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Figure 1 Axial positron emission tomographic (PET) images and the co-registered computed tomographic (CT) images from 2 patients, 1 (patient A) who manifested low ¹⁸ F-fluorodeoxyglucose (FDG) uptake in the region of the carotid plaque and 1 (patient B) with high FDG uptake in the region of the carotid plaque. The region of the excised carotid plaque is noted with arrows . (A) Carotid plaque specimen taken from the patient with low FDG uptake (patient A). The corresponding trichrome-stained histologic specimen demonstrates a collagen-rich plaque with low lipid content, and CD68 staining on the high-powered images demonstrates limited macrophage infiltration. These histologic features are consistent with a metabolically stable and potentially clinically stable plaque. (B) Carotid plaque specimen taken from the patient with high FDG uptake (patient B). The corresponding trichrome-stained histologic specimen demonstrates a complex plaque with a necrotic core, and the CD68 staining demonstrates intense macrophage infiltration. These histologic features are consistent with a metabolically unstable plaque which is vulnerable to rupture.