Arterial wall imaging: evaluation with 16-section multidetector CT in blood vessel phantoms and ex vivo coronary arteries

Plaque characteristics on coronary CT angiography associated with the positive findings of fractional flow reserve and instantaneous wave-free ratio

BACKGROUND

Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are useful in determining indications for revascularization of coronary artery disease (CAD). Although the discordance of FFR and iFR was noted in approximately 20%, this cause has not been well established. We investigated patient background and features on coronary CT angiography (CCTA) showing not only FFR- and iFR-positive findings but also discordance between FFR ≤ 0.8 and iFR ≤ 0.89.

METHODS

Subjects were consecutively treated in 83 cases with 105 vessels in which stenosis of 30-90% was detected at one vessel of at least 2 mm or more in the major epicardial vessels and FFR and iFR was performed within subsequent 90 days, among suspected CAD which underwent CCTA. The factors affecting not only FFR- and iFR-positive findings, respectively, but also discordance between FFR and iFR was evaluated using logistic regression analysis on per-patient and per-vessel basis.

RESULTS

FFR- and iFR-positive findings were observed in 42 vessels (40.0%) and 34 vessels (32.3%), respectively. Discordance between FFR ≤ 0.8 and iFR ≤ 0.89 was observed in 22 vessels (21.0%) of 21 patients. In multivariate logistic analysis, LAD (OR 3.55; 95%CI 1.20-11.71; p = 0.0217) and lumen volume/myocardial weight (L/M) ratio (OR 0.93; 0.86-0.99, p = 0.0290) were significant predictors for FFR-positive findings. For iFR-positive findings, LAD (OR 3.86; 95%CI 1.12-13.31; p = 0.0236) was only significant predictor. In FFR ≤ 0.8 and iFR > 0.89 group (15 vessels, 14.3%), positive remodeling (PR) (OR 5.03, 95%CI 1.23-20.48, p = 0.0205) was significant predictor. In FFR > 0.8 and iFR ≤ 0.89 group (7 vessels, 6.7%), there were no significant predictors.

CONCLUSION

On CCTA characteristics, a relevant predictor for FFR-positive findings included low L/M ratio. PR was significant predictor in FFR-positive, iFR-negative patients among those with discordance between the FFR and iFR.

State of the art of coronary computed tomography angiography

OBJECTIVES

The aim of this paper is to evaluate contrast media (CM) bolus geometry and opacification patterns in the coronary arteries with particular focus on patient, scanner and safety considerations during coronary computed tomography angiography (CCTA).

KEY FINDINGS

The rapid evolution of computed tomography (CT) technology has seen this imaging modality challenge conventional coronary angiography in the evaluation of coronary artery disease. Increases in spatial and temporal resolutions have enabled CCTA to become the modality of choice when evaluating the coronary vascular tree as an alternative in the diagnostic algorithm for acute chest pain. However, these new technologic improvements in scanner technology have imposed new challenges for the optimisation of CM delivery and image acquisition strategies.

CONCLUSION

Understanding basic CM-imaging principles is essential for designing optimal injection protocols according to each specific clinical scenario, independently of scanner technology.

IMPLICATIONS FOR PRACTICE

With rapid advances in CT scanner technology including faster scan acquisitions, the risk of poor opacification of coronary vasculature increases significantly. Therefore, awareness of CM delivery protocols is paramount to consistently provide optimal image quality at a low radiation dose.

CT-pathologic correlation of non-calcified atherosclerotic arterial plaques: a study using carotid endarterectomy specimens

OBJECTIVE

Pathologic features of atherosclerotic plaques on CT are not established. We compared CT values among pathologically confirmed plaque constituents and evaluated their ability to distinguish plaque constituents.

METHODS

50 histopathological images of carotid endarterectomy samples from 10 males and 2 females (age 54-74 years, average 65.9 years) were examined. We compared pre-operative CT [pre-contrast (CT-P), early post-contrast phase (CT-E), delayed post-contrast phase (CT-D)] of lipid-rich necrotic core (NC) and fibrous tissue (F) plaque components with pathological images. The ability of features to differentiate plaque components using several discrimination techniques were compared.

RESULTS

CT values of NC and F were 36 ± 13, 45 ± 11 (mean ± standard deviation, Hounsfield unit, HU), 41 ± 17, 69 ± 18, and 44 ± 16, 70 ± 13 in CT-P (p < 0.01), CT-E (p < 0.0001), and CT-D (p < 0.0001), respectively. The threshold, sensitivity, and accuracy for distinguishing NC from F were 44 HU, 74%, and 68%; 55 HU, 85%, and 85%; and 63 HU, 92%, and 84% in CTP, CT-E, and CT-D, respectively. CT-P had lower accuracy than CT-E and CT-D (both p < 0.05), but CT-E and CT-D were similar. CT-E and CT-D yielded 90 and 91% sensitivity and accuracy, respectively in linear discrimination analysis.

CONCLUSION

In both pre- and post-contrast CT, CT values were lower in NC than F. Although values overlapped, using two-phase post-contrast CTs improved discrimination ability.

ADVANCES IN KNOWLEDGE

Our findings may help to establish computer-aided diagnosis of vulnerable atherosclerotic plaques in future.

Sexual Dimorphism of Coronary Artery Disease in a Low- and Intermediate-Risk Asymptomatic Population: Association with Coronary Vessel Wall Thickness at MRI in Women

Purpose

To demonstrate the association between coronary vessel wall thickness (VWT) measured at MRI and coronary artery disease (CAD) risk in asymptomatic groups at low and intermediate risk on the basis of Framingham score.

