acute non-ST elevation myocardial infarction (NSTEMI) and patients with stable coronary artery disease (CAD) by coronary computed tomography angiography (cCTA) correlated with virtual histology intravascular ultrasound (VH-IVUS).

MATERIALS AND METHODS

Sixty patients (35 with NSTEMI) were included. Corresponding plaques were assessed by dual-source cCTA and VH-IVUS regarding volumes and percentages of fatty, fibrous, and calcified component; overall plaque burden; and maximal percent area stenosis. Possible differences between patient groups were investigated. Concordance between cCTA and VH-IVUS measurements was validated by Bland-Altman analysis.

RESULTS

Forty corresponding plaques (22 of patients with NSTEMI) were finally analyzed by cCTA and VH-IVUS. cCTA plaque analysis revealed no significant differences between plaques of patients with NSTEMI and stable CAD regarding absolute and relative amounts of any plaque component (fatty: 20 mm³/13% versus 17 mm³/14%; fibrous: 81 mm³/63% versus 80 mm³/53%; calcified: 16 mm³/14% versus 26 mm³/26%; all P > .05) or overall plaque burden (153 mm³ versus 165 mm³; P > .05), nor did VH-IVUS plaque analysis. VH-IVUS measured a higher area stenosis in patients with NSTEMI compared to patients with stable CAD (76% versus 68%, P = .01; in cCTA 69% versus 65%, P = .2). Volumes of fatty component were measured systematically lower in cCTA, whereas calcified and fibrous volumes were higher. No significant bias was observed comparing volumes of overall noncalcified component and overall plaque burden.

CONCLUSION

Plaques of patients with acute NSTEMI and of patients with stable CAD cannot be differentiated by quantification of plaque components. cCTA and VH-IVUS differ in plaque component analysis.

Changing views of the biomechanics of vulnerable plaque rupture: a review

This review examines changing perspectives on the biomechanics of vulnerable plaque rupture over the past 25 years from the first finite element analyses (FEA) showing that the presence of a lipid pool significantly increases the local tissue stress in the atheroma cap to the latest imaging and 3D FEA studies revealing numerous microcalcifications in the cap proper and a new paradigm for cap rupture. The first part of the review summarizes studies describing the role of the fibrous cap thickness, tissue properties, and lesion geometry as main determinants of the risk of rupture. Advantages and limitations of current imaging technologies for assessment of vulnerable plaques are also discussed. However, the basic paradoxes as to why ruptures frequently did not coincide with location of PCS and why caps >65 μm thickness could rupture at tissue stresses significantly below the 300 kPa critical threshold still remained unresolved. The second part of the review describes recent studies in the role of microcalcifications, their origin, shape, and clustering in explaining these unresolved issues including the actual mechanism of rupture due to the explosive growth of tiny voids (cavitation) in local regions of high stress concentration between closely spaced microinclusions oriented along their tensile axis.

Beyond Coronary Stenosis: Coronary Computed Tomographic Angiography for the Assessment of Atherosclerotic Plaque Burden

Coronary computed tomographic angiography (CCTA) is emerging as a key non-invasive method for assessing cardiovascular risk by measurement of coronary stenosis and coronary artery calcium (CAC). New advancements in CCTA technology have led to the ability to directly identify and quantify the so-called "vulnerable" plaques that have features of positive remodeling and low density components. In addition, CCTA presents a new opportunity for noninvasive measurement of total coronary plaque burden that has not previously been available. The use of CCTA needs also to be balanced by its risks and, in particular, the associated radiation exposure. We review current uses of CCTA, CCTA's ability to measure plaque quantity and characteristics, and new developments in risk stratification and CCTA technology. CCTA represents a quickly developing field that will play a growing role in the non-invasive management of cardiovascular disease.

Imaging assessment of cardiovascular risk in asymptomatic adults

OBJECTIVE

This article will address the role of coronary artery calcium (CAC) and carotid intima-media thickness screening in asymptomatic at-risk adults and the broader concept of vulnerable plaque as it applies to this population.

CONCLUSION

Imaging for assessment of cardiovascular risk in asymptomatic adults has been the subject of considerable interest and some controversy. The incorporation of CAC and carotid intima-media thickness assessment into recent guidelines reflects the growing evidence base for these applications.

Coronary atherosclerosis imaging by coronary CT angiography: current status, correlation with intravascular interrogation and meta-analysis

Coronary computed tomography angiography (CTA) allows coronary artery visualization and the detection of coronary stenoses. In addition; it has been suggested as a novel, noninvasive modality for coronary atherosclerotic plaque detection, characterization, and quantification. Emerging data show that coronary CTA-based semiquantitative plaque characterization and quantification are sufficiently reproducible for clinical purposes, and fully quantitative approaches may be appropriate for use in clinical trials. Furthermore, several lines of investigation have validated plaque imaging by coronary CTA against other imaging modalities such as intravascular ultrasound/"virtual histology" and optical coherence tomography, and there are emerging data using biochemical modalities such as near-infrared spectroscopy. Finally, clinical validation in patients with acute coronary syndrome and in the outpatient setting has shown incremental value of CTA-based plaque characterization for the prediction of major cardiovascular events. With recent developments in image acquisition and reconstruction technologies, coronary CTA can be performed with relatively low radiation exposure. With further technological innovation and clinical research, coronary CTA may become an important tool in the quest to identify vulnerable plaques and the at-risk patient.

