A, CT image of a plaque with luminal irregularity, low attenuation and positive remodeling. B, High FDG uptake within the same plaque, predominantly within the positively remodeled, low-attenuation region. Source: Circulation: Cardiovascular Imaging 2012;5:69-77.

Inflammation, as assessed by 18F-FDG-PET uptake and histology, is increased in plaques containing high-risk morphological (HRM) features and rises with increasing number of HRM, according to a study in the January issue of Circulation: Cardiovascular Imaging. Study authors suggested that data support the concept that inflammation accumulates relative to the burden of morphological abnormalities.

While several HRM of plaques, especially in combination, are associated with an increased risk of a clinical event, the study authors noted that the relationship between plaque inflammation and number of HRM is not well understood.

In the study, 34 patients underwent 18F-FDG-PET imaging, and the researchers assessed carotid atherosclerotic inflammation (target-to-background ratio). In addition, in a subset of 10 subjects with carotid stenosis who underwent carotid endarterectomy, the researchers histologically assessed inflammation (CD68 staining).

Ahmed Tawakol, MD, of the cardiac MR PET CT program at Massachusetts General Hospital in Boston, and colleagues then examined vessel wall morphology using CT for the presence of visible plaque and presence of three HRM: positive remodeling, luminal irregularity and low attenuation. They analyzed a total of 100 vascular segments, of which 69 contained visible plaque (26 plaques with at least one HRM). Inflammation, by FDG uptake (target-to-background ratio), was higher in plaques with (versus without) HRM (mean: 2.21 vs. 1.66) and increased with the number of HRM observed.

Similarly, the researchers found that inflammation within atherosclerotic specimens (percent of CD68 staining) was higher in plaques with (versus without) HRM (median: 10 vs. 0) and increased with the number of HRM observed.

This study demonstrated that inflammation, as assessed by both FDG uptake and histology, is increased in plaques containing one or more HRM, according to Tawakol and colleagues. They further concluded that the degree of inflammation increases with increasing number of HRM.

“Accordingly, the data support the concept that inflammation may act as a common mechanism to translate risk associated with HRM,” they wrote. “Additional studies are warranted to evaluate the potential utility of combining inflammation imaging with structural imaging for the assessment of atherothrombotic risk.”

Looking to the future, Tawakol et al said that anticipated technological advancements, such as the development of PET/MRI, the capability “to measure both PET activity and plaque morphology on automatically co-registered images requiring little user input probably will make measurement of plaque inflammation and morphology more widely accessible.” Additionally, they predicted that development of novel tracers with greater sensitivity and specificity for inflammation will improve the accuracy of PET measures of plaque inflammation.