Materials and Methods

A total of 131 asymptomatic adults were prospectively enrolled. All participants underwent CT angiography for scoring CAD, and coronary VWT was measured at 3.0-T MRI. Nonlinear single and multivariable regression analyses with consideration for interaction with sex were performed to investigate the association of traditional atherosclerotic risk factors and VWT with CT angiography-based CAD scores.

Results

The analysis included 62 women and 62 men with low or intermediate Framingham score of less than 20%. Age (mean age, 45.0 years ± 14.5 [standard deviation]) and body mass index were not different between the groups. Age, sex, and VWT were individually significantly associated with all CT angiography-based CAD scores (P < .05). Additionally, sex was a significant effect modifier of the associations with all CAD scores. In men, age was the only statistically significant independent risk factor of CAD; in women, VWT was the only statistically significant independent surrogate associated with increased CAD scores (P < .05).

Conclusion

In asymptomatic women, VWT MRI was the primary independent surrogate of CAD, whereas age was the strongest risk factor in men. This study suggests that VWT may be used as a CAD surrogate in women at low or intermediate risk of CAD. Further longitudinal studies are required to determine the potential implication and use of this MRI technique for the preventative management of CAD in women.© RSNA, 2019.

Multislice Computed Tomography Capabilities in Assessment of the Coronary Arteries Atherosclerotic Lesions

Until today, there are no universally accepted methods for detection of unstable atherosclerotic plaques, even though many recent studies were devoted to this issue. In this article we present modern possibilities of computed tomography in visualization of atherosclerotic coronary lesion, including the detection of unstable lesions, whot in turn, can help in diagnosing subclinical exacerbation of ischemic heart disease and in the stratification of risks of acute coronary events.

Optimization of Computed Tomography Coronary Angiography for Improved Plaque Detection

OBJECTIVE

The study aims to optimize visualization of the coronary wall during computed tomography coronary angiography.

METHODS

A coronary plaque phantom was scanned on a wide-volume computed tomography scanner. Spatial resolution, contrast resolution, and vessel wall thickness were measured at different x-ray tube currents and voltages.

RESULTS

Spatial resolution ranged from 0.385 to 0.625 mm and was significantly lower at higher currents. Contrast-to-noise ratio was significantly higher at higher currents. The most accurate wall thickness measurements were quantified at 300 and 400 mA for 80 and 100 kVp and 300 mA for 120 and 135 kVp.

CONCLUSIONS

Lower spatial resolution at higher currents was due to added blur from increased focal spot size. Contrast-to-noise ratio was higher at higher currents owing to decreased quantum noise. Wall thickness was measured more accurately at intermediate currents with midrange contrast-to-noise ratio but optimal spatial resolution. For accurate coronary wall thickness measurement, contrast-to-noise ratio is compromised to achieve optimal spatial resolution.

Coronary atherosclerosis and dilation in hyper IgE syndrome patients: Depiction by magnetic resonance vessel wall imaging and pathological correlation

BACKGROUND AND AIMS

Autosomal dominant hyper-IgE (AD-HIES) is a primary immunodeficiency caused by mutations in STAT3. Elevated levels of IgE, an ineffective immune response, connective tissue abnormalities, and coronary arterial dilation and tortuosity characterize AD-HIES. To date, coronary artery evaluation in AD-HIES patients has been limited to lumenography measurements. Direct in vivo coronary vessel wall (VW) imaging may allow for better interrogation of coronary vessel abnormalities. The goal of this prospective study was to evaluate the coronary VW of AD-HIES patients using Magnetic Resonance Imaging (MRI) and histology. VW image findings were compared in healthy subjects and subjects with coronary atherosclerotic disease (CAD).

METHODS

A total of 28 subjects (10 with AD-HIES, 8 healthy, 10 with CAD) were studied by coronary VW MRI imaging. Additionally, a post-mortem coronary artery from one VW imaged AD-HIES patient was examined.

RESULTS

Coronary VW in AD-HIES was thicker than in healthy controls but not significantly different from VW thickness in CAD subjects. AD-HIES coronaries showed increased VW area compared to healthy controls and CAD subjects. On histology, the AD-HIES coronary artery had findings consistent with atherosclerotic plaque, but had minimal luminal narrowing, deficient adventitia thickening and absence of both internal and external elastic laminae.

CONCLUSIONS

This is the first study to demonstrate subclinical coronary atherosclerosis in AD-HIES patients on VW imaging by MRI. Histologic evaluation confirmed the presence of atherosclerosis with lack of supportive adventitial thickening and elastic components. These findings suggest mechanisms for coronary dilation in AD-HIES and thereby help direct clinical management.

Coronary plaque characterization using CT

OBJECTIVE. In this article, we review the histopathologic classification of coronary atherosclerotic plaques and describe the possibilities and limitations of CT regarding the evaluation of coronary artery plaques. CONCLUSION. The composition of atherosclerotic plaques in the coronary arteries displays substantial variability and is associated with the likelihood for rupture and downstream ischemic events. Accurate identification and quantification of coronary plaque components on CT is challenging because of the limited temporal, spatial, and contrast resolutions of current scanners. Nonetheless, CT may provide valuable information that has potential for characterization of coronary plaques. For example, the extent of calcification can be determined, lipid-rich lesions can be separated from more fibrous ones, and positive remodeling can be identified.

