Abstract 3411: Combined PET-CT Assessment of Carotid Plaque Inflammation: A Human Histopathological Study
Objectives: Given the importance of inflammation in atherosclerosis, a non-invasive method to assess plaque inflammation is needed. Prior studies show that FDG-PET imaging predicts plaque inflammation in humans. We tested the hypothesis that the addition of CT imaging data to PET can enhance characterization of plaque inflammation.
Methods: Seven patients with severe carotid stenosis underwent PET/CT imaging within one month prior to carotid endarterectomy (CEA). PET imaging was performed 3 hours after FDG administration (13 mCi), and the ratio of carotid plaque to venous blood pool FDG uptake was determined (TBR). Shortly after FDG administration, 64-slice MDCT imaging was performed for delineation of PET activity and to identify hypodense or positively remodeled plaques. For each patient, three axial sections along the common carotid and internal carotid arteries were analyzed by PET and CT (at the carotid bifurcation, and 0.5 and 1.0 cm above the bifurcation). At CEA, the carotid plaques were removed and plaque inflammation was determined (anti-CD68 antibodies) at locations corresponding to the sections evaluated by the imaging techniques. The FDG-PET images were analyzed independently of the CT images, and all image analyses were performed blinded to the histology. Subsequently, a PET-CT score was calculated, whereby the value for TBR was added to a value derived from the CT images (+1 for presence of hypodense plaque, +1 for positive remodeling, +2 for presence of both).
Results: Consistent with prior observations, there was a significant correlation between inflammation measured histologically, and the FDG signal (TBR), (R=0.67, p<0.001). Further, there was a significant correlation between the presence of either positive remodeling or hypodense plaque (<40 HU) with plaque inflammation (r=0.62, p<.003, and r=0.64, p<0.002, respectively). Moreover, there was a stronger correlation between the PET-CT score for each patient and the macrophage staining from the corresponding histological sections (R=0.72, P<0.001).
Conclusions: We establish that PET in combination with CT may provide added information (compared to PET alone) for characterization of plaque inflammation. The validity of this PET-CT score requires prospective assessment.