Rationale and Objectives
The characterization of plaques based on their computed tomography (CT) number is important for the detection of vulnerable atherosclerotic plaques. An earlier in vitro study showed that intravascular attenuation affected the attenuation of coronary atherosclerotic plaques. We attempted to validate this finding in vivo and here we introduce a dual-phase coronary CT angiography (CCTA) technique to address this issue.
Materials and Methods
Institutional ethics committee approval and informed consent were obtained. Thirty patients (30 noncalcified plaques) underwent dual-phase CCTA. Two CT datasets were obtained, one with coronary artery enhancement and the other without coronary artery enhancement. The CT number of the plaque and the adjacent vessel lumen was measured in a circular region of interest on curved planar reconstruction images. The region of interest setting was consistent between the two CT datasets. We performed linear regression analysis of the changes in the CT numbers (ΔHounsfield unit), calculated by subtracting the two CT datasets, for the lumen and for the plaque. We also evaluated the relationship between plaque attenuation on nonenhanced coronary artery images and luminal attenuation with and without contrast enhancement.
Results
The ΔHounsfield unit for the plaque and the lumen showed a strong correlation (r = 0.61). There was no significant correlation between plaque attenuation on nonenhanced coronary artery images and luminal attenuation with and without contrast enhancement (r = 0.23 and 0.24, respectively).
Conclusions
Intravascular attenuation changed the attenuation of coronary atherosclerotic plaques. Using the copy-paste technique, the CT number of identical plaques can be measured in registered dual-phase CCTA images for the evaluation of coronary plaques.
Introduction
Coronary computed tomography angiography (CCTA) has shown good potential for the detection, quantification, and characterization of coronary artery plaques . However, a previous phantom study reported that the increased attenuation of the contrast material in a silicon coronary artery phantom determined an increase in the measured attenuation of the plaque made of rubber material . In a human ex vivo study , coronary lumen attenuation affected the attenuation values used to define the composition of coronary plaques. These findings have not been fully validated in vivo and the best scanning protocol for the identification and the characterization of noncalcified plaques remains to be established.
The 320-row CT scanners combine faster gantry rotation (0.275 seconds) and wide volume coverage (16 cm) . They make it possible to perform two consecutive (dual-phase) CCTA at the same electrocardiogram (ECG) phase but at different heartbeats in a single breath-hold without having to move the patient. In dual-phase CCTA, two CT datasets (one with contrast enhancement and the other without contrast enhancement in the coronary arteries) can be obtained by optimization of the first- and the second-phase scan timing . As two acquisitions are performed at the same anatomic location, the two CT datasets can be registered accurately with dedicated application software . Consequently, the CT number of identical noncalcified plaques can be measured on nonenhanced and enhanced coronary artery images using the copy-paste technique, and the relationship between plaque attenuation and coronary artery enhancement can be determined.
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Materials and Methods
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Study Population
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CT Scanning and Contrast Infusion Protocols
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Quantitative Image Quality Analysis
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CT Radiation Dose
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Statistical Analysis
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Results
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Table 1
Summary of the Attenuation Values Measured on Dual-phase Scans
Number First Phase Second Phase_P_ Value Lumen 30 75 ± 23 HU 435 ± 110 HU <0.01 Plaque 30 36 ± 25 HU 107 ± 40 HU <0.01
HU, Hounsfield unit.
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Discussion
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