Comprehensive plaque assessment by coronary CT angiography

Most acute coronary syndromes are caused by sudden luminal thrombosis due to atherosclerotic plaque rupture or erosion. Preventing such an event seems to be the only effective strategy to reduce mortality and morbidity of coronary heart disease. Coronary lesions prone to rupture have a distinct morphology compared with stable plaques, and provide a unique opportunity for noninvasive imaging to identify vulnerable plaques before they lead to clinical events. The submillimeter spatial resolution and excellent image quality of modern computed tomography (CT) scanners allow coronary atherosclerotic lesions to be detected, characterized, and quantified. Large plaque volume, low CT attenuation, napkin-ring sign, positive remodelling, and spotty calcification are all associated with a high risk of acute cardiovascular events in patients. Computation fluid dynamics allow the calculation of lesion-specific endothelial shear stress and fractional flow reserve, which add functional information to plaque assessment using CT. The combination of morphologic and functional characteristics of coronary plaques might enable noninvasive detection of vulnerable plaques in the future.

Histogram analysis of lipid-core plaques in coronary computed tomographic angiography: ex vivo validation against histology

PURPOSE

In coronary computed tomographic angiography (CTA), low attenuation of coronary atherosclerotic plaque is associated with lipid-rich plaques. However, an overlap in Hounsfield units (HU) between fibrous and lipid-rich plaque as well as an influence of luminal enhancement on plaque attenuation was observed and may limit accurate detection of lipid-rich plaques by CTA. We sought to determine whether the quantitative histogram analysis improves accuracy of the detection of lipid-core plaque (LCP) in ex vivo hearts by validation against histological analysis.

MATERIALS AND METHODS

Human donor hearts were imaged with a 64-slice computed tomographic scanner using a standard coronary CTA protocol, optical coherence tomography (OCT), a histological analysis. Lipid-core plaque was defined in the histological analysis as any fibroatheroma with a lipid/necrotic core diameter of greater than 200 μm and a circumference greater than 60 degrees as well as a cap thickness of less than 450 μm. In OCT, lipid-rich plaque was determined as a signal-poor region with diffuse borders in 2 quadrants or more. In CTA, the boundaries of the noncalcified plaque were manually traced. The absolute and relative areas of low attenuation plaque based on pixels with less than 30, less than 60, and less than 90 HU were calculated using quantitative histogram analysis.

RESULTS

From 5 hearts, a total of 446 cross sections were coregistered between CTA and the histological analysis. Overall, 55 LCPs (12%) were identified by the histological analysis. In CTA, the absolute and relative areas of low attenuation plaque less than 30, less than 60, and less than 90 HU were 0.14 (0.31) mm2 (4.22% [9.02%]), 0.69 (0.95) mm2 (18.28% [21.22%]), and 1.35 (1.54) mm2 (35.65% [32.07%]), respectively. The low attenuation plaque area correlated significantly with histological lipid content (lipid/necrotic core size [in square millimeter] and a portion of lipid/necrotic core on the entire plaque) at all thresholds but was the strongest at less than 60 HU (r = 0.53 and r = 0.48 for the absolute and relative areas, respectively). Using a threshold of 1.0 mm2 or greater, the absolute plaque area of less than 60 HU in CTA yielded 69% sensitivity and 80% specificity to detect LCP, whereas sensitivity and specificity were 73% and 71% for using 25.0% or higher relative area less than 60 HU. The discriminatory ability of CTA for LCP was similar between the absolute and relative areas (the area under the curve, 0.744 versus 0.722; P = 0.37). Notably, the association of the low attenuation plaque area in CTA with LCP was not altered by the luminal enhancement for the relative (P = 0.48) but for the absolute measurement (P = 0.03). Similar results were achieved when validated against lipid-rich plaque by OCT in a subset of 285 cross sections.

CONCLUSIONS

In ex vivo conditions, the relative area of coronary atherosclerotic plaque less than 60 HU in CTA as derived from quantitative histogram analysis has good accuracy to detect LCP as compared with a histological analysis independent of differences in luminal contrast enhancement.

Characterization of atherosclerotic plaque: a contrast-detail study using multidetector and cone-beam computed tomography

A Hindmarsh-Rose model perceptibility phantom containing inserts with various in vitro atherosclerotic plaque compositions was constructed and imaged on a clinical 64 slice multidetector (MDCT) system using 80 and 120 kVp settings and two other cone-beam (CBCT) systems at 80 kVp. Perceptibility of the simulated lipid-fibrotic plaque solutions in the images was evaluated by six observers. The effective doses of the protocols employed were estimated using phantom CTDI-vol measurements placed at identical settings. The CBCT system allowed reduction in effective dose in comparison with the conventional MDCT system for imaging of the carotid plaque phantoms without degrading image quality. The CBCT dose was less than MDCT, with a mean dose of 1.14 ± 0.01 mSv and 1.11 ± 0.02 mSv for MDCT using two measuring techniques vs. 0.35 ± 0.01 mSv for CBCT. The image quality analysis showed no significant differences in the contrast-detail (C-D) curves of the best performing CBCT vs. clinical MDCT (p &gt; 0.05) using a Mann-Whitney U test. Results indicate that low-tube-potential CBCT may produce comparable C-D resolution for phantom-based representations of soft plaque types with respect to MDCT systems. This study suggests that the utility of low kVp CT techniques for evaluating carotid vulnerable atherosclerotic plaque merits further study.

Apoprotein B, small-dense LDL and impaired HDL remodeling is associated with larger plaque burden and more noncalcified plaque as assessed by coronary CT angiography and intravascular ultrasound with radiofrequency backscatter: results from the ATLANTA I study

Background

Apoprotein B–containing lipoproteins are atherogenic, but atheroprotective functions of apoprotein A–containing high‐density lipoprotein (HDL) particles are poorly understood. The association between lipoproteins and plaque components by coronary computed tomography angiography (CTA) and intravascular ultrasound with radiofrequency backscatter (IVUS/VH) has not been evaluated.

