Carotid atherosclerotic plaque progression and change in plaque composition over time: a 5-year follow-up study using serial CT angiography

Abstract

Background and purpose: Serial in vivo imaging of atherosclerosis is important for understanding plaque progression and is potentially useful in predicting cardiovascular events and monitoring treatment efficacy. This prospective study aims to quantify temporal changes in carotid atherosclerotic plaque volume and plaque composition using MDCTA.

Materials and methods: In 109 patients with TIA or ischemic stroke, serial MDCTA of the carotid arteries was performed after 5.3 ± 0.7 years. The carotid bifurcation was semiautomatically registered for paired baseline follow-up datasets. Outer vessel wall and lumen boundaries were defined using semiautomated segmentation tools. Plaque component volumes were measured using HU thresholds. Annual changes in plaque volume and plaque component proportions were calculated.

Results: One-hundred-ninety-three carotid arteries were analyzed. Plaque volume decreased in 31% and increased in 69% of vessels (range -5.6-10.1%/year). Overall, plaque volume increased 1.2% per year (95% CI, 0.8-1.6, P ≤ .001). Plaque composition changed significantly from BL (fibrous 66.4%, lipid 28.8%, calcifications 4.8%): fibrous tissue decreased by 1.5%, lipid decreased by 1.8%, and calcification increased by 3.3% (P < .001). Intraobserver reproducibility of all volume and proportion measurements was good (ICC 0.78-1.00) and interobserver reproducibility was moderate (ICC 0.76-0.99).

Conclusions: Changes in carotid plaque burden and plaque composition can be quantified by using serial MDCTA. Plaque burden development is a heterogeneous and slow process.

Fig 1.

Explanation of the method of semiautomated registration of vessel wall range of interest. 3D reconstructions of the lumen segmentations of a carotid bifurcation at FU (A) and at BL (B). Lumen segmentation is semiautomatically generated after clicking 3 initialization points in the CCA, the ICA, and the ECA, respectively (red dots), separately in both FU and BL datasets. From this lumen segmentation, CLLs are extracted (orange line). On the FU CTA, the vessel range containing atherosclerotic plaque is defined by clicking another set of initialization points (blue dots). The absolute distances along the CLL between the 3 blue points are measured and copied to the CLL of the BL CTA (yellow line), which define the range on axial images to be analyzed by the automated plaque segmentation tool (green dots).

Fig 2.

Semiautomatically generated plaque segmentations on matched BL and FU axial MDCTA images just above the level of the carotid bifurcation. The time interval between the scans is 5.8 years; a slight plaque progression with an increase in calcifications is visible. Red = lumen; green = fibrous tissue; yellow = lipid; white = calcification.