Comparison of the relation between the calcium score and plaque characteristics in patients with acute coronary syndrome versus patients with stable coronary artery disease, assessed by computed tomography angiography and virtual histology intravascular ultrasound

A considerable number of patients with an acute coronary syndrome (ACS) who present with a 0 or low calcium score (CS) still demonstrate coronary artery disease (CAD) and significant stenosis. The aim of the present study was to evaluate the relation between the CS and the degree and character of atherosclerosis in patients with suspected ACS versus patients with stable CAD obtained by computed tomography angiography and virtual histology intravascular ultrasound (VH IVUS). Overall 112 patients were studied, 53 with ACS and 59 with stable CAD. Calcium scoring and computed tomography angiography were performed and followed by VH IVUS. On computed tomography angiography each segment was evaluated for plaque and classified as noncalcified, mixed, or calcified. Vulnerable plaque characteristics on VH IVUS were defined by percent necrotic core and presence of thin-cap fibroatheroma. If the CS was 0, patients with ACS had a higher mean number of plaques (5.0 ± 2.0 vs 2.0 ± 1.9, p <0.05) and noncalcified plaques (4.6 ± 3.5 vs 1.3 ± 1.9, p <0.05) on computed tomography angiography than those with stable CAD. If the CS was 0, VH IVUS demonstrated that patients with ACS had a larger amount of necrotic core area (0.58 ± 0.73 vs 0.22 ± 0.43 mm(2), p <0.05) and a higher mean number of thin-cap fibroatheromas (0.6 ± 0.7 vs 0.1 ± 0.3, p <0.05) than patients with stable CAD. In conclusion, even in the presence of a 0 CS, patients with ACS have increased plaque burden and increased vulnerability compared to patients with stable CAD. Therefore, absence of coronary calcification does not exclude the presence of clinically relevant and potentially vulnerable atherosclerotic plaque burden in patients with ACS.

Imaging of subclinical atherosclerosis: questions and answers

An increasingly important public health issue is the identification, stratification, and optimal management of individuals with subclinical atherosclerosis. This review addresses those aspects of noninvasive imaging of subclinical atherosclerosis that are most available and relevant to the practicing radiologist.

Noninvasive imaging of the vulnerable atherosclerotic plaque

Atherosclerosis is an inflammatory disease, complicated by progressively increasing atherosclerotic plaques that eventually may rupture. Plaque rupture is a major cause of cardiovascular events, such as unstable angina, myocardial infarction, and stroke. A number of noninvasive imaging techniques have been developed to evaluate the vascular wall in an attempt to identify so-called vulnerable atherosclerotic plaques that are prone to rupture. The purpose of the present review is to systematically investigate the accuracy of noninvasive imaging techniques in the identification of plaque components and morphologic characteristics associated with plaque vulnerability, assessing their clinical and diagnostic value.

[Relationship among RR interval, optimal reconstruction phase, temporal resolution, and image quality of end-systolic reconstruction of coronary CT angiography in patients with high heart rates: in search of the optimal acquisition protocol]

The purpose of this study is to elucidate the relationship among RR interval (RR), the optimal reconstruction phase, and adequate temporal resolution (TR) to obtain coronary CT angiography images of acceptable quality using 64-MDCT (Aquilion 64) of end-systolic reconstruction in 407 patients with high heart rates. Image quality was classified into 3 groups [rank A (excellent): 161, rank B (acceptable): 207, and rank C (unacceptable): 39 patients]. The optimal absolute phase (OAP) significantly correlated with RR [OAP (ms)=119-0.286RR (ms), r=0.832, p<0.0001], and the optimal relative phase (ORP) also significantly correlated with RR [ORP (%)=62-0.023RR (ms), r=0.656, p<0.0001], and the correlation coefficient of OAP was significantly (p<0.0001) higher than that of ORP. The OAP range (±2SD) in which it is highly possible to get a static image was from [119-0.286RR (ms)-46] to [119-0.286RR (ms)+46]. The TR was significantly different among ranks A (97 ± 22 ms), B (111 ± 31 ms) and C (135 ± 34 ms). The TR significantly correlated with RR in ranks A (TR=-16+0.149RR, r=0.767, p<0.0001), B (TR=-15+0.166RR, r=0.646, p<0.0001), and C (TR=52+0.117RR, r=0.425, p=0.0069). Rank C was distinguished from ranks A or B by linear discriminate analysis (TR=-46+0.21RR), and the discriminate rate was 82.6%. In conclusion, both the OAP and adequate TR depend on RR, and the OAP range (±2SD) can be calculated using the formula [119-0.286RR (ms)-46] to [119-0.286RR (ms)+46], and an adequate TR value would be less than (-46+0.21RR).