Methods and Results

Quantitative, 3‐dimensional plaque measurements were performed in 60 patients with CTA and IVUS/VH. Apoproteins, lipids, and HDL subpopulations were measured with 2‐dimensional (2D) gel electrophoresis, and correlation was assessed with univariate and multivariable models. ApoB particles were associated with a higher proportion of noncalcified plaque (NCP) and a lower proportion of calcified plaque (small, dense low‐density lipoprotein cholesterol and high‐density NCP: r=0.3, P=0.03; triglycerides and low‐density NCP: r=0.34, P=0.01). Smaller, dense, lipid‐poor HDL particles were associated with a shift from calcified plaque to NCP on CTA (α3‐HDL% and low‐density NCP: r=0.32, P=0.02) and with larger plaque volume on IVUS/VH (α4‐HDL%: r=0.41, P=0.01; α3‐HDL%: r=0.37, P=0.03), because of larger dense calcium (α4‐HDL%: r=0.37, P=0.03), larger fibrous tissue (α4‐HDL%: r=0.34, P=0.04), and larger necrotic core (α4‐HDL%: r=0.46, P<0.01; α3‐HDL%: r=0.37, P=0.03). Larger lipid‐rich HDL particles were associated with less low‐density NCP on CTA (α2‐HDL%: r=−0.34, P=0.02; α1‐HDL%: r=−0.28, P=0.05), with smaller plaque volume on IVUS/VH (pre‐α2‐HDL: r=−0.33, P=0.05; α1‐HDL%: r=−0.41, P=0.01; pre‐α2‐HDL: r=−0.33, P=0.05) and with less necrotic core (α1‐HDL: r=−0.42, P<0.01; pre‐α2‐HDL: r=−0.38, P=0.02; α2‐HDL: r=−0.35, P=0.03; pre‐α1‐HDL: r=−0.34, P=0.04). Pre‐β2‐HDL was associated with less calcification and less stenosis by both modalities.

Conclusions

ApoB and small HDL particles are associated with larger plaque burden and more noncalcified plaque, whereas larger HDL and pre‐β2‐HDL particles are associated with plaque burden and less noncalcified plaque by both CTA and IVUS/VH.

Stenosis quantification of coronary arteries in coronary vessel phantoms with second-generation dual-source CT: influence of measurement parameters and limitations

OBJECTIVE

The purpose of this study was to use second-generation dual-source CT to assess the influence of size, degree of stenosis, luminal contrast attenuation, and plaque geometry on stenosis quantification in a coronary artery phantom.

MATERIALS AND METHODS

Six vessel phantoms with three outer diameters (2, 3, and 4 mm), each containing three radiolucent plaques (72.2 HU) that simulated eccentric and concentric 43.8%, 75%, and 93.8% stenoses were made with a 3D printer system. These phantoms were filled with an iodine-saline solution mixture at luminal attenuations of 150, 200, 250, 300, and 350 HU and were attached to a cardiac motion simulator. Dual-source CT was performed with a standardized ECG-gated protocol (120 kV, 360 mAs per rotation) at a simulated heart rate of 70 beats/min. Two independent readers quantified the degree of stenosis using area-based measurements.

RESULTS

All measurements were highly reproducible (intraclass correlation, ≥ 0.791; p < 0.001). The mean measured degree of stenosis for a phantom with a 3-mm outer diameter at 250-HU luminal attenuation was 49.0% ± 10.0% for 43.8% stenosis, 71.7% ± 9.6% for 75.0% stenosis, and 85.4% ± 5.9% for 93.8% stenosis. With decreasing phantom size, measurement error increased for all degrees of stenosis. The absolute error increased for measurements at a low luminal attenuation of 150 HU (p < 0.001) and for low-grade stenoses compared with medium-and high-grade stenoses (p < 0.001).

CONCLUSION

The results are an overview of factors that influence stenosis quantification in simulated coronary arteries. Dual-source CT is highly reproducible and accurate for quantification of low-density stenosis in vessels with a diameter of 3 mm and attenuation of at least 200 HU for different degrees of stenosis and plaque geometry.

A meta analysis and hierarchical classification of HU-based atherosclerotic plaque characterization criteria

Background

Many computed tomography (CT) studies have reported that lipid-rich, presumably rupture-prone atherosclerotic plaques can be characterized according to their Hounsfield Unit (HU) value. However, the published HU-based characterization criteria vary considerably. The present study aims to systematically analyze these values and empirically derive a hierarchical classification of the HU-based criteria which can be referred in clinical situation.

Material and Methods

A systematic search in PubMed and Embase for publications with HU-criteria to characterize lipid-rich and fibrous atherosclerotic plaques resulted in 36 publications, published between 1998 and 2011. The HU-criteria were systematically analyzed based on the characteristics of the reporting study. Significant differences between HU-criteria were checked using Student’s t-test. Subsequently, a hierarchical classification of HU-criteria was developed based on the respective study characteristics.

Results

No correlation was found between HU-criteria and the reported lumen contrast-enhancement. Significant differences were found for HU-criteria when pooled according to the respective study characteristics: examination type, vessel type, CT-vendor, detector-rows, voltage-setting, and collimation-width. The hierarchical classification resulted in 21 and 22 CT attenuation value categories, for lipid-rich and fibrous plaque, respectively. More than 50% of the hierarchically classified HU-criteria were significantly different.

