Noninvasive Tissue Characterization of Coronary Arterial Plaque by 16-Slice Computed Tomography in Acute Coronary Syndrome

Non-Calcified Coronary Artery Plaque on Coronary Computed Tomography Angiogram: Prevalence and Significance

OBJECTIVE

We aimed to assess the prevalence of non-calcified plaque (NCP) on computed tomography angiography (CCTA) in symptomatic and asymptomatic individuals. In addition, we seek to compare plaque assessment on CCTA with intravascular ultrasound-virtual histology (IVUS-VH) and to assess the prognostic value of non-calcified plaques (NCPs).

BACKGROUND

The CCTA can characterize coronary plaques and help quantify burden. Furthermore, it can provide additional prognostic information which can enable further risk stratification of patients.

METHODS

We performed a broad comprehensive review of the current literature pertaining to CCTA and primarily isolated NCP in symptomatic and asymptomatic patients. In addition, our review included studies correlating plaque on CT with IVUS-VH.

CONCLUSIONS

NCP is the initial precursor of calcified plaque and serves as a prominent marker of early coronary atherosclerosis. By detecting NCP during early stages, several measures can be implemented which can alter the evolutionary course of the underlying disease. This can potentially lead to a lower incidence of cardiovascular events.

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.

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.

Model generation of coronary artery bifurcations from CTA and single plane angiography

PURPOSE

To generate accurate and realistic models of coronary artery bifurcations before and after percutaneous coronary intervention (PCI), using information from two image modalities. Because bifurcations are regions where atherosclerotic plaque appears frequently and intervention is more challenging, generation of such realistic models could be of high value to predict the risk of restenosis or thrombosis after stent implantation, and to study geometrical and hemodynamical changes.

METHODS

Two image modalities have been employed to generate the bifurcation models: computer tomography angiography (CTA) to obtain the 3D trajectory of vessels, and 2D conventional coronary angiography (CCA) to obtain radius information of the vessel lumen, due to its better contrast and image resolution. In addition, CCA can be acquired right before and after the intervention in the operation room; therefore, the combination of CTA and CCA allows the generation of realistic preprocedure and postprocedure models of coronary bifurcations. The method proposed is semiautomatic, based on landmarks manually placed on both image modalities.

RESULTS

A comparative study of the models obtained with the proposed method with models manually obtained using only CTA, shows more reliable results when both modalities are used together. The authors show that using preprocedure CTA and postprocedure CCA, realistic postprocedure models can be obtained. Analysis carried out of the Murray's law in all patient bifurcations shows the geometric improvement of PCI in our models, better than using manual models from CTA alone. An experiment using a cardiac phantom also shows the feasibility of the proposed method.

CONCLUSIONS

The authors have shown that fusion of CTA and CCA is feasible for realistic generation of coronary bifurcation models before and after PCI. The method proposed is efficient, and relies on minimal user interaction, and therefore is of high value to study geometric and hemodynamic changes of treated patients.

3D modeling of coronary artery bifurcations from CTA and conventional coronary angiography

Coronary artery bifurcations are regions where the atherosclerotic plaque appears more frequently and where the percutaneous treatment is more challenging. To analyze these important vascular regions, in this paper is proposed a method for the extraction of realistic 3D models of coronary bifurcations combining information from pre operative computer tomography angiography (CTA) to obtain the 3D structure of the vessels and pre and post operative conventional coronary angiography (CCA) to extract a more accurate estimation of the lumen radius before and after stenting. The method proposed is semiautomatic, starting from a set of user defined landmarks, and has been successfully applied to data from five patients that underwent endovascular treatment in a coronary bifurcation. The results obtained are satisfactory by visual inspection and in comparison with manual measurements.

Relationship between degree of remodeling and CT attenuation of plaque in coronary atherosclerotic lesions: An in-vivo analysis by multi-detector computed tomography

Multi-detector CT (MDCT) permits non-invasive visualization of the coronary arteries. Coronary plaque can be visualized, and earlier studies have indicated that the CT attenuation measured in atherosclerotic plaques is influenced by plaque composition. Also, MDCT has been shown to permit assessment of remodeling of coronary atherosclerotic lesions. It is assumed that both lipid-rich plaques and those that display positive remodeling are more prone to rupture and erosion. We thus evaluated the relationship between remodeling and CT attenuation of coronary atherosclerotic plaque by MDCT.

METHODS

Seventy-six patients were investigated by contrast-enhanced 64-slice CT. One-hundred twelve atherosclerotic lesions without substantial calcification and visualized with high image quality were selected. Multiplanar reconstructions orthogonal to the coronary artery were rendered at the lesion and the proximal reference site. Cross-sectional vessel areas were measured to determine the remodeling index (RI: lesion vessel area/reference vessel area) and the CT attenuation of plaque was measured by fitting a region of interest to the plaque area. CT attenuation of plaque was correlated to the presence of positive remodeling index (RI>1.05).

RESULTS

The mean cross-sectional vessel area in the lesion was 0.25+/-0.08 cm(2), the mean reference vessel area was 0.22+/-0.09 cm(2). The mean CT attenuation of the atherosclerotic plaque in the lesions was 71+/-26 HU. CT attenuation of plaque was significantly lower in 72 lesions that displayed positive remodeling (59+/-22 HU) than in 40 lesions with no or with negative remodeling (91+/-20 HU, p<0.001).

CONCLUSIONS

Positive remodeling of coronary atherosclerotic lesions correlates to lower CT attenuation of plaque, which has been demonstrated to be associated with lipid-rich plaque. Both characteristics indicate increased risk for plaque rupture and subsequent events and could thus prove useful when the use of CT imaging for the detection of "vulnerable plaque" is considered.