Carotid artery plaque characterization using CT multienergy imaging

Abstract

Background and purpose: Carotid artery plaque types can be categorized with CT according to their HU values. The purpose of this work was to analyze carotid artery plaque characteristics by using multienergy imaging.

Methods and materials: Thirty-two consecutive patients (23 men; median age, 70 years) were retrospectively analyzed. Carotid arteries were studied with a multienergy CT scanner. All patients received a 15-mL timing bolus of contrast medium to synchronize the data acquisition followed by an injection of 60 mL of contrast medium at a 5-mL/s flow rate. Plaque analysis in 64 carotid arteries was performed, and datasets were reconstructed by using a dedicated workstation. For each plaque, the HU value was quantified with a 2-mm-square region of interest at monoenergy values of 66, 70, 77, and 86 keV. The Wilcoxon test was used to test the differences in HU values in the plaques at different kiloelectron volts.

Results: Four carotid arteries were excluded due to the absence of plaque, and another 7, because of the presence of calcified plaques. In the remaining 53 carotid arteries, Wilcoxon analysis showed a statistically significant difference in HU values among the monoenergy values of 66, 70, 77, and 86 keV (P=.0001). In particular, we found that with the increase in monochromatic kiloelectron volt values, there is a statistically significant reduction in the HU value of the plaque.

Conclusions: Results of this study suggest that the HU values of plaque may significantly change according to the selected kiloelectron volt; therefore, the HU-based plaque type (fatty, mixed, calcified) should be classified according to the energy level applied.

Fig. 1.

An 83-year-old male patient. In the 4 panels, the HU value (white arrows) is visible at the different monochromatic energy levels (gray arrowheads): 66 (A), 70 (B), 77 (C), and 86 keV (D). This plaque is in the fatty category by using all 4 energy levels.

Fig. 2.

A 76-year-old male patient. In the 4 panels, the HU value (white arrows) is visible at the different monochromatic energy levels (gray arrowheads): 66 (A), 70 (B), 77 (C), and 86 keV (D). This plaque is in the mixed category for 66 (A), 70 (B), and 77 keV (C) but is in the fatty category with 86 keV (D) energy.

Fig. 3.

Box-and-whisker plot of the attenuation values according to the different kiloelectron volt levels.

Fig. 4.

Graph shows the HU values of the plaque. The attenuation value of 60 HU, which is considered the threshold between mixed and fatty plaques, is visible (the HU values >60 are visible in the shaded area of the graph). The dotted rectangle indicates the plaques in which a classification shift occurred according to the energy level.

Fig. 5.

Bland-Altman plot analysis at 66 (A), 70 (B), 77 (C), and 86 keV (D).