Conclusion

In conclusion, variations in the reported CT attenuation values for lipid-rich and fibrous plaque are so large that generalized values are unreliable for clinical use. The proposed hierarchical classification can be used to determine reference CT attenuation values of lipid-rich and fibrous plaques for the local setting.

The napkin-ring sign indicates advanced atherosclerotic lesions in coronary CT angiography

OBJECTIVES

This study sought to determine the accuracy of plaque pattern assessment by coronary computed tomography angiography (CCTA) to differentiate between early and advanced atherosclerotic lesions as defined by histology.

BACKGROUND

A ringlike attenuation pattern of coronary atherosclerotic plaques termed as napkin-ring sign (NRS) was described in CCTA of patients who had acute coronary syndrome.

METHODS

All procedures were performed in accordance with local and federal regulations and the Declaration of Helsinki. Approval of the local ethics committees was obtained. We investigated 21 coronary arteries of 7 donor hearts. Overall, 611 histological sections were obtained and coregistered with CCTA images. The CCTA cross sections were read in random order for conventional plaque categories (noncalcified [NCP], mixed [MP], calcified [CP]) and plaque patterns (homogenous, heterogeneous with no napkin-ring sign [non-NRS], and heterogeneous with NRS).

RESULTS

No plaque was detected in 134 (21.9%), NCP in 254 (41.6%), MP in 191 (31.3%), and CP in 32 (5.2%) CCTA cross sections. The NCP and MP were further classified into homogenous plaques (n = 207, 46.5%), non-NRS plaques (n = 200, 44.9%), and NRS plaques (n = 38, 8.6%). The specificities of NCP and MP to identify advanced lesions were moderate (57.9%, 95% confidence interval [CI]: 50.1% to 65.6%, and 72.1%, 95% CI: 64.7% to 79.4%, respectively), which were similar to the homogenous and heterogeneous plaques (62.6%, 95% CI: 54.8% to 70.3%, and 67.3%, 95% CI: 58.6% to 76.1%, respectively). In contrast, the specificity of the NRS to identify advanced lesions was excellent (98.9%, 95% CI: 97.6% to 100%). The diagnostic performance of the pattern-based scheme to identify advanced lesions was significantly better than that of the conventional plaque scheme (area under the curve: 0.761 vs. 0.678, respectively; p = 0.001).

CONCLUSIONS

The assessment of the plaque pattern improves diagnostic accuracy of CCTA to identify advanced atherosclerotic lesions. The CCTA finding of NRS has a high specificity and high positive predictive value for the presence of advanced lesions.

How to assess non-calcified plaque in CT angiography: delineation methods affect diagnostic accuracy of low-attenuation plaque by CT for lipid-core plaque in histology

AIMS

To compare the accuracy of two plaque delineation methods for coronary computed tomographic angiography (CTA) to identify lipid-core plaque (LCP) using histology as the reference standard.

METHODS AND RESULTS

Five ex vivo hearts were analysed by CTA and histology. LCP was defined by histology as fibroatheroma with core diameter/circumference >200 μm/>60° and cap thickness <450 μm. In CTA, plaque was manually delineated either as the difference between the inner and outer vessel walls (Method A) or as a direct tracing of plaque (Method B). Low-attenuation plaque was defined as an area with <90 Hounsfield units. Of 446 co-registered cross-sections, 55 (12%) contained LCP. In CTA, low-attenuation plaque area was larger as assessed with Method A compared with Method B (difference: 120 ± 60%). Although low-attenuation plaque was associated with the presence of LCP, the delineation Method B yielded higher diagnostic accuracy than Method A [area under the curve (AUC): 0.831 vs. 0.780, respectively, P = 0.005]. After excluding 'normal' cross-sections by CTA (n = 117), AUC for detecting LCP became similar between both methods (0.767 vs. 0.729, P = 0.07, respectively).

CONCLUSION

Low-attenuation plaque in CTA is a diagnostic tool for LCP but prone to error if plaque is defined as the area between the inner and outer vessel walls and normal cross-sections are included in the assessment.

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.

Progress in atherosclerotic plaque imaging

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

Coronary artery plaques: cardiac CT with model-based and adaptive-statistical iterative reconstruction technique

OBJECTIVES

To compare image quality of coronary artery plaque visualization at CT angiography with images reconstructed with filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model based iterative reconstruction (MBIR) techniques.

METHODS

The coronary arteries of three ex vivo human hearts were imaged by CT and reconstructed with FBP, ASIR and MBIR. Coronary cross-sectional images were co-registered between the different reconstruction techniques and assessed for qualitative and quantitative image quality parameters. Readers were blinded to the reconstruction algorithm.

RESULTS

A total of 375 triplets of coronary cross-sectional images were co-registered. Using MBIR, 26% of the images were rated as having excellent overall image quality, which was significantly better as compared to ASIR and FBP (4% and 13%, respectively, all p<0.001). Qualitative assessment of image noise demonstrated a noise reduction by using ASIR as compared to FBP (p<0.01) and further noise reduction by using MBIR (p<0.001). The contrast-to-noise-ratio (CNR) using MBIR was better as compared to ASIR and FBP (44±19, 29±15, 26±9, respectively; all p<0.001).

CONCLUSIONS

Using MBIR improved image quality, reduced image noise and increased CNR as compared to the other available reconstruction techniques. This may further improve the visualization of coronary artery plaque and allow radiation reduction.

Reproducibility, accuracy, and predictors of accuracy for the detection of coronary atherosclerotic plaque composition by computed tomography: an ex vivo comparison to intravascular ultrasound

PURPOSE

To determine the reproducibility, accuracy, and predictors of accuracy of computed tomography (CT) angiography to detect and characterize coronary atherosclerotic plaque as compared with intravascular ultrasound.