Flat-panel versus 64-channel computed tomography for in vivo quantitative characterization of aortic atherosclerotic plaques

BACKGROUND

Flat-panel computed tomography (FpCT) provides better spatial resolution than 64-channel CT (64-CT) and may improve in vivo quantitative assessment of atherosclerotic plaques.

METHODS AND RESULTS

Lesions in 184 aortic histology sections from 6 Watanabe heritable hyperlipidemic rabbits were quantitatively compared with 64-CT (image thickness, 0.625 mm) and FpCT (image thickness, 0.150 mm) images. Images were re-oriented perpendicular to the vessel centerline. For detecting plaque, FpCT and 64-CT were not significantly different (sensitivity, 76% vs 66%; P=NS). Although FpCT was significantly more sensitive (42% vs 0%; P=<0.001) for detecting eccentric lesions, the area under the curve (AUC) for FpCT (0.6) was not significantly different from that for 64-CT (0.45; P=NS). In detecting plaques with ≤ 10% lipid (low attenuation foci), FpCT was significantly more sensitive than 64-CT (24% vs 0.7%; P<0.00) and had a significantly greater AUC (0.6 vs 0.5; P<0.006). Additionally, FpCT was more sensitive (65% vs 0%; P<0.00) in detecting plaques with ≤ 5% calcium (high attenuation foci) but not in detecting branch points. Both FpCT and histology allowed us to detect low-attenuation foci as small as 0.3mm in diameter, whereas 64-CT allowed us to detect only low-attenuation foci ≥ 1.5mm in diameter.

CONCLUSIONS

Flat-panel CT seemed to have more potential for quantitatively screening low-risk small atherosclerotic lesions, whereas 64-CT was apparently more useful when imaging established, well-characterized lesions, particularly when measuring the vascular wall thickness in a rabbit model of atherosclerosis.

[Comparison of radiation dose reduction of prospective ECG-gated one beat scan using 320 area detector CT coronary angiography and prospective ECG-gated helical scan with high helical pitch (FlashScan) using 64 multidetector-row CT coronary angiography]

BACKGROUND

A high radiation dose associated with 64 multidetector-row computed tomography (64-MDCT) is a major concern for physicians and patients alike. A new 320 row area detector computed tomography (ADCT) can obtain a view of the entire heart with one rotation (0.35 s) without requiring the helical method. As such, ADCT is expected to reduce the radiation dose. We studied image quality and radiation dose of ADCT compared to that of 64-MDCT in patients with a low heart rate (HR≤60).

METHODS

Three hundred eighty-five consecutive patients underwent 64-MDCT and 379 patients, ADCT. Patients with an arrhythmia were excluded. Prospective ECG-gated helical scan with high HP (FlashScan) in 64 was used for MDCT and prospective ECG-gated conventional one beat scan, for 320-ADCT. Image quality was visually evaluated by an image quality score. Radiation dose was estimated by DLP (mGy･cm) for 64-MDCT and DLP.e (mGy･cm) for 320-ADCT.

RESULTS

Radiation dose of 320-ADCT (208±48 mGy･cm) was significantly (P<0.0001) lower than that of 64-MDCT (484±112 mGy･cm), and image quality score of 320-ADCT (3.0±0.2) was significantly (P=0.0011) higher than that of 64-MDCT (2.9±0.4). Scan time of 320-ADCT (1.4±0.1 s) was also significantly (P<0.0001) shorter than that of 64-MDCT (6.8±0.6 s).

CONCLUSIONS

320-ADCT can achieve not only a reduction in radiation dose but also a superior image quality and shortening of scan time compared to 64-MDCT.

[A new acquisition method with pacemaker resetting of coronary multidetector-row computed tomography for reduction of radiation dose in patients with pacemaker]

We proposed a new acquisition method of coronary MDCT achieved by pacing rate resetting and/or propranolol or verapamil injection in patients with a pacemaker. Coronary MDCT was undertaken in 57 patients with a pacemaker (DDD: 51, VVI: 6) and in 2975 patients with sinus rhythm as control using Aquilion 64 (Toshiba). Pacing rate was reset to 60 beats per minute (bpm) in DDD, and spontaneous beats were suppressed by propranolol injection. Pacing rate was reset to 70 bpm in atrial fibrillation with VVI, and spontaneous beats were suppressed by verapamil injection. Coronary MDCT was undertaken using as high a beam pitch (BP) as possible. When spontaneous beats were not suppressed, we selected the optimal gantry speed and BP to get the highest temporal resolution. Image quality makes no significant difference between pacemaker and sinus rhythm. When spontaneous beats were completely suppressed (all pacing), mean radiation dose and acquisition time, respectively, decreased by 33.0% and 35.2% in DDD compared with the method recommended by Heart Navi (by Toshiba), and they decreased by 38.1% and 25.9%, respectively, in VVI compared with the method recommended by Heart Navi. We could not estimate coronary stenosis in the proximal right coronary artery by lead artifacts in 30% of DDD pacemakers. In conclusion, the new method is useful for not only reducing radiation dose and acquisition time, but also for maintaining image quality in patients with a pacemaker.