Quantification of serial changes in plaque burden using multi-detector computed tomography in experimental atherosclerosis

Clinical application of effective atomic number for classifying non-calcified coronary plaques by dual-energy computed tomography

BACKGROUND AND AIMS

Coronary computed tomography (CT) angiography allows non-invasive classification of non-calcified coronary plaques (NCCPs) based on Hounsfield unit (HU) values. This methodology, however, is somewhat limited for reliable classification of NCCPs. Therefore, we evaluated the effective atomic number (EAN) for classifying NCCPs by single-source dual-energy CT with fast tube voltage switching (SSDECT).

METHODS

We prospectively enrolled 18 patients undergoing both SSDECT and intravascular ultrasonography (IVUS). Monochromatic images at 70 keV and EAN images were reconstructed from SSDECT data sets. Regions of interest (ROIs) within NCCPs were placed on IVUS-matched SSDECT images, and mean HU values and EANs for soft and fibrous plaques, classified using IVUS, were compared with an unpaired t-test.

RESULTS

We placed 96 ROIs in 29 soft plaques and 37 ROIs in 15 fibrous plaques in 12 coronary arteries of 11 patients. The mean HU value in soft plaques (58.2 ± 32.8 HU) was significantly lower than that in fibrous plaques (103.9 ± 48.3 HU) (p < 0.001). The mean EAN in soft plaques (8.7 ± 0.5) was also significantly lower than that in fibrous plaques (9.6 ± 0.5) (p < 0.0001). Area under the curve for EAN (0.91) was significantly higher than that for HU value (0.79) in receiver operating characteristic curve analysis (p = 0.046). With a cutoff EAN of 9.3, sensitivity was 90% and specificity, 87%; whereas with a cutoff HU value of 55.0 HU, sensitivity was 62% and specificity, 93%.

CONCLUSIONS

EAN measurement by SSDECT can be clinically useful for accurately classifying soft and fibrous coronary plaques.

Combined non-invasive assessment of endothelial shear stress and molecular imaging of inflammation for the prediction of inflamed plaque in hyperlipidaemic rabbit aortas

AIMS

To evaluate the incremental value of low endothelial shear stress (ESS) combined with high-resolution magnetic resonance imaging (MRI)- and computed tomography angiography (CTA)-based imaging for the prediction of inflamed plaque.

METHODS AND RESULTS

Twelve hereditary hyperlipidaemic rabbits underwent quantitative analysis of plaque in the thoracic aorta with 256-slice CTA and USPIO-enhanced (ultra-small superparamagnetic nanoparticles, P904) 1.5-T MRI at baseline and at 6-month follow-up. Computational fluid dynamics using CTA-based 3D reconstruction of thoracic aortas identified the ESS patterns in the convex and concave curvature subsegments of interest. Subsegments with low baseline ESS exhibited significant increase in wall thickness and plaque inflammation by MRI, in non-calcified plaque burden by CTA, and developed increased plaque size, lipid and inflammatory cell accumulation (high-risk plaque features) at follow-up by histopathology. Multiple regression analysis identified baseline ESS and inflammation by MRI to be independent predictors of plaque progression, while receiver operating curve analysis revealed baseline ESS alone or in combination with inflammation by MRI as the strongest predictor for augmented plaque burden and inflammation (low ESS at baseline: AUC = 0.84, P < 0.001; low ESS and inflammation by molecular MRI at baseline: AUC = 0.89, P < 0.001).

CONCLUSION

Low ESS predicts progression of plaque burden and inflammation as assessed by non-invasive USPIO-enhanced MRI. Combined non-invasive assessment of ESS and imaging of inflammation may serve to predict plaque with high-risk features.

Lipid Interventions in Aortic Valvular Disease

Aortic valve stenosis is the most common valvular disease in the elderly population. Presently, there is increasing evidence that aortic stenosis (AS) is an active process of lipid deposition, inflammation, fibrosis and calcium deposition. The pathogenesis of AS shares many similarities to that of atherosclerosis; therefore, it was hypothesized that certain lipid interventions could prevent or slow the progression of aortic valve stenosis. Despite the early enthusiasm that statins may slow the progression of AS, recent large clinical trials did not consistently demonstrate a decrease in the progression of AS. However, some researchers believe that statins may have a benefit early on in the disease process, where inflammation (and not calcification) is the predominant process, in contrast to severe or advanced AS, where calcification (and not inflammation) predominates. Positron emission tomography using 18F-fluorodeoxyglucose and 18F-sodium fluoride can demonstrate the relative contributions of valvular calcification and inflammation in AS, and thus this method might potentially be useful in providing the answer as to whether lipid interventions at the earlier stages of AS would be more effective in slowing the progression of the disease. Currently, there is a strong interest in recombinant apolipoprotein A-1 Milano and in the development of new pharmacological agents, targeting reduction of lipoprotein (a) levels and possibly reduction of the expression of lipoprotein-associated phospholipase A2, as potential means to slow the progression of aortic valvular stenosis.

ETC-216 for coronary artery disease

INTRODUCTION

Increasing attention has focused on the role of high-density lipoprotein function as a target for cardiprotection. Apolipoprotein A-I(Milano) (AIM) involves a single amino-acid mutation of the major wild-type protein carried on high-density lipoprotein (HDL) particles. Early evidence of beneficial activities of AIM has stimulated support in its development as a potential therapy to reduce cardiovascular risk.

AREAS COVERED

The importance of HDL as a target and early data supporting the beneficial effects of AIM are reviewed. All clinical studies of AIM found in PubMed are reviewed.

EXPERT OPINION

ETC-216 represents a lipid-deplete form of HDL containing recombinant AIM. While early evidence suggests that administration of ETC-216 promotes rapid regression of coronary atherosclerosis, bringing this compound to clinical practice will require further trials that evaluate its impact on cardiovascular events.

Novel clinical applications of state-of-the-art multi-slice computed tomography

Recent years have witnessed a rapid development of multi-slice computed tomography (MSCT) technology. The number of detector rows has increased from 4-slices to the current availability of 64-slice and even 320-slice systems. In addition, images are acquired with thinner slices and faster rotation times resulting in substantially improved image quality and diagnostic accuracy. Simultaneously, effective dose reduction acquisition techniques have been developed allowing considerable reduction of the radiation dose. Conceivably, these advancements may allow further expansion of the use of MSCT beyond the visual assessment of the presence or absence of significant coronary artery disease. Indeed, a particular advantage of the technique is that in addition to evaluation of the coronary arteries it also allows assessment of cardiac structures and function. The purpose of the current review is to discuss several novel applications of cardiac MSCT, including stenosis quantification, atherosclerotic plaque imaging and prognostification as well as imaging of left ventricular function, aortic and mitral valve anatomy using state-of-the-art technology.