METHODS

Ten ex vivo human coronary arteries were imaged in a moving phantom by dual-source CT (collimation: 0.6 mm, reconstructed slice thickness: 0.4 mm) and intravascular ultrasound (IVUS). Coregistered cross-sections were assessed at 0.4 mm intervals for the presence and composition of atherosclerotic plaque (noncalcified, mixed, and calcified) on CT and IVUS by independent readers to determine reader agreement and diagnostic accuracy. Quantitative measurements of lumen and plaque area, plaque eccentricity, and intimal thickness on IVUS were used to determine predictors for the detection of noncalcified plaque by CT.

RESULTS

Within 1002 coregistered cross-sections, the interobserver agreement to detect plaque on CT was K = 0.48, K = 0.42, and K = 1.00 for noncalcified, mixed, and calcified plaque; respectively. The sensitivity and specificity of CT was 57% out of 84% for noncalcified, 32% of 92% for mixed, and 56% of 93% for calcified plaque when compared with IVUS; respectively. Misclassification occurred in 68% of mixed and 43% of noncalcified plaques. The odds of detecting noncalcified plaque in CT independently increased by 56% (95% CI: 47%-77%, P < 0.0001) with every 0.1 mm increase in maximum intimal thickness as measured by IVUS. Detection rate for noncalcified plaques was poor for plaques <1 mm (36%) but excellent for plaques >1 mm maximal intimal thickness (90%).

CONCLUSION

Reader agreement and diagnostic accuracy for the detection of coronary atherosclerotic plaque vary with plaque composition. Intimal thickness independently predicts detection of noncalcified plaque by CT with excellent sensitivity for >1 mm thick plaques.

Imaging of atherosclerosis

It is now well recognized that the atherosclerotic plaques responsible for thrombus formation are not necessarily those that impinge most on the lumen of the vessel. Nevertheless, clinical investigations for atherosclerosis still focus on quantifying the degree of stenosis caused by plaques. Many of the features associated with a high-risk plaque, including a thin fibrous cap, large necrotic core, macrophage infiltration, neovascularization, and intraplaque hemorrhage, can now be probed by novel imaging techniques. Each technique has its own strengths and drawbacks. In this article, we review the various imaging modalities used for the evaluation and quantification of atherosclerosis.

Impact of luminal density on plaque classification by CT coronary angiography

Non-invasive coronary CT angiography (CCTA) has the potential to characterize the composition of non-calcified coronary plaques. CT-density values characterized by Hounsfield Units (HU) may classify non-calcified plaques as fibrous or lipid-rich, but the luminal density caused by the applied contrast material influences HU in the plaques in vitro. The influence of luminal density on HU in non-calcified plaques in vivo is unknown. Hence the purpose of this study was to test whether plaque characterization by CCTA in vivo depends on luminal density. Two CCTA-scans using two different contrast protocols were obtained from 14 male patients with coronary artery disease. The two contrast protocols applied resulted in high and low luminal density. Eleven non- calcified and 13 calcified plaques were identified and confirmed by intravascular ultrasound. Luminal attenuation differed with the two contrast protocols; 326[284;367] vs. 118[103;134] HU (P < 0.00001). In non-calcified plaques mean HU-values was lower 48[28;69] vs. 11[-4;25] HU (P = 0.004) with the low density protocol. As a consequence three out of eleven non-calcified plaques (27%) were reclassified from fibrous (high) to lipid rich (low). For calcified plaques a less pronounced but still significant difference in HU-values was found with the low luminal density. 770[622;919] vs. 675[496;855] HU (P = 0.02).

CONCLUSION

Non-calcified plaques can be identified and classified by CCTA. However, the luminal density affects the absolute HU of both non-calcified and calcified plaques. Characterization and classification of non-calcified plaques by absolute CT values therefore requires standardization of contrast protocols.

Deformable Mock Stenotic Artery With a Lipid Pool

The comparison, evaluation, and optimization of new techniques, models, or algorithms often require the use of realistic deformable test phantoms. The purpose of this paper is to present a multilayer deformable test specimen mimicking an atherosclerotic coronary artery, suitable for mechanical testing and intravascular imaging. Mock arteries were constructed in three phases using two molds: building a first layer of polyvinyl alcohol (PVA) cryogel, adding a lipid pool and building a second layer of PVA cryogel. To illustrate the deformation of the mock arteries, one has been placed in a custom-made bath, axially stretched then inflated while acquiring intravascular ultrasound (IVUS) images. The resulting specimen presents a progressing lumen narrowing of 25% in cross-sectional area at the peak and a lipid pool. The average inner gel layer is about 0.4 mm thick and the outer about 0.6 mm. The dimensions are of the same order as clinical observations, the first gel layer mimicking the intima-media and the second layer the adventitia. In the sequence of IVUS images, the different components of the mock artery are visible and differentiable. The variation in diameter of the segmented contours is presented for a specific specimen subjected to intraluminal pressure. This double-layer stenotic mock artery is approximately the size of a human coronary artery, has a lipid inclusion, can withstand relative large deformation, suitable for (intravascular) ultrasound imaging, and has customizable geometry and wall material parameters.

Methods of plaque quantification and characterization by cardiac computed tomography

The pathologic evolution of coronary artery atherosclerosis occurs slowly over decades, which may provide an opportunity for diagnostic imaging to identify patients before clinical events evolve. Cardiac computed tomography (CT) is an emerging noninvasive imaging tool, which can visualize the entire coronary tree with submillimeter resolution. We reviewed the current status of cardiac CT to qualitatively and quantitatively determine coronary plaque dimensions and composition, and its potential to improve our understanding of the natural history of coronary artery disease as well as prevention of cardiovascular events.

Computed tomography coronary angiography plaque burden in patients with suspected coronary artery disease

PURPOSE

To determine the relationship between established cardiovascular risk factors, clinical presentation and the extent of coronary artery disease (CAD), as described with computed tomography coronary angiography.

MATERIAL AND METHODS

In this cross-sectional study, we included 567 symptomatic individuals without a history of CAD who consecutively underwent 64-slice computed tomography coronary angiography for evaluation of suspected CAD. We analyzed the prevalence of CAD depending on sex, age, symptoms and risk factors.

RESULTS

A total of 8542 segments were analyzed. No evidence of CAD was observed in 225 patients (40%), nonsignificant CAD in 221 patients (39%) and significant CAD (luminal narrowing >50%) in the remaining 121 patients (21%). CAD increased with advancing age, significantly above 50 years (P < 0.05). Female patients had a higher prevalence of normal coronary arteries and males of significant CAD (P < 0.01). With the increase of risk factors, there was a significant increase of the significant disease (P < 0.01). Typical pain with respect to atypical pain had the strongest association with significant CAD (16 vs. 38%; P < 0.05). In multivariate analysis, the number of risk factors, age, male sex and typical pain remained strong predictors of significant CAD (P < 0.0001).

CONCLUSION

Computed tomography coronary angiography may play an important role in risk stratification of patients with suspected CAD.

Vitamin K supplementation and progression of coronary artery calcium in older men and women

BACKGROUND

Coronary artery calcification (CAC) is an independent predictor of cardiovascular disease. A preventive role for vitamin K in CAC progression has been proposed on the basis of the properties of matrix Gla protein (MGP) as a vitamin K-dependent calcification inhibitor.

OBJECTIVE

The objective was to determine the effect of phylloquinone (vitamin K1) supplementation on CAC progression in older men and women.

DESIGN

CAC was measured at baseline and after 3 y of follow-up in 388 healthy men and postmenopausal women; 200 received a multivitamin with 500 microg phylloquinone/d (treatment), and 188 received a multivitamin alone (control).

RESULTS

In an intention-to-treat analysis, there was no difference in CAC progression between the phylloquinone group and the control group; the mean (+/-SEM) changes in Agatston scores were 27 +/- 6 and 37 +/- 7, respectively. In a subgroup analysis of participants who were > or =85% adherent to supplementation (n = 367), there was less CAC progression in the phylloquinone group than in the control group (P = 0.03). Of those with preexisting CAC (Agatston score > 10), those who received phylloquinone supplements had 6% less progression than did those who received the multivitamin alone (P = 0.04). Phylloquinone-associated decreases in CAC progression were independent of changes in serum MGP. MGP carboxylation status was not determined.

CONCLUSIONS

Phylloquinone supplementation slows the progression of CAC in healthy older adults with preexisting CAC, independent of its effect on total MGP concentrations. Because our data are hypothesis-generating, further studies are warranted to clarify this mechanism. This trial was registered at clinicaltrials.gov as NCT00183001.

Characterisation of the "vulnerable" coronary plaque by multi-detector computed tomography: a correlative study with intravascular ultrasound-derived radiofrequency analysis of plaque composition

AIMS

To assess plaque characteristics by multi-detector computed tomography angiography in patients with known coronary artery disease and to compare these findings with those obtained with intravascular ultrasound-derived radiofrequency analysis of plaque composition.

METHODS AND RESULTS

By computed tomography, lesions were classified on the basis of Hounsfield Units as non-calcified, calcified, or mixed. By intravascular ultrasound-derived radiofrequency analysis, plaques were classified according to the relative composition of components with specific backscatter characteristics (necrotic core, fibrous, fibro-fatty, calcium). Thin cap fibroatheroma (defined as necrotic core component >10% without evidence of fibrotic cap, calcium >5%, remodelling index >1.05) was considered as vulnerable plaque. Seventy-eight plaques were analysed. By computed tomography, 22 plaques were classified as non-calcified and 56 as mixed. A higher incidence of mixed plaques was observed among lesions causing unstable angina and non-ST elevation myocardial infarction compared to stable angina (76% vs 38%, p=0.04). Plaque composition by radiofrequency analysis was significantly different between mixed and non-calcified plaques by computed tomography. The calcium content was 6.0+/-3.2% vs 2.5+/-1.8% (p=0.001), necrotic core was 14.0+/-6.9% vs 7.5+/-5.6% (p=0.03) and fibrous tissue was 59.0+/-7.5% vs 67.0+/-5.9% (p=0.03), for mixed vs non-calcified plaques, respectively. Positive, negative predictive value and diagnostic accuracy for detection of vulnerable plaque by computed tomography was 77, 54 and 59%.

CONCLUSIONS

Mixed plaque by computed tomography correlates with plaque composition as determined by intravascular ultrasound-derived radiofrequency analysis. However, the present diagnostic accuracy of computed tomography is not high enough to support its use for non invasive detection of vulnerable coronary plaque.

Multimodality imaging of atherosclerosis (magnetic resonance imaging/computed tomography/positron emission tomography-computed tomography)

This review discusses the field of atherosclerosis imaging with magnetic resonance imaging, computed tomography and positron emission tomography techniques, and highlights important publications in this area. Future directions and challenges ahead for plaque imaging are also highlighted.

Characterization of atherosclerotic plaques in human coronary arteries with 16-slice multidetector row computed tomography by analysis of attenuation profiles

RATIONALE AND OBJECTIVES

We investigated if 16-slice multidetector row computed tomography (MDCT) allows correct classification of coronary plaques into calcified or noncalcified and further subclassification of noncalcified plaques into either lipid-rich with a necrotic core or fibrous.

MATERIALS AND METHODS

Coronary arteries of 30 isolated hearts were filled postmortem with a contrast medium and scanned with a 16-slice MDCT imager (Light Speed 16 pro, GEMS, Milwaukee, WI). Imaging parameters: collimation 16 x 0.625 mm, pitch 0.325, tube voltage 120 kV, tube current 250 mA, and gantry rotation time 500 milliseconds. The images were reformatted perpendicular to the axis of the coronary arteries (AW 4.2 software, GEMS) and analyzed by establishing attenuation profiles of the coronary cross sections (ImageJ 1.33n software, NIH, Bethesda, MD). Results were compared with the correlating histopathologic sections of the arteries.

RESULTS

Analysis of 195 CT cross-sections showed a sensitivity and specificity for the correct classification of calcified plaques of 100% and 97.3% and for noncalcified plaques of 80.8% and 95.1%, respectively. The attenuation of epicardial fat ranged from -119 Hounsfield units (HU) to 23 HU (median -71 HU), and from 93 HU to 625 HU (308 HU) for the contrast medium. Calcified plaques showed an attenuation between 333 HU and 1944 HU (1,089 HU), noncalcified plaques between 26 HU and 124 HU (52 HU). Further subclassification of noncalcified plaques showed attenuation values between 26 HU and 67 HU (median 44 HU) for lipid-rich plaques with a necrotic core and from 37 HU to 124 HU (median 67 HU) for fibrous plaques.

CONCLUSIONS

Coronary atherosclerotic plaques can be reliably identified and classified as either calcified or noncalcified by 16-slice MDCT in postmortem studies. Further differentiation of noncalcified plaques in either lipid-rich or fibrous is not reliably feasible because of substantial overlap of the attenuation.

Quantification of atherosclerotic coronary plaque components by submillimeter computed tomography

BACKGROUND

Although several investigations have shown that multi-detecor row computed tomography (MDCT) of the coronary arteries can detect noncalcified atherosclerotic plaque, it has remained unresolved if the method also determines features of a rupture-prone plaque. We set out to correlate the size of atherosclerotic plaque components with cardiac MDCT with histology.

METHODS AND RESULTS

In 30 autopsy cases, hearts were isolated, coronary arteries filled with contrast agent, and depicted with a clinical 16-row detector CT with a slice thickness of 0.63 mm. Transections of the three main coronary arteries were reconstructed and compared with histopathologic sections using light microscopy. MDCT measurements of total plaque area (r = 0.73, P < 0.0001) and calcified plaque area (r = 0.83, P < 0.0001) correlated well with histopathology, while measurements of non-calcified plaque area (r = 0.53, P < 0.0001) and lipid core size (r = 0.43; P < 0.0001) correlated less well. MDCT overestimated all plaque areas except lipid core size, which was underestimated.

CONCLUSIONS

Coronary CT provides an accurate and reproducible method for the quantitative assessment of total plaque and calcified plaque areas. However, the method is less accurate for the quantification of non-calcified plaque area and lipid core size, which is ascribed to limited spatial and contrast resolution. With the present technique, the detection of vulnerable plaques by MDCT remains uncertain.

Novel cardiovascular MRI and CT methods for evaluation of ischemic heart disease

New developments in cardiac MRI and multidetector CT (MDCT) have generated tremendous excitement for both physicians and the general public. Their roles in the diagnostic algorithm of patients with suspected coronary artery disease are rapidly evolving. In addition to cardiac catheterization, nuclear imaging techniques and cardiac echocardiography, MDCT and MRI will play increasing roles in the diagnosis of ischemic heart disease. In this review we outline imaging techniques and illustrate the various applications of cardiac MRI and MDCT in the assessment of myocardial ischemia.

Early characterization of atherosclerotic coronary plaques with multidetector computed tomography in patients with acute coronary syndrome: a comparative study with intravascular ultrasound

We compared 16-slice computed tomography (CT) with intravascular ultrasound (IVUS) in their ability to identify the culprit lesion, and to assess plaque characterization and vascular remodelling in acute coronary syndrome (ACS). Twenty patients were prospectively studied. Coronary plaque identification and characterization were compared using 16-slice CT and 40-MHz catheter-based IVUS. Minimum lumen area (MLA), cross-sectional vessel area (CVA) and vessel remodelling were determined for each comparable lesion. One hundred and sixty-nine segments were compared and 84 plaques analysed. Sixteen-slice CT detected 95% of culprit lesions (19/20). No feature suggestive of plaque rupture was detected by 16-slice CT. Attenuation measurements within all lesions revealed different values for hypoechoic (38 +/- 33 HU), hyperechoic (94 +/- 44 HU), and calcified plaques (561 +/- 216 HU), (P < 0.001). Agreement between 16-slice CT and IVUS on measuring MLA and CVA was evaluated using Bland-Altman analysis. Pearson and intra-class coefficient (ICC) were 0.81 and 0.70 for MLA, and 0.81 and 0.36 for CVA, for 16-slice CT and IVUS, respectively. Agreement between both techniques for vessel positive remodelling was moderate (kappa = 0.54, P < 0.001). Sixteen-slice CT has shown moderate accuracy in quantifying and characterizing coronary plaques compared with IVUS. Spatial resolution of 16-slice CT remains a major limitation, however, to accurately assess the complex lesions involved in ACS.